Geotechnical Laboratory Manual-II - Copy
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LAB MANUAL...
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Geotechnical and Foundation engineering Lab Manual
Geotechnical and Foundation Engineering Lab Manual
Produced by; Geotechnical laboratory manual
Engr.Saeedullah Jan Civil Engineering Department BUITEMS, Quetta
Page i
Geotechnical and Foundation engineering Lab Manual
Practical Workbook Geotechnical and Foundation Engineering This is to certify that this practical workbook contains 124 pages.
Chairman September 2012
Department of Civil Engineering Balochistan University of Information Technology Engineering & Management Sciences, Quetta
Balochistan University of of Information Technology Engineering & Management Sciences (BUITEMS), Quetta
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Geotechnical and Foundation engineering Lab Manual
THE IMPORTANCE OF GEOTECHNICAL LABORATORY TESTING Soil can exist as a naturally occurring material in its undisturbed state, or as a compacted material. Geotechnical engineering involves the understanding and prediction of the behavior of soil. Like other construction materials, soil possesses mechanical properties related to strength, compressibility, and permeability. It is important to quantify these properties to predict how soil will behave under field loading for the safe design of soil structures (e.g. embankments, dams, waste containment liners, highway base courses, etc.), as well as other structures that will overly the soil. Quantification of the mechanical properties of soil is performed in the laboratory using standardized laboratory tests.
CIVIL ENGINEERING DEPARTMENT BALOCHISTAN UNIVERSITY OF INFORMATION TECHNOLOGY ENGINEERING & MANAGEMENT SCIENCES, QUETTA
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Geotechnical and Foundation engineering Lab Manual
CONTENTS 1
IN PLACE SOIL DENSITY USING SAND CONE METHOD
2
COEFFICIENT OF PERMEABILITY (CONSTANT HEAD METHOD)
11
3
COEFFICIENT OF PERMEABILITY (FALLING HEAD METHOD)
21
4
DIRECT SHEAR TEST
30
5
ONE DIMENSIONAL CONSOLIDATION
6
STANDARD PENETRATION TEST
63
7
UNCONFINED COMPRESSION TEST
73
8
TRIAXIAL TEST
82
9
PLATE LOAD TEST
96
10
TEST
CALIFORNIA BEARING RATIO TEST
BIBLIOGRAPHY
1
42
106 118
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In situ Density By sand Cone Method
1 IN PLACE SOIL DENSITY USING SAND CONE METHOD
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In situ Density By sand Cone Method
1.1
INTRODUCTION
Basically, both the sand-cone and balloon-density methods use the same principle. That is, one obtained a known weight of damp (or wet) soil from a small excavation of somewhat irregular shape (a hole) in the ground. If one knows the volume of the hole, the wet density is simply computed as
wet
weight of damp soil volume of hole
and if one obtained the water content w of the excavated material, the dry unit weight of the material is dry wet 1 w The sand cone method is an indirect means of obtaining the volume of the hole. The sand used (often Ottawa sand) is generally material passing the No. 20 sieve but retained on the No. 30 sieve. If one has a constant-density material of, say, 1.60 g/cm³ and pouring 4800 g of this material into an irregular-shaped hole, the volume of the hole can be found by proportion as:
V 1cm 3 4800 1.60 g / cm 3 Vhole
1.1.1
wt. of material used to fill hole unit wt.of material
DEFINITIONS
BULK DENSITY Bulk density refers to the weight (mass) of soil per unit volume and the soils bulk density is normally expressed in g cm-3 (weight divided by volume).
UNIT WEIGHT Unit weight is defined as weight per unit volume.
1.2
OBJECTIVES OF TEST
The object of this test is to determine the dry density of natural or compacted soil, inplace and its degree of compaction.
1.3
SCOPE OF TEST
Once compaction criteria are established for the soil to be used at a particular site, generally with both moisture and density limitations, some means of verification of the results must be used. On all small projects and nearly all-large projects, this verification is
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In situ Density By sand Cone Method
achieved by either the sand-cone method or the balloon density method. On a few large, nuclear devices have been and are considered further.
1.4
STANDARD REFERENCES
ASTM: D 1556-64 AASHTO: T 191-61
1.5
MATERIALS & EQUIPMENT
The test equipment consists of: 1. Sand cone apparatus 2. Shovels (Digging tools) 3. Metal tray with a central circular hole of diameter equal to the diameter of the pouring cone 4. Balance accurate to 1g 5. clean, uniformly graded sand ranging from #20 to #30 sieve such as Ottawa Sand 6. Paint brush to collect soil from template 7. Hammer and three nails to fix the metal tray on the spot 8. Spoon 9. plastic air tight bag for carrying wet excavated soil from field to laboratory 10. Oven with temperature kept at about 105-110oC
Figure 1.1 Sand-Cone Apparatus
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In situ Density By sand Cone Method
Figure 1.2 Ottawa sand
1.6
PREPARATION OF SAMPLE AND TEST SPECIMEN
Carefully collect a sample from undisturbed core of soil adjacent to the points of soil moisture determination using the tins provided. Trim off excess soil and wrap core in labeled polythene bag for transport to laboratory.
1.7
ADJUSTMENT AND CALIBRATION OF INSTRUMENT
Prior to determining the bulk density of the sand and prior to conducting density tests, the technician is required to determine the weight of sand needed to fill the large cone of the density apparatus and the accompanying base plate. This weight is determined to the nearest 0.01 kilogram and is referred to as the Cone Correction. The density apparatus and the base plate are required to remain together and not be interchanged with other devices without recalculating the Cone Correction. The procedure for determination of the Cone Correction is detailed in AASHTO T 191 and is summarized as follows: 1. Fill the apparatus with the calibration sand and record the weight to the nearest 0.01 lb 2. Place the base plate on a clean, level surface 3. Invert the apparatus onto the base plate and open the valve to allow the cone and the base plate to fill with sand 4. When the sand stops flowing into the cone, shut the valve and weigh the apparatus to the nearest 0.01 lb 5. The difference between the full weight of the apparatus and the final weight after filling the cone is referred to as the Cone Correction.
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In situ Density By sand Cone Method
1.8 1.8.1
TEST PROCEDURE DETERMINATION OF MASS OF SAND FILLING THE CONE
1. Fill the clean closely graded sand in the sand-pouring cylinder up to a height of 1cm below the top. Determine the total mass/weight of Bottle + Cone +Sand (M1). 2. Open the valve and allow the sand to flow out. Close the valve when no further movement of sand is observed. Lift the jar carefully. Weigh the sand collected on the glass surface. Its mass (Mc) is the mass of sand filling the pouring cone. Or remove the bottle and cone combination from the base plate, and determine its mass (M2), thus the mass of sand to fill the cone can be determined as: Mc = M1 –M2 Pour the sand back into the cylinder, to have the same constant mass.
1.8.2
DETERMINATION OF BULK DENSITY OF SAND
1. Determine the volume of the calibrating container. It would be either mentioned or can be by measuring the diameter or by filling it with water full to the top and finding the mass of water, it is therefore V
m
For pure water normally the mass density can be taken as = 1g/cm3 2. Place the sand-pouring cylinder concentrically on the top of the calibrating container. Open the shutter and permit the sand to run into the container. When there is no further movement of sand, close the shutter. Remove the cylinder and find its mass. Thus mass per unit volume will give the bulk density of the sand. On other hand this can also be done by taking a proctor compaction mold and, using a spoon, filling it with Ottawa sand. Avoid any vibration of other means of compaction of the sand poured into the mould. When the mold is full, strike off the top of the mould with the steel straight edge, determine the mass of the sand in the mold. The bulk density of the Ottawa sand can be then be given as:
d
M V
Where M = Mass of the sand filling the mould. V = Volume of the mould (1/30 ft3) d = Bulk density of the sand.
1.8.3
DETERMINATION OF DRY DENSITY OF SOIL IN-PLACE
1. Expose about 45cm2 area of the soil to be tested and trim it down to level surface. Keep the tray on the level surface and fix it by the help of nails in its position and excavate a circular hole of approximately 10cm in diameter and 15 cm deep and collect all the excavated soil in the tray. Find the mass of the excavated soil. 2. Remove the tray, and place the sand-pouring cylinder concentrically on the hole. Open the shutter and permit the sand to run into the hole. Close the shutter when
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In situ Density By sand Cone Method
no further movement of the sand is seen. Remove the cylinder and determine it’s mass. 3. Keep a representative sample of the excavated soil for water content determination.
1.9
CALCULATIONS
Unit weight of soil
g
Dry density
d
1.10
1
RESULTS
The dry unit weight of the soil = _________g/cm3 Dry unit weight/ specific weight
1.11
d
1
ENGINEERING USES OF TEST RESULTS
This test is applied in the cases like embankment and pavement construction; and is basically a quality control test where certain degree of compaction is required. This test is also used in stability analysis of embankments and slopes, for the calculation of pressure in underlying strata for settlement problems and also designs of underground structures.
1.12
PRECAUTIONS
1. The excavation during sand cone method should be as rapid as possible to maintain the representative moisture content. 2. The field test holes may be quite small, thus the error multiple is largest is absolutely essential that no soil be lost during excavation 3. The largest possible water content sample should be used to improve test reliability. 4. When using the sand cone method avoid vibrating either the ground in the area or the sand jug as this will introduce too much sand into the hole thus causing an apparent increase in the hole’s volume.
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In situ Density By sand Cone Method
1.13
SAMPLE PROBLEM SOIL TESTING LABORATORY FIELD UNIT WEIGHT-SAND CONE METHOD
Sample No. 15 Boring No. B-21 Depth of sample 3 ft Description of Sample Reddish brown silty clay Tested by John Doe (A)
Project No. Location
SR 2828 Newell, N.C
Date
1/26/89
Determination of mass of sand filling the cone
The total mass of Bottle + Cone +Sand before filling the cone (M1)
9098gm
The total mass of Bottle + Cone +Sand after filling the cone (M2)
7268gm
Mass of the sand filling the cone (Mc) = M1- M2
1830gm
(B)
Determination of bulk density of sand
The volume of the calibrating container (V)
2305cm3
The mass of the sand in the mold/calibrating container (M3)
3400gm
The bulk density of the Ottawa sand s M 3 V (C) Determination of dry density of soil in- place
1.47 gm/cm3
The mass of the excavated wet soil M4
2658gm
The total mass of Bottle + Cone +Sand before filling the hole (M5)
9066gm
The total mass of Bottle + Cone +Sand after filling the hole (M6)
4980gm
Mass of the sand filling the hole (Mh) = M5- M6 – Mc
2256gm
Volume of hole Vh
Mh
1535cm3
s
M4 M or 4 s Vh Mh Unit weight of soil g Bulk density of soil
1.73 gm/cm3 16097 kg/cm3
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In situ Density By sand Cone Method
(D)
Water content determination
Mass of can + wet soil M7
106.41 gm
Mass of can + dry soil M8
103.38 gm
Mass water Mw = M7 – M8
3.03 gm
Mass of can M9
15.35 gm
Mass of dry soil Md = M8 – M9 Water content Dry density
d
88.03 gm
Mw Md
3044%
1
Dry unit weight/ specific weight
d
1
1.672 gm/cm3
Result The dry unit weight of the soil = ______1.672___ gm/cm3
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In situ Density By sand Cone Method
SOIL TESTING LABORATORY FIELD UNIT WEIGHT-SAND CONE METHOD Sample No. Boring No. Depth of sample Description of Sample Tested by
(A)
Project No. Location
Date
Determination of mass of sand filling the cone
The total mass of Bottle + Cone +Sand before filling the cone (M1) The total mass of Bottle + Cone +Sand after filling the cone (M2) Mass of the sand filling the cone (Mc) = M1- M2 (B)
Determination of bulk density of sand
The volume of the calibrating container (V) The mass of the sand in the mold/calibrating container (M3) The bulk density of the Ottawa sand s M 3 V (C) Determination of dry density of soil in- place The mass of the excavated wet soil M4 The total mass of Bottle + Cone +Sand before filling the hole (M5) The total mass of Bottle + Cone +Sand after filling the hole (M6) Mass of the sand filling the hole (Mh) = M5- M6 – Mc Volume of hole Vh
Mh
s
M4 M or 4 s Vh Mh Unit weight of soil g Bulk density of soil
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In situ Density By sand Cone Method
(D)
Water content determination
Mass of can + wet soil M7 Mass of can + dry soil M8 Mass water Mw = M7 – M8 Mass of can M9 Mass of dry soil Md = M8 – M9 Water content Dry density
d
Mw Md
1
Dry unit weight/ specific weight
d
1
Result The dry unit weight of the soil =
gm/cm3
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Coefficient Of Permeability by Constant Head Method
2
COEFFICIENT OF PERMEABILITY (Constant Head Method)
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Coefficient Of Permeability by Constant Head Method
2.1
INTRODUCTION
In geotechnical engineering problems measuring the flow of water through the soil is a very important consideration. Soil has pores due to inter-particle spaces (voids). The interconnectivity of voids determines the permeability characteristics of soil. Thus, rock, concrete, and other porous material may also be permeable (pervious). Materials such as clays and silts in natural deposits have considerable porosity but are practically impervious or have permeability significantly low (in comparison to sand or gravel). The coefficient of permeability of soil is important in various aspects such as: Determining the seepage through or beneath dams and levees and into water wells; in stability analyses of hydraulic structures through evaluation of uplift or seepage forces; and in regulating seepage control and design of seepage velocities to check erosion in earthen structures The other important applications are in estimation of ground water flow, percolation, surface recharge and yield from wells.
2.1.1
DEFINITIONS
PERMEABILITY Permeability is the ease with which the water flows through a soil medium.
COEFFICIENT OF PERMEABILITY The rate of flow under laminar flow conditions through a unit cross sectional are of porous medium under unit hydraulic gradient is defined as coefficient of permeability.
2.2
OBJECTIVES
To introduce a method of determining coefficient of permeability of a coarse-grained soil by constant head method.
2.3
SCOPE
The test method measures the flow rate of water through a soil specimen of a known gross cross-sectional area, applying constant head and using Darcy’s expression for determining its permeability constant.
2.4
STANDARD REFERENCE
ASTM D234-68 AASHTO T215-66
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Coefficient Of Permeability by Constant Head Method
2.5 1. 2. 3. 4. 5. 6. 7.
APPARATUS Permeability device (Permeameter) Constant head tank Thermometer, range 0 to 50oC, accurate to 0.1oC Stop watch. Graduated cylinder. De-aired distilled water Coarse-grained soils
Figure 2.1 constant head assembly
2.6
TEST PROCEDURE
1. Measure the initial mass of the pan along with the dry soil (M1). 2. Remove the cap and upper chamber of the Permeameter by unscrewing the knurled cap nuts and lifting them off the tie rods. 3. Measure the inside diameter of upper and lower chambers. Calculate the average inside diameter of the Permeameter (D). 4. Place one porous stone on the inner support ring in the base of the chamber then place a filter paper on top of the porous stone. 5. Mix the soil with a sufficient quantity of distilled water to prevent the segregation of particle sizes during placement into the Permeameter. 6. Enough water should be added so that the mixture may flow freely. 7. Using a scoop, pour the prepared soil into the lower chamber using a circular motion to fill it to a depth of 1.5 cm. A uniform layer should be formed. 8. Use the tamping device to compact the layer of soil. Use approximately ten rams of the tamper per layer and provide uniform coverage of the soil surface. Repeat the compaction procedure until the soil is within 2 cm. of the top of the lower chamber section. 9. Replace the upper chamber section, and don’t forget the rubber
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Coefficient Of Permeability by Constant Head Method
10. Gasket that goes between the chamber sections. Be careful not to disturb the soil that has already been compacted. Continue the placement operation until the level of the soil is about 2 cm. below the rim of the upper chamber. 11. Level the top surface of the soil and place a filter paper and then the porous stone on it.
Figure 2.2 Half assembled permeameter. 12. Place the compression spring on the porous stone and replace the chamber cap and its sealing gasket. Secure the cap firmly with the cap nuts. 13. Measure the sample length at four locations around the circumference of the Permeameter and compute the average length. Record it as the sample length. 14. Keep the pan with remaining soil in the drying oven. 15. Adjust the level of the funnel to allow the constant water level in it to remain a few inches above the top of the soil. 16. Connect the flexible tube from the tail of the funnel to the bottom outlet of the Permeameter and keep the valves on the top of the Permeameter open. 17. Place tubing from the top outlet to the sink to collect any water that may come out. Open the bottom valve and allow the water to flow into the Permeameter. 18. As soon as the water begins to flow out of the top control (de-airing) valve, close the control valve, letting water flow out of the outlet for some time. 19. Close the bottom outlet valve and disconnect the tubing at the bottom. 20. Connect the funnel tubing to the top side port. Open the bottom outlet valve and raise the funnel to a convenient height to get a reasonable steady flow of water. 21. Allow adequate time for the flow pattern to stabilize. 22. Measure the time it takes to fill a volume of 750 - 1000 ml using the graduated cylinder, and then measure the temperature of the water. 23. Repeat this process three times and compute the average time, average volume, and average temperature. Record the values as t, Q, and T, respectively.
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Coefficient Of Permeability by Constant Head Method
24. Measure the vertical distance between the funnel head level and the chamber outflow level, and record the distance as h. 25. Repeat step 17 and 18 with different vertical distances. 26. Remove the pan from the drying oven and measure the final mass of the pan along with the dry soil (M2).
2.7
CALCULATIONS
Using Bowles apparatus for determination permeability coefficient by measuring flow through soil under a constant head is calculated from the following equation QL k C htA Where; Q = quantity of flow, cm3 or ml L = length of the sample, cm h = applied head (constant) cm t = time interval seconds A = cross-sectional area of the sample cm2 C = Temperature correction for viscosity of water at 20C Result The coefficient of permeability of the given coarse-grained soil by Constant Head Permeability test is found to be, k =___________________cm/s. Soil
Coefficient. of Perm., k, cm/sec >10-1 10-1 > k > 10-3
Degree of Permeability
Gravel Very high Sandy gravel, clean sand, fine High to Medium sand Sand, dirty sand, silty sand 10-3 > k > 10-5 Low Silt, silty clay 10-5 > k > 10-7 Very low Clay 60 U = Degree of Consolidation Charts are also available for different values of Tv against respective values of U. d = Length of the longest drainage path in the soil sample.
1 Hi H f H dr 2 2
Hi = Initial sample thickness
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One Dimensional Consolidation Test
Hf = Sample thickness at complete consolidation under a Particular load t = Time of interest obtained from deformation v/s. time curves. In square root method where the graph is plotted between dial gauge reading and square root of t , t 90 is used. In logarithm method where graph is plotted between dial gauge reading and Log (t), t50 is used. In equation (i) the value T is put according to the value of t. If t = tu, then T = TU. Where, U shows degree of consolidation
5.1.1
DEFINITIONS
PRE-CONSOLIDATION STRESS, P This is the maximum stress that the soil has “felt” in the past.
COMPRESSION INDEX, CC The compression index, CC, which indicates the compressibility of a normally-consolidated soil.
RECOMPRESSION INDEX, CR The recompression index, CR, which indicates the compressibility of an over consolidated soil.
COEFFICIENT OF CONSOLIDATION, CV The coefficient of consolidation, CV, which indicates the rate of compression under a load increment.
NORMALLY-CONSOLIDATED SOIL A normally-consolidated soil is defined as a soil which, at the present time, is undergoing the application of a stress that is larger than any stress it has undergone in its history. That is, present n '
OVER-CONSOLIDATED SOIL An over-consolidated soil is defined as a soil which has experienced higher stresses in the past, present p '
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One Dimensional Consolidation Test
CONSOLIDATION When soil is loaded undrained, the pore pressures increase. Then, under site conditions, the excess pore pressures dissipate and water leaves the soil, resulting in consolidation settlement. This process takes time, and the rate of settlement decreases over time.
5.2
OBJECTIVES OF TEST
The consolidation test is used to measure the settlement characteristics of a clay layer.
5.3
SCOPE OF TEST
Consolidation is an important fundamental phenomenon which must be understood by everyone who attempts to gain knowledge of soil behavior in engineering applications. The main purpose of consolidation tests is to obtain soil data which is used in predicting the rate and amount of settlement of structures founded on clay. Although some of the settlement of a structure on clay may be caused by shear strain; most of it is normally due to volumetric changes. This is particularly true if the clay stratum is thin compared to the width of the loaded area or the stratum is located at a significant depth below the structure.
5.4
STANDARD REFERENCE
ASTM: D2435-70 AASHTO: T216-66
5.5 1. 2. 3. 4. 5. 6.
MATERIALS & EQUIPMENT Consolidometer Specimen trimming device Balance sensitive to 0.01 g Stop watch Moisture can Oven
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One Dimensional Consolidation Test
Figure 5.1 One dimensional consolidation apparatus
5.6
PREPARATION OF SAMPLES AND TEST SPECIMEN
1. 2. 3. 4. 5. 6. 7. 8.
Remove covering from sample. Keep track of the sample orientation. Place sample on wax paper disc and glass plate. Rough cut the diameter with a wire saw to within 1/8" of final diameter. Obtain water contents from trimmings Assemble sample in trimmer with extension disc supporting soil. Trim sample with cutting shoe and spatula, obtain second water content. Once sample is completely fitted into specimen ring, trim top and bottom with a wire saw. Make final cut on top surface with a sharp straight edge. 9. Obtain third and fourth water contents. 10. Use recess tool to create space at top of ring and trim excess soil from bottom with wire saw. Make final cut with the sharp straight edge. 11. Determine the mass of the specimen and ring (Ms+r). 12. Measure the recess from the top of ring to the soil surface (ΔHi)
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One Dimensional Consolidation Test
5.7 5.7.1
ADJUSTMENT AND CALIBRATION OF INSTRUMENTS APPARATUS CALIBRATION
1. Assemble the cell (stones, filter paper and top cap). 2. Align assembly in the loading frame. 3. Place a 1 lb seating load on the cell and obtain a zero reading on the displacement transducer. 4. Apply the same loads to the apparatus as will be used in testing the specimen. 5. At each load increment, record the displacement reading at 15 sec, 30 sec, 1 min, 2 min and 5 min. 6. The change in dial reading gives the machine deflection curve.
5.7.2
APPARATUS PREPARATION
1. Assemble the Oedometer (stones, filter paper and top cap) 2. Measure the initial z3 (height between top of cap and specimen ring). You can place a dummy specimen (block of known thickness) between the filter papers for added height. 3. Disassemble the Oedometer. 4. Grease specimen ring and cutting shoe. 5. Determine the mass (Mr) of the empty specimen ring. 6. Measure the height (Hr) and diameter (Dr) of the ring. 7. Measure the thickness of one piece of filter paper (Hfp). 8. Cut two pieces of filter paper. 9. Boil or ultrasound the stones for 10 minutes to clean and remove air 10. Cut 2 wax paper disks the diameter of the specimen.
5.7.3
APPARATUS ASSEMBLY
1. 2. 3. 4. 5. 6. 7.
Fill base with water. Insert bottom stone into base and cover with filter paper. Remove excess water with a paper towel. Place specimen and ring on stone. Cover rim with gasket. Tighten with locking ring. Cover specimen with filter paper and top stone, allow this stone to drain before placing on soil. 8. Place top cap on stone.
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One Dimensional Consolidation Test
9. Measure z3 with specimen 10. Locate assembly in loading frame with dial gauge and balance arms (this is the true weight of the assembly which is the tare load). 11. Apply one pound seating load and zero displacement transducer.
5.8
TEST PROCEDURE
1. Consolidate the specimen using a load increment ratio (ΔP/P) between 0.5 and 1.0 for loading and -0.25 and -0.50 for unloading. Note: recommended schedule S, 0.125, 0.25, 0.5, 1.0, 2, 4, 8, 4, 1, S. 2. Fill the water bath at about 1/4 the overburden stress (0.25 ksi) or within 2 hours. 3. For each increment, record the displacement transducer reading versus time. Remember that the initial portion of the curve is very important to define the start of consolidation (εs). 4. During each increment plot both root time and log time curves. 5. Apply increments after the end of primary consolidation has been reached. 6. Allow one cycle of secondary compression to occur under the maximum load and before the unload-reload cycle. 7. At the end of the test unload the specimen to the seating load and allow time for swelling. 8. Remove the water from the bath and remove the specimen from the apparatus. 9. Remove any extruded soil and oven dry. 10. Dry the surface of the specimen and determine the mass of both soil and ring. 11. Extrude the soil and obtain water content. 12. Collect washings from filter paper and inside of ring and oven dry.
5.9
CALCULATIONS
Initial Specimen Height = Hr – ΔHi - Hfp Water Content = (total mass - dry mass)/ dry mass Note: compute the total mass during the test by subtracting (axial deformation X Area X unit weight of water) from initial wet mass. This assumes that only water comes out of the specimen during consolidation. Void Ratio = (total volume - volume of solids)/ volume of solids Volume of solids = mass of oven dried soil / specific gravity Degree of saturation = specific gravity × water content / void ratio
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One Dimensional Consolidation Test
Vertical effective stress (σ'v) (when the pore pressure is zero) = (Applied load - Tare load + top cap and stone)/ Area Vertical strain (εv) = (measured axial deformation - Apparatus compression)/ Initial specimen height Note: The Apparatus compression curve is attached to this assignment Compressibility (av) = - change in void ratio / change in vertical stress Note: change in void ratio is usually taken at the end of primary but for this laboratory assignment you can use end of increment values. 2
Coefficient of consolidation (CV). (Root time) = 0.848 (drainage height) / time for 90% consolidation 2
Coefficient of consolidation (CV). (Log time) = 0.197 (drainage height) / time for 50% consolidation Note: Drainage height is computed at 50% consolidation for both cases. Hydraulic conductivity (kV) = (coefficient of consolidation compressibility unit weight of water) / (1 + average void ratio) Rate of secondary compression (cα) = change in strain per log cycle of time after primary is complete
Square root or time vs. Dial gauge reading
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One Dimensional Consolidation Test
5.10
RESULTS
The value of coefficient of consolidation is found to be _________ By square root method _________
5.11
ENGINEERING USES OF TEST RESULTS
In engineering practice, reasonably good predictions of a structure’s settlements can be made from the results of carefully run laboratory tests. Predicted settlements are larger than actual settlements more often than not. Time rate predictions are often rather poor in practice. Better predictions, naturally, can be made for those cases which have conditions more closely in agreement with the assumptions made in the theory derivation. This would be the case, for example, when the soil involved experiences most of its settlement due to primary consolidation, or when drainage conditions in the field are accurately known.
5.12
PRECAUTIONS
1. Handling of instrument must be with care. 2. Readings should be note down carefully.
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One Dimensional Consolidation Test
5.13
SAMPLE PROBLEM
GENERAL REPORT CONSOLIDATION TEST (Time vs. vertical dial reading) Client Name ________________________ Sample No. _________B-24___________ Company Name _____________________ Boring No. _________________________ Project Name _______________________ Depth of sample ____2 ft______________ Project No. _________________________ Description of Sample _____silty_______ Location of site _____________________ Tested by __________________________ Date of sampling ____________________ Comments. _________________________ Date of testing ______________________ Location ___________________________ Reporting Name ____________________ Date ______________________________ Pressure on specimen ________________ Clock time of load application __________ Time after load Vertical dial 1/2 application (t) reading t (min) (min 0.5) (in) 9:15 AM 0 0 09:15.1 0.1 0.316228 9:15:25 0.25 0.5 09:15.5 0.5 0.707107 9:16 1 1 9:17 2 1.414214 9:19 4 2 9:23 8 2.828427 9:30 15 3.872983 9:45 30 5.477226 10:15 60 7.745967 11:15 120 10.95445 1:15 PM 240 15.49193 5:15 480 21.9089 8:15 AM 1380 37.14835 CALCULATIONS RESULT
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One Dimensional Consolidation Test
GENERAL REPORT CONSOLIDATION TEST (Void ratio-pressure and coefficient of consolidation calculation) Client Name ________________________ Company Name _____________________ Project Name _______________________ Project No. _________________________ Location of site _____________________ Date of sampling ____________________ Date of testing ______________________ Reporting Name ____________________ Specimen diameter __________________ Moisture content: beginning of test __ (%) Weight of dry soil specimen ___________ Pressure P (T/ft2)
Final Dial Reading
Change in specimen height
(in) (in)
CALCULATIONS
Final specimen Height Ht(f) (in)
Sample No._________________________ Boring No. _________________________ Depth of sample _____________________ Description of Sample ________________ Tested by __________________________ Comments _________________________ Location ___________________________ Date ______________________________ Initial specimen height, Ht(i)___________ Moisture content: End of test ________(%) Gs ___ Height of solids, Hs_________ cm
Height of void
Final void ratio
Hv (in)
e
Average height during consolidation, Ht(av) (in)
Fitting time (sec)
cv from x 103(in2/sec)
t90
t90
t50
t50
RESULTS
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One Dimensional Consolidation Test
Dial Readings vs Time
Deformation dial reading
Time (min) 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.1 0.018
1
10
100
1000
10000
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One Dimensional Consolidation Test
SOIL TESTING LABORATORY CONSOLIDATION TEST (Void ratio-pressure) Void Ratio Initial void ratio, eo
1.248781
Volume of solid in specimen, Vs
27.90809
Area of specimen, A (cm2)
31.67736
Height of solid in specimen, Hs (cm)
0.881011
Pressure, P(tons/ft2)
Initial deformation dial reading at beginning of first loading(in.)
Deformation dial reading representing 100% primary consolidation, (in.)
Change in thickness of specimen, ΔH(cm)
5
6
7
(8)=((7)-(6))*2.54
(9)=(8)/(4)
(10)=(1)-(9)
0 0.4 0.8 1.6 3.2 6.4 12.8
0 0 0 0 0 0 0
0 0.0158 0.0284 0.049 0.0761 0.1145 0.158
0 0.04013 0.07214 0.12446 0.19329 0.29083 0.40132
0 0.04555 0.08188 0.14127 0.2194 0.33011 0.45553
1.25 1.204447 1.16812 1.108729 1.030597 0.919886 0.794472
Change in Void Ratio, void ratio, De e (e=eo-Δe) [Δe=ΔH/ Hs]
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One Dimensional Consolidation Test
(Coefficient of consolidation calculation) Initial Deformation Thickness of Half height of dial reading specimen at thickness of Pressure, specimen at 50% 50% specimen at P, at consolidation consolidation, 50% 2 (tons/ft ) beginning consolidation of test, Ho (in) (in) (in) (in) (3) (from dial (4)=(2)-(3) (5)=(4)/2 (1) (2) reading vs log of time curves)
Time for 50% consolidation (min)
Coefficient of consolidation (in2/min)
(6) (from dial readings versus log of time curves)
(7)=0.196(5)2/(6)
0
0.78
0.4
0.78
0.0108
0.7692
0.3846
8.2
0.003536
0.8
0.78
0.0233
0.7567
0.37835
6.4
0.004384
1.6
0.78
0.0398
0.7402
0.3701
4
0.006712
3.2
0.78
0.0644
0.7156
0.3578
3.4
0.00738
6.4
0.78
0.0982
0.6818
0.3409
3.5
0.006508
12.8
0.78
0.1387
0.6413
0.32065
4
0.005038
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One Dimensional Consolidation Test
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One Dimensional Consolidation Test
Result The value of coefficient of consolidation is found to be By square root method = By logarithm method =
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One Dimensional Consolidation Test
SOIL TESTING LABORATORY CONSOLIDATION TEST Specimen Data At beginning of test Type of specimen(checked one) undisturbed remolded Diameter of specimen, D( in.) Area of specimen , A in.2 Initial height of specimen, Ho ( in.) Initial volume of specimen (in.3) Weight of specimen ring +specimen (g) Weight of specimen ring (g) Initial wet weight of specimen (g) Initial wet unit weight Initial moisture content (%) Can no. Weight of wet soil + can (g) Weight of dry soil + can (g) Weight of can (g) Weight of water (g) Weight of dry soil (g) Initial moisture content (g) Initial dry weight of specimen (computed) (g) Specific gravity of soil
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One Dimensional Consolidation Test
Volume of solid in soil specimen cm3 Volume void in soil specimen cm3 volume of water in soil specimen cm3 (Note: Unit weight of water = 1 g/cm3) Initial degree of saturation At the End of test Can no. Weight of can + wet specimen removed from Consolidometer (g) Weight of can + oven dried specimen (g) Weight of can (g) Final weight of water in specimen Final dry weight of specimen Final moisture content Final degree of saturation % Initial void ratio Volume of solid in specimen cm3 Initial volume of specimen cm3 Initial volume of void in specimen cm3 Initial void ratio, eo
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One Dimensional Consolidation Test
(Time vs. vertical dial reading) Pressure on specimen Clock time of load application Time after load application t (min)
(t)1/2 (min 0.5)
Vertical dial reading (in)
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One Dimensional Consolidation Test
SOIL TESTING LABORATORY CONSOLIDATION TEST (Void ratio-pressure) Void Ratio Initial void ratio, eo Volume of solid in specimen, Vs Area of specimen, A (cm2) Height of solid in specimen, Hs (cm)
Pressure, P (tons/ft2)
Initial deformation dial reading at beginning of first loading (in)
Deformation dial reading representing 100% primary consolidation, (in)
(5)
(6)
(7)
Change in thickness of specimen, ΔH (cm) (8)=((7)-(6))2.54
Change in void ratio,
e (e=eo-Δe) De [Δe=ΔH/ Hs]
(9)=(8)/(4)
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Void Ratio,
(10)=(1)-(9)
61
One Dimensional Consolidation Test
(Coefficient of consolidation calculation)
Pressure, P, (tons/ft2)
(1)
Initial height of specimen at beginning of test, Ho (in) (2)
Deformation dial reading at 50% consolidation (in) (3) (from dial reading vs log of time curves)
Thickness of specimen at 50% consolidation, (in) (4)=(2)-(3)
Half thickness of specimen at 50% consolidation (in)
Time for 50% consolidation (min)
Coefficient of consolidation (in2/min)
(5)=(4)/2
(6) (from dial readings versus log of time curves)
(7)=0.196(5)2/(6)
Result The value of coefficient of consolidation is found to be By square root method = By logarithm method =
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Standard Penetration Test
6 STANDARD PENETRATION TEST
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Standard Penetration Test
6.1
INTRODUCTION
If the test is to be carried out in gravelly soils the driving shoe is replaced by a solid 600 cone. There is evidence that slightly higher results are obtained in the same material when the normal driving shoe is replaced by the 600 cone. The Standard Penetration Test was developed around 1927. It is estimated that 85% to 90% of conventional foundation design in North and South America is made using the SPT. This dynamic penetration test is used to assess the density index and to determine the bearing capacity of a sand deposit. This dynamic penetration test is used to assess the density index and to determine the bearing capacity of a sand deposit. The test is performed using a split barrel sampler, 50 mm external diameter, 35 mm internal diameter and about 450 mm (18in) in length, connected to the end of boring rods. The sampler is driven into the sand at the bottom of a cased borehole by means of 65 kg hammer falling freely through a height of 760 mm (30 in) onto the top of the boring rods.
Figure 6.1 Arrangement of SPT
Different methods of releasing the hammer are used in different countries. The borehole must be cleaned out to the required depth, care must be taken to ensure that the material to be tested is not distributed: jetting, as part of the boring operation is undesirable. The casing must not be driven below the level at which the test is to begin.
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Standard Penetration Test
Initially the sampler is driven 150mm (6in) into the sand to seat the device and to bypass any disturbed sand at the bottom of the borehole. The number of blows required to drive the sampler a further 300 mm (12in) is then recorded: this number is called the standard penetration resistance (N). The number of blows required for each 150 mm (6in) of penetration (including the initial drive) should be recorded separately. If 50 blows are reached before a penetration of 300mm (12in), no further blows should be applied but the actual penetration should be recorded. At the conclusion of a test the sampler is withdrawn and the sand extracted. Tests are normally carried out at interval of b/w 0.75 and 1.5m to a depth below foundation level at least equal to the width (B) of the foundation
6.2
OBJECT OF TEST
To determine the load bearing capacity of soils by standard penetration test. The object of the test is to determine the relative density and bearing capacity of granular sandy soils.
6.3
SCOPE OF TEST
This test method describes the procedure, generally known as the Standard Penetration Test (SPT), for driving a split-barrel sampler to obtain a representative soil sample and a measure of the resistance of the soil to penetration of the sampler. This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Figure 6.2 Equipment as mentioned under heading
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Standard Penetration Test
6.4
STANDARD REFERENCE
ASTM: D1586
6.5
MATERIALS & EQUIPMENT
The test equipment consists of: 1. Standard split-barrel Sampler (Split-spoon) 2. A casing or Drilling. 3. A thick wall Split tube Sampler, with 2” (5.08cm) OD and 1.5” (3.5cm) ID having the tube length of 18” to 24” long. 4. Guide rod. (30” or 76cm length) 5. Hammer having weight of 140lb (623N) 6. Rope. 7. Tripods 8. Steel chain (3m approx) 9. Lever support and rod 10. Pipe wrench and chain wrench 11. Pulley
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Standard Penetration Test
Figure 6.3 Solid tube sampler and driving sample
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Standard Penetration Test
6.6
TEST PROCEDURE
1. Attach the Standard split-barrel Sampler (Split-spoon) to the bottom of the drilling rod. The top of the drilling rod is attached by anvil used to transfer the hammer load to the drilling rod. The anvil connects a guide rod passing through the drop hammer. 2. Erect the tripod so that each leg must form an angle of 1200 with respect to the other and at equidistant from the center mark. Hookup pulley to the tripod with a rope passing over it, and connect one end of the rope with drop hammer to lift it up. 3. Excavate a circular or rectangular trench upto the required foundation depth (below which the bearing capacity of the soil is required) at the center mark.. 4. Gradually pull the other end of the rope (manually or by some mechanical arrangements) to erect the sampler. Make sure that the sampler assembly is vertically erected at the center mark of the testing spot in excavation. 5. Now pull the rope slowly to lift the drop hammer to the full height of the guide rod (76cm approximately) and then suddenly release the rope to provide free fall to the hammer repeatedly to drive the Standard split-barrel Sampler (Split-spoon) 18" into the soil. 6. After driving the sampler 18" into the soil count the number of blows, which are required to penetrate each of three 6" increments separately. The Standard Penetration Resistance value (N-value) is the number of blows required to penetrate the last 12", thus the N-value represents the number of blows per foot. 7. After blow counts have been obtained, remove and open the split–spoon Sampler to obtain a disturbed sample for subsequent examination and testing. 8. Determine the specific weight of the soil on the spot of the boring log to obtain the effective overburden pressure.
6.7
CALCULATIONS
Relation between N and Corrected N
5 28.5
(peck, 1974) 10 30
15 32
20 33
25 35
30 36
35 37.5
40 39
45 40
50 43
Allowable bearing capacity using N-values
6.7.1
TERZAGHI AND PECK METHOD
Terzaghi and Peck (1948) recommended that N values should be determined between foundation level and a depth of approximately B below the foundation. They proposed a correlation between allowable bearing capacity and the corrected N-values in the form of a chart. The breadth of footing and the corrected N-value are used as entry data and the
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Standard Penetration Test
allowable bearing capacity (qTP) is read off the left vertical axis. For Correction there is also a formula, which is given as follow: 2000 C N 0.77 log ` The effect of the water table may be taken into account by applying the following correction
Cw
Dw 1 1 2 D B
Where Dw = Depth of water table below the surface. D = Foundation depth below the surface. B = Footing breadth. Thus,
q a C w qTP The Terzaghi and Peck method yields quite conservative values of qa, since it attempts to ensure that the settlement is nowhere greater than 25mm, for wide footings and rafts the limiting values may be raised to 50 mm. The qTP value is the function of SPT resistance value N, and the breadth of footing. The required graph can be found in any Soil Mechanics Text Book.
6.7.2
MEYERHOF METHOD
Meyerhof (1965) suggested that the qTP value could be increased by 50 % and that no correction should be made for the water table since the effect would be incorporated in the measured N-values. Meyerhof also proposed a set of simple design relationships as follows: s N qa L for B1.25m 1.9 2 sL N B 0.33 qa for B 1.25m 2.84 B
qa
sL N 2.84
for rafts :
Where SL = permitted settlement limit (mm). N = average N-values between z = D and z = D + B. B = breadth of footing.
6.7.3
BURLAND AND BURBIDGE METHOD
Burland and Burbidge (1985) using a large number of settlement observations concluded that the depth of the zone of influence must be considered in which 75% of the settlement will occur and which may be taken approximately as:
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Standard Penetration Test
Thus the average measured N-value is therefore taken between Z = D and Z = D + Zi The compressibility of soil is stated in terms of average N-value as a grade of compressibility and compressibility index as follow
Ic
1.71 N 1.4
The allowable bearing capacity of soil is thus will be given as follow
qa
SL
2 ` B 0.7 I c 3
` is the effective overburden pressure measured from top surface to the depth of foundation.
6.8
RESULTS
SL = ____________, B = _____________, Nav = ___________
No. 1 2 3
Method
Bearing Capacity
Average
Terzaghi and Peck Meyerhof Burland and Burbidge
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Standard Penetration Test
6.9
SAMPLE PROBLEM SOIL TESTING LABORATORY STANDARD PENETRATION TEST
Sample No. 15 Boring No. B-21 Depth of sample 3 ft Description of Sample Reddish brown silty clay Tested by John Doe Specimen diameter cm Depth (z) 1st
8
Blows
2nd
16
per 6”
3rd
27
N
16 + 27=43
(KN/m2)
19
z (KN/m2)
20.27
u z w
0
` u (KN/m2)
20.27
No.
Date
1/26/89
1.536
N` =CN N
66.027
Average: N
66.027
SL = 25.1 B= 1.06 Nav = 66
SR 2828 Newell, N.C
3.5’ (1.07m)
No. of
2000 C N 0.77 log `
Project No. Location
mm m
Method
Bearing Capacity
1
Terzaghi and Peck
1320 KN/m2
2
Meyerhof
882.6 KN/m2
3
Burland and Burbidge
Average 2485.8KN/m2
5254.9 KN/m2)
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Standard Penetration Test
SOIL TESTING LABORATORY STANDARD PENETRATION TEST Sample No. Boring No. Depth of sample Description of Sample Tested by Specimen diameter
Project No. Location
Date cm
Depth (z) No. of
1st
Blows
2nd
per 6”
3rd N
z u z w
` u CN = 2000 0.77 log `
N` =CN N Aver: N Result SL = B= Nav =
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Unconfined Compression Test
7 UNCONFINED COMPRESSION TEST
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Unconfined Compression Test
7.1
INTRODUCTION
When the method of testing tube-recovered cohesive soil sample compression was first introduced, it was widely accepted as a means of rapidly evaluating the shear strength of a soil. From Mohr’s circle construction; it is evident that the shear strength or cohesion of a soil sample can be approximate where qu is always used as the symbol for the unconfined compressive strength of the soil. This computation is based on the fact that the minor principal stresses 3 are zero (atmospheric), and the angle of internal friction of the soil is assumed zero. With more knowledge concerning soil behavior available, it became evident that the unconfined compression test does generally provide a very reliable value of soil shear strength for at least three reasons: 1. The effect of lateral restraint provided by the surrounding soil mass on the sample is lost when the sample is removed from the ground. There is, however, some opinion that the soil moisture is provides a surface tension (or confining) effect so that the sample is somewhat “confined”. This effect should be more pronounced if the sample is saturated or nearly so. This effect will depend also on the relative humidity of the testing area making a quantitative evaluation of it rather difficult. 2. The internal soil condition (the degree of saturation, the pore water pressure under stress deformation, and the effects of altering the degree of saturation) cannot be controlled. 3. The friction on the end of the sample from the loading platens provides a lateral restraint on the ends, which alters the internal stresses, an unknown amount. Table 7.1 Relative consistency as a function of unconfined compressive strength Consistency qu (lb/ft2) Very soft 4000
7.1.1
DEFINITIONS
UNCONFINED COMPRESSIVE STRENGTH The compressive stress at which an unconfined cylindrical specimen of soil will fail in a simple compression test. In this test method, unconfined compressive strength is taken as the maximum load attained per unit area or the load per unit area at 15% axial strain, whichever is secured first during the performance of a test.
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Unconfined Compression Test
SHEAR STRENGTH The shear strength of soil is the resistance to deformation by continuous shear displacement of soil particles or on masses upon the action of shear stress. For unconfined compressive strength test specimens, the shear strength is calculated to be ½ of the compressive stress at failure.
7.2
OBJECTIVES OF TEST
This method determines the unconfined compressive strength (qu) of the soil sample.
7.3
SCOPE OF TEST
This test method covers the determination of the unconfined compressive strength of cohesive soil in the undisturbed, remolded, or compacted condition, using strain-controlled application of axial load. This test method provides an approximate value of the strength of cohesive soils in terms of total stresses. This test method is applicable only to cohesive materials which will not expel bleed water (water expelled from the soil due to deformation or compaction) during the loading portion of the test and which will retain intrinsic strength after removal of confining pressures, such as clays or cemented soils. Dry and crumbly soils, fissured or varved materials, silts, peats, and sands cannot be tested with this method to obtain valid unconfined compressive strength values. This test method is not a substitute for AASHTO T 234-85 which is ‘Strength Parameters of Soils using Triaxial Compression’. The values stated in SI units are to be regarded as the standard. The values stated in inchpound units are approximate.
7.4
STANDARD REFERENCE
ASTM: D2166-66 AASHTO: 208-70
7.5 1. 2. 3. 4.
MATERIALS & EQUIPMENT Unconfined compression testing machine (Triaxial Machine) Specimen preparation equipment Sample extruder Balance
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Unconfined Compression Test
Figure 7.1 Unconfined Compression Testing Device
7.6 7.6.1
PREPARATION OF SAMPLES AND TEST SPECIMEN PREPARATION OF UNDISTURBED SAMPLE
1. Obtain a sample and using the wire saw and miter box, trim the ends parallel to each other. 2. Place the sample in the soil lathe and trim it to a circular cross-section. 3. Reposition the sample in the miter box and cut it to a length of approximately 7 cm by trimming both ends. 4. Measure the average length and diameter of the sample using the veneer caliper. Weigh the sample. 5. Use the sample trimmings to determine water content of the clay.
7.6.2
PREPARATION OF REMOULDED SAMPLE
1. Remold the clay thoroughly.
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Unconfined Compression Test
2. Reform a cylindrical specimen using the sample former, taking care not to entrap air in to the clay. 3. Extrude the sample from the mould and square its ends using the miter box. 4. Measure the sample as before.
7.7
ADJUSTMENT AND CALIBRATION OF INSTRUMENTS
Standard Geotest unconfined compression machines are supplied with a double proving ring or load cell and digital display which reads directly to 0.1 lbf or 1N and have a peak hold. Proving ring models include a calibration chart in both pounds and SI units. Pounds will be supplied unless SI units are specified. Strain is measured with a 1" travel (25mm on SI versions) dial indicator. 2" (50mm) dial indicators or EDDIs can replace dial indicator as an added option.
7.8
TEST PROCEDURE
1. Remolded specimens are prepared in the laboratory depending on the proctors data at the required molding water content. 2. If testing undisturbed specimens retrieved from the ground by various sampling techniques, trim the samples into regular triaxial specimen dimensions (2.8” x 5.6”) 3. There will be a significant variation in strength of undisturbed and remolded samples. 4. Measure the diameter and length of the specimen to be tested 5. If curing the sample (treated soils), wrap the samples in a geotextile and then a zip bag. Place the sample in a humidity room maintained at a relative humidity of 90% 6. Prior to testing, avoid any moisture loss in the sample, place on a triaxial base (acrylic). The ends of the sample are assumed to be frictionless 7. The triaxial cell is placed above the sample and no confinement is applied 8. The rate of strain is maintained at 1.2700 mm/min as per ASTM specifications. 9. The data acquisition system collects real time data and the test is stopped when there is a drop observed in the strain versus load plot
7.9
CALCULATIONS Calculate the water contents, Axial load (P = Load Ring Reading x [Calibration of load ring]), strain ( = ΔL/L0 x 100%), instantaneous area (Ai = A0/(1- ), where is in decimal format), and σ1 = P/A.
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Unconfined Compression Test
7.10
RESULTS Plot a graph of σ 1 or the deviator stress as ordinate vs. ez or vertical strain in % as abscissa on Cartesian graph paper. Define qu at failure; this is s1 (peak).
Figure 7.2 Failure patterns typical of brittle specimen
7.11
ENGINEERING USES OF TEST RESULTS
1. The test results provide an estimate of the relative consistency of the soil as can be seen in Table 6.1. 2. Almost used in all geotechnical engineering designs (e.g. design and stability analysis of foundations, retaining walls, slopes and embankments) to obtain a rough estimate of the soil strength and viable construction techniques 3. To determine Undrained Shear Strength or Undrained Cohesion (Su or Cu) = qu/2 4. The unconfined compression test is usually made on undisturbed samples. It is reasonably simple and rapid to perform. It gives a very good measure of the shearing strength of cohesive soils. In somewhat granular soil its application is limited, but it does provide a good supplementary test for more complex strength tests. 5. The unconfined compression test is limited in that test conditions can be varied very little. Hence, the test may provide a good measure of the in-situ strength, but may provide only limited strength data, as the stress conditions change due to loading or construction.
7.12 1. 2. 3. 4. 5.
PRECAUTIONS Scale must be precise. Width of groove must be accurate. Depth of groove must be accurate. Handle of turning pace should be done with care. Length of closure should be of ½ inch
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Unconfined Compression Test
7.13
SAMPLE PROBLEM
SOIL TESTING LABORATORY UNCONFINED COMPRESSION TEST Sample No. 15 Project No. Boring No. B-21 Location Depth of sample 3 ft Description of Sample Reddish brown silty clay Tested by John Doe Date Proving ring calibration factor 6000 (lb/in) Specimen deformatio n = L (in)
(1) 0 0.025 0.05 0.075 0.1 0.125 0.15 0.175 0.2
Vertical strain = L / L
(2) 0 0.004181 0.008361 0.012542 0.016722 0.020903 0.025084 0.029264 0.033445
Proving ring dial reading [No. of small divisions]
Load = (Col. 3) calibration factor (lb)
(3)
(4)
0 0.0024 0.0058 0.0086 0.0116 0.015 0.0176 0.0208 0.0224
0 14.4 34.8 51.6 69.6 90 105.6 124.8 134.4
SR 2828 Newell, N.C
1/26/89
Corrected area =
Stress = (col.4)/(col.5)
A0 1
(lb/in2) or kPa
Ac
(in2) (5)
(6)
4.91 4.930613 4.9514 4.972362 4.993503 5.014825 5.036329 5.058019 5.079896
0 2.920529 7.028316 10.37736 13.93811 17.94679 20.96765 24.67369 26.45723
Result Plot a graph of s1 or the deviator stress as ordinate vs. ez or vertical strain in % as abscissa on Cartesian graph paper. Define qu at failure; this is s1 (peak).
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Unconfined Compression Test
Relationship between load per unit area and unit strain
Load Per Unit Area (lb/in2)
30 25 20 15 10 5 0 0
5
10
15
Unit Strain (in/in)
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Unconfined Compression Test
Sample No. Boring No. Depth of sample Description of Sample Tested by Specimen deformatio n = L (in)
SOIL TESTING LABORATORY UNCONFINED COMPRESSION TEST Project No. Location
Vertical strain = L / L
Date Proving ring dial reading [No. of small divisions]
Load = (Col. 3) calibration factor (lb)
Corrected area =
Stress = (col.4)/(col.5)
A0 1
(lb/in2) or kPa
Ac
(in2)
Result Plot a graph of s1 or the deviator stress as ordinate vs. or vertical strain in % as abcissa on Cartesian graph paper. Define qu at failure; this is s1 (peak).
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Triaxial Test
8 TRIAXIAL TEST
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Triaxial Test
8.1
INTRODUCTION
From an inspection of the triaxial apparatus, it is concluded that any soil pore-fluid state, from a negative or vacuum state to a fully saturate state with an excess pore-fluid pressure, can be obtained with this equipment. Drained or undrained conditions can be investigated. For a drained test, as the load is applied to the soil specimen, one can allow the pore fluid to escape by opening the appropriate valve. An undrained test can be performed by closing the soil system to the atmosphere so that no pore fluid can escape during the test.
8.1.1
DEFINITIONS
UNCONSOLIDATED-UNDRAINE TEST Which is also called the quick test (abbreviation commonly used are UU and Q test). This test is performed with the drain valve closed for all phases of the test. Axial loading is commenced immediately after the chamber pressure σ3 is stabilized.
CONSOLIDATED-UNDRAINED TEST Also termed consolidated-quick test or R test (abbreviated CU or R). In this test, drainage or consolidation is allowed to take place during the application of the confining pressure σ3. Loading does not commence until the sample ceases to drain (or consolidate). The axial load is then applied to the specimen, with no attempt made to control the formation of excess pore pressure. For this test, the drain valve is closed during axial loading, and excess pore pressures can be measured.
CONSOLIDATED-DRAINED TEST Also called slow test (abbreviated CD or S). In this test, the drain valve is opened and is left open for the duration of the test, with complete sample drainage prior to application of the vertical load. The load is applied at such a slow strain rate that particle readjustments in the specimen do not induce any excess pore pressure. Since there is no excess pore pressure total stresses will equal effective stresses. Also the volume change of the sample during shear can be measured.
8.2
OBJECTIVES OF TEST
Determination of shear parameters of soils by triaxial test.
8.3
SCOPE OF TEST
Scope of this test is to determine the shear parameters, strength-deformation characteristics pore water pressure, etc.
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Triaxial Test
From an inspection of the triaxial apparatus, it is concluded that any soil pore-fluid state, from a negative or vacuum state to a fully saturate state with an excess pore-fluid pressure, can be obtained with this equipment. Drained or undrained conditions can be investigated. For a drained test, as the load is applied to the soil specimen, one can allow the pore fluid to escape by opening the appropriate valve. An undrained test can be performed by closing the soil system to the atmosphere.
8.4
STANDARD DESIGNATION
ASTM: D2850-70 AASHTO: 234-70
Figure 8.1 Schematic diagram of triaxial test
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Triaxial Test
8.5
MATERIALS & EQUIPMENT
1. Triaxial cell. 2. Strain controlled compression machine (Figure 7.1) 3. Specimen trimmer 4. Wire saw 5. Vacuum source 6. Oven 7. Evaporating membrane 8. Calipers 9. Rubber membrane 10. Membrane stretcher
Figure 8.2 Triaxial test device
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Triaxial Test
Figure 8.3 Triaxial test apparatus
8.6 8.6.1
PREPARATION OF SAMPLES AND TEST SPECIMEN PREPARATION OF UNDISTURBED SAMPLE
1. Obtain a sample and using the wire saw and miter box, trim the ends parallel to each other. 2. Place the sample in the soil lathe and trim it to a circular cross-section. 3. Reposition the sample in the miter box and cut it to a length of approximately 7 cm by trimming both ends. 4. Measure the average length and diameter of the sample using the veneer caliper. Weigh the sample. 5. Use the sample trimmings to determine water content of the clay.
8.6.2
PREPARATION OF REMOULDED SAMPLE
1. Remold the clay thoroughly. 2. Reform a cylindrical specimen using the sample former, taking care not to entrap air in to the clay. 3. Extrude the sample from the mould and square its ends using the miter box. 4. Measure the sample as before.
8.7 8.7.1
TEST PROCEDURE PLACEMENT OF SPECIMEN IN THE TRIAXIAL TESTING MACHINE
1. Boil the two-porous stones to be used with the specimen.
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Triaxial Test
2. 3. 4. 5.
De-air the lines connecting the base of the Triaxial cell Attach the bottom platen to the base of the cell Place the bottom porous stone (moist) over the bottom platen. Take a thin rubber membrane of appropriate size to fit the specimen tightly. Take a membrane stretcher, which is a brass tube with an inside diameter of about ¼ in (6mm) larger than the specimen diameter. The membrane stretcher can be connected to a vacuum source. Fit the membrane to the inside of the membrane stretcher, and lap the ends of the membrane over the stretcher. Then apply the vacuum. This will make the membrane form a smooth cover inside the stretcher. 6. Slip the soil specimen to the inside of the stretcher with the membrane (step5) the inside of the membrane may be moistened for ease of slipping the specimen in. Now release the vacuum, and unroll the membrane-form the ends of the stretcher. 7. Place the specimen (step 6) on the bottom porous stone (which is placed on the bottom platen of the Triaxial cell), and stretch the bottom end of the membrane around the porous stone and bottom platen. At this time, place the top porous stone (moist) and the top platen on the specimen, and stretch the top of the membrane over it. For airtight seals, it is always a good idea to apply some silicone grease around the top and bottom plates before the membrane is stretched over them. 8. Using some rubber bands, tightly fasten the membrane around the top and bottom platens. 9. Connect the drainage line leading from the top platen to the base of the triaxial cell. 10. Place the Lucite cylinder from the top platen to the base triaxial cell on the base plate to complete the assembly. Note 1. In the Triaxial cell, the specimen can be saturated by connecting the drainage line leading to the bottom of the specimen to a saturation reservoir. During this process, the drainage line leading from the top of the specimen is kept open to the atmosphere. The saturation of clay specimens takes a fairly long time. 2. For unconsolidated undrained test, if the specimen saturation is not required, nonporous plates can be used instead of porous stones at the top and bottom of the specimen.
8.7.2
UNCONSOLIDATED- UNDRAINED TEST
1. Place the Triaxial cell (with the specimen inside it) on the platform of the compression machine. 2. Make proper adjustment so that the piston of the triaxial cell just rests on the top platen of the specimen. 3. Fill the chamber of the triaxial cell with water. Applying a hydrostatic pressure, 3, to the specimen through the chamber fluid. (Note: All drainage to and from the specimen should be closed now so that drainage from the specimen does not occur). 4. Check for proper contact between the piston and the top platen on the specimen. Zero the dial gauge of the proving ring and the gauge used for measurement of the vertical compression of the specimen. Set the compression machine for a strain rate of about 0.5% per minute, and turn the switch on.
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Triaxial Test
5. Take proving ring dial readings for vertical compression intervals of 0.01inch (0.254mm) initially. This interval can be increased to 0.02 inch (0.508mm) or more later when the rate of increase of loads on the specimen decreases. The proving ring readings will increase to a peak value and then may decrease or remain approximately constant. Take about four to five readings after the peak point. 6. After completion of the test, reverse the compression machine and lower the triaxial cell, and then shut off the machine. Release the chamber pressure, and drain the water in the triaxial cell. Then remove the specimen and determine its moisture content.
8.8
CALCULATIONS
1. Compute the unit strain from the deformation readings as 2. Δax = ΔL/L0 and fill in the appropriate column of the data sheet. Also compute the adjusted instantaneous area A = Ac/ (1-Δax) and place this in the appropriate column of the data sheet. The c subscript above refers to the fact that these should be the dimensions not at the start of the test, but after consolidation of the specimen. 3. Compute the axial load using the load readings. If a load (proving) ring is used, the load P is P = DR x load-ring constant where DR is the load-dial reading in units of deflection. Put these data in the appropriate column of the data sheet. 4. Compute the principal stress difference 5. (σ1 - σ3) = P/A and fill in the appropriate column of the data sheet. 6. Knowing that 7. σ1 = σ3 + (σ1 - σ3) 8. Compute the principal stress ratio: σ1/σ3
8.9
RESULTS
1. Draw a graph of the axial strain (%) vs. deviatory stress. From this graph, obtain the value of at failure ( = f) 2. The minor principal stress on the specimen at failure is 3 (i.e. the chamber confining pressure). Calculate the major principal stress at failure as
1 3 3. Draw a Mohr’s circle with 1 and 3 as the major and minor principal stresses. The radius of the Mohr’s circle is equal to Su.
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Triaxial Test
16 Stress change lb/in2
14 12 10 8 6 4 2 0 0
2
4
6 8 Axial strain %
10
12
14
Chart 8.1 Showing stress vs strain curve
Chart 8.2 Showing results of triaxial test
8.10
ENGINEERING USES OF TEST RESULTS
Triaxial test is a soils laboratory test to determine shear strength parameters. The shear strength of soil is needed to design foundation, slopes, tunnels, dams, and other geotechnical systems. It is a most widely used technique of determining the shear strength of soils.
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Triaxial Test
The sample, which is cylindrical, is tested inside a Perspex cylinder filled with water under pressure. The sample under test is enclosed in a thin rubber membrane to seal it from the surrounding water. The pressure in the cell is raised to the desired value, and the sample is then brought to failure by applying an additional vertical stress. One of the major advantages of the triaxial apparatus is the control provided over drainage from the sample. When no drainage is required (i.e. in undrained tests), solid end caps are used. When drainage is required, the end caps are provided with porous plates and drainage channels. It is also possible to monitor pore-water pressures during a test.
8.11
PRECAUTIONS
1. Limit the magnitude of the excess pore pressure by testing at a very slow strain rate, as it is impossible to have a state of no excess pore pressure 2. A drain test can take up to a week. For this duration, membrane leaks, soil set up and equipment corrosion can be significant.
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Triaxial Test
8.12
SAMPLE PROBLEM
SOIL TESTING LABORATORY UNCONSOLIDATED UNDRAINED TRIAXIAL TEST (Preliminary data) Sample No. 15 Project No. SR 2828 Boring No. B-21 Location Newell, N.C Depth of sample 3 ft Description of Sample Reddish brown silty clay Tested by John Doe Date 1/26/89 Moist unit weight of specimen (beginning of test) 122.7 lb/ft3 Moisture content (end of test) 16.9 (%) Dry unit weight of specimen 105.0 lb/ft3 Initial average length of specimen, Lo 5.82 cm Initial average diameter of specimen, Do 2.50 cm Initial area, Ao 4.91 cm2 Gs 2.78 Final degree of saturation 71.9 % Cell confining pressure, σ3 10.0 psi Proving ring calibration factor 6000 lb/in
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Triaxial Test
SOIL TESTING LABORATORY UNCONSOLIDATED-UNDRAINED TRIAXIAL TEST (Axial stress – strain calculation) Specimen deformation = δL
Vertical strain, є = δL L
Proving ring dial reading
(in) (1) 0 0.005 0.01 0.015 0.02 0.025 0.05 0.075 0.100 0.125 0.150 0.175 0.200 .225
(2) 0 0.0009 0.0017 0.0026 0.0034 0.0043 0.0086 0.0129 0.0172 0.0215 0.0258 0.0301 0.0344 0.0387
(3) 0 0.0012 0.0025 0.0037 0.0053 0.0066 0.0140 0.0201 0.0256 0.0294 0.0321 0.0337 0.0331 0.0305
Piston Load, col.3 x c.f (calibration factor) (lb)
Corrected area = Ac = Ao /1 – є (in2)
(4) 0 7.2 15 22.2 31.8 39.6 84 120.6 153.6 176.4 192.6 202.2 198.6 183
(5) 4.91 4.91 4.92 4.92 4.93 4.93 4.95 4.97 5.00 5.02 5.04 5.06 5.08 5.11
Deviatory Stress Δσ = P/Ac (lb/in2) (6) 0 1.5 3 4.5 6.5 8 17 24.3 30.7 35.1 38.2 40 39 35.8
Result 1. Draw a graph of the axial strain (%) vs. deviatory stress. From this graph, obtain the value of at failure ( = f) 2. The minor principal stress on the specimen at failure is 3 (i.e. the chamber confining pressure). Calculate the major principal stress at failure as
1 3
3. Draw a Mohr’s circle with 1 and 3 as the major and minor principal stresses. The radius of the Mohr’s circle is equal to Su.
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Triaxial Test
Stress (lb/in2)
Axial Strain vs Stress 45 40 35 30 25 20 15 10 5 0 0
0.01
0.02
0.03
0.04
0.05
Axial Strain (in/in)
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Triaxial Test
SOIL TESTING LABORATORY UNCONSOLIDATED UNDRAINED TRIAXIAL TEST (Preliminary data) Sample No. Project No. Boring No. Location Depth of sample Description of Sample Tested by Date Moist unit weight of specimen (beginning of test) Moisture content (end of test) Dry unit weight of specimen Initial average length of specimen, Lo Initial average diameter of specimen, Do Initial area, Ao Gs Final degree of saturation Cell confining pressure, σ3 Proving ring calibration factor
cm cm cm2 %
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Triaxial Test
SOIL TESTING LABORATORY UNCONSOLIDATED-UNDRAINED TRIAXIAL TEST (Axial stress – strain calculation) Cell confining pressure,σ3= Specimen Vertical Proving ring Piston Load, Corrected Deviatory deformation strain, dial reading col.3 x c.f area = Stress = δL є = δL (calibration Ac = Ao /1 – є Δσ = P/A L factor) (in) (lb) (in2) (lb/in2) (1) (2) (3) (4) (5) (6)
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Plate Load Test
9 PLATE LOAD TEST
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Plate Load Test
9.1
INTRODUCTION
1. The test results reflect only the character of the soil located within a depth less than twice the width of the bearing plate (corresponding to an isobar of one-tenth the loading intensity at the test plate). Since the foundations are generally large, the settlement and resistance against shear will depend on the properties of a much thicker stratum. 2. It is essentially a short duration test, and hence the test does not give the ultimate settlement, particularly in the case of cohesive soils. 3. Another limitation is the effect of the size of foundation. For clay soils the ultimate pressure for a large foundation is the same as that for the test plate. But in dense sandy soils, the bearing capacity increases, with the size the foundation, and the test on smaller size bearing plates tend to given conservative values.
EFFECT OF THE SIZE OF PLATE ON BEARING CAPACITY As stated in limitation 3 above, the bearing capacity of sands and gravels increase with the size of the footing. The relationship can be expressed as under Bf qf M N Bp In the above relation, M term includes the NC and Nq terms while N include N portion of the bearing capacity equation. The above equation can also be solved graphically by using more than one size plates
EFFECT OF SIZE OF PLATE ON SETTLEMENT The settlement of a footing varies with its size. Terzaghi and peck have suggested the following relationship b/w the settlement of plate (sp) and settlement of actual footing (sf) for granular soils. Bp( B 0.3 ) Sp sf B( Bp 0.3 )
2
If s is the permissible settlement of the foundation, the maximum settlement of the largest forting should be restricted to 4/3s. The corresponding settlement of the test plate (Sp) on sand, soil is given by Sp
Bp( B 0.3 ) 4 .s 3 B( Bp 0.3 )
2
DETERMINATION OF BEARING CAPACITY By extrapolating the plate load test data, one can use the following equation for all practical purposes to determine the bearing capacity of soil.
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Plate Load Test
q f qp
Bf Bp
Where qf = bearing capacity of the actual footing Bf = width of actual footing qp = bearing capacity, obtained from the plate load test Bp = width of plate However, for clays, the bearing capacity is almost independent of the footing size or the plate size. qf = qb For a c- soil, housel (1992) suggested the following expression: Q = A q + P. S Where Q = total load on bearing area A = contact area of footing or plate P = perimeter of footing q = bearing pressure beneath area A S = perimeter shear
DETERMINATION OF SETTLEMENT Settlement of prototype foundation can be estimated from the results of plate load test using following equations, after Terzaghi (1948). Bf S f Sp Bp For clays and if the sand is like an elastic material, then the settlement can be calculated from
S p ap B p
1u2 Ip E
Where Sp = plate settlement ap = applied stress Bp = width or diameter of the of the plate u = poisons ratio E = elastic modulus Ip = influence factor (0.82 for rigid plate) The settlement of the real footing of width B is related to the plate settlement by
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Plate Load Test
or
2B S f Sp B Bp
2B S f Sp B 0.3
2
for sands
2
Where Sf = settlement of a prototype foundation Sp = settlement of square plate of 0.3 m by 0.3 m Bf = width of prototype foundation Bp = width of the plate Bond (1961) has proposed the following equation for settlements
B S f Bp Sp
n 1
Where n = coefficient depending on the types of soil The value of index n can be determined by carrying out two or more plate load tests on different size plates. In absence of test data the following values of n can be adopted: Clay: 0.03 to 0.05 Sandy clay: 0.0.8 to 0.10 Dense sand: 0.4 to 0.5 Medium to dense sand: 0.25 to 0.35 Loose sand: 0.20 to 0.25
9.1.1
DEFINITIONS
DEFLECTION The amount of downward vertical movement of a surface due to the application of a load to the surface.
RESIDUAL DEFLECTION The difference between original and final elevations of a surface resulting from the application and removal of one or more loads to and from the surface.
REBOUND DEFLECTION The amount of vertical rebound of a surface that occurs when a load is removed from the surface.
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Plate Load Test
BEARING CAPACITY The pressure that a soil sample can sustain without failing is called the bearing capacity of soil.
SOIL SETTLEMENT The process of compression (reduction in the volume of voids) of soil due to the expulsion of air, water or both from the voids as a result of increased loading (such as geostatic weight or weight of structure above) is called soil settlement.
9.2
OBJECTIVES OF TEST
This experiment is used to determine the ultimate and or safe bearing capacity of the fullscale foundation.
9.3
SCOPE OF TEST
This method covers the making of non repetitive static plate load test on subgrade soils and flexible pavement components, in either the compacted condition or the natural state, and is intended to provide data for use in the evaluation and design of rigid and flexible type airport and highway pavements.
9.4
STANDARD REFERENCE
ASTM: D1194 AASHTO T 222-81
9.5 9.5.1
MATERIALS & EQUIPMENT FIELD TEST APPARATUS
The required field test apparatus is as follows 1. Load reaction equipment. Load reaction equipment consisting of a truck, trailer, anchored frame, or similar device having a dead load of at least 25,000 lb. 2. Bearing plates. Bearing plates consisting of a 30-in., 24-in., and 18-in.-diameter steel plate, each plate 1 in. thick. Aluminum alloy No. 24ST plates 1.5 in. thick may be used in lieu of steel plates. 3. Jack. Hydraulic jack capable of applying loads of at least 25,000 lb. 4. Ball joint. A ball joint to be inserted between the jack and load reaction equipment or between the jack and bearing plates to prevent eccentricity of loading.
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Plate Load Test
5. Load-measuring device. A load-measuring device consisting of either a hydraulic gage on the jack, a steel proving ring, or load cell. All are satisfactory for measuring applied load, but must be accurately calibrated. 6. Micrometers. Three dial micrometers, reading to 1/10,000 in., dial stems, and support. 7. Sand/plaster of Paris. Clean sand or plaster of Paris. 8. Cribbing. Cribbing of short pieces of hardwood or steel H- or I-beams. 9. Stopwatch. 10. Containers. Containers for undisturbed soil samples. 11. Consolidometer apparatus. 12. Cutting equipment. Necessary equipment for cutting an undisturbed specimen of the soil into a consolidometer test ring. 13. Scales 14. Oven 15. Miscellaneous tools for making moisture-content determinations.
Figure 9.1 Plate load test apparatus
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Plate Load Test
Figure 9.2 Schematic diagram of Plate load test
9.6
TEST PROCEDURE
The test pit width is made five times the width of the plate Bp. At the center of the pit, a small square hole is dug whose size is equal to the size of the plate and the bottom level of which corresponding to the level of the actual foundation (figure) the depth Dp of the hole should be such that the loading to the plate may be applied with the help of a hydraulic jack. The reaching of the hydraulic jack may be borne by either of the following two methods a) Gravity loading plate form method b) Reaction truss method In the case of gravity loading method, plate form is constructed over a vertical column resting on the rest plate, and the loading is done with the help of sand bags, stone or concrete blocks. The general arrangement of the test set-up for this method is shown in the figure. When load is applied to the plate, it sinks or settles. The settlement of the plate is measured with the help of sensitive dial gauge. For square plate, two dial gauges are used. The dial
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Plate Load Test
gauges are mounted on independently supported datum bar. As the plate settles, the ram of the dial gauge moves down and settlement is recorded. The load is indicated on the loadgauge of the hydraulic gauge of the hydraulic jack. 5Bp
D Dp
Bearing Plate
Foundation level
Bp
Sand bags
Plate form Main girder Hydraulic jack Masonry support Loading post Dial gauges
Datum bar
Test plate
Figure 9.3 Schematic diagram of Plate load test The load is applied with the help of a hydraulic jack (preferably with the remote control pumping unit), in convenient increments, say of about one-fifth of the expected safe bearing capacity or one-tenth of the ultimate bearing capacity. Dial gauges fixed at diametrically opposite ends, with sensitivity of 0.02mm, observe settlement of the plate. Settlement should be observed for each increment of load after an interval of 1,4,10, 20, 40 and 60 minutes and thereafter at hourly interval until the rate of settlement becomes less than about 0.02mm per hour. After this, the next load increment is applied. The maximum load that is to be applied corresponds to 3 time’s proposed allowable bearing pressure. The water table has a marked influence on the bearing capacity of sand or gravelly soil. If the water table is already above the level of the footing, it should be lowered by pumping and the bearing plate seated after the water table has been lowered just below the footing level. Even
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Plate Load Test
if the water table is locate above 1 m below the base level of the footing, the load test should be made at the level of the water table itself. When a load settlement curve (Fig 9.2) does not indicate any marked breaking point, failure may alternatively be assumed corresponding to settlement equal to one fifth of the width of the test plate. In order to determine the safe bearing capacity it would be normally sufficient to use a factor of safety of 2 or 2.5 on ultimate bearing capacity. Plate load data 0 4
Settlement (mm)
8 12 16 20 24 28 32
0
1
2
3
4
5
6
7
8
9
10
Load kg/cm square Chart 9.1 Load vs. Settlement
9.7
ENGINEERING USES OF TEST RESULTS
1. The Plate Bearing (or Loading) Test, is normally used to measure the short term settlement of road sub-grade or building footings under their proposed design load. The value of settlement against load is then used to check that the soil meets design load settlement criteria. The test therefore is of use to both contractors and to specifying authorities. 2. In addition to values of settlement, other soil parameters can be measured, or calculated from the plate bearing test. These include Modulus of Sub-Grade Reaction, permanent deformation characteristics of the soil and in some instances shear strength of the soil. 3. This method of testing is used for determining the modulus of reaction of soils by means of the plate bearing test and for determining the corrections to be applied to the
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Plate Load Test
field test values by means of laboratory tests. The modulus of soil reaction is required in rigid pavement design and evaluation. 4. This test method is used to estimate the bearing capacity of a soil under field loading conditions for a specific loading plate and depth of embedment but also for load tests of soil and flexible pavement components for use in evaluation and design of airport and highway pavements.
9.8
PRECAUTIONS
1. Sample should make with care. 2. Apparatus should be handled carefully.
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California Bearing Ratio Test
10 CALIFORNIA BEARING RATIO TEST
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California Bearing Ratio Test
10.1
INTRODUCTION
The CBR test was developed by California Division of Highway in 1929 as mean of classify the suitability of a soil for use as a sub grade or base course material in highway construction. The laboratory test measures the shearing resistance of a soil under controlled moisture and density conditions.
DEFINITIONS
10.1.1
CALIFORNIA BEARING RATIO The CBR for a soil is the ratio (expressed as %) obtained by dividing the penetration stress required to cause a 3-in2 area (hence, a 1.95-in. diameter) piston to penetrate 0.10 in. into the soil by a standard penetration stress of 1,000 psi. It may be expressed in the equation form as
penetratio n.stress( psi).required .to. penetrate (0.10.inches ) 100 CBR 1000 psi Note: The 1,000 psi in the denominator is the standard penetration stress for 0.10 in. penetration.
SU B G R A D E The natural soil upon which the pavement is laid. The sub grade is seldom strong enough to carry a wheel load directly.
10.2
OBJECTIVES OF TEST
This method describes the sampling of the sub grade for California Bearing Ratio (CBR)The resulting information is used for pavement design thickness.
10.3
SCOPE OF TEST
This test method is used to determine layer thicknesses and in-place California Bearing Ratio (CBR) and to obtain samples of the pavement layer, base, sub-base, and sub-grade for laboratory testing. The test method is applicable to both asphalt concrete (AC) and Portlandcement concrete (PCC) pavements. The strength of the sub grade is the main factor in determining the thickness of the pavement although its susceptibility to frost must also be considered. The value of the stiffness of the sub grade is required if the stresses and strains in the pavement and the sub grade are to be calculated.
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California Bearing Ratio Test
10.4
STANDARD REFERENCE
ASTM D1883-73
10.5
MATERIALS & EQUIPMENT
1. CBR test apparatus: Compaction mold (6-in. diameter and 7-in. height),collar, spacer disk ( 5.937 diameter and 2.416-in. height),adjustable stem and perforated plate, weights, penetration piston(3 in² in area) 2. Loading (compression) machine: with load capacity of at least 10,000 lb and penetration rate of 0.05 in./min 3. Expansion measuring apparatus 4. Two dial gages (with accuracy to 0.001 in.) 5. Standard compaction hammer 6. Mixing bowl 7. Scales 8. Soaking tank 9. Oven
Figure 10.1 CBR test apparatus
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California Bearing Ratio Test
10.6
TEST PROCEDURE
1. Place the mould with base plate containing the sample, with the top face of the sample exposed, centrally on the lower platen of the testing machine. 2. Place the appropriate annular surcharge discs on top of the sample. 3. Fir into place the cylindrical plunger and force-measuring devise assembly with the face of the plunger resting on the surface of the sample. 4. Apply a seating force to the plunger, depending on the expected CBR value, as follows. 5. for CBR value up to 5%, apply 10 N 6. for CBR value from 5% to 30%, apply 50 N 7. for CBR value above 30%, apply 250 N 8. Secure the penetration dial gauge in position. Record its initial zero reading, or reset it to read zero. 9. Start the test so that the plunger penetrates the sample at a uniform rate of 10.2mm/min, and at the same instant start the timer. 10. Record readings of the force gauge at intervals of penetration of 0.25mm, to a total penetration not exceeding 7.5mm 11. After completing the penetration test or tests, determine the moisture content of the test sample 12. Test results are plotted in the form of a load-penetration diagram by drawing a curve through the experimental points. Usually the curve will be convex upwards but sometimes the initial part of the curve is concave upwards and, over this section, a correction becomes necessary. The correction consists of drawing a tangent to the curve at its steepest slope and producing it back to cut the penetration axis. This point is regarded as the origin of the penetration scale for the corrected curve. 13. Penetrations of 2.5mm and 5mm are used for calculating the CBR value. From the test curve, with corrected penetration scale if appropriate, read off the forces corresponding to 2.5mm and 5mm penetration. Express these as a percentage of the standard forces at these penetrations. Take the higher percentage as the CBR value.
10.7
ENGINEERING USES OF TEST RESULTS
This test method is used to evaluate the potential strength of sub grade, sub base, and base coarse material including recycled materials for use in road and airfield pavements. The CBR value obtained in this test forms an integral part of several flexible pavement design methods. For applications where the effect of compaction water content on CBR is unknown or where it is desired to account for its effect, the CBR is determined for a range of water content, usually the range of water content permitted for field compaction by using agency’s field compaction specification.
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California Bearing Ratio Test
10.8 1. 2. 3. 4.
PRECAUTIONS Scale must be precise. Width of groove must be accurate. Depth of groove must be accurate. Handle of turning pace should be done with care.
10.9
CALCULATIONS
CBR value for 2.5mm (0.1in) penetration (
)
(
)
(
)
(
)
(
)
(
)
CBR value for 5.0mm (0.2in) penetration
10.10
(
)
(
)
CORRECTIONS TO CURVE
The correction to the curve and reading given on the next page should be done.
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California Bearing Ratio Test
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California Bearing Ratio Test
10.11
SAMPLE PROBLEM
SOIL TESTING LABORATORY CALIFORNIA BEARING RATIO TEST Moisture Content Determination Before compaction
after compaction
Top 1 in layer after soaking
Average moisture content after soaking
can no.
1-A
1-B
1-C
1-D
weight of can, W1 (g)
45.23
47.28
43.44
46.59
weight of can + wet soil, W2 (g)
315.94
326.01
304.71
356.37
weight of can + dry soil, W3 (g)
273.69
283.37
261.53
305.82
mc (%)=(W2-W3)/(W3-W1)×100
18.49
18.06
19.79
19.50
Average moisture content before soaking (%) = Average moisture content after soaking (%) =
18.27 19.64
Density Determination Before soaking
After soaking
weight of mold + compacted soil specimen (g)
9020.9
9036.81
Weight of mold (g)
4167.5
4167.5
Weight of compacted soil specimen (g)
4853.4
4869.31
6
6
Area of soil specimen (in2)
28.278
28.278
height of soil specimen (in.)
5
5
141.39
141.39
Wet density (lb/ft )
130.76
131.19
Moisture content (%)
18.27
19.64
110.56
109.64
Diameter of mold (in.)
Volume of soil specimen (in.3) 3
3
Dry density (lb/ft )
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California Bearing Ratio Test
Swell Data
Surcharge weight (lb) Time Date Elapsed time (hr) Dial reading(in.) Initial height of soil specimen (in.) Swell (% of initial height)
Initial swell measurement 10 10:16 AM 5/26/2006 0 0 5 0
Final swell measurement 10 10:16 AM 5/30/2006 96 0.0135 5 0.27
soaked
unsoaked
Bearing Ratio Data Check one Weight of surcharge (lb)
10
Proving ring calibration (lb/in) Penetration (in)
Proving ring dial reading (in.)
1
2
0 0.025 0.05 0.075 0.1 0.125 0.15 0.175 0.2 0.3 0.4 0.5
0 0.0004 0.0008 0.0013 0.0016 0.0019 0.002 0.0022 0.0023 0.0026 0.003 0.0032
74000
Piston load (lb) 3=2×proving ring calibration 0 29.6 59.2 96.2 118.4 140.6 148 162.8 170.2 192.4 222 236.8
Area of piston (in.2)
penetration stress (psi)
4
5=3/4
3 3 3 3 3 3 3 3 3 3 3 3
0 9.86 19.73 32.06 39.46 46.86 49.33 54.26 56.73 64.13 74 78.93
Result CBR at 0.10-in. penetration (%) = [corrected penetration stress for 0.10 in penetration (from curve of penetration stress versus penetration)]/1000×100 = 3.95 CBR at 0.20-in. penetration (%) = [corrected penetration stress for 0.20 in penetration (from curve of penetration stress versus penetration)]/1500×100= 3.78
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California Bearing Ratio Test
Penetration stress (psi)
Curve of Penetration Stress vs Penetration
90 80 70 60 50 40 30 20 10 0 0
0.1
0.2
0.3
0.4
0.5
0.6
Penetration (in.)
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California Bearing Ratio Test
SOIL TESTING LABORATORY CALIFORNIA BEARING RATIO TEST Moisture Content Determination Before compaction
after compaction
Top 1 in layer after soaking
Average moisture content after soaking
can no. weight of can, W1 (g) weight of can + wet soil, W2 (g) weight of can + dry soil, W3 (g) mc (%)=(W2-W3)/(W3-W1)×100 Average moisture content before soaking (%) = Average moisture content after soaking (%) =
Density Determination Before soaking
After soaking
weight of mold + compacted soil specimen (g) Weight of mold (g) Weight of compacted soil specimen (g) Diameter of mold (in.) Area of soil specimen (in2) height of soil specimen (in.) Volume of soil specimen (in.3) Wet density (lb/ft3) Moisture content (%) Dry density (lb/ft3)
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California Bearing Ratio Test
Swell Data Initial swell measurement
Final swell measurement
soaked
unsoaked
Surcharge weight (lb) Time Date Elapsed time (hr) Dial reading(in.) Initial height of soil specimen (in.) Swell (% of initial height)
Bearing Ratio Data Check one Weight of surcharge (lb) Proving ring calibration (lb/in)
Penetration (in)
Proving ring dial reading (in.)
Piston load (lb)
Area of piston (in.2)
penetration stress (psi)
1
2
3=2×proving ring calibration
4
5=3/4
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California Bearing Ratio Test
Result CBR at 0.10-in. penetration (%) = [corrected penetration stress for 0.10 in penetration (from curve of penetration stress versus penetration)]/1000×100 = CBR at 0.20-in. penetration (%) = [corrected penetration stress for 0.20 in penetration (from curve of penetration stress versus penetration)]/1500×100=
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Bibliography
BIBLIOGRAPHY
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Bibliography
BIBLIOGRAPHY Braja M. Das, Soil Mechanics Lab Manual, Arpad Kezdi, Hand Book of Soil Mechanics and Soil Testing, K. H. Head, Manual of Soil Laboratory Testing, Joseph E. Bowles, Engineering Properties of Soil and Their Measurements, fourth edition, BS 1377: Part 2 (1990), British Standard Methods of Test for Soil for Engineering Purposes. Cheng Liu, Jack B. Evett, Soil Properties (Testing, Measurement and Evaluation), second edition, W. L. Schroeder, Soil in Construction (fifth edition), ASTM 1988 ‘Annual book of ASTM Standards’ Book of Standards Volume: 04, Publisher: Taylor & Francis, Volume 22, Number 7 / 2004 Ashworth Manual, Embankment and Bas’, Prof. Krishna Reddy, UIC, Engineering Properties of Soils Based on Laboratory Testing Soil mechanics work book Dr. J. T. Germaine, Civil engineering material laboratory Bardet, Jean-Pierre. (1997), Experimental Soil Mechanics. Prentice-Hall, Means, R.E. and Parcher, J.V. (1963), Physical Properties of Soils Ajay K. Duggal and Vijay P. Puri, Laboratory Manual in Highway Engineering, H. S. Moondra, Rajiv Gupta, Lab Manual for Civil Engineering, http://www.vulcanhammer.net “Laboratory Soils Testing” http://www.mastrad.com/speed.htm http://www.geneq.com/catalog/en/large_speedy.html http://www.mbt.co.id/equipment/so-430.html
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Bibliography
http://www.humboldtmfg.com/c-5-p-222-id-5.html http://www.aimil.com/Search/ProductDetails.aspx?Id=913 http://www.udot.utah.gov/dl.php/tid http://www.sddot.com/pe/materials/docs/matlsman/sd http://www.civl.port.ac.uk/projects/geotech/geo4.html http://geotech.uta.edu/lab/Main/atrbrg_lmts/index.htm http://www.astm.org/cgi-bin/softcart.exe/database.cart/redline_pages/d4318.htm?e+mystore http://www.civl.port.ac.uk/projects/geotech/geo5.html http://www.stl-inc.com http://www.atechcenter.com/hyd1.html http://www.uwe.ac.uk/geocal http://www.webstore.ansi.org
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