Laboratory 3 - Point Load Test

FACULTY : CIVIL & ENVIRONMENTAL ENGINEERING DEPARTMENT : GEOTECHNICAL & TRANSPORTATION ENGINEERING LABORATORY : ENGINEERING GEOLOGY & GEOPHYSIC LABORATORY

NO. OF PAGES: EDITION: NO. OF CHECKING:

1/5 LAB 3

EFECTIVE DATE :

8/1/2007

TOPIC : ROCK STRENGTH - POINT LOAD TEST (LAB 3)

AMENDMENT DATE:

8/1/2007

1.0 OBJECTIVE This experiment deals with determination of rock strength when a certain load implied on the rocks. Students should be able conducted the experiment, understanding the theory and recognize the rock strength on different types of rocks in Malaysia.

2.0 LEARNING OUTCOMES a) b) c)

To determine a rock strength on different types of rock formation in Malaysia. To evaluate the physical properties of rocks for civil engineering application. To understand the theory rock test.

3.0 THEORY This apparatus, also named Franklin Press (1970), is used to obtain quick information concerning rock strength. Point load measurement represents one of the most widely used in classification tests for rocks, both in the field and in the laboratory. A rock piece is subjected to a compression load along its diameter with two apposite conical platens. The index of rock strength is calculated from the following: IS = P D Where P is the maximum applied load and D the core diameter. The test consists to compress up to failure a core or irregular block of rock sample by the application of a point load by a couple of steel conical points of standard size. The load required obtaining the failure of the sample and the distance between the conical points before and after the test is then measured. Three test methods are generally carried on are compression along a diameter, axial compression and compression on irregular pieces. The distance between the points must be between 30 and 85 mm and the shape ratio as indicated in Figure 1.

4.0 EQUIPMENT AND MATERIALS a) b) c)

Digital or manual rock strength index apparatus ( Point Load Test ) Irregular pieces rock samples Clear safety goggles

Prepared by

:

Lecturer

Name

:

Mohamad Faizal bin Tajul Baharuddin & Mohd Hazreek Bin Zainal Abidin

Signature

:

Date

:

8 January 2007

FACULTY : CIVIL & ENVIRONMENTAL ENGINEERING DEPARTMENT : GEOTECHNICAL & TRANSPORTATION ENGINEERING LABORATORY : ENGINEERING GEOLOGY & GEOPHYSIC LABORATORY TOPIC : ROCK STRENGTH - POINT LOAD TEST (LAB 3)

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2/5 LAB 3

EFECTIVE DATE :

8/1/2007

AMENDMENT DATE:

8/1/2007

5.0 PROCEDURE The apparatus consists of a load frame 55kN capacity with hydraulic loading ram actuated by hand pump. Students should tests on block and irregular lump. Check first on the block and lumps to be tested respect the shape prescription here indicated:

15 ≤ D ≤ 85

0.3 ≤ D/W ≤ 1.0

0.5 D ≤ L

Where; D = Distance of the contact conical points (mm) W = Average width (Waverage) of the sample perpendicular to the loading direction (mm) L = Distance between the contact conical points and the nearest free end (mm) Ten (10) irregular lump samples should be tested from the same original type of rock. Mark the desire test orientation on the sample with lines along the surface. These lines are used for centering the sample before the test and checking the proper stress orientation along the compression to failure. Close the valve of the hydraulic circuit of the hand pump. Insert the extension rod the jacket lever and zero set the digital readout unit. Insert the sample between the conical points along a direction perpendicular to the end faces of the core, far from the ends or edges: act on the jack to close the platens to the core. Check that the digital manometer records a small load and operate with the pump to increase the load steadily such that the failure occurs within 10 to 60 sec. record the maximum force displayed by the digital manometer (the peak load value is frozen on the display) and measure again the distance D of the points. If a partial failure occurs (Figure 2), the test result is not considered. 6.0 RESULT AND ANALYSIS The results should have the point load strength index, Is (MPa). The Is is calculated as follows: Is = P (1000) DE2 Where; P = Peak resistance expressed in kilo Newton (kN) DE = Equivalent diameter of the core expressed in millimeter (mm) For diametrical tests, with blocks or irregular lumps: DE2 = 4 A / π Where; A = Waverage x D = represents the minimum cross sectional area of a plane through the platen contact points. Diameter correction factor should be performed if the samples diameter is not close to 50 mm. Therefore; F = (D / 50)0.45

Is(50) = Is x F

To calculate the average point load index, Is(50) for a type of rock, at least 10 point load test are required; from these tests, reject the highest and lowest strength value, and average the others. The relationship between the average point load index, Is(50) and uniaxial compression strength as follows; c = α Is(50)average α = 20 for soft rock α = 24 for hard rock

(after Broch & Franklin, 1972; Bieniawaski, 1975)

Where; c = uniaxial compression strength → Tabulate all the results in Table 1 attached.

FACULTY : CIVIL & ENVIRONMENTAL ENGINEERING DEPARTMENT : GEOTECHNICAL & TRANSPORTATION ENGINEERING LABORATORY : ENGINEERING GEOLOGY & GEOPHYSIC LABORATORY

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3/5 LAB 3

EFECTIVE DATE :

8/1/2007

TOPIC : ROCK STRENGTH - POINT LOAD TEST (LAB 3)

AMENDMENT DATE:

8/1/2007

7.0 QUESTION AND DISCUSSION

(1)

Why point load strength index, Is(50) obtained are not recommended to be used as design input parameters?

(2)

Describe generally the differences between index and direct test.

(3)

Explain the discontinuities in rock and their effect on strength.

8.0 CONCLUSION Conclude your results of the point load strength index, Is(50) and uniaxial compression strength in the Table 1 by rate its significance or applications in civil engineering or construction industry.

FACULTY : CIVIL & ENVIRONMENTAL ENGINEERING DEPARTMENT : GEOTECHNICAL & TRANSPORTATIONAL ENGINEERING LABORATORY : ENGINEERING GEOLOGY & GEOPHYSIC LABORATORY

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4/5 LAB 3

EFECTIVE DATE :

8/1/2007

TOPIC : ROCK STRENGTH - POINT LOAD TEST (LAB 3)

AMENDMENT DATE:

8/1/2007

Note 1 – Legend: L = Length, W= width, D = depth or diameter and De = equivalent core diameter

Figure 1

Load Configuration and Specimen Shape requirement

FACULTY : CIVIL & ENVIRONMENTAL ENGINEERING

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5/5

DEPARTMENT : GEOTECHNICAL & TRANSPORTATIONAL ENGINEERING LABORATORY : ENGINEERING GEOLOGY & GEOPHYSIC LABORATORY

EDITION: NO. OF CHECKING:

LAB 3

EFECTIVE DATE :

8/1/2007

TOPIC : ROCK STRENGTH - POINT LOAD TEST (LAB 3)

AMENDMENT DATE:

8/1/2007

NOTE 1 - (a) valid diametral tests; (b) valid axial tests; (c) valid block tests; (d) invalid tests

Figure 2

Typical Modes of Failure for Valid and Invalid Tests

Table 1

Sample No.

Length, L (mm)

Depth, D (mm)

Upper width, W1 (mm)

Lower width, W2 (mm)

Results and Analysis Average width, Waverage (mm)

Load, P (kN)

Equivalent diameter of core sample, DE2 (mm2)

Point Load Index Strength, Is (MPa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Average point load index, Is(50) (MPa) = _____+_____+_____+_____+________________________________ = ________

Hence, uniaxial compression strength UCS of rock, c = α Is(50)average (MPa) c = ____________ ____________

F

Is(50) (MPa)

Sketches sample diagram before & after failure (use attachment)