CVE40001-KHO+LEE+TAN-PVD-SEM1-2015

Swinburne University of Technology Faculty of Engineering, Computing and Science ASSIGNMENT AND PROJECT COVER SHEET

CVE40001

Geotechnical Engineering TU1 01/2015 Tutorial Group: CHOO CHUNG SIUNG PREFABRICATED VERTICAL DRAIN DESIGN 5 MAY 2015 Date Received:

Unit Code: Semester / Year: Lecturer Name: Assignment Title: Due Date:

Unit Title:

We declare that this is a group assignment and that no part of this submission has been copied from any other student's work or from any other source except where due acknowledgment is made explicitly in the text, nor has any part been written for us by another person. Student ID

Family Name

Other Names

Sections Written

1

4322754

KHO

KEVIN KA YONG

2

4309561

LEE

SIMON YEW SENG EQUALLY DIVIDED

3

4327268

TAN

SZE NIAN

EQUALLY DIVIDED

EQUALLY DIVIDED

Marker's comments:

Total Mark: Extension certification: This assignment has been given an extension and is now due on _____________ Signature of convenor: _____________

Signature

Swinburne University of Technology (Sarawak Campus) Assessment of Student’s Assignment Subject Code / Name: Assessment for: Tutorial session:

CVE40001 Geotechnical Engineering (Sem 1, 2015) PVD Assignment (10% of unit marks) Mon 1:30 / Tue 3:30 / Thu 1:30

Name of Group: Name(s) of Student(s):

KEVIN KHO KA YONG, SIMON LEE YEW SENG, TAN SZE NIAN

TREPORT WRITING / ePRESENTATION / LAYOUT xt(2 marks)

Excellent 1.0 pt

V. Good 0.8 pt

Good 0.6 pt

Acceptable 0.4 pt

Poor 0.2 pt

V. Poor 0.1 pt

Total

Reporting format (Intro, Body, Appendix, etc.)

Effective use of Tables & Figures Total marks out of 2 for Report Writing Skills TECHNICAL CONTENT (7 marks)

Excellent 1.0 pt

V. Good 0.8 pt

Good 0.6 pt

Acceptable 0.4 pt

Poor 0.2 pt

V. Poor 0.1 pt

Total

Cross-sections of sub-surface conditions Characterisation of soil properties Technical design of ground improvement scheme Bearing capacity considered EXCEL spreadsheet computation of ground improvement scheme Appropriate charts and figures to help explanation Geotechnical instruments for monitoring of ground improvement Total marks out of 7 for Technical Content USE OF ENGLISH (1 mark)

Excellent 1.0 pt

V. Good 0.8 pt

Good 0.6 pt

Acceptable 0.4 pt

Poor 0.2 pt

V. Poor 0.1 pt

Grammar, spelling, ability in getting points across Total marks out of 1 for Use of English Grand total marks out of 10 Grand total as 10% of unit mark Overall comments, if any:

Total

CVE 40001 Geotechnical Engineering - PVD

Table of Contents 1

Introduction ....................................................................................................... 2

2

Objective ............................................................................................................ 2

3

Executive Summary ........................................................................................... 3

4

Cross-sectional view of sub-surface soil profile ................................................ 4

5

Plots and Graphs ............................................................................................... 6

6

Assumptions ..................................................................................................... 11

7

PVD Design ...................................................................................................... 12

9

Tabulation of Calculations .............................................................................. 16

10

Amount of PVD required .............................................................................. 19

11

Geotechnical Instrument ............................................................................... 20

12

Recommendations .......................................................................................... 24

13

Conclusion ...................................................................................................... 24

14

Appendix ........................................................................................................ 25

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CVE 40001 Geotechnical Engineering - PVD

1 Introduction

Construction along riverbanks is common in Sarawak as it has a vast river network. Typical riverine development includes construction of buildings, waterfronts, jetties and bridges. Construction along riverbanks is usually very challenging because of the presence of soft soil deposits, which are naturally weak and very compressible. Sometimes these soft soil deposits could reach thickness in excess of 60m before a firm later is found. If the consolidation process of the soft soils takes up too much time and differential settlement is found to be potentially damaging to services such as water pipes and high-tension electrical cables, then the viability of project will be questioned. A system of prefabricated vertical drain (PVD) with surcharge load to accelerate consolidation by shortening the drainage path is one of the most popular methods of soft ground improvement. It is also one of the most general methods used to increase the shear strength of soft soil and control its post-construction settlement. The predicted smear zone and effects of drain unsaturation are compared with laboratory data obtained from large-scale radial consolidation tests. Since the permeability of soils is very low, consolidation time to the achieved desired settlement or shear strength might take too long. By using the pre-fabricated vertical drains technology (PVD), the drainage path can be shortened from the thickness of the soil layer to the radius of the drain influence zone, which means the acceleration of consolidation.

2 Objective

Our objectives is to provide the cross-sectional view of the sub-surface soil profile and to provide a complete design calculation for the selection and design of PVD, necessary surcharging height, amount of topping up of sand fill considering finished platform levels, which is needed to achieve 90% consolidation of approximately 22,000m2 of the riverine land in 6 months. Bearing capacity of the ground is also checked to determine the amount of the surcharge height that is needed. An Excel file that asks for all necessary input values to design the PVD will be produced together with this report. Not only that, the necessity of geotechnical instruments is to be explained on how it is able to monitor ground improvement works.

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CVE 40001 Geotechnical Engineering - PVD

3 Executive Summary

This report provides an analysis and evaluation of designing the preloading and prefabricated drains (PVD). It consists of the application of Meyerhof`s method to calculate the bearing capacity of the clay layer. The formulas for finding surcharge height, settlement with preload as well as the consolidation time, and degree of consolidation, U% are shown in the report. There are some graphs and charts that are added in together with its explanation. Besides that, the amount of PVD required is also been calculated and showed in this report. Different type of geotechnical instruments and their necessity that is important in monitoring of the ground improvement works are displayed in this report. The last part of this report will be interpreting the result that obtained from the calculation as well as some recommendations for the project.

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CVE 40001 Geotechnical Engineering - PVD

4 Cross-sectional view of sub-surface soil profile

Figure 1. Cross-Sectional Soil Profile Between Borehole 1 and Borehole 2

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CVE 40001 Geotechnical Engineering - PVD

Figure 2. Cross-Sectional Soil Profile Between Borehole 2 and Borehole 3

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CVE 40001 Geotechnical Engineering - PVD

5 Plots and Graphs Plots of Moisture Content Against Depth

Natural Moisture Content against Depth 0.00 0.00

Natural Mositure Content (%) 20.00 40.00 60.00 80.00

100.00

2.00 4.00

Borehole 1

6.00

Borehole 2

Depth (m) 8.00

Borehole 3

10.00 12.00 14.00 16.00

Graph 1. Plots of Moisture Content against Depth Plots of Cu Against Depth

Graph of Cu against Depth 0.00 0.00

Undrained Cohesion Strength, Cu (kN/m2) 5.00 10.00 15.00 20.00

25.00

1.00 2.00

Depth (m)

3.00

Borehole 1 Borehole 2

4.00

Borehole 3 5.00 6.00 7.00 8.00

9.00

Graph 2. Plots of Cu against Depth

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CVE 40001 Geotechnical Engineering - PVD Plots of SPT ‘N’ Against Depth

Graph of SPT 'N' against Depth 0.00 0.00

10.00

SPT 'N' value 20.00 30.00 40.00

50.00

60.00

5.00

Depth (m)

Borehole 1 10.00

Borehole 2 Borehole 3

15.00

20.00

25.00

Graph 3. Plots of SPT ‘N’ against Depth

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CVE 40001 Geotechnical Engineering - PVD Computation of Consolidation Graph To construct the graph, we had used the data from the lab test, which give us various points at different depth. Below each graph are the steps on how Cc is calculated before using that particular value for design of PVD.

Void ratio against Pressure (log scale) for Borehole 1 UD2 2 1.9 1.8

1.7 Void Ratio, e 1.6 1.5 1.4 1.3 1.2 10

100 Pressure (kPa)

1000

Graph 4. Graph of Consolidation for Borehole 1 UD2 soil sample. Cc Calculation: Obtain gradient to find Cc

Therefore, Cc for soil sample obtained from Borehole 1 UD_2 is : (

)

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CVE 40001 Geotechnical Engineering - PVD

Void ratio against Pressure (log scale) for Borehole 1 UD3 1.6 1.5 1.4 Void Ratio, e 1.3 1.2 1.1 1 10

100 Pressure (kPa)

1000

Graph 5. Graph of Consolidation for Borehole 1 UD3 soil sample. Cc Calculation: Obtain gradient to find Cc

Therefore, CC for soil sample obtained from Borehole 1 UD_3 is : (

)

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CVE 40001 Geotechnical Engineering - PVD

Void ratio against Pressure (log scale) for Borehole 2 UD1 2.2 2

1.8 Void Ratio, e 1.6

1.4 1.2 1 10

100 Pressure (kPa)

1000

Graph 6. Graph of Consolidation for Borehole 2 UD1 soil sample. Cc Calculation: Obtain gradient to find Cc

Therefore, CC for soil sample obtained from Borehole 2 UD_1 is : (

)

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CVE 40001 Geotechnical Engineering - PVD

Void ratio against Pressure (log scale) for Borehole 2 UD3 2.5 2.3 2.1 Void Ratio, e

1.9 1.7 1.5 1.3 1.1 10

100 Pressure (kPa)

1000

Graph 7. Graph of Consolidation for Borehole 2 UD3 soil sample. Cc Calculation: Obtain gradient to find Cc

Therefore, CC for soil sample obtained from Borehole 2 UD_3 is : (

)

6 Assumptions

Before proceeding to the design of PVD, there were few assumptions made and will be listed below. Meyerhof’s method will be used to calculate the bearing capacity of soil There will be no point load on the surface Load will be acting on the surface Fill Unit Weight is to be 19 kN/m3 Factor of Safety is to be greater than 2 Time available to consolidate will be 6 months PVD used will be from Azko with Nylon web as core material and Geotextile as filter material. This PVD has a size of 100mm x 6mm There will be a smear factor of 0.8 Diameter of well is to be assumed as 0.1m

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CVE 40001 Geotechnical Engineering - PVD

7 PVD Design

To help end readers understand the formulation and computation of the PVD design, workings will be shown for the first clay layer of Borehole 1. The rest of the clay layers will be tabulated and given appropriate explanation. Step 1: Determine Bearing Capacity of soil To determine the bearing capacity of the clay layer, we will be using Meyerhof’s method. Meyerhof’s Method

c = 13.6 kN/m2 (referring to lab report) Nc = 5.14 for = 0 Sc = 1 + 0.2 Kp = 1 + 0.2 tan2 45 x = 1.2 √

√

(

)

as there is no point load = 0 as the load is on the surface

Step 2: Determine surcharge height Max surcharge height = Allowable surcharge height =

(Adopt FOS = 2)

Therefore, assume surcharge height as 2.5m with pressure of 47.5kPa From the consolidation graph of BH1 UD2, Pc = 49kPa Total applied pressure = Pc + Psurcharge = 49 + 47.5 = 96.5kPa

From lab report, cv = 5.8m2/yr t = 6 months Hd = 4.8m (single drainage) Tv = 0.13, with Tv we can get U% from Figure 2.2 which was 9%. To determine the required preload, we need to refer to Figure 2.1. Pp = 0.7 x 19 = 13.3kPa Po = 49kPa from consolidation graph 12

CVE 40001 Geotechnical Engineering - PVD

, from Figure 2.1 Pf = 2.48 x 13.3 = 32.98kPa Total Preload required = Pf + Pp = 46.28kPa We assumed a surcharge pressure of 47.5kPa, which is greater than required preload pressure. therefore it is adequate to adopt surcharge height of 2.5m. Step 3: Find the settlement with preload Mv method To get mv, we need to use total applied pressure (96.5kPa) to refer to the lab report. = 0.72 H = 4.8m (soil profile) = 47.5kPa (surcharge pressure) 100% consolidation settlement = 164.16mm 90% consolidation settlement = 147.74mm 10% consolidation settlement =16.42mm Cc method {

(

)}

eo = 1.86 (from consolidation graph) P0 = 49 kPa (from consolidation graph) Cc = 0.478 (from consolidation graph) H = 4.8m (soil profile) = 47.5kPa (surcharge pressure) 100% consolidation settlement = 262.36mm 90% consolidation settlement = 236.12mm 10% consolidation settlement =26.24mm Critical settlement 100% consolidation settlement, = 262.36mm 90% consolidation settlement, = 236.12mm 10% consolidation settlement, =26.24mm

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CVE 40001 Geotechnical Engineering - PVD Step 4: Consolidation Time, Tv and Degree of Consolidation, U% Total applied pressure = Pc + Psurcharge = 49 + 47.5 = 96.5kPa

From lab report, cv = 5.8m2/yr t = 6 months Hd = 4.8m (single drainage) Tv = 0.13, with Tv we can get U% from Figure 2.2 which was 9%. Therefore PVD is required! Step 5: PVD Design Referring to Figure 2.4, we were able to determine that Uv% = 40% Total consolidated settlement with PVD, Sv = = 104.94mm Remaining settlement to treat, St = Sp – Sv = 236.12 – 104.94 = 131.18mm ̅ ̅

( (

)( )(

) )

We will be using PVD from Azko with Nylon web as core material and Geotextile as filter material. This PVD has a size of 100mm x 6mm. There will always be a smear effect affecting the efficiency of the PVD. So we assume the efficiency of the PVD to be lowered by 20%. Smear factor, f = 0.8 (

)

Diameter of well, Dw = Therefore we adopt Dw = 0.1m.

(

)

m

From Geotechnical properties of Singapore Marine Clay, it is found that C h = 2-3Cv. Therefore, we assumed Ch to be 2.5 of Cv, which is 2.5 x 5.8 = 14.5m2/year.

With Tw and ̅, we can refer to Figure 2.5 to get the value of n, which is 26.

In our design, we will be adopting the square pattern configuration.

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CVE 40001 Geotechnical Engineering - PVD Maximum spacing, S = Provide 100mm diameter well with square spacing of 2m. Step 6: Check the U% achieved in 6 months Horizontal Flow S = 2m Dw = 0.1m De = 1.128S = 2.256m

( ) Time factor due to radial drainage, Degree of Consolidation due to radial drainage,

,

*

+-

Vertical Flow

From lab report, cv = 5.8m2/yr t = 6 months Hd = 4.8m (single drainage) Tv = 0.13, with Tv we can get U% from Figure 2.4 which was 40% or 0.4.

̅

̅ ( )( ) ̅ ( )( ) (Primary consolidation had been consolidated in 6 months)

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CVE 40001 Geotechnical Engineering - PVD

9 Tabulation of Calculations

In this section, we will tabulate all the values calculated for the ease of understanding. For borehole 2, we divided the clay layer into 2 layers with equal thickness. This is due to the fact that lab and field test had been performed on the clay in different depth. As of such, different data had been observed. Therefore, separation of the clay layers will help the design to be more conservative and cost effective.

Bearing Capacity of soil c Nc Sc dc Bearing Capacity (kPa)

Borehole 1 Clay 1 Clay 2 13.6 22.3 5.14 5.14 1.2 1.2 1.2 1.2 100.66 165.06

Borehole 2 Clay 3 Clay 4 9.3 4.8 5.14 5.14 1.2 1.2 1.2 1.2 68.83 35.53

Borehole 1 Clay 1 Clay 2 5.30 8.69 2.65 4.34 2.5 2.5 49 65 47.5 47.5 96.5 112.5

Borehole 2 Clay 3 Clay 4 3.62 1.87 1.81 0.93 0.9 0.9 38 44 17.1 17.1 55.1 61.1

Surcharge Height Max Surcharge height (m) Allowable Surcharge height (m) Proposed Surcharge height (m) Pre-consolidation Pressure, Pc (kPa) Pressure due to surcharge (kPa) Total applied pressure (kPa) Find Tv Cv (m2/year) T (months) Hd (m) Tv Refer to Fig 2.2, U%

5.8 6 4.8 0.13 9

11 6 3.7 0.40 55

0.9 6 4.3 0.02 0

1.1 6 4.3 0.03 0

Find required preload Pp (kPa) Po (kPa)

13.3 49

13.3 65

13.3 38

13.3 44

0.27

0.20

0.35

0.30

2.48 32.984 46.284

0.9 11.97 25.27

2.93 38.969 52.269

2.88 38.304 51.604

47.5 2.12

47.5 3.47

17.1 4.03

17.1 2.08

Pf (kPa) Preload required, Pf + Pp (kPa) Proposed Pressure (kPa) Factor of Safety, FOS

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CVE 40001 Geotechnical Engineering - PVD

Settlement with preload Borehole 1 Clay 1 Clay 2

Borehole 2 Clay 3 Clay 4

0.72 4.80 47.50

0.55 3.70 47.50

1.7 4.80 17.10

1.7 4.80 17.10

0.16416 0.14774 0.01642

0.09666 0.08700 0.00967

0.13954 0.12558 0.01395

0.13954 0.12558 0.01395

1.86 49 0.478 4.80 47.50

1.48 65 0.369 3.70 47.50

1.9 38 0.655 4.80 17.10

2.2 44 0.743 4.80 17.10

100% settlement (m) 90% settlement (m) 10% settlement (m)

0.26236 0.23612 0.02624

0.14573 0.13116 0.01457

0.19438 0.17495 0.01944

0.17657 0.15891 0.01766

Critical settlement 100% settlement (m) 90% settlement (m) 10% settlement (m)

0.26236 0.23612 0.02624

0.14573 0.13116 0.01457

0.19438 0.17495 0.01944

0.17657 0.15891 0.01766

Mv method mv H (m) (kPa) 100% settlement (m) 90% settlement (m) 10% settlement (m) Cc method eo Po (kPa) Cc H (m) (kPa)

Consolidation Time, Tv and Degree of Consolidation, U% Borehole 1 Clay 1 Clay 2 Max Surcharge height (m) 5.30 8.69 Allowable Surcharge height (m) 2.65 4.34 Proposed Surcharge height (m) 2.5 2.5 Pre-consolidation Pressure, Pc (kPa) 49 65 Pressure due to surcharge (kPa) 47.5 47.5 Total applied pressure (kPa) 96.5 112.5 Find Tv Cv (m2/year) t (months) Hd (m) Tv Refer to Fig 2.2, U% PVD is required for each four layers.

5.8 6 4.8 0.13 9

11 6 3.7 0.40 55

Borehole 2 Clay 3 Clay 4 3.62 1.87 1.81 0.93 0.9 0.9 38 44 17.1 17.1 55.1 61.1 0.9 6 4.3 0.02 0

1.1 6 4.3 0.03 0

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CVE 40001 Geotechnical Engineering - PVD

PVD Design Refer to Fig 2.2, U% Consolidated settlement, Sv (m) Settlement to treat, St (m) Average consolidation, ̅ Uh Dw (m) Ch (m2/year) Tw Refer to Fig 2.5, n De (m) Adopt square pattern Max spacing, S (m) Adopted Spacing, S (m)

Borehole 1 Clay 1 Clay 2 40 72 0.10494 0.17942 0.13118 -0.04827 1 1 1 1 0.1 0.1 14.5 27.5 725 1375 26 42 2.6 4.2 2.30 2

3.72 2

Borehole 2 Clay 3 Clay 4 18 20 0.05983 0.06039 0.11511 0.09853 1 1 1 1 0.1 0.1 2.25 2.75 112.5 137.5 13 14 1.3 1.4 1.15 1

1.24 1

U% achieved in 6 months Adopted Spacing, S (m) Dw (m) De (m) n Fn

Borehole 1 Clay 1 Clay 2 2 2 0.1 0.1 2.256 2.256 22.56 22.56 2.37 2.37

Borehole 2 Clay 3 Clay 4 1 1 0.1 0.1 1.128 1.128 11.28 11.28 1.67 1.67

Horizontal Flow Ch (m2/year) t (months) Rate of consolidation, Th Degree of consolidation, Uh (%)

14.5 6 1.42 99.19

27.5 6 2.70 99.99

2.25 6 0.88 98.54

2.75 6 1.08 99.43

Vertical Flow Cv (m2/year) t (months) Hd (m) Tv Refer to Fig 2.2, U% Average consolidation, ̅ Average consolidation, ̅ (%)

5.80 6.00 4.80 0.13 40 1.00 99.51

11.00 6.00 3.70 0.40 70 1.00 100.00

0.90 6.00 4.30 0.02 17 0.99 98.80

1.10 6.00 4.30 0.03 20 1.00 99.54

Primary consolidation had been achieved in 6 months’ time with the designed configuration of PVD from Azko with well diameter 0.1m and square spacing of 2m for Borehole 1 area and 1m spacing for Borehole 2 area.

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CVE 40001 Geotechnical Engineering - PVD

10 Amount of PVD required

The total area for the development is 22,000m2. Due to insufficient data for Borehole 3, we are unable to design PVD for area surrounding it. Therefore, the development area will be divided equally into two parts. One part will be using PVD designed using data from Borehole 1 and so for the other part. Borehole 1 Area of each part = 11,000m2 Spacing, S= 2m Effective drainage area = S2 = 4m2 Number of PVD Points =

points

Depth of each PVD points = 9.70m Total length required = No. of PVD point x Depth = 2,750 x 9.7 = 26,675m Borehole 2 Area of each part = 11,000m2 Spacing, S= 1m Effective drainage area = S2 = 1m2 Number of PVD Points =

points

Depth of each PVD points = 8.80m Total length required = No. of PVD point x Depth = 11,000 x 8.8 = 96,800m Total length of PVD required would be 123475m.

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CVE 40001 Geotechnical Engineering - PVD

11 Geotechnical Instrument

Deformation of soil involves the combined effect of elastic, plastic and viscosity. Therefore the deformation behavior is rather complex. In addition to the complex nature of soil deformation, the additional stresses imposed on the soils are varied not only in terms of magnitude but also in the directions. This makes the prediction of deformation of soil to be extremely difficult. However, geotechnical engineers have been predicting ground behavior in advance with the help of finite difference or finite element computer modeling. Nevertheless in most cases performances were far from predictions due to the complexity of the soil profile, parameters and hence loading conditions. Therefore geotechnical instrumentation fills the gap between prediction and performance and saves the soil mass failure as well as damages to the structure on the ground. Geotechnical instrumentation can provide construction control as well as performance monitoring. First one will provide safe construction of earth as infrastructure on the soil whereas the second one provides in-situ soil parameters from the back analysis, from which a more economical and safe design can be established. Many natural and man-made structures such as slopes, buildings, dams, bridges and tunnels need monitored to determine periodically such parameters of the structures as deformations and the states of stress. The aims of structural monitoring can vary from one project to another but generally fall into the following: a) safety assurance - Many structures can fail under certain conditions. Monitoring is often one of the most effective ways to understand the safety status of such structures. b) validation of design assumptions - Some parameters such as those defining the properties of soil or rock of a cut slope are often assumed at the design stage based on some field investigations. Results of monitoring during or after a construction can help to validate such assumptions so to carry out remedial work if necessary or to improve future designs. c) scientific experiments and research - Results from monitoring measurements may lead to new discovery or help to expand existing knowledge. The parameters of a structure that need monitored are many but the most common ones are deformation, load, stress, strain, and ground water pressure. A great number of methods are available for structural monitoring. These methods can however generally be classified into geodetic (surveying) methods and geotechnical methods. Geodetic methods are mainly used to monitor deformations while geotechnical methods can be used to determine some other important parameters beside deformations. The two types of methods complement each other in most of the times in terms of the types of information that they can obtain. It should be noted here that the above classification of the monitoring methods is mainly used in the fields of surveying and geodesy. The engineers and geologists often refer all the methods as geotechnical methods.

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CVE 40001 Geotechnical Engineering - PVD

There are a variety of geotechnical instruments that have been developed for monitoring the ground improvement works. Extensometers - Extensometers are used to measure the relative movements between points. They can be applied to measure the movements across a crack, inside or on the surface of a slope. Extensometers are made of various types of material, such as steel tapes and wires, tensioned or untensioned steel rods, and fiberglass, for different conditions of application. Extensometers usually use mechanical micrometers, electrical resistance and variable reluctance transducers. They are commonly used for slope stability monitoring. They can be used either on the surface or inside a slope, and very easily linked to a data logger and alarm system.

Figure 3. Extensometer Inclinometers - Inclinometers are used to measure the subsurface lateral displacement of soil or rock. An electrical probe is usually lowered through a guide casing to the base of a near vertical borehole. The probe is then pulled up while the inclination information of the probe in two orthogonal planes is registered at certain intervals. The lateral displacements of the borehole can be determined by comparing the measured profiles of the borehole obtained at different times. Boreholes of up to 200 m in depth can be measured using inclinometers. In practice it is usual to extend a borehole into stable ground in order to have a common reference point to compare borehole profiles for determining displacements. Inclinometers can also be placed permanently at important locations to log data continuously. In this situation the inclinometer is acting as a tilt meter.

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CVE 40001 Geotechnical Engineering - PVD

Figure 4. Inclinometer Piezometer - An open standpipe piezometer requires sealing off porous filter element so that the instrument responds only to groundwater pressure around the filter element and not to groundwater pressures at other elevations. Piezometers can be installed in fill, sealed in boreholes, or pushed or driven into place. The water surface in the standpipe stabilizes at the piezometric elevation and is determined by sounding with a probe. Care must be taken to prevent rainwater runoff from entering open standpieps, and an appropriate stopcock cover can be used, ensuring that venting of the standpipe is not obstructed.

Figure 5. Piezometer Cell Settlement System - The TCP cell settlement system is used for the measurement and control of vertical movements which includes the construction control of road embankments and earth dams and study of the displacement of individual soil layers. The standard TCP system comprises

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CVE 40001 Geotechnical Engineering - PVD two spherical cells half-filled with an anti-freeze solution and connected to a reading panel. A hand pump is used to push back the anti-freeze solution to the reading panel. The difference in elevation between the two cells can then be read directly on the two sight tubes mounted on the reading panel. The TCP cell is installed directly in the fill whereas the TCP-R cell and reading panel are usually mounted on a stable concrete platform.

Figure 6. TCP cell settlement system Electrical Dipmeter - The most commonly used probe is an electrical dipmeter, consisting of a two conductor cable with a cylindrical stainless steel weight at its lower end. The weight is divided electrically into two parts, with a plastic bushing between, and one conductor is connected to each part. The upper end of the cable is connected to a battery and either an indicator light, buzzer, or ammeter. When the probe is lowered within the stand pipe and encounters the water surface, the electrical circuit is completed through the water and the surface indicator is actuated. For small-diameter stand pipes where the water level is no deeper than about 15ft, a coaxial cable with bared ends can be used. When selecting instruments, the overriding desirable feature is reliability. In evaluating the economics of alternative instruments, the overall cost of procuring, calibration, installation, maintenance, monitoring, and data processing should be compared. Instruments should have a good past performance record and should always have maximum durability in the installed environment. Zones of particular concern should be identified, such as structurally weak zones, most heavily loaded zones, zones where highest pore water pressures are anticipated. Last but not least, locations should be selected so that data can be obtained as early as possible during the construction process.

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CVE 40001 Geotechnical Engineering - PVD

12 Recommendations

Appropriate Prefabricated Vertical Drain (PVD) had been designed to achieve 90% consolidation in 6 months times to prevent failure of soil layers and structures. However, this design had been proposed using data from only two boreholes. Due to this reason, data obtain might not be sufficient to fully adjust to the real life settlement. Therefore, the design proposed may not be as cost effective and economic. We strongly recommend more boreholes to be bore throughout the development area so that more accurate data can be accumulated to design the most effective and economical soil improvement. Not only that, lab test should also be carried out to find out the properties of the soil so that design can be carried out. Borehole 3 had been bored but insufficient lab test had been carried out for us to know the necessary value.

13 Conclusion

The whole development area is being split into 2 parts, which each will be implement with PVD design from both Borehole 1 and Borehole 2. Area 1 will be topped with 2.5m of preload while Area 2 will be topped with 0.9m of surcharge. The current R.L. is 2.8m and requires another 0.7m to reach the platform level which is 3.5m. As both areas are loaded with surcharge more than that, additional surcharge will be cut off after 6 months. Area 1 will be installed with PVD with well diameter of 0.1m and spacing of 2m to the depth of 9.7m while Area 2 will be installed with well diameter of 0.1m and spacing of 1m to the depth of 8.8m. The total length of PVD to be ordered for this project is 123475m.

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CVE 40001 Geotechnical Engineering - PVD

14 Appendix

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CVE 40001 Geotechnical Engineering - PVD

26

CVE 40001 Geotechnical Engineering - PVD

27