SETTLEMENT OF AN EMBANKMENT TREATED WITH PRELOADING AND PREFABRICATED VERTICAL DRAIN OF EAST-COAST HIGHWAY PHASE 2 (A CASE STUDY)

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1 1rrrrnnr SETTLEMENT OF AN EMBANKMENT TREATED WITH PRELOADING AND PREFABRICATED VERTICAL DRAIN OF EAST-COAST HIGHWAY PHASE 2 (A CASE STUDY) NUR ANIS AD LINA BINTI MAT NOOR Report submitted in partial fulfillment of the requirements for the award of Bachelor of Civil Engineering Faculty of Civil Engineering and Earth Resources UNIVERSITI MALAYSIA P AHANG JUNE 2012

2 v ABSTRACT Soft soils are not suitable for construction of buildings or facilities without having soil improvements. The soil improvements that are used in the chosen site are Preloading and Prefabricated Vertical Drain (PVD). Analysis of settlement is important to evaluate the site before the construction begins. The objectives of the study are, to predict settlement of an embankment based on Terzaghi One Dimensional Consolidation analysis, to obtain the final settlement by using Asoaka's method based on monitoring data and to compare the soil properties from the lab data with back calculated based on the firn:il settlement. Using Terzaghi One Dimensional Consolidation Method, prediction of the total settlement is 287mm. The data from monitoring record are used to plot Asoaka's Graph in order to get the actual settlement which is 13mm, then being used to back calculate soil properties. The soil properties those are back calculated based on field settlement are different from those obtained from lab data. The differences can be seen by the correlation between the field and lab, which are for the Coefficient of Vertical Consolidation, Cv field = 0.04 Cv lab, the correlation for Coefficient of Horizontal Consolidation, ch field = 0.04 ch lab, the correlation for the Compression Index, Cc field = Cc lab and the correlation of Recompression Index, Cr field = 0.06 Cr lab. This particular correlation can be used as a design guideline to similar site condition.

3 Vl ABSTRAK Tanah lembut tidak sesuai untulc pembinaan bangunan atau kemudahan tanpa kaedah pembaikan tanah. Pernbaikan tanah yang digunakan di tapak yang dipilih adalah Pra-Pembebanan dan Saliran Pugak Pasangsiap. Analisis pemendapan penting untuk menilai tapak sebelum pembinaan bermula. Objektif-objektif kajian ini adalah, untulc rneramalkan pemendapan tambakan berdasarkan Analisis Pengukuhan Satu Dimensi Terzaghi, untulc mendapatkan pemendapan sebenar dengan menggunakan kaedah Asoaka berdasarkan data pemantauan dan untulc membandingkan sifat-sifat tanah dari data makmal dengan kiraan semula berdasarkan pemendapan sebenar. Menggunakan Analisis Pengukuhan Satu Dimensi Terzaghi, pernendapan yang diramalkan adalah 287mm. Data daripada rekod pemantauan digunakan untulc mendapatkan Graf Asoaka untuk mendapatkan pemendapan sebenar iaitu 13mm dan seterusnya digunakan untulc kiraan semula sifat-sifat tanah. Sifat-sifat tanah yang dihitung semula berdasarkan pemendapan tapak adalah berbeza berbanding pemendapan yang diperolehi di makmal. Perbezaan sifat tanah dapat dilihat daripada korelasi di antara hasil kajian di tapak dan di makmal, di mana untuk Pekali Pengukuhan Menegak, Cv tapak = 0.04 Cv makmal, korelasi Pekali Pengukuhan Mendatar, ch tapak = 0.04 ch makmal, korelasi bagi Indeks Pemampatan, Cc tapak = Cc makmal dan korelasi Indeks Pemampatan Semula, Cr tapak = 0.06 Cr makmal. Korelasi ini boleh digunakan sebagai garis panduan reka bentuk untulc tapak yang mempunyai keadaan sama.

4 TABLE OF CONTENTS Page TITLE PAGE DECLARATION DEDICATION ACKNOWLEDGEMENT ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS LIST OF APPENDICES I 11 lll IV v Vl Vll Vll IX x XI CHAPTER! INTRODUCTION 1.1 Introduction 1.2 Problem Statement 1.3 Objectives 1.4 Scope and Limitation CHAPTER2 LITERATURE REVIEW 2.1 Introduction 2.2 Settlement Immediate Settlement Primary Consolidation Secondary Compression Settlement 2.3 Consolidation One Dimensional Consolidation Theory Degree of Consolidation l Compression Index (Cc) Recompression Index (Cr)

5 2.3.3 Terzaghi Theory of Consolidation Pre-loading Prefabricated Vertical Drains (PVD) Prefabricated Vertical Drains and Preloading Laboratory Test One-Dimensional Consolidation Test Settlement Prediction and Interpretation by 30 Observational Methods Hyperbolic Method Asaoka Method Soil Investigation Purpose of a Soil Investigation Program Soil Improvement Vibroflotation Dynamic Compaction Stone Columns Compaction Piles Compaction Grouting Drainage Techniques Field Instrumentation Settlement/Heave Monitoring Settlement Plate/Platform Remote Settlement (Gauge Monitoring 39 Tubes) Inductive Coil Gauge (Deep Settlement 39 Monitoring) Borehole Extensometer (Deep Settlement 40 Monitoring) Horizontal Inclinometer (Settlement 40 Monitoring)

6 CHAPTER3 METHODOLOGY 3.1 Introduction 3.2 One Dimensional Terzaghi Method 3.3 Consolidation Analysis Using Hansbo Method 3.4 Back Calculation of Soil Properties 3.5 Comparison of Result 3.6 Summary CHAPTER4 ANALYSIS AND RESULTS 4.1 Introduction 4.2 Magnitude of settlement and time taken to reach 90% consolidation by using Terzaghi's and Hansbo's Method 4.3 Analysis by Using Asoaka's Method 4.4 Analysis of ch by using Asoaka's Method 4.5 Back Calculation of Field Soil Characteristics CHAPTERS CONCLUSION AND RECOMMENDATION 5.1 Introduction 5.2 Conclusions 5.3 Recommendations

7 Vlll LIST OF TABLES TABLE NO TITLE PAGE 2.1 Correlation for Compression Index, Cc Compression and Recompression of Natural Soils 2.3 Time Factor as function of percentage of consolidation Predicted Settlement and Time Taken Total Settlement from Asoaka Plot Back Calculated Field Soil Properties 50

8 IX LIST OF FIGURES FIGURE NO TITLE PAGE 2.1 Influence Chart for Vertical Stress Embankment Loading - Infinite Extent Consolidation Settlement Concept of Pre-Loading and Surcharge Odometer test for measuring consolidation behaviour Notation and Terminology used for Oedometer Compression Curves Hyperbolic Method to Predict Future Settlement Graphical Method of Asoaka Methodology of Study Simplified Soil Profile 46

9 x LIST OF SYMBOLS e Cc Cr (J 0 n Void ratio Initial void ratio Compression index Recompression index Coefficient of vertical consolidation Coefficient of horizontal consolidation Thickness of compressible layer unit weight Initial effective stress Increment stress for filling material Settlement Time factor Degree of Consolidation Time interval Equivalent diameter of soil cylinder Equivalent diameter of drain Drain spacing ratio

10 XI LIST OF APPENDICES APPENDIX TITLE PAGE A Specification for Prefabricated Vertical Drains (PVD) 53 B Borehole Log for Borehole 11 c D E Borehole Location Generalised Soil Profile (Mainline) from CH.94,500 to 56 f'.h.9.s.200 Settlement calculation using One Dimensional Terzaghi's Analysis F G Sample Calculation of Settlement Using One Dimensional Consolidation in Theory Terzaghi 58 Method Calculation for Consolidation Analysis using Hansbo' s Method 60 H Sample Calculation of Consolidation Analysis Using Hansbo's Method 62 I J K L Calculation of Asoaka's Analysis Sample Calculation for Asoaka's Method 66 Asoaka's Plot Settlement Record for Settlement Plate

11 1 CHAPTER I INTRODUCTION 1.1 INTRODUCTION In general, preloading and vertical drain are the most suitable for predominantly fine-grained, inorganic high water-content and low-strength soils. Typically, the site essentially are normally consolidated or only lightly overconsolidated. The consolidation settlement of soft clay subsoil creates a lot of problems in foundation and infrastructure engineering. The settlement of soft clay soils also creates problems during the construction and after the construction has done. Apart from low shear strength, the primary consolidation would take long time to be complete due to its low permeability. To shorten this consolidation time, vertical drains are installed together with preloading on a constructed embankment that lay on soft clay layer. Vertical drains are artificially-created drainage paths which can have a variety of physical characteristic. Preloading techniques, particularly when used together with vertical drains, are similar to other ground improvement techniques. They have great potential benefit in a number of situations in geotechnical practice. Preloading with vertical drains requires time for the dissipation of excess pore pressure and the settlement to occur. This may be an important consideration in the overall design. The function of Prefabricated Vertical Drain (PVD) is to allow drainage to take place in both vertical and horizontal directions over a much shorter drainage

12 2 path so that the rate of consolidation can be accelerated and the consolidation time can be greatly reduced. The primary use of PVD is to accelerate consolidation to greatly decrease the settlement time of embankment over soft soils. However, for a PVD to perform its function, an extra surcharge needs to be used during this process. The surcharge will create extra stresses that will induce extra pore pressure to dissipate easily via PVD this increasing settlement is a short period. PVD are band shape (rectangular cross section) products consisting of a geotextile filter material surrounding a plastic core. 1.2 PROBLEMSTATEMENT Soil is a foundation for all type of construction structure which is located on earth. For sites underlain by deep layers of fill or soft or loose soils, conventional practice was to either remove and replace the unsuitable soils or bypass them with expensive deep foundations. Today, in-situ improvement is a viable alternative and in most instances proves to be the most economical means to mitigate an undesirable situation. Structures can stand firmly on a soil, and it needs a great strength to support loads within the structure. The problem of stability and settlement of the soft soil are the major challenge to engineer. In some areas in this country where soft' clay are the major part of the soil, constructing a highway on it could be complicated and design plan must carefully be made. The high settlement of the soft clay is due to the one of the major factor that is high compressibility properties of soft clay. This is happened from the fact that soft clay are finer in particles and being too cohesive with the presence of water. High settlement could affect the movement of the whole structure and it would be ended up with the cracks and landslides.

13 3 The presence of water could have made the soil become unstable. It is because, soft clay have the lowest value of permeability where water are hard to get through it particles and this is the reason why soft clay have a high moisture content. The soil particles have high tendency to bond closely with one another that make soft clay become easily compressed when it's undergoing compaction activity. Because of the weaknesses of the soft clay, the improvement of the soil should be done. Some of the soil properties need to be assumed based on literature review and previous projects because it cannot be obtained from the Site Investigation. If the assumptions of soil properties are not accurate, it will affect to the embankment and PVD design. To get the 90% consolidation time for the clay to settled, it will take long time and to reduce the consolidation time, soil improvement should be done. 1.3 OBJECTIVES From the problem statements that are stated before, the objectives of the study has been identified. The objectives of this study are: 1. To predict settlement of an embankment based on Terzaghi 1-D consolidation analysis. 11. To obtain the final settlement by using Asaoka's method based on monitoring data To compare the soil properties that obtained from lab data with back calculated based on the final settlement.

14 4 1.4 SCOPE AND LIMITATION This project is using the site investigation and settlement monitoring data collected from the construction of East-Coast Highway Phase 2, from CH. 91,800 to CH. 103,240. The study was based on SI data collected from 1 borehole along the CH. 94,500 to CH. 95,200. The borehole log data are used to determine general soil profile. The case study is focusing on settlement criteria only.

15 5 CHAPTER II LITERATURE REVIEW 2.1 INTRODUCTION The construction of building, roads, bridge and harbours on soft clay are facing the higher risk for settlement and stability problem. This has become the main geotechnical problem in soft clay engineering. Brand & Brenner stated that soft clay is defined as clay that has the shear strength less than 25kPa Pl. Soft clay cause many problem for geotechnical engineers since it is highly compressible, high liquid limit and high plasticity. Clay. is define as soils particles having sizes below 2µm which can be determine at site by its feel that is slightly abrasive but not gritty and clay also feel greasy Clays are flake shape microscopic particles of mica, clay minerals and other minerals. Clay is a common type of cohesive soil which has small particle size that cannot be separated by sieve analysis into size categories because there are no practical sieve can be made with the so small opening. Clay is said as a submicroscopic mineral particle size of soil which has the fine texture. When is clay present in dominant proportions compare with silt and sand, the soil is described as having a fine or heavy texture. Fine textured soils are plastic and sticky when wet but hard and massive when dry.

16 6 Clay is said to be surface active which means that much happen on their surface, and clay minerals are cohere to each other and adhere to larger minerals particles. Their surface can absorb and holds water, organic compounds, plant nutrients ion and toxic ions. 2.2 SETTLEMENT Settlement of the subsoil supporting the embankment will take place during and after filling. In carrying out stability analyses, it is necessary to estimate the magnitude of settlement which occurs during construction so that the thickness of the fill can be designed to ensure stability. An iterative process is required in the estimation of settlement because the extra fill (more load) required to compensate for settlement will lead to further settlement. The two-dimensional consolidation can be solved numerically using solutions ed by Terzaghi One Dimensional Consolidation analysis. The result of settlement can be conveniently divided into three stages: 1. Initial/Immediate Settlement, Si 11. Primary Consolidation Settlement, Sc iii. Secondary Compression, S 5 The calculation of the total settlement is: ST = S, + Sst + S; Where: ST = total settlement, Sc = primary consolidation settlement, Ss = secondary compression settlement, S; = immediate settlement (2.1)

17 Immediate Settlement The deformation of dry soil and of moist and saturated soils without any change in the moisture content, it will cause the immediate settlement to happen. The immediate settlement calculations are generally based on equations that derived from the theory of elasticity. Excess pore pressure will set up in the clay during the application of the load, but relatively little drainage of water will occur since the clay has a low permeability. theory as: Estimation of initial settlement can be carried out using elastic displacement Si= :L- 1 (I.q)dh Eu Where, Si q dh Eu = immediate settlement = Applied Stress I Pressure on the subsoil = Thickness of each layer (2.2) = undrained elastic modulus of clay (Young's Modulus or modulus of elasticity) I = Influence factor

18 8 A useful chart is given by Osterberg and Shown in Figure 2.1. The chart allows estimation of the initial settlement of the embankment ? " 0 ~... " -:> :::: t:: ~ ~--1_._~fl'f-l ,..q-+--1+~, Lu...;~ O /'fl't : i+...'--+--<.i-~~ q :Unit loo d d-z.. f q '001 ) 1 'oal{) 2 '64:00 of z Figure 2.1: Influence Chart for Vertical Stress Embankment Loading - Infinite Extent Primary Consolidation Settlement With time, the excess pore water pressure dissipate as drainage occurs and he clay undergoes further settlement due to volume changes as stress is transferred from pore pressure due to effective stress. The rate of volume change and corresponding settlement is governed by how fast the water can drain out of the clay under the induced hydraulic gradients.

19 9 expression: One dimensional primary consolidation settlement can be estimated using the n [ Cr 0"' 1 p Sc= L --log--+--loa-- Cc o-' vf? i i=! 1 + eo 0"' 1 VO 1 + eo t:> 0"' 1 VC (2.3) Where, Sc = Consolidation Settlement Magnitude a' vo = Initial vertical effective stress a' vf = Final vertical effective stress = <>' vo + L'-.a' v 2:: o" vc a' vc = Preconsolidation Pressure I Yield Stress Hi = Initial thickness of incremental soil layer i of n. ea = Initial voids ratio Cc = Compression Index Cr = Recompression Index Secondary Compression Settlement Even after complete dissipation of the excess pore pressures and the effective stresses are about constant, there will generally be further volume changes and increased settlement which is termed as Secondary Compression.

20 10 (2.4) Where: Ss = Secondary Compression Settlement Ca= secondary compression index ep = void ratio at the end of primary consolidation H 1 = Initial thickness of incremental soil layer, i of n. t = time for calculation 2.3 CONSOLIDATION Consolidation is the process by which an increase in stress causes water to flow out of the soil accompanied by volume reduction. Consolidation is a process that occurs in clay and silt. With sands and gravels, pore water drainage from the voids occurs almost instantaneously as load is applied and is not normally referred to as consolidation. Any process which involves decrease in water content of a saturated soil without replacement of water by air is referred to consolidation One Dimensional Consolidation Theory Consolidation settlement is calculated based on the value of either the coefficient of volume compressibility (rnv) or the compression indices (Cc and Cr). Considering the layer of saturated clay of thickness H shown on Figure 2.2. Due to construction, the total vertical of stress in an element layer of thickness dz at depth z is increased by change in stress, f1(j '.

21 11 ul i ' , I i 1 J<r' t I I t I * <!: t t t ' Figure 2.2 Consolidation Settlement The one-dimensional consolidation theory, where the excess pore water pressure (u), depth within the clay layer (z) and time (t) are related by the following governing differential equation of layer i in any kth time section is [JJ: OU o 2 u -=Cot v oz 2 (2.5) Where: Cv = Coefficient of vertical consolidation z = depth within clay layer t = time related u = excess pore water pressure

22 12 Where Cv is the coefficient of consolidation and is defined by: k c =--...,... v (mvrj (2.6) Where: Cv = Coefficient of vertical consolidation mv = Volume of compressibility r w =Unit weight of water Additional stress (~11 ') will results in the increase of corresponds to l11 ' - l1 0 ' and a decrease in void ratio corresponds to ~e = e 0 - e1. By knowing the ratio of the change in void ratio to the change on the effective stress the settlement of normally consolidated clay due to change of stress (~l1 ') is given as (2.7) Where: Sc = Settlement Cc = Compression index H = Thickness of compressible layer l1' = Initial effective stress ~()'= Stress from the filling material

23 Degree of Consolidation The average degree of consolidation as a function of time factor for Terzaghi's theory of consolidation by vertical flow can be expressed as: (2.8) c For Tv= ~ < 0.2 H o U, = J- :, ex{ ":T J (2.9) (2.10) Where: Uv = Degree of consolidation Tv = Time factor Cv = Coefficient of vertical consolidation H = Thickness of compressible layer The coefficient of consolidation, Cv, can be obtained from oedometer tests at the levels of effective stress similar to those anticipated under embankment loading. Another reliable way to determine Cv is from field in-situ permeability tests together with mv from laboratory oedometer consolidation tests:

24 14 kt c =...,...---,- v (m.rw) (2.11) Where k = permeability from field permeability tests mv = coefficient of compressibility Yw = density of water The use of field values of k will give better representative effects of large scale soil structure and permeability, not able to be reflected in laboratory tests. Since the permeability and compressibility of the soil reduce with increase in effective stress (under embankment loading), the value of Cv should be modified to reflect the state of stress over the period during which settlement rates are being calculated. Primary Consolidation Settlement as a function of time U = 81 xloo s (2.12) Where: U = degree of consolidation (%), S = ultimate primary consolidation settlement, S 1 = primary consolidation settlement at time t

OP-13. PROCEDURES FOR DESIGN OF EMBANKMENT

Page 1 of 8 WORK INSTRUCTIONS FOR ENGINEERS TYC Compiled by : LSS Checked by : GSS Approved by : OP-13. PROCEDURES FOR DESIGN OF EMBANKMENT Page of 8 13.0 13.1. OVERALL PROCEDURES This section will briefly