EVALUATION OF BEARING CAPACITY DUE TO RADIAL EXPANSION

USING EXPANDING PILES

POUYA MOLKARAIE

UNIVERSITI TEKNOLOGI MALAYSIA

EVALUATION OF BEARING CAPACITY DUE TO RADIAL EXPANSION

USING EXPANDING PILES

POUYA MOLKARAIE

A project report submitted in partial fulfilment of the

requirements for the award of the degree of

Master of Engineering (Civil - Geotechnics)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

JUNE 2013

v

ABSTRACT

The engineering community is familiar with different techniques to improve

the bearing capacity and settlement characteristics of weak cohesive soils. Preload

piers or expanding piles are newly invented method for improving soft soils by

means of radial compression. These piers are inserted in the soil and expanded about

three times their original cross-sectional area. Due to this expansion, the surrounding

soil will be radially stressed, which results in consolidation and general stiffening.

The main objective of this research was to investigate improvement in the bearing

capacity and settlement changes in a soft clay (Kaolinite) due to applying a preload

pier. To gain this goal, soil samples of Kaolinite with undrained shear strength of 15

kPa was prepared in cubic boxes. Then two concrete piles were casted in these soil

samples; first one in a cavity expanded by an expanding pile to reach 6 cm diameter

and the other one casted in a bored cavity with the same diameter(without

expansion). Then piles were tested by loading them until failure. Load testing of the

piles yielded a load settlement graph. Based on the graph applying a preload pier

improved bearing capacity of the soil up to 12 percent. Settlement of the pile

decreased by 11 percent.

vi

ABSTRAK

Komuniti kejuruteraan biasa dengan teknik-teknik yang berbeza untuk

meningkatkan keupayaan galas dan ciri-ciri pemendapan tanah jelekit yang lemah.

Tiang pra-muat atau cerucuk berkembang adalah kaedah yang baru dicipta untuk

menambah baik tanah lembut dengan cara mampatan jejarian. Tiang-tiang ini

dimasukkan ke dalam tanah dan mengembang kira-kira tiga kali ganda luas keratan

rentas asal. Disebabkan perkembangan itu, tanah sekitarnya akan tertekan berjejarian,

dimana ia mengakibatkan pengukuhan dan pengerasan umum. Objektif utama kajian

ini adalah untuk menyiasat penambahbaikan dari segi keupayaan galas dan

pemendapan tanah liat lembut (Kaolinit) disebabkan oleh penggunaan tiang pra-muat.

Untuk mencapai matlamat ini, sampel tanah Kaolinit dengan kekuatan ricih tak

tersalir, 15kPa telah disediakan dalam kotak kubik. Kemudian, dua cerucuk konkrit

di acukan ke dalam sampel tanah; yang pertama dalam ruang yang dikembangkan

dengan cerucuk berkembang untuk mencapai 6 cm garis pusat dan satu lagi di

acukan dalam ruang digerudi dengan garis pusat yang sama (tanpa pengembangan).

Kemudian cerucuk-cerucuk telah diuji dengan mengenakan beban sehingga gagal.

Ujian beban cerucuk menghasilkan graf pemendapan beban. Berdasarkan kepada

graf, penggunan tiang pra-muat, keupayaan galas tanah meningkat sehingga 12

peratus. Pemendapan cerucuk pula telah dikurangkan sebanyak 11 peratus.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE OF PROJECT

DECLARATION

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

ABSTRAK

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF ABBREVIATIONS

LIST OF SYMBOLS

i

ii

iii

iv

v

vi

vii

x

xi

xiv

xv

1 INTRODUCTION 1

1.1 Background of the Study

1.2 Mechanisms Of Improvement By Preload Piers

1.3 Research Motivation

1.4 Objectives

1

2

2

3

2 LITERATURE REVIEW 4

2.1 Background of Information 4

viii

2.2 Determination of bearing capacity based on load test

2.3 Soil improvement methods

2.3.1 Introduction

2.3.2 Prefabricated vertical drains

2.3.3 Stone columns

2.3.4 Deep soil mixing

2.3.5 Jet grouting

2.3.6 Soil nailing

2.3.7 Mini-piles

2.4 Influence of improvement methods on bearing capacity

2.5 Concept of preload piers or expanding piles

2.6 Installation process of preload piers

2.7 Preload pier improvement mechanism

2.8 Zone of influence during installation of preload piers

5

8

8

9

11

14

17

18

19

20

21

23

23

24

3 RESEARCH METHODOLOGY 26

3.1 Introduction 26

3.2 Physical modeling

3.2.1 Soil sample preparation

3.2.2 Expanding pile embedment and concrete pile

casting

3.2.3 Casting of concrete pile (in non-expanded soil)

3.2.4 Load testing of concrete piles

27

27

32

39

40

4 RESULTS AND DISCUSSIONS

4.1 Introduction

4.2 Basic test results

4.2.1 Water content and unit weight

45

45

45

46

ix

4.2.2 Atterberg limits

4.2.3 Permeability test

4.3 Load test results

46

49

52

4.4 Comparing load test results with a numerical modeling

results

54

5 CONCLUSIONS 57

5.1 Summary of the work 57

5.2 Conclusions 58

5.3 Suggestion for future works 59

REFERENCES

60

x

LIST OF TABLES

TABLE NO. TITLE PAGE

4.1

4.2

fall cone test results for liquid limit determination

Falling head permeability test results

48

51

xi

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1

2.2

2.3

2.4

Plot of load vs. net settlement

Determination of load bearing capacity

Determination of load bearing capacity by Chin Fung

Kee (1977) method

Butler and Hoy’s Method (1977)

6

6

7

7

2.5

3.1

3.2

Configuration of preload pier(Biringen, 2006)

Cubic boxes for filling soil

Mixing clay and water in the mixer

24

29

29

3.3

3.4

3.5

3.6

3.7

3.8

3.9

3.10

3.11

Preloading soil samples

Determination of undrained shear strength by Vane shear

test

Maintenance of soil sample

Expanding pile (in expanded state)

Extracting soil by the T-shaped extractor

Extracted cylinder of soil for expanding pile embedment

Soil expansion due to inflation of the expanding pile

Monitoring the diameter of the expanding pile

Placing a plastic shield to prevent bulging of the soil

30

31

32

33

35

35

36

36

37

xii

3.12

a) The steel bar and the screw b) narrow rods welded to

the steel bar

38

3.13 Concrete casting

39

3.14 Casted concrete pile

40

3.15

3.16

3.17

Load cell and hydraulic jack setting

Steel plate and steel pipe for loading (Loading is in

progress)

Load testing mechanism. Steel plate, steel pipe, load cell,

LVDT

42

43

44

4.1

4.2

4.3

4.4

Liquid limit determination by Penetration-moisture

content graph

Load settlement graph for piles in expanded and

non-expanded soil

Load settlement graph. Settlement comparison

Load-settlement graphs for piles with and without

expansion, in different diameters

48

53

54

55

4.5

Simulation of stone column expansion: (a) model of

improved soil; (b) modeling column expansion; (c)

discretized improved soil.

56

xiv

LIST OF ABBREVIATIONS

FEM - Finite Element Method

ASCE - American Society of Civil Engineers

ASTM - American Society for Testing and Materials

BS - British Standard

LVDT - Linear Variable Differential Transformer

LL - Liquid Limit

PL - Plastic Limit

PI - Plastic Index

xv

LIST OF SYMBOLS

c’ - Effective cohesion

u Pore pressure

' - Effective friction angle

γ - Unit weight

γw - Unit weight of water

- Total normal stress

k - Permeability

D - Diameter

t - Time (second)

1

CHAPTER 1

INTRODUCTION

1.1 Background of the Study

Construction on soft soils remains a trouble making foundation engineering

challenge as usually a significant load is imposed by the new structure and the

available shear strength of the soft clay is low thus applying a method for improving

of soil characteristics seems to be necessary. The engineering community is familiar

with different techniques to improve the bearing capacity and settlement

characteristics of weak cohesive soils. Some of the in situ techniques to improve the

properties of soft ground (e.g. soft clays) prior to placement of foundations are

preloading, deep cement/lime mixing, stone columns, grouting (Henn, 1996;

Moseley, 1993).

Besides these better known methods, a novel approach has recently been

proposed to achieve soft ground improvement by means of applying radial

compression using Preload Piers. Preload Piers can be performed as pre-treatment or

site improvement before a structure or embankment is built. They are intended

especially for soft ground construction and can be placed anywhere between ground

surface to 15 m depth at relatively close spacing (about 2 m on center). Preload piers

can be utilized to stiffen soil at a cost which is significantly less than that

encountered in using aggregate piers or other soil reinforcing systems.

2

1.2 Mechanisms Of Improvement By Preload Piers

The idea behind the Preload Piers is densification in the radial direction due

to consolidation of the soil. The improvement would result in an increase in the

stiffness of the soil which enables to solve the problems raised by soft soils. The

preload pier method includes the boring a cavity in the section of ground and

applying at least one elongate expandable member which can be distended from

normal to expanded configuration, which will provide densified soil adjacent to

expandable member.

Preload pier technique could be applied in soft clays in two main functions.

First method is to place piers directly under foundation, thus each of them assist load

bearing capacity duo to an increment in side friction. Second, is to install preload

piers as a group, so they improve the surrounding soil by densification and radial

consolidation and will result in a pier-soil composite with enhanced stiffness and

strength, which is capable of bearing loads without exceeding settlement limitations.

1.3 Research Motivation

A search of the literature review has indicated that researches have done

mostly on load capacity of vertically loaded piles. Seed and Reese (1957)

investigated the influence of adjacent soil on the load capacity of a pile by focusing

on the improved skin friction, but not on the stiffness improvement of the soil.

Moseley (1993) studied influences of preloading on the stiffness of the soil by

focusing on soils which are preloaded vertically but a theoretical approach which

provides prediction in vertical stiffness changes in response to radial preloading is

not investigated so much. One of the few researches around vertical stress and strain

changes in soils due to preloading has done by Biringen (2006). This research

investigated improvement in vertical stress-strain-strength properties of a normally

consolidated soft clay in response to preloading in radial direction.

3

In summary, going through literature has shown that an investigating of

changes in bearing capacity of a soft soil due to Preload Pier application and

consequent improvement in bearing capacity adjacent to pile is a soil mechanics

problem has received little or no attention. Also, it is not clear how much bearing

capacity improvement can be expected due to stress changes caused by a radially

expanding pier. Thus my research will focus on investigating influences of installing

expanding piers on bearing capacity of adjacent soft clay.

1.4 Objectives

In this study, I will investigate influence of applying preload pier in a soft

soil. Focus of this study will be on monitoring changes in the soil duo to radial

expansion of a pier. The main objectives of this study are:

i. To determine ultimate bearing capacity of the soft soil adjacent preload piers

ii. To investigate settlement in the soft soil due to installation of expanding piers

iii. Modeling a preload pier in expanded and non-expanded status, and

comparing the results.

60

REFERENCES

Alimohammadi, P., Nazir, R., Kassim, Kh. A., Javani, N., 2013. Evaluation of

Settlement in Expanding Piers due to Radial Consolidation in Soft Clay. EJGE,

18, pp.889–899.

Baumann, V. and Bauer, G.E.A. (1974) The performance of foundations on various

soils stabilized by the Vibro-Compaction Method, Canadian Geotechnical

Journal, Vol. 11, No. 4, pp 509-530.

Biringen, E., 2006. Radial preloading for ground improvement. Doctor of

Philosophy, University Of Wisconsin-Madison, United States.

Bowles, J.E., 1997. Foundation Analysis And Design. (5th

ed.) Singapore: McGraw-

Hill.

Broms BB (1991). Stabilization of Soil with Lime Columns. Foundation Engineering

Handbook, 2nd Edition, Ed. Hsai-Yang Fang Van Nostrand Reinhold, New

York, pp. 833-855.

Budhu, M., 1999. Soil mechanics and foundations. United states: JohnWiley & Sons.

Coyle, H. M., & Castello, R. R. (1981). New design correlations for piles in sand.

Journal of the Geotechnical Engineering Division, 107(7), 965-986.

Das., B.M., 2007. Principles of Foundation Engineering. (6th

ed.), United States:

Thomson.

Das., B.M., 2009. Shallow foundations bearing capacity and settlement. (2nd

ed.),

United states: Taylor & Francis Group.

Dehghanbanadaki, A., Ahmad, K. & Ali, N., 2013. Stabilization of Soft Soils with

Deep Mixed Soil Columns – General Perspective. EJGE.

Etezad, M., Hanna, A. M., & Ayadat, T. (2006). Bearing capacity of groups of stone

columns. In Proceedings of the Sixth European Conference on Numerical

Methods in Geotechnical Engineering, Graz (pp. 781-786).

Fellenius, B.H., 1980. The analysis of results from routine pile load tests. Ground

Engineering, 13(6), pp.19– 31.

61

Fox, N. S. (2002). U.S. Patent No. 6,354,768. Washington, DC: U.S. Patent and

Trademark Office.

Goughnour, R.R. and Bayuk, A.A. (1979) Analysis of stone column – soil matrix

interaction under vertical load, Proceedings of the International Conference on

Soil Reinforcements, Paris, pp 271-277.

Henn, R. W. (1996). Practical guide to grouting of underground structures, ASCE

Press, New York.

Holm, G. (2001) Deep mixing. Soft Ground Technology ASCE, 105‐122.

Hughes, J.M.O. and Withers, N.J. (1974) Reinforcing of soft cohesive soils with stone

columns, Ground Engineering, Vol. 7, No. 3, pp 42-49.

Larsson, S. (2003) Mixing processes for ground improvement by deep mixing, PhD

thesis. Royal Institute of Technology, Stockholm, Sweden.

Li, A.L. & Rowe, R.K., 2001. Combined effects of reinforcement and prefabricated

vertical drains on embankment performance. Canadian Geotechnical Journal,

38(6), pp.1266–1282.

McCabe, B. A., McNeill, J. A., & Black, J. A. (2007). Ground improvement using

the vibro-stone column technique. In Joint meeting of Engineers Ireland West

Region and the Geotechnical Society of Ireland.

Moseley, M.P. (1993). Ground Improvement., Chapman & Hall, Boca Raton, 218.

Priebe, H.J. (1995) The design of Vibro Replacement, Ground Engineering (Dec), pp

31-37.

Porbaha, A. (1998) State of the art in deep mixing technology, part I. basic concepts

and overview. Ground Improvement, Vol. 2, No. 2, 81‐92.

Ryan R. Berg, P.E.; Barry R. Christopher, Ph.D., P.E. and Naresh C. Samtani, Ph.D.,

P.E., 2009. Design and Construction of Mechanically Stabilized Earth Walls

and Reinforced Soil Slopes – Volume I., 1.

Seed, H. B., and Reese, L. C. (1957). The action of soft clay along friction piles.

Trans. Am. Soc. Civ. Eng., 122, 731-754.

Slocombe, B.C. (2001) Deep compaction of problematic soils, Problematic Soils,

Thomas Telford (London), pp 163-181.

Taube, B.M.G., 2008. Prefabricated Vertical Drains-The Squeeze Is On. Geo-Strata,

pp.1–3.

U.S. Army Corps of Engineers, 1992. Bearing capacity of soils. United States,

Washington, DC.

62

U.S. Army Corps of Engineers, 2003. Guidelines On Ground Improvement For

Structures And Facilities. United States, Washington, DC.

Vesic, A. S. (1972). Expansion of cavities in infinite soil mass. J. Soil Mech. Found.

Div, Am. Soc. Civ. Eng, 98(SM3), 365-29.

Zahmatkesh, A. & Choobbasti, A.J., 2010. Settlement Evaluation Of Soft Clay

Reinforced By Stone Columns , Considering The Effect Of Soil Compaction. ,

3(May), pp.159–166.