STUDY ON THE SINGLE AND GROUP OF SOIL CEMENT PILE FOR HIGH RISE BUILDING

The advantages of soil cement pile are reducing settlement for construction, reinforcing soft soil, increasing load bearing capacity for work foundation, highly mechanized construction,

The doctoral dissertation has finished at Danang University of Technogogy - Da nang University

Science Instructor:

1 Prof.Dr Nguyen Truong Tien

2 AProf Dr Phan Cao Tho

Reviewer 1: Prof.Dr Trinh Minh Thu

Reviewer 2: Prof.Dr Do Nhu Trang

Reviewer 3: Dr Tran Dinh Quang

Da nang - 2015

INTRODUTION

1 Study Issues

Soil cement pile is the product of the techniques of mixing cement in local soil – by deep mixing method, processing of forming the pile after the setting of cement The advantages of soil cement pile are reducing settlement for construction, reinforcing soft soil, increasing load bearing capacity for work foundation, highly mechanized construction, rapidly progressing construction, reducing costs by using local soil, reducing waste

of soil and environment pollution

For soil cement piles constructed in sandy soil, the unconfined compressive strength is from (3.010)MPa, so it can be applied as pile foundation bearing load construction of high rise buildings in the permitted conditions However, the stiffness of the SCP is small so that the conduct between the pile - soil, pile – soil - pile in the group will be different from the usual kind of concrete pile The main focuses, then, are the strength properties of materials sand-cement, load transfer mechanism, mobilization

of side friction, tip resistance of single pile, the pile in the groups and determining group factor, and applying in the design stage for high-rise

buildings This is the foundation of my dissertation: "Study on the single and group of soil cement piles for high-rise building."

2 The purpose of the dissertation

- Develop a database of properties of the material strength of cement piles by wet mixing method for some types of soil: sand, sandy-clay, aims to create soil cement pile with high strength, bearing load for foundation construction

soil Study of the load transmission, the mobilization of side friction and tip resistance of single pile and group soil cement pile from full scale model test, as

a basis for evaluation of soil cement pile for bearing load applications

- Analyze of group soil cement pile by numerical model and building correlation about group factor for soil cement pile

- Study on the strength characteristics of the material pile SCP by experiments in the laboratory and the field

- Experiment on the full scale model test for single and group soil cement pile by static load compression with strain gages and analyze the results

- Numerize simulation by Finite Element Method to verify the model test and practical projects, developing simulation to construct correlation group factor for group soil cement pile

- Develop procedures calculations and computer program software SCPile to automate calculation and design for soil cement pile foundation

- Soil cement pile by wet method, for sandy soils, sandy – clay on area

of Quang Nam-Da Nang city, not use additives

- The dissertation focuses on analyzing the soil cement pile bearing vertical load

- Scope of applied: the high-rise building to level II (lower 19 floors)

on sandy areas Danang and other area with similar geological

7 New contributions of the dissertation

- Developing a database of correlated about unconfined compressive strength and bending strength of material SCP for 04 soil types

- Analyzing the load transmission and distribution side friction, tip resistance for single pile and pile group from full scale model test Determine the coefficient of side and tip resistance by formulations Meyerhof to apply calculation bearing capacity of single SCP

- Analyzing the mobilizing resistance of piles in groups, determination

of group factor and recommended calculating load capacity for SCP foundation by teamwork "Group"

- Developing graphs and equations determining goup factor of the group SCP according to the number of pile with different distances from the 3D numerical simulation

- Developing the procedures of calculation and the software program of SCPile automated calculation, design of SCP foundation and applied to one real projects

8 The structure of the dissertation

In addition to the introduction, table of contents, list of references, scientific published, drawings, tables, appendices, thesis consists of 130 pages is organized in five chapters:

Chapter 1: Overview of the soil cement pile

Chapter 2: Some results of experimental studies on the characteristics of the strength soil cement pile

Chapter 3: Study the the single and group soil cement piles by full scale model test

Chapter 4: Numerical simulation and construction of the correlation groups factor for soil cement pile

Chapter 5: Application of soil cement piles for high rise building

CHAPTER 1 OVERVIEW OF SOIL CEMENT PILE 1.1 Introduction

1.1.1 Process of establishment and development of SCPile

The soil cement pile originally is researched and applied in Sweden and Japan in the 1960s, and then now gained popularity in the worldwide market Two construction methods has usually been used are the wet and dry mixing methods Since 1980s, The soil cement pile (SCPile) in Vietnam has frequently been applied to the improvement of soft soil, they also have used for building

1.1.2 Applications of soil cement pile

The applications of SCPile in Sweden, Japan and other countries has commonly been used to the improvement of soft ground In Vietnam, the research and application of SCPile in two principle directions: piles to the improvement of soft soil and piles bearing, including application of SCPile bearing in high buildings in geology condition is sand could increase efficiency, reduce costs

1.1.3 Deep mixing methods of soil cement pile

In the deep mixing method, soft soil is stabilized in situ by two major techniques: the dry method of deep mixing is used for soft soil with high humidity from (60  200)% and the wet method of deep mixing is applied to soil has water content smaller Experiments in the thesis by the wet method

1.1.4 A number of domestic and foreign research on SCPile

Includes two major groups: Group studies about strength characteristic

of piles by laboratory experiments, field studies and other, studying mechanical bearing load of sigle and SCPile group

Most studies have focused for the purpose use cement to improve soft clays, organic soils, soil swellings The thesis going to continue to develop

on the basis of this approachs with SCPile application for bearing of the building foundation on sandy soil

1.2 Strength characteristics of SCPile

For SCPile bearing for works, characteristics that have affect the significant important of which is: unconfined compressive strength, qu (in the room and field), bending strength qb, elastic modulus E50

1.3 Basic calculations for single and SCPile group

1.3.1 Load-bearing capacity of single pile

Includes load bearing capacity follow the material of pile and the ground, with the methods of calculation of Broms (1984) [1], Japan [37], Jiehan (2011) [56] These methods are based on the application of the SCPile to improvement of soft clay ground Some calculations based on formulas from SPT testing results such as Meyerhof and Japan, however, the coefficients of the skin resistance and the tip resistance are inappropriate and should be determined from the results of experiments

1.3.2 Calculation of pile groups SCPile

- Ultimate bearing capacity of SCPile group: usually be applied according to viewpoint of pile foundation work as style "Block" of Bergado

by Equation (1.9) and (1:11), the method of Broms by Equation (1:12) Method of Bouassida and Porbaha by Equation (1:13) and (1:14) has more advance, but still the concept equivalent background For SCPile group, this position is not reasonable So, need to determine a suitable method for practical applications

- The effect of pile groups: be assessed through the efficency pile groups The methods according to Feld's (Equation 1:15), Terzaghi and Peck (Equation 1:16), Convese-Labarre (Equation 1:17), Coduto (Equation 1:18) and Seyed & Bakeer (Equation 1:20) In this follow-Labarre Convese

is applied more widely However these methods are applied to hard piles For SCPiles which have smaller stiffness and behavior between pile - soil, pile - soil - pile have more difference Thus, the effect of pile groups is need

to research additionally and determination of the efficiency pile groups

1.4 Geological features in Da Nang - Quang Nam and application prospects SCPiles for high rise buildings

The research and the survey’s results show that the geological characteristics of Da Nang city is sandy soil which is distributed over the surface with the thickness from 13m to 18m This sand is reasonable to use the solution

of SCPile for high buildings to level II (19 floors), contributing to decrease costs

Figure 1.15 A typical geological section of Danang city [4]

1.5 Some problems exist in study on SCPile for high rise buildings 1.5.1 Some problems exist

Material: The study material for soil-cement pile concentrated for the purpose of handling the soft clay soil is not suitable for applications such as

a SCPile solution for bearing load

Bearing capacity of piles and pile groups: methods for calculating the bearing capacity of the pile and pile groups follow material and ground are based on shear strength of soft soil around piles and pile groups This calculation does not suitable with the opinion SCPile work as piles

1.5.2 The task of the dissertation

This dissertation develops on the strength of SCPile material for specific types of soil which can be applied for constructing bearing piles Researching on the working process of single pile and SCPile group through full scale model and 3D simulation At the same time, establishing a calculation process to initially applied in the calculation, the practical design

CHAPTER 2 SOME RESEARCH RESULTS OF STRENGTH

CHARACTERISTICS FOR SOIL CEMENT PILE’S MATERIAL 2.1 Introdution

The working process of the SCPile as the transmission of SCPile, mobilizing resistance, pile group effects, horizontal bearing capacity which will depend on two properties: unconfined compressive strength qu and bending strength of pile qb Therefore, before analyzing the working of single pile and pile group is need to have the results of research on the characteristics and relative strength This chapter presents the results of laboratory experiments on the properties of the material strength of SCPile

2.2 The scope of sampling and testing of soil, cement

Scope of soil sampling: The laboratory will focus for 04 soil groups include: group No.1: clayey sand soil, group No.2: fine-grained sand, group No.3: small-grained sand and group No.4: coarse-grained sand

Grain size distribution

0 10 20 30 40 50 60 70 80 90 100

Figure 2.2 Grain size distribution of 04 soil types

The laboratory experiments about properties of soil is examined through XRF machine to determine the amount of oxides in the soil Cement and water: The chemical testing of the two types of cement PCB30 and PCB40 were also analyzed Use clean water to mix the sample

2.3 Method of testing and calculation the result

Figure 2.4 The laboratory experiments programme and analysis

The mixing, casting and curing samples and calculating the results by (TCVN9403: 2012)[20] Compression and bending samples on automatic that can produce chart of stress - strain by Trapezium software

2.4 Results of experimental studies

2.4.1 Results of compressive testing

Some charts show of the relationship between qu-ax-t, và E50 - qu - ax

Figure 2.16 Relationship qu-ax-t for

fourth soil type

Figure 2.20 Relationship E50 - qu - ax

for fourth soil type

Table 2.7 The sum of strength growth q u - t

Table 2.8 The relative equation of strength growth q u - t

clayey sand soil

(group 1)

fine - grained sand (group 2)

small-grained sand(group 3)

coarse-grained sand (group 4)

q u =0,52Ln(t)-0,13 q u =0,66Ln(t)+0,37 q u =0,75Ln(t)+2,03 q u =1,05Ln(t)+2,43

q u14 =(0,43÷0,67)q u28 q u14 =(0,62÷0,8)q u28 q u7 =(0,63÷0,694)q u28 q u7 =0,58q u28

q u21 =0,56q u28 q u56 =(1,15÷1,46)q u28 q u21 =0,56q u28 q u14 =0,79q u28

q u56 =(1,04÷1,25)q u28 q u90 =(1,31,8)q u28 q u56 =(1,04÷1,25)q u28 q u56 =1,208q u28

2.4.2 Results of bending testing

Some graphs show of the relationship between qb-t-ax và qu-qb-ax

Figure 2.28 Relationship qb-t-ax for

fourth soil group

Table 2.15 The sum of relative qb - qu for soil groups

(No1)

fine - grained sand (No2)

small-grained sand (No3)

coarse-grained sand (No4)

Discussion: The relative results between qb and qu have changes less than the results are found by Professor Terashi who performed on both the reinforce blinder is combination of cement and lime qb/qu = (0,1÷0,6)[39]

2.4.3 Establishment relationship between cement a x and q u

Figure 2.33a Impact of chemical constituents of soil to qu

2.4.5 Relationship strength between laboratory and field experiments

Combining experiments on three projects have got rate among quf field experiments strength quf and the strength of the laboratory experiments qul:

quf = (0,621,5) qul

2.5 Conclusion of chapter 2

Results Chapter 2 has established strength growth equation qu, qb over time and an amount of cement ax, qu-E50-ax Determine the ratio of bending strength qb and qu, build the relationship between an amount of cement ax

and qu and contrary for 04 soil types At the same time, evaluate the effect

of grain size distribution via coefficient Pd and chemical properties of soil

to soil strength qu, assess relationship between quf field experiments strength

quf and the strength of the laboratory experiments qul

CHAPTER 3 STUDY ON WORKING OF SINGLE AND GROUPS OF SCPILE BY

FULL SCALE MODEL EXPERIMENT 3.1 Introdution

The purpose of the model construction: The construction of full scale model is to find about the movement of stress - strain, the transmission mechanism, mobilization of skinl friction, resistance in the top of single pile and pile group (SCPile) Based on the analysis of experimental results will determine the bearing capacity factor, efficiency of pile groups and the percentage distribution of the load capacity of the piles in the group Technologies, equipment and standards apply: SCPile by technology of Japan, wet mixing method There are devices used to measure the axial strain are Geokon 4911 and 4200 The standards applied and references: ISO 4903: 2012, ISO 9393: 2012, ASTM D1143

Figure 3.5 Distribution of physical

properties of soil with depth

Layer 1: Fine sand

Strain gages Telltale d=22mm

Strain gages Telltale d=22mm

Strain gages Telltale d=22mm

Group 05 SCPiles Model D600, l=7,5M

TP1

TP2 TP3

TP6

TP7

TP8 TP10 TP9

Pile raft Concrete 35Mpa

Steel tube D60 d=1,2mm (A9)

Steel tube D60 d=1,2mm (A9) Steel tube D60d=1,2mm (A9)Steel tube D60

d=1,2mm (A9)

Layer 1: Fine sand depth : 2m

Layer 2: Clay sand, depth: 2,0m

-Layer: Medium sand, depth 5,5m

Layer 1: Fine sand depth : 2m

Layer 2: Clay sand, depth: 2,0m

-Layer 3: Medium

120

12

Figure 3.8 Drawwing of full sacle load tets for sigle and group SCPile

3.3 Establish models and conduct experiments

Some pictures constructing and loading full sacle model test

Table 3.2 Design layout of test equipment for model

SCPiles have diameter 600mm, length 7.5 m, qutk = 5,5MPa