(Luận văn thạc sĩ) a study on bearing capacity of shaft – grouted bored piles and barrettes for high rise in ho chi minh city

VIETNAM NATIONAL UNIVESITY HANOI VIETNAM JAPAN UNIVERSITY PHAM THI THUY DUONG A STUDY ON BEARING CAPACITY OF SHAFT – GROUTED BORED PILES AND BARRETTES FOR HIGH-RISE IN HO CHI MINH CITY n MAJOR: INFRASTRUCTURE ENGINEERING CODE: 8900201.04QTD RESEARCH SUPERVISOR Dr NGUYEN TIEN DUNG MASTER’S THESIS Hanoi, 2021 TABLE OF CONTENTS n LIST OF TABLES i LIST OF FIGURES ii LIST OF ABBREVIATIONS iv CHAPTER INTRODUCTION 1.1 General Introduction 1.2 Necessity of Research 1.3 Objective and Scope of Research 1.3.1 Objectives of the Study 1.3.2 Scope of the Study .4 CHAPTER LITERATURE REVIEW 2.1 Principle of the Shaft Grouting Technology 2.1.1 Grout Materials and Equipment 2.1.2 Construction Procedure .9 2.2 Existing Studies on Shaft-Grouted Piles 12 2.3 Theory for Calculate Bearing Capacity of Drill shaft 16 2.3.1 Method of FHWA (FHWA-NHI-10-016) 16 2.3.2 Method of Vietnam Standard (TCVN10304-2014) 17 2.4 Theory for Converting Strain to Load 19 2.5 Linear Regression Analysis 24 CHAPTER METHODOLOGY 25 3.1 Introduction 25 3.2 The Procedure for Determining Correlation between ru and SPT N60; Correlation between ru and ζ’v 25 3.3 Evaluation of Appropriate Soil Type for Applying Shaft Grouting Technology 27 3.4 The Procedure to Comparison of Shaft Grouted Pile and Plain Pile 30 CHAPTER DATABASE AND ANALYSIS RESULTS 31 4.1 Database of Test Piles 31 4.1.1 List of Projects 31 4.1.2 Geological Conditions .33 4.1.3 Test Pair Piles 35 4.2 The Correlation between ru and SPT N60 36 4.3 The Correlation between ru and Effective Vertical Stress ζʹv 38 4.4 Evaluation the Appropriate Soil Type for Applying Shaft Grouting Technology 39 4.5 Comparison of Shaft Grouted Pile and Plain Pile 41 CHAPTER CONCLUSIONS AND RECOMMENDATIONS 46 5.1 Conclusions 46 5.2 Limitations and Suggestions 46 REFERENCES 47 n ABSTRACT In recent years, high-rise buildings have been constructed extensively in Ho Chi Minh City (HCMC) to cope with the increasing demand for living and office spaces Drilled shafts (bored piles) for the high-rise buildings in the city, especially in the central districts along the Saigon river, are often installed up to depths of 70 to 80 m to ensure the bearing capacity To reduce many risks and high costs from installing very long piles, the shaft grouting method has been applied extensively to drilled shafts in the city to increase the resistance of the shafts or to reduce and shaft length with a designated resistance Although the method has been applied extensively, there is still no comprehensive study on the effectiveness of the shaft grouting method regarding the geological conditions of the city It is very necessary to make a comprehensive study on the effectiveness of the shaft-grouted piles in the city The effectiveness of the shaft grouting method was evaluated by comparing the ultimate (unit) shaft resistance of shaft-grouted piles with that of plain (not grouted) n piles For this, a database of 34 well-instrumented drilled shafts and barrettes from 12 projects in the city was brought into analytical analyses Results from the analyses indicate that the ultimate shaft resistance of shaft-grouted piles in both clayey and sandy soils in general increases approximately 1.8 times that of the plain piles Besides, analyses on suitable soil types indicate that, in general, the stiffer/ denser the soil, is the better the effectiveness of the method The soil has SPT-N larger than 10 (stiff clay, very stiff clay, hard clay, medium dense sand, dense sand, and very dense sand) is suitable to apply the shaft grouting method It was found that long drilled shafts for buildings along the Saigon river can be shorted significantly by applying the shaft grouting method to the lower portion of the piles The shorter grouted piles not only satisfy the required resistance but also help the construction cost up to 10% compared with that for the longer plain ones ACKNOWLEDGEMENTS I would like to express my sincere appreciation to the lecturers of Master of Infrastructure Engineering Program for their help during my undergraduate at Vietnam Japan University (VJU) First of all, I am very grateful to Dr Nguyen Tien Dung, who guided me to conduct this thesis for the part one year He spent a lot of time telling me complicated issues in geotechnical engineering Not about knowledge, he also taught me valuable lessons about the seriousness and carefulness of scientific research These valuable lessons will follow me throughout the future study I would like to acknowledge the sincere inspiration from Prof Nguyen Dinh Duc and Prof Hironori Kato Their lectures covered not only specialist knowledge but also the responsibility and mission of a new generation of Vietnam I am grateful to Dr Phan Le Binh for his support in the last two years since I have studied at Vietnam Japan University Thanks to him, I have learned the professional courtesy of Japanese people n as well as Japanese culture I would also like to acknowledge the staff of Vietnam Japan University, Mr Bui Hoang Tan for their help and support I would also like to Fecon company as well as other members of Fecon‟s lab, where I had 30 meaningful days internship at The laboratory It was very helpful to me Finally, I want to spend thank my parents and friends for their unflinching support in the tough time Their support, spoken or unspoken, has helped me complete my master thesis LIST OF TABLES Table 2.1 Summary of typical design parameters following author‟s experience 15 Table 3.1 SPT-N value soil property correlations for (a) granular (sandy) soil 28 Table 4.1 The information of projects in Ho Chi Minh city 32 Table 4.2 The information of three test pair piles 35 Table 4.3 The resistance ratio of grouted over not grouted 37 Table 4.4 The resistance ratio of grouted over not grouted 39 Table 4.5 The construction cost saving percentage comparison with plain pile and shaft grouted pile 45 n i LIST OF FIGURES n Figure 1.1 The section and details of tested piles from Gouvenot‟s research Figure 2.1 Detail of Tube a manchette Figure 2.2 The land view in the grouting process Figure 2.3 Simulate the grout affected area and the grout section cross Figure 2.4 The grouting diagram CINTAC 15 System – JEANLUTZ Figure 2.5 The grouting machine Figure 2.6 The process to construct the shaft grouted bored pile, barrettes pile Figure 2.7 Details of grouting and instrumentation of Saigon and Song Viet project 10 Figure 2.8 Cross-section and layout of instrumentation 10 Figure 2.9 The process of water cracking (a) and shaft grouting (b) 11 Figure 2.10 Illustration diagram of the grout pipe cross-section, flows paths, the section of the grouted sample 11 Figure 2.11 Variation of gain in load with injection 13 Figure 2.12 The Stocker‟s research result 13 Figure 2.13 The comparison mobilized friction value between the grouted pile and plain pile tests in Hong Kong 14 Figure 2.14 Summary the mobilized shaft resistances of clayey soil (a) and sandy soil (b) versus N value 15 Figure 2.15 Idealized layering for computation of compression resistances 17 Figure 2.16 Frictional model of unit side resistance for drilled shaft 17 Figure 2.17 The diagram to evaluate p coefficient 19 Figure 2.18 Near pile-head gage level secant stiffness vs measured strain 20 Figure 2.19 Load transfer mechanism for piles, the variation of f(z) with depth 23 Figure 2.20 The mobilized shaft resistance at some strain gauge levels 23 Figure 3.1 Flow chart to evaluate correlation between ru with N60, ζʹv 26 Figure 3.2 Illustration plain pile and grouted pile to evaluate shaft resistance increment 27 Figure 3.3 Flow chart to evaluate suitable soil type 29 Figure 3.4 Flow chart to compare grouted pile and plain pile 31 Figure 4.1 The location of projects in Ho chi minh city 31 Figure 4.2 The soil properties and SPT-N value from data of Ho Chi Minhʹs project 34 Figure 4.3 Illustration of the three test pair piles 36 Figure 4.4 Correlation of ru and N60 for Clayey soil 36 Figure 4.5 Correlation of ru and N60 for Sandy soil 37 Figure 4.6 Correlation of ru and ζʹv for Clayey soil 38 Figure 4.7 Correlation of ru and ζʹv for Sandy soil 38 ii Figure 4.8 The correlation of the shaft grouting cost to increase one shaft resistance unit versus Standard penetration test blow count for clayey soil 40 Figure 4.9 The correlation of the shaft grouting cost to increase one shaft resistance unit versus Standard penetration test blow count for sandy soil 41 Figure 4.10 The load – settlement relation chart of pair (TP-01 and TP-02) 42 Figure 4.11 The load – settlement relation chart of pair (TP-04 and TP-05) 42 Figure 4.12 The load – settlement relation chart of pair (TP1-1 and TP3-1) 43 Figure 4.13 The shaft resistance accumulated of pair (TP-01 and TP-02) 44 Figure 4.14 The shaft resistance accumulated of pair (TP-04 and TP-05) 44 Figure 4.15 The shaft resistance accumulated of pair (TP1-1 and TP3-1) 44 n iii LIST OF ABBREVIATIONS Abase Ac Cg Cs cu D Es Et fL K L lc,i ls,i N ru zi p β δ  ζ n N60 Ns,i n QHL QSG QSG qBN RB RS rs rs,c rs,s The cross-sectional area of bearing at the shaft base (m2) Circumference of pile at strain gage Shaft grouting cost Circumference of pile at depth z (m) Undrained shear strength Diameter of pile (m) The secant stiffness modulus of pile material (kPa) The tangent stiffness modulus of pile material (kPa) The coefficient depends on the ratio length over diameter Coefficient of horizontal soil stress Unit length (m) Length of pile in clayey soil layer i (m) Length of pile in sandy soil layer i (m) The number of blows required to penetrate the soil 30cm from Standard penetration test The Corrected N-index for 60% efficient energy The average SPT index in sandy soil layer i Number of layers providing side resistance The load at the pile head (kN) The load at the strain gauge (kN) The increment load at the strain gauge (kN) Nominal unit base resistance (kPa) Nominal base resistance (kN) Nominal side resistance (kN) The unit shaft resistance (kPa) Nominal unit side resistance of layers i for clay (kPa) Nominal unit side resistance of layers i for sand (kPa) The ultimate unit shaft resistance or fully mobilized unit shaft resistance (kPa) Thickness of layers i (m) The coefficient base on the ratio between undrained shear strength and average effective stress Side resistance coefficient (beta method) Effective stress angle pf friction for the soil shaft interface The strain (mm) Stress (load divided by cross section area) iv ζʹh ζʹv B S Horizontal effective stress (kPa) Effective vertical stress (kPa) Resistance factor for base resistance Resistance factor for side resistance n v n (a) Sai Gon center (PTP-1) (b) Everrich (TP1) Figure 4.2 The soil properties and SPT-N value from data of Ho Chi Minhʹs project 34 4.1.3 Test Pair Piles To perform comparative analysis on-resistance of shorter shaft-grouted piles with longer not grouted piles, six pile was chosen and compared following each pair, pair 1: TP-01 and TP-02, pair 2: TP-04 and TP-05, pair 3: TP1-1 and TP1-3 The information of pile as following: Table 4.2 The information of three test pair piles Plot Pile type Pile length (m) Diameter/ Size (m) Rmax/RD (MN) IST/SG Grouted depths (m) Test date TP1 Bored 75.00 1.2 23/13.5 Y(11)/N - 12/12/2019 TP2 Bored 61.00 1.2 23/13.5 Y(10)/Y 36.0-60.0 26/11/2019 TP4 Bored 60.00 1.0 20.5/11 Y(10)/Y 36.0-59.0 28/11/2019 TP5 Bored 75.00 1.0 20.5/11 Y(10)/N - 13/12/2019 TP1-1 Bored 70.30 1.2 22.56/11.28 Y(8)/N - 28/6/2020 TP3-1 Bored 60.30 1.2 22.56/11.28 Y(7)/Y 34.3-60.3 22/6/2020 Pair Test pile name Pair n Plot 1-13 Pair Plot 1-14 Pair 35 Figure 4.3 Illustration of the three test pair piles n 4.2 The Correlation between ru and SPT N60 In this section, the correlation was researched between the mobilized unit shaft resistance ru and the the corrected SPT-N value, summarized in the figure 4.4 and figure 4.5 with clayey soil and sandy soil Figure 4.4 Correlation of ru and N60 for Clayey soil for not grouted and grouted pile 36 Figure 4.5 Correlation of ru and N60 for Sandy soil for not grouted and grouted pile Based on data from 34 piles and the procedures discussed above, there are 180 out of 360 strain gauge levels were fully mobilized Out of 180 fully mobilized data points, soils at 124 were grouted and 56 levels were not grouted The number of fully mobilized points classified as clayey soil and sandy soil is 80 and 100 strain gage levels, respectively Among these, some data points with SPT-N index and effective vertical stress too small were excluded because the gauge level at or very near ground n surface leading to unreliable results For very soft to soft clays, N60 < (Clayton,1993), the SPT-N value obtained is very small so this study ignored the SPTN index smaller than to ensure regression more stabilized From the statistical method, the correlation was established between these parameters ru and N60 as well as check through least squares regression For the not grouted data point, k varies was evaluated almost 3.21 and 3.61 for clayey soil and sandy soil, respectively For the grouted data point, the k value obtained from the analysis is 5.64 and 6.24 for clayey soil and sandy soil, respectively Table 4.3 The resistance ratio of grouted over not grouted Grouted Not grouted Ratio Clay ru = 5.643N60 ru = 3.209N60 1.758 Sand ru = 6.237N60 ru = 3.614N60 1.726 SPT-N 37 The table shows the correlation between the ru value and N60 index as well as shows the ratio of k value between the grouted pile and not grouted pile The data set therein suggested that the ru value of grouted pile would roughly be 1.75 times larger than ru value of not grouted pile (plain pile) in clayey soil and sandy soil 4.3 The Correlation between ru and Effective Vertical Stress σʹv In the  method, the ru value is proportional to the effective vertical stress following form: Figure 4.6 and figure 4.7 present the correlation between ru and ζʹv with fully mobilized data points For the not-grouted data point, β varies were evaluated almost 0.25 and 0.28 for clayey soil and sandy soil, respectively For the grouted data point, the β value obtained from the analysis is 0.47 for both clayey soil and sandy soil n Figure 4.6 Correlation of ru and ζʹv for Clayey soil for not grouted and grouted pile Figure 4.7 Correlation of ru and ζʹv for Sandy soil 38 for not grouted and grouted pile Table 4.4 shows the correlation between the ru value and  coefficient as well as shows the ratio of value between grouted pile and not grouted pile The ru value from grouted pile would roughly be 1.83 and 1.68 times larger than ru value of not grouted pile (plain pile) in clayey soil and sandy soil, respectively Table 4.4 The resistance ratio of grouted over not grouted σʹv Grouted Not grouted Ratio Clay ru = 0.468 ζʹv ru = 0.256 ζʹv 1.828 Sand ru = 0.473 ζʹv ru = 0.282 ζʹv 1.677 4.4 Evaluation the Appropriate Soil Type for Applying Shaft Grouting Technology Figure 4.8 presents the change of the cost-benefit with several soils belong to clayey soil It is clear that the cost-benefit has changed considerably from soft clay to stiff clay To increasing 1kpa shaft resistance waste average 18,252 VND with soft clay, n however the cost is average 10,768 VND with stiff clay; 4,375 VND with very stiff clay and around 3,511 VND with hard clay To increasing 1kpa shaft resistance, in comparison to soft clay, the construction cost is decreased to 0.58 times for stiff clay; 0.24 times for very stiff clay; 0.19 times for hard clay The grouting method is most effective in clayey soils arranged in descending order with hard clay (SPT-N: 30-60), very stiff clay (SPT-N: 15-30), Stiff clay (SPT-N: 9-15), Soft clay (SPT-N < 8), respectively The correlation between the cost-benefit and SPT-N index was shown by the power equation (4.1) 39 Figure 4.8 The correlation of the shaft grouting cost to increase one shaft resistance unit versus Standard penetration test blow count for clayey soil Figure 4.9 presents the change of the cost-benefit with several soils belong to sandy n soil It is clear that the cost-benefit has changed considerably from loose sand to medium sand To increasing 1kpa shaft resistance waste average 11,390 VND with loose sand, however the cost is average 6,500 VND with medium sand; 2,924 VND with dense sand and around 2,116 VND with very dense sand To increasing 1kpa shaft resistance, in comparison to loose sand, the construction cost is decreased to 0.57 times for medium dense sand; 0.28 times for dense sand; 0.19 times for very dense sand The grouting method is most effective in sandy soils arranged in descending order with dense sand (SPT-N 25-50), medium dense sand (SPT-N 11-24), loose sand (SPT-N < 10) The correlation between the cost-benefit and SPT-N index was showed by the power equation (4.2) 40 Figure 4.9 The correlation of the shaft grouting cost to increase one shaft resistance unit versus Standard penetration test blow count for sandy soil 4.5 Comparison of Shaft Grouted Pile and Plain Pile n Three pairs pile was compared through the load-deflection and shaft resistance accumulated The load-deflection at the pile head for the shaft grouted pile and the not grouted (plain) pile is presented in figure 4.10, figure 4.11, figure 4.12 Figure 4.10 compares the TP-02 shaft grouted pile with TP-01 not grouted pile test result The figure shows that at the (18.5 MN) 140% design load TP-01, the total settlement of pile head 20.22 mm Maintain load level 140%, the settlement was increased 34.62 mm At the (18.5 MN) 140% design load TP-02, the settlement head pile is 18.8 mm Similar to Figure 4.10, Figure 4.11 compares the TP-04 shaft grouted pile with TP-05 not grouted pile test result The figure shows that at the (17.3 MN) 186% design load TP-05, the total settlement of pile head 30.6 mm At the (17.3 MN) 186% design load TP-04, the settlement head pile is 20.5 mm In addition, figure 4.12 shows that at the (14.1 MN) 125% design load TP1-1, the total settlement of pile head 22 mm At the (14.1 MN) 125% design load TP3-1, the settlement head pile is 16.82 mm 41 P=18,5MN; S = 18,8mm P=18,5MN; S = 34.62mm Figure 4.10 The load – settlement relation chart of pair (TP-01 and TP-02) P=17,3MN; S = 20,75mm n P=17,3MN; S = 30,6mm Figure 4.11 The load – settlement relation chart of pair (TP-04 and TP-05) 42 P=14,1MN; S = 16,82mm P=14,1MN; S = 22mm Figure 4.12 The load – settlement relation chart of pair (TP1-1 and TP3-1) Figure 4.13, figure 4.14, figure 4.15 gives information about shaft resistance accumulated for each pair's pile Among these, the grouted depth of TP-02 is from depth 36 m to 60 m, the grouted depth of TP-04 is from 36 m to 59 m, the grouted n depth of TP3-1 is from 34.3 m to 60.3 m By the analysis, the shaft resistance accumulated was evaluated with each load level at pile head and perform it along with the depth of pile at each strain gage From these figures, it is clear that the depth from pile head to the grouting starting point then the shaft resistance accumulated of both grouted pile and not grouted pile is equal On the other hand, the shaft resistance accumulated of the grouted pile at the grouted area was increased significantly comparison with the shaft resistance accumulated of not grouted pile from the depth 36 m with TP-02 and TP-04, from the depth 34.3 m with TP3-1 to the toe pile 43 Figure 4.13 The shaft resistance Figure 4.14 The shaft resistance accumulated of pair (TP-01 and TP-02) accumulated of pair (TP-04 and TP-05) n Figure 4.15 The shaft resistance accumulated of pair (TP1-1 and TP3-1) 44 The results was presented in Table 4.5 show that test grouted pile TP-02 saves 10.9% construction cost comparison with test plain pile TP-01 Similar to pair 1, the grouted TP-04 and TP3-1 save 11.3%, 7.8% construction cost comparison with test plain pile TP-05 and TP1-1, respectively Table 4.5 The construction cost saving percentage comparison with plain pile and shaft grouted pile Plot Pair Test pile name Pile length (m) Diameter/ Size (m) Rmax/RD (MN) Grouted depths (m) Cost saving percentage TP-01 75.00 1.2 23/13.5 - TP-02 61.00 1.2 23/13.5 36.0-60.0 10.90% TP-04 60.00 1.0 20.5/11 36.0-59.0 11.30% TP-05 75.00 1.0 20.5/11 - TP1-1 70.30 1.2 22.56/11.28 - TP3-1 60.30 1.2 22.56/11.28 34.3-60.3 Pair Plot 1-13 Pair Pair n Plot 1-14 7.80% 45 CHAPTER CONCLUSIONS AND RECOMMENDATIONS 5.1 Conclusions This study presents the effectiveness of shaft grouting method in increasing shaft resistance of very long bored piles (drilled shafts) and barrettes using analytical method The following are key conclusions drawn from the study 1) In both clayey soil and sandy soil, the ultimate shaft resistance ru value of grouted piles would roughly be 1.8 times larger than ru value of not grouted piles (plain piles) 2) Results from analyses on suitable soil types indicate that, in general, the stiffer/denser the soil is, the better the effectiveness of the method The soil has SPT-N larger than 10 (stiff clay, very stiff clay, hard clay, medium dense sand, dense sand and very dense sand) is suitable to apply shaft grouting method 3) Long drilled shafts installed along the Saigon river can be shorted significantly by shaft grouting the lower portion of the piles The test pair piles from actual n projects show that the shorter grouted piles (10 to 15 m shorter) still satisfy the design resistance required for the longer plain piles The reduction of the pile length reduces many risks from the construction of very long piles Especially, the shorter grouted piles help reduce the construction cost up to 10% compared with that for the longer plain ones 5.2 Limitations and Suggestions Limitation: In my thesis, the research is still limited The shaft grouted zone is not simulated in FEM (Finite element method) to study on the soil behavior in more detail in and after shaft grouting with each pressure level Suggestion: The research result about the correlation of ultimate shaft resistance ru and 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