Tài liệu Nghiên cứu ảnh hưởng của lớp xi măng đất gia cố mặt nền đến sức chịu tải ngang của cọc đứng, ứng dụng cho đập trụ đỡ vùng đồng bằng sông cửu long (tt)

MINISTRY OF EDUCATION MINISTRY OF AGRICULTURE AND AND TRAINING RURAL DEVELOPMENT VIETNAM ACADEMY FOR WATER RESOURCES & TRAN MINH THAI RESEARCH THE EFFECT OF SURFACE SOIL CEMENT REINFORCEMENT LAYER ON THE LATERAL BEARING CAPACITY OF VERTICAL PILES, APPLIED TO PILLAR DAM IN THE MEKONG DELTA Speciality: Hydraulic engineering Code No: 9.58.02.02 SUMMARY OF TECHNICAL DOCTORAL DISSERTATION Hanoi 2020 The dissertion was completed at: VIETNAM ACADEMY FOR WATER RESOURCES Supervisor: - Prof. Dr. Nguyen Vu Viet - Prof. Dr. Tran Dinh Hoa Reviewer 1: Reviewer 2: Reviewer 3: The dissertation is going to be presented to academy evaluation committee, which is held at Vietnam Academy for Water resources, address: 71 Tay Son Street, Dong Da, Ha Noi. In …………, 2020 at ….. The dissertation can be found at: - National library in Viet Nam; - Library of Viet Nam Academy for Water Resources. 1 INTRODUTION 1. The urgency of the Subject Vietnam is a country which has a long coastline and many large rivers flowing into the sea stretching from the North to the South. In recent years, the harshness of nature has become more evident, such as climate change, rising sea levels, greater storms and floods, and the shortage of fresh water which has greatly affected life and socio-economic development of the country. The Mekong Delta is a region with great potential, hold an important role in socio-economic development and is a key in the national food security strategy. The big policy of Government is to continue researching and investing in constructing sea dykes, regulating estuarine areas in tidal areas in order to prevent and mitigate natural disasters as well as protect economic people and livelihoods, contribute to the development of the country The current water control works, the Pillar dam is becoming more and more widely used, becoming a scientific solution to gradually replace traditional works, especially reflected in the large hydraulic works which is contructed in coastal estuaries. In order to further improve the efficiency of technology application, it is necessary to continue researching and perfecting both theory and experiment. on unexplained issues. For Pillar dam, it is often suffer from great horizontal loads. In addition to the solution of oblique piles, the reinforcement of the foundation surface layer will be able to increase the lateral bearing capacity of the pile foundation. In order to determine the appropriate size for the reinforcement layer and evaluate how the impact on the lateral bearing capacity of the pile foundation of the supporting pier has so far been unresolved. Therefore, the the Subject is urgent and practical. 2. Research purposes - In oder to a scientific basis, perfecting the theory in calculating and the design of Pillar Dam. - Proposing the form and structure of the surface reinforcement layer to increase the lateral bearing capacity for foundation pile of Pillar Dam in the Mekong Delta. 3. Research Methods Method of theoretical research: - Research and analyze relevant technical information published through documents such as books, newspapers, design standards ... Domestic and Foreign. - Using mathematical model to research and analyze the influence of the reinforcement layer on the lateral bearing capacity of single piles, thereby selecting the reasonable size of the surface reinforcement layer corresponding to the types of piles. Experimental research methods: Experimenting physical models, measuring, evaluating lateral bearing capacity of piles in cases of working on natural soft ground and the ground after 2 surface layer reinforcement. On that basis, compared with the established theoretical research method, there was a conclusion about the method of calculating the lateral bearing capacity of the pile, which is the basis for the stability of the pile foundation of the Pillar Dam in Mekong Delta; Professional solution: Organize scientific conferences and critical review meetings, including scientists who have in-depth knowledge of the research area of the PhD student, to comment, evaluate and critique the research results. 4. Research object The horizontal axial strength of single vertical piles in case of reinforcing the surface layer of pile foundation side at the tip of pile head of the Mekong Delta. 5. Research scope - Structure: Vertical single pile in the foundation of Pillar Dam on soft ground in the Mekong Delta. - Pile material: reinforced concrete piles - Reinforcing: Reinforcing the foundation surface layer of the top of pile with soil cement piles which is used deep mixing technology 6. Scientific and practical significance of the thesis - The dissertation has established a scientific basis for calculating the reinforcement of pile foundation surface (new structure, natural ground combined with cement by deep mixing method), which increases the horizontal resistance of the foundation of the Pillar dam in Mekong Delta, where the soft ground characteristics are detrimental to construction. - The research results of the thesis have been applied in pile foundation design and to complete the theory of Pillar Dam. 7. New contributions of the thesis - The dissertation has proposed a new solution to increase the lateral bearing capacity of the pile foundation of Pillar Dam in the Mekong Delta and determine the reasonable size of this reinforced part. - The thesis has built a relationship between the load and horizontal displacement (p ~ y) for the representative weak soil type and for the foundation surface reinforcement layer. Thereby determining the foundation and method of determining lateral bearing capacity to apply the design of the pile foundation of Pillar Dam. 8.The layout of the thesis The layout of the thesis consists of: Introduction; 4 main chapters; Conclusions and recommendations; Published articles and Reference 3 CHAPTER 1: OVERVIEW OF PILLAR DAM AND SOLUTIONS TO INCREASE LATERAL BEARING CAPACITY FOR PILE FOUNDATIONS IN SOFT GROUND AREAS 1.1 Overview of Pillar dam 1.1.1. Introduction of Pillar dam technology The principle of Pillar dam is to bring the entire force into the work to separate pillars, then transfer them to the ground through the pillars. Between the pillar is the gate and waterproof structure. Figure 1.1: Model of Pillar dam The advantage of Pillar dam is possible to construct it on the natural river, to build constructions in weak geological conditions, with the depth of the soft soil layer as in the coastal estuaries or ancient alluvial areas. 1.1.2 Research situation and application of Pillar dams in the world From the early years of the twentieth century, the type of river containment working as Pillar dam has been researched and applied many countries. Large-scale works are concentrated in countries with strong scientific and economic development such as Germany, England, etc. with the task of preventing tides or controlling tides and preventing flooding. 1.1.3 Research situation and application Pillar dam in Viet Nam Pillar dam technology was researched by the Institute of Water Resources Research from 1991-1995 in the National Independence scientific Project KC1210. Structure and principle of Pillar dam as shown in figure 1.1. Up to now, the Pillar dam technology has been applied to build many riverbarrier construction in Viet Nam and brought tremendous economic and technical efficiency, such as: Thao Long (TT Hue), Nhieu Loc-Thi Nghe (Ho Chi Minh City), Bien Nhi, Bao Chau, Vam Dinh (Ca Mau), Nha Mat (Bac Lieu), Bau Dien (Tien Giang), Kenh Cut (Kien) Giang), Cau Xe (Hai Duong),... Currently, Ho Chi Minh City Flood Control Project are applying Pillar dam technology to build, the width of gate is from 40 - 160m; 4 1.1.4. Issues that need to be further researched when applying the Pillar dam in the Mekong Delta and Vietnam Although the Pillar dam has been researched and applied in Vietnam for a long time, but the condition of the deep water level and large water column caused a great horizontal load, the design of this construction is still difficult due to the possibility of Horizontal resistance is limited compared to traditional constructions. For the Mekong Delta, the deep soft soil layer is also a difficulty when applying Pillar dam. For a long time, measures to increase the lateral bearing capacity of pile foundation were oblique piles or large oblique piles. Therefore, necessary to continue researching other solutions to increase the lateral bearing capacity of pile foundation. 1.2 General assessment of geology in the Mekong Delta to the working ability of pile foundation which is regularly subjected to horizontal load 1.2.1. Distribution and characteristics of soft soil in the Mekong Delta The Mekong Delta is covered by quite thick young sediments, the common composition of this layer is weak soil: weak clay, flowing sand, mud ... According to the characteristics of geology, engineering geology, hydrogeology where divided into five soft land areas. This soft clay has the most basic physical and mechanical characteristics as follows: + Natural density of soil: γ = 14.5 ÷ 15.5kN / m3 + Natural soil moisture: w = 75% ÷ 65% + Natural hollow coefficient of soil: e = 1.5 ÷ 2.0 + Mechanical characteristics of soil: φ = 4o ÷ 5o, c = 5 ÷ 6kPa + Distortion characteristics of soil: Eo = 500 ÷ 600kPa The thickness of soft clay in the Mekong Delta is usually from 0 ÷ 40m. 1.2.2. Geological foundation of Pillar dam constructed in the Mekong Delta Based on the geology summation at works which is applicated of Pillar dam technology in the Mekong Delta, within the range of 0 to 5 m, the soil at the top of the pile (φ = 3-5o, c = 1–5kPa, γ = 1.5 –1.65kN / m3). 1.2.3. The note when contructing Pillar dam in the Mekong Delta - Most of the Pillar dam have pressure on the foundation p> 300 ÷ 500kPa, so it is needed to treat the foundation when contructing. The soil has a small water permeability coefficient, so the consolidation speed is slow, subsidence is long. Therefore, so reinforcing surface treatment should pay attention to solutions to accelerate the drainage process so that the ground consolidates quickly. - The relationship between stress and deformation of weak soils is nonlinear, so the application of the extended Winkler model is consistent with the working reality of the lower ground of dam. - Foundation solution for the Pillar dam is to use pile foundations, which be used to rconcrete piles, bored piles, prestressed concrete piles, steel piles ... 1.3. Solutions to increase lateral bearing capacity for pile foundation Pile foundation of Pillar dam is usually subject to large horizontal load, there are 2 main solutions to strengthening of the foundation is: arrangement of oblique 5 piles in the foundation or increasing the lateral bearing capacity of the single pile in the pile group. Each solution has different advantages, disadvantages and application conditions. For Pillar dam, the proposed solutions must be convenient because the pillars have a load capacity of several hundred to a few thousand tons for a pillar, so the number of piles is so many. 1.3.1 Solution of oblique piles: Use oblique pile or large oblique pile to move horizontal load to axial load. 1.3.2. Solution to reinforce surface layer 1.3.2.1. Influence of soil around the pile to lateral bearing capacity of the pile When the pile is under horizontal force, the ground on the side of the pile appears to resist the force. The chart of the resistance force of cohesive soils is shown in Figure 1.2: Figure 1.2: Distribution of soil resistance pressure on piles For cohesive soils, the value is considered constant, the depth arising at a depth of 1.5d from the ground. The mechanical properties of the soil and topsoil greatly affect and directly affect the lateral bearing capacity of the pile. When improving the properties of the surface reinforcement layer, the lateral bearing capacity of the pile will improve compared to the natural soft ground in the Mekong Delta. The handling options are as follows: 1.3.2.2. Use crushed stone, grit or other raw materials Use this material on the ground around the pile because of the large internal friction angle, large ground ratio. Reinforcement can be carried out before or after the installation of the pile. The downside is that it is difficult to inspect the construction in the country. The contact between the pile and the rock layer will be uneven, resulting in inaccurate calculations. 1.3.2.3 Using solution to improve the ground by soil-cement pile The solution to improve the soft ground for pile foundations with deep mixing method technology is to create cement piles in the soft soil layer of the pile foundation surface. Forms such as: reinforcing the scope under the pillar footing, around the bearing piles or reinforcing the blocks surrounding the pillar footing. For pillar dam, the author proposes solutions to reinforce under pillar footing. The calculation of piles in this case the reinforced layer is converted to a base layer and calculated as the case of multi-layer foundation. This solution is relatively simple, however, specific calculations need to be made based on geological conditions, type of foundation, type of pile as well as reinforced cement content. This solution is most suitable and effective for pile foundations with the substrate surface is soft ground. 6 1.3.2.4. Use concrete mortar Bottom layer of concrete is often used with concrete grade B20 (M250). The disadvantage is that the elasticity of the bottom concrete layer is not available, so the lateral bearing capacity of this layer is difficult to determine; often the depth of the bottom layer is much smaller than the depth of influence of horizontal load so the effectiveness of the solution is not high. This solution is suitable and effective for pile foundations with sandy or hard clay foundation. 1.3.3. Selecting the research solution of the thesis In thesis, the author focus on researching solutions to increase the lateral bearing capacity of single piles in the pile group. These types of reinforcement materials have the effect of increasing lateral bearing capacity for pile foundations, but the construction ability can greatly affect the research results. In those categories, the reinforcement soil cement piles was selected to research. 1.4 Researches on soil-cement reinforcement for soft soil 1.4.1 The situation of application of soil cement to reinforce in the world and in VN Technology to improve soil by cement, cement - lime has been researched and applied since the 1960s, typically the US and Japan. This technology is used in many road and railway projects such as: nailing, stabilizing excavations, stabilizing slopes, reducing vibration ... In Vietnam, the research of deep soil consolidation was started in the early 1980s. In 2002, a number of projects began to use soil cement piles to reinforce the weak ground. In hydraulic works, since 2005 the soil-cement pile has begun to be applied. The initial goal was to treat the ground waterproofing of the sluices. After that, the soil cement piles are further researched for the purpose of waterproofing and reinforcing the foundation for other types of works. 1.4.2 Researches on soil-cement piles in reinforcing soft ground in the Mekong Delta Vietnam Academy for Water Resources has applied the soil-cement pile technology in foundation treatment and waterproofing of hydraulic works in the Mekong Delta and it has brought about certain technical and economic efficiency. Some specifications of common soil cement piles in the Mekong Delta: Pile diameter: 60cm - 80cm Cement content: usually use 300kg/m3 The compressive strength depends on the soil type (Table 1.1): Table 1.1: Strength of soil cement pile with some typical soft soil types Compressive strength (kPa) TT Soil type (28 days) (90 days) 1 Clay mixed, flowing plastic 634-906 1032-1123 2 Flexible plastic clay 630-814 886-1057 3 Clay 430-690 684-980 4 Peatification 184-236 116-164 5 Organic clay and mud 551-973 856-1156 7 1.4.3 pplication of soil cement piles to reinforce pile foundations in Japan Since 2001, Japan has begun researched and applied soil cement piles to increase the lateral bearing capacity for pile foundations, such as the Yabegawa Bridge of the Ariake Expressway Project, Fukuoka district, Japan. The bored piles were used with the depth of 50m, the reinforced soil cement pile with the length and depth of B = 16.8m and Hgc = 10.5m. The application of soil cement pile has brought remarkable economic and technical efficiency, especially the reduction of vertical piles, reduced horizontal displacement and better earthquake resistance. However, the design methodology was not established, but only field experimented at each individual site. 1.5 Conclusion of chapter 1 - Although it has been researched and applied in practice, there are still many issues that need to be further research and complet in theory to apply the design, especially to the soft ground in the Mekong Delta. - The solution to increase lateral bearing capacity for single piles and for pile foundations selected for research orientation in the thesis is the solution to reinforce the surface layer of pile foundation surface, the top of the pile with soil cement piles – deep mix method technology. - Currently, there is no announcement on the calculation theory to determine the scope of the reinforcement layer, so it is necessary to research by mathematical models and field experiments to give methods to identify and evaluate the effectiveness of The above mentioned reinforcement solution is used for lateral bearing capacity of pile. CHAPTER 2: SCIENTIFIC BASIS OF SURFACE LAYER REINFORCEMENT SOLUTION 2.1 Factors affecting of surface reinforcement layer to pile foundation When the Pillar dam has a Surface reinforcement layer, foundation is changes properties and ground state stress, which will affect: - Affect lateral bearing capacity of single pile. - Affect vertical load capacity and negative friction phenomenon of pile. - Affect lateral bearing capacity of pile groups - Affect the load capacity of the ground under the surface reinforcement layer - Influence of surface reinforcement layer on the settlement of pile foundation. 2.2 Method of calculating single pile under horizontal load 2.2.1 The methods for calculating currently applied single-piles For the stability problem of pile foundations in general and pile foundation in particular always comes from the research results of a single pile. So the calculation of a single pile is not only important. Currently, there are many methods of calculating single piles, each calculation method has 3 basic characteristics such as: Model of soil environment surrounding the pile; Properties 8 of the relationship between soil reaction (p) and lateral displacement of pile (y); How to solve the problem. 2.2.2 Analyze and select the method of calculating single pile. Due to the working characteristics of the base dam piles in the Mekong Delta should group methods based on the ultra-limited resistance of piles such as the Broms method and the Meyerhof method has many limitations because it is not applicable to the multi-layer background and not Consider reaching the intensity of the soil. The method "curve p ~ y" for the calculation of the foundation pile in the Mekong Delta is quite suitable by piles in multi-layer background and long piles. Currently, with the development of computer technology, the commercial software calculates piles, using curve theory p ~ y to solve the problems of more and more piles and high reliability, typical such as: the Software Lpile compution; Ensoft Group; Midas Software; Software FB_Pier... 2.3 Researching the influence of surface reinforcement layer in depth 2.3.1. Theoretical basis is determined the depth affecting hah surface layer The thickness of the surface soil layer plays a decisive role to the displacement and internal force of the pile. Depth influence is particularly important. It depends on the type of pile, the physical and mechanical properties of the surface layer The influence depth is determined by some basic formulas as follows: (2-1) h = 2.(d + 1) ah hah = 3,5d + 1,5 (2-2) The influence depth hah which according to (2-1) and (2-2) is a basis for comparison with the research results to determine a reasonable depth of reinforcement. 2.3.2 Research the influence of depth of surface reinforcement layer on lateral bearing capacity to pile foundation using mathematical model - The purpose of calculation is to determine a reasonable depth of reinforcement, that value the pile and ground reinforcement have maximum horizontal load. From there, propose a formula to determine a reasonable depth of reinforcement layer. - The purpose of the calculation is to determine a reasonable depth of reinforcement with that value the pile and reinforcement foudation have the largest horizontal force from which propose a formula for determining a reasonable reinforcement layer depth. - Selecting the type of research piles calculated in the model is reinforced concrete piles which dimensions is accordance with commonly used reality, the length of the selected piles must satisfy the condition of being a "long pile" type. - Select reinforcement method: reinforce the suface soil layer of foundation with soil cement pile, the reinforcement layer is around pile. 9 - Diagram of calculation: Calculating for cases natural ground; determine the reasonable depth for each type of pile in case reinforcement by soil-cement. - To research the lateral bearing capacity, it is necessary to base on the theory of p ~ y curve. When assigning a pile to a forced displacement the pile will have a horizontal force that is directed against the direction of the forced displacement. - Calculation parameters: + Choosing reinforced structure is a type of soil cement pile D100cm, cement content 300kg/m3 + Calculation of soil cement pile parameters works as an equivalent background. + Soil: Representative soil sample was taken in My Tho, Tien Giang: Cu (kPa) φ (degree) g (kN/m3) Layer1 14.2 4,35 15,8 Indicator of soil cement pile: Cc (kPa) φ (degree) 400 35 2.3.2.5. Calculation results a) Case of the existing ground (natural foundation): g (kN/m3) 18,0 Biểu$đồ$quan$hệ$giữa$SCTN$với$kích$thước$cọc$nền$tự$nhiên$ 40" 35" 30" Sức$chịu$tải$ngang$(kN)$ Figure 2.1: Relationship diagram between lateral bearing capacity with pile size, natural ground 25" 20" 15" 10" 5" 0" 5" 10" 15" 20" 25" kích$thước$cọc$(cm)$ 30" 35" 40" b) Calculation results for reinforcement cases with different depth for each type of pile as shown in Figure 2.2: Biểu"đồ"quan"hệ"giữa"sức"chịu"tải"ngang"với"độ"sâu"gia"cố"" Figure 2.2: Relationship diagram between lateral bearing capacity and reinforcement depth "Sức"chịu"tải"ngang"(kN)" 250" 200" SCTN"Cọc"20" 150" SCTN"Cọc"35" 100" STCN"Cọc"40" SCTN"cọc"10" 50" SCTN"cọc"30" 0" 0" 0,5" 1" 1,5" 2" 2,5" Độ"sâu"gia"cố"(m)" 3" 3,5" 4" 4,5" 10 2.3.2.7. Proposing the method of determining the depth of reinforcement Biểu#đồ#quan#hệ#giữa#kích#thước#cọc#với#độ#sâu#gia#cố# From the results of 4" y"="12,473x "+"0,2719x"+"1,3726" the research of the depth R²"="0,99499" 3,5" of the pile corresponding to the pile type, the 3" author has determined 2,5" the reasonable 2" reinforcement depth value of pile types, 1,5" thereby building a 1" relationship between the 0" 0,05" 0,1" 0,15" 0,2" 0,25" 0,3" 0,35" 0,4" 0,45" reinforcement depth and kích#thước#cọc#(m)# pile size as figure 2.3. Figure 2.3: Relationship diagram between reinforced depth and pile size From the chart have got the formula to determine the reasonable depth of reinforcement as follows: Độ#sâu#gia#cố#(m)# 2 Hgc = 12.5D2 + 0.27D + 1.37 (2-3) D is the diameter or edge of the pile (m) 2.4 Research the influence of surface reinforcement layer on the ground 2.4.1. Theoretical basis for determining the size of reinforced layer on the ground a) Theoretical basis On the ground, the reinforcement area must be large enough for the surface reinforcement layer to work well to increase the lateral bearing capacity of the pile in the foundation. Types of reinforcement applicable: Reinforcing the entire area of the bottom of the pillar; Reinforced around the perimeter of the pillar b) Permissible horizontal displacement of pile foundation of Pillar Dam Determine the permissible horizontal displacement of the pile as a basis for lateral bearing capacity research with the scope of reinforcement on the ground. Horizontal displacement allows taking according to the current standards, but for Pillar dam, in order to ensure the good working of the valve gate structure and the waterproofing structure, select the allowed horizontal displacement of the pile [y] = 25mm. 2.4.2 Research the influence of surface reinforcement layer on lateral bearing capacity of pile foundation using mathematical models The purpose of calculation is to determine the reasonable length of reinforcement which lateral bearing capacity is max. From that, propose a method to determine the length of the reinforcement layer and build the relationship between lateral bearing capacity with the piles types. Using software of Geotechnical Midas GTS NX version 2014 - Korea GTS NX to research the reinforcement length. 11 Calculation of cases with changing layer lengths: Begin equal to 5D, then gradually increase each level compared to 25cm, until the influence of the length of the reinforcement layer is over. The method chosen for calculation is the reduction method ϕ, c. The principle of calculation is to gradually reduce the shear resistance of the substrate to the point where an instability occurs. The rate of maximum reduction in shear strength at that time was considered to be the minimum safety factor. Calculating diagram: - The model is built on Midas - GTS software. - Geological parameters of the foundation and reinforcement layer section 2.3 - Model size: + Model length and height vary with each pile size (equal to 2 times the pile length); + The width of the model is not less than 5D (D is the diameter of pile). + Depth of reinforced block calculated by the formula (2-3) + Width of reinforcement block resemble the width of model + Single pile has the length of each pile size (Table 2.1) Table 2.1: Size of research model determining reasonable reinforcement length pile size (cm) Reinforced Reinforced Length No depth (m) width (m) of piles Square Round centrifugal (m) pile pile piles 1 10x10 10 10 1,52 0,5 6 2 20x20 20 20 1,92 1,0 6 3 30x30 30 30-6 2,58 1,5 15 4 35x35 35 35-6 3,00 1,75 15 5 40x40 40 40-6.5 3,48 2,0 15 6 60 60-9 6,03 3,0 30 2.4.2.1. Calculation results Calculate and build a relationship diagram between lateral bearing capacity with reinforcement length for each type and size of research piles as follows (Figure 2.4 is typical square pile): Figure 2.4: Relationship diagram between lateral bearing capacityof square piles and reinforcement length 2.4.2.2. Commenting on the research results: When increasing the length of reinforced blocks, the lateral bearing capacity of piles increased, but to a certain extent, despite the increase in length, the lateral bearing capacity has not increased. This shows that, reinforcing length Lgc to a 12 certain critical value will maximize the influence of reinforcement. Reasonable reinforcement length depends only on the size of pile D and not on the shape of pile. 2.4.2.3. Propose a formula to determine the length of reinforcement Biểu&đồ&quan&hệ&giữa&kích&thước&cọc&với&chiều&dài&gia&cố& From the results of calculating the reasonable reinforcement length of piles, the author built a relationship 5,0" diagram between the depth of reinforcement and pile size as shown in Figure 2.5.4,5" Chiều&dài&gia&cố&(m)& 4,0" Figure 2.5: Relationship diagram between reinforcement length and pile size y"="$1,9536x2"+"5,0707x"+"1,1901" R²"="0,98429" 3,5" 3,0" 2,5" 2,0" 1,5" 1,0" 0" 0,1" 0,2" 0,3" 0,4" 0,5" 0,6" 0,7" kích&thước&cọc&(m)& From there, formulate a formula to determine the reasonable reinforcement length as follows: Lgc = -1.95D2 + 5.07D + 1.19 (m) (2-4) After determining the reasonable reinforcement length, the author calculates and builds a relationship diagram between lateral bearing capacity with the size of the types of piles as shown in Figure 2.6. 230# 210# 190# Sức$chịu$tải$ngang$(kN)$ Figure 2.6: Relationship diagram between lateral bearing capacity and size of pile types 170# 150# cọc#vuông# 130# cọc#tròn# 110# cọc#ly#tâm# 90# 70# 50# 5# 10# 15# 20# 25# 30# 35# 40# 45# 50# 55# 60# 65# Kích$thước$cọc$(cm)$ 2.5 Conclusion of chapter 2 - By using the method of software numerical analysis, the author has clarified the influenceiveness when reinforcing the pile foundation layer with soil cement pile, detail: + After reinforcement, the hardness and intensity of the pile surface on the top of the pile increasing the pile's lateral bearing capacity is improved. + The reinforced range lateral bearing capacity of pile is linearly correlated, however, to a certain reinforcement range, the influence of the reinforcement block is not further promoted. 13 + The value of the reinforced range to which point even though the scope of expansion is increased but the lateral bearing capacity of vertical pile does not increase, is called a reasonable depth and length of reinforcement. - This chapter, the author has built a method to determine the reasonable size of reinforced blocks using soil cement pile to increase the lateral bearing capacity of pile as well as determine the calculated lateral bearing capacity of single piles after reinforcement. - The results of the research by mathematical model should be verified by a physical model in the same condition of the ground and soil cement reinforcement layer to clarify the effectiveness of the reinforcing block and recommend supplementing to the theory of foundation calculation. CHAPTER 3: EXPERIMENTAL RESEARCH THE INFLUENCES OF REINFORCEMENT LAYER BY PHYSICAL MODEL 3.1 General introduction to experimental research The objective of the thesis is to apply the solution of reinforcing surface layer of pile foundations in the Mekong Delta, so the experiments are conducted in the representative area in this regon with the commonly used piles. Due to the limitations of the experimental equipment, the 1.5 - 2m thick reinforcement cannot be done by creating soil cement reinforcement layer, therefore, in this experiment, the layer of soil cement reinforcement has the same specifications as the soil cement pile but mixed by machine and poured by hand. 3.2 Objectives, content and requirements of the experiment 3.2.1. Objective of the experiment Experimenting, measuring, assessing the lateral bearing capacity of piles in cases of working on natural soft ground and the foundation after surface layer reinforcement. On that basis, compared with the theoretical method studied, from which there is a conclusion about the influenceness of the solution of reinforcing the foundation layer of the surface facing the horizontal load of the pile foundation, as a basis for calculating the foundation design piles for pillar dam in the area of the Mekong Delta; Through physical model experiments, we can determine the base k and build p ~ y curves for natural ground and surface layer after reinforcement. 3.2.2. Experimental research method From the method of calculating the lateral bearing capacity of a single pile, the measurement research on physical model with a ratio of 1: 1, load and displacement of the pile head in the case of working piles in natural soft ground and the ground after reinforcing the surface layer; Measure the surface displacement of the reinforcing block to assess the reasonable range of the reinforcement layer. 3.2.3. Scope of experimental research: Representing the natural soft ground in the Mekong Delta, the experiment was conducted in My Tho City, Tien Giang Province. 14 3.2.4. Object of experimental research: Vertical single pile with horizontal load, surface reinforced layer is soil- cement piles 3.2.5. Research content. The results of the mathematical model have identified the reasonable reinforcement scope for each type of pile. Building physical models and measure some specific cases to compare results with theoretical methods. From there, there was a conclusion about the reinforcement solution and recommendations in calculating a single pile under horizontal load. 3.3 Building experimental models and laboratory equipment 3.3.1. Building experimental models Building an experimental model with a scale of 1: 1 at the actual scene in the Mekong Delta - in My Tho City, Tien Giang Province, including: + Experimental piles: Reinforced concrete piles, square piles with cross sections of 10x10cm, 20x20cm and 35x35cm, round piles with diameter D = 10cm, 20cm and centrifugal piles D40cm. The length of the piles is determined after checking the soil foundation where the testing piles, with piles of 10cm and 20cm sides of 6m length, with piles of 35cm and 40cm sides of 15m length. + Pedestal: Including 3piles (30x30cmx12m), closed in triangles, piles are poured with reinforced hexagon reinforced concrete 50cm; + Frame support system, sheave, jack, cast steel + Experimental ground includes 2 cases: natural ground and reinforced concrete ground layer. The reinforced concrete layer in the experiments carried out in this research was used according to the grade of cement piles commonly used in the Mekong Delta and the size as Table 3.1. Table 3.1: Parameters of piles and reinforced experimental models Pile type (cm) Reinforced block size (m) Pile length (m) Square pile Deep Wide Long 10 6,00 1,52 1,00 2,48 20 6,00 1,92 2,00 3,06 35 15,00 3,00 3,50 3,77 Round pile 10 6,00 1,52 1,00 2,48 20 6,00 1,92 2,00 3,06 40 15,00 3,48 4,00 3,96 3.3.2. Experimental equipment and instruments Experimental equipment consists of three parts: loading equipment, jet equipment, measuring equipment, as shown in Figure 3.1: 1. Jetpack; 2. Pre-buried steel plates; 3. Jet rack 4. Pressure sensor 5. Jack; 6. Experimental pile; 7: Benchmarking; 8. Displacement sensor; 9. Steel plate for monitoring displacement of the ground. 15 Figure 3.1: Diagram of experimental equipment The main equipment for the experiment includes: a) Load device: use the jack to load, the force measuring sensor to measure the impact load b) Jet equipment The jet is greater than 1.5 ∼ 2 times the maximum estimated load-bearing capacity of the experiment, the stiffness in its direction of force shall not be less than the rigidity of the experiment pile itself. c) Arrange a benchmark to measure the displacement at the point of impact force of the pile, using a steel rod to be inserted into the soil 1.5m deep as a reference point. The entire system of standard equipment is arranged independently to reduce the impact of reinforced blocks and ground. d) Measuring devices: - Two-dimensional mechanical jacking: To increase and discharge the impact load into the pile head - Loadcell 20 tons: displays the impact force value at the top of the pile - Data taker: Device to record measurement data is transmitted to a computer, can connect and record data simultaneously on multiple measurement modules. - Induction displacement measurement rods across the pile head: - Bar displacement sensor for measuring the area of influence of the reinforcing layer: - Wire displacement sensor for measuring the area of influence of the reinforcement layer - Slotted surcharge weight: To measure the horizontal displacement of the pile head according to each different load level. - Equipment to record measurement signals: use to record data from measuring devices for display on computers. - Laptop: For saving and processing data from Data taker - Digital camera: To take photos of experiments. e) Other equipment: - Water pump: Serving water pump in and out of experiment scope - Piling machine: is a form of diesel hammer with hammer head weight> 2.0T placed on the crane array> 20T to serve the experimental pile driving. - Equipment for excavating soil and reinforced concrete blocks; 3.4 Cases and sequences of experiments 3.4.1. Experimental cases 16 Lực$ngang$đầu$cọc$(kN)$ The experiment cases to determine horizontal load and displacement include: a) Experiments on natural ground: Horizontal load and continuous record until the displacement pile is 10mm, take the value to calculate the ground coefficient of the natural soil, then continue the load to the displacement value of 25mm and until the pile or foundation is broken destructive. During horizontal load, data on horizontal force and displacement are measured and recorded in computer. b) Experiment with reinforced background: The top layer of pile foundation is reinforced with cement-soil layer. For each type of pile will have different thickness and width of cement reinforcement layer. The experiment is similar to the experiment on natural ground, however, the reinforced layer behind the pile is measured to determine the displacement of the reinforced area on the ground. 3.4.2. Installation of equipment and experiment sequence a) Installation of equipment: To accomplish the purpose of experimenting, measuring the impact force, displacement of the pile head, the displacement of the reinforced layer behind the pile, at locations where the comparisons of the measuring heads are to be compared. b) Experimental sequence + Construction of jet posts. + Preparing experimental piles with sufficient strength, driving piles to be submerged in the ground at the experimental positions, except for the tip of 0.5m to set the horizontal force point. + Digging deep soil and constructing reinforcing blocks according to reasonable size. Sampling and curing sample (9 indicators) + Install a displacement measuring device in the reinforced foundation at the points behind the pile + Experimenting XMĐ samples at 28 days and 91 days. After 28 days of conducting experiments pushing the pile for each individual module. 3.5. Experimental results 3.5.1 Experimental results for square piles Experimental results 170" 160" for all types of square 150" 140" piles are shown by 130" diagrams of relationships 120" 110" between load and pile 100" 90" head displacement p ~ y TH"nền"tự"nhiên" 80" 70" in two cases: natural and 60" TH"nền"gia"cố" 50" reinforced are shown in 40" each diagram, typically 30" 20" as follows: 10" 0" 0" 5" 10" 15" 20" 25" 30" Chuyển$vị$ngang$đầu$cọc$(mm)$ Figure 3.2: P ~ y relationship diagram for square pile 35x35cm 35" 40" 17 Lực$ngang$đầu$cọc$(kN)$ 3.5.2 Experimental results for round piles 50" Experimental results 45" for the types of round 40" piles are shown by the 35" diagram of the 30" relationship between the 25" TH"nền"tự"nhiên" load and pile head 20" TH"nền"gia"cố" displacement p ~ y in 15" 10" two cases: natural and 5" reinforced are shown in 0" each diagram, typically 0" 5" 10" 15" 20" 25" 30" 35" 40" Chuyển$vị$ngang$đầu$cọc$(mm)$ as follows: Figure 3.3: Relationship diagram p ~ y for round pile D10cm From the results of the physical model research, the relationship between Biểu$đồ$quan$hệ$SCTN$với$kích$thước$cọc$vuông$thí$nghiệm$ lateral bearing capacity and pile size is obtained: 160" Lực$ngang$đầu$cọc$(kN)$ 140" 120" 100" 80" TH"tự"nhiên" 60" TH"gia"cố" 40" 20" 0" 0" 5" 10" 15" 20" 25" 30" 35" 40" Kích$thước$cọc$(cm)$ Biểu$đồ$quan$hệ$SCTN$với$kích$thước$cọc$tròn$thí$nghiệm$ Figure 3.4: Diagram of lateral bearing capacity and square pile size 180" Figure 3.5: Diagram of lateral bearing capacity and round pile size Lực$ngang$đầu$cọc$(kN)$ 160" 140" 120" 100" 80" TH"gia"cố" 60" TH"tự"nhiên" 40" 20" 0" 0" 5" 10" 15" 20" 25" Kích$thước$cọc$(cm)$ 30" 35" 40" 45" 3.5.3 Comment on the experimental results From the diagrams of relationship between load and displacement shows that within the permissible range of support pillar (<25mm) the lateral bearing capacity increases proportional to the pile diameter. In the case of reinforcing 18 ground, outside the permissible displacement range (up to 25mm) the load value tends to be inversely proportional to the displacement, which indicates that the reinforced mass forms a critical displacement. Experimental results also show that the critical displacement value of piles, the pile size does not have a large difference, which means that the soil cement layer has reached the destructive boundary, so it is not influence. about transposition. Therefore, it can be concluded that the increase in horizontal bearing capacity of the pile depends on the type of pile, the shape of the pile, the ground and reinforced materials. The critical value of displacement depends on the material used to reinforce the surface layer. 3.6 Compare field experiment results with calculation model 3.6.1 Comparison of lateral bearing capacity of piles Through field test results and calculations with the same pile foundation size and ground parameters, the author found that, for natural cases, the results between experiments and calculations are relatively similar. In the case of reinforcement found that the actual load capacity is lower than the calculation of about 5%. Table 3.2 Comparing lateral bearing capacity of square pile between calculation and experiment Size Comparing between calculation experiment pile experiment and calculation (%) 10 45,6 42,62 93,5 20 93,2 90,37 97,0 35 164,3 156,21 95,1 Average 95,2 Table 3.3 Comparing lateral bearing capacity of round pile between calculation and experiment Comparing between experiment Size pile calculation experiment and calculation (%) 10 42,9 40,66 94,8 20 90,2 85,59 94,9 40 176,5 167,99 95,2 Average 94,9 3.6.2 Comparison of the sphere influence of the reinforcement layer on the ground On the experimental field diagram, the author has installed the displacement measurement points (2,3,4,5,6) of the reinforced layer surface behind the pile, respectively, 40cm, 80cm, 120cm, 160cm and 200cm. Points 4, 5 and 6 cannot be monitored and measured for any displacement value. Thereby the author found that the influence of the reinforcement layer is very small.