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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: Hy

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

VIETNAM ACADEMY FOR WATER RESOURCES

Supervisor:

- Prof Dr Nguyen Vu Viet

- Prof Dr Tran Dinh Hoa

In …………, 2020 at …

The dissertation can be found at:

- National library in Viet Nam;

- Library of Viet Nam Academy for Water Resources

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

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

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

- 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

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

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 KC12-

10 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 barrier 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;

river-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

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

1.3.2.2 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

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

(28 days) (90 days)

1 Clay mixed, flowing plastic 634-906 1032-1123

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

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:

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

5 , 1 5 ,

- 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

diagram between lateral

bearing capacity with pile

size, natural ground

b) Calculation results for reinforcement cases with different depth for each type of pile as shown in Figure 2.2:

Figure 2.2: Relationship

diagram between lateral

bearing capacity and

reinforcement depth

2.3.2.7 Proposing the method of determining the depth of reinforcement

From the results of

the research of the depth

of the pile corresponding

to the pile type, the

author has determined

reinforcement depth

value of pile types,

thereby building a

relationship between the

reinforcement depth and

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:

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

y"="12,473x 2 "+"0,2719x"+"1,3726" R²"="0,99499"

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

+ 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

No

pile size (cm) Reinforced

depth (m)

Reinforced width (m)

Length

of piles (m)

Square

pile

Round pile

centrifugal piles

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