Information about PhD thesis of Postgraduate. Nguyen Manh Tuong

ABSTRACT OF THESIS

1. The urgency of the research topic.

Ho Chi Minh City (HCMC) concentrates many civil and industrial constructions. However, this area is located on soft soil with poor load capacity, especially with dynamic loads. In industrial zones, locating machine foundations to withstand dynamic loads of different frequencies, amplitudes and intensity. The above loads from the structure transmitted to the pile, or from the surrounding ground affect the pile causing the pile itself, the extreme deformation zone around the pile has different effects.

Research to calculate the dynamic load capacity of the pile foundation supporting the project as well as find out the decrease in load capacity after the project is under dynamic load is now necessary. The calculation of the effect of dynamic load on the pile load has many methods but dispersion results. The static test method is reliable but costly and time consuming and has no results on the effect of dynamic loads on the pile load. To add to the effect of dynamic load on the pile load capacity is multiplied by the coefficient on the static load capacity of the pile. The construction of experimental models to determine the foundation pile calculation parameters of the foundation soil has actually been proven to simulate well the pile operations in the ground. Through the analysis and comparison of the pile static compression test results and simulation with different dynamic parameters, find out the parameters of the ground to simulate the stress-deformation state of the pile and the behavior of the ground around the pile there is plastic deformation.

2. The purpose of the thesis

Study on simulation of static compression test to find out suitable soil model and select reasonable parameters. Consider applying suitable soil model to study stress path with different properties and conditions of the soil. Selecting the modeling parameters of the ground to simulate the stress - deformation state of the pile and the soil behavior in the area with plastic deformation around the pile. Research engineering geology, hydrogeology and analyzing and evaluating the ability to affect the load capacity under dynamic load in the area. Research and build a small-scale physical model, conduct dynamic load tests on piles to determine the effect of dynamic loads on the load capacity and settlement of the pile. Analyze the dynamic behavior of the pile when subjected to dynamic loads at different frequencies. Study the effects of the ratio L/D, the effect of pile - foundation, consider the immediate load capacity under dynamic loads. Set the correlations Force - Deflection, Force - Bow resistance, Force - Ratio of Side resistance/ tip resistance in the pile under dynamic load on the sandy soil of HCMC.

3. Object and scope of the research

- Object of the thesis is the right center compression pile influenced by dynamic load in the sandy environment.

- Scope of the study: The above multi-layered area is the clay and clay layers with poor load capacity, the sand layers below are selected to place the piles in this range.

Therefore, the dissertation's research focuses on the effect of dynamic load on the pile in the medium compact sandy soil layer in the area of HCMC. This is a popular soil layer and is rated to be quite good under static load. From there, it is necessary to study the pile when under dynamic load will be reduced and the effects of friction for the pile section in this soil layer on the pile load capacity. Study of single pile bearing vertical axial load. The experimental model uses absolute hard pile to eliminate all effects of load distribution and measurement results. The effects of the pile-to-pile connection were ignored and not examined in the study. The load acting on the foundation is the cyclic load. The research frequency to influence is the frequency of stimulation that causes mechanical responses, not to the response frequency of the pile - pile station system.

4. Approach and methodology

Statistical methods: Collect, analyze, and synthesize research results. Statistical processing, analyzing experimental results, establishing correlations with modern data processing software. Experimental methods: Experimental research to conduct experiments on physical models in the room to serve as a basis for comparative analysis and comparison of results. Numerical simulation method: Research on simulating static compression test using Plaxis software for comparative analysis. Using data processing software to find results between numerical simulations and field experiments find out correlations in the ground model.

5. The new contributions of the thesis

1) Constructing a static pile test model to study the effects of physical parameters on the pile load capacity under static load and decrease when subjected to dynamic loads with the sand foundation. From there, studying the effects of the dynamic parameters on stress- strain, pile load capacity and find the correlations.

2) Propose the settlement-frequency correlation equations for pile with smooth surface, pile with rough surface. Correlation equations between Force - Unit friction - Tip resistance, Force - Ratio Fs0 / tip resistance, Force - Ratio of Fs1 / tip resistance for different L/D piles.

3) Perform simulations of static compression experiments to find out MCC (Modified CamClay) model with the closest results compared with static compression test results. The study shows that the parameters most strongly affect the simulation results of static compression test. Using the MCC model to simulate the destructive compression to find the extreme load capacity of the pile.

4) Proposing correlation coefficients in static compression test λ/κ in cycle 1, cycle 2 and general correlation λ/κ in both cycles. The correlation equations M, Lambda, Kappa in the MCC model of Plaxis software in the simulation of the static compression test to determine the pile load capacity.

6. Scientific and practical significance

The thesis initially contributes to clarify the effects of dynamic and static loads through simulation of static compression experiments as well as small-scale physical model experiments. Thereby proposing correlation equations between frequency and settlement, force and strain, force and resistance relationship.

The results of the study provide data to serve as a basis for analyzing the impact of
dynamic loads in the design of pile load capacity considering the effect of dynamic loads that may appear in HCMC construction conditions

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See Detail: SUMMARY OF THE DOCTORAL THESIS - NGUYEN-MANH-TUONG