Applied Mechanics and Materials Vols. 204-208

Abstract: The consolidation of frozen soil is a coupled action of temperature and deformation. Using moving boundary method and taking the void ratio as a variable, the large strain thaw consolidation mathematical model is built according to Gibson’s large strain consolidation theory and thermal conductivity equation with consideration of phase change. In order to verify the model, a simple example is simulated by FEM software. The result shows that the consolidation range and consolidation rate are decided by the temperature boundary; the change of void and deformation are influenced by pore pressure dissipation and the thaw process in permafrost are delayed by consolidation process.

Abstract: Base on general three dimension nonlinear numerical simulation software, mechanism of composite soil-nail retaining structures in foundation-pit engineering are analyzed in this paper. Research contents include construction process simulation of excavation by steps, soil nailing installation and panel manufacture etc. Tension distribution range of soil layer, bottom heaving in the pit and axial force distribution along nail etc. are analyzed through the comparison of mechanical characteristics between computational results and field test data in the case of micro pile composite soil-nail support engineering. The action mechanism and working performance of composite soil-nail retaining support are also systematically studied and theoretical basis can be provided in optimal design, popularization and application.

Abstract: Post-grouting technology is an effective method of improving mud cake in the pile tip and debris in the pile side. What’s more, it is also considered as a great method to improve the bearing capacity of the cast-in-situ bored pile. The post-grouting technology is used in the foundation of a tall office building in Shan Dong province. For this project, comparing results of the static load test and the theoretical calculation, some conclusions can be made that the bearing capacity of post-grouting pile is 126.5% more than that of unpost-grouting one, the ratio between the tip resistance and the side resistance of the post-grouting pile are 39.8% and 60.2% respectively, and the ratio between the tip resistance and the side resistance of the unpost-grouting pile are 28.9% and 71.1% respectively. It is estimated that the cost of cast-in-situ bored piles using post-grouting technology is 45%~50% cheaper than the unpost-grouting piles.

Abstract: Acoustic emission technique is an important technique for monitoring crack propagation and failure process of rock, coal and concrete material. A uniaxial compression test with acoustic emission monitoring on coal and rock samples’ deformation and failure process were carried out. Failure precursor information of rock, coal and concrete material were studied through contrast analysis the experiment result include acoustic emission signals, strain, load correlation of sample inner crack propagation to failure process. The test provided necessary data to further understand on rock burst failure disaster. The test result provides a theoretical basis for further application of acoustic emission for prediction coal rock dynamic disaster, assessment rock and concrete structure stability and study rock concrete material failure process mechanism.

Abstract: This paper introduces the principle of the elastic-plastic model based on Mohr -Coulomb failure criteria, Combination of a tailings dam introduces the modeling analysis process, according to the actual project analyses the stress and deformation calculation results of rationality.

Abstract: From an engineering reality, in order to solve complex stratigraphic drilling problems and improve construction efficiency, the method of combination of large diameter DTH hammer and the pile driver with a special long spiral drill multifunctional is proposed. This method has the characteristics of simple equipment, fast, effective, low cost etc. It can quickly drill through layers of gravel, stone, weathered bedrock, reach to depth up to above 25m. It has been widely used in embedded engineering methods of precast piles, the long spiral rock-socketed piles, piles into the rock currently. The study of this construction method has not only wide range of applications, but also has a wide range of practical and theoretical significance.

Abstract: To study the evolution of meso-structure of unsaturated intact loess during wetting, a series of CT-triaxial-collapse tests were conducted using CT-multi-function triaxial apparatus. The distinct CT images and detailed CT data were attained nondestructively during wetting. A parameter and an evolution variable which characterized evolution of meso-structure were defined based CT data. An equation describing the evolution of structure during wetting was proposed. The equation reflected the influences of net cell stress, deviatoric stress and suction on the evolution of meso-structure. In the equation, volumetric strain, deviatoric strain and incremental degree of saturation are included.

Abstract: This paper explores the interaction system of nonlinear foundation soil and nonlinear gravity pier. Superstructure resilience model employed ideal elasto-plastic model, foundation adopted tensionfree-consolidated elasto-plastic Winkler foundation model with experimental support. Through an account case of a gravity pier, this paper concludes that co-action of foundation soil and bridge pier needs to be considered in design of seismic prevention for bridge.

Abstract: The parabolic-apex numerical back-analysis method (PNBM) was proposed to obtain such physical-mechanics parameters as Young's modulus and lateral pressure coefficient of surrounding rock by 3D FEM numerical analysis based on in-situ monitoring data. Taking Xiang-an Subsea Tunnel (located in Xiamen, Fujian Province, China) for example, adopting the PNBM using ABAQUS software, three dimensional elastic-plastic FEM-PNBM of tunnel surrounding rock was validated using in-situ monitoring data. The results show as follows: Using the PNBM, not only may high calculation precision be obtained, better meeting the demand of actual projects, but also more reasonable and reliable physical mechanics indices of surrounding rock such as Young's modulus and lateral confinement pressure coefficient, may be obtained. The applicability and the simplicity of this proposed method also support its usefulness.

Abstract: Taking into consideration both stress dispersion effect and shear strength of crust layer, based on Flamant formula of polar coordinates representation and Mohr-Coulomb strength criterion, this paper deduces a new formula of critical edge pressure of natural soft foundation considering the realistic coefficient of lateral earth pressure. A calculation method of critical embankment height on natural soft foundation is proposed. The limit value of the result calculated by the new method is also put forward, which can ensure the reliability of the method applied. Additionally, critical embankment height at different thickness of crust layer h2, width of embankment loading B, soft layer soil coefficient of lateral earth pressure K0, crust layer soil coefficient of lateral earth pressure K1 is studied. Researches discover that the change of h2, B and K0 has significant influences on critical embankment height; a calculation result of critical embankment height is significantly partially high when the coefficient of lateral earth pressure is equal to 1 under this assumption.