Applied Mechanics and Materials Vols. 256-259

Abstract: Because of unique properties of locked sand (very high friction angle and very low cohesion), a new pillar design method based on present basic pillar design theories must be developed. Wilson theory puts its focus on confining pressure, which is related to friction angle and cohesion. Triaxial tests results show that locked sand at Pattison mine has an average friction angle of 57°, which means the strength of the material increases rapidly with the confining pressure, and average cohesion of 2.6 MPa. Results show that choosing Wilson theory as basic pillar design theory not only considers the high friction angle of locked sand, but also minimizes the effects of Wilson’s hypothesis of neglecting the unconfined strength.

Abstract: Apparent particle size grading is the important characteristic of super-high bench dumping site, and the critical factors with the impact of its stability and disaster prevention are the fragmentation distribution and shear strength parameters of granular. With the copper mine dumping site which had the feature of apparent particle size grading, the thesis carried out the study of on-site particle size investigation and indoor laboratory. The particle-size distribution law with the changing of dumping-site height was analyzed and quantitative relationship between the fragmentation distribution and shear strength parameters of granular was discussed. The research results indicated that coarse-grain contents and maximum grain size were increased significantly according to the decreasing of dumping-site height, which showed that the dumping-site had the feature of apparent particle size grading. The coarse particle content in the grain size composition and internal friction angle φ of shear strength parameters increased with the obvious increment of the distribution value B. The relationship between distribution value B and the internal friction angle φ could be expressed by exponential function curve.

Abstract: GPR is used to detect rock surrounding the hand-dug pile foundations of a bridge for the highway surrounding Fuzhou, capital of Fujian Province, so as to evaluate the rock the stabilities of the rocks on the outer side of the file foundations and at the base of the file foundations and thickness of overburden over the base rocks. In this paper, some parameters are selected for detection, such as antenna of center frequency 100 MHz, data acquisition time window of 500ns , offset distance of 1 m，which can meet the effective detection range (depth) of 20 m or more . Annular cross-section method is used at the bottom of Piles , and vertical cross-section method is used on the side of piles. The results show that GPR records can provide a number of clear and accurate information such as the rock cliff boundaries of pile lateral wall , the internal structure at the bottom of pile and pile lateral wall.

Abstract: In order to test the validity of regional outburst prevention measures that combined the bedding boreholes and layer-through boreholes in 3104 coalface, according to the relevant provisions, used drilling index, pre-pumping index and gas index to evaluate the effect of removing outburst in 3104 coalface. The evaluation results shown that through the pre-pumping gas, the rate of pre-pumping gas was 53.7%, more than 30%; residual gas content was 2.85～5.07m3/t, less than 8m3/t; residual gas pressure was 0.01～0.02MPa, less than 0.74 MPa. Therefore, the coalface has eliminated the danger of outburst and created favorable conditions for safety mining.

Abstract: Two geotechnical centrifuge model tests of a soil-structure system with different burial depths are performed to investigate the interaction between soil and structure. The tests are performed at 50 gravitational centrifuge accelerations and the input motion is Kobe wave. This paper focuses on the accelerations and displacements in the soil-structures system. The peak accelerations and displacements along the axis of the structure and along the vertical line 17cm away from the axis are presented. The acceleration and displacement response due to the interaction between soil and structure are studied.

Abstract: Pile driven-operations is an important means to control floods, anti-flood spiral pile is a kind of flood control equipment which is lightweight, high work efficiency and low labor intensity. It is important to research the soil variables to further clarify the mechanism of pile-soil interaction in driven process. Soil constitutive model was built as the SPH particles; pile-driven process was simulated by dynamics software. By tracing the SPH (Smoothed Particle Hydrodynamics) particles, contrasting and analyzing the movement of soil particles at different times and depths because of friction, extrusion, and shear effect of pile were achieved. The mechanism of pile - soil interaction in the driven process was clarified by analyzing and comparing the simulation results, which make up the lack of theoretical analysis and experimental methods. It will provide useful suggestions on the design of spiral pile and reducing the secondary damage to dam.

Abstract: The earth-rock cofferdam on deep overburden is the main study object. The cofferdam filling and dam excavation process were numerical simulated using FEM code ANSYS .Main research focused on stress and deformation characteristic of cofferdam and concrete cutoff wall during completion and excavation process.Analysis showed that displacements of cofferdam and cutoff wall distribute well in x, y, z directions with acceptable magnitude, stress characteristic values are less than design standard. The results indicate that cofferdam and cutoff wall are safe and stable both in construction and operation.

Abstract: This paper is used to study on the analysis and prediction of surface subsidence caused by pipe roof reinforcement method construction. Take one of the Shenyang's sewage disposal projects to be investigated, it monitored on field surface subsidence in the construction of under drain. During the measurement and monitoring, except for conventional measurement of surface subsidence according to code and peripheral convergence and so on, in order to analysis changes of stress and strain of the pipe roof in the whole construction of under drain. It also respectively arranges JMZX-212 intelligent string type of strain gauge in both internal and external sides of vault and hence. It used the Element Birth/Death of finite element software basing on the field data, using elastic-plastic and nonlinear finite element method. Material constitutive relationship used moor-coulomb model, simulating the process of tunnel of excavation and support, researching and stimulating the surface subsidence. The surface settlement of value was calculated applying finite theory via the numerical simulation, it based on prototype of engineering, which was approximately in accord with the measured value in field. The correctness of soil constitutive model chosen and boundary conditions used is verified, meanwhile, the numerical simulation shows the validity of the method .the results provide reference to similar construction method in the future.

Abstract: In order to analyze rubber powder influencing on cement-soil, axial compression stress-strain curves and a series of damage relationship curves are obtained by unconfined compression test and circulating load-unload test. The damage process of rubberized cement-soil could be divided into four phases including internal tiny crack closing, cracking, crack stable extension and crack unstable extension. Rubber powder increased stress and strain threshold values of cement-soil. 10% was the best rubber powder content. Rubber powder can impede cement-soil inner tiny holes and crakes to occur and develop, so that damage resistance and deformation capability are improved.

Abstract: The energy dissipation law of rock material are analyzed comprehensively by studying the energy exchange between test machine and rock sample in two typical stress-strain curve of unloading tests. The relationships between energy, deformation and confining pressure in unloading confining pressure failure process are expected to be found based on energy dissipation analysis. It shows that the energy dissipation is greatly related to the failure characteristic of rock material and confining pressure. Both two unloading tests show that energy dissipation has a nonlinear relationship with time and linear relationship with lateral deformation. The much the confining pressure is in unloading condition, the more the energy dissipation is under the same lateral deformation, and the obviously the rock sample suffers brittle failure.