Advanced Materials Research Vols. 243-249

Abstract: DaGangShan power station in China is being excavation at 1500 meters deep below earth surface, where the surrounding rock is affected by high initial geo-stress. Deep excavation of rock tunnels causes release of high initial geo-stress and produces unloading action. As thus, a series of representative unloading tests on hard granite from DaGangShan power station are carried out to simulate dynamically excavation process, and in unloading tests, the stress path of decreasing confining pressure along with increasing axial pressure is accepted. The results of tests show as follows: (1) Under unloading condition, lateral deformation occurs in the unloading direction and volumetric strain changes from compression deformation to dilation deformation. (2) Under unloading condition, crack deformation appears, which results in Poisson’s ration rise and deformation modulus decrease. (3) Under unloading condition, hard granites behave brittle failure and Mogi-coulomb criterion can well describe the failure characteristics.

Abstract: Cyclic loads are commonly encountered in geotechnical engineering; however most constitutive models do not account for the effect that such loads can have on the mechanical behaviour of soils and rocks. This work is concerned with the behaviour of jointed rock and, as the overall mechanical behaviour of jointed rock is usually dominated by the mechanical behaviour of the joints, it is focused on the behaviour of rock joints under cyclic loads. In particular, an extension of the existed constitutive model for cyclically loaded rock joints is presented. Variations of rock joint stiffness in both the normal and the shear directions of loading due to surface degradation are taken into account. The degradation of asperities of first and second order is considered, while a new relation is proposed for the joint stiffness in the normal direction during unloading. Numerical simulation results show good agreement of model predictions with existing experimental results.

Abstract: With the establishment of large municipal solid waste landfills, the interaction of geological environment in landfill (seepage field, stress field and temperature field, etc.) has not to be ignored. The multi-field coupling problem of the municipal solid waste landfill is getting attention. But at present the study mainly concentrated on the solid-liquid-gas-heat coupling problem, the study of the waste gas of the municipal solid waste landfill is less. Gas diffusions, gas emissions, and gas collection are related to the secondary pollution problems of the municipal solid waste landfill. This paper established mathematical model which based on the solid-liquid-gas-heat interaction and researched the gas migration rule of the municipal solid waste landfills. The mainly work are as follows: (1) the definite conditions of dynamic model, (2) the solution of dynamic model, (3) results and analysis. The main conclusions are as follows: (1) Pore pressure along the gas flow direction is nonlinear distribution and shows decline trend. As time increases, the pore pressure of each horizontal section decreases. (2)The volumetric strain of the municipal solid waste landfill is nonlinear distribution along the gas flow direction and shows an increasing tendency. As time increases, volumetric strain of each horizontal section increases.(3)As the change of time, the pore pressure first increases, then decreases.(4) In the initial stage, as the change of time, gas output increases rapidly. When it achieves the maximum size, the production quantity of gas reduces and gradually tends to be a quantitative value.

Abstract: The layered rock mass consists of kinds of stratifications whose mechanical properties are not wholly identical with each other. In order to figure out its strength failure criterion, the variable bond strength failure criterion is proposed depending on Mohr-Coulomb yield criterion and the change law of the strength parameters varying with the dip angle of stratification plane (that is the angle between the maximum principal stress and the stratification plane). What’s more, the criterion is verified by physical model test and numerical simulation adopting assembly language VC++6.0. Compared with the results of physical model tests and numerical simulation, it is shown that the stress distributions and failure regions are elliptic in shape and that the maximum failure regions are vertical to the stratification planes. That the results obtained in the physical model test are compatible with those numerically obtained verifies the correctness of variable bond strength failure criterion.

Abstract: Reinforced concrete shaft lining were prefabricated on the ground at one vertical shaft engineering in Tangshan city,and the strength grade of concrete is up to C60. Take this vertical shaft engineering as the example,some problems may be encountered in the process of production of reinforced concrete shaft lining has been discussed.Furthmore, it also puts forward methods to solve the problems available for prefabrication of shaft lining in the future.

Abstract: The porosity of solid skeleton is changed under muddy water infiltration, and thus the permeability is also changed. A concentration of 30% muddy water compared with clear water, is experimented to simulate the movement of small particles. The relationship between solid skeleton permeability, porosity and time is obtained from experiments. The relationships among fraction void and permeability coefficient in such cases are presented. The relationship expressions are studied. Some novel laws are obtained as follows: because of the hindrance effect by the small particles, permeability coefficient decreases gradually over time, but clear water has no influence on the permeability coefficient; at the beginning, the porosity of solid skeleton decrease rapidly over time. Then it is stabilized latterly, they two are in monotone decreasing parabolic curve relationship; The relationship curve of cumulative infiltration capacity and time is a monotonically increasing curve which slope becomes smaller; the infiltration concentration fall first and rises later. The results provide a theoretical basis for muddy water infiltration.

Abstract: Analysis of rock acoustic emission characteristics in complete stress-strain process under uniaxial compression shows that the evolution process of rock deformation and damage can be divided into five stages—compaction, linear elastic deformation, accelerate inelastic deformation, damage and development, plastic flow. Acoustic emission characteristics of rock can well reflect its compressive deformation and damage evolution process. Acoustic emission time series of typical plastic coal is comparatively dispersed and presents group shock type. The acoustic emission frequency events and their energy of coal are bigger around the damage point, but the maximum amplitude and the secondary maximum amplitude have not much difference. The acoustic emission events and their energy of very uniform and dense fragile limestone are mainly concentrated in a very short period of time before its damage and the acoustic emission time series manifests as isolated shock type. For sandstone whose homogeneous degree lies between typical plastic coal and very uniform and dense fragile limestone, its acoustic emission time series manifest as main shock type.

Abstract: The finite element model with artificial boundary was used to simulate dynamic response of an underground circular structure (tunnel, cavern) and displacement of the ground surface under incidence of Rayleigh wave, and to quantitatively analyze the effects of incident wavelength, diameter of structure, and liner stiffness on ground surface displacement amplification. The numerical results show that, the surface displacement amplitude with a tunnel can be 1.3 times of that for the case of without the tunnel. It is suggested that the effects of a tunnel on ground motion should be considered when the tunnel is planned and designed.

Abstract: The dynamic shear modulus (DSM) is the most basic soil parameter in earthquake or other dynamic loading conditions and can be obtained through testing in the field and in the laboratory. By using the resonant column tests, the effect of the consolidation ratios on the nonlinear behavior of DSM versus the shear strain, G/G_max-γ, for two types of sands and fourteen types of undisturbed silty soil is investigated and its effect on the surface response spectrum is presented in the paper. The results here indicate that consolidation ratios have certain effect on the shape of the nonlinear behavior of DSM versus the shear strain and G/G_max increases with increasing of the consolidation ratios. By comparing to the isotropic consolidation, the consideration for the actual anisotropic consolidation makes the acceleration peak amplitude increase and makes the characteristic period decrease. For the incidence of the strong seismic excitation, the effect of the anisotropic consolidation on earthquake ground motion should be considered.

Abstract: Aimed at stability of rock slope, the attitude of structural plane is statistically analyzed with a combined method of rose diagram and pole equidensite diagram, and the preferred structural planes which are dominant in stability of slope were further determined by a lot of factors such as the terrain and topographical features of slope, the lithologic characters and the development of structural plane. Besides, the stereographic projection method is applied to qualitative analysis for the stability of rock slope. The results show that preferred structural plane can effectively reveal the nature of rock slope stability and provide a dimensional discriminant approach for stability of rock mass slope.