Experimental Study on Creep Behavior and Crack Evolution of Stratified Structural Sandstone under Segmental Constant Load

The hazards induced by stratified rock mass creep are still one of the major problems that threaten the safety of underground engineering. This paper takes safe construction of underground roadway in Urumqi mining area as the research background. In this study, we mainly adopted rock mechanics experiments to accomplish the research on creep behavior and crack evolution of stratified structural sandstone. Creep deformation characteristics of stratified structural sandstone under different load were revealed; also, we analyzed the reason why a part of rock samples failed but others were not under the same load. Creep behavior and crack evolution of rock samples without stratified structure have significant randomness. The crack evolution and failure characteristics of stratified structural rock samples were mainly manifested as failure along and cutting through structural plane and their combined forms. Creep strain, creep duration, and creep rate of rock samples with stratified structure had a nonlinear relationship with applied load, such as exponential function or logarithmic function. Understanding the evolutionary relationship between the above parameters and load provides a basis for obtaining the creep behavior of stratified rock mass under different load conditions.

FEATURES OF PROPAGATION OF HYDRAULIC FRACTURES IN STRATIFIED ROCK MASS

In hydraulic fracturing commonly used in mining, it is important to determine the shapes and sizes of created fractures. The governing factor in this case is the structure of rock mass which is often stratified. This study analyzes the influence of strengths of the layers and their stress states on the shapes of the growing fractures. Numerical modeling shows that in hydraulic fracturing with low-viscous fluids, fractures grow mostly in a layer having lower tension or compression strengths. The calculations carried out for the analyzed cases provide the values of tension strength and external compression for hydraulic fractures to grow only in one layer. It is shown that the increase in the breakdown fluid viscosity weakens this effect.

A Thermal Effect Model for the Impact of Vertical Groundwater Migration on Temperature Distribution of Layered Rock Mass and Its Application

On the basis of the one-dimensional heat conduction–convection equation, a thermal effect model for vertical groundwater migration in the stratified rock mass was established, the equations for temperature distribution in layered strata were deduced, and the impacts of the vertical seepage velocity of groundwater and the thermal conductivity of surrounding rocks on the temperature field distribution in layered strata were analyzed. The proposed model was employed to identify the thermal convection and conduction regions at two temperature-measuring boreholes in coal mines, and the vertical migration velocity of groundwater was obtained through reverse calculation. The results show that the vertical temperature distribution of the layered rock mass is subject to the migration of the geothermal water; the temperature curve of the layered formation is convex when the geothermal water travels upward, but concave when the water moves downward. The temperature distribution in the stratified rock mass is also subject to the thermal conductivity of the rock mass; greater thermal conductivity of the rock mass leads to a larger temperature difference among regions of the rock mass, while weaker thermal conductivity results in a smaller temperature difference. A greater velocity of the vertical migration of geothermal water within the surrounding rock leads to a larger curvature of the temperature curve. The model was applied to a study case, which showed that the model could appropriately describe the variation pattern of the ground temperature in the stratified rock mass, and a comparison between the modeling result and the measured ground temperature distribution revealed a high goodness of fit of the model with the actual situation.

Numerical Modeling on Anisotropy of Seepage and Stress Fields of Stratified Rock Slope

Stratified rock mass is a common rock mass structure and distributed widely on the earth’s crust. High-density distribution of stratified structural planes in the stratified rock mass has a great influence on the mechanics properties of the rock mass, such as anisotropy of stress and seepage. Therefore, anisotropy is the inherent characteristic that must be considered in the stratified rock mass as well as the stratified rock slope stability. According to the anisotropic characteristics of stratified rock mass, an anisotropic seepage-stress coupled model for the mechanical behavior of stratified rock slope is proposed based on the anisotropy elasticity theory. The model is validated by simulating seepage and stress fields of an idealized slope using the finite element method. The deformation and stress-dependent permeability of the slope are predicted and compared well with the previous study, thus confirming its capability in characterizing the response of rock slope that is dominantly affected by rock anisotropy. Finally, the model is used to simulate the anisotropic properties of a stratified rock slope of Fushun west open-pit mine, China. The simulation is in good agreement with the actual measurement, which means the proposed model is capable of simulating anisotropic properties of the stratified rock slope.

Analysis of Deformation and Failure Characteristics of Stratified Rock Mass around Underground Opening Based on a Microstructure Tensor Approach

In order to have a good understanding of the geotechnical behavior around underground opening excavated in stratified rock mass, numerical simulation of a gate-shaped cavern excavation was conducted by applying a transversely isotropic model base on microstructure tensor method. The simulations were performed under the assumption that both the beddings and the in-situ middle stress vector run parallel with the cavern. Effect of the dip angle of beddings and that of in-situ major stress vector on deformation and failure of rock mass around the cavern was investigated. The mechanism underneath the image of deformation and failure was also discussed. It is found that the dip angle of beddings has less influence than the in-situ stress on deformation while the dip angle of bedding and the direction of in-situ major stress vector are equally important to the failure of surrounding rock mass.

Computer Aided Design for Safety Analysis of Excavation in Stratified Rock Tunnel

Stratified rock mass is widely existing in tunnel engineering. The most relevant feature of stratified rocks is the occurrence of very persistent bedding, which makes the rock-mass highly non-isotropic. A number of techniques for designing underground excavations in stratified media have been described in the literature, like theoretical method and laboratory test, which can only be applied in analyzing the problem with simple geometry and costs much expense. Recently, with rapid development of computer technique, numerical simulation methods have been widely applied in engineerin. Among all the numerical simulation methods, fast lagrangian explicit finite difference code of continua (FLAC3D) is widely used to solve practical problems, especially in field of elasto-plastic characteristic, large deformation analysis and construction procedure. So in the present paper, numerical simulation for the failure mode of stratified rock mass after tunnel excavation is done by FLAC3D, which can give further guidance to understand the anisotropic characteristic of stratified rock mass.

Three Dimensional Numerical Modeling for the Stratified Rock Slope and the Parametric Analysis

Stratified rock mass has been widely existing in geotechnical engineering. With obvious transversely isotropic characteristic, stability of stratified rock mass is not only related to strength of intact rock but also to the inclination and characteristic of structure plane. The parameters of the structure plane have great impact on the stability of stratified rock mass. For the stratified rock mass is no homogenous, the homogenous model is not suitable to describe the characteristic of stratified rock mass. Then building an appropriate becomes necessary. In the present paper, Ubiquitous-joint model is introduced to describe the characteristic of rock mass, and the strength reduction method based on the Ubiquitous-joint model is proposed, which then is used to calculate the safety factor of slope, while the relationships between safety factor, strength properties of structure plane are analyzed, whose results can give guidance for the real practice.