Wenhao Shi

Numerical simulation on slope stability analysis considering anisotropic properties of layered fractured rocks: a case study

Anisotropy is one of the natural properties of layered fractured rock, and it plays an important role in slope stability analysis, which is a vital problem in the geotechnical engineering. However, in the present engineering design, rock mass is simply treated as isotropic material, which fails to take into account the anisotropic properties. This work begins with formulizations of the anisotropic seepage-stress coupled model for the layered fractured rock slope stability analysis based on the equivalent continuum theory. Next, the model is applied in the numerical simulation of the southern slope of an open-pit mine in China to understand the mechanism of the existing failure strain as well as the failure mechanism of the potential landslide. The computed water table and damage zone have been compared with the field measurements and found to be in good agreement with field observations. Finally, the effective measures to prevent the slope failure and strengthen the slope stability have been suggested. The proposed model successfully applied in the case study indicated that it is much more feasible and efficient comparing with using the traditional isotropic coupled model in such layered fractured rock slopes stability problems.

Numerical Modeling of Non-Darcy Flow Behavior of Groundwater Outburst through Fault Using the Forchheimer Equation

AbstractIn a groundwater outburst through a fault, the velocity is generally so high that the relationship between the velocity and the hydraulic gradient deviates from the linear Darcy regime. Thi...

Deformational behavior of underground opening using a stress-seepage coupled model considering anisotropic characteristics

Fractures have a dominant effect on the mechanical response of a rock mass subjected to mining operations. A numerical finite element model describing the anisotropic property of elasticity and seepage was used in this study to assess the drift spacing at the Heishan metal mine in Hebei Province, China. The fractured rock mass is assumed to be transversely isotropic, and the influence of joint orientation on the anisotropic properties of elasticity of the surrounding rock mass around roadways was investigated. The associated stress field and fracture pattern of the surrounding rock mass were also numerically studied. The results indicate that the existence of joint planes greatly affects the stress field and fracture patterns, and the principal direction of joints can control the failure pattern of the surrounding rock mass around drifts.

Numerical simulation of the free surface and water inflow of a slope, considering the nonlinear flow properties of gravel layers: a case study

Groundwater is an important factor of slope stability, and 90% of slope failures are related to the influence of groundwater. In the past, free surface calculations and the prediction of water inflow were based on Darcys law. However, Darcys law for steady fluid flow is a special case of non-Darcy flow, and many types of non-Darcy flows occur in practical engineering applications. In this paper, based on the experimental results of laboratory water seepage tests, the seepage state of each soil layer in the open-pit slope of the Yanshan Iron Mine, China, were determined, and the seepage parameters were obtained. The seepage behaviour in the silt layer, fine sand layer, silty clay layer and gravelly clay layer followed the traditional Darcy law, while the gravel layers showed clear nonlinear characteristics. The permeability increases exponentially and the non-Darcy coefficient decreases exponentially with an increase in porosity, and the relation among the permeability, the porosity and the non-Darcy coefficient is investigated. A coupled mathematical model is established for two flow fields, on the basis of Darcy flow in the low-permeability layers and Forchheimer flow in the high-permeability layers. In addition, the effect of the seepage in the slope on the transition from Darcy flow to Forchheimer flow was considered. Then, a numerical simulation was conducted by using finite-element software (FELAC 2.2). The results indicate that the free surface calculated by the Darcy–Forchheimer model is in good agreement with the in situ measurements; however, there is an evident deviation of the simulation results from the measured data when the Darcy model is used. Through a parameter sensitivity analysis of the gravel layers, it can be found that the height of the overflow point and the water inflow calculated by the Darcy–Forchheimer model are consistently less than those of the Darcy model, and the discrepancy between these two models increases as the permeability increases. The necessity of adopting the Darcy–Forchheimer model was explained. The Darcy–Forchheimer model would be applicable in slope engineering applications with highly permeable rock.

Mechanical and energy release characteristics of different water-bearing sandstones under uniaxial compression:

This paper presents the experimental results of calcium argillaceous cemented sandstones with different water contents under uniaxial and cyclic loading conditions. The effects of the water content status on peak strength, deformation, and dissipated energy are discussed. Meanwhile, the acoustic emission energy is also studied based on the accelerating energy release theory and energy distribution density function. The experimental results show that the water content has remarkable effects on the peak strength and elastic modulus by a decrease of 37–58% and 15.7–21% after being saturated, respectively. Both the accumulated dissipated energy and dissipated energy generating ratio of dry specimens are higher than those of the saturated specimens. The acoustic emission energy release rate of dry specimens is higher than those of the saturated specimens, which means a high tendency of sudden failure for dry specimens. Moreover, the distributions of acoustic emission absolute energy are consistent with the normal density distribution function, and the AE energy expectations of dry specimens are higher than those of the saturated ones in the loading process and they show an obvious increasing trend on approaching failure. These conclusions will be helpful for the illumination of water-weakening effects on the mechanics parameters and failure mechanism analysis in view of the releasing energy.