Dynamic limit equilibrium analysis of sliding block for rock slope based on nonlinear FEM

Traditional rigid body limit equilibrium method （RBLEM） was adopted for the stability evaluation and analysis of rock slope under earthquake scenario. It is not able to provide the real stress distribution of the structure, while the strength reduction method relies on the arbitrary decision on the failure criteria. The dynamic limit equilibrium solution was proposed for the stability analysis of sliding block based on 3-D multi-grid method, by incorporating implicit stepping integration FEM. There are two independent meshes created in the analysis： One original 3-D FEM mesh is for the simulation of target structure and provides the stress time-history, while the other surface grid is for the simulation of sliding surface and could be selected and designed freely. As long as the stress time-history of the geotechnical structure under earthquake scenario is obtained based on 3-D nonlinear dynamic FEM analysis, the time-history of the force on sliding surface could be derived by projecting the stress time-history from 3-D FEM mesh to surface grid. After that, the safety factor time-history of the sliding block will be determined through applying limit equilibrium method. With those information in place, the structure＇s aseismatic stability ean be further studied. The above theory and method were also applied to the aseismatic stability analysis of Dagangshan arch dam＇s right bank high slope and compared with the the result generated by Quasi-static method. The comparative analysis reveals that the method not only raises the FEM＇s capability in accurate simulation of complicated geologic structure, but also increases the flexibility and comprehensiveness of limit equilibrium method. This method is reliable and recommended for further application in other real geotechnical engineering.

Experimental study on sliding shaft lining mechanical mechanisms under ground subsidence conditions

Aimed at more than 60 shaft linings damaged in Huaibei, Datun, Xuzhou and Yanzhou mine areas, this paper presents a new type of sliding shaft lining with asphalt blocks sliding layer. By model test, it is obtained that the deformation characteristics and the mechanical mechanisms of the sliding shaft lining under the condition of ground subsidence. The research results provide a testing basis for the sliding shaft lining design. By now, this kind of sliding shaft lining had been applied in 9 shafts in China and Bangladesh.

Analytical expressions for determining the stability of cohesionless soil slope under generalized seismic conditions

In recent major earthquakes, the researchers have found the need for consideration of vertical seismic acceleration for the stability analysis of the man-made and natural slopes. However, in most past studies, the performance of slopes has been assessed by accounting only the horizontal seismic component of the ground motion, without giving due weightage to the effect of vertical component. In the present study, analytical expressions are derived to determine the factor of safety, yield seismic coefficient and consequently the seismic displacement of cohesionless soil slope under combined horizontal and vertical components of the ground motion. The derivation uses the Newmark's sliding block approach, in which the soil slope with a planar failure surface within the framework of conventional pseudo-static analysis is assumed to follow the Mohr-Coulomb failure criterion. The effects of vertical seismic coefficient on the stability of cohesionless slope have been studied through a set of graphical presentations for a specific range of soil parameters. It is observed that overlooking the effect of the vertical component of the ground motion on factor of safety and the displacement while designing the slope may be detrimental, resulting in the slope failure. The general expressions presented in this paper may be highly useful in the field of earthquake geotechnical engineering practice for designing the cohesionless soil slopes under combined horizontal and vertical seismic loads.

Jet Vectoring Control Using a Novel Synthetic Jet Actuator

A primary air jet vectoring control system with a novel synthetic jet actuator （SJA） is presented and simulated numerically. The results show that, in comparison with an existing traditional synthetic jet actuator, which is able to perform the duty of either ＂push＂ or ＂pull＂, one novel synthetic jet actuator can fulfill both ＂push＂ and ＂pull＂ functions to vector the primary jet by shifting a slide block inside it. Therefore, because the new actuator possesses greater efficiency, it has potentiality to replace the existing one in various appli- cations, such as thrust vectoring and the reduction of thermal signature. Moreover, as the novel actuator can fulfill those functions that the existing one can not, it may well be expected to popularize it into more flow control systems.

Cyclic load testing of pre-stressed rock anchors for slope stabilization

The objective of this research was to assess the characteristics of seismic induced damage and the deformation patterns of pre-stressed cement-grouted cables that are used for rock slope stabilization projects subjected to quasi-static cyclic loading.The experimental configuration includes the installation of 15 pre-stressed cables in a slope model made of concrete blocks(theoretically rigid rock mass) on top of a pre-existing sliding surface.The study showed that:(i) The pre-stressed cables exhibited great seismic performance.Rapid displacement of the model blocks was observed after the complete loss of the initial pre-stress load under continued applied cyclic loads and exceedance of the state of equilibrium,which implies the higher the initial pre-stress load,the better the seismic performance of the rock anchor;(ii) The failure of the pre-stressed cables was due to fracture at the connection of the tendons and cable heads under cyclic loading.The sequence of failure had a distinct pattern.Failure was first observed at the upper row of cables,which experienced the most severe damage,including the ejection of cable heads.No evidence of de-bonding was observed during the cyclic loading;(iii) The stress distribution of the bond length for pre-stressed cables was highly non-uniform.High stress concentrations were observed at both the fixed end and the free end of the bond length both before and immediately after the state of equilibrium is exceeded.The results obtained can be used to evaluate the overall performance of pre-stressed rock anchors subject to seismic loading and their potential as rockfall prevention and stabilization measures.