New methods of safety evaluation for rock/soil mass surrounding tunnel under earthquake

The objective of this work is to obtain the seismic safety coefficient and fracture surface and proceed with the seismic safety evaluation for the rock mass or soil mass surrounding a tunnel,and the limitation of evaluating seismic stability is considered using the pseudo-static strength reduction.By using the finite element software ANSYS and the strength reduction method,new methods of seismic safety evaluation for the rock mass or soil mass surrounding a tunnel are put forward,such as the dynamic finite element static shear strength reduction method and dynamic finite element shear strength reduction method.In order to prove the feasibility of the proposed methods,the results of numerical examples are compared with that of the pseudo-static strength reduction method.The results show that 1) the two methods are both feasible,and the plastic zone first appears near the bottom corners; 2) the safety factor of new method Ⅱ is smaller than that of new method I but generally,and the difference is very small.Therefore,in order to ensure the safety of the structure,two new methods are proposed to evaluate the seismic stability of the rock mass or soil mass surrounding a tunnel.A theoretical basis is provided for the seismic stability of the rock mass or soil mass and the lining surrounding a tunnel and also provided for the engineering application.

Analysis of Slope Stability with Dynamic Overloading from Earthquake

The analysis of slope earthquake stability is one of the most important research subjects in geotechnical engineering and earthquake engineering.Two different concepts of slope earthquake stability are put forward：strength reserve stability and dynamic overloading stability.The first concept of slope earthquake stability has been widely accepted,and relative analysis methods are also well de-veloped;the second one,however,is seldom mentioned until now,and the failure criterion and the analysis method based on this concept are yet to be explored.What are researched are just the failure criterion and the analysis method of dynamic overloading earthquake stability.The criterion of critical earthquake peak acceleration for the dynamic overloading stability of a slope and its analysis method,the load increasing method（LIM）,are put forward.The dynamic overloading earthquake stability of a loess slope at Changshougou（长寿沟） in Baoji（宝鸡） City,Shaanxi（陕西） Province,China,is analyzed with LIM.The analysis result reveals that the dynamic overloading earthquake stability of the slope is quite high to the action of the earthquake ground motion,with exceeding probability of 10% in the next 50 years.

Seismic stability of loess tunnels under the effects of rain seepage and a train load

Loess tunnels are widely used in transportation engineering and are irreplaceable parts of transportation infrastructure. In this paper, a dynamic finite element method is used to analyze the coupled effects of a train vibration load and rainfall seepage. By calculating the variation in the safety factor of a loess tunnel because of the effects of various factors, such as different rainfall intensities and soil thicknesses, the dynamic stability of the loess tunnel is studied under the condition of a near-field pulse-like earthquake. The results show that the security and stability of the tunnel decrease gradually with decreasing burial depth. In addition, the plastic strain of the tunnel is mainly distributed on both sides of the vault and the feet, and the maximum value of the critical strain occurs on both sides of the arch feet. Because of the effects of the train vibration load and rainfall seepage, the safety factor of the loess tunnel structure decreases to a certain degree. Moreover, the range and maximum value of the plastic strain increase to various degrees.