The Reliability Research Of Tunnel Lining By Subset Simulation Method And Its Improved Method

ABSTRACT:With the high-speed development of the economic in our country, extra-long tunnels, the high dam of more than200meters in height, urban subway project, some complex structures and a few of major projects are under construction. To treat the safety of such project should be attached more important. Although the method of traditional safety factor can reflect the safety of engineering in a certain extent, not take into account the uncertainty and random variables. It cannot evaluate the safety of engineering fully and accurately. So the development of the reliability theory is of great significance for the safety evaluation of engineering.This paper mainly introduces the basic principle of the Monte Carlo method, the first order second moment method, the response surface method, which is used in the reliability analysis. Also it analyzes the advantages and disadvantages of each method in practical application. According to the advantages and disadvantages of the common used method, this paper describes the basic idea of Subset Simulation, the choose of the intermediate failure event, the implementation steps, and the Markov Chain Monte Carlo in the process of subset simulation in details. Also it introduces the advantages and disadvantages of the Subset Simulation. The paper considers the influence of the result for the subset simulation by the increasing number of Markov chain and the length of Markov chain, and proposing the possibility of improving the subset simulation method. According to the characteristics of the subset simulation method, the improved subset simulation method can be improved by two directions, which can improve or replace the Monte Carlo method (MC) sampling or markov chain Monte Carlo simulation (MCMC) sampling.This paper considers the characteristic of the subset simulation, number theory, importance sampling method, proposing a combination reliability analysis method by the three kinds of reliability analysis method. With the numerical example, this paper verifies the possibility of its accuracy and its application. Also the new combination method is analyzed and compared with other methods from the calculation precision, the number of sample points. The improved method has better precision, and it has the advantage of the number of sample points and the coefficient of variation of failure probability.In this paper, under the background of the large section loess tunnel in Lan-yu railway, the model is established with the mechanical model of load-structure. With the Probabilistic Design System and the language of APDL in ANSYS, this paper establishes the reliability analysis file of the two secondary lining of large section loess tunnel. And it analyses the load effect of tunnel secondary lining by the method of Monte Carlo, getting the statistical characteristics of the force and eccentricity. And analyzing the random variables for the sensitivity of axial force, bending moment, eccentricity.Finally calculating the reliability index and failure probability of every cross section by subset simulation method and improved method. Through the calculation we can see the two methods have advantages in computational efficiency and accuracy of lining reliability problems. It can be seen from the reliability index that the project position under the vault on tunnel lining section and spandrel position may appear cracking. The lining will not be crushed, but we should pay attention to monitoring the spandrel and arch feet of the lining which its reliability index at the critical value.