Reliability Analysis Of The Stability Of Slope Based On Transfer Coefficient Method And Its Application

Slope stability has long been a hotspot in geotechnical engineering because of its importance.Traditionally, the limit equilibrium method is most widely used. Some simplified algorithms (like transfer coefficient method) show off their simple calculation, applicability and convenience to good effect, and have been very popular in the irrigation department and the railway department. However, the transfer coefficient method is too simple and assumptive to make sure that it is scientific and accurate. During the engineering practice, people have realized the uncertainty of soil properties, especially the variability of physical and mechanical parameters. What's more, it is hard to see the real situation of slope engineering because the traditional stability analyses do not take the variability of parameters into consideration. On the contrary, the reliability analysis method based on random probability theory could fully consider the variability of rock and soil parameters. Therefore, the design and evaluation of project on the basis of reliability analysis is of great significance to the development of slope stability analysis.Present reliability analyses of slope stability are all based on limit equilibrium model. This paper use transfer coefficient method to do reliability analysis of slope stability. The specific content and conclusions are as follows:(1)In this paper, it describes the basic theory of slope stability analysis and reliability analysis and does a deep research on the drawbacks of transfer coefficient method and the impact on error. It brings forward a new improved method which can consider the unbalanced torque result from groundwater, slope loading, seismic force and other additional loads and meet the torque balance during calculation. Then it establishes a improved analysis model and compiles the corresponding calculation program.(2)Aiming to the complex situation where the safety factor in reliability calculation is not an explicit expression, taking the improved transfer coefficient method as simulated technique, a new response surface method based on transfer coefficient method was established. It can determine the approximate limit state equation. Computer programs of improved response surface method and Monte-Carlo method are compiled by MATLAB.They can calculate reliability index in multilayer slope and any configuration slip surface of slope. They have much using flexibility in scope and have no limit in distribution and correlation of random variables. The sensitivity analysis of parameters can be realized by changing the mean, variance and correlative coefficient of the random variables.(3)The accuracy and efficiency of the improved method and the availability of the procedure have been tested and verified. Results show transfer coefficient method which considering Moment equilibrium condition is closer to result of result of strict method. There exists error between results of improved response surface method and Monte-Carlo results, but within 10%. It proves that the improved method has a better accuracy. And analyze the distribution, correlation and variability of the random variables; reliability under the influence of procedures applied. The result shows that influence of the types of random variables distribution onβnot only is related to the mean and deviancy, but also related to the value of variables andβ; the influence of random variables onβget bigger when the mean of variables get bigger; the influence of correlation of random variables onβis more distinct. What's more, different mean or deviancy coefficient, the degree of influence will be different.(4) Choosing the left bank of the Yalong River as an example, considering a variety of working conditions, apply transfer coefficient method, improved transfer coefficient method combined with M-P method to analyze the uncertainty of its stability. The result shows that response surface method and Monte Carlo analysis method are close; the biggest error is 8%. That is to say the accuracy of improved method can meet the requirement of engineering application. The stability of slope is good. However, the stability had an obvious decrease after heavy rains and earthquake; the security storage is small and the probability being destroyed is big (5%~30%); considering the change of water level, stability was significantly reduced, the water level fell to the bisect after heavy rain and earthquake. bisect 1, bisect 2 and bisect 3 is less stable, the probability of being destroyed is greater than 30%, it belongs to moderate- risk-slope; it is possible to lose stability and measures should be taken. The degree of slope stability safety is too high when not considering variability of physical and mechanical parameters; it is dangerous, overestimating the stability safety of slope. While the result of considering variability of physical and mechanical parameters will reflect fact well, considering factor are more overall; The concept of probability of being destroyed is clear, the physic significance is more reasonable, better describing the degree of safety of slope. Reliability analysis is a useful implementation for the traditional safety factor evaluation system; it is deserved to research in depth and a good analysis method to be spread.