Instability Mechanism And Control Measures Of Bedding Steep Slope In High Intensity Seismic Area

With the rapid development of construction in China, the projects such as large and super large hydropower engineering, traffic and municipal engineering in mountainous area are growing. A lot of natural bedding steep slopes and engineering high cut slopes are formed along the line of projects by construction transformation or natural disturbance due to complex geological and terrain conditions of mountainous area in Sichuan-Chongqing region. The bedding steep slopes at southwest area of China are in the critical state of collapse caused by Wenchuan earthquake. The failure and collapse of bedding steep slopes possibly have serious harm to people’s life safety and state property. Therefore, the stability analysis and study of bedding steep slope in high intensity seismic area and its security control has important academic value and a wide range of social and economic benefits. In this paper, the instability mode and control method of bedding steep slopes in Sichuan-Chongqing region were studied deeply by means of theoretical research, software programming, numerical simulation and slope geological mechanical model tests. The main research contents were as follows:(1) Based on the collection and analysis of characteristics information of slope instability and failure, the structure characteristics and failure modes of bedding steep slope were summarized, and the typical failure modes of high intensity seismic area were studied combined with the seismic factors.(2) The buckling mechanical model of bedding steep slope was established on the basis of small-deflection buckling theory, and the calculation method of critical load of small-deformation buckling was presented. The relationship and change rules of dimensionless load coefficient and rock plate geometry size with different cases of thickness were discussed detailedly, and the instability criterion was given. The calculation results in this paper had good consistency with the corresponding results of energy method.(3) On the basis of nonlinear large-deflection buckling theory, the failure mechanism of bedding rock steep slope was discussed and analyzed, and the calculation method of post-buckling deformation characteristics of bedding rock steep slope was established. The double trigonometric series was adopted to put forward the decision method of instability mode of sliding mass in bedding steep slope under unidirectional bearing state and reveal the rules of the size effect on critical load and load-displacement changing of soft bedding steep slope.(4) The anti-slide pile protection stress model of bedding steep slope considering influence factors of vertical load and loading segment’s pile length was established, and the influence rules of vertical load and loading segment’s pile length on anti-slide pile mechanical characteristics. The relationship of anti-slide pile width, pile spacing and rock arch ring thickness was established based on the rock arch effect between horizontal piles, and the design optimization method of anti-slide pile spacing and pile diameter of bedding steep slope protection was presented. The optimization method of reasonable double-row anti-slide piles was studied by numerical simulation and model test combined with engineering cases providing a theoretical basis for the protection design of anti-slide pile in bedding steep slope.(5) With the support of large bedding steep slope located at station project in the section of Chengdu to Chuanazhusi of Cheng-Lan high-speed rail, the geological mechanics model tests for instability mechanism and control method of bedding steep slope were carried out to discuss the mechanical characters and deformation failure mechanism of bedding steep slope. With the development of test bench composed by high strength composite steel structure and the adoption of servo hydraulic loading system and optical fiber grating real-time information monitoring system, deformation and mechanical characteristics were studied under different conditions of slide mass thickness and loading. According to the monitoring data of model test of bedding steep slope reinforced by anti-slide piles, the changing rules of body strain and buckling ultimate load of anti-slide pile under different landslide thrusts were analyzed to reveal the resistance mechanism and protective effect of anti-slide pile in bedding steep slope. The monitoring value in test basically agreed with the calculated results given by rock plate buckling model.(6) The dynamic response characteristics of bedding rock slope under seismic load was studied. Firstly, the qualitative analysis on the displacement characteristics of layered slope under seismic load was carried out using shear- beam model; secondly, the numerical software of ABAQUS was adopted to simulate the influence of seismic wave on bedding slope with different amplitude, frequency and duration. The changing rule of slope and the mechanical properties of slope with and without anti-slide pile under seismic load were studied, and the resistance slip effect of anti-slide pile was analyzed.Based on mechanical mechanism study of high steep rock bedding slope instability and Control method in highly seismic zone, relying on a large steep bedding slope along the Chengdu-Lanzhou railway, theory analysis, numerical simulation and field monitoring data comparative analysis were integrated used to establish the control system of high steep rock bedding slope in highly seismic zone. The results can provide references for the steep slope stability analysis and design of anti-slide pile protection.