Study On Stability And Support Of Consequent Bedding Rock Slope

Based on the project of the consequent bedding rock slope in the railway from Chongqing to Huaihua, deformation and failure mechanism, stability analysis and support measures of consequent bedding rock slope are studied in detail by multiple methods.1. On the basis of investigation of lots of typical sites of consequent bedding rock slope, consequent bedding rock slope are classified into five typical types by the combination of lithology, the engineering geology character of each types are described as well.2. The major influence factors of stability and the deformation and failure modes of consequent bedding rock slope are summarized. The major influence factors include geology factor, engineering factor and other factors. The deformation and failure modes consists of sliding and fracturing, sliding and compression cracking, bending and fracturing, plastic flowing and fracturing, sliding and bending, sliding and splitting and bedding sliding.3. The relation between the deformation discipline of layered rock slope due to excavation and the intersection angle of the strata and the slope strike direction are studied in detail by finite element method and model test. The results show that when the intersection angle exceeds 40 degrees for layered rock slope with one free face and 60 degrees for layered rock slope with two free face, there seems to be little probability of bedding slip of the slope, and the slope may not defined as consequent bedding rock slope.4. The formula used to calculate the bedding slip range of the consequent bedding rock slope with failure mode of sliding and fracturing due to road cutting is presented considering the reduction of shear strength of the bedding plane due to unloading and weathering. Also, the formula used to estimate the stability of the consequent bedding rock slope with slip-bending mode is established by the application of elastic-plastic plane theory which can consider the influence of both slope length and the plasticity of rock mass.5. The unloading effect of the slope due to excavation is described. According to the regularities of the slope displacement distribution and the status of the joints,the slope falls into three parts which are excavation damaged zone, slight disturbed zone and undisturbed zone.6. Based on the unloading effect of the cutting slope, a method used to estimate the stability of the cutting slope is presented. The steps which are required to deal with this problem are: 1). Establishment of the zoning models of the cutting slope according to the unloading degree. 2). Choice of the mechanical parameters of the unloading rock mass by zone. 3). Calculation of the safety factor and potential slip surface by finite element strength reduction method based on the mechanical parameters of the unloading rock mass.7. Basic steps for slope stability analysis considering the effect of unloading are established. The steps are: 1). Obtainment of the original engineering geology conditions. 2). Choice of original mechanical parameters of rock mass and establishment of the general geology model. 3). Estimate of the range of the excavation damaged zone based on the range of tensile stress zone and shear damaged zone of the slope. 4). Choice of the mechanical parameters of the unloading rock mass by zone and calculation of the safety factor and potential slip surface using strength reduction method. 5). Design of the support measures and correlative parameters.8. A light support system for reinforcing consequent bedding rock slope is presented. The light support system includes grouting and micropiles system. According to the arrangement of the micropiles, the micropile system is classified into three types which are independent micropiles system, planar truss micropiles system and space truss micropiles system. The application region and reinforcement mechanism of the light support system are also studied. The design procedure and relative calculating theory of the light support system are described in detail as well.9. Based on the laboratory test of grout proportioning, geomechanical model test and field test, the mechanism and support measures of the consequent bedding rock slope is studied. The results show that grouting can enhance the shear strength of the structural plane, the micropiles system is easily use in field and can control the deformation of the consequent slope evidently. So, the design philosophy of applying the light support system instead of the heavy support structure such as anti-sliding piles and prestressed cable anti-sliding piles withlarge section in reinforcing the consequent bedding rock slope is feasible.