| Chongqing-Zunyi expressway is an important expansion branch of Lanzhou-Haikou National Expressway,which is of great significance to promote the rapid and high-quality development of regional economy.However,in the process of construction,there are a lot of deformation and failure of highly weathered slope with the clastic-scattered rock masses,which seriously hinder the process of highway completion.Therefore,this paper takes ZK57 slope designed as a four grades high-cut slope within ZK57+555 m～ZK57+713 m mileage of Chongqing-Zunyi expressway in Guizhou Province as the research object.According to the engineering geological background,the structure type and failure characteristics of the slope,based on the field monitoring technology,the deformation and failure mode,development stage and stability influencing factors of the slope are analyzed.The evolution processes,strain-displacement characteristics and future development trends of the slope in the excavation and construction under the natural and rainstorm states are simulated by using the FLAC 3D software.The sensitivities of six influencing factors closely related to the stability of excavated slope are studied by using grey correlation method.Finally,the design of slope mitigation measures is carried out.The main conclusions are as follows:(1)Under the high structural transformation,the slope had been forming a similar homogeneous structure type with the clastic-scattered rock mass,and the highly weathered interface was obvious.Under the coupling effect of excavation and rainfall,the slope seriously creepsliding and fracturing,and this process is divided into three stages: deformation start stage,progressive transition stage and accelerated failure stage.Under the influence of rainfall,the slope in the main sliding area gradually changes from the strong deformation stage to the sliding stage,which has the characteristics of “large deformation occurs in heavy rain,and small deformation occurs in light rain”.(2)Through the numerical simulation analysis of FLAC 3D software,it is found that the unreasonable design of slope excavation ratio is the primary factor for the failure of slope.The fracturing at the slope top,the compression cracking at the slope waist and the shear failure at the slope toe under rainstorm state are more serious than those under natural state.With the increase of excavation depth,the slope gradually changes from circular arc sliding in homogeneous rock masses to polygonal line sliding along the highly weathered soft surface.(3)The slope stability coefficient is highly sensitive to the changes of internal friction angle,cohesion and slope platform width,and moderately sensitive to the changes of the slope height,the weight of rock masses and slope excavation ratio.It is suggested that the slope platform width should be emphatically considered in the design of cutting slope.(4)Based on the results of FLAC 3D and sensitivity analysis,the mitigation measures of reducing slope excavation ratio,widening slope platform,strengthening slope waist with prestressed anchor-rope and lattice beam and strengthening slope toe with anti-slide pile are proposed.And through the feasibility analysis and construction monitoring verification,the design scheme is feasible,which can provide a reference for the engineering treatment of a large number of similar slopes along the highway line and in Guizhou Province. |
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