Comparative Study On Excavation Schemes For High Slope With Soft Rock Of Tongjiashan

Tongjiashan section of East Qinhuai River in Nanjing is close to Shangba River.According to the flood control standard of the main zone of Nanjing city,the slope of Tongjiashan needs to be excavated to widen the riverway.The high slope incuding soft rocks of Tongjiashan in East Qinhuai River of Nanjing city is studied in this paper,based on field geological survey,the strength characteristics and mechanical parameters of the slope rock mass are studied.The failure modes of the rock mass under different excavation methods are analyzed,and the overall stability of the slope after excavation is evaluated.Two different excavation schemes are proposed at the end.The main research contents and results of this paper are as follows:(1)By field engineering geological survey,the engineering geological condition of Tongjiashan slope is analyzed.The soft rock slope is determined to be the study area according to the experimental study of rock mass.To determine the stratigraphic distribution,regional structural characteristics,rockmass structure and structural plane characteristics.(2)JRC-JCS model is adopted to obtain the mechanical parameters of the structural plane.The effects of Joint Roughness Coefficient(JRC)and Joint Compression Strength(JCS)on the mechanical parameters of the structural plane are analyzed.The mechanical parameters determined by different methods arecompared and analyzed.According to BQ method,the quality classification and evaluation for rock mass in each layer of the slope are carried out,the quality of Tongjiashan rock mass is divided into IV and V grades.(3)Based on the Hoek-Brown strength criterion,the mechanical parameters of the slope rock mass are determined by using the method of geological strength index.The relationship between BQ value,RMR value and geological strength index(GSI)is studied.The results of rock mechanics parameters obtained by different methods are compared and analyzed.The rock mass mechanical parameters obtained by the geological strength index(GSI)method is adopted in the study.(4)The failure modes of different excavation schemes for slope are analyzed by using the method of stereographic projection.According to the results of failure modes,two different slope excavation schemes are proposed.The stability of circular arc sliding and wedge sliding of the two excavation schemes are evaluated.In view of the uncertainties of slope structural plane and rock mass mechanical parameters,the stability of the slope after excavation is analyzed by Monte Carlo method.(5)Based on stability,the difficulty of construction,project cost,environmental protection and land expropriation,the two excavation schemes are compared and analyzed.The homogeneous rock mass and jointed rock mass are considered.The deformation and development trend of the excavated slope are simulated by finite element method,and the specific excavation scheme is finally determined.