APPLICABILITY EVALUATION OF PREDICTION METHOD FOR LARGE DEFORMATION OF SOFT SURROUNDING ROCK IN LIANHUA TUNNEL

Evaluation of geological conditions and excavation risks is one of the important stages in the process of design and construction of underground engineering. It is very important to estimate and identify the potential trend of deformation of rock mass when selecting appropriate excavation methods and support systems. In the present study,we study the potential deformation trend of rock mass in Lianhua tunnel of Pinglian expressway. Firstly,we introduce the engineering geological environment,engineering characteristics of surrounding rock,rock mass quality evaluation and field measured deformation of Lianhua tunnel. Then,the deformation trend of Lianhua tunnel is predicted by empirical method and semi-empirical and semi-theoretical method. The predicted results are compared with the actual results of deformation monitoring. The results indicate that the large deformation of Lianhua tunnel is mainly affected by the loose and broken soft surrounding rock,abundant underground and surface water,fault fracture zone and tectonic activities. For Lianhua tunnel,there are problems in the current large deformation prediction methods: the empirical method mainly predicts the deformation trend based on the results of rock mass quality classification,which has certain subjectivity. A certain deviation exists between the prediction results and the actual deformation results. For semi-empirical semi-theoretical method,the prediction effect of based on the relationship between the strength and stress of surrounding rock is pretty good,but the results of Jethwa's method,Hoek's method and ISRM method based on the ratio of strength of surrounding rock and geo-stress are relatively conservative. To sum up,the surrounding rock quality classification,ground stress measurement,groundwater and geological structure exploration shall be carried out objectively and carefully in the stage of engineering investigation and design. The large deformation trend and value shall be predicted by combining the empirical method and semi-empirical and semi-theoretical method,so as to provide sufficient and reliable basis for the design and construction.