Studies On Rock Mass Stability Of Tunnel And Its Reliability Analysis Based On Block Theory

Due to the failure of natural stress state of rock masses in the course of theconstruction of tunnel, unload rebounding of surrounding tunnel rock masses andstress redistribution occurs. When the rebounding stress and redistribution stresssurpass the bearing capacity of surrounding rock masses, some blocks will losestability along structural planes, and finally cause the failure of engineering rockmasses. This will directly disturb tunnel construction and influence the safety andprogress of construction.Since Dr. Genhua Shi formally advanced the Block Theory in the 1980s, thisresearch method has become comparatively mature and the Block Theory has beenwidely accepted day by day with the thorough understanding and study by the homeand abroad scholars.In the thesis, through the example engineering entity of Shawan tunnel inShenzhen and DaLiangshan tunnel in Zhejiang province, Block Theory builds entitymodels of tunnel and structural planes. Modeling process of Block Theory,determination of boundary condition and selection of geometry model as well asgeometry parameters of block body are introduced in detail. A stability analysis of theblock body consisting of tunnel free-face and structural planes in rock masses iscarried out by applying vector operation. Using the program of Unwedge v.3.0 carriesout an appraisal of block stability and the procedure of evaluating stability isdemonstrated in detail. The results acquired from Unwedge v.3.0 are compared with theanalytical solution, and a satisfactory result is obtained. Furthermore, using Unwedgev.3.0 does a support structural design of tunnel. Then this paper does a comparativeanalysis between the stability appraisal with the consideration of field stress and thatwithout consideration of field stress. At last, some researches on sensitivity of factorswhich influences block body stability are done and their approximate relationshipcurves are obtained.In the last section this thesis does a preliminary study on reliability index of theblock body stability of Da Liangshan tunnel, and introduces the current developmentstatus of reliability method. The limit state equation of block body stability isestablished and the reliability index of block body is acquired making use of JCalgorithm. Then a comparative analysis is done between reliability method and safetyfactor method.