The Tunnel Excavation And Its Slope Stability In The Accumulation Body

During the process of designing of highways in Tibetan areas of Sichuanprovince(including Expressways of Wen-Jiu, Ma-Kang, Mian-Jiu and Wen-Ma) and theLi-Xiang Express, it is found that talus are widely spreading along the tunnel entrances.The talus collapsing from the rock to the foot of slopes have looser structure, lowerintensity and poorer stability. These features of the talus bring extremely greatdifficulties to the design and construction of tunnels. Based on the Local Joint Fund ofChongqing Jiaotong University Traffic Civil Engineering Materials NationalEngineering Laboratory’s “Study on the Stability of High Slope of Talus Based on theTheory of Discrete Element”(Number:LHSYS-2013-007), summarizing thetalus-related research findings of experts and scholars at home and abroad, the thesisestablishes the evaluation method of the slope, and explores a quick, economical andsafe excavation mode from the conventional way of excavation. Through the evaluationof the slope’s stability and excavation of the stimulant tunnel entrance of Zoumaling,the thesis comes to the following conclusions:①Through the direct shear test, it tries to test the anit-shear strength of talus ofdifferent density by the method of applying large direct shear apparatus on Chongqingtypical talus samples. It is found that when the density loose talus increases from0.3to0.6, the internal friction angle is enlarged from25.67°to32.53°, and cohesion isincreased from5.13Kpa to32.29Kpa.②Through the analysis of the instability of the tunnel’s slope in talus, the thesisputs forward two kinds of sliding slope instability mode: the circular sliding of deepbedrock and the interface sliding of shallow bedrock. With the using of the relatedformula, it also deduces the mechanism of slope instability in the case of tunnelexcavation’s disturbance.③It stimulates the excavation of tunnels with talus by using three dimensionalfinite element program ANSYS on conventional excavation methods (full face tunnelingmethod, benching tunneling method, pilot tunnel method). By comparison, it draws aconclusion that, among the three methods, the influence of the benching tunnelingmethod on the stability of surrounding rock and slope is the smallest. ④It comprehensively evaluates stability of Zoumaling tunnel slope by using thetraditional limit equilibrium method and the finite element program Plaxis2D for on;and by using of discrete element particle flow code PFC2D, it stimulates numericallythe entrance slope excavation’s influence on stability. Through the comparison of theparticle displacement, it comes to the conclusion that the bolt technology can have asignificant effect on slope reinforcement.⑤By applying the three-dimensional finite element program ANSYS, it simulatesthe early stage support of different rigidity. Through monitoring the stress ofsurrounding rocks after the tunnel’s excavation, it obtains the tunnel’s optimum supportrigidity.⑥By using the three-dimensional finite element program ANSYS and thethree-step core soil reservation excavation, it analyzes the displacement of surroundingrock and slope and change of plastic zone. The results show that after the first step ofthe ring excavation there are certain displacements of surrounding rocks and slopes;after the second step of left-step excavation, the displacements of surrounding rocks andslopes become smaller; then the surrounding rocks and slopes are almost in stable state.