Study On Concealed Karst Caverns With Mountain Tunnel Safety Thickness Prediction And The Research Of Stability

As our country the strategy of western develop greatly carry out, in the karst regionof Southwest China construction of the mountain tunnels are relatively more up,encounter the karst problem would bound to increase, which how to reasonablydetermine the concealed karst caverns with mountain tunnels between the critical safetythickness of concealed karst cave and analysis of the stability of the tunnel structureeffects on the trait is the key.This thesis, the construction of Chongqing chengkou toSichuan Wanyuan fast channel’Baizhishan mountain tunnel as engineering background,in the light of the above two key problems do the following aspects of content research:①Through the summary of concealed karst cave with tunnel safetythickness’research status, combined with the mechanics of rock mass surrounding rockstress in the basic theory of knowledge, picked out the effects of concealed dry karst andtunnel safety thickness of the main factors are as follows: karst relative to theexcavation of tunnel position; karst near the tunnel span (from the side of the ellipsecavities in the horizontal or vertical span of research variables); karst shape change (bychanging the oval cave high cross to realize); rock cohesion, internal friction angle, bulkdensity, elastic modulus, poisson’s ratio and the depth of the tunnel or cavern.②Using the finite element analysis software Ansys11.0numerical simulation tool,the eight main factors (cave cavern span, ratio of height to span of rock, cohesion,internal friction angle, bulk density, elastic modulus, poisson’s ratio and the depth oftunnel) are set into eight levels, the uniform distribution to the L64(89)orthogonal tablein the concealed karst cave in tunnel respectively according to the above, is right andjust below the three position concealed karst cave and tunnel safety thickness byorthogonal test. And draw the safety thickness respectively with eight factors affectingthe change curve of different thickness, the safety factors characteristic curves wereanalyzed and summarized, from the characteristic curve can be found, safety thicknessand many influencing factors there is a good linear relationship, although the numericalsimulation in the process of doing a lot of assumptions and simplifications, buteventually the curves obtained in whole or show certain regularity, and a lot of changescan be used to explain the knowledge of mechanics. Eventually, using multipleregression method were given above is right, and the tunnel and concealed karst caveunder critical safety thickness prediction formula.③Analysis of concealed karst cave on the stability of the tunnel structureinfluence, with Baizhishan mountain tunnel K29+020section as the analysis object,focuses on the analysis of concealed karst cave is just above、right and under the tunnelthe three special position when the distance between the cavity and the tunnel, karstcave the height span ratio and span of tunnel surrounding rock displacement, internalforce of support structure and the axial force effect on characteristic, summed up someuseful information, for similar tunnel design, construction and research provide usefulsign and reference.