Research Of Surrounding Rock At Tunnel Imports Stability And Bolt Support Parameters By Unloading Theory

Currently, NATM (new Australia tunneling method) is the main tunnelingexcavation method. Stability of surrounding rock after excavation hasattracted increasing attention due to composite geology and unknown innerinformation of it. Generally, geology around entrance of tunnel is bad andshallow buried, it is a common practice to incur collapse during construction.As a result of it, research into stability of surrounding rock in area of entranceis significant.Regarding WuTongsha tunnel in Pu-Yong high way as the projectbackground, in-situ test and numerical simulation basing on new-built yieldlaw are applied to analysis stability of surrounding rock in area of entrance.Main results are as follows:1By analyzing stress during excavation, conclusion that surrounding rockis unloading which is different from normal loading rock can be draw.Currently, there is no ensured constitutive equation that can be applied toreflect mechanic capability of unloading rock. In this paper, new model can beobtained by combining and optimizing Duncan-chang model with uniformtheory, and it is verified that this new-built model is suitable for the mechanicfeature of unloading rock.2Rules of deformation of surrounding rock is discussed by monitoringcorrelative displacement on site combined with construction condition. Leastsquare method is used to obtain deformation equation varying with time,thereby, optimum time to put second support is ensured.3New-built model is input into finite analysis software(ANSYS) to proceedsecondary development,3D excavation process is simulated. comparedcomputed results with in-situ monitored data, Duncan-chang model tailor toreality further which is superior than D-P rule included in software. Then,stability is verified by analyzing corresponding situation of stress-strain and support.4Theoretical method is applied to analysis feature of rock relaxation andnumerical simulation is employed to find out the location of rock relaxation;parameters of anchor (length and space of anchor) are assured with the aid oftheory of rock relaxation, finally, whether it is rational is proved by numericalsimulation.