Spatial deformation prediction method of fractured rock tunnel based on quantified <i>GSI</i> and its application

In the construction of tunnels, rock mass mechanical parameters are always difficult determination and prediction of tunnel deformation is hard to obtained accurately. To solve these problems, this paper proposed a new theoretical calculation method of geological strength index (<i>GSI</i>) combined indoor rock mechanics test and geometric information of rock mass obtained by three-dimensional dense reconstruction technology. And the elastic-plastic rock mechanics based on the Hoek-Brown strength criterion was used to establish a novel theoretical analysis method to predict deformation of tunnel in broken rock mass. The case studies indicated that the average<i> GSI</i> value of surrounding rock of a highway tunnel in Xiamen is 44. If the lining structure provided 0.002~0.02 times of the initial in-situ stress to the surrounding rock, the thickness of plastic zone was declined by about 50%, and the radial displacement was reduced by about 40%. Increasing the supporting pressure of lining structure could decrease the radius of plastic zone and radial displacement obviously. The nonlinear relationship between the support pressure and the radius of the plastic zone became more obvious with the decrease of <i>GSI</i> value, and the relationship between the support pressure and the radial displacement of the tunnel was also the similar change law. The relative deviation between the predicted value and the measured value was not less than 1.51%. The proposed method could effectively reflect the influence of surrounding rock fragmentation and tunnel construction on the plastic zone and displacement, which provides a new way for rapid and safe prediction of rock tunnel excavation stability based upon digital technology.