| The problem of weak surrounding rock is very common in tunnel design and construction.Due to the poor self-stabilization ability of weak surrounding rock,the surrounding rock is prone to large deformation and long deformation time,which has an important impact on the safety of tunnel construction and the long-term stability of surrounding rock.At present,the research on deformation prediction of soft surrounding rock tunnel is still not clear enough,the initial support design mainly relies on engineering experience,and there are extreme phenomena of insufficient safety or too conservative.Therefore,based on the project of "research on large deformation of weak surrounding rock and the prevention and control technology of lining cracking of Pingtian tunnel",this paper systematically studied the deformation of weak surrounding rock and the bearing capacity of initial support as well as the application research by means of theoretical analysis,numerical simulation,field monitoring and field test.The main work and achievements are as follows:(1)Based on BQ classification method,the fast classification diagram-matic method of surrounding rock is established,and the method of dynamic classification correction of weak surrounding rock grade is put forward by using the geological radar and geological sketch as the dynamic correction method,which is applied in Pingtian tunnel construction to guide tunnel design and construction.(2)According to cavity expansion methods,establishes the calculation model of the deformation of tunnel excavation unloading and supporting to analysis on the deformation of surrounding rock under different supporting force development.And considering rock dilatancy characteristics under the influence of the volume change,deduce the analytical expressions of surrounding rock stress and displacement by using linear uncorrelated flow law to describe the dilatancy characteristics of rock mass.(3)Based on the analysis of the mechanism of the combined support of "bolting and shotcreting + steel arch support" in the soft surrounding rock tunnel,the calculation model of the Combined Support Arch is established,which is formed by the interaction of Bolt,shotcreting layer,steel arch support and surrounding rock.It reflects the relationship between deformation of surrounding rock and bearing capacity under the combined support,and determines the proportion of each supporting component to share the load of surrounding rock.(4)Combined with the prediction calculation model of tunnel deformation and the calculation model of bearing capacity of initial support,taking the allowable relative displacement of tunnel as the deformation control objective,the design and optimization model of initial support parameters is established.This model can be used to guide and optimize the design of support parameters of "anchor spray + Steel Arch support" in soft surrounding rock tunnel.The above theory is applied to engineering practice,and is compared with numerical simulation. |
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