Study On Entrance Technology Of Tunnel Under Expansive Silty Clay Ground

Relying on the project of Mudanjiang Aimin tunnel entrance section and the site monitoring data,the methods of displacement inversion,numerical simulation and comparative analysis are used to study the relevant parameters of expansive silty clay.The construction technology and method of full-section surface grouting are introduced.The stress characteristics of tunnel support after grouting are analyzed.The main research work is as follows:(1)The process of three accidents in the initial construction of the entrance section is introduced.The cause of the accident are analyzed and corresponding treatment measures are put forward.(2)The characteristics of expansive silty clay witch swelling and shrinkage,fissures and over-consolidation are summarized combined with soil instability on site.Based on the actual monitoring data,the relevant mechanical parameters of the expansive soil such as Kelvin shear modulus,Kelvin viscosity coefficient,Maxwell shear modulus and Maxwell viscosity coefficient are obtained by displacement inversion method,which are input FLAC3 D model to get the theoretical displacement in order to compare with the measured displacement.It was found that the error was within the allowable range of the project.(3)The mechanical parameters of surrounding rock after grouting that get by displacement inversion are input to the FLAC3 D model to compare displacement,and initial support stress of tunnel in the case of 0.6m excavation and 1.2m excavation.It was found that the maximum displacement of 0.6m excavation is about 30% less than the maximum displacement of 1.2m excavation.The maximum principal stress and minimum principal stress of the initial support in the case of 0.6m excavation are 1% and 2.4% larger than 1.2m excavation respectively.It can be seen that 0.6m excavation can better control the displacement of the tunnel surrounding rock.(4)Construction technology and method of the full-section grouting are introduced.The stress monitoring data of initial support and secondary lining at DK293+090 is analyzed.The comparison of displacement monitoring data before and after grouting shows that the displacement value is about 50% less than that before grouting.It is found that the growth rate of the surrounding rock pressure and the steel arch stress is decreased obviously after grouting.The pressure of the surrounding rock has decreased by 36%,82%,66%,56%,56%.The steel arch stress has reduced by 51%,74%,70%,33%,85%.It can be seen that the displacement and stress of the key position of the tunnel surrounding rock are decreased,which indicates that the full-section surface grouting has a significant effect on improving the properties of expansive silty clay and improving the stability of surrounding rock.