Analysis On Construction Stability Of Large Span And Small Distance Tunnel In Coastal Mountains

In recent years,small clear distance tunnel has been widely used in China's highway construction.The domestic and foreign design,research and construction technicians have conducted systematic research and practical work on them,with the construction of a large number of small clear-distance tunnels,but many problems remain to be solved.The factors of affecting the complex conditions of long-span small clear-distance tunnel construction stability mainly are the following aspects:the tunnel where the rock contains cracks and other weak structures,the vibration of tunnel blasting,the surrounding rock affected by groundwater,the rheological properties of rock mass.In this paper,the above issues are studied in connection with the Dadongshan Tunneling Project of Bohai Road(Phase 1)in Dalian.The main research contents and achievements are as follows:(1)The GP algorithm,DE algorithm and the joint model are combined to establish a method of back analysis of surrounding rock parameters.First of all,according to the joint design of joint parameters in orthogonal design,the three-dimensional numerical simulation is carried out through the joint model,and the key parameters are selected by means of sensitivity analysis.Then,the joint parameter-nonlinear expression of surrounding rock displacement is realized through the coupling algorithm of Gaussian-differential evolution(GP-DE).Differential evolution algorithm is used to realize the inversion of joint parameters,and the deformation characteristics of surrounding rock under different reinforcement measures are analyzed.The results of engineering studies show that the precision of back analysis is high.The pre-grouting anchor reinforcement of surrounding rock is better for the construction of large-section and small clear-distance tunnel support,which can meet the engineering safety requirements.The conclusion of the study can provide theoretical basis for the excavation and rock wall reinforcement of large-section and small clear-distance tunnel under similar conditions,which is instructive for engineering practice.(2)The umerical calculation method is used to study the effect of tunneling in small clear tunnel under different blasting construction methods,and the analysis points out the weak part of the retrograde tunnel under the influence of the first tunnel blasting.The vibration condition of the monitoring point at the time when the tunnel passes through the building is analyzed through the field test of blasting seismic effect and the actual monitoring value of the site,on the basis,and a scheme of tunnel blasting blasting through nearby buildings is put forward.The proposed control scheme of tunneling blasting is applied to the construction.The results show that blasting excavation effectively ensures the stability of adjacent buildings and meets the vibration control standard of blasting safety regulations.(3)Considering the role of groundwater on the surrounding rock,the construction methods for small clear distance tunnels under different surrounding rock levels are simulated,and the changes of the mechanical properties of the surrounding rock mass and the rock mass in the middle column during each step of excavation are analyzed under two work methods(CD method and double-sidewall pilot method).Considering the thickness of the grouting layer and the impermeability coefficient,the reasonable grouting parameters of the tunnel in the rich water area are studied.The reasonable grouting parameters are put forward to provide certain theoretical basis for the design and construction of large span and small clear distance in the future.(4)The rheological characteristics of surrounding rock of Dadongshan Tunnel Project are studied under the influence of groundwater based on nonlinear western model.The influence of the construction process of small clear distance tunnel under three conditions and the time effect on the surrounding rock stability after excavation is analyzed.The stability of tunnel surrounding rock is quantitatively evaluated by unit state index.The change of permeability coefficient of rock mass with the stability of surrounding rock is obtained,and the reasonable application of the second lining support time is proposed by the permeability contact between ZSI(Zone State Index)and unit,which provides a reference for practical engineering.