Theoretical Investigation On Time-dependent Mechanical Behaviours Of Interact Between Large Deformation Rock And Support In Soft Tunnel

In recent years,with the strategic implementation of the Belt and Road Initiative,the infrastructure construction gradually transfers to more complex and difficult advancing mountain region in the western China,result in being confronted with the problem of“long,large,difficult and deep” in tunnel construction.In the tunnel construction,the boom of Large-Deformation problems in the soft and weak rock mass gradually prove to be restricting bottleneck problem of China’s economic development and underground space construction.Currently,the “resisting tunnel deformation with stiffness support”support scheme is far from meeting relevant tunnel design requirements for Largedeformation problem in the deep-buried soft rock tunnel under high geo-stress.Based on incompatible deformation between surrounding rock and traditional stiffness design,the yielding support scheme is proposed,which carries out yielding material to make controlled deformation of pressure-relief for surrounding rock,ensuring support within bearing capacity and achieving the purpose of tunnel stability.The yielding support possess irreplaceable superiority in the Large-Deformation tunnel construction under soft rock.Therefore,theoretical basis investigation of the yielding support design in the deep soft rock tunnel under high geo-stress is conducted by a great practical significance and engineering value.Based on the theory of tunnel excavation-support,the primary support design in the large deformation under the soft rock tunnel is conducted by profound investigation and is considered by rheological behaviours of soft rock.The mechanical response of soft rock tunnel of high geo-stress under the combined support between rockbolts and lining is conducted based on the construction experience of existing tunnel.The theoretical calculation method of deep soft rock tunnel under yielding support is derivated and the mechanical mechanism of internal deformation of yielding structure is revealed,investigating sensitivity parameters of yielding structure.The main research contents of the thesis are listed as follows:(1)Aiming at the different rheological model on influence of tunnel support for deep circular tunnel under hydrostatic pressure and the viscoelastic and viscoelasticviscoplastic mechanical theory,the mechanical respose of surrounding rock under the combined support between rockbolts and lining is derivated and the main controlled factors of tunnel deformation in the large deformation rock is investigated.The different support parameters on the restraint effect and internal mechanics law of surrounding rock under combined support between rockbolts and lining is revealed based on compatible deformation between tunnel support and surrounding rock and considering stress release coefficient of tunnel face advancement and non-associated plastic flow rule.Based on the parametric investigation,the tunnel displacement between elastic and plastic zone is not almost affected by the plastic parametric variable under viscoelastic-viscoplastic model,but there is very significant influence on bolt-reinforcement pressure,lining pressure and tunnel displacement,resulting in relatively less than tunnel deformation in the viscoelastic model.And difference value of tunnel deformation between viscoelastic model and viscoelastic-viscoplastic model is affected by plastic parameters.(2)Aiming at the influence of interface contact on the tunnel deformation,the equation of friction slip is established and the interface contact relationship between surrounding and lining is defined.The mechanical model of slip contact between surrounding rock and lining is proposed and the calculation method of mechanics response under the friction interface contact between rheological rock mass and support is derived.Comparing with existing theory and numerical calculation method,the correctness and reliability of proposed solution is validated.The conclusions of parametric investigation are obtained,as following: The friction coefficient is positively correlated with the vault stress and negatively correlated with the waist stress.There is a significant effect on the local deformation of tunnel with different installation time under tunnel friction contact,resulting in performing elliptical deformation of surrounding rock.In addition,there is a constant value without time-varying at the position of interface between lining and surrounding rock under friction slip interaction.However,this position gradually moves towards the vault with the increase of friction coefficient.(3)Based on the problem of tunnel excavation under radial yielding support,the mechanical model of interaction relationship between rock under the circular tunnel of viscoelstic-plastic geomaterial and radial yielding lining is proposed,and the timedependent solution of mechanical response of surrounding rock at each support stage is derived and considered the influence of stress path,tunnel face advancement and support installation delay in the deduce process,revealing operating principle of compressible layer and improving tunnel safety performance.Based on the theoretical calculation,a comprehensive parametric investigation is conducted,including yielding stress,yielding length and elastic modulus of compressible layer,lining installation time and plastic parameters of surrounding rock.The investigation results show below: the increasing yielding stress and elastic modulus of the compressible layer will lead to decrease threshold of tunnel displacement,but the tunnel displacement affected by the yielding length of compressible layer is opposite.Simultaneously,there is a positive effect on tunnel convergence within a certain of threshold range of elastic modulus and yielding stress,and the yielding support of compressible layer will be transformed into rigid support without playing the role of pressure relief after exceeding this threshold.(4)Based on the theory of viscoelasticity,The mechanical behavior of large deformation bolt and circumferential yielding support is proposed and then the interaction method between surrounding rock and support system is established,obtaining timedependent solution of mechanics response of soft rock tunnel under the circumferential yielding support considering influence of tunnel face advancement and yielding support system installation delay.The investigation found that the increasing yielding stress of large deformation rockbolts under combined support between large deformation rockbolts and circumferential yielding lining will result in decreasing tunnel displacement and lining pressure,which help the tunnel convergence of large deformation soft rock and is cost saving of circumferential yielding lining.The installation time of large deformation rockbolts and circumferential yielding lining present a positive correlative with the influence of tunnel deformation.Namely,the earlier the installation time will lead to be the faster the tunnel convergence and the smaller the tunnel deformation,but this also result in increasing the support pressure.