Study On Creep Disturbance Effect Of Geopolymer Cemented Coal Gangue-fly Ash Backfill Under Dynamic Load Of Bridge

With the rapid development of transportation in China,the problem of bridges crossing the goaf becomes more and more serious.When the filling method is used to fill the goaf under the bridge construction position,the filling body will creep under the action of overlying strata and and the self-weight load of the bridge,and when the depth of the goaf is shallow,the filling body will be disturbed by the vehicle load on the bridge.Under the combined dynamic and static loads,the filling body will produce creep disturbance effect,which seriously affects the long-term filling effect and bridge stability after goaf filling.Therefore,it is of great practical significance to explore the creep disturbance effect of filling body and to study the effect of goaf under filling bridge.In this paper,in order to study the creep disturbance effect of filling body,a new creep disturbance testing machine was developed.and its principle,error and accuracy were analyzed.By using this machine,the uniaxial creep disturbance test of a new type of filling material called geopolymer cemented coal gangue-fly ash backfill（GCGFB）was carried out with step loading,and the creep disturbance law of GCGFB was obtained.The creep disturbance constitutive model of GCGFB was established,and its secondary development was carried out based on FLAC^3D platform.Finally,the long-term stability of goaf under dynamic and static loads with different engineering conditions is discussed by numerical simulation..Research results show that:（1）Dynamic disturbance has a significant influence on the creep process of GCGFB.The continuous disturbance impact breaks the creep stability state of GCGFB,accelerates the creep process of GCGFB and reduces the long-term strength of GCGFB;（2）The creep disturbance effect of GCGFB is closely related to the stress level of GCGFB and the impact energy of dynamic disturbance.The greater the disturbance impact energy,the larger the deformation value produced by GCGFB and the shorter the time to reach the failure strain.Under low disturbance energy,the disturbance deformation caused by GCGFB is negatively correlated with the stress level,showing the law of impact hardening.Conversly,under high disturbance energy,the disturbance deformation caused by GCGFB is positively correlated with the stress level,showing the law of impact softening;（3）Based on the improved fractional Burgers model,a creep disturbance constitutive model of GCGFB is established by introducing a disturbance element and a strain triggered non-linear viscous dashpot.The relevant parameters are fitted and the applicability of the model is proved;The creep constitutive model is redeveloped by using the secondary development platform provided by FLAC^3D.The validity of the model is verified by comparing with the experimental data.（4）The numerical simulation of goaf filling and bridge construction is carried out by FLAC^3D.The displacement field variation,stress field variation,bridge structure stress characteristics and bridge structure deformation characteristics under different engineering conditions of goaf are discussed.The simulation results show that the goaf treated by GCGFB under three different engineering conditions can meet the requirements of bridge construction.The creep and dynamic action simulation of goaf filling body is carried out.The creep model under creep action is chosen as the developed constitutive model.The attenuation method of model parameters is used in dynamic action.The simulation results show that GCGFB can maintain long-term stability under dynamic and static load,and the long-term filling effect of goaf is good.The paper has 63 pictures,16 tables,and 83 references.