Study On The Seismic Reinforcement And Shaking Table Test Of The Sinking Loess Cave

The loess cave is the main building construction form on the Loess Plateau.It conforms to nature,leans against mountains and cliffs,has simple construction and low cost.Among the soil layers,it has better fire performance and longer service life.Therefore,the loess cave dwelling is a model of "low cost,high environmental protection,and low energy consumption".At the same time,the loess cave dwelling also carries a lot of red spirits,such as the Zaoyuan Revolutionary Site and Yangjialing Revolutionary Site.The red bases in the form of these cave groups symbolize the outstanding qualities of the revolutionary predecessors who are self-reliant and hard-working.For hundreds of years,the loess cave dwellings have long been subjected to natural environment weathering,rain erosion and earthquakes,coupled with human damage and lack of protection awareness,making the status of loess cave dwellings living conditions not optimistic.However,according to research and literature review,it is found that a large number of existing loess caves are located in high-intensity earthquake fortification areas.Once an earthquake disaster occurs,it will directly endanger the lives and property of the people.However,most of the domestic and foreign studies on the reinforcement of loess kiln tunnels are still static,and there is a lack of research on reasonable reinforcement schemes from the perspective of structural earthquake resistance.Based on this research group,the shaking table test of the model loess cavern model reinforced by brick arch coupons was carried out,and the seismic performance and seismic failure mode of the reinforced loess cave model were studied and analyzed,which provided an important theoretical basis for the future strengthening and repair of the loess cave model.The main work of the thesis is as follows:(1)The Huangtukeng kiln in Sanyuan County,Shaanxi Province was selected as the prototype,and an underweight test model was designed based on Bucking-ham πtheorem and the performance of the shaking table equipment,in addition,the layered shear box is used to simulate the infinite boundary conditions around the loess cave,so as to ideally eliminate the reflection and scattering effects of seismic waves at the boundary.(2)Aiming at the damaged loess cave model,the brick arch voucher,water glass and the replacement method of the failed soil mass were adopted in total.In order to better compare the aseismic reinforcement effect of kiln caves,the reinforcement methods of the east and west kiln caves are slightly different,thus laying a theoretical foundation for more effective evaluation of the reinforcement scheme.(3)In order to study and analyze the dynamic characteristics and dynamic response characteristics of the reinforced loess cavern,Xi’an artificial wave,Taft wave and El-centro wave were selected as the ground motion input.The natural frequency,damping ratio,stiffness,acceleration response,displacement response,shear force distribution and energy dissipation curve of the structure under earthquake were measured.The analysis results show that the first-order natural frequency of the model structure is 7.227 Hz,and the first-order damping ratio is 5.5%;the displacement response of the cave vault is weaker than that of the mid-leg and side-leg arch feet,but the acceleration response of the vault is strong.The acceleration response of the mid-leg and side-leg arch feet is different;the displacement response and acceleration response of the mid-leg and side-leg arch feet of the cavern are different,and the changes of the two responses along the depth direction are different.(4)Combined with the experimental phenomena and experimental analysis results,the seismic performance of the reinforced loess kiln tunnel was studied.The research results show that: under the action of the lateral earthquake,the model produces shear deformation in each soil layer,but because the arch vault is reinforced with brick arch,the stiffness is enhanced,so the shear cracks are transferred from the original vault area to the kiln top area;During the entire loading process,the middle leg has cracks extending obliquely downward and the side leg is almost not damaged.This is because the side leg is constrained by the surrounding soil and the overall stiffness is greater than the middle leg.Shearing of the east kiln hole The damage occurred later and the damage was smaller than that of the west kiln hole,which shows that the reinforcement effect of the reinforcement of the east kiln hole is significant.(5)The anti-seismic behavior and performance quantification index of sinking loess kiln caves were studied.The results are as follows: the arch foot-vault convergence deformation was used to quantify the seismic performance of loess kiln caves,on the basis of experimental study of seismic performance of loess cave before and after reinforcement,five performance level failure criterions were proposed according to their failure forms,and the corresponding arch foot-vault convergence deformation limits were given.It is suggested that the limit values of convergence deformation of arch foot-vault corresponding to normal use,temporary use,use after repairing,life safety and near collapse are 1/400,1/205,1/100,1/60and1/40 respectively.(6)From the perspective of engineering cost,scientific calculation and analysis of the seismic reinforcement technology of the loess cave dwelling were carried out.The analysis results show that the seismic reinforcement technology proposed in this paper has good economics and generalizability.The average reinforcement cost per square meter is only 62.18 yuan.It can become the main technical means for strengthening and repairing loess caves in the future.