Centrifuge Tests On Ground Surface Rupture Induced By Strong Earthquake

Surface ruptures caused by strong earthquakes have always attracted much attention in site evaluation.How to predict the overlying soil deformation characteristics and surface rupture law caused by fault displacement scientifically,and to specify the setback distance of engineering construction are the current research focus,which is the difficult problems in the formulation of seismic codes,as well as one of the key issue to make the best use of urban land resources.The solution of this problem requires a lot of earthquake disaster data,however,The lack of data reflecting the process of seismic surface rupture has become a bottleneck for further research in this field.Therefore,experiment,which is widely regarded as an important means for modern science to explain and explore the laws of nature,will undoubtedly become a powerful tool and effective method to overcome this bottleneck.Based on the current research results,a geotechnical centrifugal model test is used to study the surface rupture of the seismogenic fault in this paper.The deformation process of overlying soil under reverse fault dislocation is simulated successfully by means of self-designed model test parameters and self-developed displacement device;the deformation evolution process of dry sand and wet sand surface are given through the quantitative analysis of surface monitoring data and the application of PIV,which makes it possible to simulate the complex seismic geology problem of soil deformation and rupture.In addition,new phenomena not mentioned in previous tests have been observed due to the increase of simulated thickness and monitoring accuracy of overburden soil,which provided objective test data for the revision of relevant specifications.The following main research conclusions are drawn.1.Review on the research progress of different methods in the field of surface rupture of strong earthquakes,the further research work is put forward.The frontier research of all kinds of tests in the field of surface rupture of strong earthquakes are summarized,the concepts of earthquake,active fault,engineering active fault and surface rupture of strong earthquake and their relations are clarified.The existing problems are discussed and the future research directions are put forward.2.A model box and its accessory equipment for simulating reverse fault dislocation under high-g gravity environment are designed,which is helpful to achieve the expected test goal.In this paper,the selection of centrifuge,the development of stagger,error analysis,monitoring system layout and boundary simplification treatment are analyzed,the model box and auxiliary device for model test of thrust fault centrifugation were developed,try to reduce the resistance of the pushing process while improving the sealing of the boundary as much as possible,so the simulated thickness of overlying soil on the thrust fault was successfully increased to 40 m,which is the largest soil thickness simulated by geotechnical centrifuge.3.The relevant test parameters are designed and demonstrated,which provides a guarantee for the development of the test.Based on the test conditions and the earthquake disaster data,the test parameters of the reverse-fault centrifugal model are designed,which mainly includes the geometric parameters of the model,the physical parameters of the model,the mechanical parameters provided by the centrifuge,the geometric parameters and kinematics parameters of surface of bedrock.According to the performance of the centrifuge and the principle of similarity,the rationality of the test design parameters is demonstrated,which provides reference for relevant researchers to carry out experimental research in this field.4.The characteristics of surface deformation evolution are summarized,and the surface avoidance distances corresponding to different magnitudes are given,which provided the experimental support for the formulation and modification of related specifications.Based on the quantitative analysis of a large number of high-precision surface monitoring data obtained in the 100 g gravity environment,the deformation characteristics of the surface with the increase of the amount of bedrock dislocation during the process of thrust fault dislocation are presented.The critical dislocation amount of the surface uplift and the exposed position of the surface rupture have been estimated,and the translation rules of the surface scarp have been studied,accordingly,the surface deformation process can be divided into four stages: surface uplift stage,uplift deformation stage,escarp translation stage and deformation mitigation and lag stage.Based on the standard of dangerous building appraisal and the statistical relationship of seismic damage parameters,ground avoidance distances corresponding to different magnitudes are given.5.The deformation characteristics of soil and the law of fracture plane expansion were revealed,It enriches the research results of surface rupture caused by strong earthquake.The Geo PIV technology was used to study the soil deformation and shear strain zone of dry sand and wet sand under different bedrock dislocation,accordingly,three stages of the development of fracture plane are put forward,the mechanism of soil deformation caused by reverse fault movement are revealed.Finally,a method for predicting the expansion of soil fracture and determining the up-breakpoint of fault are given,which provides an important experimental basis for engineering application.Because of the complexity of surface rupture caused by earthquake,the geotechnical centrifuge model test is an important way to explore the problem.The results of this research have certain theoretical significance and important engineering value for further studying the soil deformation and determining the avoidance distance of the surface rupture caused by the reverse fault,It also provides a reference for the study of seismic surface rupture by geotechnical centrifuge.