Based On The Non-contact Monitoring System Of Cemented Sand And Gravel Dam Structure Model Test Research

The cemented sand and gravel dam（CSG dam）is a new type of dam improved and developed on the basis of the concrete face rockfill dam and the roller compacted concrete gravity dam.It has many advantages,such as simple construction,material saving,overcurrent during construction,good seismic performance and low requirements on foundation conditions.It is regarded as a“green dam type”with broad development prospects.In order to explore the safety mechanism of its operation,domestic and foreign scholars have carried out model test research on the dam type.However,the model material leads to the problem that the ability of the naked eye to identify cracks is weak,the arrangement of monitoring facilities is easy to affect the dam structure,and cannot be monitored globally.In this paper,the Oyuk CSG dam in Turkey is taken as the prototype,and the non-contact monitoring system designed by ourselves is introduced into the structural model test of CSG dam.The strain,displacement,failure mode,failure mechanism and overload safety of the model are analyzed.At the same time,the nonlinear finite element method is used to carry out numerical simulation and comparative analysis,which verifies the effectiveness of the model test and the non-contact monitoring system.The research has important theoretical significance for further revealing the spatial and temporal evolution mechanism of CSG dam failure and establishing more accurate strength criteria.The main contents of this paper are as follows:（1）A series of experimental studies were carried out on the model materials of CSG dam.Based on the neural network prediction model of physical and mechanical parameters of CSG model materials accumulated by the research group,five groups of material ratios were randomly selected for specimen pouring.The triaxial shear test was carried out on the model specimens,and the elastic model E,cohesion C and friction coefficient f were all within the error range,which verified the validity of the CSG material prediction model.At the same time,the model specimen is selected to carry out the PIV pre-test.By judging the critical failure state of the model material,it is shown that the damage caused by the external force can be reflected in the displacement vector and displacement cloud diagram in time.The failure criterion of the model is:when the displacement vector presents a chaotic state and the displacement velocity difference presents a large and obvious color contrast,the model is destroyed.This experiment provides a research basis for the introduction of non-contact monitoring system into CSG dam structure model test,and provides a new method for systematically studying the failure process and failure mechanism of CSG dam（2）The non-contact monitoring system is used to carry out the application research on the failure test of CSG dam structure model.The test results show that the main failure modes of CSG dam model are shear failure at dam heel and penetrating cracks between dam body and dam foundation.And during the crack penetration,the dam body will show a trend of turning upstream counterclockwise,resulting in dam heel subsidence and dam toe uplift.Through the test,the deformation and displacement distribution characteristics of the dam are analyzed,and the crack initiation safety factor K₁=2.8,the nonlinear safety factor K₂=2.8～4.4,and the ultimate overload safety factor K₃=4.4 of the Oyuk CSG dam are obtained.The difference between the PIV displacement capture results and the traditional displacement meter monitoring results at the dam crest of the model test is analyzed,and the displacement values,inflection points and displacement trends of the two corresponding parts are almost the same.In addition,PIV can still analyze the displacement results and obtain the displacement characteristics of the whole dam body in places where the traditional displacement meter cannot monitor,such as the dam foundation surface and the upstream side of the dam body.In the process of crack evolution,the high power laser lamp can well monitor the process of crack initiation,development and penetration,and has good applicability in the model test.The feasibility of the application of non-contact monitoring system in CSG dam model test is proved.（3）The nonlinear finite element calculation of Oyuk CSG dam is carried out.The results show that the tensile stress occurs at the dam heel and the shear failure occurs in the model,which is the weak position of CSG dam.The model shows a displacement trend of counterclockwise deflection to the upstream based on the dam toe;the finite element calculation limit overload safety is K_p=4.0.The finite element calculation results are basically consistent with the model test results,which fully illustrates the good effect of the two methods in the stability analysis of CSG structure and the feasibility of the application of non-contact monitoring system in model test.In summary,the CSG dam structure model test in this paper can better simulate the damage of the prototype structure.The introduction of the non-contact monitoring system is helpful to explore the mechanical characteristics,deformation development process and stability of the whole structure.The test results are basically in line with expectations.