Study On Failure Behavior And Vulnerability Of Masonry Structure Caused By Ground Cracks On Slow-moving Landslides

Since the Three Gorges Reservoir has been impounded,most of the landslides have shown seasonal deformation characteristics of long-term slow and short-term acceleration under the effects of reservoir water level fluctuation and rainfall.The buildings on these landslides were damaged by the slow ground displacement,resulting in serious threats to the lives and property safety of the residents.However,the traditional methods for assessing the vulnerability of buildings to landslide hazards are more focused on fastmoving landslides.Qualitative and semi-quantitative methods are mostly used,and less attention is paid to the vulnerability of buildings on slow-moving landslides.The article takes the slow-moving landslides in the Three Gorges reservoir area and the masonry structures as the research objects.The landslides ground displacement characteristics and the movement patten are considered.The failure behavior of masonry structure impacted by different landslide deformation.A quantitative evaluation model of vulnerability on masonry structure caused by different ground cracks on slow-moving landslides is built by field investigation,physical model test and numerical simulation method.Finally,the vulnerability model is validated by the field examples.And the suggestions and measures for disaster prevention and mitigation in the construction of buildings in mountainous areas are proposed in terms of building site selection and construction properties.The main contents and results are as follows:(1)The research on the movement patten of slow-moving landslides in TGR area based on filed monitoring data.104 colluvial landslides in TGR area is taken as the study object.During the observation period and accelerated movement period,the landslide ground displacement,the moving velocity and ground deformation properties are analyzed.The ground cracks of different movement stages,different positions and different characteristics are summarized.The main results are shown as: All landslides almost go through the uniform movement stage,and the elapsed time is very long and the landslide velocity is smaller.When the landslides are affected by the rainfall and reservoir water fluctuation during the flood season,it will appear to local glide,which just corresponds to the periodic short acceleration movement period.The macroscopic deformation of the ground surface basically matches with the monitoring curve.(2)The damage characteristics analysis of masonry structures on slow-moving landslides based on field investigation.The detailed investigation of slow-moving landslides and masonry structures in TGR area is done by the specially designed field survey form for the damage state of masonry structures affected by landslides ground cracks.The failure behaviors of the buildings affected by landslide ground cracks is summarized.Finally,the different damage response of masonry structures under the influence of different ground cracks of landslides are analyzed.The main results are shown as: among the damaged parts of the buildings,cracks near door and window openings and cracks in walls and corners accounted for the largest percentage.The masonry structures affected by different landslide cracks show different damage responses.(3)Experimental study on physical models of failure behaviors of masonry structures affected by ground cracks on slow-moving landslides.Masonry building models are made of brick and concrete at a scale of 1:10 to physically simulate the damage in structures caused by ground tension and shearing cracks commonly developed on slowmoving landslides.The tension and shearing crack opening process is simulated through a load-controlled table with an aperture on which the building model is constructed.The strain on the wall and its foundation were measured,and the damage of the model(crack formation and evolution for each loading step)was collected,described and analyzed.The main results are shown as: the strain values in the model foundation and wall will change suddenly when the model appears to cracks.The model damages start at the foundation,with cracks extending from the wall bottom to the top or conners of wall along the foundation damaged position.The macroscopic cracks of the walls in both models are basically consistent with the field observation.(4)Numerical simulation study on damage response of masonry structures affected by ground cracks on slow-moving landslides.Based on the experimental model,the damage responses of masonry structure under tension mode and shear mode are analyzed by using ABAQUS finite element method based on the separated modeling approach and concrete plastic damage theory.The numerical simulation results are compared with the physical model test results.And then according to the same loading protocol and model parameters,the failure loads of masonry structures under different angular between ground tension cracks and the building,and the damage response of masonry structures under the ground extrusion deformation are analyzed.The main results are shown as: the numerical simulation results are basically consistent with the test results,indicating that the numerical simulation is reliable.When the angle between the ground tension crack and the long axis of the building is 30°～45°,the structural resistance is weakest and most vulnerable.The macroscopic cracks of the walls in numerical model under extrusion are basically consistent with the field observation.When the same masonry structures are subjected to ground tension,shear and extrusion respectively,the damage degree of the models from high to low is tension mode,shear mode and extrusion mode.(5)Quantitative vulnerability modeling of masonry structures affected by ground cracks on slow-moving landslides.Firstly,based on the field investigation and the code,a quantitative criterion for the damage degree of masonry structures is proposed.Then the structural danger level is divided into 4 classes,and the vulnerability value of the structure can be obtained by constructing 4 different member functions and damage percentages.The vulnerability curves are constructed based on the physical model test data.And then the vulnerability curve is then verified by filed cases.Finally,the suggestions for disaster prevention and mitigation in the construction of buildings in mountainous areas are proposed from the site selection stage,construction stage and maintenance stage respectively.The main results are shown as: based on the quantitative criteria of damage degree of masonry structure and vulnerability analysis method proposed in this article,the vulnerability curves of masonry structure under landslide tension and shear ground crack are obtained by Weber function,and the fittings are as high as 0.996 and 0.944.Based on the field cases,the vulnerability curve of masonry structure under the influence of ground tension cracks is verified.The relative errors between the calculated and measured values are 4% and 5.1%,respectively,indicating that it has a good model fit.