| In recent years,there have been frequent road surface subsidence accidents.For example,the West Third Ring Expressway auxiliary road in Zhengzhou has experienced as many as 18 road subsidence accidents in just eight months.Road collapse accidents not only damage the pavement structure of the city,but also pose a serious threat to the surrounding buildings and the safety of people’s lives and properties,causing a strong negative social impact.Therefore,the prediction and repair of urban road collapse accidents has become one of the hot spots in the society.In this paper,the indoor model test and numerical simulation method are used to study the formation and development of underground voids caused by pipeline leakage under traffic load,and the influence of underground cavity depth and shape on the stability of urban pavement.The following researches have mainly been conducted:(1)Taking the Zhengzhou area as the background,the physical and mechanical parameters of Zhengzhou silt were obtained by laboratory tests such as liquid-plastic limit test,compaction test and specific gravity test,and dynamic triaxial test was used to study the modulus of Zhengzhou silt with cumulative axial strain.The trend of change gives the formula for attenuation of Zhengzhou silt.(2)A model test of the road subsidence caused by pipeline leakage was conducted.A visualized semi-structural model device was made and a detailed design of the indoor test program was given.Influence of the type of load,the depth of pipeline,the distance between pipeline and runoff channel,pipeline and runoff channel relative position were considered separately.The development of the underground caverns induced by the pipeline leakage and the expansion mechanism were studied.(3)Model test results show that compared to the static load,the dynamic load will increase to the time of the final failure;when the dynamic load value is small,the upper layer of soil will be compacted and the stability of road increase.While the dynamic load value is larger,it will accelerate the expansion of cracks and causeground collapse accidents.An increase in the distance between the pipeline and the lower drain channel will increase the damage duration and the destruction surface,the probability of the void extending to the surface will also increase.Increasing the depth of the pipeline can reduce the disturbance of the load to the underground cavity,the underground cavity is slow to develop,the stability is better,and the surface settlement is also smaller.When the formation time of the drain channel is pushed back,the soil’s soaking area expands,the self-weight of the soil increases,the strength and deformation modulus weaken,the formed void size increases,the surface settlement value increases,and the surface is more prone to collapse.(4)Using the USDFLD user subroutine to conduct the secondary development of ABAQUS,then introduce the attenuation model of the soil modulus following the dynamic load into ABAQUS.The finite element model of the underlying underground cavity road was established to study the influence of the type of load,depth of underground burial and the size of void on pavement stability.The results show that when the pavement deformation is large,the traffic load must be considered as a dynamic load in order to obtain a more accurate result;the road stability increases first and then decreases with the increase of the soil thickness over the void.The road surface settlement increases with the increase of the height and span of the void,after reaching a certain critical point,the settlement value will increase suddenly,and the road surface will be destroyed. |
