Study On Cavity Collapse Mechanism And Rapid Detection Method Of Underlying Voids In Urban Roads

The urban road collapse has the characteristics of concealment,sudden,inducement and harmful.With the development of underground space in city,The laying of underground pipe network and the construction of underground track affect the stability of subgrade and the safety of pavement structure,It even caused the collapse of city surface road,posing a serious threat to traffic,pedestrian safety and ground building.Therefore,the in-depth study of the formation mechanism and main disaster factors of urban road collapse has important theoretical and practical significance to prevent and control such urban geological disasters for the protection of personal safety and the reduction of property losses.Based on the statistical analysis of 125 cases of road collapse in four typical cities in the southeast of China,this thesis considers that the formation factors of underground cavities in urban road collapse in the southeast of China are soil properties,karst,heavy rainfall,disturbance of underground engineering and leakage of underground pipelines.The leakage of underground water pipes(including water pipes and rainwater and sewage pipes)is the main source of the formation and development of underground cavities.Because the change of groundwater level and the repeated action of vehicle load are the inducement of accelerating the development of cavity and causing the collapse of pavement.The main work and research results are as follows:1.Based on the theory of groundwater dynamics,the process of leakage failure of underground pipeline is analyzed,and the expressions of critical groundwater level drop amplitude and critical groundwater velocity are derived when clay layer and sand layer form underground cavity around the soil around the leakage failure of underground pipeline.Based on the plastic limit equilibrium theory,the critical span before the collapse state of the underground cavity is deduced,and the relationship between the critical span and the thickness of the overlying soil layer,the characteristics of the surrounding rock and the external load is analyzed.2.The mechanical model of vehicle load with two degrees of freedom in vehicle road coupling vibration system is established.The analysis shows that when the vehicle speed is a certain value,the vehicle road coupling system resonates,and the vehicle cycle load is the most harmful to the vehicle road coupling system;the smoother the road surface,the less the vibration of vehicle load,the less the additional cycle load the road structure bears,and the subgrade The higher the stability.3.This thesis analyzes the basic conditions and collapse mechanism of four collapse modes,i.e.undercutting,blasting,vacuum suction and vibration,establishes the mathematical model of the road structure of the underlying cavity,and analyzes the influence of load type,buried depth of underground cavity and cavity size on the stability of the subgrade by using FLAC3 D.The results show that the vehicle load has a large dynamic effect on the deformation of the pavement;with the increase of the depth of the cavity,the road stability increases,and finally tends to be stable;with the increase of the height and span of the underground cavity,the road settlement first increases to the critical value,and then suddenly decreases,and the road appears a destructive trend;with the decrease of the cohesion of the surrounding rock and soil,the road settlement suddenly increases,and the soil mass suddenly increases Cohesion has a great influence on the stability of road voids.4.A variety of underground cavity models are established,and GPRMAX software is used to simulate and analyze the response characteristics of reflected electromagnetic wave,such as phase,amplitude and two-way travel time.The detection results show that the effective and rapid detection of underground cavities under urban roads can be realized by reasonably arranging survey lines,selecting appropriate technical parameters and adopting GPRMAX method.Selecting appropriate technical parameters and adopting GPR method can realize the effective and rapid detection of underground cavities in urban roads.