| With the rapid development of urban construction and population,traffic congestion has become one of the maj or problems in China.In order to improve the urban traffic environment,the development of underground space plays an important role in urban construction.As a way of urban public transportation,the subway can make full use of underground space and alleviate the pressure of ground traffic.It has become the main way of urban infrastructure and transportation in the 21st century.According to the data of China Association of Metros(CAMET),as of 2018,493 cities in 72 countries and regions have established urban rail transit with a total mileage of more than 26100 km.Among them,metro account for 54%.And 35 cities in China have opened urban rail transit,with a mileage of 5766.7 km.The urban geological conditions in China are complex,and the construction of metro will inevitably cross the karst areas.It will encounter many disasters,such as ground collapse,water inrush and so on,which will result in significant economic losses and casualties,and affect the design,construction and safety operation of tunnels.In this paper,the fine exploratory characterization of karst caves and the stability of shield tunnels are the main research contents.Based on the shield tunnel project of Jinan Metro,combined with laboratory experiments,theoretical analysis'numerical calculation,model test,software development and field application,the refined detection method,morphology characterization and coupling calculation.stability analysis of surrounding rock,and prediction model of critical safety distance in karst area are studied.The main results are as follows:(1)On the basis of systematic analysis of hydrogeological characteristics of spring area,the development conditions and mechanism of karst area along Jinan line are analyzed.Three type of development mechanisms are put forward,and it includes direct karst type,indirect karst type and confined karst type.The comprehensive exploration system of karst disaster sources combining "from the near to the distant" and "regional refinement" is proposed.The karst development scale,filling type and elevation characteristics along Jinan Metro are revealed,and the spatial location relationship between karst caves and shield tunnels is analyzed statistically.These contents provide geological basis and research guidance for subsequent research.(2)The application effects of laser detection in anhydrous caves and water?bearing caves are discussed.In order to solve the problem of limited detection distance caused by laser fading too fast in water,the quantitative attenuation characteristics and maximum detection distance of multi-wavelength laser in water?bearing karst caves were studied.The attenuation characteristics of different wavelength and power laser in various fillings of water-bearing karst cave and turbidity were explored.According to the test results,the optimal selection of detection laser in actual project is studied and the three-dimensional point cloud method of cave shape is obtained.The calculation formula of point cloud coordinate splicing under complex karst cave is solved and applied to engineering practice.(3)Based on the point cloud processing platform of Geomagic,a method for determining the optimal sampling interval of point clouds is proposed,and a Geomagic-Comsol coupling numerical model interface is constructed to realize the numerical analysis of the stability of complex karst caves.The mechanical properties of surrounding rocks under simplified karst cave model and complex morphology caves model are compared and analyzed,and the results show that the plastic zone of the local irregularity is more concentrated.(4)Aiming at the high irregularity of karst cave geometry,three-level digital characterization parameters of geometric boundary are proposed.The first level includes Shape Factor(SF).Aspect Ratio(AR)and Sphere Like(SL),the second level includes Angularity Factor(AF)and Convexity Factor(CF),and the third level is Roundness Factor(RF).Based on the principle of discrete Fourier transform,the transformation process of geometric boundary from time domain to frequency domain is realized by means of equal progressive angle sampling and waveform analysis.Fourier universal morphology characterization factor is constructed,and the response relationship between Fourier morphology characterization factors of different sequences and three-level characterization parameters is determined.The XVI digitized quantitative characterization parameters of complex morphology caves are simplified to two(D2 and D3)to provide the research basis for the establishment of the response relationship between mechanical properties and geometric form.(5)Based on the upper limit method,a three-dimensional mechanical instability model of karst cave located in front of the tunnel,above circumferential side of the tunnel and below circumferential side of the tunnel is established,and the analytical solution of critical thickness of rock mass is deduced.The sensitivity analysis curves of different parameters to critical safety distance are drawn by Matlab,and the influence of rock mass parameters,karst cave parameters and geometric parameter on the critical safety distance are analyzed.The 36 numerical calculation conditions of irregular geometric karst caves were designed,and the Fourier morphology characterization factor of the geometric boundary with "Honest Azimuth" was calculated.The critical safety distance between irregular karst caves and tunnels under corresponding conditions was calculated by optimizing dichotomy and instability criterion of the rock mass.Through the numerical results of different conditions,the quantitative response relationship between critical safety distance and geometric form of karst is established under three mechanical models.(6)A test system for composite EPB shield tunneling in spring area is developed.The model test system includes a three-dimensional visualization simulation system,a composite EPB shield tunneling test machine,a 3D printing simulation system,a multi-parameters intelligent control system of water pressure in karst caves,a laser scanning measurement system for ground settlement and a multi-data monitoring and acquisition system.The composite EPB shield tunneling test machine can simulate the shield construction in different strata,and the unearthed function is good.Shield tunneling machine can adjust its height according to the size of model.It has the characteristics of multi-function,intelligence and high reusability,so as to better meet the geological requirements of shield tunneling in urban metro.The water inrush model test caused by shield tunneling is carried out.Based on the 3D printing technology of soluble materials,a new preparation method of irregular karst caves is proposed.The ground settlement during shield tunneling is monitored in real time by three-dimensional laser real-time scanning technology,and the three-dimensional ground settlement models at different excavation stage are constructed.The evolution law of physical information during shield tunneling is revealed through data collection and analysis.State identification of the process of water inrush during excavation by the moisture content of the sample.(7)The software of multi-parameter characterization and stability criterion is developed.It includes engineering information and karst database module,multi-parameter input and initial evaluation module,shape characterization and visualization module,safety distance correction calculation module,safety treatment scheme and intelligent decision-making module.The software can establish a database of karst development characteristics.It has the visualization function of karst cave morphology,and can analyze automatically the three levels of karst cave morphology characteristics through polar coordinates in Matlab.Furthermore,it can analyze whether the karst cave need to be treated.The refined exploration data can provide guidance for the governance.The software system can provide pertinent governing parameters and treatment scheme to optimize the grouting effect and be applied to Jinan metro project. |
PDF Full Text Request