Studies On Collapse Mechanisms And Stability Analysis Of Karst (Soil) Caves Under Embankments

Karst collapse is the most prominent geological hazard in covered karst areas, which brings threat and influence to the life and production of human beings, especially in transportations. The stability of embankments in karst areas, stability evaluation of karst (soil) caves, design and evaluation of their reasonable treatment methods are still problems that have not been well solved. Therefore, the contract section All of Yong Wu Highway was taken as the research object, the karst geology engineering was seen as the geological background, and the typical geological generalized model was abstracted. To contribute to the settlement of above-mentioned problems, a large number of theoretical analysis and numerical simulations were carried out by establishing similar models. The main research contents are as follows:(1) First, various mechanical mechanisms of superposition and coupling of karst collapse were introduced briefly. The mechanical mechanisms of several modes of karst collapse were cognized systematically. Then, the 3D numerical models which are identical to the indoor testing models of tunnels were established by using the finite element software ABAQUS and karst collapse mechanisms were:analyzed by using the loading coefficient method and finite element strength reduction method. By comparing the results between the numerical simulations and indoor model tests, the feasibility of strength reduction method of the karst stability analysis was verified.(2) The stress distribution states of circular karst caves, ellipsoidal karst caves and rectangular karst caves were analyzed by using elasticity theory. Then the stress state distribution equations based on the Mohr-culomb’s, Tresca’s, Mises’ or Drucker-Prager’s failure criterion were deduced. Meanwhile, the influence of groundwater on the collapse of soil caves was briefly introduced.(3) Aimed at the main effect factors which may affect the stability of karst caves and embankments, including different roof thicknesses of karst caves, different embankment heights, different locations, heights and spans of karst caves, a large number of 3D numerical simulations were conducted. The method which combines the results of finite element analysis with the bending, shear and tensile strengths in structural mechanics were presented to estimate the safety thicknesses of karst cave roofs.(4) Aimed at the main effect factors which may affect the stability of soil caves and embankments, including different embankment heights, different locations, heights and spans of soil caves,3D numerical simulations were carried out. At the same time, the safety depths of the foundation treatments in soil cave areas were determined by integrating the results of numerical analysis and half-qualitative method. Finally, the effective stress finite element method which is able to consider the coupling behaviours of seepage and deformation was adopted to analyse the influence of water table fall on stresses, displacements and pore pressures around the soil caves.(5) Based on the treatment measure of soil caves in practical engineering, the 3D finite element model which is similar to the actual situation was set up. Assuming a soil cave subgrade is treated or not, the settlements of the embankment, roof stability of the soil cave and its lateral displacements were compared. It can be used for references in similar engineering designs.