| China's karst landforms are widely distributed,especially in the western provinces of Guangxi,Guizhou,Yunnan,etc.,and as the transporta tion infrastructure continues to advance to the western region,the route design cannot completely avoid the cave development area.When the subgrade under the cave,it is prone to collapse,causing engineering accidents.Therefore,this paper relies on National Natural Science Foundation of China project “The study of pile vertical bearing mechanism and design calculation method in karst area”(Number: 51278187),the following research work is carried out on the stability of the roof of the cave under the karst area:Firstly,the effect of the subgrade acting on the roof of the cavern is divided into permanent and variable effects according to the variability of time,and the combination of load effects is combined with the current standards,then the influence of the main factors on the stability of the roof of the cave is considered and the assumptions is made reasonably.It is assumed that the additional stress at any point on the roof of the cavern under the non-uniform subgrade load is obtained based on the Boussinesq solution,the calculation results are superimposed on the self-weight of the soil and the roof to obtain the maximum bending moment and maximum shear force of the roof of cave,and then the roof is subjected to bending and shear stability analysis.Secondly,the main methods for analyzing the stability of karst roof in karst area are summarized from qualitative,semi-quantitative and quantitative aspects.In view of the current theoretical methods,the stability of single-cavity caves under the subgrade is explored,and in actual engineering,there is the possibility of two deep holes under the subgrade.Therefore,after the second iteration is completed by the Schwarz alternation method,two holes are obtained.The stress at the most dangero us point on the side of the circular cave is deeply buried,and the stability of the soil is judged by the Griffith failure criterion.Then,the factors affecting the stability of the cave are analyzed.Thirdly,the upper bound theorem and the lower bound theorem of finite element limit analysis are briefly introduced,and the finite element limit analysis method is used to eliminate the advantages of artificial static stress field and maneuvering speed field.The finite element limit analysis software OptumG2 is used to focus on the overlying soil.The effects of layer load,karst span,karst height,rotation angle,horizontal distance,vertical distance and rock physical and mechanical parameters on the ultimate bearing capacity of the subgrade and the ult imate failure mode of the karst roof.Finally,when the cave roof is subjected to stability check,there is the possibility of instability,the geological survey report and geophysical data should be combined to formulate the scheme for the construction of the subgrade in the karst area.Aiming at the diseases that the underlying karst caves may cause to the subgrade,the general treatment techniques of the filling method and crossing method for subgrade are briefly introduced.The application of the strong tamping method in the treatment of the karst area is discussed,and the treatment technology is successfully applied on the actual project of Tanshao Expressway and Guiwu Expressway. |
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