Study On Bearing Mechanism And Treatment Technique Of Karst Roof Under Subgrade

With the rapid development of chinese economy,the development of the western region is a major strategic task that must be pushed forward.Therefore,the construction of basic transportation facilities is also constantly pushing forward the central and western regions.There are large areas of karst landforms in the central and western regions,which will form underground rivers,underground rivers and karst caves after the dissolution of groundwater.In the construction of embankment in the above karst area,the potential karst cave will be a difficult factor to ignore in the design of embankment bearing capacity.Therefore,the bearing mechanism and treatment technology of karst roof under subgrade are studied in this paper in combination with the research innovation project of Hunan Province Postgraduate Students"Research on Bearing Mechanism of Pile Foundation under Complex Loading and Related Foundation Reinforcement Method in Karst Area".Firstly,the basic assumptions and theoretical basis of the limit analysis method are introduced in detail,and the solving steps of the finite element limit analysis method are introduced,and then the relevant numerical model is established based on the finite element limit analysis software Optum G2.After verifying the correctness of the analytical model,a dimensionless ultimate bearing capacity parameter N_c was defined to measure the influence of various factors on the undrained bearing mechanism of the karst cave under the subgrade.Through a series of parameter analysis in-depth analysis of the single cavity when the load eccentricity e/B sized,karst cave,karst cave,cave shape and the change of soil shear strength k B/c_u0 dimensionless parameters on the influence of the subgrade bearing capacity,test results indicate that the NCS with e/B,R/B decreases with the increasing of diameter（hole）,with the alpha/B（cave of eccentricity）,beta/B（cave depth）,the k B/cu0 increases,the e/B and k B/cu0 is the key factor that affect the bearing capacity of subgrade.Then the bearing mechanism of three kinds of double circular karst caves with different layout under eccentric load is discussed by using similar method.In addition,three typical failure modes are summarized while analyzing the effects of each variable.The conclusions can be used for reference in engineering design.Second,more intuitive analysis of the underlying caves load-bearing mechanism of subgrade,designed load eccentricity,thickness of cave roof subgrade underlying cave,cave position under the action of indoor model test,get the limit bearing capacity of subgrade underlying cave when load eccentricity,ultimate bearing capacity curve of karst cave eccentricity,through the analysis of the results of indoor model test after the conclusion obtained by finite element limit analysis method to confirm and supplement.Next,when the bearing capacity of the roof of the karst cave under the roadbed fails to meet the requirements,it is necessary to take targeted treatment plans for the roadbed in the karst area in combination with the karst special geological survey report.This paper mainly introduces the common grouting method and crossing method in the treatment of karst subgrade,and then emphatically discusses the design parameters of the dynamic compaction method in the treatment of underlying karst subgrade.Finally,based on the example of Guiwu Expressway,the finite element limit analysis is carried out to find the safe thickness of karst roof,and the results that meet the requirements of roof thickness in the field are obtained through comparison.