Study On Calculating The Safety Thickness Of Rock Socketed Pile Roof In Karst Area

With the further development of highway construction in our country,some highway bridges have to be designed to through the karst area,resulting in the bridge foundation being build above the karst roof.As the hydrogeological conditions in karst area are very complicated and there are many influencing factors,the existence of underlying karst cave greatly enhances the difficulty of foundation in designing and construction,and seriously affects the construction of highway and bridge in karst area.Therefore,it is necessary to study deeply on bearing characteristics of karst roof and its minimum safety thickness.Based on former researches and combined with National Natural Science Foundation of China project “The study of pile vertical bearing mechanism and design calculation method in Karst area”(Item Number:51278187),following studies have been made:Firstly,this paper summarizes the researching condition,classification and application of pile foundation,arranges the characteristics of karst and its harmfulness for the project.By analyzing the research of karst piles at home and abroad,the load transfer mechanism of karst piles is summarized.Secondly,the calculation model of the safety thickness of cave roof is established with considering the influence of embedded rock in the karst area.Combined with the elastic mechanics,the formula to check the bending stability,punching shear stability and shear stability of karst roof is infered.The feasibility of this method is verified through an engineering example.The effect of the ratio of the thickness to span of rock and the friction coefficient of the pile on the determination of the safe thickness of the karst roof are analyzed.Then,a finite element model is established by ABAQUS witch considers the influence of embedded rock.The engineering examples and the method in this paper are used to verify each other.By changing the roof span,rock thickness and ultimate tensile strength of rock,researching the impact of them on the roof stability,and get the change rule of the safety thickness under different thickness-span ratio conditions.Finally,through calculating the engineering project with the method in this page,the traditional method and the numerical method,the difference between the method and the traditional method is compared.According to the possible problems in the construction of the karst pile,the corresponding solution had been presented.