Research On Design And Calculation Method Of Pile In Karst Area Considering Lateral Resistance Of Pile And Rock

China’s karst landforms are widely distributed,especially in the western mountainous areas of Guizhou and Yunnan.When the pile foundation is in the karst development area,the collapse of the roof of the piles is very easy to occur,resulting in serious engineering accidents.Therefore,it is very important to carry out the bearing mechanism,failure characteristics and the stability of the roof in the karst area.In this paper,relying 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 done on the calculation method of piles in karst area considering the lateral resistance of pile rock:Firstly,the characteristics of rock mass,pile-rock interface,rock-embedded depth and other factors on the vertical bearing mechanism of rock-socketed piles in karst area are considered.The load transfer characteristics of rock-socketed piles in karst area are analyzed,and the relevant calculation modes of pile-soil side friction resistance,pile-rock side resistance and pile tip resistance are researched.According to the deformation characteristics and failure mechanism of the rock,the anti-punching,anti-shear and anti-bending failure models of the roof in the karst area are calculated too.Secondly,the stability of karst cave roof is introduced,mainly from three aspects of qualitative analysis,semi quantitative analysis and quantitative analysis.Then,considering the influence of the side resistance of pile to the stability of cavern roof,a simplified calculation model is established to consider the influence of side resistance of pile and rock,and the method of checking the punching,cutting and bending resistance of the roof is improved.Thirdly,according to the basic principle of limit analysis and the finite element analysis,the ultimate bearing capacity of the roof of the cave is considered.The influence of the friction coefficient,the roof slab thickness,the roof span,the height of the cave,the rock parameters GSI,mi and uniaxial compressive strength on the ultimate bearing capacity of pile foundation is analyzed,and the ultimate failure mode of the roof is calculated.Finally,the calculation of the engineering example shows that the lateral friction resistance of the rock-embedded section accounts for a larger proportion of the bearing capacity.When the rock depth is longer and the rock quality is better,the traditional design method ignoring the side friction of the rock section will be too conservative.Therefore,by the comparative analysis,it can be seen that the side resistence of rock should be taken into account in the practical engineering design.