The Bearing Mechanism And Experimental Research Of Bridge Pile Foundation In Karst Area

Along with the high-speed development of western China, Karst terrain isencountered more in the construction of road, bridge and harbor. Therefore theproblems about the interaction between piles and Karst caves, the socketed depth ofpiles, the stability of Karst cave roof, as well as the minimal safe thickness havealways been hot topics in research. Due to the complexity and uncertainty of Karstterrain, the study about piles in Karst area is fairly difficult. Based on formerresearches and combined with National Natural Science Foundation of China project“The study of pile vertical bearing mechanism and design calculation method in Karstarea”(Item Number:51278187), following studies have been made:Firstly，brief conclusion about current researches about piles in Karst area ismade in this dissertation.Then based on the load transfer behavior of ordinarysocketed piles, combined with the characteristics of the interaction between piles andcave roofs, the load transfer equations under different roof thickness are assumed andtestified by large-scale indoor model tests. Considering the variety of rock properties,the calculation models about socketed depth of both soft and hard rocks are proposedrespectively, thereby deducing an analytical method to calculate minimal socketeddepth. Through model and situ tests, the correctness of this method is checked, andparameter analysis is conducted.Aiming to study vertical load mechanism of piles and failure modes of cave roofs,based on similarity principles, the large-scale indoor experiment about the interactionof piles and cave roofs is designed. By a set of tests, the simulation material of caveroof is decided, and4model tests are designed according to different thickness ofcave roofs. Cave roofs of different thickness (0.5d,1d,2d and3d) are loaded, theload transfer characteristics, the displacement curve of roof caves and their failuremodes are obtained. Last, theoretical analysis about the results of tests is carried out.Adopting FLAC3D to simulating the indoor model tests, the displacement curve ofcave roof and the failure modes are compared with the simulating results, to verifyexperiment results. Considering the drawbacks about the lack of variation of spans ofcave roofs, FLAC3D is used to analyze the effects of different thickness-span ratio,targeting on obtaining the law of the effects of different thickness-span ratio onbearing capacity, thus verifying the results of model tests further.