Calculation Method And Experimental Study On Ultimate Bearing Capacity Of Rock Stratum At Pile End Of Underlying Cavity Row Pile And Pile Group Foundation

In the southwest region of China,where infrastructure construction is vigorously promoted,karst landforms are widely distributed.When engineering construction is carried out in this region,there are often karst areas in the construction area.The existence of karst cavities brings difficulties and safety hazards to engineering construction,especially the construction of foundation parts.Pile foundation is the most common foundation form in engineering.How to properly deal with the influence of underlying cavity on the bearing capacity of pile foundation in karst area is an important topic for engineering design and construction.It is of great significance to study the ultimate bearing capacity of pile tip rock for improving the bearing capacity theory of underlying cavity foundation and guiding the design of underlying cavity foundation engineering.Based on the National Natural Science Foundation of China “Study on Vertical Bearing Mechanism and Design Calculation of Rock-socketed Piles Through Karst Cave”(Project Number: 51878270),this paper intends to study the ultimate bearing capacity and failure mode of the rock layer at the end of the underlying cavity piles and pile groups.The main research contents and achievements include:(1)According to the similarity principle,the destructive test of bearing capacity of single pile,row pile and group pile foundation pile end rock under the condition of cavity in laboratory simulation is carried out.The pile top load and pile top settlement of the simulated pile foundation in the test were measured and recorded,and the load-settlement curve was plotted and analyzed.The bedrock failure body at the pile end separated from the cavity roof strata after failure was taken out,and the shape of the failure body under the condition of single pile,row pile and group pile was observed and compared.It was found that the morphological curve of the rock failure body at the pile end of row pile and group pile foundation was related to the morphological curve of the failure body under the condition of single pile;(2)According to the test phenomenon,it is speculated that the possible failure modes of the rock strata at the pile end of the underlying empty pile and the pile group,and it is proposed that the failure mode of the bedrock at the pile end of the underlying empty pile is similar to the overlapping of multiple piles,and the overall bearing capacity of the bedrock at the pile end of the underlying empty pile can be calculated by calculating the area of the overlapping part.When analyzing the failure mode of rock stratum at pile end under the condition of pile group,the pile group is equivalent to a large foundation whose shape is the envelope connection of peripheral foundation piles.The ultimate bearing capacity of rock stratum at pile group end is calculated by using the relationship between single pile and the shape function of bedrock failure body at pile group end.By comparing the experimental loading data with the theoretical ultimate bearing capacity,it is found that they are in good agreement;(3)The numerical software is used to simulate the failure of pile end rock under different pile foundation layout.By using the advantages of numerical modeling,the failure modes and ultimate bearing capacity of rock strata at the end of row piles and group piles under different pile spacings are explored.Based on the results of indoor model test,theoretical calculation and numerical simulation,it is proved that the text analysis of the failure mode and calculation method of the bedrock at the end of the pile and the pile group is feasible.