Calculation Method For Design Of Pile Foundation Considering Differentia Of Ground And Pile In Karst Region

In the booming development of infrastructure construction in China, a largeamount of buildings and structures under construction or in plan would be built in thekarst region which is widely distributed over the country. When pile foundation isused in this region, complicated Karst stratum encountered would render engineeringrisk due to the underlying caves and grooves. It should be very prudent to treat thecave underlying the base of pile and it is common in design and construction of pilefoundation in karst region to pierce through encountering caves. Under mostcircumstances, not every pile for the foundation of structures is resting on the cave,only a small part of piles for pile group have underlying caves at the pile base. Designfor pile foundations in this differential ground is of great theoretical and practicalsignificance. Herein theoretical analysis and numerical simulation were combined toinvestigate this issue systematically and deeply at a moderate degree, Main worksdevoted into the below as follows:With respect to the particularity of the bearing mechanism of the pile foundationand designing methods in the karst region, the safe thickness of cave roof, bearingmechanism and mechanical property of pile subject to vertical loads were analyzedfirstly. Considering the fact that the pile-beam foundation has high integral rigidityand stability, the technique of reinforcing the straining beam between the primarypiles to be a reinforced cross beam to redistribute the vertical loads was employed toincrease the stability of cave roof, thus the designing idea of collaborative action ofcave roof, pile and cap beam was proposed.In order to investigate the interaction system of cave roof and pile, cave roof wasidealized to be two typical mechanical models with some corresponding assumptionsaccording to the geometry and boundary conditions of cave roof. The ratio ofthickness and span was used to divide cave roofs into thin plate and medium plate,and corresponding calculation formula of settlement was derived employing thin platetheory and Reissner theory respectively. Nonlinear finite element analysis ADINAwas used to simulate the working characteristic of cave roof with span in range of3-10m and thickness in range of1-10m, the influence of thickness, span, ratio ofthickness and span, pile diameter and other factors on the settlement of cave roof wasanalyzed in detail. Thirdly, taking the difference of pile induced by underlying cave into account,the calculation method for the internal forces of the pile foundation in Karst regionwas proposed. Based on the analysis of ground variance under each pile of pilefoundation, a new designing idea of considering the reinforced straining beam, pileand cave roof into an entirety was given. Computing formula for internal forces ofreinforced straining beam and pile, stiffness of pile resting on intact rock bed andunderlying cave were derived. Thus a design course for pile foundation withunderlying differential ground was developed.Finally, the optimization design for a practical case was conducted, and thecalculation method in this paper was verified.