Experimental Study And Working Mechanism Analysis On Composite Foundation With Capped Sparse Piles To Control Settlement

Composite foundation with capped sparse pile to control settlement has been applied abroad in expressway roadbed, dam foundation, port project and airport runway. The design of PTC pile(Pre-stressed Tubular Concrete pile) with cap applied in expressway deep soft soil ground has differ from that of architecture engineering, it has not appropriate criterion at present It has not mature method to optimize the parameter of the pile with cap under the condition of soil stabilization and the allowable settlement, the research of working mechanism of pile-soil has also not been analyzed and researched deeply. Now the existing practical problems are as follows, how to consider composite pile-soil stress ratio, share of load, size of pile cap, distance of piles, length of pile, thickness of cushion while it has been designed. The settlement calculation method of pile with cap composite foundation has also not mature. The present design of it has been adopted the method of enlarging the distance of piles and fully using the interaction of pile-soil. According to above discussion, this paper study and analyze the mechanics character of it by spot experiment, theory analysis and FEM analysis. Main content are as follows.1. The full-scale spot tests of composite foundation with capped sparse pile to control settlement have been done in order to analyze working mechanism and master mechanical behavior of it. The test results can verify useful reference for the engineering design and provide a guide to design it.2. The load-settlement calculation model of composite foundation with capped sparse pile to control settlement has been put forward on the base of the design load of expressway road, the mode of soil besides pile cap settlement calculation has also been put forward for the single pile with cap composite foundation. The results of the ordinary methods of composite foundation have been analyzed, and the results of it have been compared. The soil besides pile cap settlement calculation can replace the total settlement of composite foundation.3. The new conception of composite pile-soil stress ratio and composite area replacing rate have been put forward in order to describe the mechanical behavior of composite foundation with capped sparse pile to control settlement Based on soil mechanics and elastic theory, reasonable assumption, adopting the method of the equal settlement section, considering the status of top of pile cap and bottom of pile penetrating up and down, the calculation formula of rigid pile composite foundation with cap have been proposed, which shows the characteristic of layered soil and 3D settlement deformation of it. The effect factors of the distance of two piles, the length of pile, size of pile cap, modulus of cushion, modulus of underlying soil layers, modulus of soil besides pile cap and K₀ have been discussed for composite pile-soil stress ratio and the place of equal settlement section.4. Based on reasonable assumption and elasticity theory, adopting the load transfer function method, the linear analysis of composite single pile with cap has been done. The control differential equation and analytical formulas of the relation of between pile settlement, vertical displacement of soil under pile cap, pile axial stress, vertical stress of soil under pile cap, the friction force of pile cap-side and load level, depth.5. Based on reasonable assumption and elasticity theory, adopting the load transfer function method, the linear analysis of single pile with cap composite foundation has been done. The controldifferential equation and analytical formulas of the relation of between pile settlement, vertical displacement of soil under pile cap, vertical displacement of soil besides pile cap, pile axial stress, vertical stress of soil under pile cap, vertical stress of soil besides pile cap, the friction force of pile-side, the friction force of soil middle of pile caps and load level, depth..6. Based on the spot test and engineering application, considering the non-harmony of vertical deformation of pile, s...