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Grouting pile is a new soft soil foundation treatment method with characteristics such as no vibration, no noise, no soil compaction, light construction machines and quick construction velocity and so on. At present, study on reinforcement mechanism and design calculation method of composite foundation of grouting pile is initially started without design specifications, so it is usually required to draw on design specifications of stump pile when designing composite foundation of grouting pile while grouting pile has its characteristics and difference although reinforcement mechanisms and construction processes of two types of piles are similar. Sedimentation formula of composite foundation of grouting pile with cover plate is educed and a suitable deformation mode is proposed by aiming to deformation characteristics of composite foundation of grouting pile with cover plate under embankment load on basis of relevant sedimentation theories of composite foundation by combination of characteristics of composite foundation of grouting pile. The sedimentation calculation formula of grouting pile with cover plate under embankment load is educed according to balance relation of force and displacement coordination conditions by elastic theory and sedimentation calculation model established is validated by sedimentation monitoring documents of one expressway in China.

Based on the load transfer mechanism about the bi-level model, this paper studies on the influence about frictional force in side-pile of cement soil plug which pre-stressed pipe pile is implanted into a large diameter bidirectional cement mixing pile in a concentric manner. On the basis of the analysis of soil-compacting direction, theory of cavity expansion has been adopted to analyze the disturbance on the side soil in the pile driving process of pre-stressed pipe pile in MPSC. According to the lower core pile, the radial stress of pile-soil contact surface before and after the complete occlusion of cement soil plug is calculated combining the shear strength of foundation soil after disturbance. The eigenvalues of lateral friction before and after complete occlusion of soil plug are adopted according to comparison between the length of soil plug and outer pile. Considering extruding densification of core pile, improvement coefficient is implied in modifying the ground soil and outer pile, the calculation Equation for lateral friction of MPSC has been developed.