In recent years, with the rapid development of the coastal economy and hydraulic reclamation technology, the large-scale and large-thickness hydraulic-fill saturated silt fine sand foundations have been formed in the reclamation areas. Such foundations often show the characteristics of easy liquefaction and low bearing capacity, which brings great difficulties to practical project. The dynamic compaction method is a safe and economic method for reinforcing the soft foundations. However, due to the complex mechanism of dynamic compaction of saturated sand foundations, the empirical formula, numerical simulation and other methods are difficult to reflect the objective situation or are not convenient for field application, resulting in the lack of practical methods for the engineering design of effective reinforcement depth. On the basis of reinforcement mechanism, a calculation method of effective reinforcement depth considering the depth of the tamping pit, the depth of compacted shell and the influence area depth of the compacted shell is established. The calculation value is more consistent with the on-site tamping test result, which shows that the calculation method of the effective reinforcement depth proposed in this paper can objectively reflect the reinforcement characteristics of saturated sand foundations under dynamic compaction and has good engineering applicability and reliability.

Now, on the basis of hydrostatic pressure difference of overall stress method, the fluid-solid coupling analysis of saturated slope by strength reduction limit analysis method is realized by adjusting soaking surface and using the action of levitating force, but the changing of pore pressure in the process of strength reduction is not resolved. In this paper, the asynchronous load transfer process on the solid skeleton and free water of soil-rock was explained from the relations of the strength parameters of solid phase (c,φ) and the strength parameters of liquid phase (pore water pressure). The effective stress strength reduction limit analysis method and the approximate determination method of pore pressure increment were advanced, and the pore pressure increment-strength reduction limit analysis method was realized on the basis of hydrostatic pressure difference of overall stress method. The research shows that zero-pore pressure surface increase 0.34~0.44 m(4%~5%) than the safety factors of strength reduction limit analysis method, this is close to the empirical value (0.5 m) that was used in the fluid-solid coupling analysis of saturated slope.