Abstract: The pile-soil stress ratio is an important parameter for calculating the bearing capacity and settlement of the pile-net composite foundation, which is related to the consolidation settlement of the foundation and has obvious time-varying characteristics. The calculation theory of loosening earth pressure based on Terzarghi soil arch model is discussed on the assumption that the soil of sliding surface reaches limit state, and it is not suitable for the calculation of pile-soil stress under the condition of small deformation of pile-net foundation. Therefore, on the basis of Terzarghi model, the equivalent stiffness ideal elastic-plastic model is adopted for the transfer function of relative displacement surface, and the theoretical solutions of pile-soil stress and soil arch height are derived by combining the equilibrium equation of soil element with the deformation coordination equation. The quantitative variation of pile-soil stress and the membrane effect with each design parameter is analyzed systematically. The results show that the improved method is more applicable than the existing arching algorithm model. With the increase of pile-soil differential settlement, the arching height and pile-soil stress ratio gradually increased, and the arching ratio decreased in hyperbolic shape, while the membrane effect works gradually. The arching effect is significantly weakened by increasing the filling load, and the pile-soil stress ratio decreases with the increase of pile spacing and increases with the increase of cohesive force. Based on the improved method and the field measured data, the time-varying characteristics of pile-soil stress are analyzed, and the rationality of the method is verified. The method proposed can be used as a reference for the calculation of pile-soil stress on the pile-netted foundation.

Key words: pile-net composite foundation, pile-soil stress ratio, soil arching effect, membrane effect, time-varying characteristics