昆明地区静压桩承载力的探讨

Bearing capacity of jacked piles in the Kunming region

摘要:

主要介绍了压桩力与单桩竖向极限承载力的关系，以及利用压桩力估算单桩竖向极限承载力的方法。在试桩阶段，位于饱和软土的摩擦桩，压桩力较低，桩的承载力主要来自土体恢复后桩侧的摩阻力。根据静载荷试验检测结果，用单桩竖向极限承载力除以压桩力，引出一个系数，称为压力比，通过分析比较，得出在昆明地区的正常压力比，静压预制管桩在1.3～2之间，静压预制方桩在2.5～5之间。用压桩力乘以压力比，可以估算单桩竖向极限承载力。还简要介绍了挤土效应和超孔隙水压力对桩的承载力的影响。在工程桩施工时，地层中的土体和孔隙水被挤压，形成孔隙水压力，会产生一个向上的浮力，导致已施工的桩上浮，单桩承载力显著降低。

Abstract:

The relationship between the jacking force and the maximum vertical bearing capacity of a single pile is introduced with a method of estimating the maximum vertical bearing capacity of a single pile by use of the jacking force. In the stage of trial piling, friction piles in the saturated soft soil provide a low bearing capacity, since the bearing capacity of the pile is mainly determined by the frictional resistance on the pile sides after the soil is restored. According to results obtained from the static load test, a coefficient called pressure ratio can be derived through dividing the maximum vertical bearing capacity of a single pile by the jacking force on piles. By comparison, the normal pressure ratios are obtained for the Kunming area, which falls between 1.3 and 2 in the case of jacked prefabricated pipe piles, and between 2.5 and 5 in the case of jacked prefabricated square piles. The maximum vertical bearing capacity of a single pile can be estimated with multiplying the jacking force by the pressure ratio. The influence of the soil compaction effect and the excessive pore water pressure on the bearing capacity of piles is briefly introduced. Soil and pore water in the stratum are compacted in sinking the engineering piles, generating the pore water pressure which creates an upward buoyancy and causes the constructed piles to float; thus reducing the bearing capacity of the single pile.