基于扩孔理论的挤密砂桩复合地基桩土应力比计算方法

Determination of pile-soil stress ratio for compaction foundation using cavity expansion theory

基于圆孔扩孔理论,考虑挤密砂桩挤密过程中砂桩本身的挤密体积变化,建立了砂桩桩身压缩模量的计算方法。采用Mohr-Coulomb屈服准则计算桩周土屈服区范围,同时结合桩间土的e-p曲线压缩理论,提出了基于扩孔理论的桩周土平均压缩模量计算公式,从而提出了考虑埋深影响的分层桩土应力比计算方法。结合越南河内-海防高速公路实际工程进行了计算分析,随着套管直径增大(0.5~0.6 m),挤密砂桩和桩周土的压缩模量都变小,但平均桩土应力比增大,从2.56增大至2.72,这符合《复合地基技术规范》中对于无实测资料时,桩间土强度低时桩土应力比取大值,桩间土强度高时取小值的规定。桩土应力比理论计算结果处于规范建议取值2~3之间。说明理论方法合理可靠,从而提高了挤密砂桩设计的科学性。

Based on cavity expansion theory, a method for calculating compression modulus of sand compaction pile is developed by considering the change of sand pile volume in the compaction process. The yield zone of the soil around the pile is calculated by Mohr-Coulomb yield criterion. Using the e-p soil compression curve, a formula for average compression modulus is deduced. A method considering the influence of buried depth is proposed for calculating pile-soil stress ratio of sand compaction pile. The Honai-Haiphong highway project in Vietnam is selected as a case study. Analysis indicates that as the casing pipe diameter increases from 0.5 m to 0.6 m, the compression modulus of sand compaction piles and soil around pile decrease, and the average pile-soil stress ratio increases from 2.56 to 2.72. This confirms the statement in Technical Code for Composite Foundation that the pile-soil stress ratio adopts the low value for the soil around pile with high strength, or vice versa. The theoretical calculation result of the pile-soil stress ratio is between 2 and 3 suggested by specification, demonstrating the theoretical method is reasonable and reliable, and greatly improves the sand compaction pile design.