土工织物散体桩加固粉土路基机理研究

Research on Reinforcement Mechanism of Silt Embankment Using Geotextile Discrete Material Pile

摘要:

泗许高速公路地处淮北平原，该地区以粉土或粉细砂为主，在地震荷载作用下易于液化，公路建设应考虑抗液化措施。本文对土工织物散体桩的抗液化性能、复合地基承载力等进行研究，提出采用土工织物散体桩复合地基加固粉土路基的方法并对其加固机理进行分析。通过有限差分数值计算和现场试验两种方法，从超孔隙水压消散、承载力、桩土应力比、桩身应力等角度分析了土工织物散体桩加固粉土路基的加固机理，并提出土工织物散体桩优化设计的建议。

Abstract:

Sixu expressway is located in the Huaibei Plain，which is covered by silt or silty sand.However，because this type of soil is prone to liquefaction under seismic loading，liquefaction resistance measures should be considered when engineering projects are planned for this region.The liquefaction resistance of a geotextile discrete material pile and the bearing capacity of a composite foundation are examined in this study.In addition，the reinforcement mechanism of the geotextile discrete material pile with a silt subgrade is determined.The pore water pressure dissipation，bearing capacity of the composite foundation，pile-soil stress ratio，and pile body stress were researched by using the finite difference method and field testing，which is beneficial for obtaining the reinforcement mechanism of the composite foundation.Moreover，this paper presents design proposals of a geotextile discrete material pile.The results indicate that under seismic loading，a geotextile discrete material pile can effectively drain and successfully achieve anti-liquefaction.The excess pore pressure ratio increases with distance from the pile axis，and the silt becomes more inclined to liquefaction.An engineering example is used with numerical calculation to determine that effective pile spacing is 2 m，or approximately 3.3 times the pile diameter.Further，in the silt foundation，the bearing capacity of the single geotextile discrete material pile is 50% larger than that of gravel pile under the same conditions，and the composite foundation bearing capacity of the geotextile discrete material pile is 25% more than that of gravel pile.In static load testing of the composite foundation，soil pressure boxes are respectively buried at the top of the pile，at the bearing plate，and at the contact surface of the pile and soil to determine the bearing capacity of the pile and soil under the action of static load.In the two types of composite foundations，the pile-soil stress ratio increases with an increase in the upper load.This change in the geotextile discrete material pile is more prominent because geotextiles have additional lateral restraint effects on pile bodies.When the composite foundation is under a large load，the deformation of the pile is less than that of the soil；thus，a change occurs in the pile-soil stress ratio.Moreover，geotextiles have obvious reinforcement effects for the gravel pile，although damage is possible when excessive tension is placed on the ring.When the soil cannot provide adequate lateral pressure，lateral displacement of pile body is easily produced，and damage by ballooning can occur. The pile body stress test shows that maximum stress appears at four times the pile diameter range，which proves that the design of geotextile discrete material pile based on ballooning damage is reasonable.Hence in order to avoid damage on the top of the pile，it is necessary to reasonably select the geotextile material in consideration of the pile bearing conditions or to assume reinforcement measure in the area of pile body stress concentration.