武汉软土深基坑被动区加固参数优化分析

Parameter Optimization Analysis of Deep Foundation Pit Reinforcement in Passive Zone in Wuhan Soft Soil

在武汉地区市政项目建设中的深基坑开挖往往面临周边建筑紧邻、地下管线复杂、软土覆盖深厚等问题,深基坑变形控制要求高。对于软土地区的超深基坑,基坑内被动区土体加固作为一种超前支护方式对深基坑的变形控制效果十分显著。以武汉市黄孝河、机场河水环境综合治理二期工程中的常青公园地下调蓄池工程软土深基坑为例,结合武汉和上海地区的工程经验及相关规程,通过现场和室内土工试验获得基坑各土层的物理力学参数,结合PLAXIS 3D岩土有限元分析软件建立了基坑三维数值模型,对基坑围护桩体水平位移和内支撑轴力进行了数值模拟,并将数值模拟结果与监测结果进行了对比,并对基坑加固体的尺寸参数和物理力学参数对基坑变形的影响进行了模拟分析。结果表明:基坑围护桩体水平位移和内支撑轴力的数值模拟结果与监测结果的变化规律基本一致,验证了数值模型模拟的精确性和合理性;对于矩形截面的加固体,加固体宽度的有效值范围为0.5H~1.0H,超过该有效值范围后基坑中间软土易出现“拱起效应”;加固体深度的有效值范围为0.8H~1.3H,超过该有效值范围后对基坑变形控制的影响不明显;基坑加固体内摩擦角和压缩模量的增大可以有效控制基坑的变形,基坑加固体黏聚力的变化对基坑变形的控制效果不明显。该研究结果对类似基坑工程加固体设计具有参考价值。

As excavation of deep foundation pits in the construction of municipal projects in Wuhan often faces problems such as close proximity to surrounding buildings, complex underground pipelines, and deep soft soil coverage, deep foundation pits require high deformation control.For ultra-deep foundation pits in soft soil areas, soil reinforcement in the passive zone of the foundation pit has a significant effect on the deformation control of deep foundation pits as an advanced support method.Taking the Huangxiao River and the Changqing Park underground storage tank foundation pit in the second phase of the comprehensive treatment of the water environment of the airport river as an example, combining the experience of Wuhan and Shanghai and related regulations, the physical mechanical parameters of each soil layer were obtained through field sampling tests and indoor geotechnical experiments.Combined with PLAXIS 3 D geotechnical finite element analysis software, the three-dimensional numerical model of the foundation pit was established.Furthermore, the simulted horizontal displacement and supporting axis force of foundation pit containment piles were compared with the monitored results.And the impact of shape and size parameters and physical and mechanical parameters of the reinforced soil of the foundation pit on foundation deformation was simulated and anlyzed.The results are as follows: the simulated results are basically consistent with the monitored results, which verifies the accuracy and validity of the numerical model;for the reinforcement of the rectangular section, the effective value range of the reinforcement width is 0.5H~1.0H,in which H is the reinforcement depth, while after the effective range is exceeded, the soft soil in the middle of the foundation pit appears “arching effect”;the effective range of the reinforcement depth is 0.8H~1.3H,beyond which the effect on deformation control is not obvious.The angle of internal friction and compression modulus of the added solids are more effective in controlling the stability of the pit, and the control of cohesion is less effective.The results provide reference for the reinforced soil design of similar foundation pit project.