复合重力坝支护在软土地区污水处理厂基坑中的应用研究

Application of the Composite Gravity Dam in a Deep Excavation Support of a Wastewater Treatment Plant in Soft Soils

随着城市人口不断增加,现代化更新速度加快,对提标改造各类污水处理厂已成为城市污水治理工程建设的发展趋势。以已施工完成的上海某污水处理厂多单体综合基坑作依托,基于PLAXIS有限元软件的HSSmall模型对综合坑水泥土搅拌桩重力坝中内插H型钢的复合重力坝支护进行研究分析,根据数值分析结果和监测数据对基坑变形和稳定性进行研究。研究发现:①对于污水处理厂一些特殊单体,基坑平面尺寸较大,深度5 m~7 m左右,采用常规板式围护+内支撑体系不仅增加造价而且增加主体结构施工难度,而复合式重力坝从根本解决该问题;②复合重力坝围护体系在浅基坑局部落深的6.95 m范围内有着较好的可行性和工程应用效果,可在今后基坑支护中作为悬臂围护的补充形式;③软土地区采用HS模型模拟基坑开挖具有较好的收敛性且与实际监测数据较为接近;④现场监测结果表明复合重力坝中H型钢和钢管可以提供较大的侧向刚度,抵抗大部分土压力,一定程度上控制了坝体侧斜;⑤复合重力坝可以解决大部分实际工程问题,开坑深度建议在5~7 m之间。研究结论对今后类似工程可提供技术支撑。

With the ever increasing of urban population,the speed of modernization and renewal,and the continuous improvement of residents’living standards,upgrading of various wastewater treatment plants has become the development trend of the urban wastewater treatment projects.This paper presents a case history of a comprehensive deep excavation for a wastewater treatment plant in Shanghai.The gravity supporting structure formed by soil-cement mixing with HP pile insertions is numerically simulated by using the commercial finite element analysis software PLAXIS.The HS-Small soil constitutive model is implemented in the analysis of the deformation and stability of the supporting structure and the analytical results are compared with the construction monitoring data.The results show that:(1)for some special elements of the waste treatment structures,the footprint size is large and the required excavation depth is about 5m~7m.The conventional plate enclosure+internal support system not only increases the cost but also has the construction difficulty of the main structure,while the compound gravity dam can resolve the above problems;(2)The composite gravity dam supporting system has good feasibility and engineering application effect in the range of 6.95m local depth of shallow foundation pit,which can be used as a supplementary form of cantilever retaining in the future deep excavation support.(2)The HS model used to simulate deep excavation in soft soil area has good convergence and is close to the monitored data;(3)The field monitoring results show that the H-section steel and steel pipe in the composite gravity dam can provide large lateral stiffness,resist most of the earth pressure,and control the slope of the dam body to a certain extent.(4)Composite gravity dam can solve most of the problems in practical engineering,and the pit depth is suggested to be between 5 and 7 m.