复合地基极限承载力与稳定研究进展

State-of-the-Art Review of Ultimate Bearing Capacity and Stability of Composite Foundations

我国软土地基分布区域广泛,大量建设工程位于软弱土地基,需进行适当的地基处理才能满足工程建设要求.复合地基技术具备提高地基承载力、控制地基沉降和工后沉降效果好、工期短的优点,能够满足高层建筑、高速公路、高速铁路、道路、重载堆场等工程对软弱与不良地基处理的高承载力与稳定性、低沉降(工后沉降)、大面积快速高效与经济处理的迫切要求,逐渐发展成为我国对软弱土地基处理的主要手段.本文在国内外大量研究成果基础上,阐述了复合地基的形成条件以及分类方法,着重对刚性基础下复合地基承载力和柔性荷载作用时复合地基稳定性的有特色和代表性的研究进行回顾和总结.依据桩体自身强度是否发挥,将复合地基的破坏模式分为内部破坏(如:剪切破坏、弯曲/受拉破坏、鼓胀破坏)和外部破坏(如:刺入破坏、倾覆破坏等)两大类.相应地,应考虑不同破坏模式对复合地基极限状态的影响.此外,若仅考虑桩体同时发生破坏会高估复合地基的整体稳定性,对工程造成重大安全隐患.因此,建立考虑桩-土体系渐进破坏的稳定分析方法是十分必要的.最后,本文对性能化设计概念在复合地基技术中的应用前瞻进行了探讨,以期对提高复合地基理论水平和发展绿色节约型复合地基技术有所裨益.

Soft soils are widely distributed in China,and projects are commonly conducted on soft ground. Thus,an appropriate ground improvement technology is needed to meet the construction requirements. The composite foundation with column-type technology has the advantages of high-efficiency improvement of foundation bearing capacity,control of foundation settlement and post-construction settlement and short construction period. It can meet the requirements of high bearing capacity and stability,low settlement(long-term settlement),and high efficient and economical treatment of large areas of weak and poor grounds of high-rise buildings,highways,high-speed railways,roads,high-loaded landfill and other projects. Therefore,the composite foundation technology has been gradually developed into the main treatment method for weak grounds in China. On the basis of prior investigations,this paper summarizes that the formation conditions and classification methods of composite foundations. A considerable attention has been focused on the bearing capacity and the stability of composite foundations under a rigid footing and an embankment load,respectively. Based on whether the column strength has been fully mobilized,the failure mechanism of composite foundations can be categorized as internal failure(e.g. shear failure,bending/tension failure,bulging failure)and external failure(e.g. punching failure,tilting failure). Accordingly,the influence of failure mechanism should be considered during the limit state analysis. Additionally,an overestimate of stability is found when a simultaneous failure of columns is assumed,and this overestimate may cause a safety risk in engineering practice.Therefore,the establishment of a progressive failure analysis of pile-soil system is thus essential. Finally,this paper discusses the application of the concept of performance-based design in the technology of composite foundation. Improvements in theoretical level and new technology of composite foundations are expected.