劲芯水泥土桩复合地基承载路堤失稳破坏机理研究

The stability issue of composite foundation has been treated more seriously as some land slide accidents were successively happened in the column-supported embankments of high way and railway in China. As a new technique of ground improvement, stiffened deep mixed (SDM) column has an expansive prospective in the future. However at present, there is a lack of design method to evaluate stability of a foundation with SDM columns, which could easily result in an irrational design. Therefore, this program performs a model test of SDM column-supported embankment, which can carefully monitor the performance of columns in whole process. Based on the model test, the internal mechanism of slope failure induced by the column failure in a form of step by step can be investigated. Then, three-dimensional numerical analysis is conducted to analyze the development of stress and strain in soil and column, and plastic zone during the evolutionary process of slope failure. In additional, the effect of different types of SDM column on the embankment stability is explored. Finally, a theoretical analysis is performed to establish a design method to evaluate the stability of SDM column-supported embankment based on the mechanism of step by step failure. The research is significantly meaningful in both academic and practical phases to reveal failure mechanism of SDM column-supported embankment, to perfect the design theory of SDM column-reinforced soil, and to develop the techniques of ground improvement for embankment of high way and railway over soft soil.

随着我国陆续发生了一些复合地基承载公路与铁路路堤的失稳破坏事故，复合地基稳定性问题越来越受到人们的重视。劲芯水泥土桩是一种新型的地基处理技术，具有广阔的应用前景。但目前尚缺乏对劲芯水泥土桩复合地基稳定性计算方法的研究，容易造成设计的不尽合理。为此，本课题设计了能够精细化全程监测桩体性能的劲芯水泥土桩承载路堤模型试验，分析劲芯水泥土桩渐进式破坏引起路堤失稳的内在机理；其次，采用三维数值分析研究劲芯水泥土桩承载路堤失稳过程中桩体和土体应力应变的变化、塑性区的开展规律，探究不同桩型结构对路堤稳定性的影响；最终，通过理论分析建立基于渐进式破坏机理的劲芯水泥土桩复合地基承载路堤稳定性计算方法。研究成果对于揭示劲芯水泥土承载路堤的失稳破坏机理，完善劲芯水泥土桩复合地基设计理论和计算方法，以及发展软土地区高速公路和铁路路基处理技术具有十分重要的理论和实际意义。

随着我国陆续发生了一些复合地基承载铁路与公路路堤的滑坡事故，稳定性问题越来越受到人们的重视。劲芯水泥土桩是一种新型的地基处理技术，具有广阔的应用前景。但目前尚缺乏对劲芯水泥土桩复合地基稳定性计算方法的研究，容易造成设计的不尽合理。为此，本课题通过模型试验、三维数值分析和理论研究，阐明桩体破坏模式、桩体破坏和路堤失稳的内在联系，研究了劲芯水泥土桩承载路堤失稳过程中桩体和土体应力应变的变化、塑性区的开展规律，建立了基于渐进式破坏机理的劲芯水泥土桩复合地基稳定性计算方法。研究结果表明，在路堤荷载下，路面正下方的桩体首先发生压剪破坏，桩体丧失部分功能，导致附加荷载往桩间土传递，桩间土由于较低的抗剪强度发生滑动趋势，引起路堤坡面下桩体发生弯曲破坏。随着附加荷载的继续增加，路面正下方桩体完全破坏丧失其功能。坡面下的桩体破坏与滑动面的产生可能同时发生。在所有桩体丧失其功能后，抗滑力仅依靠地基土的抗剪强度，路堤很快就发生失稳破坏。考虑路堤在失稳过程中桩土应变不协调，采用反映水泥土抗压、抗拉，以及应变软化特性的本构模型能够较好地与模型试验揭示的桩体破坏模式吻合，不考虑桩体应变软化的分析方法会高估路堤的稳定性。基于桩体的破坏模式，以及桩体和土体在路堤失稳过程中的相对作用，提出了反映桩土发挥性能的强度折剪方法，用以计算复合地基承载路堤稳定性。研究成果对于揭示劲芯水泥土复合地基的失稳破坏机理，完善劲芯水泥土桩复合地基设计理论和计算方法，以及发展软土地区高速公路和铁路路基处理技术具有十分重要的理论和实际意义。