不排水桩准饱和复合地基的固结特性

自然界广泛分布准饱和天然地基,研究不排水桩准饱和复合地基的固结特性具有理论意义和工程应用价值。假定桩土之间满足等应变条件,并考虑孔隙流体压缩性,建立了不排水桩准饱和复合地基的固结控制方程。根据荷载施加瞬间比流量等于零的性质确定了孔压初始条件,利用分离变量法和叠加法得到了总应力随深度不变时瞬时加载、单级线性加载和随时间任意变化加载下的孔压解析解答。推导了固结度和即时沉降的计算公式。考虑孔隙流体压缩性时复合地基既产生即时孔压也产生即时沉降。含气率越大,初始孔压和按固结沉降定义的固结度越小;含气率和桩的压缩模量越大,即时沉降越大。即使含气率只有0.2%,预应力管桩复合地基的即时沉降占总沉降的比率也高达97.3%。上述研究表明,由于地基经桩体加固后等效压缩模量大幅增加和孔隙水的体积模量随含气量大幅减小,因此在不排水桩准饱和复合地基固结分析中必须考虑孔隙水的压缩性,否则会造成较大的理论偏差。

Consolidation behavior of nearly saturated composite ground with impervious piles

Nearly saturated natural ground is widely distributed in nature, and the study of the consolidation characteristics of nearly saturated composite ground with impervious piles has theoretical significance and engineering application value. Based on the assumption of the equal strain condition between soil and pile and considering the compressibility of pore fluid, a consolidation governing equation was derived for nearly saturated composite ground with impervious piles. The initial condition of pore pressure was determined according to the property that the specific flow is equal to zero at the moment of loading. Using separate variable method and superposition method, the analytical solutions of pore pressure were obtained under instant loading and single ramp loading and under the loading which remained constant with depth and changed arbitrarily with time. The calculation formulae of consolidation degree and immediate settlement were derived. When the compressibility of pore fluid was taken into account, the composite ground produced not only immediate pore pressure but also immediate settlement. The higher the air content was, the smaller the initial pore pressure and the consolidation degree defined by consolidation settlement were. The higher the air content and the compressive modulus of pile were, the larger the immediate settlement was. Even when the air content was only 0.2%, the ratio of immediate settlement to total settlement exceeded 97.3% in the pre-stressed pipe pile improved ground. Since the equivalent compressive modulus of soil ground significantly increased with the installation of piles and the bulk modulus of pore-water significantly decreased with air contents, the research reveals that it is necessary to take into account the compressibility of pore-water in the consolidation behavior analysis of nearly saturated composite ground with impervious piles, otherwise it will cause large theoretical errors.