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. © 2021, Editorial Board of Journal of Harbin Institute of Technology. All right reserved.