Consolidation Analysis Of Composite Ground With Impervious Pile In Multi-layered Foundation

The related theory of composite ground is an important research topic in the field of geotechnical engineering, among which th e consolidation theory has been one of the focuses of the study of composite ground theory. According to the pile material, composite ground can be divided into composite ground with discrete material pile and composite ground with bonding material pile. The pile of composite ground with discrete material pile is(such as sand pile, gravel pile) drainage pile, which is the main drainage channel in composite ground. In contrast, the pile of composite ground with bonding material pile(such as cement soil pile, lime soil pile) can be regarded as impervious pile, which’s permeability is usually less than the permeability of soft soil around pile. At present, the stud y on the consolidation theory of composite ground with discrete material pile has been studied deeply, but the results of the study on the consolidation theory of composite ground with impervious pile are still few. In view of this situation, this paper does an in-depth study on the consolidation problem of composite ground with impervious pile in multi-layered foundation, in order to develop the consolidation theory of composite ground and guide the construction settlement control. The main content and work are as follows:First, established an consolidation model of composite ground with undrained end bearing pile in double-layered foundation, obtained the general solution of super static pore water pressure of double-layered composite foundation with undrained end bearing pile under time-dependent loading, and then gave the consolidation degree expression in two common cases of the instantaneous load and single-stage uniform load. And the solution was verified through comparison validation and degradation validation, to prove the correctness of the answer.Then, this paper studied the consolidation problem of composite ground with undrained end bearing pile in multi-layered foundation, and obtained the consolidation degree expression of each layer and of the whole composite foundation. In addition, the consolidation characteristics of multi-layered composite ground with undrained end bearing pile were analyzed. The results show that: if the loading rate is faster, the hole diameter ratio is smaller, the compression modulus of pile and soil is greater and the soil permeability is greater, the faster the consolidation is; if the permeability of soil which is closer to the drainage surface is bigger, the influence on the consolidation rate is bigger; when a layer of soil permeability is greater, if the layer height ratio is larger, the faster the consolida tion is.Finally, we considered when the soft soil foundation is thick, the pile of composite foundation does not enter the bearing layer, so the pile can be regard as floating pile. In this case, the consolidation problem of composite foundation with undrained floating pile under time-dependent loading was studied, and the analytic expressions of the consolidation degree were obtained. The consolidation rules we have got are as follows: when the hole diameter ratio and the relative reinforcement depth are less than a certain limit, due to the barrier effects of impervious pile to the vertical seepage of underlying layer soil, the consolidation rate of composite foundation with undrained floating pile is even smaller than the consolidation rate of natural foundation under the same conditions.