【作者】 刘加才；

【导师】 赵维炳； 施建勇；

【作者基本信息】 河海大学 ， 岩土工程， 2004， 博士

【摘要】 排水固结预压法加固软土地基是常用且经济的一种软土地基处理方法，砂井(包括塑料排水板等竖向排水通道)常被用来加速软土地基的固结。随着科学技术发展、经济水平的提高，一些工程建筑物对工后变形的要求越来越高。砂井地基的设计也相应地从控制稳定为主转为控制变形为主。为适应这一转变，本文对层状砂井地基的固结问题进行了系统的研究，在砂井地基固结理论的基础上提出了实用设计方法。 论文主要展开了如下几个方面的研究工作： (1)、对现有简单未打穿砂井地基的固结理论进行了探讨，并对其渗透面上的连续条件进行了改进，使之能够反映孔压沿径向分布，在竖直方向上的孔压分布也更为合理。用现有简单未打穿砂井地基固结解答，本文解答及有限元数值解对一工程算例分析表明，本文解计算结果更接近有限元数值解结果，反映了砂井地基固结的基本规律。基于广义Viogt流变模型，提出了排水砂井未贯穿的均质地基的粘弹性固结分析方法。 (2)、将现有砂井地基固结理论由双层砂井地基、简单未打穿砂井地基推广到成层砂井地基。可以考虑砂井打设区和下卧层均为多层的情况，具有更广泛的应用性。根据其求解原理，将该解答编制成应用程序。 (3)、利用叠加原理，推导了变荷载作用下成层砂井地基的固结解答。该解答可以考虑加载对时间导数不连续的情况，如荷载突变，或对时间导数左右不相等。通过数学变换，得到了真空堆载联合预压的固结解答。研究表明，土层固结越快，加载历时对其平均固结度的影响越大；加载时间相对较短时，加载情况对加载期内平均固结度影响较大，对后期几乎没有影响。在一般设计中可将多级加载转换为简单的线性加载进行后期固结度的计算。 (4)、对砂井地基在半透水边界条件下的固结问题进行了研究，给出了双层砂井地基、简单未打穿砂井地基、成层砂井地基在半透水边界条件下的具体解答。对算例分析表明边界条件对砂井地基固结的影响较大，半透水参数对其相邻土层的固结影响比远离该边界的土层的固结大得多。在砂垫层表面排水不畅或下卧层底部存在不完全排水通道时，应考虑半透水边界。 (5)、提出考虑初始孔压非均匀分布，土层前期固结应力影响及固结过程中应力—应变关系的非线性固结分析方法。将土层细分、时间分段方法，使得细分土层在一时间段上近似线弹性体，结合解析解理论，逐个时间段对系统进行固结分析即可获得砂井地基的非线性。算例分析表明土层细分和时间离散是有效的。 (6)、将本文理论应用于工程实际，提出了基于本文理论的实用砂井地基设计方法，以及根据现场实测资料确定砂井地基平均固结度的方法。考虑砂井地基的成层性及平均固结度沿深度并非均匀分布，提出层状砂井地基工后计算方法。依据层状砂井地基固结理论，利用最小二乘方法，提出了根据实测沉降预测砂井地基变形的合理方法。更多还原

【Abstract】 Drainage preloading has been found the most economical method for ground improvement for these soft deposits and it is widely used in soil improvement. Sand drains including prefabricated vertical drains and other vertical drain channels are usually used to accelerate the consoliation process of soft clay, silt and other compressible materials. According to technology development and economic growth some buildings are required to have smaller value of the post-construction settlemnt. The design criterion for the ground with sand drains has been changed from controlling the stability to controlling the post-construction deformation. To adapted to the change, consolidation theory of ground with sand drains is studied systematically, and an applied design method is put forward.The main research work in the paper is listed as followed:(1) The consolidation theory on ground with partially sand drains is discussed and the continuity conditions at the plane of penetration were improved so that it can reflect pore pressure gradient in radial direction and rationalize pore pressure dissipation in vertical direction. An engineering case is analyzed using the analytical methods and the FEM numerical method. It is shown that results obtained by the present analytical method is closer to those obtained by FEM numerical method than by the existing analytical method. It can reflect consolidation of ground with partially pentrated vertical drain wells well and truly. Based on general Viogt rheological model, consolidation theory of homogeneous ground with partially penetrated sand drains has been developed.(2) The existing consolidation theory of double-layered ground with sand drains and of ordinary ground with partially penetrated sand drains has been extended for consolidtion analysis of general layered ground with full or partially penetrated sand drains. Analytical solutions and derivation process for it have been offered. The theory can be applied widely because it can take into account the condition that the section with or without vertical drains containe multi- strata. An application program based on the solution principle has been coded.(3) Based on the principle of superposition, solution for consolidation of layered ground with vertical drains under time-dependent loading has been developed. The surcharge can be loaded arbitrarily, such as stiff loading and ramp loading, which will induce some breakpoint when differentiated with respect to time. Solution for vacuum combined with surcharge is also been obtained through some mathematical processing. It is shown that, the faster the stratum consolidated, the more it is affected by the loading condition. It is also shown that the differences of average degree consolidtion affected by loading condition is larger during loading period than at any other time. There is hardly difference when time is large enough. Multi-ramp loading can be replaced by simple ramp loading to calculate average degree ofconsolidation in late stage in engineering design.(4) The problem of consolidation of ground with sand drains for impeded boundaries has been studied. Analytical solutions have been developed for double-layered ground with vertical drain, for simple ground with partially penetrated and for general layered ground with sand drains. Analysis for impeded boundaries shows that impeded boundaries parameters has great effect on the system consolidation and it affected the conjoint stratum more than that away from. Impeded boundaries should be take into account when drainage path is hindered in sand cushion or there is partially drainage path in the bottom strata of the system.(5) In practical engineering, initial excess pore pressure is dependent on depth; preconsolidated pressures for all strata are not a unit value; stress-strain relation is nonlinear. These factors mentioned above are taken into consideration for nonlinear consolidation analysis of ground with sand drains. In the nonlinear consolidation analysis, stratum and time are divided into many parts so that every更多还原