考虑非达西渗流及变井阻的竖井地基大应变非线性固结理论研究

The method of drainage consolidation by vertical drain wells is widely adopted to treat soft clays, however, the non-Darcian flow law in soft clays, varied well resistance effects, the characteristics of nonlinear consolidation and large-strain consolidation cannot be simultaneously considered in the consolidation theory of soft clays with vertical drain wells. Combining with the consolidation permeability test of soft clays, non-Darcian flow in soft clays and the characteristics of nonlinear compression and permeability are analyzed, and the relationship between void ratios and the compression and permeability of soft clays are developed. The variation of the discharge capacity of vertical drain wells are measured by using single drain well model test in the process of consolidation, and the spatial and temporal variations of varied well resistance effects are also developed. The theory of large strain nonlinear consolidation of soft clays by vertical drain wells with consideration of the non-Darcian flow and varied well resistance is developed, and the solutions for this consolidation model are also deprived. The curves of settlement versus time at different points of highway are compared with the curve of deprived consolidation theory to verify the reliability of consolidation theory. Based on the developed theory of Large-strain consolidation, the evaluation methods of settlement of soft clays by vertical drains are established under complex conditions. The research findings of the project have a positive effect on the development of the consolidation theory of soft clays with vertical drains, and also provide a more comprehensive theoretical support for the calculation of settlement in large infrastructure construction projects such as highways, airports.

竖井排水固结法广泛用于软黏土地基处理，但目前的竖井地基固结理论不能同时考虑软黏土自身固结特性，如黏土中的非达西渗流、非线性压缩与渗透、大应变及变井阻效应等。项目紧密结合软黏土试样的室内渗透固结试验，剖析软黏土中的非达西渗流现象及非线性固结特性，建立非达西渗流下软黏土渗透、压缩特性与孔隙比间的非线性关系。依据单井模型试验测试竖井不同深度处通水量随时间变化，建立井阻在固结中的时空演变规律。在此基础上，建立考虑非达西渗流和变井阻的竖井地基大应变非线性固结模型并给出解答。现场实测高速公路竖井地基不同点处的荷载、沉降变形与时间关系曲线，将实测结果与固结解结果对比以验证固结理论的可靠性。应用建立的软黏土竖井地基大应变非线性固结理论，建立复杂条件下软黏土竖井地基变形评价方法。项目成果可极大地丰富和发展软黏土竖井地基固结理论，同时也为公路、机场等大型基础设施建设工程中的软黏土地基变形计算提供理论支撑。

吹填土层的强度增长及变形特性均与竖井地基固结理论息息相关。但对全面考虑土体非线性压缩渗透特性、变井阻效应和非达西渗流影响的竖井地基大应变非线性固结理论尚缺乏系统性研究。围绕研究目标主要开展如下工作：（1）基于100余组软土室内压缩及渗透试验数据，认为双对数模型能更好地描述高压缩性软土的非线性压缩和渗透特性；（2）分析并评估了现有的变井阻时空演化模型，认为竖井渗透系数随固结时间指数衰减、随深度线性衰减能更好地描述竖井井阻在固结中的变化规律；（3）在此基础上，基于实际地基处理中的堆载预压及真空联合堆载预压，分别建立了能够考虑土体非线性压缩渗透特性、井阻时空效应、高压缩性软土的大变形特性以及软土在低水力坡降下偏离达西定律的竖井地基系列固结模型，并获得相应固结模型的解答；（4）应用以上所建立的竖井地基固结一系列模型及其解答，开展不同工况下竖井地基固结计算，绘制大量可供实际工程使用的竖井地基固结计算图表；（5）此外，拓展了竖井-碎石桩组合型复合地基固结模型的解析理论；获得较薄高压缩性软土层在理想排水边界和变排水边界的大应变非线性固结精确解析解。结果表明：当土层应变达15%时，天然地基大、小应变固结理论间的计算偏差可达15%，而竖井地基大、小应变固结理论间的计算偏差为10%；考虑变井阻效应的竖井固结速率会明显慢于其常井阻下的固结速率，且变井阻下的竖井地基固结速率更与实测数据相符；如果要忽略土中竖向渗流在固结过程中的影响，在变井阻固结模型中竖井深度与有效半径之比（H/re）应达到16，而常井阻固结模型中H/re应达到12；非达西渗流与达西渗流下竖井地基的固结度差异可达到10%，一旦竖井有效半径与竖井半径比（re/rw）超过13，竖井地基固结计算就有必要考虑土中的非达西渗流现象。项目研究成果可极大地丰富和发展软土的竖井地基固结理论，为实际软土固结计算提供理论支撑；获得的精确解析解为大应变非线性固结数值计算提供理论验证途径。