Analysis of 1D large strain consolidation of structured marine soft clays

Abstract

Structured soft clays are widely distributed in the coastal regions of China. The characteristics of the natural structure greatly influence the compressibility and permeability of marine soft clays and should be considered in the theory of their consolidation. When a large surcharge load is applied to a structured clay deposit, large strains can be induced in the clay layer due to the high compressibility, where the consolidation process follows the large strain assumption. However, there are few published theories of consolidation in which both the natural structure of marine soft clays and the large strain assumption can be considered simultaneously. In this study, a novel large strain consolidation model for structured marine soft clays was developed by considering the variation of structural yield stress with depth and using different calculation methods for initial effective stress of structured clay deposits in the Lagrangian coordinate system. The corresponding solution was derived by the finite difference method. Finally, the influences of the natural structure of soft clays and different geometric assumptions on consolidation behavior were investigated. The results show that the dissipation rate of excess pore water pressure of structured clays under the large strain assumption is expected to be faster than that under the small strain assumption, and the difference in consolidation behavior between the two assumptions increases with the strain level of natural structured clays. If the strain level in the clay layer is more than 15%, the difference in consolidation behavior between the large and small strain assumptions must be considered.

概要

目 的

天然沉积的结构性软土分布广泛, 但能考虑结构性影响的大应变固结理论鲜有报道. 本文考虑结构屈服压力随初始有效应力的变化及土体结构性对压缩与渗透特性的影响, 建立结构性软土的大应变固结模型. 研究结构性及初始有效应力对大应变固结性状的影响, 并探讨结构性软土大、 小应变固结性状的差异, 以提高软土固结计算的精准度.

创新点

• 1. 建立考虑天然沉积软土结构性影响的一维大应变固结模型, 且该模型能考虑结构屈服压力随初始有效应力的变化;

• 2. 分析天然结构性软土大、 小应变固结性状的差异, 为实际工程中的软土固结计算提供理论依据.

方 法

• 1. 总结结构性软土对压缩和渗透特性的影响及结构屈服压力与初始有效应力间的关系;

• 2. 通过理论推导, 构建考虑结构性影响的软体一维大应变固结模型 (公式 (15) 和 (16));

• 3. 通过对模型进行数值求解, 分析软土结构性对大应变固结性状的影响, 以及考虑结构性影响的大、 小应变固结性状的差异.

结 论

• 1. 大应变假定下结构性软土中超静孔压的消散速率要比小应变假定下快, 且这种差异随着土层应变增大而增大; 当应变值超过 15% 时必须采用大应变假定.

• 2. 如果土层的初始有效应力计算方法相同, 则大、 小应变不同假定下土层的最终沉降值是相同的.

• 3. 相同几何假定下, 初始有效应力计算方法对超静孔压消散速率几乎无影响, 但对沉降变形影响明显.

• 4. 大、 小应变假定下固结性状间的差异随结构屈服压力的增大而减小.