Fine‐grained marine sediments containing large undissolved gas bubbles are widely distributed around the world. Presence of the bubbles could degrade the undrained shear strength (su) of the soil, when the gas pressure ug is relatively high as compared with the effective stress in the saturated soil matrix. Meanwhile, the addition of bubbles may also increase su when the difference between ug and pore water pressure uw becomes smaller than the water entry value, causing partial water drainage from the saturated matrix into the bubbles (bubble flooding) during globally undrained shearing. A new constitutive model for describing the two competing effects on the stress‐strain relationship of fine‐grained gassy soil is proposed within the framework of critical state soil mechanics. The gassy soil is considered as a three‐phase composite material with compressible cavities, which allows water entry from the saturated matrix. Bubble flooding is modelled by introducing an additional positive volumetric strain increment of the saturated clay matrix, which is dependent on the difference between pore gas and pore water pressure based on experimental observations. A modified hardening law based on that of the modified Cam clay model is employed, which in conjunction with the expression for bubble flooding, can describe both the detrimental and beneficial effects of gas bubbles on soil strength and plastic hardening in shear. Only two extra parameters in addition to those in the modified Cam clay model are used. It is shown that the key features of the stress‐strain relationship of three fine‐grained gassy soils can be reproduced satisfactorily.

中文翻译：

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细粒含气土的本构建模：一种复合方法

含有大量未溶解气泡的细粒海洋沉积物广泛分布于世界各地。当气体压力 ug 与饱和土壤基质中的有效应力相比相对较高时，气泡的存在会降低土壤的不排水剪切强度 (su)。同时，当 ug 与孔隙水压力 uw 之差小于入水值时，气泡的加入也可能使 su 增加，导致在全局不排水剪切过程中部分水从饱和基质排入气泡中（气泡溢流）。在临界状态土力学的框架内，提出了一种新的本构模型，用于描述细粒含气土的应力-应变关系的两种相互竞争的影响。含气土壤被认为是具有可压缩空腔的三相复合材料，允许水从饱和基体进入。通过引入饱和粘土基质的附加正体积应变增量来模拟气泡驱，这取决于基于实验观察的孔隙气和孔隙水压力之间的差异。采用基于修正凸轮粘土模型的修正硬化定律，结合气泡驱替的表达式，可以描述气泡对土壤强度和剪切塑性硬化的不利和有利影响。除了修改后的 Cam 粘土模型中的参数外，仅使用了两个额外参数。