Constitutive modelling of fine‐grained gassy soil: A composite approach

Abstract

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 (s u ) of the soil, when the gas pressure u g is relatively high as compared with the effective stress in the saturated soil matrix. Meanwhile, the addition of bubbles may also increase s u when the difference between u g and pore water pressure u w 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. K E Y W O R D Sclays, constitutive relations, offshore engineering, partial saturation, pore pressures, shear strength

A state-dependent constitutive model for coarse-grained gassy soil and its application in slope instability modelling

“…The large strain formulation, as proposed by (see also ABAQUS User Manual (Hibbitt et al, 2016)), is adopted in the stress integration scheme. The numerical implementation schemes largely follow those employed by Gao (2012) and Gao et al(2020), where more details are provided. The implemented gassy sand model in ABAQUS was verified by comparing its predicted results…”

“…Increasing offshore construction activities on gas-bearing seabed have generated interests in developing theoretical models of gassy soils. For fine-grained gassy soil, constitutive models that enable a unified description of both 'detrimental' and 'beneficial' effects of gas on the host soil have been developed, by formulating gas-dependent yielding function, dilation function and hardening law (Gao et al, 2020;. While for coarse-grained gassy soil, previous theoretical developments have primarily focused on modelling the 'beneficial' effect of gas on loose sand in migrating static liquefaction (Pietruszczak & Pande, 1996;Grozic et al, 2005;Lü et al, 2018), with few attempts to describe the 'detrimental' effect of gas on dense sand under undrained loading.…”

Effective skeleton stress and void ratio for constitutive modeling of fiber-reinforced sand

“…FRS is a composite material with sand particles, fibers with anisotropic orientation and pore water. Composite approaches have thus been routinely used in modeling the mechanical behavior of such soils [8,11,14,15,26]. An alternative method is proposed here.…”

“…The features of Eqs. (12) and (14) for pure sand have been discussed extensively in the existing literature [13,20,21], and therefore, they will not be elaborated here. There will be discussion on how Eqs.…”

A Review of Gassy Sediments: Mechanical Property, Disaster Simulation and In-Situ Test

“…In the other category, the air bubbles are much larger than the soil particles and pore size. The bubbles rearrange the soil particles and thus affect the soil structure (Hong et al, 2020a;Gao et al, 2020). This microstructure often exists in fine-grained air-bearing soils, as shown in Figure 3.…”