A constitutive model for gassy clay

Fine-grained marine sediments often contain gas bubbles that can cause many geotechnical problems. This soil has a composite structure with gas bubbles fitting within the saturated soil matrix. The gas cavity has a detrimental effect on the soil stiffness and strength when they are filled with undissolved gas only. The gas cavity can be filled with gas and pore water due to ‘bubble flooding’. Bubble flooding has a beneficial effect on the soil stiffness and undrained shear strength because it makes the saturated soil matrix partially drained under a globally undrained condition. A critical state constitutive model for gassy clay is presented which accounts for the composite structure of the soil and bubble flooding. The gas cavity is assumed to have a detrimental effect on the plastic hardening of the saturated soil matrix. Some of the bubbles can be flooded by pore water from the saturated soil matrix which leads to higher mean effective stress of the saturated soil matrix. Consequently, both soil stiffness and strength increase. Only one new parameter is introduced to model the detrimental effect of gas bubbles on plastic hardening. The model has been validated by the results of three gassy clays.

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A Practical Saturated Sand Elastic-Plastic Dynamic Constitutive Model and Application

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.446-449.1621 ◽

2012 ◽

Vol 446-449 ◽

pp. 1621-1626 ◽

Cited By ~ 2

Author(s):

Yan Mei Zhang ◽

Dong Hua Ruan

Keyword(s):

Constitutive Model ◽

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Stone Columns ◽

Saturated Sand ◽

Multidimensional Model ◽

Excess Pore Water Pressure ◽

Elastic Plastic ◽

Excess Pore

A practical saturated sand elastic-plastic dynamic constitutive model was developed on the base of Handin-Drnevich class nonlinear lag model and multidimensional model. In this model, during the calculation of loading before soil reaches yielding, unloading and inverse loading, corrected Handin-Drnevich equivalent nonlinear model was adopted; after soil yielding, based on the idea of multidimensional model, the composite hardening law which combines isotropy hardening and follow-up hardening, corrected Mohr-Coulomb yielding criterion and correlation flow principle were adopted. A fully coupled three dimension effective stress dynamic analysis procedure was developed on the base of this model. The seismic response of liquefaction foundation reinforced by stone columns was analyzed by the developed procedure. The research shows that with the diameter of stone columns increasing, the excess pore water pressure in soil between piles decreases; with the spacing of columns increasing, the excess pore water pressure increases. The influence of both is major in middle and lower level of composite foundation.

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Modelling coating cohesion effect on soil mechanical stability and permeability of the biopore - matrix interface pore region

10.5194/ismc2021-38 ◽

2021 ◽

Author(s):

Luis Alfredo Pires Barbosa ◽

Horst H. Gerke

Keyword(s):

Axial Compression ◽

Mechanical Stability ◽

Transport Processes ◽

Spherical Particles ◽

External Loading ◽

Hydraulic Permeability ◽

Matrix Interface ◽

Pore Region ◽

Soil Matrix ◽

Soil Stiffness

Biopore surface is often characterized by finer particles and increased concentration of polysaccharides from root and earthworm exudates, presenting physico-chemical properties different from those of the soil matrix. Such exudates controls not only the wettability or sorption properties but also the adhesive forces of the surrounding soil particles. Thus, increased mechanical stability may be expected on biopore-matrix interface affecting preferential flow and transport processes, as well. However, it is still unknown (i) to what extent the particle cohesion in the coated region is able to increase the resilience of the biopore to an external loading and (ii) how it affects the permeability of the biopore-matrix pore region. We created a discrete element model (DEM) model of a hollow cylindrical soil sample with a coated biopore in the center (i.e., 1 cm height, 1 cm outer and 0.6 cm inner diameter). The spherical particles in the model presented diameter of 0.13 mm for the coated material and 0.22 mm for the soil matrix. The cohesion among particles in the soil matrix was set to a constant value of 10.9 MPa while the cohesion among particles in the coated region varied between 10.9 and 50.9 MPa. The sample was subjected to axial compression and the force and cracks recorded. The permeability in the radial direction from the biopore to soil matrix was calculated using ImageJ and a 3D stokes solver (FDMMS). The increment in the coating cohesion increased the overall soil stiffness in terms of the Young&#8217;s modulus. Before axial compression, the calculated hydraulic permeability for the interface coating and matrix was 182 &#956;m2. After compression, although the lower coating cohesion resulted in a larger number of cracks, permeability increased with coating cohesion. This suggests that with increasing soil stiffness, the cracks decrease in number but increase in length (i.e. improved connectivity).

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Mitigation of liquefaction triggering due to bio-gas-induced desaturation using element tests and the strain energy approach

Earthquake Spectra ◽

10.1177/87552930211041641 ◽

2021 ◽

pp. 875529302110416

Author(s):

Mohammad Hassan Baziar ◽

Omid Eslami Amirabadi

Keyword(s):

Pore Water ◽

Strain Energy ◽

Water Pressure ◽

Gas Bubbles ◽

Energy Approach ◽

Degree Of Saturation ◽

Ammonium Ion ◽

Triaxial Tests ◽

Treated Sample ◽

Urease Enzyme

Currently, conventional remediation of liquefaction triggering may have many environmental effects, and this important issue has led researchers to look for more sustainable methods. In this research, one of the new bio-improvement methods (biogas) has been used to generate gas bubbles within a soil, susceptible to liquefaction. Using this method, two bio materials create ammonium ions and carbonate, in which ammonium ion is converted into nitrate due to the presence of bacteria in water, and they are eventually converted to nitrogen gas in an anaerobic condition. The nitrogen bubbles created in water reduce the soil’s degree of saturation, which in effect increases the soil’s resistance to liquefaction occurrence. In this study, two sources of urease enzyme were used to reduce the soil degree of saturation. The effects of various parameters, including the optimum concentration of each substance for optimum time to generate gas bubbles, as well as the effect of the oxygen amount in water were investigated using monotonic triaxial tests. The results illustrated that the addition of the mentioned two substances to the oxab (water with 60 ppm oxygen) or tap water decreased the pore water pressure due to desaturation. Finally, the energy approach was used to test the substance containing the amount of oxab with the highest decrease in pore water generation, here called “optimum selection,” in the cyclic triaxial device, and the results were analyzed to evaluate liquefaction occurrence. The outcome of these results revealed that compared with the strain energy of the non-treated sample, the treated sample had a much higher strain energy; in other words, the treated sample needed a larger amount of loading to trigger liquefaction.

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Evaluation of a simplified soil constitutive model considering implied strength and pore-water pressure generation for one-dimensional (1D) seismic site response

Canadian Geotechnical Journal ◽

10.1139/cgj-2018-0893 ◽

2020 ◽

Vol 57 (7) ◽

pp. 974-991 ◽

Cited By ~ 1

Author(s):

Xuan Mei ◽

Scott M. Olson ◽

Youssef M.A. Hashash

Keyword(s):

Constitutive Model ◽

Shear Strain ◽

Pore Water ◽

Pore Water Pressure ◽

Site Response ◽

Water Pressure ◽

Generation Model ◽

Cyclic Shear ◽

Centrifuge Tests ◽

Spectral Accelerations

Pore-water pressure (PWP) generation can lead to soil softening and liquefaction of sandy soils during earthquakes, with potential influence on site response and seismic design. The authors evaluated the generalized quadratic/hyperbolic (GQ/H) constitutive model, which captures small-strain stiffness, large-strain shear strength, and is coupled with a widely used cyclic strain–based PWP generation model (termed GQ/H+u). A suite of cyclic direct simple shear tests with a range of relative densities (∼30%–80%) and effective vertical stresses (∼25–200 kPa) and dynamic centrifuge tests with liquefiable sands were used to evaluate the ability of the GQ/H+u model to simulate cyclic soil behavior. Results indicate that GQ/H+u provides reasonable estimates of PWP increase during cyclic shear, with differences between measured and computed excess PWP ratios (ru) for both element and centrifuge tests generally smaller than 0.1. Computed spectral accelerations are comparable to centrifuge test measurements, with almost no bias at medium to long periods (T > 0.4 s) when the computed maximum shear strain (γmax) was smaller than the limit shear strain (γlimit). When computed ru > 0.8 and computed γmax > γlimit, spectral accelerations may be underestimated at both short and long periods as dilative behavior is not captured by GQ/H+u.

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Numerical Modeling of Thermally Induced Pore Water Flow in Saturated Soil Surrounding Geothermal Piles

IFCEE 2015 ◽

10.1061/9780784479087.151 ◽

2015 ◽

Cited By ~ 2

Author(s):

Omid Ghasemi-Fare ◽

Prasenjit Basu

Keyword(s):

Numerical Modeling ◽

Water Flow ◽

Pore Water ◽

Saturated Soil ◽

Thermally Induced

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Amelioration of Wolffersdorff Hypoplastic Constitutive Model Considering Intergranular Strain Tensor

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.638-640.355 ◽

2014 ◽

Vol 638-640 ◽

pp. 355-359

Author(s):

Bao Lin Xiong ◽

Chun Jiao Lu

Keyword(s):

Constitutive Model ◽

Pore Water ◽

Cyclic Load ◽

Pore Water Pressure ◽

Water Pressure ◽

Strain Tensor ◽

Excess Pore Water Pressure ◽

Intergranular Strain ◽

Hypoplastic Constitutive Model ◽

Excess Pore

Under cyclic load, the major shortcoming–ratcheting is produced in Wolffersdorff hypoplastic constitutive model. For eliminating ratcheting, Wolffersdorff hypoplastic model is ameliorated based on intergranular strain tensor. The added parameters in ameliorated model are determined by optimization method. Under cyclic load of triaxial consolidation undrained condition, the mechanics features of sand are described by the ameliorated Wolffersdorff hypoplastic constitutive model. Preliminary result shows that with increasing times of cyclic load excess pore water pressure is increased gradually and effective stress is reduced gradually. When effective is reduced to zero, the liquefaction happens. So in many projects, excess pore water pressure must dissipate by means of some measures. The sand liquefaction under the dynamic load is avoided.

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Semi-analytical and semi-numerical method for the single soil layer consolidation problem

Engineering Computations ◽

10.1108/ec-10-2015-0297 ◽

2017 ◽

Vol 34 (3) ◽

pp. 960-987 ◽

Cited By ~ 4

Author(s):

Tao Cheng ◽

Keqin Yan ◽

Jun-Jie Zheng ◽

Xian-Feng Luo ◽

Ding-Bang Zhang ◽

...

Keyword(s):

Constitutive Model ◽

Numerical Method ◽

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Stress Path ◽

Surface Model ◽

Model Framework ◽

Content Type ◽

Simplified Solution

Purpose This paper aims to present a simplified solution method for the elasto-plastic consolidation problem under different stress paths. Design/methodology/approach First, a double-yield-surface model is introduced as the constitutive model framework, and a partial derivative coefficient sequence is obtained by using numerical approximation using Gauss nuclear function to construct a discretization constitutive model which can reflect the influence of different stress paths. Then, the model is introduced to Biot’s consolidation theory. Volumetric strain of each step as the right-hand term, the continuity equation is simplified as a Poisson equation and the fundamental solution is derived by the variable separation method. Based on it, a semi-analytical and semi-numerical method is presented and implemented in a finite element program. Findings The method is a simplified solution that is more convenient than traditional coupling stiffness matrix method. Moreover, the consolidation of the semi-infinite foundation model is analyzed. It is shown that the numerical method is sufficiently stable and can reflect the influence of stress path, loading distribution width and some other factors on the deformation of soil skeleton and pore water pressure. Originality/value Original features of this research include semi-numerical semi-analytical consolidation method; pore water pressure and settlements of different stress paths are different; maximum surface uplift at 3.5a; and stress path is the main influence factor for settlement when loading width a > 10 m.

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Numerical Evaluation of The Nonlinear Behavior of Soil-Pile Interaction Under The Effect of Coupled Static-Dynamic Loads

10.21203/rs.3.rs-1201856/v1 ◽

2021 ◽

Author(s):

Duaa Al-Jeznawi ◽

ISMACAHYADI Mohamed Jais ◽

Bushra S. Albusoda

Keyword(s):

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Three Dimensional ◽

Ground Surface ◽

Frictional Resistance ◽

Saturated Soil ◽

Shaking Table ◽

Physical Models ◽

Soil Layers

Abstract Liquefaction of saturated soil layers is one of the most common causes of structural failure during earthquakes. Liquefaction occurs as a result of increasing pore water pressure, whereby the rise in water pressure occurs due to unexpected change in stress state under short-term loading, i.e., shaking during an earthquake. Thus, general failure occurs when the soil softens and eliminates its stiffness against the uplift pressure from the stability of the subsurface structure. In this case, the condition of soil strata is considered undrained because there is not enough time for the excess pore water pressure to dissipate when a sudden load is applied. To represent the non-linear characteristics of saturated sand under seismic motions in Kobe and Ali Algharbi earthquakes, the computational model was simulated using the UBCSAND model. The current study was carried out by adopting three-dimensional-based finite element models that were evaluated by shaking table tests of a single pile model erected in the saturated soil layers. The experimental data were utilized to estimate the liquefaction and seismicity of soil deposits. According to the results obtained from the physical models and simulations, this proposed model accurately simulates the liquefaction phenomenon and soil-pile response. However, there are some differences between the experiment and the computational analyses. Nonetheless, the results showed good agreement with the general trend in terms of deformation, acceleration, and liquefaction ratio. Moreover, the displacement of liquefied soil around the pile was captured by the directions of vectors generated by numerical analysis, which resembled a worldwide circular flow pattern. The results revealed that during the dynamic excitation, increased pore water pressure and subsequent liquefaction caused a significant reduction in pile frictional resistance. Despite this, positive frictional resistance was noticed through the loose sand layer (near the ground surface) until the soil softened completely. It is worth mentioning that the pile exhibited excessive settlement which may attribute to the considerable reduction, in the end, bearing forces which in turn mobilizing extra end resistance.

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COMPOSED COEFFICIENT TECHNIQUE FOR MODELLING BARRETTE GROUPS

Malaysian Journal of Civil Engineering ◽

10.11113/mjce.v31n1.510 ◽

2019 ◽

Vol 31 (1) ◽

Cited By ~ 1

Author(s):

Mahmoud El Gendy ◽

Hassan Ibrahim ◽

Ibrahim El Arabi

Keyword(s):

Finite Element ◽

Soil Structure ◽

Linear Equations ◽

Large Section ◽

Element Mesh ◽

Soil Matrix ◽

Soil Stiffness ◽

Real Practice ◽

Surrounding Soil ◽

Coefficient Technique

Most of soil structure interaction methods for analyzing large-section supports such as barrette foundation modeling and the surrounding soil are using 3D finite element (FE) models. In which, the model leads to a large finite element mesh, and consequently a large system of linear equations to be solved. In this paper, Composed Coefficient Technique (CCT) is adapted for analyzing barrette group. The technique considers the 3D full interactions between barrettes and the surrounding soil. Due to the high rigidity of the barrettes relative to the surrounding soil, a uniform settlement for the barrettes can be considered. This is done to compose the stiffness coefficients of the soil matrix into composed coefficients, which consequently leads to a significant reduction in the soil stiffness matrix. An application for analyzing barrette group by CCT technique is carried out on a real subsoil. The application presents guidelines and diagrams for barrette group that may be used in real practice.

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