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The resistance to liquefaction of soils can be significantly increased by slightly reducing the degree of saturation. Many experimental studies demonstrated that the augmented compressibility of the pore fluid mixture composed by entrapped bubbles within a continuous fluid phase reduces the amount of seismically induced excess pore water pressure. On the contrary, interpretation through constitutive models of the cyclic response of nearly saturated soils, often referred to as gassy soils, is by far less explored in the literature. This paper addresses this topic by considering the gas–water mixture as a homogeneous equivalent fluid whose compressibility has been used along with the elastoplastic constitutive model formulated by Dafalias and Manzari (2004). The model has been calibrated on the experimental data obtained from monotonic triaxial tests on saturated sandy soils and then validated with the results of cyclic triaxial tests on saturated and non-saturated liquefiable sandy soils. The selected calibration has been used to perform parametric analyses by varying the initial conditions of the soil (i.e., the relative density and degree of saturation), thus further emphasizing the beneficial effect of quasi-saturated fluid to delay the onset of liquefaction instabilities. [ABSTRACT FROM AUTHOR]

In this paper, by introducing a new yielding mechanism based on the widely acknowledged double-structure theory, the original UH model for unsaturated soils is extended to capture the behaviour of expansive clays. A novel expansion potential is further established to evaluate the effect of overconsolidation on the volume change of unsaturated expansive clays during wetting. With only one additional parameter, the proposed model can describe the behaviour of both wetting-collapse and wetting-induced swelling for unsaturated clays. Comparisons between model predictions and test results show a good agreement which verifies the capability of the proposed model in charactering the features of unsaturated expansive clays under various stress histories and stress paths. [ABSTRACT FROM AUTHOR]

The bearing capacity of shallow foundation is significantly affected by stratum uncertainty, mainly including geological uncertainty and spatial variability of soil properties. This paper aims to develop a general framework of shallow foundation to characterize the influence of two types of uncertainties on bearing capacity quantitatively. The geological uncertainty is simulated by Markov random field with different borehole schemes. The spatial variability is characterized using random field theory considering variations of the vertical scale of fluctuation. The bearing capacity of shallow foundation analysis is then conducted based on the proposed calculation framework. Borehole data and soil properties collected from Shenzhen Mawan are adopted as an example to illustrate the proposed framework. A reduction factor is developed to reveal the relationship of two category uncertainties on bearing capacity. A contribution rate indicator is defined to quantitatively evaluate the impact of two category uncertainties. Results show that the geological uncertainty greatly influences the calculation results when boreholes are sparse. However, spatial variability dominates in two kinds of uncertainties when having relatively more boreholes. [ABSTRACT FROM AUTHOR]

The site investigation is a key part of the design of tunnel construction projects, as it provides accurate geotechnical parameters. A systematic site investigation, which consists of mainly in situ tests and laboratory sample tests, was conducted for the Haimen-Taicang river-crossing tunnel project on Yangtze River. This paper aims to analyze and compare the piezocone penetration testing (CPTU) and dilatometer test (DMT) results of both onshore and under-river subsoils to provide insights into the interpretation of the in-situ tests. The accuracy of well-documented interpretation methods based on CPTU and DMT was discussed. Current empirical correlations between in-situ test results and unit weight, undrained shear strength and constrained modulus of the subsoils were checked, and their site adaptability was discussed in detail. A series of site-specific correlations were derived based on the analysis of the in-situ tests and the comparison between the in situ tests interpretation and the laboratory results. In order to reduce the errors between testing locations caused by soil variability and get the consistent understanding of soil behaviors, CPTU–DMT correlations were reviewed and improved based on local testing results. [ABSTRACT FROM AUTHOR]

This paper proposes a powerful hybrid Eulerian–Lagrangian (HEL) approach for the analysis of cavity expansion problems. The new approach is applied to analysing the non-self-similar expansion process of a hollow cylinder of critical state soils, considering arbitrary saturation states of soils and both drained and undrained conditions. A closed-form solution for the stresses and displacements in the elastic zone is presented, taking the state-dependent soil moduli and outer boundary effect of the soil cylinder into account. Adopting large strain theory in the plastic zone, the non-self-similar cavity expansion process is formulated into a set of partial differential equations in terms of both Eulerian and Lagrangian descriptions, which is solved by a newly proposed algorithm. The HEL approach is compared with the conventional Eulerian and Lagrangian approaches for the cavity expansion analyses. It is found that the new approach can reduce to the Eulerian approach when the self-similar assumption is satisfied and to the Lagrangian approach when stress–total strain relationships are obtained analytically. Finally, the expansion process is proven to be non-self-similar by showing the stress and deformation paths, and the finite thickness of soil cylinders may greatly influence the cavity expansion behaviour, especially with a small thickness ratio. The HEL approach can provide useful tools for validating advanced numerical techniques for both saturated and unsaturated soils and interpreting pressuremeter tests in small-size calibration chambers. [ABSTRACT FROM AUTHOR]

An advanced constitutive framework for unsaturated soils, the UTUH model, is proposed in this paper, which considers the joint effect of time, suction and overconsolidation within the framework of sub-loading surface plasticity. A reference line, namely the instantaneously normal compression line (INCLs) for unsaturated soils, is introduced from a conceptual framework drawn from constant rates of strain test results to determine creep time and overconsolidation states of unsaturated soils. Subsequently, an isotropic elasto-viscoplastic constitutive model for unsaturated soils is produced by combining viscous deformation with mechanical and hydraulic deformation through overconsolidation parameter. Net stress, suction and time are adopted as fundamental constitutive variables and time-dependent loading collapse yield surface is derived to characterize the relationship between yield stress, suction, and time. Then, an extension to a triaxial stress state is built in the space of mean effective stress, suction, deviator stress and time variable. The hardening of yield surface and sub-loading surface is controlled by viscoplastic volumetric strain and unified hardening parameter. The performance of the proposed UTUH model is addressed through four numerical studies, and the proposed model is validated against experimental data from the literature. [ABSTRACT FROM AUTHOR]

The critical state line (CSL) is important for characterizing soils' properties. However, particle breakage is inevitable for granular soils such as rockfill. Therefore, the impact of particle breakage on CSL has always been one of the main focuses. Unfortunately, it has not yet been adequately resolved how particle breakage influences CSL quantitatively. Large-scale drained triaxial shearing tests of rockfill materials under various initial gradations, initial void ratios and confining pressure have been conducted in this paper. It shows that particle breakage could result in decrements in both of the stress ratio and void ratio at the critical state. The equation for a critical state line with none breakage (NBCSL) was theoretically derived and demonstrated. The intercept and gradient of CSL and NBCSL are inextricably related because of particle breakage, which has been quantified as follows: the intercept of CSL is identical to NBCSL's, and the gradient of CSL is a breakage-related constant plus that of NBCSL. In other words, the CSL and NBCSL of rockfill materials has actually been described by a unified equation. Based on this, the translation and rotation of CSL induced by changing gradation and void ratio can be explained from the essence of particle breakage. [ABSTRACT FROM AUTHOR]

Biological-formed fossilized diatom sediments have unique physical, electrical, and mechanical properties due to the shape, internal open porosity, and brittleness of the individual particles. The presence of diatoms strongly influences the overall behavior of soils. However, engineers and researchers find this influence challenging to quantify because measuring fossilized diatom content is elusive. This paper uses simple physical, electromagnetic, and mechanical engineering measurements to characterize the response of the artificial soils prepared with known amounts of fossilized diatoms under different pore-chemistry fluid and mechanical environments. Soils with high fossilized diatom content tend to retain high quantities of water even under high NaCl-concentration pore fluid. This response results from the internal porosity and is not a function of electrical forces on the particle surface. Furthermore, internal porosity governs electrical and mechanical properties under different pore fluid environments. Despite having elevated Liquid Limits, soils with high fossilized diatoms content do not deform while drying and changing pore fluid salt concentration. However, fossilized diatoms are brittle and offer high compressibility and low particle crushing stress (around 2–4 MPa). Our results show that simple physical and index tests can help assess the effect of fossilized diatoms' in soils, and provide a framework to predict the engineering properties of natural soils containing a wide range of fossilized diatoms even when diatom content cannot be precisely measured. [ABSTRACT FROM AUTHOR]

Digital image correlation (DIC) and particle image velocity (PIV) are highly effective non-contact methods to accurately measure full-field deformations in transparent soil model testing (TSMT). The nature of transparent soils combined with the rapid development of three-dimensional (3D) DIC/PIV techniques means that the acquisition of the full internal 3D deformations is now technically feasible. However, current approaches focus on two-dimensional (2D) in-plane displacements and typically ignore out-of-plane displacements. This paper presents an approach of combining 3D-DIC with optical slicing to observe 3D movements of transparent soil using custom MATLAB programming. A rigid body motion (RBM) test of a transparent soil sample is first conducted to estimate the accuracy of the proposed algorithm. A vertically loaded circular footing test is subsequently performed as a proof of concept; multiple-slice images of the soil are captured using a new experimental apparatus and processed by the 3D-DIC algorithm, and the resultant 3D displacements of all slices are reconstructed to visualize the soil deformations in 3D space. The findings confirm that the proposed 3D-DIC algorithm is accurate and the optical slicing with supplementary spatial reconstruction method enables visualization of transparent soil in 3D space, which can be used in future TSMT. [ABSTRACT FROM AUTHOR]

There are two major challenges for the use of enzyme-induced carbonate precipitation (EICP)-based soil improvement method: cost and treatment effect. Optimizing the parameters of the treatment solution is one way to enhance the treatment effect and/or reduce the treatment cost. In this study, three key factors: the initial pH (i.e. pH0) of the enzyme solution used to prepare the treatment solution (i.e. the mixture of enzyme solution, CaCl2 and urea), the urease activity of the treatment solution and the concentration of cementation solution (i.e. CaCl2 and urea) are investigated. Crude soybean enzyme solution and the one-phase-low-pH injection method are adopted for the treatment of sand. The results show that the pH0 of the enzyme solution affects the urease activity of enzyme and thus the urease activity of the prepared treatment solution. It is discovered in this paper that there is a threshold pH value for the treatment solution. Only when the pH of the treatment solution is higher than the threshold pH value, calcium ions convert completely into calcium carbonate. There is also a threshold urease activity which is affected by the concentration of cementation solution, CCS. The optimal CCS is 1.0 M. When the CCS is higher than 1.75 M, the urease activity of soybean enzyme solution would be completely lost. These findings are important in guiding the application of EICP treatment using the crude soybean enzyme in real soil improvement projects. [ABSTRACT FROM AUTHOR]

Fused quartz and a suitable pore fluid with the same degree of refractive index are widely used to manufacture the transparent sand, which can be used to emulate the behavior of saturated natural sands in visualization model tests. Based on previous research, the static properties of transparent sand are comparable to those of natural sands, but whether the dynamic characteristics of transparent sand made from fused quartz with different pore fluids are similar to those of natural sand has not been proved so far. In the paper, dynamic behavior (undrained cyclic behavior, liquefaction resistance, and flow characteristics) of fused quartz sand and natural soils of the same grade at four different pore fluids are compared through undrained cyclic triaxial experiments. Findings indicate that dynamic characteristics of transparent sand are significantly influenced by pore fluids, and the dynamic behavior of transparent soil made from fused quartz and mixed oil exhibits similar dynamic properties to natural soils. [ABSTRACT FROM AUTHOR]

This paper presents an elastoplastic model to estimate the hydromechanical behavior of unsaturated soils based on state boundary hypersurface. Through mechanical hypersurface, the influence of saturation on yield stress can be expressed in a full form rather than an incremental form. Two hydraulic hypersurfaces and one mechanical hypersurface are proposed to establish the model. Two hydraulic hypersurfaces, composed of degree of saturation, void ratio and matrix suction, define the plastic hydraulic boundary. The elastic hydraulic behavior of unsaturated soils can be represented by scanning lines between these two hydraulic hypersurfaces. The mechanical hypersurface, composed of degree of saturation, void ratio and effective stress, defines the plastic mechanical boundary. The elastic mechanical behavior of unsaturated soils can be represented by scanning lines below the mechanical hypersurfaces. A large number of laboratory tests are used to validated the proposed model, showing that it can reasonably capture important features of the hydromechanical behavior of unsaturated soils. [ABSTRACT FROM AUTHOR]

This document is a reply to a discussion on a paper titled "3D image-based method to measure soil stiffness in triaxial tests." The authors respond to comments made by the discusser regarding the post-image analysis of the 3D-PIV method. They address concerns about stereophotogrammetry, refraction effects, and the calibration method. The authors argue that their method is accurate and meets the requirements for small strain stiffness measurements in triaxial tests. They also discuss proposed improvements to the system, including attaching targets to the triaxial chamber and using ray tracing techniques. The authors conclude that their method is cost-effective and provides accurate measurements for routine soil stiffness testing. [Extracted from the article]

Landslides due to catastrophic weather events, especially heavy rainfall, have risen significantly over the last several decades, causing significant damage and affecting the health and livelihoods of millions of people. Using tree roots to bio-engineer shallow slopes has been proven to be a cost-effective, sustainable measure and thus has gained increasing popularity. As slope failure often occurs under heavy precipitation, it is important to understand the mechanical interactions in the soil matrix surrounding a root to better estimate the reinforcement capacity of a root system, especially as the soil undergoes wetting from drier conditions. However, very few studies of root reinforcements have considered the effects of degree of saturation on behaviour. In this study, steel wires are used as a root analogue to explore the impact of root geometry, soil dilation and soil saturation on the pull-out behaviour of a root and three commonly used unsaturated soil strength models have been used to interpret the pull-out results. It was found that roots with larger diameter did not contribute to additional resistance. Also, a linear relationship between degree of saturation and pull-out strength was identified over a large range of suctions and one of the unsaturated soil strength models seemed to provide a more reasonable interpretation. The results will help future bioengineering slope design by improving the understanding of soil-root interface behaviour, including the effect of root diameter in slippage failure and greater emphasis on the importance of taking degree of saturation into account in unsaturated soil strength models. [ABSTRACT FROM AUTHOR]

Lightweight geomaterials have been widely used as seismic buffers in geotechnical engineering. A kind of biobased lightweight geomaterial, lightweight sand-mycelium soil (LSMS), which consists of host soil, substrate material (wheat bran), and hyphae, was proposed in this study. To investigate the dynamic properties of LSMS, a series of strain-controlled cyclic triaxial tests were performed. The effect of substrate material content and effective confining pressures on the dynamic properties of LSMS was studied. The results showed that the LSMS is capable of self-sustaining because sand particles and wheat bran are bonded by mycelium from fungal growth. The normalized shear modulus ( G d / G 0 ) of LSMS decreased, and the influence of effective confining pressures on G d / G 0 was weakened with increasing substrate material content ( W s ). The damping ratio of LSMS was strain dependent, and there is a threshold in the shear strain where the influence of W s on the damping ratio becomes different. Based on the experimental results, the models considering the influence of W s on LSMS are proposed for shear modulus and damping ratio characteristics. The dynamic characteristics of LSMS show that as a lightweight geomaterial, it can be used as a seismic buffer. [ABSTRACT FROM AUTHOR]