This work first describes a local thermal non-equilibrium (LTNE) model for investigating thermally induced deformations and stresses in a porous medium partially saturated with a wetting fluid and a non-wetting fluid. The LTNE model assumes that the two fluid phases experience the same temperature variation, which is different from that of the solid matrix in a continuum material particle. The temperature differential between the solid and fluid contributes to the thermally induced fluid content variations for both the wetting and non-wetting fluids. The LTNE model is subsequently employed to examine the thermally induced pore pressures and stresses around a cylindrical hole in an infinite partially saturated porous medium subjected to a uniform temperature variation at the hole boundary. Closed-form, asymptotic short-time solutions for the temperatures, thermal pore pressures, and thermal stresses are obtained using the Laplace transform technique. For a partially saturated porous medium with the non-wetting fluid saturation close to its residual saturation (i.e., porous flow is dominated by the wetting fluid), the numerical results indicate that partial saturation increases the thermal pore pressure of the wetting fluid as well as the thermal radial stress under LTNE. Compared with the results under local thermal equilibrium (LTE), the thermal pore pressures are reduced by LTNE in the partially saturated medium. In the meantime, LTNE leads to slightly higher thermal radial stress.

Abstract Sabkha environments are a prevalent topographic feature in arid coastal areas. Along the Arabian Gulf, sabkhas overlie substantial hydrocarbon reservoirs and exhibit intricate lithological characteristics and an extremely shallow water table. These factors contribute to elevated seismic velocities and signal distortion. Static correction, a crucial initial step in seismic reflection processing, is employed to mitigate the impact of shallow surface layers. In this study, we investigate the variations in seismic properties along the uppermost part of mature and developing sabkhas. We employed high‐resolution seismic experiments with geophone spacing of 10 cm to explore the upper tens of centimeters. Conventional surveys with a 2 m spacing complement this approach to investigate deeper layers. Both sabkhas exhibit a unique characteristic of a partially saturated zone, which affects the seismic velocity, leading to lower velocities and consequently influencing the accuracy of the static correction. The high‐resolution surveys demonstrated superior accuracy to conventional approaches in determining the top of the partial saturation zone and hardground layer, hence resulting in a more reliable velocity delineation. Moreover, velocities derived from conventional, replacement, and tomogram approaches resulted in unreliable static corrections in mature coastal sabkha compared with developing inland sabkha, attributed to the considerable geological complexity that is characteristic of mature coastal sabkha environments. Carrying out a high‐resolution seismic survey in sabkha environments is therefore necessary to mitigate near‐surface velocity effects.

The anelastic properties of seismic waves (attenuation and velocity dispersion) in partially saturated rocks depend on the spatial distribution of pore fluids. We map the fluid distributions in three sections of a limestone core sample with X-ray computed tomography (CT) scans and obtain the radii and volume fractions of the gas patches. These statistical data are input into an infinituple-porosity model with partial saturation, the results of which are compared with the forced oscillation (from 0.004 to 100 Hz) and ultrasonic (1 MHz) measurements, and the results of other approaches (the fractal model, the continuous random media model, and the finite-element method). The anelastic properties indicate significant differences among different sections due to fluid distribution. We find that it is possible to effectively characterize seismic anelasticity in a partially saturated limestone by using actual fluid distributions from CT scans and an appropriate petroelastic model. The agreement between the theory and the experiment proves the validity of our approach.

Abstract Liquefaction occurs in saturated granular soils. It is common practice in liquefaction assessments to assume soil located below the groundwater table to be fully saturated. However, numerous studies have shown many instances of soil below the water table were only partially saturated. A decrease in the saturation, even in small amounts, can significantly increase the liquefaction resistance of soil. This means that ignoring partial saturation in a liquefaction assessment may lead to an underestimation of liquefaction resistance. This research aims to investigate the degree of soil saturation on the field and its effects on liquefaction resistance at the Yogyakarta - Bawen toll road. The influence of partial saturation in a simplified liquefaction potential evaluation was calculated using the KS correction factor proposed by Hossain et al. Additionally, soil saturation on the field was measured using P-wave velocity (VP ) measurements with seismic refraction method. Liquefaction potentials without considering the effect of partial saturation were calculated for three sites at the Yogyakarta - Bawen toll road. The results indicated the presence of potentially liquefiable layers at all investigation sites. Compressional wave velocity tomograms showed soil layers situated below the water table were only partially saturated. Taking this into account, liquefaction potentials were recalculated with partial saturation correction factor applied. The recalculation produced an increased liquefaction resistance and, consequently, an improved liquefaction safety factor above 1.00 for all layers. These results demonstrated the influence of partial saturation on liquefaction resistance and highlighted the importance of partial saturation investigation in liquefaction potential studies.

Abstract Soil liquefaction caused by earthquakes is a devastating occurrence that can compromise the foundations of buildings and other structures, leading to considerable economic losses. Among the new remedies against liquefaction, Induced Partial Saturation (IPS) is regarded as one of the most promising technologies. In order to improve liquefaction resistance and the fluid phase‘s compressibility, gas or air bubbles are introduced into the pore water of sandy soils. This article deals with the general laboratory evaluation of a sand under partially saturated conditions and under cyclic loading to assess if this technology is applicable for a ground improvement of the examined soil. The use of the Axis Translation Technique for sample desaturation and diffusion‐stable butyl membranes significantly influences the laboratory results. Additionally, it is found that the trapped air bubbles of the partially saturated samples act like a damping mechanism, which are reflected in the stress paths of the deviator stress over the mean pressure with an inclination of 1 : 3.

Wave-induced fluid flow, widely accepted as a dominant loss mechanism of wave attenuation, can lead to significant seismic attenuation due to mesoscopic heterogeneities such as partial saturation. However, dependence of fluid distribution on microstructure in partially saturated porous media remains unclear. To quantify the relationship between microstructure and fluid distribution, a saturation fractal dimension is applied on the assumption of pore fractal distribution and gas patch fractal distribution. By integrating the Biot-Rayleigh theory, a theoretical model of partially saturated fractal porous media is established. The results indicate that the scales of fluid flow and the magnitude of peak attenuation are significantly influenced by the maximum gas patch size and the pore fractal dimension. Our model is further validated by comparing it with laboratory measurements. The findings indicate that the variations in the maximum gas patch size correspond to the variations in fluid distribution, and the peak attenuation will reach its maximum magnitude when the saturation fractal dimension equals the pore fractal dimension. The discrepancies between the measurements and modeling results are discussed, revealing that, in addition to microstructure, factors such as rock properties, boundary conditions, and saturation methods significantly influence the fluid distribution, as well as velocity dispersion and attenuation. Our theory provides a reasonable explanation of dispersion and attenuation in fieldwork, thereby presenting a novel perspective for future endeavors in forward modeling and seismic inversion.

ABSTRACT The finite element analysis was carried out to investigate the performance of pile foundations with dimensions (0.6 × 12) m in diameter and length, respectively, which is embedded in fully and partially saturated soils within Baghdad city. The behaviour of partially saturated clay is investigated through many factors, such as the degree of saturation, water table depth, clay shear strength, negative pressure head, soil density, permeability function, volumetric water content function, and unsaturated soil modulus (H). This study examined the adhesion factor (α) in piles at different water tables, saturation degrees, and the impact of partial soil saturation on the final shaft resistance. It is concluded that the pile capacity rises as the soil becomes partially saturated due to the water table dropping at varying depths and saturation levels. The study determined that the respective degrees of saturation and reduction of the water table in the three soils significantly influenced the skin friction values caused by partial soil saturation. The shaft resistance increases quickly when the water table is dropped to 2 and 4 metres. It is discovered that when matric suction is increased to a particular value, the shaft resistance decreases.

The economics of solar farms favour short piles that lie predominantly in the active zone where seasonal changes in moisture and degree of saturation occur. Pile design requires knowledge of shaft friction, yet information on interface friction for partially saturated clays is little reported, particularly for high-plasticity clays. Through this paper, the shear behaviour of a high-plasticity expansive clay is examined by using the results from soil-on-soil and soil-interface shearing on partially saturated specimens, using a direct shear box apparatus. The results demonstrate the transition of the response from plastic to brittle as suction increases, and illustrate that dilation is an inherent characteristic of unsaturated soil under shear enhancing soil strength in addition to the effects of the high suctions which are inherent to high-plasticity clays. While dilation is not significant at soil-interfaces, enhanced strength mobilization is observed due to the suction. The soil failure envelope shows a nonlinear increase in strength with suction, estimated from the soil-water retention curve, with interface tests showing a reduction in strength with suction beyond the air-entry value. An effective stress interpretation is shown to explain the interface response provided the parameter χ is evaluated from the shear tests accounting for the effects of dilation.

Sediments can facilitate the electrochemical processes that drive the corrosion of buried metallic components. Common analyses and guidelines emphasize the effect of pore fluid conductivity on soil corrosivity and overlook the effect of partial saturation; yet, most buried metals are situated within the vadose zone. The detailed experimental study reported herein used mass loss measurements from passive corrosion tests, X-ray microtomography, and image analyses to examine the evolution of corrosion in C-steel coupons embedded in sand specimens mixed with de-ionized water and brine at various degrees of saturation. Experimental observations show that corroding cells preferentially form at contacting grains, and that the evolution of corrosion is biased by the variability in packing density and saturation, while fluid conductivity plays a lesser role. Above all, results highlight the critical importance of percolating gas and water phases, and show that water–grain–metal interfaces restrict the actively corroding area to a fraction of the entire metal surface. A complementary macroscale analysis anticipates asymptotic conditions based on mass and charge conservation, and the transport of corroding agents and residuals. Together, the measurements and model results highlight the significant impact of the degree of saturation on corrosion rates and mass loss.

Density gradient structure foams prepared by novel two-step foaming strategy: Performance, simulation and optimization

The aim of this paper is to study the behavior of enlarged base piles embedded within partially saturated soils under compression and uplift loading. This type of pile is rarely excavated and cast on-site. Accordingly, to construct an enlarged base pile model, an excavator was designed and manufactured to give appropriate shape through drilling and casting in the laboratory through the design and manufacture of an excavator to produce piles with a shaft of 35 mm in diameter, 500 mm in length, and a base of 80 mm in diameter inclined at an angle of 60 degrees. Three different partial saturation soils were achieved by lowering the water level below the soil surface 20, 40, and 60 cm and measuring the suction force of each stage using a Tensiometer. The average matrix suction results were 6.4, 7.6, and 9.1 kPa for each lower water level, respectively. The test results showed that the bearing capacity of the enlarged base piles under compression load in partially saturated soil was higher than that in the case of full saturation because of matrix suction, with an improvement rate of 2.5–4.5 times compared with the case of fully saturated soil. Additionally, test results showed that the enlarged base piles subjected to uplift loading in partially saturated soil were significantly improved compared with the fully saturated condition, with an improvement rate of 1.5 - 3 times. The reason for this is the apparent surface cohesion of the sandy soil, which increases the bearing capacity of the sandy soil. This study sheds light on the phenomenon of apparent surface cohesion of sandy soil and the extent of its effect on increasing the soil’s resistance to the loads placed on it. Doi: 10.28991/CEJ-2024-010-10-08 Full Text: PDF

Despite additional availability of laboratory data from water-saturated sandstone at seismic frequencies, measurements of rock samples saturated with high viscous fluids, particularly at partial saturation, are still rare. To quantify the effects of fluid viscosity and saturation levels on seismic dispersion and attenuation characteristics, we conducted two comparative forced-oscillation measurements in partially saturated sandstone with varying fluid viscosity (e.g., water, glycerin) at seismic frequencies (2–400 Hz). The results demonstrate that fluid viscosity and saturation levels substantially influence the dispersion and attenuation characteristics at the measured frequencies. Significant dispersion and attenuation are observed in the presence of a relatively small amount of gas (approximately 6%–8%) for glycerin and water saturation cases but vary in their magnitudes and characteristic frequencies. Specifically, the maximum extensional attenuation (approximately 0.024) occurs at approximately 200 Hz for water-saturated rock at 94% saturation, whereas at approximately 30 Hz with a peak of 0.032 for glycerin-saturated rock at 92% saturation. Based on theoretical modeling analysis, we suggest that mesoscopic fluid flow might be a dominant mechanism accounting for the observed attenuation in partial water or glycerin saturation, while the microscopic (squirt) flow mechanism possibly dominates the fully saturated cases.

Geotechnical properties of surficial beach sediments affect beach erosion and shoreline changes. This study sets out to measure relative density, moisture content, friction angle, and shear strength of sandy beach surface sediments from dune to swash zone towards the goal of assessing their importance in sandy beach morphodynamics. Methods of sediment sampling, a conductivity based moisture probe, field penetrometers, and a field vane shear were deployed to collect data at the sandy Atlantic-side beach in Duck, North Carolina. The tools used were assessed based on their operability in the beach environment and data quality, and results are discussed in the context of beach morphodynamics. A digital field vane shear provided an efficient and direct method of measuring shear strength, but the difficulty of computing stresses on the failure plane, which is necessary to validate the results, ultimately reduced the usability of this instrument. The results from three penetrometers were compared to a partially-saturated bearing capacity model, where a portable free-fall penetrometer yielded the best fit. However, a modified velocity-dependent strain rate correction factor (K=0.31vi) was required to convert dynamic sediment resistance to a quasi-static resistance for the partially saturated sands. A small-scale digital push in penetrometer also achieved a positive correlation when compared to moisture content, but the small tip diameter (5 mm) coupled with the grain size at the beach (0.35 mm) raised concerns about the ability to derive an accurate measure of strength. It was determined that estimating strength parameter using a partially saturated bearing capacity model was appropriate for water contents less than 25% by volume, or anywhere in the crosshore above the swash to the dune. Relative density and moisture content were found to be closely linked, with partial saturation resulting in samples that featured negative relative densities up to −40%.

Site response analysis (SRA) is an important aspect of seismic design that considers the impact of local site conditions on the ground response during earthquakes and plays a key role in the design of structures that interact or are made with soil. Although previous studies have demonstrated that factors such as the degree of saturation influence the site response, incorporating partial saturation into analysis has not been widely practiced. Numerical analysis tools exist; however, they are often unable to directly assess the influence of partial saturation, especially under seismic conditions. This is often caused by the missing implementation of constitutive models and finite elements able to account for partial saturation of soils under cyclic conditions. For this reason, a review of the most common constitutive models developed with a view to describing unsaturated soil behaviour subjected to cyclic loads is presented, followed by a critical discussion on their applicability to finite element frameworks, with the aim of providing a wide panorama of the available constitutive platforms suitable for implementation in numerical codes. Therefore, we present and discuss the mechanical and hydraulic properties of the constitutive models that can be applied to the analysis of boundary value problems, and specifically for SRA, focusing on partially saturated soils under cyclic loading conditions. It was observed that many constitutive model frameworks for cyclic loadings are based on the bounding surface or two‐surface theories, and some of them are coupled with hydraulic behaviour through the Soil Water Retention Curve (SWRC) or its variations. Two main approaches were identified based on the mechanical features, while regarding the hydraulic behaviour, the main distinction lies in the selected SWRC. Furthermore, certain constitutive models have been implemented in finite element software for numerical analysis of geotechnical earthquake engineering problems.

This paper focuses on the evaluation of effects of partial saturation on the liquefaction response of two free-field level-ground deposits from Christchurch (New Zealand). The first deposit is composed of vertically continuous liquefiable soils with a low-resistance critical zone at shallow depth and is typical of sites that manifested moderate-to-severe liquefaction at the ground surface in several events during the 2010-2011 Canterbury earthquake sequence. The second deposit consists of liquefiable soils of low liquefaction resistance interbedded with non-liquefiable layers, and is typical of sites that did not manifest liquefaction in any of the 2010-2011 seismic events. High-resolution measurements of compression wave velocity (Vp) have indicated the existence of a partially saturated zone at shallow depth below the groundwater table in both deposits, though with somewhat different characteristics. We assess the performance of the two deposits for the 22 February 2011 Christchurch earthquake using simplified liquefaction triggering analysis as well as advanced nonlinear dynamic analysis. Partial saturation effects are considered in both types of analyses by “correcting” the liquefaction resistance of the partially saturated soils on the basis of an empirical Vp-based relationship. The analyses indicate that partial saturation contributes to the formation of a specific sequence of system-response mechanisms that collectively act to mitigate liquefaction manifestation in the case of the interbedded deposit. In the case of the vertically continuous deposit, however, the mitigating effect of partial saturation is counteracted by system-response mechanisms that intensify the effects of liquefaction. The results highlight the importance of considering the effects of partial saturation in the context of the overall system response of liquefying deposits and consequent liquefaction manifestation.

Liquefaction, a common issue in cohessionless, saturated soils under static and dynamic loading. Inducing partial saturation is a recent method to mitigate the liquefaction of sand by generating gas or air in the pores of saturated sand. Since the fluid bulk stiffness of soil is very sensitive to the presence of gas or air, a small volume of bubbles can significantly affect the pore pressure response to loading. However, conventional measures against soil liquefaction are often expensive and unsuitable for existing structures. This study aimed to assess the effectiveness of the air injection method in preventing liquefaction in saturated sand using cyclic triaxial apparatus. Stress-controlled triaxial tests were performed on loose saturated and treated sand considering different cyclic stress ratio and confining pressure. Additionally, this study examined the durability of entrapped air bubbles under field conditions that may lead to dissolution or escape of air bubbles. To evaluate the long-term stability of the bubbles tests were conducted on partially saturated sand under hydraulic gradient flow condition. The results demonstrated a significant improvement in liquefaction resistance for the treated sand, with a reduced degree of saturation ranging from 95% to 80%. Furthermore, in durability study after downward water flow, the degree of saturation of partially saturated sand slightly increased and remained stable, indicating long-term stability

The paper studies the possibility of attenuating the wave intensity on the surface of a half-space by installing a barrier based on the solution of a three-dimensional problem of the dynamic theory of partially saturated poroelasticity using the boundary element method. The basic idea of using a wave barrier is to create an obstacle to the propagation of surface waves over the territory occupied by structures or constructions. Open or unfilled trenches can be effective when organizing this method of protection. In the paper, numerical modeling is performed using the boundary element method based on the combined use of boundary integral equations of the direct approach of the three-dimensional isotropic theory of poroelasticity and the integral Laplace transform. To describe the poroelastic medium, the Biot model of a poroelastic material in the case of partial saturation is used. The solution in the time domain is obtained using a method based on quadrature formulas for calculating the convolution integral and referred to hereinafter as the step method. The problem of the action of a dynamic load on a deformable partially saturated poroelastic half-space with a vertical barrier in the form of a trench is considered. To assess the efficiency of wave damping by a barrier on the surface of a half-space, the amplitude reduction factor is calculated for different values of the saturation coefficient of the poroelastic material of the half-space, geometric dimensions of the barrier and boundary conditions. Graphs and maps of the amplitude reduction factor are provided. The simulation results show that the presence of a barrier in the form of a trench leads to a decrease in the Rayleigh wave amplitude at points located behind the trench, for all considered values of the parameters under study. It is also shown that the condition of permeability or impermeability of the trench boundary does not have a noticeable effect on its properties in reducing the intensity of surface waves. The results obtained can be useful for developing effective methods for protecting buildings and structures from dynamic effects.

Abstract Geometric heterogeneities in tight reservoir rocks saturated with a fluid mixture may exhibit different scale distribution characteristics. Conventional models of rock physics based on poroelasticity, which usually consider single‐scale pore structure and fluid patches, are inadequate for describing elastic wave responses. A major challenge is to establish the relationship between the wave response at different spatial scales and frequencies. To address this problem, three sets of observational data over a wide frequency range were obtained from a tight oil reservoir in the Ordos Basin, China. Ultrasonic measurements were made on eight sandstone samples at partial oil‐water saturation at 0.55 MHz. Data from six borehole measurements and seismic profiles were acquired and analyzed at about 10 kHz and 30 Hz, respectively. Analysis of the cast thin sections shows that dissolution pores and microcracks generally develop, with fractal dimensions of the pores ranging from 2.45 to 2.67 for the samples with porosities between 5.1% and 10.2%. Compressional wave velocity and attenuation were estimated from the observed data. The results show that the velocity dispersion from seismic to ultrasonic frequencies is 10.02%, mostly occurring between sonic and ultrasonic frequencies. The attenuation is stronger at higher oil saturation. The relationships between velocity, attenuation, and wavelength were established and can be used for further forward modeling and seismic interpretation studies. A partial saturation model has been derived based on effective differential medium theory and a double double‐porosity model, assuming that the medium contains fractal cracks and fluid patches. The effects of scale and saturation on wave responses are prevalent. Modeling results consistent with observed data show that the radii of cracks and fluid patches range from 0.1 μm to 2.8 mm, affecting ultrasonic, acoustic, and seismic attenuation. The multiscale data and proposed model quantify the relationship between fracture and fluid distributions and attenuation and could be useful for upscaling to the reservoir scale. The study helps improve the understanding of seismic wave propagation in partially saturated rocks, which has potential applications in seismic exploration, hydrocarbon production in reservoirs, and CO2 sequestration in aquifers.

Effects of partial saturation on the liquefaction resistance of sand and silty sand from Christchurch

Coupled hydro-mechanical model for partially saturated soils based on Cam-Clay plasticity