Journal of Geotechnical and Geoenvironmental Engineering

The soil sorptive potential (SSP) has been recently theorized as the physical source for matric potential and local pore-water pressure. It consists of four distinct physicochemical potentials with electromagnetic nature: van der Waals, electrical, cation and surface hydration, and osmosis. A general framework is developed to link the SSP, soil water density (SWD), specific surface area, and soil water retention curve (SWRC), providing an experimental way to determine the SSP and SWD functions. The experimentally determined SSP and SWD functions for different clays accord well with the theoretical SSP and measured SWD data, validating the framework. The parameters governing the SSP, i.e., Hamaker constant and structural parameters, are identified through inverse modeling of the water sorption isotherms (SWRC) of different clays, falling within the ranges reported in the literature and thus further confirming the validity of the SSP concept and its determination framework. The variability analysis of different clays, i.e., Georgia kaolinite, Wyoming montmorillonite, Denver claystone, and Denver bentonite, indicates that the SSP can vary up to 6 orders of magnitude, resulting in the same orders of magnitude change in compressive pore-water pressure and abnormal $1.3\mathrm{g}/{\mathrm{cm}}^3$ in soil water density.

This paper demonstrates reliability-based analysis of tensile strength and pullout limit states for mechanically stabilized earth (MSE) walls constructed with steel-strip reinforcement. Five different reinforcement tensile load models, three different pullout models, and one tensile strength model were examined. The accuracy of each model was assessed probabilistically using bias statistics in which bias was the ratio of the measured value to the predicted value. The tensile limit state included uncertainty in the tensile strength due to variability in original strength of the steel and variability in potential loss of strength due to corrosion. Reliability-based analyses were carried out considering the accuracy of the load and resistance models that appear in each limit state equation plus uncertainty due to the confidence (level of understanding) of the engineer at the time of design. The reliability index was computed using Monte Carlo simulation of the tensile strength limit state and a convenient closed-form solution that is easily implemented in a spreadsheet for the pullout limit state. A MSE wall example was used to demonstrate the general approach and to compare margins of safety using different load and resistance model combinations and reinforcement strips of different initial thickness.

A framework for the estimation of coseismic deformations in the postliquefaction regime is developed based on an extensive database of available cyclic undrained stress-controlled tests on clean sand samples without static shear bias, covering a wide range of relative densities. Based on fundamental experimental observations, a compliance rate is defined as the postliquefaction shear strain rate per cycle over the shear stress amplitude. Semiempirical relationships of the compliance rate as a function of relative density are developed to provide guidance for estimating postliquefaction shear strains. The proposed framework provides a basis for the calibration of advanced constitutive models capable of capturing postliquefaction strain accumulation. A calibration methodology is proposed using both existing liquefaction resistance curves and the newly developed semiempirical relationships for estimating postliquefaction shear strain accumulation. The validity of the proposed methodology is demonstrated by numerical simulations, using the PM4Sand model, of two well-documented centrifuge tests focusing on liquefaction-induced demands on engineering structures.

Because of the recent advancements in hardware and reconstruction algorithms, multiphase flow modeling in porous media is experiencing a shift toward using advanced imaging techniques such as X-ray computed tomography in conjunction with direct numerical simulations. This approach captures heterogeneities in soil samples utilized in laboratory testing and results in quick and less tedious predictions compared to the existing methods. In this paper, an experimental setup is developed specifically to validate numerical predictions of the soil water retention curve (SWRC) for two types of sands with identical size but distinct grain morphology of round (Ottawa sand) and angular particle shape (Q-Rok). The complex 3D pore network is captured noninvasively using high-resolution attenuation-based X-ray computed tomography. The numerical predictions are carried out by solving a Young-Laplace equation using the pore morphology method. The experimental results and numerical predictions match well, including the effect of hysteresis in SWRC measurements. The spatial distribution of pore water and pore air corresponding to different capillary suctions is obtained from numerical predictions, providing greater insights into the hydromechanical behavior of partially saturated soils. The sensitivity of the voxel size on simulations is quantified by predicting the pore size distribution of Ottawa sand at three different tomography resolutions.

Steel-reinforced high-density polyethylene (SRHDPE) pipe was developed to overcome the disadvantages of steel and high-density polyethylene (HDPE) pipes. In consideration of the long-term serviceability of buried pipes, the time-dependent performance of SRHDPE pipes deserves investigation. In this study, three 8-m (26.2-ft) SRHDPE pipes were installed in a trench in the field with a soil cover thickness of 0.9 m (3 ft). The backfill materials were well-graded aggregate base 3 (AB3) aggregate and poorly-graded crushed stone. A new concept, equivalent pipe stiffness factor, was proposed to consider the large difference in stiffness between pipe and soil for calculating pipe deflection under long-term conditions. The test sections were instrumented with earth pressure cells, displacement transducers, and strain gauges and monitored continuously for 680 days. Measured data indicated that earth pressures increased with time in both AB3 aggregate and crushed stone sections. Vertical arching factor (VAF) increased faster in the crushed stone section than that in the AB3 aggregate section. Pipe deflections in both sections increased with time. The maximum pipe deflections in the AB3 aggregate and crushed stone sections were 0.3% and 0.4% of the pipe diameter at 680 days after installation, respectively. Strains of plastic valley, plastic cover, and steel ribs in both sections were all smaller than the AASHTO limit within 680 days. Finally, empirical relationships were developed for the VAF and the equivalent pipe stiffness factor in order to predict the performance of SRHDPE pipes at a given time.

Understanding the transport and deposition behavior of particles within porous media is of importance because clogging can degrade the long-term performance of hydraulic infrastructure (e.g., artificial recharge system, cutoff walls, and infiltration structures) due to the reduction of hydraulic conductivity. In addition, the deposition behavior significantly affects the transport of contaminants that are favorably adsorbed to particles. Between the various factors affecting deposition behavior, geochemical conditions can affect both the interaction energy between particles and the porous medium, as well as aggregation behavior of particles; however, the impact of prevailing geochemical conditions on particle transport and deposition is not well understood, particularly when the particles are clay minerals. Therefore, a series of soil column tests was performed to study the transport of kaolinite under variable solution chemistry (pH and ionic strength) and flow rate (low and high). The observed deposition profiles and breakthrough curves of kaolinite particles revealed that the reduction of hydraulic conductivity was most significant at low pH ($\mathrm{pH}\sim 3$), regardless of flow rate. In addition, the reduction of hydraulic conductivity due to clogging was a stronger function of solution chemistry at low flow rates, which is attributed to the impact of solution chemistry on the size of kaolinite clusters, the interaction energy between sand and kaolinite, as well as the impact of hydrodynamic force on deposition behavior of kaolinite.

The objective of this study was to evaluate the strength reduction of heat-treated and non-heat-treated needle-punched geosynthetic clay liners (NP GCLs) at elevated temperatures. For this purpose, a series of stress-controlled rapid-loading shear tests were performed on two NP GCLs with similar peel strength but different heat treatment. Tests were performed at temperatures of 20°C, 40°C, 60°C, and 80°C under three different normal stresses (20, 40, and 60 kPa). Internal shear behavior of NP GCLs was described as a three-mechanism conceptual model. Elevated temperature resulted in a systematic decrease in the shear stress at failure in both heat-treated and non-heat-treated NP GCLs. The internal shear strength and shear deformation mechanisms in NP GCLs are dependent on the strength of reinforcement fibers and fiber bundle–geotextile connection. Thus, the internal shear behavior of NP GCLs as a function of temperature was evaluated via changes in the tensile modulus of monofilament fibers and entanglement strength of fiber bundle–geotextile connections. In heat-treated GCLs, an increase in test temperature to 80°C reduced the tensile modulus of reinforcement fibers. In non-heat-treated GCLs, an increase in test temperature to 80°C reduced the fiber bundle–geotextile entanglement strength. These reductions in tensile modulus and fiber bundle entanglement strength corresponded to reductions in internal shear strength of NP GCLs.

Mixing discrete flexible fibers into sand is a reinforcement technology that increases the sand’s strength as well as ability to resist liquefaction. This study demonstrates the mechanisms by which the applied loads are distributed across and shared by a sand’s skeleton, the fibers, and the pore water in drained and undrained triaxial compression tests. It is shown how the effective stress on the sand skeleton may be quantified by invoking the rule of mixtures and separate constitutive laws for the fibers and sand skeleton. It is also shown how the fibers alter the load paths experienced by the sand skeleton. Most notably it is shown how the fibers prevent liquefaction and that the conventionally defined pore water pressure ratio may incorrectly indicate otherwise. Alternate and more suitable pore water pressure ratios are introduced, accounting for the transversely isotropic orientation distribution of fibers that prevails in most fiber-reinforced soils, that gives an accurate indication of how far away the reinforced sand skeleton is from a liquefied state. The new pore pressure ratios, which are dependent on the direction of the principal stresses and account for the fiber orientations, are for use in any situation when the potential liquefaction of fiber-reinforced sand is a concern. Use of the conventional pore pressure ratio, which until now has been the only one employed in the literature, may make the fiber-reinforcement technology appear less effective at suppressing liquefaction than it actually is. This may, incorrectly, hinder its uptake in industry.

A technique to predict the response of laterally loaded battered piles in sandy soils is developed based on soil–pile interaction. The proposed method employs the concepts of the strain wedge (SW) model, which were originally developed for laterally loaded vertical piles. Unlike current practices that use a multiplier for the $p–y$ curve of the vertical pile, the suggested technique accounts for soil and pile properties and the direction and magnitude of the pile batter angle from the vertical position in the calculation of the pile lateral response and the assessment of the $p–y$ curves. The developed model shows the effect of pile battering on the predicted $p–y$ curve at varying depths compared to the $p–y$ curve of the vertical pile (i.e., a varying $p–y$ multiplier). The model has been validated through comparisons with full-scale and model-scale pile load tests.

Significant research conducted over the last 20 years has shown that engineered clay barriers for chemical containment applications can behave as semipermeable membranes that restrict the migration of aqueous-phase chemicals (solutes), thereby enhancing the containment function of the barriers. The ability of such clays to restrict solute migration is characterized by a membrane efficiency coefficient, $\omega$, that typically ranges from zero for no solute restriction (i.e., no membrane behavior) to unity for complete solute restriction ($0\le \omega \le 1$). Measurement of $\omega$ for such clays requires an estimate of the maximum chemico-osmotic pressure difference across the clay, $\mathrm{\Delta }\pi$. To date, estimates of $\mathrm{\Delta }\pi$ and $\omega$ have been determined almost exclusively using the van’t Hoff equation, which is based on the difference in the molar concentrations of simple salts (e.g., KCl and NaCl) in electrolyte solutions bounding the clay specimen. However, the van’t Hoff equation is limited by the assumption that the electrolyte solutions are ideal (i.e., infinitely dilute), such that some error typically is incurred when the van’t Hoff equation is used to estimate $\mathrm{\Delta }\pi$ and $\omega$ for real (nonideal) electrolyte solutions. Therefore, the purposes of this paper are to describe the use of the more fundamental method for estimating $\mathrm{\Delta }\pi$ and $\omega$ based on the differences in water (${\mathrm{H}}_2\mathrm{O}$) activity and to quantify the error associated with the use of the van’t Hoff equation in determining $\omega$. The results indicate that the error in the calculated $\omega$ based on the use of the van’t Hoff equation relative to the use of the water activity method is $\le 9.3\%$ for KCl or NaCl concentrations less than $\sim 2\mathrm{M}$. Also, previously reported values of $\omega$ for bentonite-based membranes based on the van’t Hoff equation were reevaluated using the water activity method. The resulting error in $\omega$ based on the use of the van’t Hoff equation was $\le 8.0\%$, and the $\omega$ resulting from the use of the van’t Hoff equation was more conservative (lower) than that based on the use of water activity, resulting in a slight underestimate of the effect of $\omega$ on transport.