Journal of Geotechnical and Geoenvironmental Engineering

This paper presents two modifications to the traditional formulation of the load-transfer method; a distinct unloading path is defined for the load-transfer functions, and the displacement variable is modified to consider the effects of passive soil displacements. The discrete formulation can account for different properties along the pile depth, as in the case of soil layering. Modeling distinct unloading functions enables loading cycles to be simulated as well as the analysis of residual loads. An instrumented pile load test is used to calibrate the method. Example computations are presented and discussed, highlighting the main features of the model.

Premature failures in chemically stabilized expansive soils cost millions of dollars in maintenance and repair. One reason for these failures is the inability of existing stabilization design guidelines to take into account the complex interactions between the clay minerals and the stabilizers. It is vital to understand these complex interactions, as they are responsible for the improved strength and reduction of swelling/shrinking in these soils, which in turn affects the overall health of the infrastructure. This research study examined the longevity of chemically stabilized expansive soils subjected to wetting/drying conditions, with a major focus on clay mineralogy. Eight different natural soils with varying clay mineralogy were subjected to wetting/drying durability studies after they were stabilized with chemical additives including quicklime and cement. Performance indicators such as volumetric strain and unconfined compressive strength trends were monitored at regular intervals during the wetting/drying process. It was observed that clayey soils dominant in the mineral montmorillonite were susceptible to premature failures. It was also noted that soils dominant in other clay minerals exhibited early failures at lower additive contents. For the first time, an attempt was made to address the field implications of the laboratory studies by developing a correlation that predicts service life in the field based on clay mineralogy and stabilizer dosage.

Microbially induced calcite precipitation (MICP) is a biomediated cementation process that uses natural microbial enzymatic activity to improve the geotechnical properties of granular soils. In this study, two sets of experiments are completed using soil samples obtained from different depths to evaluate the feasibility of stimulating native ureolytic microorganisms for MICP at depths relevant to geotechnical applications. Batch and column experiments completed using five different stimulation solutions demonstrate that stimulation of native microbial ureolysis is improved with an enhanced stimulation solution, which differs from a standard stimulation solution used in previous studies through initial solution pH adjustment to 9.0 and higher concentrations of ammonium chloride and yeast extract of 100 mM and $0.2\mathrm{g}/\mathrm{L}$, respectively. A sterile sampling and column testing program is completed using soil materials obtained at shallow (2 m), middle (5.9 m), and deep (12 m) depths from a geotechnical boring and treated with both standard and enhanced stimulation solutions. Despite significant differences in stimulated urea degradation between soil depths and stimulation solution types, all tested columns achieved ureolysis rates sufficient to induce MICP, although at different times. Following 14 cementation treatments, soil columns achieved final $V_s$ values as high as $\mathrm{1,020}\mathrm{m}/\mathrm{s}$ and unconfined compressive strengths as high as 1.9 MPa. The results of this study suggest that native ureolytic microorganisms may be successfully stimulated in natural soil deposits to induce calcite precipitation at treatment depths up to 12 m for geotechnical ground improvement.

A series of centrifuge tests were conducted to examine self-weight consolidation, dynamic response, liquefaction potential, and slope stability of mine tailings alone and in mixtures with waste rock. Mixture ratio of waste rock to tailings by dry mass varied around the region of a rock skeleton just-filled with liquefiable mine tailings (roughly $2.3:1$ in this case). The performance of three mixtures was compared to that of tailings in terms of pore pressure dissipation, shear wave velocity, soil acceleration, lateral displacement, pore pressure buildup, liquefied depth, settlement, and slope stability. Comixing proved to be a promising alternative to conventional separate disposal. Consolidation time and settlement were reduced significantly, and shear wave velocity increased with increasing rock content. The improvement in dynamic response was not pronounced when the tailings proportion was larger than required to fill the rock skeleton but became very apparent when that ratio was reached or surpassed.

The monotonic behavior of pond ash was studied experimentally and with a particular focus on evaluating the applicability of critical state soil mechanics framework in synthesizing and modeling the observed mechanical behavior. Specimens were reconstituted with a paste deposition technique that closely mimics the wet disposal of dominantly fine coal ash in ash ponds. This technique can produce segregation-free specimens over a wide range of as-formed density states. The test results indicated that the observed behavior was similar to granular geomaterials, except that only nonflow behavior could be observed in undrained shearing. More importantly, a unique and consistent critical state line (CSL) in triaxial compression was obtained in both $q\text{-}{p}^{\prime }$ and $e\text{-}\log (p^{\prime })$ planes irrespective of its drainage conditions, initial density states, and stress histories. The CSL in the $e\text{-}\log (p^{\prime })$ plane was used to predict behavior patterns. It was found that the state parameter, as defined relative to the CSL in $e\text{-}\log (p^{\prime })$ plane, correlates with important modeling parameters. Thus, this study unambiguously supports the applicability of critical state soil mechanics framework in synthesizing and modeling the behavior of pond ash.

This paper presents the results of cone penetration tests performed in layered, uniformly graded silica sand samples prepared inside a calibration chamber specifically designed for digital image correlation (DIC) analysis. The tests aimed to investigate the effect of a layer interface on the cone penetration resistance as well as on the soil displacement and deformation fields resulting from cone penetration. The results, which are also of interest in connection with the calculation of the base resistance of piles embedded in bearing layers, are interpreted based on the sensing distance and development distance concepts. The results show that the sensing and development distances are affected by the density of the soil on either side of the layer interface. Based on the results obtained in this paper, the sensing and development distances are of the order of 2.2–5.4 cone diameters. The vertical displacement profile next to the shaft of the penetrating cone changes significantly near the layer interface, which implies that the vertical displacement profile can be used to identify the presence of a layer interface in a DIC test. The incremental displacement and deformation analyses within the sensing distance show that, when the cone starts sensing the underlying sand layer, the average direction of the soil displacement rotates toward the underlying layer for strong-over-weak layers and away from it for weak-over-strong layers. It is also observed that the size of the shear strain bulb next to the cone surface increases when reaching a strong layer and decreases when reaching a weak layer.

Chemical containment barriers comprising sodium bentonite (Na-bentonite) have been shown to exhibit semipermeable membrane behavior under saturated conditions. Since membrane behavior results in restricted migration of aqueous-phase chemicals (solutes), the existence of membrane behavior in bentonite-based barriers can significantly improve the containment function of the barriers. However, some bentonite-based barriers exist under unsaturated conditions, and the extent to which the degree of saturation, $S$, of the barrier affects the existence and magnitude of membrane behavior has not been evaluated heretofore. Accordingly, the membrane efficiency coefficient, $\omega$, of Na-bentonite was measured in the laboratory at constant $S$ in response to applied differences in potassium chloride (KCl) concentrations under closed-system conditions. The results indicated that, for a given $S$, $\omega$ decreased as the source concentration of KCl ($C_{ot}$) increased, which is consistent with previous studies based on $S=1.0$. However, for a given $C_{ot}$, $\omega$ increased with decreasing $S$, as expected on the basis that a reduction in $S$ corresponds to a reduction in the water-filled pore space accessible for solute migration. Overall, $\omega$ ranged from 0.31 at $S=1.0$ with $C_{ot}=50\mathrm{mM}$ KCl to 0.75 at $S=0.79$ for $C_{ot}=20\mathrm{mM}$ KCl. Although the range in $S$ that was evaluated was limited by the testing conditions, which resulted in test durations ranging from 232 to 335 days, the results of this study provide the first quantitative evidence illustrating the effect of $S$ on $\omega$ for Na-bentonite.

A series of full-scale lateral load tests of fully instrumented piles in cohesive soils were carried out to assess the lateral response of piles in free-field and near a slope condition. The test piles were loaded laterally using a hydraulic actuator to observe load-displacement relationship at loading elevation, axial strain response, and rotation response. It was found that the proximity of slope significantly affects the maximum lateral load capacity of the piles, but not significantly when the piles are installed at 8D (where D is pile diameter) or greater from the slope crests. In addition, it was observed all the piles except the 0D pile resulted in similar initial stiffness for the load-displacement curves, and the piles closer to the slope showed less passive resistance at smaller displacement. Using the test records, $p\text{-}y$ curves for each test pile were back-calculated. By normalizing the $p\text{-}y$ curves for the piles near the slope with the ones on the level ground at any soil displacement and depth, the $p$-multipliers accounting for the slope effects in lateral load analysis are derived. Based on the calculated $p$-multipliers, it was found that effects of adjacent slope to lateral behaviors of piles can be explained as a function of soil displacements; the $p$-multipliers are larger at small soil displacements and vice-versa.

This study investigates the hydraulic conductivity ($K$) of binary mixed soils containing two different-sized silica particles, with the ultimate goal of developing the porosity ($n$) and equivalent particle size ($d_{eq}$) estimating formulas for binary mixed soils. Theoretical backgrounds for $K$ of mixed soils were reviewed. In addition, a series of constant head permeameter tests for mixtures with three different size ratios between small and large particles were performed. It is demonstrated that the $K$ of tested materials decreases with an increase in volume fraction of small particles ($S{C}_V$) when $S{C}_V<S{C}_V^{*}$ (volumetric critical small particle content) because of the decreases in both $n$ and $d_{eq}$. In contrast, when $S{C}_V>S{C}_V^{*}$, $K$ shows less change with $S{C}_V$ because of the offset mechanism between increased $n$ and decreased $d_{eq}$. Additionally, $n$ and $d_{eq}$ estimating methods for mixed soils are suggested in this study and compared with the experimental results.

In this study, the lateral load–carrying capacity of micropiles was investigated focusing on the effect of micropile inclination. A series of model load tests was conducted for both single (SMP) and group (GMP) micropiles with various configuration conditions of inclination angle, load direction, and micropile spacing. To clarify the load-carrying mechanism of inclined micropiles, a finite-element (FE) analysis was performed. The lateral load–carrying capacity of inclined SMPs increased with $\theta$ up to 30° for $\delta =0°$, whereas opposite trends were observed for $\delta =180°$. The lateral load–carrying capacity of inclined GMPs increased continuously with $\theta$ owing to the fixity effect with micropile cap. From the results of FE analyses it was found that the main resisting components of inclined micropiles for the lateral load–carrying capacity are the passive failure zone and skin friction mobilized along the micropile surface. Design methods for single and group micropiles subjected to lateral loads were proposed. The values of regression coefficients were evaluated using the results from the model tests and FE analyses. To check the validity of the proposed methods, full-scale field load tests were conducted and used to compare measured and estimated load capacities. Estimated results obtained using the proposed method were in good agreement with measured results.

This paper presents a case study on the jacking load during the installation of Gongbei tunnel pipe roof using microtunneling. The pipe roof, consisting of 36 pieces of 1,620-mm-diameter steel pipes along a curved alignment, provides the preexcavation support for the Gongbei tunnel, which has a cross-sectional area of $338{\mathrm{m}}^2$ and a length of 255 m. The design jacking load was compared with the field measurement, and the difference was investigated. The equation for estimating the face penetration thrust during the slurry type microtunneling was recommended, and a formulation for predicting the total jacking load of the segmented steel pipe along the curved alignment was developed on the basis of the force equilibrium analysis. The unit side frictional resistance and the frictional coefficient of the steel pipes were derived on the basis of the statistical analysis of the field data. The findings from this paper can provide guidance for the design of the jacking load during microtunneling operations for the installation of steel utility pipelines and pipe roofs.

Cyclic behavior of soils is often modeled using the Masing rules. When these rules are applied, hysteretic damping at large strains is overestimated. A non-Masing hysteresis model that reduces the size of hysteresis loops can better capture the damping behavior of soils measured in laboratory testing. A generalized non-Masing hysteresis model is proposed and shown to be compatible with a broad range of constitutive modeling frameworks. The proposed model is implemented in a superposition-type parallel-series distributed element model as well as a continuous and a piecewise linear one-dimensional backbone formulation in addition to a hyperbolic one-dimensional backbone formulation. Bidirectional and unidirectional element-level simulations are conducted. The proposed model is shown to produce non-Masing hysteretic behavior without dependence on the underlying constitutive modeling framework.