Journal of Geotechnical and Geoenvironmental Engineering

The application of silica stabilizers to a liquefiable ground covered by existing structures is a challenge to engineers. This paper provides details of ground improvement under the runway and around the common ducts of Fukuoka International Airport. The ground was improved via a newly developed controlled curved drilling machine to enable controlled permeation grouting under the runway without any disturbance to its operation. At this stage approximately 100 m of the runway has been improved. Experiments on the gel time and the form of chemical diffusion at different injection times secured the improvement of ground in the desired zone, and a posttreatment investigation confirmed this improvement.

This paper presents a numerical investigation of the effect of consolidation on the transport of a volatile organic compound (VOC), trichloroethylene (TCE), through a composite liner system comprising a geomembrane liner (GML) overlying and intimate contact with a geosynthetic clay liner (GCL). The numerical simulations were conducted using the model CST2, and considered coupled consolidation and contaminant transport with representative geometry, material properties, and applied stress conditions. The simulation results indicate that, depending on conditions, GCL consolidation can have significant effects on TCE mass flux, cumulative mass outflow, and distribution of contaminant concentration within the GCL, not only during the course of consolidation but also long after consolidation has ceased. Because of the small thickness of the GCL, consolidation-induced advection is insignificant. However, consolidation can significantly impact TCE transport through the GCL via changes in GCL material properties, including decreases in thickness, porosity, and effective diffusion coefficient. In general, the effects of GCL consolidation increase with increasing magnitude of applied stress, decreasing loading period (i.e., increasing loading rate), and increasing variation in the effective diffusion coefficient. The traditional performance assessment approach neglects GCL consolidation and fails to consider associated changes in material properties and, thus, can lead to significantly different results. Simulation results indicate that, in general, when the applied stress is lower than 125 kPa or the exponent for porosity-dependent effective diffusion coefficient is lower than 4, the effect of consolidation on TCE transport through the GML/GCL composite liner is insignificant, with differences in performance of the GML/GCL composite liner resulting from consolidation being less than 15%.

Tunnel excavation inevitably induces stress changes in the surrounding soil leading to significant ground movements and additional stress in nearby pipelines. Most previous studies simplified tunnel–pipe interaction as a plane strain problem and focused on the case in which the pipeline intersects the tunnel perpendicularly. In this study, centrifuge tests were conducted to investigate the three-dimensional response of the ground and pipeline to tunneling, considering different pipeline orientations with respect to the tunneling direction. When the tunnel face was located within $\pm 1.25D$ (tunnel diameter) away from the monitoring section, the ground settlement and pipe strain induced were more than 95% of the maximum recorded. When the pipeline intersected the tunnel perpendicularly, the maximum pipe strain always occurred above the tunnel centerline. However, when the pipeline intersected the tunnel at an angle of 60°, the location of maximum pipe strain shifted as the tunnel advanced. The maximum tunneling-induced pipe settlement and strain were up to 20% greater in this case than when the pipeline intersected the tunnel perpendicularly. The pipe settlement and strain may be underestimated if an oblique intersection is simply taken as a perpendicular one.

It is well known that partial saturation increases the shear strength and dilatancy of unsaturated sand. However, little research has been carried out on the actual stress-dilatancy relationship. This paper shows that the increase in peak shear strength caused by partial saturation is consistent with an increase in dilatancy, and that conventional stress-dilatancy theories are still valid for unsaturated sand. The use of state indexes as a proxy for dilatancy were investigated and extended to unsaturated sands. Additionally, these indexes can be used to establish a critical state line that is based on material properties only. The validity of the stress-dilatancy theories and the use of state indexes offer simplicity in modeling the shear behavior of unsaturated sand. This will be demonstrated in this paper with the Nor-Sand model, with which the wetting collapse can be explained as a consequence of a loss of dilatancy characteristics.

The small-strain shear modulus $G_0$ is a fundamental property governing shear wave propagation in soil. It depends on fabric of soil particles, soil water content, and stress state. The dependency of $G_0$ on stress and water content was assessed by using the suction stress-based effective stress principle. Here the variation of $G_0$ with water content was compared with soil-water retention (SWR) behavior and suction stress behavior for 12 soils under zero total stress conditions. A recently established SWR model enables the distinction of capillary and adsorption regimes for better interpretation of the correlation between $G_0$ and suction stress. It is demonstrated experimentally that the variations of both $G_0$ and suction stress follow the same pattern but differ by a dimensionless scalar. Further correlation of the scalar with SWR provides good predictions of suction stress for different soils in the capillary regime. The established correlations among SWR, suction stress, and $G_0$ further confirm the validity of the suction stress-based effective stress principle.

Constrictions in the void space between soil particles govern hydraulic conductivity, internal stability, and filtration performance of sands and gravels. Various analytical, numerical, and image-based methods have been proposed to measure void constrictions based solely on analysis of particle and void geometry. These geometric constrictions are increasingly being used in models to predict hydraulic conductivity or filtration performance. However, both of these phenomena depend not only on the void geometry, but also on the directions and magnitudes of fluid velocities within the void space. This paper presents computational fluid dynamics (CFD) simulations performed on microcomputed tomography (microCT) images of voids in real sands, as well as idealized materials generated by discrete element modeling (DEM). Laminar flow conditions are considered and an alternative definition of a void constriction is presented, the hydraulic constriction, which is based on fluid velocities rather than void geometry. The data show that for laminar flow, where Darcy’s law is applicable, the position, size, and orientation of hydraulic and geometric constrictions share many similarities, but there are measurable differences, which should be considered in hydraulic conductivity and filtration analyses.

The seismic response of underground reservoir structures is a complex soil–structure interaction problem that depends on the properties of the earthquake motion, surrounding soil, and structure. More experimental and field data of the response of these structures under different boundary conditions are needed to validate analytical and numerical tools. This paper presents the results of four centrifuge experiments that investigate the seismic performance of reservoir structures, restrained from rotational movement at their roof and floor, buried in dry, medium-dense sand and compacted, partially saturated, silty sand. This study focuses on the influence of backfill soil properties, cover, and slope on accelerations, strains, lateral distortions, and lateral earth pressures experienced by the buried structure. The structure to far-field acceleration spectral ratios were observed to approach unity with added soil confinement, density, and stiffness. Both dynamic thrust and accelerations on the structure showed a peak near the effective fundamental frequency of the backfill soil. The addition of a shallow soil cover and stiffness slightly increased seismic earth pressures and moved their centroid upward, hence slightly amplifying seismic moments near the base. The added stiffness, density, and apparent cohesion of the compacted site-specific soil did not influence the magnitude of dynamic earth pressures significantly but often moved their centroid upward. A sloping backfill reduced the earth pressures and bending moments near the top of the wall because of the reduced soil mass. The trends in the experimental results indicate that new analytical procedures and design guidelines are needed to account for the backfill soil conditions and ground motions for which these underground structures must be designed.

This paper examines the use of variable penetration rate cone testing to investigate the influence of drainage conditions on the estimation of engineering properties and liquefaction potential for natural deposits of sands with fines and silty soils. A detailed cone penetration test (CPT) investigation was performed at four historic liquefaction sites that are partially drained during standard cone penetration and contain liquefied sands with fines and sandy silts. Cone drainage conditions and their effect on cone measurements are evaluated at penetration rates ranging from 0.002 to $20\mathrm{cm}/\mathrm{s}$, and a systematic method for evaluating the relative contributions of rate effects is presented. The influence of penetration rate and drainage conditions on estimates of engineering properties and liquefaction potential is examined. Results demonstrate that partially drained conditions can have a significant influence on estimates of friction angle, relative density, and state parameter. The effects of partial drainage provide insight into the empirical fines content adjustment factors used in liquefaction triggering analysis, indicating that partial drainage effects likely contribute to some, but not all, of the shift that occurs in triggering curves with increasing fines content.

Conventional design guidelines for buried pipelines are based on the assumption that soil is either dry or fully saturated. In unsaturated soils, such an assumption may lead to underestimation of load from externally imposed ground movement. Such loads are generated because the water meniscus between soil particles creates an additional interparticle force due to suction, which in turn makes the soil stiffer and stronger. This paper presents a methodology for predicting lateral loads on pipelines in unsaturated sandy soils by investigating soil-pipe interaction with full-scale tests and characterizing unsaturated soil behavior with properties from triaxial tests. A constitutive model was developed, and finite-element (FE) simulations were performed and compared with the full-scale test results to validate the modeling process. Additional FE simulations were conducted to assess the maximum lateral load on pipelines buried in different Class II unsaturated sands. The full-scale tests and FE simulations show that increased strength and stiffness associated with soil suction increases lateral loads on pipelines and thus need to be considered when designing pipelines for externally imposed ground movement. The modeling procedures and results can be used to predict lateral loads on underground pipelines subjected to construction and earthquake-induced ground movements, landslides, and subsidence. Because most pipelines are buried in unsaturated soil, the results have widespread relevance in design and construction.

A number of strategies exist to account for the epistemic uncertainty and aleatory variability in shear-wave velocity ($V_s$) profiles used in site response analyses. Epistemic uncertainty may be accounted for by using median and bounding-type profiles (e.g., $\pm 20\%$), while aleatory variability may be accounted for by using $V_s$ randomization procedures. A robust, quantitative method to help judge how well these statistically derived $V_s$ profiles represent actual subsurface stiffness or layering conditions is currently not available. This paper presents a surface-wave dispersion approach for evaluating statistical models meant to account for $V_s$ uncertainty in site response. Specifically, surface-wave dispersion data from two geologically disparate sites were used to generate $\mathrm{1,000}{V}_s$ profiles and layered earth models whose theoretical dispersion curves fit within the uncertainty bounds of the experimental data collected at each site. Additionally, theoretical dispersion curves generated from statistical $V_s$ profiles such as the median, bounding-type, and randomly generated $V_s$ profiles for each site were compared with the experimentally measured dispersion data. It was found that the theoretical dispersion curve from the median $V_s$ profile provided a satisfactory fit to the experimental data, but the theoretical dispersion curves from bounding-type $V_s$ profiles did not. Furthermore, randomly generated $V_s$ profiles resulted in some theoretical dispersion curves that fit the experimental data and many that did not. The authors recommend comparing theoretical dispersion curves for candidate $V_s$ profiles and layered earth models with the measured dispersion data at a site prior to using the candidate profiles to account for uncertainty in site response analyses as a quantitative way to judge if the $V_s$ profiles represent realistic site conditions.

Uncertainty in site response analyses can be attributed to a number of parameters, including analysis methods, input ground motions, nonlinear dynamic soil properties, and shear-wave velocity profiles. In this paper, several approaches commonly used to account for shear-wave velocity ($V_s$) uncertainty in site response are investigated. Specifically, the $V_s$ profiles considered are categorized into three groups: (1) $V_s$ profiles determined directly from surface-wave inversion, (2) simple statistical $V_s$ profiles derived indirectly from the surface-wave $V_s$ profiles (including bounding-type, median, and other percentile $V_s$ profiles), and (3) statistically based, randomly generated $V_s$ profiles. A companion paper discusses the development of these $V_s$ profiles for two international blind-study sites. In this paper, the effects of using each approach to account for $V_s$ uncertainty in site response are investigated by linking the dispersion misfit values for each $V_s$ profile to variability in equivalent linear site response estimates. Clear trends exist between variability in site response estimates and dispersion misfit values at both sites. Thus, the experimental dispersion data can be used to help select suites of $V_s$ profiles, generated either directly from inversion or through a randomization model, that account for uncertainty in a meaningful way without including unrealistic statistical profiles that result in too much site response variability.

Alternative laboratory approaches for cyclic permeation-desiccation experiments on geosynthetic clay liner (GCL) specimens are compared. Permeation cycles for hydraulic conductivity ($k$) are conducted in flexible-wall permeameters. Subsequent desiccation cycles are conducted using one of three approaches: (1) unconfined desiccation involving drying under controlled relative humidity (RH) with no external stress; (2) axially constrained desiccation involving drying under controlled RH and axial stress simulating one meter of cover soil; and (3) a novel in-permeameter method, where specimens are desiccated without physical disturbance by flushing the permeameter endcaps with controlled-RH gas. Comparison metrics include image analysis of bentonite crack patterns, cycle duration, uniformity of water content, and evolution of $k$ for up to seven wet-dry cycles. All three methods result in similar water content, crack intensity, and hydraulic conductivity response, despite the fact that stress conditions during drying and disturbance to specimens are very different. Observed similarity indicates that internal flaws in the bentonite (e.g., reinforcing fibers), rather than external stress conditions, control desiccation crack initiation and propagation.

Results of a numerical finite-element (FE) simulation are presented to evaluate stress changes that affect the results of cone penetration tests (CPT) made at a test section after blast densification. The two-dimensional (2D) FE simulation was not used to predict liquefaction, as the pore-pressure distribution immediately after each blast and the extent of liquefaction, determined from field observations of ground-surface settlements and pore-pressure measurements, were an input rather than a result. A fully coupled FE formulation was employed to compute time-dependent deformations and stress changes that result from dissipation and seepage of input excess pore pressures. Computed results indicate stress levels within the targeted loose sand decrease near the edge of the blast zone as a result of stress redistributions that take place during reconsolidation, and likely contribute to decreased penetration resistance observed near the perimeter of the zone. Outside the blast zone, computed stress levels increased in areas that did not liquefy, and likely contributed to small increases in penetration resistance measured at these locations. However, computed results suggest that stress levels near the center of the zone remain unchanged, yet penetration resistance at the test section did not increase despite significant amounts of settlement. Occluded gas bubbles in the soil matrix resulting from gas released by the explosives affect the mechanical response of the sand postblasting during the CPT. Recommendations are made concerning evaluation of ground improvement after blast densification.

Finite-element simulations are conducted to assess the capability of an anisotropic bounding surface model in simulating ground response due to deep excavations. The model assumes a nonassociative flow rule that allows for the simulation of not only strain-hardening, but also strain-softening response. It can be degenerated into anisotropic and isotropic forms of the bounding surface model employing associative flow. After integrating the model into a commercial finite-element code, two deep excavation case histories were simulated. The simulation results are compared with published field measurements and with those obtained using the anisotropic Sekiguchi-Ohta and MIT-E3 models. Satisfactory agreement between finite-element simulations and field measurements in terms of lateral wall deflections and ground surface settlements was realized. The difference in results between the nonassociative and associative versions of the anisotropic bounding surface model was found to be rather small given the fact that most parts of the ground likely did not approach failure and did not exhibit softening. Comparing the results obtained from the anisotropic bounding surface model with the Sekiguchi-Ohta and MIT-E3 models indicated a slight difference.

An improved vacuum preloading method was developed to consolidate clay-slurry fill that is hydraulically placed in seawater for land reclamation. This method adopted both a vacuum and an air-pressurizing system. In the vacuum system, a new connector to connect each prefabricated vertical drain (PVD) directly to a horizontal vacuum pipe is used in lieu of a horizontal sand blanket. In the air-pressurizing system, compressed air is injected into the soil to accelerate consolidation. Field pilot tests using both the improved and the existing vacuum preloading systems were carried out at the same site. The testing data showed that better consolidation results were achieved using the improved vacuum preloading method.

Since its inception in the early 1970s, the stress-based simplified procedure has become the standard of practice worldwide for evaluating liquefaction triggering potential. Central to this procedure is the stress reduction coefficient, $r_d$, which allows the estimation of the seismically induced stresses at depth in a soil profile without the need to perform a numerical site response analysis. Proposed herein is a new $r_d$ relationship that was developed from equivalent-linear site response analyses performed on soil profiles representative of those in the liquefaction case history databases. The input motions used in the analyses are representative of those from shallow crustal earthquakes. Two variants of the $r_d$ relationship are presented that allow it to be used when the profile’s shear-wave velocities are either known or unknown, with the former yielding values having less uncertainty. Additionally, calibration coefficients are provided for both active and stable continental tectonic regimes. In comparison with other $r_d$ relationships that are commonly used, the relationship proposed herein should yield values that have less bias and uncertainty.