Journal of Geotechnical and Geoenvironmental Engineering

Tailings dams, which are storage structures for tailings, often are constructed using the tailings itself. A large number of tailings dam failures have been reported recently, especially due to static liquefaction, and can be attributed to a lack of knowledge of the geotechnical principles to be used and the lack of characterization of tailings as they continuously are produced and used as construction materials. Furthermore, the majority of past research work has been based on triaxial conditions even though it is believed that direct simple shear conditions may better represent the in situ condition of a tailings dam structure. This paper characterized the behavior of a tailings material from a copper tailings storage facility in Canada using the critical state soil mechanics framework using constant volume (undrained), drained, and constant shear drained shearing tests in direct simple shear space. The correlation between a modified state parameter (${\psi }_m$) with instability state and the flow potential was investigated. Special attention was paid to the behavioral features of the material such as pore-water pressure generation, flow rule and dilatancy, phase transformation, characteristics state, and how they correlate with ${\psi }_m$. The differences in behavior from that of natural granular soils were highlighted.

Geotechnical engineering practice commonly estimates the properties and behavior of well-graded soils using methods and relationships developed based on the behavior of clean, poorly graded coarse-grained soils. The influence of gradation on the strength and stress-dilatancy behavior of coarse-grained soils is complex because it depends on the soil state, which is complicated by the use of parameters that can bias and obscure the effects of gradation (i.e., void ratio versus relative density or state parameter). This study examines the effect of gradation and particle size on the drained and undrained triaxial compression behavior of pluviated poorly graded and well-graded soils sourced and sieved from a single deposit. A series of 69 triaxial tests were performed on soil specimens with a range of initial state parameters. Wider gradations resulted in a reduction in the slope and intercept of the critical state line (CSL), whereas increasing particle size for poorly graded soils resulted in an increase in the CSL slope and intercept. The results indicate an increase in peak friction angle and maximum dilation angle for soils with wider gradations for any given state parameter. The peak drained and undrained strengths at any given state parameter are shown to increase with range of particle sizes as a result of the increase in dilative tendencies. However, the contribution of the maximum rate of dilatancy to the difference between the peak and critical state friction angles appears to be unaffected by gradation. Finally, the Bolton framework was found to underpredict the difference between peak and critical state friction angles at any given relative density.

The longevity of two white multilayered textured geomembranes, manufactured with a smooth edge for welding, is examined when immersed in synthetic municipal solid waste leachate at five temperatures (40, 55, 65, 75, and 85°C) for 50 months. The textured and smooth parts of the geomembranes had similar initial chemical and physical properties, but the core of the smooth edge was thinner. It is shown that, depending on the relative effects of the difference in the core thickness and the surface area exposed to a solution, antioxidant depletion of the textured portion may be either faster or slower than the smooth edge. However, due to the lesser core thickness of the smooth edge of both geomembranes, the degradation in the tensile stress at break properties at 85°C is faster for the smooth edge than for the textured portion of the roll even when the antioxidant depletion was faster for the textured part. Thus, any assessment of the likely service life of the textured geomembrane requires consideration of both the smooth and textured portions of a multilayered textured geomembrane.

Motivated by recent failures of tailings storage facilities (TSFs) around the globe, the tailings community is actively working to better understand the mechanical behavior of mine tailings. This study presents a geotechnical characterization (at both the laboratory and field scales) of copper mine tailings from a TSF located in an area with high seismicity, which makes assessing their response to static loading (e.g., static liquefaction) and earthquake-induced demands (e.g., cyclic-induced liquefaction) of primary importance. We discuss relevant aspects in the behavior of the examined mine tailings, including compressibility, stiffness, and the liquefaction (static and cyclic) response. Salient findings include the following: (1) the void index concept appears to characterize the compressibility of mine tailings regardless of ore source; (2) the stiffness-confinement dependence for the examined tailings contrasts with typical sand models; (3) theoretical particle size distributions that promote packing are useful for understanding trends in the location of the critical state line; (4) the examined tailings can experience static and cyclic liquefaction regardless of fine contents (insights on the observed responses are shared); (5) commonly used strain-based criteria are not robust enough to identify the cyclic liquefaction onset, thus we propose different criteria based on mechanistic descriptors; (6) the cyclic response of the examined tailings is affected by coupled stress-compressibility effects and their postliquefaction response fit within the expected response of natural silty soils; and (7) our assessment of state-of-practice liquefaction triggering procedures, in the context of the recently proposed $\mathrm{\Delta }Q$ method, suggests a comparable performance for the tailings examined in this study. In addition, a soil behavior index ($I_C$) of 2.9 is consistent with the $\mathrm{\Delta }Q=20$ as suggested in the literature for assessing liquefaction susceptibility of the examined tailings.

Near-surface seafloor properties affect offshore mining and infrastructure engineering. Shallow seafloor sediments experience extremely low effective stress, and consequently, these sediments exhibit very low in-situ density, shear wave velocity, and shear stiffness. We combined data extracted from the literature with new laboratory and field results to develop a comprehensive understanding of shallow seafloor sediments. First, we explored the sediment-dependent self-compaction characteristics starting with the asymptotic void ratio at the interface between the water column and the sediment column. The asymptotic void ratio depends on the particle size and shape in coarse-grained sediments and on mineralogy and pore fluid chemistry in fine-grained clayey sediments; overall, the asymptotic void ratio correlates with the sediment-specific surface and compressibility. Second, we developed a fork-type insertion probe to measure shear wave velocity profiles with depth. Detailed data analyses confirm the prevalent role of effective stress on shear wave velocity ${\mathrm{V}}_{\mathrm{s}}=\alpha ({\sigma }_m^{\prime }/\mathrm{kPa}{)}^{\beta }$, and the inverse relationship between $\alpha$ and $\beta$ parameters reveals that electrical interactions alter the velocity profile only in very high specific surface area sediments at very low effective stress and shows that ray bending affects the computed velocities only in the upper few centimeters (for the probe geometry used in this study). Probe insertion causes excess pore fluid pressure and effective stress changes; the ensuing time-dependent diffusion detected through shear wave velocity changes can be analyzed to estimate the coefficient of consolidation. Shear wave velocity profiles and velocity transients after insertion provide valuable information for sediment preclassification and engineering design.

An extreme rainstorm can cause thousands of landslides and kill hundreds of people. In the changing climate, fatal rainstorms become more frequent and intense. The current landslide emergency management evaluates hazard intensities but lacks key information on likely consequences. This study presents a novel prompt quantitative risk assessment method for rain-induced landslides. The proposed method automatically generates a one-page risk assessment report within minutes to support effective risk communication, resource allocation, and emergency response. The propagation of uncertainties is quantified in a scientific probabilistic framework. The proposed method is tested using 83 major rainstorms during 1995–2016 in Hong Kong. The method accurately predicts the number of affected buildings and the number of potential fatalities and identifies rainstorms that can trigger fatal landslides. The proposed method contributes to the advancement of landslide emergency management from hazard-informed to risk-informed, which will significantly enhance societal resilience and facilitate climate change adaptation.

A number of incidents of pile tip damage and extrusion buckling have been reported within the offshore industry, generally arising during driving of relatively thin-walled tubular pile foundations through hard layers or potentially heterogeneous sediments. The issue has become of particular concern with modern trends toward larger diameter piles, with higher ratios of diameter to wall thickness, for monopile or jacket foundations of offshore wind turbines. The paucity of good-quality data available in the public domain about this kind of failure has impaired the development of simple design guidelines for industry to address the issue. The paper presents results from a series of centrifuge model tests where pile tip damage and extrusion buckling were observed during driving of either (1) undamaged cylindrical piles into a sand bed containing a layer of different sizes of boulders, or (2) predented piles into medium dense homogeneous sand. Following a previously reported pilot study, a new and higher energy model pile-driving hammer was designed to permit driving through the hard layers and allow pile embedment by up to five diameters. Two test beds were prepared, one of which contained boulder layers of different sizes either near the surface or at a depth of about one pile diameter, into which piles of two different diameter to wall thickness ratios were driven. The test series led to observations of pile tip damage that ranged from abrupt tip crumpling to gradual extrusion buckling. For 2 of the 22 piles installed, dent growth during installation was detected by optical fiber sensors attached to the piles. For the uninstrumented piles, damage was deduced from the trends in blow counts during installation, with later confirmation from detailed visual inspections and laser scanning, and also from careful layer by layer excavation of each sample. The high-quality database generated from the model tests forms a valuable resource for further study and validation of advanced numerical models to simulate pile tip damage and for calibration of simple guidelines for practical design.

A series of compression tests were carried out on two types of calcareous sand to study the time-dependent behavior of calcareous sand under oedometric conditions. Consolidation, creep, stress relaxation, and constant strain/stress rate tests were conducted. At the same time, the effects of input energy and grain shape on particle breakage were investigated. The test results show that a large amount of particle breakage occurs in the calcareous soils under different modes of loading, leading to a significant time effect on the oedometric compression responses. Under the same level of vertical stress, the large-grain calcareous sand has a higher creep or relaxation rate. Over-consolidated sand has a much smaller creep or relaxation response than normally consolidated sand, and the response decreases with an increase in the overconsolidation ratio. Loading rate has an influence on the compressibility of calcareous sand, especially when the particle breakage is significant. In addition, it is also shown that a unique relationship exists between the relative breakage and the input energy for the same kind of calcareous sand, which is independent of the loading mode.

The influence of excavation rate, geometric layout, and hydraulic conductivity of basal and retained soils on the fully coupled solid–fluid behavior of braced excavations in cohesive soils is presented. Fully coupled excavation analyses were performed using the hypoplasticity clay model to reproduce the constitutive soil behavior combined with Biot’s consolidation theory. A method aimed at predicting excavation-induced ground movements using excess pore-water pressure ratios as a function of site-specific groundwater considerations is presented for the determination of the recommended type of excavation analysis (i.e., drained, partially drained, or undrained). Results obtained from the numerical simulations indicated that excavation rate to hydraulic conductivity ratios, $\mathrm{ER}/k$, smaller than 0.1 and larger than 10,000 can be analyzed under drained and undrained conditions, respectively. The proposed method was validated with published case histories, and its ability to estimate excavation performance in terms of excess pore-water pressures and excavation rates is presented in this paper.

Distributed acoustic sensing (DAS) is a relatively new technology used in many geophysical applications. The versatility, high spatiotemporal resolution, and sensitivity to surface waves make DAS ideal for rapid deployment surveys such as earthquake-aftershock monitoring and hazard assessment. However, these applications usually rely on trenched cable installations that are time consuming and cost-prohibitive to deploy, or on existing telecommunication fibers that are limited in spatial coverage. To examine the potential of untrenched surface deployments, we acquired DAS data in continuous mode for one hour on a rapidly deployed fiber array composed of six parallel linear subsections directly on the surface with different fiber-ground contact conditions. We applied ambient interferometry and adopted a simplified method to determine the average shear-wave velocity of the top 30 m ($V_{S30}$). Our methodology resulted in robust $V_{S30}$ estimates for each surface deployment subsection that are consistent with collocated 1-m-deep trenched cables. The implications of these findings support DAS as a viable method for noninvasive-deployment surface surveys for rapid earthquake hazard and damage assessment.

Opened to traffic in 2016, the Pioneer Mountain-Eddyville (PME) realignment was a major highway infrastructure project that began in 2005 and created approximately 9 km of new highway on US Route 20 in the Oregon Coast Range. Due to the renewed activity of a series of paleolandslides that traversed the project right-of-way, deliver of the construction project was significantly delayed. Owing to the size and activity of these slope failures, a large monitoring network of piezometers and other instrumentation was deployed as a precursor to the installation of an extensive system of horizontal drain arrays (176 km of drain length) intended as one means of landslide mitigation through control of in situ groundwater. Because there is limited guidance regarding monitoring the long-term performance or design life of horizontal drains, hydrological data in drained areas were monitored as a means of observing performance during and after project completion. This case study describes observations of groundwater behavior prior to—and after—drain installation, thereafter proposing site planning–level metrics for evaluating the continued function of horizontal drain systems. Drain function is considered through groundwater response to precipitation, but also through a simple evaluation of water storage in the catchment of each landslide. The four paleolandslides—Cougar Creek, Crystal Creek, Eddy A/B, and Eddy C/D—demonstrate different responses to drain installation and long-term performance. Using simple metrics based on monitoring, added indices for evaluating long-term horizontal drain performance at the site scale are proposed. Consistent with the Observational Method, these criteria may serve as additional guidance for a monitoring-based framework for evaluating the life cycle of horizontal drains as a landslide mitigation system and a basis for planning drain maintenance or added mitigation measures.

The assumption of local thermal equilibrium (LTE) between solid and fluid phases commonly is used for studies of heat transfer in saturated soil and is valid for a wide range of conditions. However, for certain conditions, the heat transfer process may give rise to local thermal nonequilibrium (LTNE) in which adjacent solid and fluid phases have different temperatures. This note presents the results of a numerical study of the validity of the LTE assumption for one-dimensional heat transfer in a saturated soil layer with fluid flow. For the conditions investigated, the LTE assumption holds for soil with particle sizes smaller than the gravel range. For soil with particles sizes in the gravel range and larger, the LTE assumption may be valid or invalid, depending primarily on fluid discharge velocity, with higher fluid velocity values more likely to produce LTNE conditions.

As a result of weathering, the mechanical behavior of granite residual soil differs from that of sedimentary soil. Although the mechanical properties of granite residual soil have been studied extensively, its strength anisotropy is yet to be established. Previous work has revealed the association between the principal stress direction $\alpha$ and soil shear strength, but little is known about how the intermediate principal stress affects the soil strength. This paper presents the shear-strength parameters under various combinations of $\alpha$ and the intermediate principal stress factor $b$ as obtained through undrained hollow-cylinder torsional shear tests performed on samples of natural granite residual soil. The test results confirmed the considerable effect of $b$ on the shear strength and highlighted the differences between the soil studied here and those studied previously. It was found that $b$ affects the undrained strength and mobilized frictional angle (or ultimate stress ratio) differently, with increasing $b$ leading to lower undrained strength but higher frictional angle. In addition, the degrees to which $b$ affects undrained strength and frictional angle are not the same and depend on the $\alpha$ value at which the soil is sheared. Therefore, two parameters are proposed to quantify that difference. This study extends the understanding of the strength anisotropy of granite residual soil and provides data for soil behavior under various values of $b$.