Journal of Geotechnical and Geoenvironmental Engineering

A new method and instrument were developed for in situ measurement of the gas diffusion coefficient ($D_g$) and gas coefficient of permeability ($k_g$) of unsaturated soil. Air containing tracer gas of volumetric concentration of 5%–10% was continuously pumped into a point source at a constant flux rate ($q_0$) until approaching steady state. Then, the pseudo-steady-state tracer gas concentration ($C_{r0}$) and gas gauge pressure ($\mathrm{\Delta }{P}_{r0}$) were recorded at a distance ($r_0$) away from the point source. The $D_g$ and $k_g$ were determined through the $C_{r0}-q_0$ and $\mathrm{\Delta }{P}_{r0}-{\mathrm{q}}_0$ relationships, respectively. Soil column tests (silty sand) and field tests (sandy lean clay) were conducted to validate the new method. The in situ measured $D_g$ and $k_g$ were comparable with those of undisturbed specimens measured by a two-chamber apparatus. The in situ measurement of $D_g$ and $k_g$ ranged from ${2\times 10}^{-8}{\mathrm{m}}^2{\mathrm{s}}^{-1}$ to ${4\times 10}^{-6}{\mathrm{m}}^2{\mathrm{s}}^{-1}$ and ${1.9\times 10}^{-8}{\mathrm{ms}}^{-1}$ to ${3.9\times 10}^{-7}{\mathrm{ms}}^{-1}$, respectively. The measurement accuracy increased at deeper depth, due to reduced boundary effect at soil surface. The measurement of in situ $D_g$ was more susceptible to the boundary effects than that of $k_g$ at shallower depth (i.e., 20 cm deep) in general. The field test results showed that the ratio of in situ $D_g$ (or $k_g$) to that measured by the element tests was generally between 1.2 and 3.3 at or below depth of 0.30 m, due to the in situ heterogeneity of soil.

The ground-improvement technique is commonly used to restrain the wall displacement induced by excavation and resist the basal heave for deep excavations in soft clays. In this paper, a three-dimensional finite-element stability analysis was conducted to evaluate the effect of different ground-improvement properties and patterns on enhancing the factor of safety against basal heave in deep excavations. The results showed that a large downward movement of soil behind the wall could induce a large upward movement below the excavation, which is mainly resisted by the weight of the interior soil mass and the frictional resistance acting on the contact surface area between the wall and the soil inside the excavation. When the ground improvement was not contacted with the wall, the failure initially occurred on the wall interface, causing the soil inside the excavation to move upward along with the ground improvement, which resulted in an insignificant increase in the factor of safety. Hence, the ground improvement should be contacted to the wall to establish a higher basal heave resistance, where the increase of the safety factor was governed by the amount of the ground improvement that contacted the wall. Furthermore, a simplified method was proposed to calculate the factor of safety with and without ground improvement, which was validated by the results from the finite-element method.

A granular soil may undergo liquefaction failure due to excess pore water pressure ($\mathrm{\Delta }u$) generation when subjected to cyclic loading such as an earthquake. Several past studies indicated $\mathrm{\Delta }u$ generation may be independent of cyclic stress ratio (CSR), whereas others contradicted this observation. A soil element in its natural state often remains in $K_0$ consolidation state, i.e., subjected to nonzero static shear stress ratio (SSR). Using the discrete element method (DEM), this study performs a large number of cyclic triaxial tests and evaluates various factors influencing the magnitude and rate of $\mathrm{\Delta }u$ generation under symmetric and nonsymmetric cyclic loading conditions. The study also evaluates the capabilities of several existing $\mathrm{\Delta }u$ generation models to predict the development of $\mathrm{\Delta }u$ under different failure scenarios. It was observed that the generation of $\mathrm{\Delta }u$ can be influenced by CSR for specimens subjected to symmetrical cyclic loading and by both CSR and SSR for nonsymmetric cyclic loading conditions. A new prediction model for $\mathrm{\Delta }u$ generation was developed along with an objective framework to estimate its input parameters. The model showed good agreement with the DEM simulation results.

A research study was conducted to accelerate engineering property improvements by using novel silica-based coadditives along with a traditional calcium (Ca)-based stabilizer. Silica-based compounds, crystalline-silica (CS) rich waste product, and laboratory-grade nanosilica (NS) were used as coadditives with dolomitic hydrated lime to treat problematic expansive soil to study their efficacy in accelerating improvements in various engineering characteristics. The optimum dosages of the CS and NS additives with dolomitic hydrated lime were first determined based on unconfined compressive strength property, before and after capillary soaking. These dosages were subsequently corroborated by performing one-parameter and multiparameter statistical analyses. Using these optimized dosages, various engineering tests were performed on the treated soils. These tests included free-swell and linear shrinkage strains, unconfined strength with and without capillary soaking, and resilient modulus studies at curing periods of 0 (6 h), three, and seven days. Supplemental microstructural analyses were performed to gain insights into the factors responsible for the observed improvements in engineering properties. Test results indicated that treatment with hydrated lime and both silica-based coadditives is effective in stabilizing problematics soil as compared with lime treatment alone. Among the two silica-based coadditives, NS treatment provided comparatively higher accelerated improvements in the soil properties after seven days of curing than CS treatment. Mineralogical studies revealed that NS is more reactive than CS as a coadditive; hence, NS has been effective in providing equivalent long-term engineering strength gains while reducing swelling- and shrinkage-related volume-change properties in a relatively short time period.

Postwildfire forests are dynamic environments. Wetting-induced shallow landslides are observed at varying times after wildfires, but the reasons are not fully known. This study investigates the time-dependent changes in soil properties and mechanical and hydrologic soil behavior of hillslopes after the 2019 Williams Flats Wildfire near Keller, WA and demonstrates the implications of these changes to slope stability. Soil water repellency, organic content, fine content, soil water retention curve, hydraulic conductivity, friction angle, and in-situ suction-saturation data provides initial evidence that soil properties fluctuate over a year after the wildfire. The results therefore suggest that soil properties that are measured immediately after the wildfire are misleading for long-term slope stability analysis. The stability of a steep (45°) slope is found to be most affected by the fluctuations in friction angle and soil water retention over the year. The comparison of suction-saturation response near a burned and unburned location demonstrates the effects of macropores that are formed after the wildfire and evapotranspiration on slope stability. The hillslope stability at the unburned location reduces rapidly in April upon snowmelt, whereas the stability at the burned location, which has macropores, shows the rapid decrease in late-January, with the onset of snowfall.

In the 2016 Kaikoura earthquake, liquefaction of gravelly soils from reclaimed fills occurred in CentrePort, Wellington, New Zealand. This study presents constant volume monotonic and cyclic simple shear tests on well-graded gravel with sand collected from CentrePort. A large-scale cyclic simple shear device is utilized to evaluate the monotonic, cyclic, and postcyclic responses of the sandy gravel soils. Specimens prepared at various relative densities were subjected to a vertical effective stress of 100 kPa and then monotonically and cyclically sheared. After the cyclic loading, the postcyclic response was evaluated, including volumetric compression or monotonic shear with or without dissipation of excess pore water pressure. Shear wave velocity was measured before and after the cyclic loading. The results show that the well-graded sandy gravel has a high potential for liquefaction, with higher relative density specimens having higher liquefaction resistance. Postcyclic volumetric strain is primarily correlated with density and maximum shear strain during cyclic loading. Postcyclic reconsolidation causes densification of the liquefied specimens, resulting in higher monotonic shear resistance, while postcyclic monotonic shear without dissipation of excess pore water pressure reveals that substantial shear strain is required to develop the shear resistance. Shear wave velocity was significantly reduced after liquefaction, but recovered to slightly higher than its precyclic shear values after reconsolidation. Compared to other gravelly and sandy soils, the well-graded sandy gravel showed a similar or slightly higher liquefaction resistance than gap-graded and uniform gravels. Moreover, the well-graded sandy gravel had a relatively lower ultimate postcyclic volumetric strain due to a small variation between its maximum and minimum void ratios. The results advance our understanding of the liquefaction resistance and subsequent postcyclic responses of the well-graded sandy gravel soils.

Whereas moist-tamped specimens of silts and sands are most used in engineering practice to characterize tailings, offshore sediments, and fluvial/alluvial deposits, design parameters derived from moist-tamping data sets can be significantly different from those obtained from slurry or underwater deposition. This study shows that moist-tamped silty and sandy specimens may exhibit phase transformation at stress ratios that are 25% to 50% lower than those observed for slurry-deposited specimens. Conversely, the small-strain stiffness of the moist-tamped specimens tested can be 50% higher than those from slurry deposition. With tailings dams’ performance receiving increased worldwide attention due to recent dam failures in several parts of the world, this study provides new, specific, and concerning insights about the crucial impact that the selection of moist tamping can have on design parameters. More realistic and rigorous laboratory testing procedures involving tailings remain a key requirement for engineering assessments of tailings behavior. A novel slurry-deposition setup is presented that allows underwater reconstitution of silts, sands, and their mixtures, yielding high-quality uniform specimens. Systematic uniformity checks, which are mandatory to avoid segregation of silty materials, are described. A detailed analysis of typical errors affecting initial void ratio evaluation is also presented to ensure that comparisons between different methods are done with the highest degree of confidence possible.

Anisotropic characteristics of granular soil consolidated to various initial stress states were evaluated under generalized strain paths using hollow cylinder torsional shear tests. Fraser River sand samples prepared by water pluviation were subjected to isotropic and anisotropic consolidation stresses, and sheared undrained along strain paths with constant intermediate principal strain parameter and various principal strain directions. Anisotropic stress response and stress-strain trends were examined by controlling the orientation of principal strains (${\alpha }_{\epsilon }$) with respect to the depositional axis. A decrease in strain hardening tendency is observed as the major principal strain rotates towards the bedding plane. Considering different levels of anisotropic consolidation stresses also allowed a detailed examination of how initial static shear affects the responses. In particular, generated principal stresses and their directions, as well as the pore pressure responses, were closely examined. Novel findings are presented on the range of intermediate principal stress parameters ($b_{\sigma }$) associated with the undrained plane strain condition where a value of $b_{\sigma }$ in the range of 0.2–0.4 was found to correspond to plane strain conditions.

Energy piles are a consolidated underground heat exchanger alternative to traditional boreholes in ground source heat pump (GSHP) systems. Previous works focused on assessing the differences between piles and boreholes, but few assessed small piles in operational conditions. Moreover, most of these studies centered around cylindrical concrete piles, overlooking short screw piles. Using in-situ testing, established analytical methods, and advanced three dimensional (3D) finite element model simulations, this work assesses three thermal response tests (TRT) executed in different energy pile structures, one being a unique group of eight short energy screw piles connected in series, located in the same site in Melbourne, Australia. Detailed numerical analysis provided reliable soil and structure thermal parameter predictions and detailed computations allowed the study of thermal effects for the energy screw piles steel components. The results show limited impact of the steel components on effective thermal conductivity, but a reduction in thermal resistivity that may provide a speedier thermal exchange in short term GSHP operation. In addition, the more traditional TRT rigs and analytical interpretation provided reasonable results for the pile group in series, and show a similar performance to a borehole heat exchanger of similar pipe length; however, the short piles engage only the upper soil layers, with potentially lower thermal conductivity. TRT in single short screw piles require careful consideration, because common rigs may be unable to cater for the required low fluid flow rates and heating power. Thus, for the cases assessed herein, the pile group TRT proved to be more reliable than individual pile testing, due to their short length.

One of the ways to install plate anchors in deep seabed is to drop the anchor system from the sea level and allow it to initially embed in the seabed under its own weight. Further dragging would cause the anchor to rotate and embed further into the seabed. There could be difficulties of getting the anchor plate horizontal or mooring line to be perpendicular to the plate where the maximum pullout capacity could be achieved. As part of the investigations, various aspects of the plate performance were examined through centrifuge testing in which the plate orientation and pullout angles were varied. It was presumed that dynamic stability of the anchor (during field installation) can be achieved by having the plate in biwing configuration. Therefore, the performance of the biwing anchors having different spacing between the plates was also examined in the centrifuge testing program and the findings were compared with predictions obtained through finite-element modeling (FEM). Both pullout directions and the plate angles considerably influenced the pullout capacity factors. The comparison between the predicted pullout capacity using FEM and measured pullout capacity for biwing anchors at shallow embedment depths was excellent. However, the FEM-predicted pullout capacity was noticeably lower than the measured ones for deep anchors. Pullout capacity of biwing anchors at shallow embedment depth increased as the spacing between the plates $S$ increased from 0 to $0.5B$. However, there appears to be a slight reduction in the performance in deep embedment anchors. This is also reflected in FEM findings.