Journal of Geotechnical and Geoenvironmental Engineering

Microbial induced calcium carbonate precipitation (MICP) offers a robust technique to improve strength and stiffness properties of subsurface soils supporting infrastructures. Several unknown factors, including the MICP reactive transport parameters, however, limit the ability to predict spatial distribution of calcium carbonate (${\mathrm{CaCO}}_3$) precipitation within a subsurface area and with depth. As it was shown that calcium carbonate distribution is highly affected by biomass profiles in subdomains, five bacteria attachment models (constant-rate, power-law, exponential, gamma distribution, and “$c_{\mathrm{s}\mathrm{t}\mathrm{r}}$ based on colloid attachment theory”) were calibrated here using data from both small- and large-scale testing programs. Out of the five models, colloid attachment theory with modified velocity and straining terms was shown to be the most promising approach in yielding the most fitted ${\mathrm{CaCO}}_3$ distribution compared with the experimental data. A new parameter, $c_{str}$, was incorporated to modify straining and the constraint peak value of biomass attachment due to straining at distances larger than a $0.14\times \mathrm{s}\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{e}\mathrm{s}\mathrm{i}\mathrm{z}\mathrm{e}$. Using the results from the numerical simulations, relationships were developed for velocity and straining coefficients of “the $c_{\mathrm{s}\mathrm{t}\mathrm{r}}$ based on colloid attachment theory” (hereafter “colloid attachment $c_{\mathrm{s}\mathrm{t}\mathrm{r}}$”) as a function of bacteria size, soil particle size, sample size, volume of injected bacteria, and soil pore volume.

Pumping-induced earth fissuring is a typical fluid–solid coupling problem involving fracture evolution. Despite recent advances in the numerical modeling of earth fissures, a holistic approach capable of predicting their evolution and understanding their behavior from fracture mechanisms is absent. This paper presents a coupled numerical method based on the framework of the material point method (MPM) and fracture mechanics for the process-oriented simulation of pumping-induced tensile earth fissures. In this method, fissure behavior is driven by the real-time stress field affected by soil consolidation. After an earth fissure initiates in the region of maximum tensile stress, it propagates in the direction of the maximum circumferential stress around the fissure tip. The great scale difference between a fissure tip and the entire model is addressed with an adaptive refinement strategy. Through the simulation of a physical model experiment reproducing pumping-induced earth fissures with the presence of a bedrock ridge, the complete fissuring process, including initiation, propagation, and arrest, is presented. The simulated fracture time (24 h after drainage), location (directly above the bedrock ridge), final length (165 mm), and morphology evolution (from straight to zigzag) of the main fissure basically were in agreement with the experimental results. The stress intensity factors (SIFs) around fissure tips, which are important fracture parameters that have not been discussed in existing earth fissure analyses, also are captured during the fissure growth. The proposed method quantifies the inhibition of geostatic stress fields in earth fissure development and correlate fissure morphology with the stress field at a fissure tip.

A common source of error in bender element testing lies in the determination of the shear wave arrival time arising from the near-field effect, which is attributed to shear wave–like motion of the compression wave obscuring the arrival of the shear waves, and can be mitigated by using a sufficiently high travel-distance-to-wavelength ($L/\lambda$) ratio. However, the $L/\lambda$ ratio also is relevant for signal interference due to side reflections, and its role in this important mechanism is far less understood. Stiff materials such as cement-treated soils, which have a very short shear wave travel time, are likely to exacerbate these errors. This paper examined the causes of travel time errors in cement-treated soil using bender element tests of standard-sized triaxial specimens, large block samples, and three-dimensional finite-element analyses. The results show that the reflection of shear waves from sample boundaries generates a second pulse in the received signal, resulting in signal distortion. This can be ameliorated at sufficiently high $L/\lambda$ ratios. The reflection of the compressional waves generates spurious prearrivals and distorts the profile of the direct shear wave even at high $L/\lambda$ ratios. Shear and compressional wave reflections can be mitigated by increasing the specimen diameter to decouple the latter from the direct shear wave arrival.

Monopiles are the favored foundation type for offshore wind turbines due to a relatively simple design and installation process. This paper investigates using coupled three-dimensional finite-element analysis the load-deformation behavior of extra-large (XL) and extra-extra-large (XXL) monopiles in low-shear strength overconsolidated kaolin clay subjected to monotonic lateral loading at varying load eccentricities. The subloading $t_{ij}$ constitutive model, robustly calibrated using data from centrifuge tests carried out by the authors, has been adopted in these analyses. For the 16 cases analyzed, a detailed discussion is provided on the behavior of XL/XXL monopiles, including their mode of deformation, lateral capacity, deflection, rotational stiffness, bending moment and shear force, and the response of the clay in terms of soil resistance and excess pore pressure. It is also demonstrated that the $p\text{-}y$ method is inaccurate in designing monopiles in this size range.

As part of the LEAP (Liquefaction Experiments and Analysis Projects), many centrifuge model tests on a sheet pile retaining wall were conducted at six different centrifuge facilities around the world. Each centrifuge facility used containers of different W/H (width of container/height of wall) ratios to model the same plane strain prototype retaining wall. Predictions of the centrifuge tests that neglected wall friction, assumed plane strain conditions, and used the CycLiq constitutive model, exhibit reasonable general agreement with tests in terms of liquefaction response. However, an overprediction of the median response of sheet pile wall displacement was observed. The study presented in this paper was motivated by a concern that friction on the side walls might be biasing results from model containers with different W/H. A numerical simulation parametric study using FLAC3D is presented to illustrate the potential effects of interface friction and container geometry on the LEAP retaining wall test results. The results show that incorporation of appropriate container geometry and soil-container friction can reduce the error between simulated and experimental sheet pile wall displacements. Soil-container friction is also shown to affect the total earth pressure and especially its distribution on the sheet pile wall, causing the actual tests to deviate from the intended plane strain conditions. For the assessed liquefaction related cases, soil-container friction has the additional effect of significantly restricting the local development of excess pore pressure and subsequent soil deformation, further contributing to its influence on the centrifuge tests. The parametric study indicates that an interface friction angle of 17.6° and $\mathrm{W}/\mathrm{H}>1$, 2, and 3 reduced horizontal wall displacements by 50%, 20%, and 10% respectively, compared to simulations neglecting wall friction. Use of containers with large $\mathrm{W}/\mathrm{H}$ is therefore recommended for future centrifuge experiments.

Earth platforms supported by rigid columns provide an effective solution for embankments founded on thick deposits of soft soils. Nevertheless, the failure mechanisms and associated soil–structure interactions remain inadequately comprehended, particularly for structures such as columns with caps or ground beams. Recent studies have reported sporadic incidents of basal instability in rigid column–supported embankments over soft soil. To gain further insight into this issue, this study investigated the foundation settlement, failure mode of rigid columns, and ground stability under staged embankment construction by centrifuge model tests. Different ground improvement schemes (head conditions) are compared, including columns, capped columns, and columned ground beams, along with natural ground as a base model. Test results show that the potential slip surfaces for embankments on soft ground are almost circular in shape, with or without capped column support. Rigid columns exhibit different failure modes across the improved domain: compression failure under the crest, bending failure under the shoulders, and tensile/bending failures near the toe. Under critical conditions, the columns near the toe collapse first, followed by the adjacent columns beneath the slope and center of the embankment. In contrast, the column failure sequence is unclear for the beam scenario. Capped columns were found to reduce the foundation displacement significantly. Given equivalent area coverage ratios, columned beams demonstrate greater efficacy in controlling ground deformation than capped columns. The interconnecting beams form a strong foundation that mitigates overstressing of subsoil, thus reducing differential and final settlements. Finally, the stability of the ground reinforced with rigid columns under embankment loading is discussed, taking into account the fracturing of columns and the function of caps and ground beams.

The ventilated well method (VWM) is a recently introduced novel dewatering and densification technique for soft soils that relies on controlled evaporation through ventilated and perforated wells traversing through the soil deposit. Several parameters, including geometry of the ventilated well, geometry of the testing mold, soil properties, and properties of the input air, govern the efficacy of the VWM. In this paper, a dimensional analysis (DA)–based approach, following Buckingham’s pi theorem, is used to derive the dimensionless $\pi$ groups for the VWM problem. Using the experimental results from the laboratory-scale implementation of the VWM and multiple regression analysis, a simple dimensionless model between the $\pi$ groups is suggested. The analysis revealed that, keeping the rest of the parameters constant, the dewatering rate increases with an increase in well diameter, air flow rate, and hydraulic conductivity of soil. However, it decreases with an increase in well height, mold diameter and osmotic suction of the pore fluid. A sensitivity analysis was also performed to understand the relative dependence of the dimensionless dewatering factor on the variation of the four other dimensionless input parameters capturing the influence of the well geometry, mold geometry, soil property, and flow property. Finally, the results from the DA-based model were compared with that obtained from a numerical model, and a good degree of agreement was observed. It is envisaged that both the DA-based model and the numerical model will be useful for scaling the VWM for future experimental work, pilot studies, and field trials.

Microbially induced calcite precipitation (MICP) is a promising bio-mediated cementation process that can improve the engineering properties of granular soils through the precipitation of calcium carbonate on soil particle surfaces and contacts. The process offers an environmentally conscious alternative to conventional soil improvement technologies which primarily rely on the use of portland cement and high mechanical energy. As the technology transitions towards field-scale application, an improved understanding of the chemical permanence of MICP will be critical towards identifying favorable applications, predicting long-term engineering behaviors, and evaluating life-cycle environmental impacts. In this study, a series of soil column and batch reaction experiments were performed in tandem with reactive transport numerical modeling to investigate the dissolution behavior of biocementation generated via microbial ureolysis. Five soil column experiments containing a poorly graded sand were treated identically to achieve average ${\mathrm{CaCO}}_3$ contents near 5% by mass and were then subjected to either 0, 5, 10, 20, or 50 identical acidic dissolution injections. A dissolution kinetic model was calibrated independently to batch experiments involving similar solutions and was incorporated into a reactive transport model to forward predict degradation expected during soil column experiments. Spatial and temporal changes in biocementation dissolution were assessed using geophysical and geochemical measurements and observations were compared to those obtained from reactive transport simulations. Results indicate that existing kinetic models can successfully capture the dissolution behavior of ureolytic biocementation; however, model parameters may require site-specific calibration using soil column experiments. Outcomes are expected to significantly improve our understanding of the dissolution kinetics of biocementation, its effects on soil mechanical properties, and provide approaches through which the chemical resilience of MICP soil improvement can be evaluated.

Spudcans are commonly installed to support jack-up vessels in construction process of offshore wind turbines (OWTs), which may induce significant soil deformation that may impact existing foundations of established OWTs. Large-deformation finite-element (LDFE) analyses were performed to investigate movements of an adjacent skirted foundation induced by spudcan penetration. A LDFE model was generated and compared with a centrifuge test and good agreement was achieved. A detailed parametric study was then undertaken to examine the influence of spudcan penetration depths, spudcan–skirt clearance, soil shear strength, and foundation skirt length ratios. The outcome of this study leads to a conclusion that the behavior of the impacted skirt is closely related to soil flow mechanisms around the skirted foundation induced by spudcan penetration. The clearance distance between the spudcan and the skirt is the key factor. Significant skirt rotation occurs when the spudcan is less than one diameter distance from the skirt, especially for a short skirt installed in stiff clay. The soil flow mechanisms around the spudcan and skirted foundation are presented and approximating expressions for estimating the maximum rotation of skirt during spudcan penetration are proposed based on intensive numerical modeling results.

Bioinspired strategies have been used in recent years to solve engineering problems in geotechnics. Inspired by the dual-anchor locomotion mechanism of razor clams, researchers are developing a new generation of self-burrowing probes for a wide range of applications such as site exploration and sensor deployment. Due to inherent complexities of the bioinspired self-burrowing mechanism, the interaction between the probe and the soil is not fully understood, hindering the development of physical prototypes. In this study, a model based on the discrete element method (DEM) is used to prove feasibility and study and optimize the self-burrowing process of a probe. The probe burrows in a gravity-settled chamber filled with a scaled discrete analogue of a silica sand. A stepwise methodology, including essential anchor expansion, tip penetration, and anchor retraction, is proposed to model the self-burrowing process. Tip oscillation is introduced to reduce penetration resistance, which enables efficient burrowing through continuous cycles. However, the reduction strategy of soil resistance consumes more than 50% of the total work done by the entire self-burrowing cycle. Micromechanical observations, such as the contact force network and the particle displacement field, are provided to clearly visualize the interaction between the soil and the probe. While the total energy necessary to penetrate is greater than that for an equivalent constant-rate penetration, the feasibility of such a probe is numerically proven.

Deep excavations in soft clays often demand heavy shoring supports. Closely spaced struts are known to impede construction within an excavation, resulting in longer construction time. This paper presents a novel strut-free retaining wall constructed by deep cement mixing (DCM). A new U-shaped DCM system (UDCM) was developed to support a 6.5-m-deep, 16-m-wide excavation in newly reclaimed land. Field measurements involving inclinometers and surface movement markers were interpreted using a fully coupled three-dimensional finite-element model. Results indicated a rotational deformation mechanism in the DCM wall. The mechanism was triggered by stress relief and basal heave. Due to the rigidity of the UDCM, the occurrence of basal heave caused the DCM walls to deflect outward toward the retained side. Such a mechanism is not typical in conventional retaining wall systems in which lateral props are installed after certain depths of excavation. The present UDCM possesses a distinctive characteristic, which is the capability to implement and activate props prior to excavation. It also is unique in that basal heave is used to regulate the rotation of the wall, thereby limiting lateral displacements during an excavation. This study includes a design chart developed for the prediction of lateral displacements with varying treatment geometries.

Tailings dams have relatively high failure rates throughout the world and the consequences of these failures often result in significant loss of life and damage to the environment and property. However, the triggers and failure mechanisms are typically hypothesized and not well understood. To investigate potential triggers and the corresponding failure mechanisms, two centrifuge model tests were conducted on loose slopes made of gold tailings using a scaled viscous fluid to induce instability in flight. A numerical back-analysis was also carried out to investigate and verify the associated mechanisms. Two failure mechanisms were observed in the centrifuge tests. In the first test, large seepage forces caused sloughing at the toe. The initially drained instability at the toe induced significant positive excess pore pressures due to the loose state, as well as to the initially higher degree of saturation in the toe region, triggering localized liquefaction at the toe (undrained response). Due to the localized liquefaction, the tailings at the toe could not support the tailings upstream of the toe, triggering a retrogressive flowslide failure. In the second test, a slope failure occurred due to drained instability, i.e., failure occurred once the drained factor of safety approached unity. No liquefaction was evident, due to the initially lower degree of saturation in the toe region, as well as to the slower rate of shearing compared to the first test. As revealed by both physical and numerical simulations, the structural collapse of the soil resulted in the drained instability of the slope, which triggered a slide-to-flow failure.

Axially loaded piles in liquefiable soils can undergo severe settlements due to a shaking event. During shaking, the settlement is caused by the reduction of its shaft and tip capacity from the excess pore pressures generated around the pile. Post shaking, additional pile settlement is caused by the surrounding soil settling due to reconsolidation and the associated development of drag load. A new displacement-based method is developed using a TzQzLiq analysis for designing axially loaded piles subject to seismic loading and liquefaction-induced downdrag. The new displacement-based design method offers several advancements to the state of practice forced-based design procedure by AASHTO’s force-based design procedure by reasonably accounting for the mechanisms that occur on axially loaded piles during and post shaking. It accounts for the initial drag load on the pile, redistribution effects resulting in large excess pore pressures in the non-liquefied layers, and reduction in the pile’s shaft and tip capacity from excess pore pressures around the pile. The new design procedure estimates the pile settlement and axial load distribution during the entire shaking event, i.e., during shaking and reconsolidation. Design steps are provided describing the procedure for obtaining design curves on the settlement and drag load on piles with varying pile lengths. The length of the piles is then selected based on serviceability criteria and the pile’s structural strength. Finally, the new design procedure is applied on piles used in centrifuge model tests, and results are compared, followed by an example design problem that illustrates the applicability of the new method in practice.

Buildings are often located in close proximity to each other in urban settings. Seismic structure-soil-structure interaction near two adjacent buildings (${\mathrm{SSSI}}_2$) on liquefiable soils has previously been investigated and shown to be consequential. However, these studies did not evaluate the impact of multiple ${\mathrm{SSSI}}_{3+}$ (exceeding three buildings in a cluster) on key engineering demand parameters (EDPs). In this paper, we systematically explore the influence of ${\mathrm{SSSI}}_{3+}$, building spacing (S) in relation to width (W), arrangement, and location in a larger cluster on building EDPs. ${\mathrm{SSSI}}_{3+}$ is shown to reduce the foundation’s average settlement compared to an isolated structure (SSI) or even two adjacent structures (${\mathrm{SSSI}}_2$). Similar to ${\mathrm{SSSI}}_2$, however, ${\mathrm{SSSI}}_{3+}$ notably amplifies the permanent rotation of side or corner structures compared to an isolated counterpart or the neighboring center structure(s). The resultant tilt magnitude of corner structures experiencing ${\mathrm{SSSI}}_{3+}$ is greater than those under ${\mathrm{SSSI}}_2$ at $\mathrm{S}/\mathrm{W}<0.3$, while a slight reduction is observed for ${\mathrm{SSSI}}_{3+}$ at greater spacings ($0.3<\mathrm{S}/\mathrm{W}<1$). These rotations cannot be captured in a model of SSI or ${\mathrm{SSSI}}_2$. In all models considered, the direction and magnitude of flexural drifts within the superstructure are shown to depend on the orientation and magnitude of foundation rotation, which are themselves sensitive to building spacing and cluster arrangement. Overall, the numerical sensitivity study presented in this paper shows that ${\mathrm{SSSI}}_{3+}$ can adversely influence the performance and damage potential of corner or side structure-foundation systems compared to more simplistic cases of SSI and ${\mathrm{SSSI}}_2$ at $\mathrm{S}/\mathrm{W}<0.3$, which should be considered particularly for L- or square-shape cluster configurations.

In mountainous areas, urban development often takes place on slow-moving ground, which over time may inflict severe damage on buildings and infrastructure. This process can be accelerated significantly by new construction near existing structures. Although for stable ground conditions the problem of excavation-induced damage has been studied extensively, for slow-moving landslides the question of how to reduce damage to neighbors remains open. This paper presents a general finite-element modeling procedure which allows for a full-scale investigation of the landslide excavation problem. The evaluation of structural damage follows an existing approach, in which the effect on the neighboring buildings is deduced from greenfield displacements, using the limiting tensile strain method, correlated with damage categories. The results of the study, which was inspired by real landslide cases, show that failing to estimate the correct compression state of the landslide can lead to significantly higher damage to close neighbors than in the case of a stable slope. Designing the anchors close to the true in situ earth pressure reduces the damage potential, but can result in enormous anchorage costs, if situated in a compressed landslide zone. Excavating farther from neighbors allows for a significant reduction in the required anchor support, which the proposed procedure helps to quantify. Another distinctive feature of excavations within landslides is the development of considerable compressive strains in the sliding direction along the lateral sides of the excavation. It is shown that these compressive strains also have the potential to damage neighboring buildings.

Hydrochar is a biomass-derived carbon-rich material produced by the hydrothermal carbonization process which requires less energy than the pyrolysis production of biochar. The effectiveness of using hydrochar to amend soil properties, especially hydraulic conductivity, and the underlying mechanism that hydrochar follow remain unknown. This study measured the effects of grass feedstock and grass-derived hydrochar produced at two temperatures (180°C and 240°C) on the pore size distributions (PSDs) and saturated hydraulic conductivity ($k_{\mathrm{s}}$) of compacted silty-clay sand. Hydrochar affected the $k_{\mathrm{s}}$ through predominantly the change of macropores of amended soil. Specifically, the addition of 180°C hydrochar [with a 60% specific gravity ($G_{\mathrm{Hs}}$) of the soil] at the mass proportion ($f_{\mathrm{H}}$) of 2.5% evolved the PSD from unimodal to trimodal, creating a more open soil structure and increasing the $k_{\mathrm{s}}$ by more than half an order of magnitude. When $f_{\mathrm{H}}$ exceeded the threshold of 2.5%, the improvement of $k_{\mathrm{s}}$ decreased in effectiveness following the compression of macropores. The 240°C hydrochar that has a larger $G_{\mathrm{Hs}}$ (than the 180°C case) has a high threshold of 5% and introduced a great increase in $k_{\mathrm{s}}$. Test results highlight the importance of avoiding adding excessive hydrochar to prevent the reduction of the effectiveness of drainage improvement.

The bearing resistance of energy piles in the presence of temperature effects has not been thoroughly investigated, preventing the perfecting of energy pile design methods. Quantifying the relationship between soil suction and the temperature of unsaturated soils therefore becomes an important step in predicting the bearing resistance of energy piles. A new constitutive model based on interfacial energy and thermodynamic theories is therefore presented to predict the effect of temperature on soil suction as well as the soil–water characteristic curve (SWCC) in this paper. The analytical model for the nonisothermal matric suction was developed by combining five different temperature-dependent functions for the surface tension, air–water contact angle, void ratio, and thermal expansion of solid and water density, thereby providing a more complete approach than the one that considers surface tension only. The proposed formulation was expressed under a simplified form which is believed to be a useful and convenient tool to apply to a range of possible field situations. The temperature-dependent relationship of soil suction was then used to extend existing isothermal SWCCs to nonisothermal conditions that allow obtaining the SWCC at any temperature. The validity of the proposed model was verified by comparison to several test data sets for five different soils: swelling clay, hard clay, clayey–silty soil, ceramic material, and sand. The satisfactory agreement between predicted and measured curves proved that the proposed model had good performance in predicting the effect of temperature on the SWCCs of unsaturated soils. The nonisothermal SWCC model was then coupled with bearing resistance theory to produce a simplified method for analysis of energy piles. The results showed that the proposed method successfully predicted pile resistance at various temperatures when compared to experimental data. The pile resistance reduced as the temperature rose for a specific degree of saturation or if the soil was in an undrained condition. However, water evaporation may cause a decrease in water content and an increase in matric suction as the temperature increases. Therefore, as soils dry out, pile resistance may increase with increasing temperature.

Developing empirical correlations between the shear-wave velocity ($V_s$) and the standard penetration test (SPT) blow count has been a long-term practice for sandy, silty, and clayey soils. However, the existing correlations are not suitable for gravelly soils because the SPT is not particularly reliable for gravelly soils due to the interference of SPT sampler with relatively large-size gravel particles. Hence, in the present study, a new correlation has been developed between $V_s$ and the dynamic cone penetration test (DPT) resistance for gravelly soils. The DPT, which consists of a 74-mm-diameter cone to reduce the interference of large particles, has recently been used to correlate the liquefaction resistance of gravelly soils. A large database has recently been developed based on both DPT and $V_s$ data collected from different companion sites all around the world to develop new liquefaction triggering procedures. Based on this database, linear and log-linear correlations have been developed considering the effect of vertical effective stress. Results showed that the correlations among the uncorrected DPT and $V_s$ resistance and the vertical effective stress are much stronger in comparison with the correlation obtained between the overburden-corrected DPT resistance and $V_s$. A reasonable agreement was observed between the measured and computed $V_s$ for both linear and log-linear correlations.