Journal of Geotechnical and Geoenvironmental Engineering

Low-amplitude repetitive drained loading may hinder the long-term performance of engineered and natural systems. This study examines the volumetric and shear response of a uniform quarzitic sand subjected to repetitive drained simple shear loading under constant vertical stress while tracking the evolution of the secant stiffness and the small-strain shear modulus. We explore the effects of initial density, initial shear stress and cyclic shear stress amplitude to identify criteria that can be used to anticipate asymptotic volumetric and shear states. We analyze experimental results in reference to the sand response under monotonic simple shear loading. All specimens evolved toward some asymptotic terminal void ratio $e_T$ when subjected to simple shear cycles. Contractive specimens exhibited unceasing shear strain accumulation and ratcheting when the normalized shear stress exceeded ${\tau }^{*}=({\tau }_o+\mathrm{\Delta }\tau )/{\tau }_{\mathrm{ult}}>0.85$; on the other hand, dense-dilative specimens exhibited ratcheting only when the normalized shear stress exceeded ${\tau }^{*}=({\tau }_o+\mathrm{\Delta }\tau )/{\tau }_{\mathrm{ult}}>1.25$. The small-strain $G_{\max }$ and the secant $G_{pp}$ shear moduli increased during repetitive shear cycles to reflect early fabric changes followed by abrasion/fretting among enduring contacts. Results obtained in this study allow us to propose simple guidelines to predict the asymptotic shear and volumetric response of uniform sands subjected to repetitive simple shear loading for first-order engineering analyses.

This study presents a simplified resonant column testing method to obtain small-strain dynamic properties of soils in both torsional and flexural vibrations. The method exploits free vibration decay responses of the system produced by manual excitation while the specimen is subjected to an isotropic effective confining stress produced by a vacuum pressure. This method is readily applicable to standard resonant column and torsional shear devices and triaxial cells by attaching a metal bar with one or two accelerometers for manual excitation, but not using an electromagnetic driving plate. This paper describes the apparatus design, test procedure, system calibration, and data analyses, as well as the test results of dynamic properties of a dry sand, including small-strain elastic moduli and damping ratios obtained from the torsional and flexural modes. The results confirm that the suggested method can capture strain-dependent characteristics up to the strains of $\sim {10}^{-4}$ beyond typical elastic threshold strains, although the isotropic effective confining stress is limited to $\sim 90\mathrm{kPa}$. This unique testing method provides remarkably consistent and reliable measurement for the dynamic properties of soils, and it avoids any possible bias from the counterelectromotive force.

This study presents a range of numerical modeling to evaluate the pullout capability of suction anchors subjected to inclined mooring loading in a clay-over-silty-sand deposit. Comprehensive numerical models were generated, which were validated against existing centrifuge testing and numerical modeling results. A parametric study was then carried out to assess the effects of the anchor length, padeye location, mooring angle, and layered deposits on the pullout capacity of suction anchors. According to the numerical simulation results, the following key design factors were obtained: (1) the optimal padeye position, (2) the ultimate horizontal and vertical pullout abilities, and (3) the horizontal load distributions at different padeyes. A simple framework of calculating the combined $VH$ surfaces of the anchors was developed for preliminary prediction of the pullout capacity of suction anchors in a clay-over-silty-sand deposit that provides the optimized location of padeyes and more accurate prediction for the holding capacity of anchor. The design method proposed by this study can contribute to optimize and improve the current design guideline for more accurately predicting the bearing capacity of anchors in clay-over-silty-sand soil deposits.

Similar to sand solidification with microbially induced carbonate precipitation (MICP), the MICP technique can also be used to bond loess particles and improve the collapsibility of loess. However, existing theoretical models related to MICP sand solidification cannot be used to guide the application of loess solidification. Based on the properties of loess, the present study revised the transport model of biomass. The revised biomass transport model enabled the calculation of the biomass distribution. Moreover, considering the effects of nutrients in the cementation solution and the ions of inorganic salts contained in loess on urea hydrolysis, a new urea hydrolysis equation for MICP loess solidification was obtained. A revised theoretical model for loess solidification is proposed. In addition to the biomass distribution, the contents and distribution of calcium carbonate, and the porosity of solidified loess were calculated using the proposed model. The results are consistent with the results measured during loess solidification tests, demonstrating the feasibility and practicability of the proposed model. This revised theoretical model lays a solid foundation for the solidification of loess and preventing loess from collapsing.

Physical models have suggested a large reduction in bearing capacity of simple foundations due to overtopping tsunami scour. We use the results of these tests to create scoured foundation geometries for simple breakwater-type structures and investigate the change in the system’s capacity due to scour through the use of simple two-dimensional (2D) numerical analysis using an advanced constitutive model. The particular aspects of the construction of such models and the general applicability of the method are also discussed. A simple method for estimating the reduction in capacity due to scour is proposed through the use of modified vertical, horizontal force, and moment (VHM) failure surfaces. The general method for creating such simplified scour-dependent failure surfaces is described thoroughly, such that the process can be replicated for other foundation configurations or scour problems. Results indicated that even a small amount of scouring can lead to a substantial reduction in the horizontal and moment capacity of a foundation, the effect of scour is shown to be a nonuniform contraction of the failure envelope, where both the ultimate vertical capacity $V_0$ as well as the relative ratios between vertical, horizontal and moment capacity are strongly affected by the presence of scour. Such a conclusion demonstrates clearly how simply increasing the unscoured factor of safety of such structures is not sufficient to guarantee stability in the event of scouring. The presented methodology for determining the scoured failure surfaces provides a simple, logical means to estimate the performance of such systems undergoing scour.

Seismically induced landslides can often cause severe human and economic losses. Therefore, it is worth assessing the seismic performance of slopes through a reliable quantification of the permanent displacements induced by seismic loading. This paper presents a new semiempirical relationship linking the permanent earthquake-induced displacements of slopes to one or two synthetic ground motion parameters developed considering the Italian seismicity, and a comparison with existing simplified displacement models is illustrated. Once combined with a fully probabilistic approach, these relationships provide a useful tool for practicing engineers and national agencies for a preliminary estimate of the seismic performance of a slope. In this perspective, the predictive capability of different semiempirical relationships is analyzed with reference to the permanent displacements evaluated for the Italian seismicity assimilating the slope to a rigid body and adopting the Newmark integration approach. The consequences of the adoption of these relationships on the results of the probabilistic approach are illustrated in terms of displacement hazard curves and hazard maps for different slope scenarios.

In the literature, the influence of spatial variability of the undrained shear strength of foundation soils on the bearing capacity of footings is limited to footings seated directly on the foundation. This is an unlikely arrangement in practice. This paper revisits the footing problem by considering a thin granular layer between a strip footing and soft foundation soil using analytical and stochastic numerical modeling. The analyses are extended to the case of a geosynthetic-reinforced granular layer and to the idealized case of no granular layer. The study shows that the probability that the ultimate bearing capacity for the footing is smaller than the deterministic design value is greater for all three scenarios with randomly uniform clay soil than for the same soil with isotropic or anisotropic spatial variability of strength at practical levels of reliability index $\beta$ (e.g., $\beta \ge 3.09$ for a permanent footing). The reason for this outcome, which may appear counterintuitive, is explained. Design charts are provided to estimate the deterministic design bearing capacity of a rigid strip footing required to meet a range of target reliability index for the three footing scenarios examined in this study.

Understanding the failure process in frozen porous rock is of great importance to both geomorphology research and engineering design in cold regions. The mechanical behavior of frozen porous rock has its own particularity due to the existence of ice and unfrozen water in pores. To investigate the failure process in frozen rocks, uniaxial compression tests on oven-dried, air-dried, and water-saturated sandstones at 15°C and $-20°\mathrm{C}$ were conducted, and the electrical resistances of rock samples were monitored during compression, with which the pressure-melting effect of pore ice can be interpreted. Moreover, the phase composition of pores in sandstone before and after freezing was measured through the nuclear magnetic resonance (NMR) method. The results show that the initial water content of frozen rock changes the variation trend of electrical resistance, that is, the starting point of increasing stage in electrical resistance is shifted from the microcrack propagation stage in frozen oven-dried and air-dried samples to the stress peak in the frozen water-saturated sample. Also, the electrical resistance of frozen water-saturated rock decreases by 29.4% in the microcrack compaction stage, which is 7.4 times higher than that of frozen oven-dried rock and 4.3 times higher than that of frozen air-dried rock. Finally, 96% of pore water (free water, capillary water, and amounts of adsorbed water) is frozen in the saturated rock. The freezing point of water in microcracks is severely depressed by the strong capillary pressure, while the stress concentration effect in microcracks enlarges the applied pressure greatly and eventually induces pressure melting of pore ice. Based on the results and analysis, we suggest that the pressure-melting effect works primarily in the microcrack compaction stage and microcrack propagation stage and remolds the failure process of frozen saturated sandstone by altering the interaction between ice and pore (or microcrack).

Results from both laboratory and in-situ cone penetration tests (CPTs) on predominantly sandy silt platinum tailings from an operational mine in South Africa are reported. The CPTs were conducted with four different cone diameters at varied penetration rates. With the results interpreted in terms of the normalized tip resistance and the initial state parameter, in addition to dissipation tests, it was possible to identify the CPTs affected by significant partial drainage effects. A review of the partial drainage concept enabled the formulation of a novel characteristic surface approach, which uses a unified continuous equation to estimate the state parameter from the CPT data from drained to partially drained and undrained regimes and from contractive to dilative states. A review of different methods for the estimation of the coefficient of consolidation, and hence the normalized penetration velocity, enables a comparison of the estimated state parameter with independent values calculated from recovered saturated samples, showing the ability of this technique to infer the state parameter from CPT tests where partial drainage occurs.

This paper presents a profound solution for a novel method of dewatering dredged sludge using a combined geotextile tube and vacuum-assisted prefabricated horizontal drains. Firstly, an analytical model was proposed to provide a basis for the design of the proposed approach. This two-dimensional plane-strain consolidation model was based on Gibson’s large-strain theory, incorporating the horizontal and vertical flows with consideration of the self-weight, nonlinear compressibility, and hydraulic conductivity of soil. Secondly, the numerical solution obtained using the alternative direction implicit method was compared with the existing one-dimensional model for verification. Thirdly, a field trial was carried out to evaluate the performance of the proposed approach and analytical model. Finally, the effects of various major design parameters on the consolidation efficiency of the tube system were also investigated through a parametric study to establish an optimal design. This study showed that a higher consolidation efficiency and an earlier optimal efficiency point could be achieved when decreasing the horizontal drain interval and increasing the tube height. Furthermore, surcharge preloading induces a more significant effective stress increment in soil than vacuum preloading of the same magnitude.

Displacement piles are driven to support a wide range of structures. However, analysis of the stress and strain fields developed during their installation remains one of the most challenging problems in geotechnical engineering. Advances in design methods, particularly for sand sites, have had to rely on an imperfect analogy between pile and cone penetration test (CPT), rather than modeling pile installation itself. Recent physical model experiments have provided benchmark data sets that describe the stress and deformation patterns developed around displacement piles penetrating sand masses. Following from large-deformation finite-element analyses that captured the stresses measured in the Grenoble 3S-R calibration chamber NE34 sand experiments, this paper presents simulations of the displacements measured in equivalent high-quality experiments conducted at Purdue University with dense, angular #2Q-ROK silica sand. A modified Mohr-Coulomb model with state-dependent parameters was calibrated to match element tests conducted by the authors, and an arbitrary Lagrangian-Eulerian scheme was applied in the simulations. The evolution and distribution of the deformations induced by pile penetration are compared with the experiments. Predictions for the deformation and strain fields applying during and after pile installation are presented, showing broad agreement between the simulations and experiments. The predicted and measured pile capacities are also compared and contrasted. Points of divergence between the simulations and tests are highlighted and their implications for numerical modeling are discussed.

Mining operations produce large quantities of waste rocks, which are usually disposed of in waste rock piles, but can also be valorized in mine haul roads. The engineering performance of these haul roads significantly depends on the mechanical characteristics of the materials used for the construction. However, available experimental studies on coarse-grained waste rocks are relatively limited, mainly because of their large grain size and the scarcity of adapted testing equipment. In this study, a series of repeated load and monotonic triaxial tests (specimens 300 mm in diameter and 600 mm in height) were carried out to evaluate the resilient modulus, permanent deformation, and shear strength of coarse-grained waste rocks (up to 60 mm in diameter) with different gradations. Results showed that an increasing in maximum particle size and compaction effort resulted in a larger resilient modulus and shear strength and smaller permanent deformation. The optimal gravel-to-sand ratio to maximize resilient modulus and shear strength was around 5. Permanent strain was relatively constant when the gravel-to-sand ratio was between 1 and 5, but it decreased significantly when the ratio increased to 8. The impact of fines content and water content on the mechanical properties was relatively limited. Also, the ${\mathrm{M}}_{\mathrm{R}}\text{-}\theta$ model and Rahman and Erlingsson model showed good fitting performance for resilient modulus and permanent strain, respectively. Finally, neuroevolution of augmenting topologies (NEAT) was used to develop a machine learning model for predicting the resilient modulus of waste rocks, based on 265 data sets. The model showed reliable accuracy, simple topology, and high generalizability capacity. The findings described in this article should be beneficial for the valorization of waste rocks in pavement engineering.

Monopiles, which have been most extensively used in the offshore wind industries, are usually subject to threats from local scour. The effects of local scour on the bearing capacity of monopiles have been studied based on deterministic soil properties and local scour dimensions. However, the properties of the seabed soil and the dimensions of the local scour both have uncertainty. In this study, a new nonstationary random field model, which can better simulate the nonstationary characteristics of the seabed clayey soil and result in a safer probabilistic design of foundations, is proposed to characterize the spatial variability of the seabed clayey soil. Then, the effects of the spatial variability of the seabed clayey soil and the uncertainty of the local scour depth on the bearing capacity of monopiles are investigated under both uniaxial loading and vertical-horizontal-moment (VHM) combined loading using the random finite-element method combined with kriging metamodeling technique and Monte Carlo simulation. The undrained shear strength of the seabed clayey soil was simulated with a lognormally distributed nonstationary random field, and the local scour depth was treated as a uniform random variable. The negative correlation between them was also considered. The results show that the factor of safety required for the local scoured seabed decreased from 3.3 to 2.6 as the negative correlation was enhanced, greater than or equal to that [factor of safety $(\mathrm{FS})=2.6$] for the intact seabed. The procedure of analyzing the design failure envelop of a monopile in spatially variable clayey soil with a local scour proposed in this study can provide a reference for geotechnical engineers.

The Millennium Tower is a 58-story reinforced concrete building that was constructed in San Francisco, California, between 2005 and 2009. The Tower is founded on an embedded pile-supported mat with pile tips bearing in dense marine deposits that overlie an overconsolidated marine clay layer known locally as Old Bay clay. This clay layer experienced stress increases from Tower self-weight and from multiple episodes of dewatering between 2006 and 2018 at the Tower site and neighboring sites, including one that was sustained for 6 years. Settlements of the Tower foundation have been measured since 2006, and lateral deflections of the Tower have been inferred and measured since 2009. The data show that during multiple episodes of “loading” (from stress increase or dewatering), settlements initially accelerated and then gradually slowed over time, as expected from consolidation principles. Similarly, lateral deflections (from foundation tilt) (1) accelerated following foundation construction activities at adjacent sites (dewatering and excavation); and (2) oriented toward adjacent excavations, which at various times occurred to the project south, north, east, and west of the Tower site. An objective of this paper is to describe this case history, including the geotechnical site conditions and results of a monitoring program that tracked foundation settlements, Tower tilt, groundwater levels at the Tower site, and ground inclinations over time. We also evaluate soil deformation mechanisms that likely produced the movements. We find that settlement amounts and time variations are well captured by one-dimensional and three-dimensional analyses of volume change in Old Bay clay and other foundation soils from primary consolidation and secondary compression, provided that time variations of stress increase and groundwater level are accounted for. Three-dimensional analyses also capture time variations of lateral deflections, which were caused by volume change and shear deformations in foundation soils, the latter having been affected by unloading from adjacent excavations.

Reports on the serviceability stage and long-term performance of embedded retaining structures are scarce, even more so in areas with background settlements. This paper presents a case study of an excavation with a permanent sheet pile wall in soft sensitive clay in Uppsala, Sweden. The monitoring data span the short-term and four years of the serviceability stage. The monitoring data are compared with finite element analyses using the rate-dependent Creep-SClay1S model. A historic groundwater drawdown is accounted for in the modeling and challenges with respect to the proper initialization of the in situ stress state, preconsolidation pressure, fabric, and bonding are discussed. The results show that even though the background settlements are somewhat underpredicted, the horizontal displacements as well as anchor forces were captured rather accurately. This valuable case study of the short- and long-term behavior of a permanent sheet pile wall in soft sensitive clay confirms the performance of using this cost-effective solution for a permanent construction. Furthermore, the paper highlights the challenges of an accurate description and modeling of the initial in situ state.