Journal of Geotechnical and Geoenvironmental Engineering

The shear strength of granular materials is influenced by many factors that include particle morphology, gradation, mineralogy, fabric, material density, applied stresses, boundary conditions, and loading path. In recent years, three-dimensional (3D) imaging techniques such as computed tomography enabled researchers to quantify sand particle morphology based on 3D images of particles. This paper presents an experimental investigation of the influence of particle morphology (i.e., surface texture, roundness, form, and sphericity), specimen density, and initial mean stress on the shear strength properties of dry specimens of silica sands and glass beads. Spherical glass beads as well as three other sands (with different morphologies) with grain sizes between U.S. Sieve No. 40 (0.42 mm) and Sieve No. 50 (0.297 mm) were tested at 15-, 50-, 100-, and 400-kPa confining pressures under axisymmetric triaxial compression. The influence of particle morphology on stress-strain response and volume change behavior as well as peak state and critical state (CS) friction and dilatancy angles was examined. The triaxial test results of Toyoura and Hostun RF sands collected from the literature were included in the analyses. Simple statistical models capable of predicting the peak and CS friction angles as well as dilatancy angle by providing particle surface texture, roundness, sphericity, relative density, and initial mean stress as input parameters were developed. The results show that morphology parameters highly influence dilatancy angle, CS, and peak state friction angles.

A substantial body of laboratory and field observations on compression and consolidation of soft clay and silt deposits as well as organic soils, suggest a soil behavior according to Hypothesis A and the $C_{\alpha }/C_c$ law of compressibility. Yet the isotaches compression concept and isotaches consolidation models have been used to predict and promote Hypothesis B and also create confusion regarding the $C_{\alpha }/C_c$ law of compressibility. There is a lack of observed evidence supporting Hypothesis B as it was originally defined. The isotaches compression concept consists of expressing secondary compression observed for 20-mm thick laboratory specimens in terms of vertical strain versus effective vertical stress, for a series of vertical strain rates. The isotaches consolidation models, without justification, then either explicitly or implicitly use secondary compression observed for laboratory specimens during primary consolidation of field layers. These Hypothesis B-based settlement analyses are expected to significantly overestimate end-of-primary (EOP) settlement for field construction on soft ground.

This paper presents the results of tensile load tests performed with instrumented model piles with different surface roughnesses jacked into sand samples in a half-circular calibration chamber with digital image correlation (DIC) capability. Digital images of the model piles and sand were taken during each test; processing of these images using the DIC technique yielded the soil displacement and strain fields in the sand. Data from local sensors and DIC show that an increase in the roughness of the shaft results in an increase in the average unit shaft resistance and in the displacements and strains in the soil next to the shaft of the pile. Guidance is provided for consideration of pile shaft surface roughness in the calculation of the tensile limit unit shaft resistance of jacked piles in sand.

The focus of this research was the real time assessment of rock strength during drilled shaft installations in Florida. Measures of unconfined compressive strength, a function of rock strength used commonly in shaft design, are provided through five monitored drilling parameters: torque, crowd, rotational speed, penetration rate, and bit diameter. This study is part of a larger project in which laboratory and field investigations were performed. This paper covers the laboratory portion of the investigation in which synthetic limestone blocks were cast at four design strengths representative of Florida limestone and drilled in a controlled environment. The laboratory drillings revealed that torque provides a better correlation with unconfined compressive strength than crowd force, which was found to be the case independent of drilling parameter groupings, and when groupings based on variations in bit diameter and the penetration rate to rotational speed ratio were enforced. During the analysis, multiple drilling equations were investigated, and a unique relationship was developed with Teale’s specific energy equation for nonpercussive rotary drilling using a rock auger.

Instrumented pile tests are vital to establish the performance of a pile and validate the assumptions made during initial design. Conventional instrumentation includes vibrating wire strain gauges and extensometers to measure the change in strain or displacements within a pile. Although these strain and displacement gauges are very accurate, they only provide strain/displacement readings at discrete locations at which they are installed. It is therefore common to interpolate between two consecutive points to obtain values corresponding to the data gaps between points; in practice, these discrete instrumented points could be tens of meters apart, at depths corresponding to different soil layers, and hence simple interpolation between the measurement points remains questionable. The Brillouin optical time-domain reflectometry fiber optic strain sensing system is able to provide distributed strain sensing along the entire length of the cable, enabling the full strain profile to be measured during a maintained pile load test. The strain data can also be integrated to obtain the displacement profile. This paper presents three case studies which investigate the performance of three concrete bored piles in London using both conventional vibrating wire strain gauges and distributed fiber optic strain sensing during maintained pile load tests, which enable comparisons made between the two instrumentation systems. In addition, finite-element analyses show that the ability to measure the full strain profiles for each pile is highly advantageous in understanding the performance of the pile and in detecting any abnormalities in the pile behavior.

A long-term soil column study was carried out to investigate the methane (${\mathrm{CH}}_4$) removal capacity of landfill cover soil and biochar-amended cover soil under simulated landfill cover conditions. Terminal batch assays were conducted following the long-term column tests to quantify potential oxidation rates in cover materials at three depths targeting the middepths of distinct soil layers in each column. Potential methane oxidation rates among the materials varied in response to moisture content and were also affected by the methane exposure history. During long-term incubation testing, 10%–biochar-amended soil columns had higher average methane removal efficiencies than an unamended soil control at inlet methane loads ranging from $\sim 50$ to $200\mathrm{g}{\mathrm{CH}}_4·{\mathrm{m}}^{-2}·{\text{day}}^{-1}$. Methane oxidation rates in cover materials following exhumation varied widely following an initial lag phase, ranging from very low rates ($<1\mathrm{\mu g}{\mathrm{CH}}_4·{\mathrm{g}}^{-1}·{\text{day}}^{-1}$) to relatively rapid rates similar to those observed in landfill cover soils (up to $270\mathrm{\mu g}{\mathrm{CH}}_4·{\mathrm{g}}^{-1}·{\text{day}}^{-1}$). Highest overall methane oxidation rates were observed in 10%–biochar-amended soils in both column and batch assays, and this is attributed to the favorable soil moisture regime promoted by the high water-holding capacity of biochar, as well as to its high internal porosity and surface area. In addition, the improved water retention of biochar-amended soil also enhanced the performance by reducing the formation of desiccation fissures and the emissions of landfill gas through these fissures via advective flow.

Seismic slope displacements are estimated for earth structures or natural slopes subjected to interface earthquakes in subduction zones. The fully coupled, nonlinear seismic slope displacement model captures the important influence of the system’s yield coefficient $k_y$, its initial fundamental period $T_s$, and the ground motion’s spectral acceleration at a degraded period of the slope taken as $1.5T_s$. The model separates the probability of zero displacement (i.e., $<0.5\mathrm{cm}$) from the distribution of nonzero displacement, so that low values of calculated seismic displacement do not bias the results. The input ground motion is the primary source of uncertainty in assessing seismic performance of an earth slope or system. Thus, a comprehensive database containing 810 two-component ground motion recordings from subduction zone interface earthquakes was developed and used to compute seismic slope displacements. The resulting model provides seismic displacement estimates similar to those from the previous model that was developed using shallow crustal earthquakes along active plate margins, but there are a few important differences. The subduction zone earthquake-induced slope displacement model can be implemented rigorously within a fully probabilistic framework or used deterministically to evaluate seismic displacement potential.

The paper presents a new mechanism-based two-step approach for assessing spudcan penetration resistance in three-layer stiff-soft-stiff clay sediments. An alternative approach is also proposed, establishing a direct correlation between spudcan and cone penetration resistances. The approaches are developed based on the results from a parametric study through large-deformation finite-element analyses and validated against centrifuge test data and a case history. These can be taken as a “top-down” approach. The bearing capacities are evaluated at the seabed, at the depth of maximum bearing capacity in the first (stiff) layer, at the depth of triggering squeezing in the second (soft) layer, and at the second–third layer interface successively, followed by the estimation of the penetration resistance profile in the third (stiff) layer. For the mechanism-based approach, design formulae are also proposed for assessing the limiting cavity depth, variation of the soil plug height, and equivalent undrained shear strength of the second layer that accounts for the effect of the third layer. The depth of triggering squeezing in the second layer is estimated through an iterative approach to incorporate the effect of the soil plug trapped beneath the advancing spudcan, which leads to earlier squeezing. For the alternative approach, design correlations are established between cone tip and spudcan penetration resistances. A direct comparison between the estimated profiles using the proposed design approaches and the “bottom-up” approach recommended in the current international design standard confirms the benefit of using the former.

To determine the reliability of deep geological repositories for radioactive waste, understanding the mechanical interactions between the host rock and structures is of great importance. Among repository concepts, high-level activity waste disposal cells consist of drilled underground horizontal microtunnels with a steel casing (0.9 m diameter). The French Andra’s Underground Research Laboratory conducts ongoing research activities to characterize the casing reliability over an initial period of at least 100 years, for reversibility purposes. Several experiments are dedicated to short-term mechanical analyses of the 500-m-deep host rock formation. Due to the complex hydromechanical response of the rock to drilling, unintuitive mechanical loadings are observed in comparison with the surrounding lithostatic equilibrium stress state. In this work, these short-term mechanical loads applied on glass tubes inside a borehole are investigated. A finite-element model is developed to predict adequate load scenarios, source of the anisotropic continuum damage.

In this paper, the ultimate bearing capacity of two closely spaced rigid strip footings with rough base on granular soil is examined based on enhanced limit equilibrium, plastic limit analyses, and finite-difference solutions. The enhanced limit equilibrium and plastic limit analyses are developed on the basis of two proposed failure mechanisms in association with an optimization algorithm. The limit analysis is conducted by using the kinematic element method (KEM), and finite-difference package is used for numerical simulations. The efficiency factors of bearing capacity are calculated at various spacings between two neighboring footings for practical range of friction angles ($25°\le \varphi \le 40°$) in accordance with different solutions. Thereafter, the results obtained from the proposed solutions are compared with those reported from existing experimental, theoretical, and numerical studies. In addition, the reliability of the proposed mechanisms is justified through a series of comparisons with the failure patterns and the shear bands obtained from numerical simulations at different spacings. These comparisons indicated that despite the relative simplicity of proposed solutions, bearing capacities and failure patterns are in excellent accordance with numerical, analytical, and experimental results.

The rocking behavior of a shallow foundation of a bridge pier has emerged as an effective mechanism for reducing the seismic load on the superstructure during a strong earthquake. However, a lack of understanding regarding the rocking behavior of shallow foundations has hindered the application of the rocking foundation design philosophy to construction. In this study, the soil-rounding effect on embedded foundations was evaluated to increase understanding of the rocking mechanism. A centrifuge apparatus was used to conduct horizontal slow cyclic tests on an embedded shallow foundation model for three different slenderness ratios (i.e., structure height divided by foundation length) at a centrifugal acceleration of 20 g. The soil-rounding phenomenon was examined according to variations in the soil pressure under the foundation during cyclic loading, and the shape of the rounded soil surface was evaluated as a function of the slenderness ratio. The ultimate moment capacity of the shallow foundation was observed to increase with the side soil pressure; this was verified by comparing the side soil earth pressure with the overturning moment. The rocking mechanism of the embedded shallow foundation was evaluated by focusing on soil rounding.

The failure modes of geocell-reinforced retaining walls differ from those of rigid retaining walls, for which only limited information is available in the literature. In the present study, a series of centrifuge model tests was carried out to investigate the performances of geocell-reinforced retaining walls at limit equilibrium under various conditions. Digital image analysis was employed to determine the displacement vectors of soil and geocell-reinforced soil, which were used to obtain the failure surface and $g$-level at limit equilibrium. The effects of the geocell pocket size, geocell layer height, geocell membrane tensile stiffness, and backfill surface loading location on the stability and failure mode were investigated. In addition, the preferred layout of geocell-reinforced sections, additional reinforcement layers, and two-tiered geocell retaining walls were studied. The test results indicate that the stability of geocell-reinforced retaining walls could be improved by reducing the spans between the welded spots of geocells, increasing geocell-membrane stiffness, and connecting additional geogrid layers to geocell walls. Two-tiered geocell retaining walls performed better than single-tiered ones at the same height. It was also found that the limit equilibrium method for slope stability analysis may be employed to predict the stability and critical failure surfaces of geocell-reinforced retaining walls. Some limitations of the present study are also discussed.

Ground investigation techniques such as the pressure meter and the standard penetration test give discrete distribution of information with depth, whereas few others such as the cone penetration test provide continuous profiling. A need to have continuous data still exists for many projects in which the design depends heavily on a reliable soil profile. Since the 1970s, measuring while drilling (MWD) has been used mostly for qualitative description of the subsurface. The technique consists of observing and recording the drilling process in terms of advance rate, penetration thrust, rotation rate, torque, drilling fluid pressure, and flow to provide a fairly accurate representation of the stratigraphy while advancing a borehole in soils and in rock. A study at a specially constructed test embankment was used to evaluate the potential of drilling parameters to deliver quantitative in addition to qualitative data from instantaneous drilling logs. The embankment, consisting of eight distinct zones of different soil types and materials, allowed measurements of MWD parameters under various drilling and soil conditions. The drilling variables studied included drilling methods (rotary drilling and rotary percussive drilling), drilling procedures, and use of different drilling tools. Subsurface conditions included gravel, sand, clayey sand, silt, clay, reconstituted chalk, in addition to a buried layer of concrete and a layer of hollow polymer blocks. The measurements were analyzed as individual drilling parameters or a combination of parameters known as compound parameters. The compound parameters allowed the determination of the most efficient drilling techniques to advance boreholes in these different materials. Using histograms and frequency distributions, the results obtained at the test embankment in these different geological conditions suggest that MWD measurements have the potential to provide geotechnical engineers with reliable stratigraphic details that are necessary to build an accurate geological model of the subsurface.

This study includes the determination of soil-pile separation lengths and frequency-amplitude responses of single and group piles under rotating machine-induced coupled (horizontal and rocking) vibrations by experimental investigation. Estimation of boundary zone soil parameters responsible for the measured nonlinear responses of the soil-pile systems with an analytical approach are another aspect of the present study. To fulfill these objectives, forced vibration tests were performed in the field on a single pile and a $2\times 2$ pile group made of hollow steel piles of length 5.8 m with an outer diameter of 0.166 m to determine the frequency-amplitude responses for different eccentric moments under a static load of 15 kN. In addition to that, the soil-pile separation lengths of single and group piles are determined by measuring the contact pressure between the pile and soil. The numerical analysis of the pile foundations is performed with a continuum approach using the soil-pile separation lengths obtained from the dynamic pile tests. Comparing the analytical frequency versus amplitude responses with the experimental response curves, the best possible variation of boundary zone soil parameters is determined for different eccentric moments. From the results, it can be concluded that the continuum approach analysis is very capable of predicting the accurate nonlinear responses of the single and group piles. The variations of stiffness and damping of the soil-pile systems with frequency are also presented for both horizontal and rocking modes of vibration using the numerical analysis. The pile-soil-pile interaction phenomenon of the $2\times 2$ pile group is also investigated by calculating the group efficiency ratios (GER) of the pile group for different eccentric moments and vibration modes.

Experiments were conducted to evaluate the hydraulic conductivity of geosynthetic clay liners (GCLs) containing granular sodium bentonite that were permeated with coal combustion product (CCP) leachates. Chemical properties of the CCP leachates were selected from a nationwide survey of CCP disposal facilities. Five synthetic leachates were selected from this database to represent a range of CCP disposal facilities: typical CCP leachate (geometric mean of CCP chemistry), strongly divalent cation leachate (aka low-RMD leachate), flue gas desulfurization (FGD) residual leachate, high ionic strength ash leachate, and trona ash leachate. Typical GCLs from two U.S. manufacturers were used. Hydraulic conductivity tests were conducted on non-prehydrated and subgrade hydrated (by compacted soil for 60 days) GCL specimens at effective stresses ranging from 20 to 450 kPa. At 20 kPa, GCLs permeated directly had high hydraulic conductivity ($>{10}^{-6}\mathrm{m}/\mathrm{s}$) to trona leachate and moderate to high hydraulic conductivity (${10}^{-10}$ to ${10}^{-7}\mathrm{m}/\mathrm{s}$) to the other CCP leachates. Hydraulic conductivity was strongly related to the ionic strength of the leachate and inversely related to the swell index of the bentonite when hydrated in leachate, as demonstrated in past studies on leachates from other waste streams. Increasing the effective stress from 20 to 450 kPa caused the hydraulic conductivity to decrease up to three orders of magnitude. Hydration on a subgrade prior to permeation has only modest impact on the hydraulic conductivity to CCP leachate. Hydration by permeation with deionized (DI) water prior to permeation with trona leachate resulted in hydraulic conductivity up to three orders of magnitude lower than obtained by direct permeation, suggesting that deliberate prehydration strategies may provide chemical resistance to CCP leachates.

A new section of a freeway was constructed as part of the European route E372 in the eastern region of Poland. One portion of the project required construction of an embankment over organic clay of a thickness of up to approximately 9.5 m. Controlled modulus columns were chosen to transfer the load from the embankment to the deeper and stronger soil deposits. Excessive settlements were detected during embankment construction, and as a result one section of the embankment needed to be reconstructed before completion of the road structure. Excessive settlements continued after the road structure was completed, particularly at the locations of culverts; at one location displacement reached 20 cm within several months. The disruption of the load transfer from the embankment to the columns at culvert locations was the likely cause of this serviceability failure. Simulations of consolidation settlement of the soft soil between the columns at one location indicated that the soil carried as much as approximately 40% of the load, thus only 60% of the load was transferred to the columns. Large culverts placed above the columns interfered with arching formation, affecting the load transfer process. In addition, discontinuity in the load transfer platform may have contributed to reduced effectiveness of the column support system. Other factors are also discussed in the paper. Remedial design included replacement of some volume of the embankment with expanded polystyrene (EPS) block geofoam (lightweight fill). At one location, in addition to EPS, drilled shafts were used to transfer the load to deeper deposits. After completion of the remedial construction, the expressway was put into service. Within the following 8 months, pavement settlements of 6–14 mm were recorded, and no distress to the pavement was reported in the following 12 months ending in early 2016.

From 2005 to 2010, a large excavation (approximately $\mathrm{26,000}{\mathrm{m}}^2$ in plane) was conducted in stiff clay deposits for the Gate of the Orient building in Suzhou, China. To reduce project cost and shorten construction duration, composite earth-retaining systems were designed for this excavation, i.e., removal of the uppermost 7.85 m of soil was conducted mostly by the sloped open-cut method, leaving one side supported by soil nailing wall (SNW); subsequent excavation to a depth of 21.5 m was retained by multipropped continuous bored pile (CBP) wall; final excavation of two inner pits to 30.0–30.7 m deep was supported by a SNW along with jet-grouting of basal soils. In spite of this, lateral wall displacements in this case were comparable to those of multipropped excavations in Suzhou. Because of a high phreatic level and confined artesian water, composite dewatering plans were adopted. Because the waterproof curtain did not extend deeply into the underlying confined aquifer, for the sake of saving cost, discharging artesian water inside the pit incurred a dramatic drawdown in the artesian level outside the pit, accompanied by significant ground settlements. It turned out that the methods in the literature for predicting excavation-induced ground settlements were not applicable to this case any more. For a large excavation not following zoned-construction procedure, corner-stiffening behavior was significant. In this case, deformations near the pit middle span were up to 2.5 times those near corners. Beyond recognition, excavation in stiff clay incurred noticeable basal rebound as well, which was up to one-fourth that in soft clays. Generally, excavations in stiff clay caused smaller lateral wall displacement than excavations in soft clays; their maximum lateral wall deflections mostly occurred above the excavation surface instead of equally above and below the excavation surface in soft clays.

The Gorkha earthquake (${\mathrm{M}}_{\mathrm{w}}=7.8$) of April 25, 2015, caused widespread damage in the Kathmandu Valley. At a gently sloping site, known as Lokanthali, large ground fissures and tension cracks with vertical offsets in excess of 1 m, were observed along a ridge for a distance of about 1 km. The authors conducted a postearthquake engineering field reconnaissance of the affected areas, surveyed the topography of the site, performed subsurface explorations, conducted in situ shear strength tests, and performed dynamic simple shear as well as bender element tests, on soil samples from the site. Additionally, numerical analyses were performed to understand the seismic vulnerability of the site. The numerical geomechanical modeling showed that the site was most likely affected by seismically induced landslide movements. Results of this study provide a valuable case history of moderate seismic shaking and landslide movement, which may be used by researchers for the calibration of simplified Newmark models.

The pullout resistance of reinforcement is an important parameter in the design of reinforced earth structures. Existing design procedures consider the pullout resistance of reinforcement from axial pull. However, the kinematics of failure clearly establish that the reinforcement is pulled obliquely along the slip surface. The response of reinforcement to oblique pull is equivalent to an application of axial and transverse components of oblique pull. In this study, details are provided of a novel experimental test setup used to examine the response of smooth-metal-strip reinforcement subjected to transverse pull at one end. A large-size test chamber of dimensions (length, width, and depth) with an arrangement to conduct transverse pullout of reinforcement is developed. The pullout response of smooth-metal-strip reinforcements to transverse pull is obtained for three different normal stresses of 17, 52, and 87 kPa. Transverse pullout resistance factors of smooth-metal-strip reinforcements corresponding to different transverse displacements of the reinforcement are proposed and found to range from 0.6 to 2.9, corresponding to transverse displacements of 20–30 mm.

Helical piles are being used extensively in engineering applications in western Canada. There are insufficient studies on the axial load-transfer mechanism (ALTM) for helical piles, which require successful instrumentation of the piles. A field testing program, including two axial compression and two axial tension tests, was carried out on helical piles installed at two test sites consisting of clayey and sandy soils, respectively. The ALTM was investigated using strain gauges measurements. The development of the shaft and helix resistance as the axial displacement proceeded was established. The zone along the shaft where the shear resistance was not developed was estimated to be 2.5–5 times the helix diameter.

Consolidation-induced solute transport is an important process for a variety of engineering applications involving contaminated soil and other compressible porous media. This note presents a benchmark problem and numerical solutions for solute transport caused by one-dimensional consolidation of a saturated contaminated soil layer under large strain conditions. The solutions describe solute breakthrough and concentration profiles and can be used to check the accuracy of other analytical and numerical models. With regard to consolidation, the solutions account for vertical strain, soil self-weight, nonlinear constitutive relationships, and changing material properties during the consolidation process. With regard to solute transport, the solutions account for advection, diffusion, dispersion, and linear equilibrium sorption.