Journal of Geotechnical and Geoenvironmental Engineering

In this study, results of plate load tests performed on saturated and unsaturated silty sand samples are presented. Very little is known about how to interpret the plate load test when performed on unsaturated soils comprising silt–sand mixtures because the few published studies have been limited to either unsaturated clean sands or clays. The new plate load test results are interpreted using a bearing capacity equation, applicable when nonuniform $\chi s$ profiles prevail in the soil, where $\chi s$ is the contribution of suction to the effective stress. The interrelation between $\chi s$, strength, and bearing capacity is shown. There is good agreement between measured and computed bearing capacities. Assuming $\chi s$ remains constant during a plate load test, compared to assumptions of constant suction or constant moisture content, simplifies interpretation without significant loss of accuracy. For a particular soil density, the bearing capacity for an unsaturated condition is found to be much larger than that for a fully saturated condition. It is also shown that the effect of suction on the bearing capacity is dependent on the initial location of the hydraulic state on the soil–water characteristic curve. Failing to account for suction and the hydraulic loading history may lead to incorrect interpretations. It is also demonstrated how plate load tests may be used to infer the value of $\chi s$ at the soil surface.

In the French conventional railway substructure, the interpenetration of ballast grains and subgrade fine soils that occurred over years of operation has created a new layer, namely, an interlayer. The in situ investigation on this interlayer showed that the content of ballast grains decreases over depth, with the lower part characterized by a matrix of fines with inclusions of coarse grains. In this study, the permanent deformation of a material simulating the lower part of interlayer soil was investigated at six different volumetric inclusion contents $f_v$ (volumetric ratio of the inclusion grains to the total sample) by performing cyclic triaxial tests. The results indicate that at a given cycle, the permanent deformation decreases with the increase of $f_v$, and the evolution of permanent deformation is strongly influenced by the loading history. To further investigate the effect of inclusion content, a method that allows eliminating the influence of loading history and estimating the end-stage permanent deformations at different stress levels was applied. Quadratic polynomial and bilinear fitting methods were used to fit the variations of the estimated end-stage permanent deformations with $f_v$, showing a proper similarity between the two methods at high loading amplitudes (higher than 15 kPa). Furthermore, the testing results revealed the existence of a characteristic volumetric inclusion content $f_{v\text{-}\mathrm{cha}}$ by bilinear fitting method, separating two zones with different inclusion effects. This observation is strongly supported by the X-ray microcomputed tomography (μCT) scans performed on the as-compacted samples. When $f_v$ ranges from 0 to 20% (smaller than $f_{v\text{-}\mathrm{cha}}$), the fines constitute the skeleton of the sample, and the permanent deformation decreases rapidly with the increase of $f_v$. By contrast, when $f_v$ increases up to 35–45% (larger than $f_{v\text{-}\mathrm{cha}}$), the inclusions dominate the skeleton of the sample, leading to a slight decrease of permanent deformation with $f_v$.

Sands containing pumice particles are widely distributed over the Waikato Basin, North Island in New Zealand. These pumiceous sands, due to the vesicular nature and presence of internal voids in the particles, are highly crushable, compressible, and lightweight; factors which make them problematic from an engineering point of view. In this paper, in order to investigate the effect of particle shape and crushing on the undrained cyclic behavior of natural pumiceous sands, we report the results of undrained cyclic triaxial tests performed on natural pumiceous sand and Toyoura sand with different relative densities. The test results illustrate that natural pumiceous sands show significantly different cyclic behavior when compared with Toyoura sand. For instance, during the cyclic triaxial test, pumiceous sands start to deform from the start of the cyclic loading, and the axial strain gradually increases until 5% double amplitude axial strain is reached. In contrast, Toyoura sand undergoes a significant number of cycles with negligible deformation, followed by a sudden increase in deformation in a few cycles, to reach 5% double amplitude axial strain. In addition, pumiceous sands initially show a very contractive behavior under the application of cyclic loading, but after a few more cycles, this changes to a very strong dilative behavior. Due to the formation of a stable soil skeleton inside the pumiceous specimens, instability is not observed and the liquefaction resistance of pumiceous sands is considerably higher than that of Toyoura sand under the same relative density.

The soil shrinkage curve (SSC) defines a constitutive relationship between soil volume and water content under drying conditions. Nearly all work to date considers a zero volume shrinkage for water content below a certain value such as shrinkage limit, which contradicts some recent experimental evidence of pervasive nonzero shrinkage for clayey soils. This paper uses a soil-water retention (SWR)-based conception to theorize such nonzero shrinkage behavior by considering the mechanical effect of capillary and adsorptive SWR mechanisms. A mathematical equation for SSC in the full water content range is developed, which conceptualizes a linear relation for adsorption shrinkage and a sigmoid relation for capillary shrinkage. The equation is validated with test data for a variety of soils. For given soils, the maximum adsorption water contents inferred independently from the SWR and SSC data are highly correlated, with a factor of 2.47. The analysis shows that the adsorption shrinkage rate is strongly correlated with the SWR characteristics of specific surface area (SSA) and cation exchange capacity (CEC). A universal exponential form between the adsorption shrinkage rate and SSA and between the adsorption shrinkage rate and CEC is discovered for silty and clayey soils.

A geologic profile often is composed of multiple material zones due to complex geologic processes. Uncertainties associated with the geologic profile can be categorized into two groups: (1) intralayer variability, which refers to the variation of material properties within the same layer; and (2) interlayer variability, which refers to the uncertainties associated with the interlayer boundaries. The inter- and intralayer spatial variabilities have significant impact on the design and construction of geotechnical structures. This paper proposes an integrated random field model to characterize the inter- and intralayer spatial variabilities of multilayer geologic profiles simultaneously. A transition zone is used to describe the gradual transition of material properties at the interlayer boundary. The proposed model is applied to characterize the spatially variable cone tip resistance at a study site and to evaluate the effects of the integrated spatial variability of undrained shear strength on the reliability of a two-layer soil slope. Both the inter- and intralayer spatial variabilities influence the reliability of the slope. The intralayer variability is relatively more significant for the slope example in this study.

In the present-day context, man-made sources of ground-borne vibration are rising at a very rapid rate due to increasing construction work, blasting activities, and rapidly expanding rail and road traffic systems. As a consequence, amplified levels of ground-borne vibration occur, causing annoyance to residents living in nearby areas, posing a threat to the stability of old structures, and interfering with instrumentation works in industries. This paper discusses an investigation into the use of trenches as a means of mitigating ground vibration caused by propagation of surface (Rayleigh) waves. Two- and three-dimensional (2D and 3D) finite-element models were developed using PLAXIS for identifying key factors affecting the vibration isolation efficiency of open and infill trenches. Parametric studies were carried out, and the results were analyzed to arrive at optimum values of geometrical and material properties of trenches. Numerical analysis showed that, for open trenches, normalized depth is the decisive factor and width is of importance in trenches that are very shallow. For infill trenches, it was observed that low-density materials perform exceedingly well as infill materials but their performance is highly sensitive to the relative shear-wave velocity between the infill material and the in situ soil. Finally, an in-depth analysis was carried out to investigate the performance of polyurethane foam trenches in mitigating vibrations caused by harmonic loads. The analysis was extended to study the effectiveness of these geofoam barriers in damping out the vibrations generated by a moving train. In this case, barrier efficiency was shown to increase with increasing train speed. The key findings suggest that trenches are a simple and effective solution for reducing ground-borne vibrations.

Microbially induced carbonate precipitation (MICP) through denitrification can potentially be applied as a bio-based ground improvement technique. Two strategies involving multiple batch treatments in a modified triaxial test setup were used to study the process efficiency. Both strategies aim to achieve 1 weight percentage (% by weight) of precipitated calcium carbonate (${\mathrm{CaCO}}_3$) and differ in number of flushes, hydraulic residence time, and substrate concentrations. In the experiment with few flushes and high substrate concentrations the microbial process was inhibited, only 0.28% by weight ${\mathrm{CaCO}}_3$ was measured in the sand after 5 weeks of treatment. The regime with many flushes and low substrate concentrations stimulated microbial growth resulting in 0.65% by weight ${\mathrm{CaCO}}_3$ within the same time period. Biomass growth and nitrogen gas production were stable throughout the experiment at low concentration, reducing the hydraulic conductivity of the sand, which eventually led to clogging. Precipitation rates up to 0.26% by weight/day ${\mathrm{CaCO}}_3$ were observed. Applying a suitable substrate regime and residence time is important to limit inhibition and maintain the cell activity, allow for an efficient conversion, and generate a good precipitation rate.

Geotechnical design codes have been migrating toward reliability-based design (RBD) concepts. ISO 2394 identified the characterization of model uncertainty as one of the critical elements in the geotechnical RBD process. This paper collects a large number of field axial load tests on helical piles for model uncertainty assessment as required in developing RBD. At the ultimate limit state (ULS), the model uncertainty is represented by a model factor, which is defined as a ratio of measured resistance over calculated resistance. The measured resistance is interpreted from load test data using the methods recommended in the helical pile industry, while the existing empirical or semiempirical methods are applied for resistance calculations. A hyperbolic model with two parameters is adopted to fit the measured load-settlement data. The uncertainties within the load-settlement curves are captured by a bivariate random vector containing the hyperbolic parameters as its components. Statistical properties of the model factors such as means, coefficients of variation, and probability distributions are determined from the database. Moreover, several copulas are evaluated to establish the correlation structure within the hyperbolic parameters. Finally, the ULS model statistics are incorporated into the calibration of the resistance factor in the load and resistance factor design (LRFD) of axially loaded helical piles.

Offshore foundation systems are constantly evolving to meet the needs of developments in the energy sector. These developments may be induced by the requirements of moving into ever deeper water for hydrocarbon recovery or creating foundation systems for renewable energy sources such as offshore wind farms. One such approach is that foundation systems are developed that combine several foundation elements to create a hybrid system. In this way it may be possible to develop a foundation system that is more efficient for the combination of vertical and lateral loads associated with the offshore environment, and in particular wind-powered generators. This paper presents the results from a physical and numerical modeling program undertaken to investigate the performance of hybrid, monopiled footing foundations under combined monotonic loading conditions in sand.

One-way cyclic loading induced by traffic loads will give rise to the cyclic variation of normal stress components of all three directions, including one vertical and two horizontal ones. The cyclic horizontal normal stress perpendicular to the driving direction is considered to be negligible compared to the other one parallel to the driving direction. Recognizing this, the coupling of cyclic vertical normal stress and cyclic horizontal normal stress parallel to the driving direction is simulated by the combination of cyclic major and intermediate principal stresses based on an advanced true triaxial apparatus. A parameter of coefficient of cyclic intermediate principal stress, $b_{cyc}$, is introduced to characterize the coupling effects. A series of one-way cyclic true triaxial tests was performed on a remolded saturated clay, and the emphases were placed on the permanent major and intermediate principal strains. Test results show that the cyclic intermediate principal stress has great influence on the deformation characteristics, and the influences on the permanent major and intermediate principal strains are very different. The permanent major principal strains were found to decrease linearly with the increase of $b_{cyc}$, and a critical value of $b_{cyc}\approx 0.48$ appeared to exist, at which the permanent intermediate principal strains changed the direction from tension to compression.

Deep foundations may need to resist torsional loads, resulting from wind loading on traffic sign and signal pole structures, or seismic loading on curved or skewed bridges. Although design methods for deep foundations at the ultimate limit states are readily available, no significant effort exists to quantify the accuracy of existing load transfer–based torsion-rotation methods to predict the full-scale, in-service rotation performance that considers state-dependence of the soil. To facilitate the serviceability and ultimate limit state design of geometrically variable deep foundations constructed in multilayered soils, this paper presents a torsional load transfer method using a finite-difference model (FDM) framework. Simplified state-dependent load transfer models that relate the unit torsional resistance to the magnitude of relative displacement are developed considering soil-structure interface shear test results. The proposed FDM methodology is validated by comparison with existing analytical solutions and with physical model tests. Parametric studies are conducted to illustrate the role of various design parameters and demonstrate significant effects of nonlinear soil-structure response on the torsional behavior of deep foundations, including the effects of pressure-dependent softening at the soil-structure interface.

A finite element analysis of a hypothetical excavation was conducted to investigate recent stress-history effects on excavation-induced ground movements. The numerical simulations were conducted using a hypoplasticity model for clays which is capable of modeling small strain nonlinearity, soil anisotropy, and recent stress-history effects. The recent stress-history effects noted in previous laboratory experiments were reasonably reproduced by the model. Numerical simulations of the hypothetical excavation made through glacial clays are presented to illustrate the effect of preexcavation recent stress-history on computed ground movements. Lateral wall deformations caused by excavations in these soils with different recent stress histories resulted in computed movements that differed by a factor of two. These results suggest that recent stress-history effects should be considered when serviceability requirements dictate the design of a support system for which deformations must be limited to prevent damage to adjacent structures or infrastructure.

In this study, two predictive models for seismic slope displacements are developed based on an equivalent-linear fully coupled sliding mass model and 3,714 ground-motion recordings selected from the Next Generation Attenuation (NGA)-West2 database. Both predictive models use the sliding system’s yield acceleration and initial fundamental period $T_s$ as predictor variables, whereas they use different sets of vector intensity measures (i.e., spectral acceleration at a degraded period of the system $1.5T_s$ and Arias intensity in one model; peak ground acceleration and spectral acceleration at 2 s in another). The models are developed following the framework of model BT07, a predictive model for estimating the sliding displacement based on the fully coupled sliding mass analysis. The framework consists of two parts, namely, the probability of “zero” displacement ($<1\mathrm{cm}$) and the statistical distribution of “nonzero” displacement ($\ge 1\mathrm{cm}$). The proposed models in this study can be regarded as updates of the BT07 model, which can be used for estimating earthquake-induced displacements for a wide range of slope cases.

Dynamic analysis of single and group piles under vertical vibration is carried out in this paper using the cone model to investigate the effect of different parameters on the response of single and group piles. Using a parametric study, the effect of material damping, Poisson’s ratio, and slenderness ratio of single piles on dynamic stiffness coefficients and frequency–amplitude response are considered. Effect of damping ratio on dynamic response of a $2\times 2$ pile group is also investigated. Field test results from the literature are used to verify of effectiveness of the cone model for the dynamic analysis of group piles. The reported tests were conducted on a large pile group consisting of 102 piles embedded in a homogeneous soil deposit. Comparisons of results obtained from the analysis with experimental results showed reasonably good agreement.