Journal of Geotechnical and Geoenvironmental Engineering

Prediction models of shear wave velocity ($V_s$) based on standard penetration test (SPT) blow counts ($N$) are widely used in design practice. Recently, a $V_s$ prediction model that uses multiple predictor variables (e.g., $N$ and effective overburden stress) was suggested by several researchers to improve prediction capability. However, the application of these models to design practice is limited because calibrating the regression parameters for a site-specific condition is difficult because of multicollinearity in the model. This study describes the problem of this recently suggested $V_s$ prediction model and proposes a calibration procedure to develop a site-specific model. The framework is based on conditional probability theory and can be applied to any site. Two application examples are presented to develop the site-specific model depending on data availabilities. The first application considers a site where only $N$ are available from several borings, and the second application considers a site where both $N$ and $V_s$ are available from several locations. The examples show that the conditional probability approach is useful to obtain the site-specific $V_s$ prediction model.

Six instrumented static-load test piles driven at four different locations along the LA-1 highway alignment in coastal Louisiana provided the opportunity to study the soil-setup behavior in relation to the soil properties. The instrumented piles consisted of six square prestressed-concrete (PSC) test piles of different sizes and different lengths. Both soil boring and piezocone penetration tests (PCPT) were conducted at each test-pile location to characterize the subsurface soil conditions. The testing program consisted of performing dynamic-load tests (DLTs) at predetermined time intervals, followed by one static-load test (SLT) at the end. These piles were instrumented with vibrating-wire sister-bar strain gauges along their length. Case pile-wave analyses were performed on the DLT data to calculate the soil-resistance distributions along test piles. Design parameters such as the adhesion factor $\alpha$ and the effective stress coefficient $\beta$ were also backcalculated. The $\alpha$ values ranged from 0.68 to 1.78, and the $\beta$ values ranged from 0.11 to 0.32. The load test results showed that the shaft resistances increased significantly with time, while the toe resistances remained almost constant with time for all test piles. The rates of setup parameter $A$ for individual soil layers were calculated using the unit shaft resistances. The resulting average $A$ values for clayey and sandy soils were 0.36 and 0.16, respectively. The setup parameters of individual soil layers were correlated with soil properties, which showed that the $A$ parameter decreases with increasing undrained shear strength ($S_u$) and increases with increasing plasticity index (PI) for clayey soil layers. A nonlinear regression model based on undrained shear strength and plasticity index was developed and proven to be applicable to other sites as well.

Prediction models of normalized modulus reduction curves ($G/G_{\text{max}}$) for clays and silts have been proposed by several researchers in the past decades. However, model uncertainties have been recognized in these studies. This study compares five prediction models of $G/G_{\text{max}}$ from previous studies, which use common predictor variables of cyclic shear strain amplitude, effective confining stress, and plasticity index. The relative differences between these models are described against these predictor variables. Then the model biases are evaluated through residual analyses using the modulus reduction database. Modulus reductions of $G$ are also discussed by combining the prediction models of $G/G_{\text{max}}$ and $G_{\text{max}}$ to illustrate the importance of these combinations. Correlations among the residuals of ln($G$) are calculated, and the correction factors of the $G/G_{\text{max}}$ model are presented conditioned on the $G_{\text{max}}$ and shear strength measurements.

Geomorphic features in the soil layers underlying a structure often have a significant effect on the underseepage behavior and the potential for initiating internal erosion. Based on the assumption that the preponderance of the underseepage risk to a levee reach is due to the geomorphic features along that reach, methodology has been developed to perform a stochastic assessment of the properties of the seepage regime with the intention of assessing the probability of internal erosion initiation. The methodology consists of a response surface-Monte Carlo analysis that takes into account the uncertainty in the subsurface geometry and soil properties in assessing the seepage regime associated with the feature. Three-dimensional finite-element seepage analyses are used to develop the response surface to take into account the inherent three-dimensional aspects of the feature. As a result of the analysis, probability distribution functions with respect to hydraulic gradient and factor of safety against heave are developed. The methodology can be adapted to any type of geomorphic feature and, as an example, a crevasse splay deposit is presented.

The impact of entraining water-soluble polyacrylate eluted from a bentonite-polyacrylate composite (BPC) in sodium bentonite (Na-bentonite) was evaluated as a means to achieve low hydraulic conductivity to aggressive ${\mathrm{CaCl}}_2$ solutions that reduce interlayer swell in conventional Na-bentonite. Up to 73% of the polymer initially contained within BPC (28.5% polymer by mass) was soluble and elutable polyacrylate. This polymer fouled pores that would typically conduct the bulk of flow in Na-bentonite permeated with aggressive ${\mathrm{CaCl}}_2$ solutions ($\ge 50\mathrm{mM}{\mathrm{CaCl}}_2$). Similar fouling was observed with kaolinite and low-plasticity clay combined with BPC, but not fine sand or nonplastic silt combined with BPC. Granular mixtures of Na-bentonite blended with BPC had hydraulic conductivity to 50 mM ${\mathrm{CaCl}}_2$ as much as 1,500 to 6,700 times lower than Na-bentonite alone. Blends of granular Na-bentonite and granular BPC with as little as 1% BPC had hydraulic conductivities lower than BPC alone when permeated with 50 mM ${\mathrm{CaCl}}_2$. However, mixtures of BPC and Na-bentonite did not exhibit low hydraulic conductivity to 500 mM ${\mathrm{CaCl}}_2$ unless the mixture contained at least 90% BPC. The findings suggest Na-bentonite-BPC mixtures have the potential to be tailored to contain specific leachate chemistries. Mixtures of BPC with other clay soils (viz kaolinite, low-plasticity clay) may also be effective in achieving very low hydraulic conductivity with aggressive solutions.

A practically oriented analytical procedure for determining the dynamic stiffness and damping (impedance coefficients) of a laterally loaded pile in soil exhibiting different types of inhomogeneity with depth, is presented. To this end, an energy method based on the Winkler model of soil reaction in conjunction with pertinent shape functions for the deflected shape of the pile are employed. A new elastodynamic model for the wave field around a pile is also introduced. The method is self-standing and free of empirical formulas or constants. Dimensionless closed-form solutions are derived for (1) the distributed (Winkler) springs and dashpots along the pile; (2) dynamic stiffness and damping coefficients at the pile head; (3) active length, beyond which the pile can be treated as infinitely long; and (4) relative contributions to the overall head stiffness and damping of the soil and the pile media. Swaying, rocking, and cross swaying-rocking impedances are considered for parabolic, exponential, and multilayered inhomogeneous soil. The predictions of the model compare favorably with established solutions, while new results are presented. An illustrative example is provided.

This paper summarizes greenfield ground movements caused by the construction of twin 7.1-m-diameter tunnels for London’s Crossrail project using earth pressure balance (EPB) tunnel boring machines (TBM). The data include surface deformations from a series of transects in Hyde Park together with subsurface data from one well-instrumented test section. Although far-field ground movements can be well-fitted using established empirical methods or simplified analytical solutions (elastic half-space), nonlinear, inelastic soil behavior is expected to affect measurements close to the tunnel. This paper considers the effects of constitutive behavior on the observed ground movements. Simple [Mohr-Coulomb (M-C)] and more-complex (MIT-S1) soil models are calibrated using results of high-quality laboratory element tests on intact London clay. The models are then used in two-dimensional (2D) numerical simulations in order to optimize three independent cavity-deformation parameters that control the spatial distribution of ground movements associated with the passage of each EPB machine. Simulations using the MIT-S1 model find maximum radial deformations at the crown of the tunnel with very small movements at the soffit, while M-C analyses show minimum deformations closer to the springline. The analyses consistently show that larger volume losses occur for the second, eastbound (EB) tunnel bore [$\mathrm{\Delta }{V}_L/V_0=0.9–1.0\%$ compared to 0.72–0.79 for prior westbound (WB)]. This result may be attributed in part to differences in EPB control parameters and/or interactions between the two tunnels that are not considered in the current analyses.

A simplified methodology is proposed for the computation of elastic response spectra at liquefiable sites, based on the widely used equivalent linear (frequency domain) site response analysis method. The actual response spectrum is obtained as the upper-bound envelope of the thus calculated response spectra corresponding to the preliquefaction and the postliquefaction segments of the seismic excitation, the former computed for the natural soil properties and the latter for the properties of the liquefied soil. The time of liquefaction onset, which separates the two seismic excitation segments, is defined in terms of the minimum factor of safety against liquefaction within the liquefiable layer. Additional guidelines are provided for the estimation of the excess pore pressure buildup and the associated soil softening during the preliquefaction segment of the seismic excitation, as well as for the definition of the liquefied soil stiffness and the hysteretic damping ratio. The proposed methodology has been calibrated against the results of rigorous elastoplastic parametric numerical analyses and its overall accuracy is further validated against seismic motion recordings from two liquefaction case studies.

The number of equivalent cycles ($n_{eq}$) concept plays an important role in geotechnical earthquake engineering and underlies the accounting for ground-motion duration in simplified liquefaction evaluation procedures, whether explicitly or implicitly. In this regard, several $n_{eq}$ correlations have been proposed over the years that were developed using a similar variant of the Palmgren–Miner (P–M) fatigue theory. The correlations presented herein were developed using an alternative implementation of the P–M theory that better accounts for the nonlinear response of the soil and for multidirectional shaking. The proposed correlations are for shallow crustal earthquakes in both active tectonic and stable continental regimes. Additionally, two forms of the correlations are presented, one being expressed as a function of peak ground acceleration ($a_{\text{max}}$). This relation shows a strong negative correlation between $a_{\text{max}}$ and $n_{eq}$, implying that motions with high amplitudes have short durations and vice versa. This negative correlation is not accounted for in most previously proposed $n_{eq}$ correlations, which could result in the erroneous weighting of the unlikely scenarios of high amplitude–longer duration and low amplitude–short duration motions in liquefaction hazard studies.

This paper proposes a constitutive model to describe the isotropic compression response of unsaturated, compacted clay under undrained conditions over a wide range of mean stresses. The total stress-based model captures the impacts of the initial degree of saturation on the apparent preconsolidation stress and the slope of the compression curve up to the point of pressurized saturation. The points of pressurized saturation for specimens with different initial degrees of saturation were predicted using a modified form of a pore-pressure analysis from the literature. The compression response for pressure-saturated specimens was dominated by the pore water, although dissolved air and soil structure may play a role for some soils. The model was calibrated using results from a series of compression tests on compacted clay specimens having initial degrees of saturation ranging from 0.6 to 1.0 and the same initial void ratio. The model was found to provide a good match to the experimental data for mean stresses up to 160 MPa, in particular due to the improvements in the analysis from the literature to evaluate the points of pressurized saturation.

Vertical-back gravity retaining walls and, in particular, quay walls have repeatedly experienced large displacements during past earthquakes, causing substantial damage to the facilities and infrastructure built on their backfill. In this analytical study, the possibility of improving the seismic performance of gravity retaining walls by changing their back-face geometry is investigated. Pseudostatic limit-equilibrium analyses are carried out to examine and compare the external and internal (structural) stability of vertical-back and broken-back walls subject to static and seismic loading conditions. The effect of wall inertia is also considered in these analyses. The results show that the horizontal thrust and the overturning moment exerted by a backfill soil are largely reduced on a broken-back retaining wall. A parametric study is subsequently carried out for comparing the static and seismic resilience and structural stability of broken-back walls with those of a vertical-back wall. The comparisons demonstrate significantly enhanced bearing capacity and external stability of a broken-back wall. It is determined that a segmental broken-back gravity wall with adequate bearing capacity and sliding stability will be also structurally stable against slippage or toppling of its concrete-block segments. These characteristics can be exploited to design resilient and less voluminous gravity retaining walls to mitigate earthquake damage.

The authors hypothesize that soil water retention (SWR) is dominated by cation hydration in soils possessing a cation exchange capacity (CEC) at high suction range. This hypothesis leads to the identification of a unitary maximum gravimetric water content $w_{mc}$, up to which all water molecules should surround the exchangeable cations. The unitary $w_{mc}$ can be obtained by using the CEC and hydration number of cations in soils. For a soil with an unknown CEC, the authors reveal that $w_{mc}$ can be found independently from either the SWR based on the hysteretic behavior of a soil’s specific moisture capacity (SMC), or from the SWR curve interpreted by a Brunauer-Emmett-Teller (BET) sorption model. The authors demonstrate experimentally that $w_{mc}$ computed independently from the previous approaches accord well with the calculated $w_{mc}$, indicating the validity of the hypothesized unitary state and applicability of the SWR-based methodology in determining the CEC of soils.

Once loose sand has liquefied, it becomes denser along with water drainage after liquefaction. Therefore, liquefied sand is regarded as more robust against liquefaction. Such sand after liquefaction is expected to liquefy again only slightly. Nevertheless, examples of repeated ground liquefaction have been reported during some earthquake events. Reliquefaction characteristics of saturated sandy ground must be estimated accurately with consideration of the liquefaction history related to past earthquakes. Moreover, the stress history affecting liquefaction strength must be considered. Cyclic triaxial tests were conducted to estimate the liquefaction strength ratio during and after liquefaction using specimens with a history of overconsolidation. The shear wave velocity, which is related strongly to the soil physical properties, was also measured in the same specimen. Results show that the stress history does not affect the specimen shear wave velocity despite increased liquefaction strength. The increased liquefaction strength induced by the stress history is eliminated by the liquefaction history.

Seismic sliding block displacements provide a useful index for the seismic performance of a slope and are computed for a suite of acceleration-time histories selected to fit a target ground motion. This paper explores the effect of different ground motion selection techniques on computed rigid sliding block displacements. In particular, capturing the characteristics of ground shaking through the consideration of the additional ground motion parameters that influence sliding displacement [i.e., peak ground velocity (PGV) and Arias intensity (Ia)] is investigated. Rigid sliding block displacements are computed for ground motion suites scaled to a target peak ground acceleration (PGA) and selected using different approaches. Two suites are selected to fit target acceleration response spectra [i.e., uniform hazard spectra (UHS) and conditional mean spectra (CMS)], and three suites are selected to fit conditional probability distributions for PGV and Ia through the generalized conditional intensity measure (GCIM) approach. The PGV and Ia distributions of the UHS suite exceed the target conditional distributions of PGV and Ia. As such, the displacements computed using the UHS suite far exceed the displacements computed for any other suite of motions considered in this study. The PGV and Ia distributions, and the displacements, for the CMS suite align well with those for the suite selected to fit the GCIM target distributions for both PGV and Ia. It is recommended that motions for sliding block analysis be selected to fit the GCIM PGV and Ia distributions conditional on PGA, although motions selected to fit the CMS can generate similar displacement results.

The recompression index ($C_r$) of fine-grained soils is conventionally determined from consolidation tests on undisturbed samples, but it has been suggested to estimate $C_r$ using empirical models (i.e., correlation equations). So far, however, only a few attempts have been made to establish correlation equations for recompression indexes. In this paper, two independent databases of experimental data on more than 100 different soils are statistically analyzed to (1) examine which index properties correlate best with $C_r$; (2) establish correlation equations between $C_r$ and index properties; and (3) evaluate the validity and reliability of the proposed equations and existing empirical models. The results of this study suggest that (1) there are significant linear correlations between the recompression index and index properties, and (2) the proposed correlation equations provide quite good estimates of recompression indexes for fine-grained soils with wide ranges of stress histories and sensitivities.

Recycled asphalt pavement (RAP) can be beneficially used as alternative construction material in geotechnical applications, but characterizing its creep response is important to account for potential viscous effects attributable to the material’s asphalt content. Effects of elevated temperature (35 and 50°C) on creep behavior of compacted RAP specimens were investigated through temperature-controlled triaxial compression tests at sustained deviator stresses. RAP compacted at room temperature (22°C) and subjected to deviator stress at elevated temperature showed creep strain and strain rate that systematically increased with increasing temperature. Time to creep rupture decreased with increasing temperature. Compaction at elevated temperature resulted in denser specimens and reduced creep strain and strain rate. Temperature effects were incorporated into a creep model that may be used to estimate strain rate of RAP at elevated temperatures. Construction of structural fills containing RAP is recommended during warm months of the year to minimize subsequent creep strain and potential for creep rupture.

This paper compares several intact rock strength criteria against an extensive database comprising 128 data sets with over 7,000 laboratory test results. It includes over 1,000 new test data from several recent tunneling projects in Australia. The database includes sedimentary, igneous, and metamorphic rocks with unconfined compressive strength (UCS) values ranging from less than 10 to over 300 MPa. The criteria assessed are Modified Weibols-Cook, Lade, Hoek-Brown and two of its modifications, and Christensen. Several interpretations and conclusions are drawn. Any of the criteria can provide good fits to test data that do not show much scatter. However, curve-fitting becomes problematic when there is variability in the test data. The variation in test data swamps the differences between criteria. On balance, the Hoek-Brown criterion, with its parameters $m_i$ and $a$ derived as recommended and extended to three dimensions in the literature where required, produces a better fit to the majority of rock types considered.

The process of remolding and subsequent recovery of soil shear strength is a common geotechnical problem, especially in the offshore environment, where foundations and pipelines are subjected to intermittent operational and environmental loads. A novel vertically oriented penetrometer (VOP) was used in a centrifuge testing program to study the changing strength of normally consolidated kaolin from successive disturbance and reconsolidation events. The VOP is used to determine soil shear strength via an interpretation akin to the laterally loaded pile. The test series involved cyclic movement of the VOP at velocities ranging from 0.3 to $30\mathrm{mm}/\mathrm{s}$, with a corresponding 100-fold variation in the duration of each cycle. For the VOP tests at low velocities with high cyclic periods, the soil resistance initially reduces, but then shows an increase that scales with the elapsed time, indicating reconsolidation. Ultimately, if the cycling continues for sufficient time, the recovery in strength from reconsolidation can exceed the weakening from remolding. A previously published framework using critical-state soil mechanics concepts is shown to capture the changing resistance well.