Journal of Geotechnical and Geoenvironmental Engineering

The demands on pile installation have increased dramatically in recent years in response to the threats from strong earthquakes, ice, and ship collision. Piles are being used for heavier loads and deeper penetrations in new environments and more remote areas. As a result, initial efforts at installation have frequently been unsuccessful. Geotechnical explorations have often been incomplete due to limited access and lack of initial funding. Contractors’ equipment has had to be changed and installation procedures modified. Case histories are presented, with descriptions of the difficulties encountered and their solutions. General guidance is provided as to preparedness with alternative equipment and procedures so as to minimize the time and cost of changes.

Seismic compression is defined as the accrual of contractive volumetric strain in unsaturated soil during strong shaking by earthquakes. We document and analyze two case histories (denoted school site and site A) of ground deformation from seismic compression in canyon fills strongly shaken by the Northridge earthquake. Site A had ground settlements up to about 18 cm, which damaged a structure, while the school site had settlements up to about 6 cm. For each site, we perform decoupled analyses of shear and volumetric strain. Shear strain is calculated using one-dimensional and two-dimensional ground response analyses, while volumetric strain is evaluated from shear strain using material-specific models derived from simple shear laboratory testing that incorporates important effects of fines content and as-compacted density and saturation. Analyses are repeated using a logic tree approach in which weights are assigned to multiple possible realizations of uncertain model parameters. At the school site, predicted settlements appear to be unbiased. At site A, the analyses successfully predict the shape of the settlement profile along a section, but the weighted average predictions are biased slightly too low. We speculate that the apparent site A bias can be explained by limited resolution of the site stratigraphy, bias in laboratory-derived volumetric strain models, and/or uncertainty in the estimated earthquake-induced settlements.

Measured solute flux breakthrough curves (FBCs) from column tests performed on a semipermeable clay membrane subjected to KCl solutions are compared with predicted FBCs using independently measured flow and transport properties. The predicted FBCs are based on three scenarios: (1) Advective–dispersive transport that neglects membrane behavior; (2) advective–dispersive transport that accounts for the concentration dependency of the effective salt-diffusion coefficient $\left(D_s^{*}\right)$ resulting from membrane behavior, referred to as partially coupled transport; and (3) fully coupled transport that includes both the explicit coupling terms (e.g., hyperfiltration, chemico-osmosis) associated with clay membrane behavior and the concentration dependency of $D_s^{*}\text{.}$ The FBCs predicted by fully coupled transport agree best with the measured FBCs. However, for the diffusion-controlled conditions of the column tests, the steady-state solute fluxes predicted by partially coupled transport are only 23–69% higher than the measured steady-state fluxes. The results imply that the advective–dispersive transport theory can be used to provide reasonably accurate, albeit somewhat conservative, estimates of steady-state solute flux through clays that behave as semipermeable membranes, provided diffusion is a significant, if not dominant, solute transport process and the concentration dependency of $D_s^{*}$ are taken into account.

To properly design a drainage layer for either landfill leachate collection systems or final covers, the designer must be able to estimate the maximum liquid head over the barrier for any proposed configuration. This paper presents four explicit formulas for estimating the maximum liquid head over an impervious sloping barrier. By means of numeric comparisons, McEnroe’s 1993 method is recommended for design of drainage layers for both bottom liners and final covers. Pipe slope is an important parameter that influences the maximum leachate head on the liner. Different combinations of base grade and pipe slope can directly affect the actual drainage behavior. If the pipe slope is steeper than the base grade, it will make a longer drainage distance and cause a high leachate head on the liner. A method for calculating the maximum liquid head in multilayered drainage media (e.g., geosynthetic and soil) is presented in the paper. The key consideration for this case is to determine the equivalent hydraulic conductivity of the combined drainage media under the phreatic surface under unconfined seepage conditions.

A substantial amount of experimental evidence suggests that Mohr envelopes of many soils are not linear, particularly in the range of small normal stresses. This departure from linearity is significant for slope stability calculations since for a wide range of practical stability problems, critical slip surfaces are shallow and normal stresses acting on such surfaces are small. The present work presents a procedure for estimating parameters of the Mohr form of Hoek and Brown empirical failure criterion, based on triaxial data. This nonlinear Mohr envelope provides significantly better representation of experimental information than the Mohr–Coulomb criterion in cases when the data set includes tests at small enough normal stress. Application of the estimation procedure to published data sets shows that effective cohesive strength of most soils is close to zero, and Mohr envelopes are continuous at the tensile strength limit.

In this paper we investigate the probability of failure of a cohesive slope using both simple and more advanced probabilistic analysis tools. The influence of local averaging on the probability of failure of a test problem is thoroughly investigated. In the simple approach, classical slope stability analysis techniques are used, and the shear strength is treated as a single random variable. The advanced method, called the random finite-element method (RFEM), uses elastoplasticity combined with random field theory. The RFEM method is shown to offer many advantages over traditional probabilistic slope stability techniques, because it enables slope failure to develop naturally by “seeking out” the most critical mechanism. Of particular importance in this work is the conclusion that simplified probabilistic analysis, in which spatial variability is ignored by assuming perfect correlation, can lead to unconservative estimates of the probability of failure. This contradicts the findings of other investigators who used classical slope stability analysis tools.

In this paper, a staged compression–immersion–direct shear test was conducted on the compacted samples of crushed mudstone aggregates, and its compressive and shear behavior are discussed with attention to cementation effects. Compression behavior of the compacted samples was influenced significantly by the compaction degree as expected. So were the shear behavior and shear strength. Immersion caused an additional compression and a reduction in mobilized shear stress and in the dilatant nature during shear at low applied pressure levels. Moreover, immersion reduced significantly the peak shear strength parameter c with only a little change in ϕ. The compression lines and critical state lines of the nonimmersed and immersed specimens seem to parallel each other, and the compression line of the nonimmersed and the critical state line of the immersed form the upper and lower bounds, respectively. A gap between the shear stress–void ratio lines of the specimens with and without immersion can be considered to represent a combined effect of cementation retained in a crushed mudstone aggregate itself and an interlocking effect of aggregates.

Empirical correlations with in situ or laboratory test results are routinely used in geotechnical designs and the uncertainty of prediction from these correlations can be substantial at times. This paper formalizes a procedure for characterizing and analyzing uncertainty in a design in which linear correlations have been used. In particular, how this design uncertainty can be reduced from gathering regional data and site-specific observations is addressed. The Bayesian approach is then applied to update empirical predictions with regional information or site-specific observations and hence to effectively reduce the uncertainty associated with the correlation. Three levels of uncertainty reduction associated with the use of an empirical correlation for design are discussed based on the availability of regional data and site-specific observations. Analyses of correlations for the shaft resistance of rock-socketed piles based on a global data set and a regional data set and for the shaft resistance of large-diameter bored piles in saporilitic soils based on site-specific observations are demonstrated as examples to implement the proposed procedure. In both examples, the uncertainty with the predictions updated by the proposed approach is significantly smaller than those directly associated with empirical correlations.

Centrifuge modeling appears useful for studying geo-environmental problems such as pollutant migration in subsurface systems. In this study, centrifuge tests were conducted to simulate a gasoline spill from a leaking underground storage tank (UST) and the subsequent subsurface migration of the gasoline. When the centrifugal acceleration reached the desired g level, the gasoline was released from the UST and then it migrated in the unsaturated soil for a prototype time equivalent to 1 year. After the centrifuge tests, soil samples were collected using sampling tubes and the concentrations of individual constituents in the light nonaqueous phase liquids (LNAPLs) were directly measured by means of gas chromatograph analysis. Two types of unsaturated soils were used to study the migration patterns of LNAPLs in unsaturated porous media. Centrifuge test data show that the migration pattern of LNAPLs is related to the soil type and the physical properties of individual constituents in the LNAPLs.

The standard penetration test (SPT) supplemented with the measurement of torque (SPT-T) may be used to obtain a direct measurement of unit skin friction $\left(f_s\right)$ between the sampler and the surrounding soil. The test is performed after the standard SPT procedure and does not compromise conventional SPT results. In order to perform the SPT-T, the split-barrel sampler is rotated after driving the ASTM specified distance and the maximum torque is measured using a calibrated torque wrench or transducer mounted to the top of the drill string. The measured torque is used along with the known geometry of the split-barrel sampler to determine a value of unit skin friction. SPT-T test results at 12 sites are presented. The results also show that the unit skin friction values obtained from the SPT-T generally correlate well with SPT $N_{60}$ values. The results may be valuable for making preliminary estimates of unit skin friction for driven piles and provide some rationale for reported correlations between $N_{60}$ and skin friction from piles.