Journal of Geotechnical and Geoenvironmental Engineering

Two series of diffusion tests were performed to examine the degradation of dichloromethane (DCM) as it diffuses through clay. The first series showed the use of a synthetic leachate with no significant initial bacterial population diffusing through a plug of intact clay; there was an induction period of 95–135 d, during which diffusion was as expected in the absence of degradation, followed by a second stage, where degradation occurred with an apparent half-life of less than 55 d at a temperature of 24°C. The second series of tests examined the diffusion of an actual leachate from the Keele Valley Landfill (KVL) (which provided both nutrients and a source of bacteria), through a compacted clay. In these tests, the induction period was reduced to 40–60 d, after which the apparent half-life was 20 d or less at 27°C. The diffusion coefficient for DCM was approximately 8 × 10⁻¹⁰ m²/s, with partitioning coefficient K_d= 1.5 cm³/g. Biological activity was confirmed by evaluating the change in the concentration of adenosine-5-triphosphate and the biological activity reaction test (BART). The degradation of DCM did not produce any detectable levels of chloromethane.

This paper presents the results of an experimental investigation on the cyclic behavior of a sand-steel interface under constant normal stress and normal stiffness conditions. The experiments were performed by using an automated interface testing apparatus called C3DSSI. A simple shear-type soil container was used to measure simultaneously the shear deformation of the sand mass and the sliding displacement at the interface. Two-way cyclic tangential-displacement-controlled experiments were performed under a constant normal stiffness condition to study the phenomenon of reduction in the maximum shear stress with cycles. This phenomenon is known to be the cause of degradation of shaft resistance in piles subjected to cyclic loading in the axial direction. Effects of the tangential-displacement amplitude and the magnitude of the normal stiffness on the cyclic response were investigated. It was concluded that the reduction in maximum shear stress was not only due to the reduction in the normal stress, but also to a greater extent due to the increased amount of mobilized sliding displacement at the interface with an increasing number of cycles. The reduction in maximum shear stress with cycles was dramatic when failure was experienced at the interface, i.e., when the shear stress-normal stress ratio (τ/σ_n) reached a peak value and subsequently approached a residual value.

Practical applications of unsaturated soil mechanics still lag behind the state-of-the-art knowledge. The main stumbling block is the time-consuming processes involved in the measurement of the unsaturated soil parameters required for the constitutive models. Recent research has shown that the soil-water characteristic curves of a soil can be used in the establishment of a number of the unsaturated soil parameters. In many applications it has become obvious that a satisfactory equation for describing the soil-water characteristic curve will simplify the determination of the soil parameters. Over the years a number of equations have been suggested. Most of these equations have limited success depending on soil types. This paper evaluates the more popular equations that have been suggested and shows that all the equations can be derived from a single generic form. One equation has been identified that performs very well for all soil types. If this equation is in common usage, useful databases on unsaturated soil parameters can be more easily established for practical applications of unsaturated soil mechanics.

This paper examines the three categories of permeability functions for unsaturated soils, including empirical, macroscopic, and statistical models. The theoretical backgrounds and performance of each category are examined against various experimental data. The paper also shows that it is possible to degenerate statistical models to macroscopic models and then to empirical models. A new empirical equation for the permeability function is suggested. The statistical model demonstrates good performance and can be readily applied. In some cases the performance of the statistical model can be further improved with the introduction of a correction factor.

Bitumen has been shown to reduce significantly the downdrag load on piles. The problem is to know how to choose the right bitumen for the job. The right bitumen must not deform excessively under gravity stresses during the storage period, must not deform excessively under dynamic stresses due to pile driving, must offer little shearing resistance and therefore downdrag during the soil settlement process, and must not let the soil particles penetrate excessively into the coating. Rational design approaches are developed for each of the four criteria on the basis of the fundamental behavior of bitumen, full-scale downdrag tests on 15 piles at a Northern and Southern site, and a series of laboratory tests. Guidelines are presented for the bitumen selection process and tips are given for the field application of the bitumen coating.

A series of column and tank tests were conducted using bromide to estimate seepage velocity through compacted clays. Bromide concentrations in effluent and sectioned-core pore water were measured. The seepage velocity estimated from the concentration-depth profile data obtained from sectioned-core pore water samples was approximately 50% greater than that estimated from the breakthrough curve data. The discrepancy is thought to be caused by the soil sample compression during coring and sectioning. The effective porosities estimated from the column/tank breakthrough curves ranged from 89 to 104% of the total porosities determined from the weight-volume phase relationship. The hydrodynamic dispersion coefficient had a linear relationship with the seepage velocity. When the mass transport parameters of contaminants through a soil liner are to be estimated using column tests, it is recommended that tracer tests be conducted for the correct estimation of the seepage velocity.

This paper presents a mathematical solution for fine particle accumulation in soil filters. The solution accounts for particle transport in the base soil and uses a lumped parameter to account for the effects of physicochemical forces influencing particle deposition. It considers particle release without subsequent entrapment in the base soil and particle deposition without subsequent release in the filter, and thus represents an upper-bound solution. The particle capture probability approach is adopted to determine the deposition in the filter. The model is demonstrated using a soil filter typically used in practice to protect fine-grained soils, and the potential for fine particle accumulation in the filter is assessed. The results show that fine particle accumulation in the filter material is significantly influenced by a deposition coefficient which is a function not only of the physical characteristics of the material, such as its particle size and pore size distributions, but also of the pore fluid composition and the size of the migrating particles in the pore stream. Because of its closed-form nature, the solution can be easily adopted in practice to assess the potential of fine particle accumulation in soil filters. A stepwise procedure is suggested to use the solution.

An isolated single pile and a large-scale test group of 16 prestressed concrete piles spaced at 3 diameters were subjected to a static lateral loading using a fixed-headed production group for reaction. The foundation consisted of sand overlying a partially cemented sand at the Roosevelt Bridge replacement, Stuart, Fla. Ten piles of the test group, six piles of the reaction group, and a single pile were instrumented with strain gauges and inclinometers. The piles were 76 cm², and approximately 16.5 m long. Standard penetration tests (SPT), cone penetration tests (CPT), DMT, and PMT in-situ tests were used to establish the soil profile and p-y curves. Subsequent to testing, the strain gauges and inclinometer data were reduced to “measured”p-y curves. The p-y curves developed from SPT correlations and PMT results provided an accurate soil representation. The single pile was subjected to 320 kN, while the pile groups were loaded to about 4,800 kN. The testing results show that the nonlinear characteristics of cracked prestressed concrete piles dominate analyses and data reduction. Consequently, the FLPIER program, with its nonlinear concrete capabilities, could predict properly the “postcracking” response. The group interaction was accurately modeled by p-y (actually p, only) multipliers, which were determined as 0.8, 0.7, 0.3, and 0.3 for the leading, middle leading, middle trailing, and trailing rows, respectively, with the overall group p-y multiplier being 0.55.

An Arias intensity approach to assess the liquefaction potential of soil deposits during earthquakes is proposed, using an energy-based measure of the severity of earthquake-shaking recorded on seismograms of the two horizontal components of ground motion. Values representing the severity of strong motion at depth in the soil column are associated with the liquefaction resistance of that layer, as measured by in situ penetration testing (SPT, CPT). This association results in a magnitude-independent boundary that envelopes initial liquefaction of soil in Arias intensity-normalized penetration resistance space. The Arias intensity approach is simple to apply and has proven to be highly reliable in assessing liquefaction potential. The advantages of using Arias intensity as a measure of earthquake-shaking severity in liquefaction assessment are: Arias intensity is derived from integration of the entire seismogram wave form, incorporating both the amplitude and duration elements of ground motion; all frequencies of recorded motion are considered; and Arias intensity is an appropriate measure to use when evaluating field penetration test methodologies that are inherently energy-based. Predictor equations describing the attenuation of Arias intensity as a function of earthquake magnitude and source distance are presented for rock, deep-stiff alluvium, and soft soil sites.