Journal of Geotechnical and Geoenvironmental Engineering

A full-scale field study was conducted using well injection depth extraction (WIDE) technology to remove trichloroethylene (TCE) from subsurface profiles with fine-grained soils. WIDE incorporates the use of geosynthetic wick drains, attached to an aboveground PVC pipe network, designed to (1) extract contaminated fluids from a specific depth using vacuum pressure, and/or (2) inject flushing solutions. Both extraction-only and concurrent injection-extraction testing schemes were conducted, and fluid flow rates, TCE recovery rates, and groundwater elevations were monitored over a $9\text{month}$ time interval. During extraction-only operational schemes, gas-phase TCE extraction rates were significantly higher than liquid-phase extraction rates due to the increased volume of air within the geosynthetic wells and PVC piping. TCE extraction rates were less than $\mathrm{2,000}\mathrm{mg}∕\mathrm{h}$ for airflow rates less than $\mathrm{100,000}\mathrm{L}∕\mathrm{h}$ , and increased significantly to $\mathrm{5,700}\mathrm{mg}∕\mathrm{h}$ as the airflow rate approached $\mathrm{600,000}\mathrm{L}∕\mathrm{h}$ . Long term testing and sampling is needed to quantify system performance and determine tailing and rebounding effects in comparison to conventional methods. The behaviors and trends observed during the field study are presented and discussed.

Tests for determining the water retention curve (WRC) can be time-consuming and tedious, especially with deformable soils for which volume change and water content have to be simultaneously monitored. In some cases, predictive models can become a practical alternative to obtain an estimate of the WRC. However, very few models are available to predict the WRC of deformable materials under increasing suction. In this paper, the modified Kovács (MK) model, developed initially for incompressible soils, is extended to describe and, in some cases, predict the WRC of deformable clayey soils. This generalization of the MK model is performed by introducing the volumetric shrinkage curve (VSC) in its formulation. A curvilinear equation is proposed to represent the void ratio-suction function $e\left(\psi \right)$ corresponding to the VSC. This VSC model and the extended MK model $\left({\mathrm{MK}}_d\right)$ are validated using experimental data taken from the literature. Empirical relationships are developed for predictive purposes to estimate the parameters involved, using basic geotechnical properties. Applications show a good agreement between measured and calculated WRC.

This paper describes pioneering research to integrate a novel “electronic nose” (EN) technology with a membrane interface probe (MIP) for rapidly screening hydrocarbon contaminated sites. The electronic nose is an automated odor recognition device that detects and identifies chemical vapors based on the principles of human olfaction. The MIP is an in situ tool that samples volatile organic compounds from the subsurface and transports the vapor through tubing to analytical devices located on the surface. The electronic nose developed for this research was first trained and tested to identify vapor samples of benzene, toluene, ethyl benzene, and xylene at three different concentration levels. The integrated EN–MIP system was then tested in gasoline-spiked aqueous soil samples in the laboratory. In situ demonstration tests were conducted in collaboration with the U.S. EPA at a gasoline-contaminated site in Rhode Island. The EN–MIP system was successful in detecting and estimating the concentration levels of gasoline contamination at various depths.

A series of static cyclic lateral load tests were performed on a full-scale $4\times 3$ pile group driven into a cohesive soil profile. Twelve 324-mm steel pipe piles were attached to a concrete pile cap $5.18\times 3.05\mathrm{m}$ in plan and $1.12\mathrm{m}$ in height. Pile–soil–pile interaction and passive earth pressure provided lateral resistance. Seven lateral load tests were conducted in total; four tests with backfill compacted in front of the pile cap; two tests without backfill; and one test with a narrow trench between the pile cap and backfill soil. The formation of gaps around the piles at larger deflections reduced the pile–soil–pile interaction resulting in a degraded linear load versus deflection response that was very similar for the two tests without backfill and the trenched test. A typical nonlinear backbone curve was observed for the backfill tests. However, for deflections greater than 5 mm, the load-deflection behavior significantly changed from a concave down shape for the first cycle to a concave up shape for the second and subsequent cycles. The concave up shape continued to degrade with additional cycles past the second and typically became relatively constant after five to seven cycles. A gap formed between the backfill soil and the pile cap, which contributed to the load-deflection degradation. Crack patterns and sliding surfaces were consistent with that predicted by the log spiral theory. The results from this study indicate that passive resistance contributes considerably to the lateral resistance. However, with cyclic loading the passive force degrades significantly for deflections greater than 0.5% of the pile cap height.

The passive resistance measured in a series of full-scale tests on a pile cap is compared with existing theories. Four different soils were selected as backfill in front of the pile cap and the load-deflection relationships under cyclic loading were investigated. The log spiral theory provided the best agreement with the measured passive resistance. The Rankine theory significantly underestimated the passive force, while the Coulomb theory generally overestimated the resistance. The displacement necessary to mobilize the maximum passive force was compared with previous model and full-scale tests and ranged from 3.0 to 5.2% of the cap height. A hyperbolic model provided the best agreement with the measured backbone passive resistance curve compared with recommendations given by Caltrans and the U.S. Navy. However, this model overestimated the passive resistance for cyclic loading conditions due to the formation of a gap between the pile cap and backfill soil and backfill stiffness reduction. Based on the test results, the cyclic-hyperbolic model is developed to define load-deflection relationships for both virgin and cyclic loading conditions with the presence of a gap.

Observations from recent earthquakes and the results of cyclic tests indicate that the Chinese criteria are not reliable for determining the liquefaction susceptibility of fine-grained soils. Fine-grained soils that liquefied during the 1994 Northridge, 1999 Kocaeli, and 1999 Chi-Chi earthquakes often did not meet the clay-size criterion of the Chinese criteria. Cyclic testing of a wide range of soils found to liquefy in Adapazari during the Kocaeli earthquake confirmed that these fine-grained soils were susceptible to liquefaction. It is not the amount of “clay-size” particles in the soil; rather, it is the amount and type of clay minerals in the soil that best indicate liquefaction susceptibility. Thus plasticity index (PI) is a better indicator of liquefaction susceptibility. Loose soils with $\mathrm{PI}<12$ and $w_c∕\mathrm{LL}>0.85$ were susceptible to liquefaction, and loose soils with $12<\mathrm{PI}<18$ and $w_c∕\mathrm{LL}>0.8$ were systematically more resistant to liquefaction. Soils with $\mathrm{PI}>18$ tested at low effective confining stresses were not susceptible to liquefaction. Additionally, the results of the cyclic testing program provide insights regarding the effects of confining pressure, initial static shear stress, and stress-path on the liquefaction of fine-grained soils.

The past studies of liquefaction phenomena during earthquakes have contributed to the development of simplified methods employing field test data to assess the liquefaction potential. Since the field data are limited by exploration cost, it is of interest to obtain valuable and meaningful distribution of liquefaction potential of an area from the limited data. This study proposes a method for assessing liquefaction potential over an extensive area according to the random field concept. The spatial structures of soil properties are estimated from the available cone penetration test (CPT) measurements. The soil properties at unsampled locations are simulated using Monte Carlo simulation. The reliability against liquefaction at every location within the study area is evaluated to map the liquefaction potential. The comparison between simulated distributions of liquefaction potential and observed liquefaction phenomena is discussed. The spatial correlation of soil property provides more information than the traditional approach that solely uses the field test data. The influences of CPT data, penetration locations, and spatial structures of soil properties on the mapping results of liquefaction potential are also discussed.

This paper discusses the effects of penetration rate on the penetration resistance in soft clay for various shaped penetrometers (cone, T-bar, ball, and plate) and for T-bars with different aspect ratios. Constant rate (“normal”) and variable rate (“twitch”) penetration tests, where the penetration rate was successively halved over eight steps with the penetrometer advanced by one or two diameters in each step, were undertaken in the beam centrifuge at the University of Western Australia. The tests were conducted on samples reconstituted from clay collected from the Burswood site in Western Australia. The twitch tests showed higher penetration resistance than the corresponding normal tests after the penetration rate had been reduced by a factor of 16 due to cumulative effects of partial consolidation. The penetration rate at which the resistance started to increase due to partial consolidation was used to estimate the consolidation coefficient, $c_v$ , of the reconstituted clay. The interpreted $c_v$ values were similar to values estimated from other consolidation data, both in the centrifuge and from laboratory Rowe cell and constant rate of strain consolidation tests. In addition, results from in situ twitch tests at the Burswood site were examined to evaluate viscous effects on the penetration resistance.

LRFD shows promise as a viable alternative to the present working stress design (WSD) approach to shallow foundation design. The key improvements of LRFD over the traditional WSD are the ability to provide a more consistent level of reliability and the possibility of accounting for load and resistance uncertainties separately. For LRFD to gain acceptance in geotechnical engineering, a framework for the objective assessment of resistance factors is needed. Such a framework, based on reliability analysis, is proposed in this paper. Probability density functions (PDFs), representing design variable uncertainties, are required for analysis. A systematic approach to the selection of PDFs is presented. A procedure such as that proposed provides a rational probabilistic basis for the development of LRFD methods in geotechnical engineering.

In shallow foundation design, the key improvements offered by LRFD over the traditional working stress design (WSD) are the ability to provide a more consistent level of reliability between different designs and the possibility of accounting for load and resistance uncertainties separately. In the development of LRFD, a framework for the objective, logical assessment of resistance factors is needed. Additionally, in order for LRFD to fulfill its promise for designs with more consistent reliability, the methods used to execute a design must be consistent with the methods assumed in the development of the LRFD factors. In this paper, a methodology for the estimation of soil parameters for use in design equations is proposed that should allow for more statistical consistency in design inputs than is possible in traditional methods. Resistance factors for ultimate bearing capacity are computed using reliability analysis for shallow foundations both in sand and in clay, with input parameters obtained from both the cone penetration test and the standard penetration test, and for both ASCE-7 2000 and AASHTO 1998 load factors. Resistance factor values are dependent upon the values of load factors used. Thus, a method to adjust the resistance factors to account for code-specified load factors is also presented.

Rainwater can infiltrate into slopes and earth dams. Given sufficient infiltrating rainfall intensity, frequency, and time, the phreatic line within the slope or dam will “mound” above its otherwise steady state position. Such a mound will increase downslope seepage and reduce downslope stability. This paper develops an approximate method for solving this transient seepage “mounding problem” and the resulting reduction in stability. It shows the following variables will reduce stability: increased rainfall intensity and duration, decreasing permeability—especially over the ${10}^{-2}–{10}^{-4}\mathrm{mm}∕\mathrm{s}$ range—and its anisotropy, increasing the slope cotangent, decreasing the depth to an impermeable underlayer, or increasing the depth to a permeable underlayer. Increasing size and effective porosity has only a time effect. In special circumstances the mounding effect can reduce slope stability by 50% and the paper includes a slope case history example.

An attempt is made to establish an analytically based estimate of the influence zone surrounding the tip of a loaded pile in sand. In the framework of the cavity expansion theory and a confined local failure mechanism, explicit expressions are derived in which the sizes of the upward and downward influence zones are properly linked with the angle of shearing resistance, the stiffness, the volumetric strain, and the mean effective stress of the sand at the pile tip. Based on a series of parametric analyses, the mean range of the influence zone is suggested. For piles in clean sand, the influence zone above the pile tip is between 1.5 and $2.5D$ and the zone below the tip ranges from 3.5 to $5.5D$ , where $D$ is pile diameter. For piles in more compressible silty sand, the influence zone extends between 0.5 and $1.5D$ above the pile tip and between 1.5 and $3D$ below the tip. Because of its analytical nature, the present study may provide a meaningful insight into the current empirical interpretations.