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Presents information on a study on the internal shear strength of adhesive-bonded, stitch-bonded, and needle-punched geosynthetic clay liners. Testing procedures; Comparison of the test data; Implications of the research findings.

Although widely used for field measurements of soil moisture, problems continue with the use of the neutron probe in clay soils comprised of over 40% clay fractions, and in the determination of the intensity of field sampling necessary to characterize a site. We examine issues associated with field practice and calibration, data analysis and estimation of variance, and error in soil moisture measurements for silty clay soils in the Imperial Valley, California, using large calibration data sets from several different layouts of neutron access tubes. Our analysis indicates that for field calibrations: (1) bulk density corrections of the count ratio data do not necessarily improve the standard errors of the water content measurements; (2) soil sampling for calibration within the access tube hole at the time of tube installation results in smaller measurement errors; (3) calibrations improve as the average soil moisture of the profile at the time of the original sampling decreases; and (4) field-wide calibrations improve, and the sampling intensity required to characterize soil moisture content decreases with an increasing soil depth. We also address aspects of the neutron probe use associated with soil salinity and polyvinyl chloride (PVC) access tubing (chloride interference), inclusion of shallow sampling data in calibrations, and instrument, calibration, and spatially related standard variances affecting field measurements. [ABSTRACT FROM AUTHOR]

Describes an experimental study in which a 305 millimeter instrumented drilled shaft was installed in a moderately expansive clay soil during the dry season and monitored over a period of about 15 months. Shear strength of unsaturated soils; Description of the test site; Details on the laboratory tests; Conclusions.

Determines the effect of clay crack flow on tail water quality and crack flow's contribution to salt leaching conducted on farm fields in Brawley, California. Soil sampling; Experiments conducted on each soils; Sampling of surface water.

Presents information on a study which examines the relationship of hydraulic conductivity of compacted clays to changes in microstructure. Overview of data on the application of random network models to quantitatively represent the minifabric of compacted clays; Results and analysis on the hypothetical simulations about the effects of cluster size on network parameters; Conclusions.

Examines the degradation of dichloromethane as it diffuses through clay. Usage of a synthetic leachate with no significant initial bacterial population; Diffusion coefficient; Clay characteristics; Biokinetic parameters for two models of substrate utilization kinetics.

Estimates seepage velocity through compacted clays using a series of column and tank tests. Concentration-depth profile; Transport parameters of contaminants; Column used in small-scale column tests; Mathematical modeling.

Investigates the influence of the method of installation and degree of soil plugging on the skin friction developed along displacement piles subjected to static axial loading in overconsolidated clay. Axial compressive skin friction; Installation disturbance; Proposal of a stress method of analysis for estimating pile skin friction.

Describes the performance of a tiedback excavation with a soil mixed wall where underlying marine clay was stabilized by deep soil mixing and jet grouting. Lateral and vertical soil displacements; Soil strains and interaction between the retained soil and a reinforced concrete box culvert.

Focuses on the results of hydraulic conductivity tests performed on five geosynthetic clay lines using seven permeant liquids and three conditions of hydration. Hydraulic conductivity; Usage of simulated fly ash leachate; Testing program and conditions of hydration; Composition of permeant liquids.

Presents a slope stability analyses on the empirical relationship for the fully softened friction angle that is a function of liquid limit, clay-size fraction and effective normal stress. Shear strength along the failure surface; Stress-strain relationships from drained triaxial compression tests; Clay and shale samples used in ring shear tests.

Evaluates the effect of several freeze-thaw cycles on the hydraulic conductivity of geosynthetic clay liners. Increases in hydraulic conductivity after one freeze-thaw cycle; Water content and thickness data after three freeze-thaw cycles; Typical measurements of temperature during freezing cycle.

Laboratory tests have been carried out in order to evaluate the improvement in engineering properties relevant to highway design and construction obtained when clayey subgrade soils are stabilized with lime or fly ash. The experimental program included California bearing ratio (CBR) tests to evaluate the bearing strength of stabilized soils used as working platforms during highway construction. The admixture of lime or fly ash caused an increase in the plasticity limit, while both the liquid limit and the plasticity index of the soils have been reduced. Substantial increases in the California bearing ratio value, higher than those of the soil-fly ash mixtures, have been obtained when the soil samples were mixed with lime. The swelling after a 4-day soaking period has been reduced with the addition of both additive materials. The increase in optimum moisture content acts subsidiarily to the increased CBR value, particularly at high lime or fly ash percentages. An analogous effect has been found for the maximum dry density reduction. [ABSTRACT FROM AUTHOR]

The article presents a study on an analysis of laterally loaded drilled shafts in rock profiles by Robert Liang, Ke Yang and Jamal Nusairat. It enumerates the various issues that the discussers have advanced in consideration of the authors. Meanwhile, it presents several graphs that depict the ultimate resistance for wedge and rock mass failure method.

The article presents a study on the singularities of geotechnical properties of complex soils in seismic regions by Ramon Verdugo. It notes that the study focuses on two highly unusual soil groups, such as the volcanic ash clays and diatomaceous soils. It also enumerates the significant findings from the trial embankments.

The article presents a commentary of the article "High-Modulus Columns for Liquefaction Mitigation," by James R. Martin II, C. Guney Olgun, James K. Mitchell, and H. Turan Durgunoglu. It aims to comment on the data and analysis for areas of the site where the stiff columns were not installed and where significant compression was observed in silt and clay layers. It stresses that data given by the researchers are insufficient enough which caused confusion on the issue that behavior of silts and clays at the Carrefour site was related to the "Chinese criteria," the criteria classifying silts and clay as being nonliquefiable if they exceed certain values of plasticity and if the percentage of clay size particles and their water contents are below certain specified values.

Comments on a study on soil deformation and excess pore pressure distribution around a driven close-ended pile conducted by researchers Juan M. Pestana et al. Cases where positive excess pore pressures were observed during piezocone penetration in stiff clays and dense clayey sand; Pile capacity in Beaumont clay before and after the end of driving; Reason for a reduction in penetration pore pressure after the rod-change.

Focuses on a study of the hydraulic conductivity of compacted clay covers placed on top of waste containment facilities. Overburden pressure concerns; Matrix suctions; Discrepancy in saturated hydraulic conductivity.

Presents the results obtained from model lime columns installed in a marine clay bed formed in a laboratory test tank. Diffusion of lime into the surrounding soil from the columns; Increases in the values of pH and lime content; Cation exchange capacity.

A review of the article "Shear Strength of Clay at Different Shear Rates," by Ivan B. Gratchev and Kyoji Sassa, is presented.

A review of the article "Shear Strength of Clay at Different Shear Rates," by Ivan B. Gratchev and Kyoji Sassa, is presented.

The article presents response on the comment of the study which determines the effect of microfabric on undrained static and behavior of kaolin clay. It recognizes the issues raised by the discussers concerning the formation of dispersed structure of kaolinite and their agreement on the changes in microfabric of clays. However, it also confirms that the formation of dispersed structure in kaolinite cannot be ruled out.

The article presents comment on the study that determines the effect of microfabric on undrained static and cyclic behavior of kaolin clay. It recognizes the method used by the authors in using different techniques to identify the microfabric of clays, which also require enough experience to accurately interpret results. It also commends the authors for successfully demonstrating that soil with flocculent fabric exhibits higher shrinkage limit than those with dispersed limit.

The article presents the authors' response on the comments of the discussers regarding their study on an analysis of laterally loaded drilled shafts in rock profiles. It notes that the deep failure model tends to control the ultimate capacity in several cases. The authors also mentioned the point of the discussers on the proposed equations that provided higher values of Ki.

The article presents the authors' response on the comments of the discussers regarding their study on a large database of geosynthetic clay liner (GCL)-geomembrane interface shear strength results. It notes that the authors have performed shear tests and concluded that the internal peak shear strength of GCL are general larger. It is commented that the large displacement design is unlikely to be governed by the internal residual shear strength of a needle-punched GCL.

The article provides an overview on the evaluation of cyclic softening in silts and clays. The authors details the occurrence of sands to clays that take place around a plasticity index (PI) of 7. One author suggests the slightly higher values of PI to define the transition of sands to clays. The author also prefers a slightly higher PI criteria to define claylike behavior (PI>10) as sandlike soils and the simplified methodology requires a certain level of conservation in its application for low to moderate risk projects. Moreover, three different approaches are suggested on the estimation of the cyclic resistance ratio (CRR) for claylike fine-grained soils in the field.

The article presents the authors' comments about the article "Parameters Affecting Soil-Water Characteristic Curves of Fine-Grained Soils," by Vikas K.S. Thakur, S. Sreedeep and Devendra N. Singh, published in the April 2005 issue of the journal. According to the authors, the findings presented in the article show that soil moisture suction in fine-grained soils such as clay soils is primarily governed by the physicochemical interactions between water and clay.

The authors discuss the study "Shaft Resistance and Setup Factors for Piles Jacked in Clay" by Prasenjit Basu and colleagues. Topics covered include the study's investigation of the effects of undrained and residual strengths of saturated clay soil on displacement piles' shaft resistance, the use of a one-dimensional finite element analysis (FEA) in the research, and the influence of residual shear stress on the pile.

Tensile strength of soil plays an important role in controlling the cracking and tensile failure of many earth structures. In this investigation, a direct tensile test apparatus was developed to determine the tensile strength of compacted clayey soil over a broad range of water contents (4.3-28.5%) and with different dry densities (). The results show that the tensile strength of compacted clayey soil significantly depends on water content. The tensile strength characteristic curve (TSCC) exhibits one peak value occurring at the critical water content around 11.5%. With increasing water content, the tensile strength increases at the dry side of and then decreases at the wet side of it. Generally, with the increase of dry density, the tensile strength also increases. Moreover, a modified model is proposed to describe the tensile strength characteristics of compacted clayey soil, and it is validated by the obtained test data. [ABSTRACT FROM AUTHOR]

Proper understanding of the field performance of lime-treated expansive soils requires the evaluation of their unsaturated properties under stress conditions similar to that in the field. This paper studied the influence of net vertical stress on the soil-water characteristic curves (SWCC) of lime-treated expansive clay. The first phase of this study investigated the influence of lime content and curing period under low net vertical stress (7 kPa) using axis translation and filter paper techniques with simultaneous measurements of sample volume change. The second phase evaluated the SWCCs of untreated and lime-treated clays under vertical stresses of 100 and 600 kPa. Different representations of SWCCs were considered in the interpretation of test results. Test results indicated that lime content had a significant effect on the shape and air entry value of SWCCs because of changes in soil microstructure, whereas curing period had a far less significant effect. Furthermore, the application of net vertical stress delayed the desaturation of samples causing increase in air entry value. On the basis of plots for the variation of void ratio versus suction, the increase in air entry value was attributed to considerable reduction in volume (void ratio) associated with the application of the net vertical stress causing samples to remain saturated up to high suctions levels. [ABSTRACT FROM AUTHOR]

Bioventing is an alternative technique to clean up contaminated soil. The purpose of this study is to assess the bioremediation of clayey soil contaminated with a blend of 80% diesel and 20% biodiesel (B20) using the bioventing and natural attenuation (NA) methods. The tests were carried out in bioreactors using soil contaminated with 4% of B20. Three airflow intensities (2, 4, and ) were tested in three different airflow intervals (1 h every 24, 36, and 48 h). The contaminant degradation was determined by the contaminant's residual fraction in the soil after 15, 30, 60, and 120 days. The highest degradation was 85% for bioventing and 64% for natural attenuation. The airflow intensities and airflow intervals showed no significant differences in the results. The use of the lowest airflow intensity () and the longest airflow interval (1-h application each 48 h) might be more economically viable for the application of bioventing as a remediation technique for residual clayey soils. [ABSTRACT FROM AUTHOR]

Presents information on a study which described soil-water characteristic curves for compacted clay barrier soils. Analysis of soil specimens; Equations to estimate parameters of soil-water characteristic curves. INSET: Closure, by James M. Tinjum et al.

Comments on a study on the performance of geosynthetic clay liners (GCL) subjected to differential settlement. Depiction of GCL before and after inducing differential settlement for a typical geotextile-encased, stitch-bonded GCL; Uses of compacted clay liners (CCL); Methods to calculate tensile strain. INSET: Closure by David E. Daniel.

The aim of this study was to calibrate the Diviner 2000 capacitance probe in the field and in the laboratory. Field calibration was carried out on an agro-forestry farm with soil of colluvial origin with two textural horizons, clay loam overlying clay. The same soil was used for laboratory calibration at the Universidad de Chile. Prior to calibration, the Diviner 2000 probe was normalized to obtain the scaled, or standardized, frequency (SF). For each method of calibration, three sets of soil moisture conditions were generated: dry, moist and saturated, with two replicates per set. The soil was evaluated with the probe at two depths per horizon, and the volumetric water content () was immediately determined gravimetrically in situ at each depth. To calibrate the probe, the values for the samples were compared with the SF values recorded by the probe and the coefficient of determination was determined through regression analysis. A nonlinear correlation was found between the SF measured by the probe and the values obtained through gravimetry for each horizon and method of calibration, with adjustment to a potential function with a high coefficient of determination (field: ; laboratory: ). The manufacturer's calibration equation proved to be quite precise in laboratory conditions, but in field conditions it underestimated the water content of both clay loam and clay soil. [ABSTRACT FROM AUTHOR]

The article presents a study that investigates a large database of geosynthetic clay liner (GCL)-geomembrane interface shear strength results by J. S. McCartney, J. G. Zornberg and R. H. Swan Jr. It notes that the authors have performed shear tests and concluded that the internal peak shear strength of GCL are general larger. It is commented that the large displacement design is unlikely to be governed by the internal residual shear strength of a needle-punched GCL.

The authors focus on research into deep building foundations and its behavior under axial and lateral loading. They mention that the prediction of load-transfer curves, both for side resistance and for end bearing, allow for the analysis of deep foundations under a range of conditions. They talk about soil properties around deep foundations after installation and how the pile capacity under axial load differs depending on if the pile was driven into consolidated clay or loose cohesionless soil. They state that research can lead to an improvement of design methods of deep foundations.

Replies to an article by Ramesh C. Gupta, on soil deformation and excess pore pressure field around a closed-ended pile, published in the July 2003 issue of the 'Journal of Geotechnical and Geoenvironmental Engineering.' Properties of soft clay; Equipments used to study these properties; Application of soil dilatancy to problems of cavity expansion.

Comments on a study which estimated the field hydraulic conductivity of compacted clay. Relationship between hydraulic conductivity and effective stress; Development of equations to relate change in hydraulic conductivity as a function of effective stress; Relationship between permeability and void ratio for soil types.