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Experimental results from physical testing are reported to examine the thickness and hydraulic performance of three geosynthetic clay liners (GCLs) overlying a geonet when subjected to vertical stresses (e.g., as may be found in a secondary leachate collection layer or hydraulic control layer in solid waste landfills). The GCL was found to intrude into the underlying geonet and the effects of GCL type and water content, temperature, applied pressure, and test duration on the final GCL thickness are examined. The results are consistent with GCL deformation from the beneficial consolidation of bentonite as opposed to lateral extrusion of bentonite. Results from fixed ring flow tests suggest that the indentations in the GCL caused by intrusion into the underlying geonet do not appear to negatively impact the hydraulic performance (permittivity or resistance to internal erosion) of the particular GCLs tested for the conditions examined. The flow capacity of the geonet in these tests was found to depend not only on the amount of GCL intrusion but also on the orientation of the geonet relative to the flow direction. DOI: 10.1061/(ASCE)GT.1943-5606.0000247 CE Database subject headings: Clay liners; Linings; Landfills; Geosynthetics. Author keywords: Geosynthetic clay liners; Lining, landfills.

The compression index is an important soil property that is essential to many geotechnical designs. Over the decades, a number of empirical correlations have been proposed to relate the compressibility to other soil index properties, such as the liquid limit. plasticity index, in situ water content, void ratio, specific gravity, etc. The reliability and thus predictability of these correlations are always being questioned. Moreover, selection between simple and complicated models is a difficult task and often depends on subjective judgments. A more complicated model obviously provides 'better fit' to the data but not necessarily offers an acceptable degree of robustness to measurement noise and modeling error. In the present study, the Bayesian probabilistic approach for model class selection is used to revisit the empirical multivariate linear regression formula of the compression index. The criterion in the formula structure selection is based on the plausibility of a class of formulas conditional on the measurement, instead of considering the likelihood only. The plausibility balances between the data fitting capability and sensitivity to measurement and modeling error, which is quantified by the Ockham factor. The Bayesian method is applied to analyze a data set of 795 records, including the compression index and other well-known geotechnical index properties of marine clay samples collected from various sites in South Korea. It turns out that the correlation formula linking the compression index to the initial void ratio and liquid limit possesses the highest plausibility among a total of 18 candidate classes of formulas. The physical significance of this most plausible correlation is addressed. It turns out to be consistent with previous studies and the Bayesian method provides the confirmation from another angle. DOI: 10.1061/(ASCE)GT.1943-5606.0000157 CE Database subject headings: Bayesian analysis: Soil compression: Correlation: Marine clays: Probability.

Super soft clays can be defined as insensitive cohesive soils that have a water content higher than the liquid limit. It is difficult to define and measure the strength of these soils using conventional soil mechanics apparatus. It is proposed that the shear strength be determined using a rotary viscometer and be defined as the shear stress at zero strain (shear strain) rate in this test of viscosity. In this paper a number of potential methods to determine the shear strength or yield stress of super soft clays is considered. The yield stress of four super soft soils, each with varying water contents, have been measured using a rotary viscometer. The results of these tests together with published data are used to develop a relationship between the yield stress and the index properties of super soft clays.

A series of one-eighth-scale strain controlled model pressuremeter tests were performed using an automated flexible wall calibration chamber testing system. Undrained model pressuremeter tests were performed with and without the internal pore-water pressure measuring piezometer needles at radial strain rates ranging from 1 to 8%/min in a controlled laboratory setup in beds of kaolin clay prepared with known stress histories. Reference strength and deformations properties were determined using one-dimensional consolidation, isotropically consolidated undrained compression (CIUC) and [K.sub.o] consolidated undrained compression (C[K.sub.o]UC) laboratory tests, and comparisons are made with the interpreted values from the pressuremeter test data. Interpretations of the undrained shear strength, initial shear modulus, shear stress-radial strain variation, limit pressure, and horizontal stress for each net pressuremeter curve were evaluated using various interpretation procedures, using the Marquardt-Levenberg algorithm. Based on the laboratory test data and the analytical interpretations, several conclusions were made regarding the effects of the rate of probe expansion on the deduced shear modulus, undrained shear strength, and limit pressure in the pressuremeter testing of clays.

Cyclic tests were conducted to study the secant shear modulus, [G.sub.s] of two reconstituted sands and three laboratory-made clays at small cyclic shear-strain amplitudes [[Gamma].sub.c] [approximately[ 0.0006%-0.02%. A recently developed direct simple shear device for small-strain testing was employed. The effects of cyclic strain amplitude ([[Gamma].sub.c]), type of soil and plasticity index (PI), vertical effective consolidation stress ([[Sigma][prime].sub.vc]), and overconsolidation ratio (OCR) were investigated. The results show that the ordinates of the normalized shear modulus reduction curve, [G.sub.s]/[G.sub.max] - [[Gamma].sub.c], generally increase as [[Sigma].sub.vc] and OCR increase. However, these effects of [[Sigma][prime].sub.vc] and OCR become smaller and may eventually disappear as the PI of the soil increases.

Chloride diffusion coefficients of 5.7 x [10.sup.-10] [m.sup.2/s], 9.0 x [10.sup.-10] [m.sup.2/s], and 9.8 x [10.sup.-10] [m.sup.2/s] were obtained from diffusion tests conducted on a single isolated layer of clayey silt, silt, or sand, respectively. The advective-diffusive movement of chloride through a two-layer soil system consisting of a compacted clayey silt underlain by either a fine sand or silt was also examined. The agreement between the experimental results and model predictions suggests that existing solute-transport theory can adequately predict chloride migration through a compacted clay layer and underlying sand or silt layer at near-saturated conditions for Darcy velocities at least up to the maximum value examined (0.0183 m/yr or 500 L/ha/d). Chloride transport was dominated by diffusion in these tests.

Cyclic constant-volume direct simple shear tests were performed on intact specimens of a sensitive clay reconsolidated to the in-situ stress state resulting in an overconsolidation ratio (OCR) of 2.2. The tests were conducted for different values of initial static undrained shear stress. The results confirmed that the high strain rate associated with cyclic loading has a significant effect on the cyclic resistance of soft clays. For up to 12 cycles, the strain-rate effect fully compensates the degradation of shear strength associated with cycling. The presence of an initial static shear stress decreases the cyclic resistance but increases the total undrained shear resistance, due to the partial or total disappearance of stress and strain reversal. The results indicate that for such a clay, the static undrained shear strength provides a conservative estimate in a pseudostatic analysis.

Field observations and numerical studies demonstrated that stone columns could accelerate the rate of consolidation of soft clays. A simplified method for computing the rate of consolidation is presented in this paper by assuming that stone columns; (1) are free draining; (2) have higher drained elastic modulus than soft clay; and (3) are deformed 1D. The formats of the final solutions in vertical and radial flows are similar to those of the Terzaghi 1D solution and the Barron solution for drain wells in fine-grained soils, respectively. Modified coefficients of consolidation are introduced to account for effects of the stone column-soil modular ratio. The new solutions demonstrate stress transfer from the soil to stone columns and dissipation of excess pore water pressures due to drainage and vertical stress reduction during the consolidation. Comparisons between the results from this simplified method and the numerical study by Balaam and Booker in 1981 exhibit reasonable agreement, when the stress concentration ratio is in the practical range (2-6). The discrepancies in the results from these two methods are discussed. This paper also includes design charts and a design example.

The influence of single-species salt solutions of various concentration, cation valence, and pH on swelling and hydraulic conductivity of nonprehydrated GCLs was examined. At similar concentration, swell was largest with NaCl, KCl, and LiCl solutions (monovalent cations [Na.sup.+], [K.sup.+], and [Li.sup.+]) and smallest with La[Cl.sub.3] solutions (trivalent cation [La.sup.3+]). Intermediate swell volumes were obtained with divalent solutions (Ca[Cl.sub.2], Mg[Cl.sub.2], Zn[Cl.sub.2], and Cu[Cl.sub.2]). Analogous results were obtained from hydraulic conductivity tests. GCL specimens permeated with solutions containing divalent or trivalent cations had higher hydraulic conductivity than GCLs permeated with monovalent solutions or deionized water, unless the divalent or trivalent solutions were very dilute ([is less than or equal to] 0.01 M). Hydraulic conductivity increased as the concentration increased, and at high concentration (1 M) only small differences existed between hydraulic conductivities measured with all solutions. Swelling and hydraulic conductivity were related to size of the hydrated cation for monovalent cations, but no relationship was observed for different species of divalent and trivalent cations provided that the valence was the same. However, pH only influenced swelling and hydraulic conductivity when the pH was very low ([is less than] 3) or very high ([is greater than] 12).

Increased hydraulic conductivity due to freeze-thaw cycles have been reported for lean clay. However, these conditions do not have the same effect on all soil types. Tests on fat clays revealed that a progressive fluctuation in hydraulic conductivity values can be found in fat clays. This could be explained by the presence of fractures that can close up and seal themselves when subjected to such conditions. Fat clays also exhibit a similar reaction after wetting and drying.