Measurements of undrained shear moduli are reported from a program of laboratory tests on reconstituted kaolin samples containing relatively large bubbles of methane gas. The experimental program included low‐frequency torsional stress‐strain loops and torsional resonant column tests, providing values of shear moduli for shear‐strain amplitudes from 0.0004% to 0.1%. At all values of strain amplitude, the reduction of shear moduli caused by the presence of gas bubbles was greater than predicted by a theoretical elastic expression. This pattern of behavior was attributed to the formation of local yield zones around the gas‐bubble cavities during consolidation prior to shear testing (a phenomenon that would also occur in‐situ within offshore sediments). The results of the research program suggest that reductions in shear moduli of up to 50% could be caused by relatively small volumes of gas bubbles, occupying just a few percent of the total soil volume. This would have considerable significance for the displacements of offshore foundations constructed on sediments containing undissolved gas.

Electroosmosis in a copper‐contaminated kaolinite was highly sensitive to chemical treatment schemes designed to remove the contamination. Non‐uniform profiles of electric field intensity and pH as well as negative pore‐water pressure develop during sustained electrokinetic treatment of clays. These nonlin‐earities and nonuniform pore‐water pressures cannot be adequately described by classical analysis. Classical analysis is based on assumptions of a uniform and constant electroosmotic permeability coefficient, for instance. An extended capillary model which includes nonuniform contributions to electroosmosis and pore pressures that vary with space and time, is developed and compared with experimental findings. Subtle changes in initial and boundary conditions of the system chemistry have a very large effect on electroosmosis in soils. For instance, acid addition at the cathode reservoir may cause reversal of the direction of electroosmotic flow. Other species, such as the citrate, may form stable complexes with copper ions, thus reducing the impact of copper on the zeta potential of the clay. The model is used to simulate these effects.

Data from dilatometer tests (DMT) are used in the development of a model for the construction of static P‐y curves in clay deposits. A procedure to account for the influence of close‐ended pile installation on the soil properties around the pile is developed. Strength modification values are presented as a function of the overconsolidation ratio (OCR). A procedure for the construction of P‐y curves using a hyperbolic model is proposed. Using the proposed procedure, analyses of three extensively instrumented pile‐load tests reported in the literature are presented. Hyperbolic P‐y curves based on coefficients of subgrade reaction from DMT and the modified $P_u$ produced load‐pile displacement relationship and moment distribution that agreed well with the measured field behavior. Results illustrated the potential of using the dilatometer test to obtain values and distributions of site specific coefficients of subgrade reaction. Predictions of the pile‐soil response using the proposed model were conducted and results indicated reasonable agreement between predicted and measured field behavior.

The feasibility of reinforcing soil with strips of reclaimed high‐density polyethylene (HDPE) was investigated in this study. Strips of HDPE were mixed with Portage sand and tested to determine the California Bearing Ratio (CBR), secant modulus, resilient modulus, and shear strength. Strips were prepared at aspect ratios of 4, 8, and 12 to examine how reinforcement of the sand is affected by the length of the strips. The tests showed that reinforcing sand with reclaimed HDPE strips enhances its resistance to deformation and increases its strength. Addition of strips increased the CBR and the secant modulus, with the CBR increasing by as much as a factor of 5. The resilient modulus also increased with addition of strips, with the greatest increases (35% increase) occurring for strip a content of 3%. Direct shear tests also showed that addition of HDPE strips increased the shear strength of the sand. Increases in friction angle as large as 18° were measured at normal stresses below the critical confining stress. Reinforcement was affected by the aspect ratio (or length) of the strips. The largest increases in all measured properties were observed for strips having an aspect ratio of 8. In some cases when an aspect ratio of 4 was used (short strips), the soil became weaker.

Results of torsional ring shear tests on cohesive soils reveal that the drained residual strength is related to the type of clay mineral and quantity of clay‐size particles. The liquid limit is used as an indicator of clay mineralogy, and the clay‐size fraction indicates quantity of particles smaller than 0.002 mm. Therefore, increasing the liquid limit and clay‐size fraction decreases the drained residual strength. The ring shear tests also reveal that the drained residual failure envelope is nonlinear, and the nonlinearity is significant for cohesive soils with a clay‐size fraction greater than 50% and a liquid limit between 60% and 220%. This nonlinearity should be incorporated into stability analyses. An empirical correlation for residual friction angle is described that is a function of liquid limit, clay‐size fraction, and effective normal stress. Previous residual strength correlations are based on only one soil index property and provide a residual friction angle that is independent of effective normal stress. For slope stability analyses, it is recommended that the residual strength be modeled using the entire nonlinear residual strength envelope or a residual friction angle that corresponds to the average effective normal stress on the slip surface.

Testing procedures and methods of analysis for determining the fracture toughness of soils using the ring test are described and values of fracture toughness measured for 132 compacted specimens of two cohesive soils are presented. The critical mode I stress‐intensity factor, the critical $J$ integral, and the tensile strength can be determined simultaneously from a single ring‐test specimen. The critical $J$ integral was approximately equal to the energy‐release rate computed from the critical mode I stress‐intensity factor measured for the same specimen. A strong correlation between fracture toughness and ring‐specimen tensile strength was found. Effects of material type, water content, soil‐placement conditions, rate of loading, and specimen size have been studied, and values of fracture toughness measured by bending tests are compared to ring‐test results. Test results show that fracture toughness of cohesive soils is affected significantly by material type and water content at time of fracture. In contrast, effects of material‐placement conditions, molding water content, and molding compactive effort are relatively unimportant.

This paper presents results of a laboratory investigation of the influence of the nonuniform stresses imposed by the Geonor direct simple‐shear (DSS) apparatus on measured stress‐strain behavior. The investigation concentrated on the influence of the apparatus on the measured strain‐softening behavior of cohesive soils during constant volume (undrained) shear. Special DSS tests were conducted on an elastic material and cohesive soils at varying overconsolidation ratios. The experimental results clearly indicate that the nonuniformity of stresses imposed by the device during undrained shear causes a decrease in the vertical effective stress with increasing shear strain. This in turn causes a reduction in the measured horizontal shear resistance at large strains. The device‐induced “unloading” probably has relatively little effect on measured peak strengths in K0 consolidated‐undrained DSS tests but certainly contributes to the pronounced strain softening typically observed.

Expansive soils, such as black‐cotton soils, create problems for structures built on them due to their high swelling and shrinkage characteristics. In the field, the magnitude of swelling depends on the soil thickness. Swelling experiments were conducted on black‐cotton soil in a geotechnical centrifuge and the results were compared with those obtained from the integration of the results of 1‐g swelling experiments under different surcharge stresses. The agreement between these results has been found to be close.