Journal of Geotechnical and Geoenvironmental Engineering

An investigation of shear mechanisms at interfaces between particles and relatively smooth materials using contact mechanics and basic friction theory reveals that a combination of sliding and plowing governs dense Ottawa 20/30 sand/smooth high density polyethylene geomembrane peak interface shear behavior. Contact area and the corresponding shear resistance during sliding increase at a slower rate than the applied normal stress, resulting in a decreasing friction coefficient and flattening of the peak strength envelope. Plowing of soil grains results in an increasing peak friction coefficient with increasing normal stress and can produce an upward curvature of the strength envelope above a critical stress level. Plowing is primarily controlled by the relative hardness of the interface materials and by grain shape with angular particles exhibiting plowing in all normal stress ranges, whereas nearly perfect spheres exhibit only sliding. High surface hardness is shown to constrain shear behavior to a sliding mode with little contribution from plowing. These findings are consistent with results reported in the tribology literature.

Unstable flow can result in the formation of fingers during infiltration into dry soil. Centrifuge modeling is a potentially useful tool to study the relationship between finger size, spacing, and velocity. It can also be used to investigate solute transport in such fingers. Physical properties of the fingers are obtained for three tests conducted at elevated acceleration levels. A fourth test was conducted at 1g. The physical parameters compare well with theoretical predictions. To assess solute transport in fingers, a known concentration of solute was introduced after the fingers had formed. The resulting breakthrough curves were analyzed using the two-region model as well as the advection dispersion equation with appropriate initial and boundary conditions. Although the two-region model is physically more plausible, it was found to match the extensive tailing observed in the breakthrough curves only marginally better than the advection-dispersion equation.

Alfaro's Peak is to be a 28-story residential building located in Makati, Manila, Philippines. The loads are high and concentrated, which necessitated supporting the building on deep foundations, penetrating into a residual soil called the Guadalupe Tuff formation encountered at a depth of approximately 15 m. The foundation chosen consisted of a perimeter diaphragm wall combined with rectangularly shaped, 2.4-m² cross section, barrettes to support interior columns. A static loading test using the Osterberg-cell (O-cell) test method was performed to study the barrette capacity and deformation behavior. This paper describes the O-cell test, summarizes a finite-element (FE) analysis performed to assist interpretation of the results, and indicates foundation design change adopted as a result of the test. The maximum applied O-cell load during the tests was 11,600 kN. The accumulated upward movement of the top plate was about 10 mm. The accumulated upward movement of the bottom plate was 58 mm, corresponding to about 6% of the barrette width. The results of testing and analyses performed show that the shaft resistance (side shear) acting on the barrette is proportional to the effective stress distribution. This means that any design based on the parameters established from the analysis of the test must include the unloading consequence of basement excavation at the site. The FE computations enabled a comparison between the O-cell test and a conventional head-down test, which indicated that the O-cell test results are representative for the behavior of the barrette in a conventional head-down test and gave insight in the overall load-transfer behavior of the barrette. The O-cell test, strain gauge instrumentation, and FE analysis gave reliable results of decisive importance for the design of the barrettes and other foundation units at the site.

This paper deals with the dynamic analysis of foundations in saturated soils. In the first part, a mathematical formulation is briefly outlined in which soil is considered as a two-phase medium comprising the soil skeleton and voids filled with a viscous fluid. Such formulation is suitable for describing a solid-fluid transition associated with the liquefaction phenomenon. Subsequently, the notion of dynamic stability is reviewed and a simple criterion is introduced, leading to the definition of a stability factor. The mathematical framework is illustrated by a numerical example involving a foundation subjected to seismic excitation. The effect of viscosity of liquefied material on the stability of the system is examined.

This paper presents the results of an evaluation of the potential release of liquids stored within a waste mass undergoing compression due to a landfill vertical expansion. The mechanism of free liquid generation is initially evaluated and data interpretation methods are developed to estimate the maximum allowable waste thickness that a landfill could reach without releasing liquids stored within the waste. The proposed conceptual framework of free liquid generation is used to evaluate the environmental implications of the vertical expansion of an unlined case history landfill located in southern California. The moisture content of waste in southern California landfills is generally below field capacity. However, if the waste is compressed, its available moisture-holding capacity will decrease and its moisture content may eventually reach field capacity. Additional compression beyond this point will squeeze liquid from the waste. Laboratory testing and field characterization programs were undertaken to evaluate the field capacity, the in-situ moisture distribution, and the unit weight profiles of the waste in the case history landfill. These experimental data were used to evaluate the ability of the landfill to continue to retain moisture after continued waste placement. The evaluation indicated that the moisture content of the waste will not reach its field capacity for the proposed final grading of the case history landfill and, therefore, that the liquids should remain within the waste mass after the vertical expansion.

Field capacity has been defined as the water content at which the drainage flux from a soil ceases, or becomes negligible. Field capacity is most commonly estimated as the water content at a pressure head of 1/3 bar, which ignores its flux-based nature. A number of authors have proposed estimating field capacity as the water content at a given (negligible) flux, assuming unit gradient conditions. This flux-based method of estimating field capacity is discussed and the differences between this method and the more common pressure-based method are illustrated. The drainage flux considered to be negligible will depend on the particular application; values between 10⁻⁶ and 10⁻⁸ cm/s were considered here. The observed differences in field capacity resulting from the negligible flux range considered produce significant differences in the available water capacity. These differences directly impact the calculated drainage. The effect of available water capacity on the water budget for waste disposal facility covers at an arid and humid site was illustrated using the HELP code. At the arid site, drainage decreased by a factor of 4 (from 25 to 6 mm/year) as the available water capacity increased from 0.101 to 0.199. At the humid site, drainage decreased from 190 to 173 mm/year over the same range of available water capacity. Finally, a simple procedure for the determination of an appropriate value for the negligible flux is discussed. Analysis of data from a lysimeter at Coshocton, Ohio, indicated that field capacity for the lysimeter soils was associated with a negligible drainage flux of about 3 × 10⁻⁷ cm/s.

The development of matric suctions in soils contributes to their shear strength, resulting in an enhanced factor of safety against bearing-capacity failure. In this paper, matric suction profiles of desiccated mine tailings are predicted from a steady-state solution for evaporative conditions, and from an isothermal mathematical model that simulates liquid and vapor water flow through soils. The shear-strength envelope with respect to matric suction is established by testing reconstituted tailings samples in a modified triaxial cell, in which matric suction can be controlled. The contribution of matric suction to the shear strength is interpreted as an additional apparent cohesion for use in bearing-capacity calculations. Because of the nonlinearity of the shear-strength profile, a numerical method of analysis is adopted to predict the ultimate bearing capacity of the desiccated tailings. A subsequent decrease in bearing capacity following 2D water infiltration into a partially capped tailings deposit and accompanying suction loss is investigated.

An analytical model is presented for the prediction of the amplification of compressional and shear waves produced by an explosion, or any other shock impact on the surface of a stratified soil deposit. This amplification is caused by multiple reflections of waves between the ground surface and an underlying parallel soil layer possessing different density and seismic velocity. The model developed may be easily applied for the protection of both buried and aboveground structures with the aid of suitable diagrams prepared in this work, which give, in a simple way, the enhancement factors by which particle velocities of direct waves should be multiplied to estimate the resultant particle velocities. The soil parameters that are taken into account in the analytical model and its simplified graphical solution are density, attenuation factor, and compressional- and shear-wave propagation velocities for the first two soil layers. Other parameters encountered are depth of the top soil layer, depth of burial of the structure, horizontal distance of the structure from the source, and trinitrotoluene equivalent of the source. The cube root scaling is considered for the attenuation of waves in soil with distance.

A pilot scale field test was conducted to demonstrate the feasibility of using prefabricated vertical drains (PVDs) for in-situ point extraction of benzene, toluene, ethylbenzene, and xylene (BTEX) under vacuum. Results indicated the achievement of an average flow rate of 16.7 mL/s for the five PVD systems. Grab samples from the effluent indicated an increase in retrieved BTEX concentration with time. Maximum retrieved concentrations in a 2-day period were ∼0.4 mg/L for benzene, 0.27 mg/L for toluene, 0.19 mg/L for ethylbenzene, and 0.025 mg/L for xylene. Based on the limited results of the pilot scale test, a full-scale remediation of the site using the PVDs system is deemed feasible.