Journal of Geotechnical and Geoenvironmental Engineering

Although the cylindrical cavity expansion theory should provide a sound basis for obtaining the undrained shear strength of clays from pressuremeter tests, the interpreted strengths are often inconsistent with data measured in high-quality laboratory tests. This paper investigates how the pressuremeter results are affected by disturbances that inevitably occur during device installation. The installation of self-boring and displacement-type pressuremeters is simulated using strain path analyses, with realistic effective stress-strain-strength properties described by the MIT-E3 model. Derived strengths obtained from the simulated expansion of displacement-type pressuremeters tend to underestimate the in situ/cavity expansion strength by amounts that depend on the relative volume of soil displaced, the time delay prior to testing, and the initial overconsolidation ratio of the clay. Interpretation procedures using the simulated contraction curves give much more reliable estimates of the true undrained shear strength. The simulated disturbance effects of self boring lead to derived peak shear stresses that are significantly higher than the reference undrained shear strengths. This overestimate depends on the volume of soil removed during installation and is enhanced when the finite membrane length is included in the analyses. Self-boring pressuremeter data from a well-documented test site in Boston confirm the general character of the predicted pressuremeter stress-strain behavior. The theoretical analyses underestimate the peak strengths derived from self-boring pressuremeter (SBPM) expansion tests, but match closely the measured postpeak resistance in the strain range of 3–6% (saddle point condition). Saddle point strengths are similar in magnitude to the shear strengths measured in laboratory undrained triaxial compression tests at this site. The current predictions are not able to explain the very high shear strengths derived from the SBPM contraction curves.

Changing the soil characteristics is a main concern to all civil engineers. Highway and foundation engineers are particularly more concerned with the subject. There are several methods to improve the soil characteristics. One of these methods is to add fine material, which fills the voids between the grains of the soil, helping to make the soil denser, thus gaining high resistance to penetration. This study uses statistical parameters of the soil grains distribution to predict the soil maximum dry density, then uses the fine biasness coefficient to predict the new density of the soil after mixing any amount of fine particles with the original soil. A mathematical formula is developed to make such a prediction. Lab testing results were compared with the results of the prediction. They were found to be in total agreement, and the margin of error was found to be quite low.

Footings are often subjected to eccentric loading due to (1) moments with or without axial forces; (2) the oblique loading; and (3) their location near the property line. Due to eccentric loading, the footing tilts and the pressure below the footing does not remain uniform. The tilt of footing increases with an increase in the eccentricity and the bearing capacity reduces considerably. Therefore, footing sizes increase and make the design uneconomical. The finite-element analysis of an angle shaped footing under eccentric loading has been carried out in the present study. One side vertical projection of footing confines the soil and prevents its lateral movement. It was concluded that footing subjected to uniaxial eccentric loads can be designed for no or negligible tilt by giving the footing an angle shape. The depth of footing projection will depend upon the eccentricity width ratio.

The use of shallow water covers (up to 2 m) to flood reactive sulfide mine tailings is a common method of reducing the environmental impact of mining. It relies on the low solubility and diffusivity of oxygen in water. In actual tailings ponds, however, wind-induced waves and turbulent mixing can lead to tailings resuspension and increased oxygen transfer. Laboratory experiments and numerical modeling were performed to examine the impact of resuspension on metal release from sulfide mine tailings, and to elucidate the nature of the flow field. The results indicated that resuspended tailings oxidized and released acidity and metals considerably more than tailings at rest. The oxidation and metal release rates increased with an increase in the degree of turbulence-induced mixing in the water cover. Computed wall shear stresses on the surface of the tailings ranged from 0.14 to 0.42 N/m², which were close to, but slightly above, the critical shear stresses of the tailings (0.12–0.17 N/m²). The flow energy was found to be positively correlated to the cumulative release of metals (zinc, nickel, copper, and ferric iron) and sulfate.

Secondary reinforcement in slopes is typically designed without any stability considerations. A rational stability analysis is attempted in this paper, based on shallow collapse mechanisms confined to the neighborhood of the slope face. The kinematic theorem of limit analysis is used to arrive at the necessary spacing of the secondary reinforcement and its strength and length. Analysis of a collapse limited to the soil between the layers of reinforcement is used to determine the required soil cohesion necessary to maintain stability. Since this cohesion depends on the size of the mechanism, the spacing of the secondary geosynthetic can be determined from this analysis. Some cohesion is usually present in the zone close to the slope face because of moisture in the soil, cementation due to a small amount of fine particles, or vegetation. Even a small amount of cohesion may have a significant effect on the stability. The strength and length of secondary reinforcement are determined from shallow collapse mechanisms engaging secondary reinforcement in tension. The slope face becomes most susceptible to failure when the soil becomes saturated, because of the seepage and buoyancy forces, and because of the loss of apparent cohesion. A more approximate analysis based on an infinite slope model is also shown. Its description is limited to the presentation of the concept. This method relies heavily on the cohesion distribution in the zone close to the slope face. Because an estimation of this distribution is difficult, the infinite slope model may be difficult to apply in practice.

A laboratory testing program was conducted to assess the use of foundry sands from gray iron foundries, typically called green sands, as hydraulic barrier materials. Foundry green sands are mixtures of fine uniform sand, bentonite, and other additives. Specimens of foundry sand were compacted in the laboratory at a variety of water contents and compactive efforts and then permeated in rigid-wall and flexible-wall permeameters to define relationships between hydraulic conductivity, compaction water content, and dry unit weight. Additional tests were conducted to assess how hydraulic conductivity of compacted foundry sand is affected by environmental stresses such as desiccation, freeze-thaw, and chemical permeation. Results of the tests show that the hydraulic conductivity of foundry sand is sensitive to the same variables that affect hydraulic conductivity of compacted clays (i.e., compaction water content, and compactive effort). However, hydraulic conductivities <10⁻⁷ cm/s can be obtained for many foundry sands using a broad range of water contents and compactive efforts, including water contents dry of optimum and at lower compactive effort. The hydraulic conductivity of foundry sand was generally unaffected by freeze-thaw, desiccation, or permeation with 0.1 N salt solution or municipal solid waste leachate, but was incompatible with acetic acid (pH = 3.5). Hydraulic conductivity of foundry sands correlates well with bentonite content and liquid limit, with hydraulic conductivity less than 10⁻⁷ cm/s being achieved for bentonite content ≥6% and/or liquid limit >20.

A static liquefaction flow failure occurred in the upstream slope of the North Dike of Wachusett Dam near Clinton, Massachusetts on April 11, 1907 during the first reservoir filling. The fine sands of the upstream dike shell liquefied and flowed approximately 100 m horizontally into the reservoir. This paper presents a description of the construction of the North Dike, failure of the upstream slope, and the results of stability analyses that were conducted to estimate the shear strength mobilized in the liquefied soils during failure. Analyses of the postfailure geometry, the prefailure geometry, and an analysis incorporating the kinetics of failure were conducted. The back-calculated shear strength considering the kinetics of failure is in agreement with other liquefaction flow failure case histories published in the literature. As a result, it is recommended that the kinetics of failure be considered to determine the shear strength mobilized during a liquefaction flow failure.

A method for estimating the local strain in a geomembrane due to the indentation of gravel particles is presented. The accuracy of various strain calculation methods is evaluated by a series of tests, and it is shown that the traditional arch elongation method provides only an approximate estimate of the magnitude of strain induced in the geomembrane due to indentation and does not adequately define the distribution of strain. Consideration of the combined membrane and bending strains as proposed here is shown to provide a better representation of the distribution of strains and enhances the evaluation of the peak strains in the geomembrane caused by local indentations. Large-scale tests are conducted using different protection layers, and the strains are reported based on both the arch elongation method and the combined bending and membrane theory. The results indicate that the best protection for the underlying geomembrane was provided by a sand-filled geocushion or a special rubber geomat, which limited strains induced by coarse (40–50 mm) angular gravel to 0.9% at 900 kPa and 1.2% at 600 kPa. The poorest performance was achieved using nonwoven geotextiles with a maximum strain of 8% being obtained with a 435 g/m² geotextile at 250 kPa and 13% with two layers of 600 g/m² geotextile at 900 kPa.