Alaa K. Ashmawy

HYDRAULIC PERFORMANCE OF UNTREATED AND POLYMER-TREATED BENTONITE IN INORGANIC LANDFILL LEACHATES

Short- and long-term exposure to inorganic solutions can cause significant degradation of the hydraulic properties of bentonite clay used in geosynthetic clay liners (GCLs). In particular, the increase in hydraulic conductivity due to cation exchange when Na-montmorillonite is subjected to leachates rich in Ca and Mg has caused problems in incinerator ash landfill liners located in wet environments, where large quantities of leachates are generated. Experimental results are presented to evaluate the immediate change in hydraulic conductivity of seven types of GCL clays upon permeation with leachate generated from three ash landfills. The composition of the ash, which is a by-product of the incineration of municipal solid waste (MSW), in turn influences the composition of the resulting leachate. Falling head permeability tests were performed on flexible-wall permeameter specimens, with back-pressure saturation. Chemical analysis shows that the three leachate products contain high, medium, and low concentration Ca and Mg cations. The clay component of GCL materials tested in this study consists of regular and polymer-treated bentonite. Polymer treatment is believed to render the clay non-reactive to many organic and inorganic chemicals. The results of this study indicate that: (1) polymer treatment is generally more beneficial if the clay is first saturated with water and not directly with the leachate; (2) high swell potential of the bentonite is more advantageous than polymer treatment, especially when low hydraulic conductivity is required in the short term and if the clay is pre-hydrated. Experiment setup and special specimen preparation procedures are also discussed.

Variations in membrane contact patterns of reconstituted sand specimens

An integral component of most triaxial tests conducted on soil specimens is the latex membrane that encloses the specimen to separate the soil from the confining medium. The penetration of the latex membrane into the peripheral voids of a sand specimen during application of confining stress can cause significant errors in subsequent triaxial test results. Analytical solutions are commonly used to account for this source of error by predicting the shape of the deflected membrane based on a sand particle-membrane contact pattern assumed to be represented by four spheres of diameter D sub 50 whose centers form a square of length D sub 50 on a plane parallel to the undeflected membrane. This paper presents the findings of a study that used image analysis to study actual contact patterns and compare these with the generally assumed configuration. The results show that the generally assumed constant configuration does not reflect the variability of actual patterns, which are a function of the specimen relative density and preparation method and may therefore grossly underestimate the amount of membrane penetration. The study shows that an increase in relative density results in a decrease in inter-contact distance, regardless of the specimen preparation method, and that the inter-contact distance at the sand-membrane interface is larger and more variable for moist tamped than air-pluviated specimens at any given density. These observations suggest that the sand-membrane contact patterns assumed by future analytical solutions, at a minimum, will need to take specimen relative density and preparation method into account if the amount of membrane penetration is to be more accurately predicted.

RECYCLED MATERIALS RELATIONAL DATABASE: DESIGN AND IMPLEMENTATION ASPECTS

Although there has been a rise in the use of recycled materials in highway and geotechnical systems, many tons of potentially useful industrial and domestic by-products are still being discarded in the United States each year.. While extensive research has been conducted to investigate the use of recycled materials in engineering applications, the dissemination of the findings is often limited. The problem is compounded by the lack of a single resource containing relevant engineering and environmental characteristics of each material; the tendency of the researchers to publish their findings in technical reports rather than archived publications; and the wide discrepancies among local and state environmental regulations and acceptability. A relational database is proposed as a method to improve dissemination and implementation of recycled materials research. A comprehensive review is conducted on data available for a wide variety of recycled environmental data and information from case histories are organized into approximately 10 tables in a relational database management system (DBMS). More than 30 parameters, including engineering properties, availability and cost, are recorded for 21 materials in a highly-organized compendium. Through a simple user interface, a vast amount of data can be stored to implement a recycled material program based on historic and current data. The DBMS is updatable and the design is amendable to account for future expansion.

An Apparatus for Direct Shear, Pullout, and Uniaxial Testing of Geogrids

In this paper, design and calibration procedures for a new large-scale testing apparatus for testing geosynthetic-soil systems are described. The multiple functionalities of the apparatus are implemented through the use of a single loading frame, driving mechanism, instrumentation, and data acquisition system for 3 distinct modes of loading: pullout, direct shear, and uniaxial loading. The design is similar to a conventional pullout device, but also includes key modifications and additional modules to adapt it for additional types of experiments. A series of pullout experiments were performed to validate the functionality of the apparatus and to examine the relationship between the geometry of the geogrid opening and its pullout resistance.