Timothy D. Stark

Aluminum Waste Reaction Indicators in a Municipal Solid Waste Landfill

Subtitle D landfills may contain aluminum from residential and commercial solid waste, industrial waste, and aluminum pro- duction wastes. Some aluminum-bearing waste materials, particularly aluminum production wastes, may react with liquid in a landfill and cause uncontrolled temperature increases, significant changes in gas composition and pressure, nuisance odors, and changes in leachate composition and quantity. Such reactions may also cause degradation of leachate quality (e.g., increased ammonia, sodium, potassium, chloride, and TDS concentrations), combustion of the surrounding waste, damage to engineered components (gas collection systems, leachate collection systems, and liner system materials), and slope instability. Temperatures exceeding 150°C (300°F), generation and accumulation of undesirable explosive and toxic gases (e.g., hydrogen, acetylene, ammonia, carbon monoxide, and benzene), and gas pressures exceeding 210 kPa (30.5 psi) have been observed. Water from leachate recirculation, precipitation, the waste, or groundwater infiltration can initiate the exothermic reaction if aluminum production wastes are present. This paper uses a case history to illustrate some indicators of an aluminum reaction and problems that can develop from such a reaction in a Subtitle D landfill. DOI: 10.1061/(ASCE)GT.1943-5606.0000581.

Constant Volume Ring Shear Apparatus

The paper describes a constant volume ring shear apparatus that allows the measurement of the undrained peak and residual shear strengths of cohesive soils. The undrained peak and residual strengths are applicable to seismic stability evaluations of slopes comprised of or founded on cohesive soil. The constant-volume ring shear apparatus is equipped with a mechanism to adjust the normal stress during shear and a new specimen container that allows undisturbed specimens to be trimmed directly into the container. The normal stress is adjusted during shear such that the height of the soil specimen remains constant. This results in a constant volume or undrained shear condition. The results of constant volume ring shear tests on normally consolidated Drammen clay are compared with the results of undrained direct simple shear tests. The comparison reveals that the undrained peak shear strength obtained using the constant volume ring shear and direct simple shear apparatuses are in agreement. However, the constant-volume ring shear apparatus allows the measurement of the undrained residual strength because it permits unlimited continuous shear displacement.

Aluminum reactions and problems in municipal solid waste landfills

Aluminum enters municipal solid waste (MSW) landfills from untreated raw curbside trash (MSW), industrial waste, and aluminum production wastes variously called dross, baghouse fines, salt cake, and other designations. Aluminum related reactions can arise and become problematic for landfill operations by generating undesirable heat, liquid leachate, and gases, such as hydrogen, hydrogen sulfide, carbon monoxide, and ammonia. Temperature excursions up to ∼150°C ( 300°F ) and landfill gas pressures exceeding 210 kPa have been observed. Water from the MSW, precipitation, injection, and/or surface water management can result in sufficient water to trigger problematic aluminum related reactions. Another source of water in a MSW landfill is leachate recirculation, which is not recommended if substantial aluminum is present in the landfill mass because it can lead to a problematic aluminum related reaction. This paper examines the chemical reactions involving aluminum in landfills and the negative consequences o...

Bromhead Ring Shear Test Procedure

Existing test procedures and a proposed modification for the Bromhead ring shear apparatus were found to yield drained residual strengths higher than values back-calculated from field case histories. A new test procedure is presented that yields drained residual strengths that are in excellent agreement with field case histories. The new test procedure utilizes the unmodified Bromhead ring shear apparatus and limits the settlement of the top porous stone, due to consolidation and/or soil extrusion during drained shear, to 0.75 mm. Since the specimen is confined radially by the specimen container, limiting the settlement of the top porous stone minimizes the wall friction that develops along the inner and outer circumferences of the specimen. The reduced wall friction results in the lowest measured residual strength and the best agreement with field case histories.

Service Life of HDPE Geomembranes Subjected to Elevated Temperatures

Subtitle D landfills may experience elevated temperatures for a variety of reasons such as hydration of combustion ash, waste biodegradation with and without leachate recirculation, aluminum production waste and combustion ash reactions, and wastes received with elevated temperature. Elevated temperatures can reduce service life or effectiveness of high density polyethylene (HDPE) geomem- branes by accelerating antioxidant depletion of geomembranes and polymer degradation. A case history is presented to illustrate the potential effects of elevated temperatures and time-temperature history on a HDPE geomembrane and the associated reduction in service life or effectiveness. The geomembrane service life was influenced by the peak temperature, e.g., 60-80°C, the duration of peak temperatures (time-temperature history), and the time to complete antioxidant depletion. This paper also discusses possible criteria for assessing the service life of geomembranes, such as applicable engineering properties, locations for service life assessments, definitions of geomembrane service life, and measures that could be adopted if service life were reduced significantly. DOI: 10.1061/(ASCE)HZ.2153-5515.0000188.

Empirical Correlations: Drained Shear Strength for Slope Stability Analyses

Empirical correlations provide estimates of parameter values for preliminary design, verification of laboratory shear test data, and confirmation of back-analysis of a failed slope. The empirical correlations presented herein use liquid limit, clay-size fraction, and effective normal stress to capture the variability and stress-dependent nature of drained residual and fully softened strength envelopes. This paper describesthetestingandanalysisusedtoincreasethenumberofdatapointsintheexistingcorrelations,expandtheresidualstrengthcorrelation to include an effective normal stress of 50 kPa, and develop correlations between values of liquid limit and clay-size fraction measured using sampleprocessedthroughaNo.40sieve(ASTMprocedure)andvalues derivedusingball-milled/disaggregated sample. Inaddition,equations are presented to express the empirical correlations used to develop a spreadsheet that estimates the residual and fully softened friction angles based on entered values of liquid limit and clay-size fraction. DOI: 10.1061/(ASCE)GT.1943-5606.0000824.

Shear Strength in Preexisting Landslides

Drained residual shear strength is used for the analysis of slopes containing preexisting shear surfaces. Some recent research suggests that preexisting shear surfaces in prior landslides can gain strength with time. Torsional ring and direct shear tests performed during this study show that the recovered shear strength measured in the laboratory is only noticeably greater than the drained residual strength at effective normal stress of 100 kPa or less. The test results also show that the recovered strength even at effective normal stresses of 100 kPa or less is lost after a small shear displacement, i.e., slope movement. An effective normal stress of 100 kPa corresponds to a shallow depth so the observed strength gain has little, if any, impact on the analysis of deep landslides. This paper describes the laboratory strength recovery testing and the results for soils with different plasticities at various rest periods and effective normal stresses.

Modified Bromhead Ring Shear Apparatus

The main factor affecting the drained residual strength measured in the Bromhead ring shear apparatus is the magnitude of wall friction developed along the inner and outer circumferences of the confined specimen. The magnitude of wall friction increases with the depth of the remolded specimen, and thus the plane of least wall friction occurs at or near the soil/top porous stone interface. As the top porous stone settles into the specimen container, the wall friction influencing the shear plane increases, causing an increase in the measured residual strength. A new specimen container is proposed for the Bromhead ring shear apparatus that allows a remolded specimen to be overconsolidated and precut prior to drained shearing. This minimizes settlement of the top platen and the horizontal displacement required to reach a residual strength condition. As a result, a multistage test can be conducted without excessive settlement and thus wall friction occurring in the new specimen container. The use of a multistage test significantly reduces the time required to establish a drained residual failure envelope. The use of an overconsolidated and precut specimen also provides a better simulation of the field conditions that lead to a large post-peak decrease in drained strength in clayshales, claystones, and mudstones, and residual strengths that are in excellent agreement with field case histories.

DIFFERENTIAL MOVEMENT AT EMBANKMENT-BRIDGE STRUCTURE INTERFACE IN ILLINOIS

Settlement of roadway pavement surfaces near highway bridge abutments often leads to abrupt grade differences at the abutments. These grade differences subject vehicles to a bump, which may lead to driver discomfort and potentially unsafe driving conditions. Furthermore, differential movement requires costly and repeated maintenance work that usually impedes the flow of traffic. The sources of differential movement in Illinois can be divided into six major categories: (a) compression or erosion of materials at the approach embankment-abutment interface, (b) a broken approach slab, (c) compression of foundation soils, (d) compression or internal erosion of embankment soils, (e) poor construction grade control, and (f) areal distortion of foundation soils. An approach gradient equal to or greater than 1/100 to 1/125 appears to cause rider discomfort and therefore is proposed as a criterion for initiating remedial measures.

Detection of Aluminum Waste Reactions and Waste Fires

AbstractAluminum production wastes (APW) placed in Subtitle D regulated landfills may react exothermically and cause uncontrolled temperature increases, large volumes of explosive and toxic gasses, increases in landfill gas pressure and flow, intense odors, undesirable changes in leachate composition, increased leachate production, and most importantly, smoldering combustion of the surrounding solid waste. The landfill liner and explosive gas extraction and leachate collection systems can be damaged by heat from the reaction and/or accompanying combustion. Slope failure also may result from increased gas and liquid pressures and the reduction of waste mass shear strength attributable to subsurface combustion compounding existing or initiating damage to engineered components. Therefore, landfills that have received APW need early detection of a potential exothermic reaction to respond promptly to prevent subsequent subsurface combustion. This paper presents techniques to quickly evaluate landfill gas and t...