James L. Hanson

Ultrasonic Testing for Evaluation of Stabilized Mixtures

Tests were conducted to evaluate the feasibility of using ultrasonic testing for stabilization applications. The ultrasonic testing consisted of determining primary-wave (P-wave) velocities of stabilized mixtures. The ultrasonic method involves a simple and fast test procedure that allows for repeated assessment of a sample over time. For the testing program, tests were conducted on a high plasticity clay stabilized with lime, cement, and fly ash and a Type F fly ash stabilized with lime and cement. Compaction characteristics of the mixtures were determined using modified Proctor tests. Unconfined compression tests were used to determine compressive strength and modulus of the mixtures immediately after sample preparation and after 7-day and 28-day curing periods. Ultrasonic tests were conducted on the compaction and compression test samples, and the test results were correlated. Variation of velocity with water content demonstrated a similar trend to the variation of dry density with water content for the soil. The velocity increased with increasing density for both soil and fly ash. For compression characteristics, velocity increased with increasing modulus for both soil and fly ash. The velocity correlated well with the unconfined compressive strength of fly ash samples. However, this trend was not as well defined for the soil. Overall, the test program demonstrated that ultrasonic testing can be used effectively to evaluate stabilized materials. P-wave velocity correlations can be used to verify the quality of field placement of stabilized mixtures and to improve mixture design procedures.

Incorporating Thermal Effects in Modeling of MSW Landfills

Heat is one of the primary byproducts of biodegradation of municipal solid waste (MSW). Biodegradation of MSW in landfills induces changes in physical properties, mechanical response of MSW, and flow of leachate within the MSW pore spaces. Moreover, biodegradation of MSW in landfills is temperature dependent and consequently the engineering properties of MSW are all influenced by waste temperatures. Thus, landfills are complex systems with interrelated processes and it is crucial to account for all these interdependencies to accurately predict the coupled behavior of MSW. In this study, a coupled-thermo-hydro-bio-mechanical model was formulated that incorporates the effect of temperature on heat generation and biodegradation of MSW. The model integrates a two-phase flow hydraulic model, a plane-strain formulation of the Mohr-Coulomb mechanical model, a first order decay biodegradation model, and a one-dimensional heat conduction model with temperature-dependent heat generation. Numerical simulations were carried out using a typical landfill configuration with leachate injection simulating a bioreactor landfill. The simulations were carried out with and without temperature effects to determine the influence of temperature on MSW behavior. The results indicate a significant influence of temperature on the MSW response (degradation and settlement) and underscore the importance of incorporating thermal effects in numerical modeling of MSW landfill systems.

Temperature effects on the swelling and bentonite extrusion characteristics of GCLs

This investigation was conducted to evaluate effects of temperature on swelling and bentonite extrusion properties of GCLs. The swelling characteristics were determined using standardized test procedures and extrusion characteristics were determined using a new test method developed by the authors. Tests were conducted on a conventional medium-weight woven/nonwoven GCL. The range of test temperatures was 2 to 98°C (swelling tests) and -5 to 100°C (extrusion tests). The extrusion tests were conducted under stresses between 100 and 400 kPa and moisture contents between 50 and 150%. Temperature had significant effects on both swell and extrusion. The swell index ranged from 21 mL/2g at 2°C to 36.5 mL/2g at 98°C, with the largest increase occurring from 20 to 40°C. The amount of extrusion ranged from nearly 0 to 40.5 g/m with generally decreasing extrusion with temperature from 2 to 100°C. At a given temperature, extrusion increased with increasing stress and moisture content.