Scott J. Wasman

Construction material properties of slag from the high temperature arc gasification of municipal solid waste

Slag from the high temperature arc gasification (HTAG) of municipal solid waste (MSW) was tested to evaluate its material properties with respect to use as a construction aggregate. These data were compared to previously compiled values for waste to energy bottom ash, the most commonly produced and beneficially used thermal treatment residue. The slag was tested using gradations representative of a base course and a course aggregate. Los Angeles (LA) abrasion testing demonstrated that the HTAG slag had a high resistance to fracture with a measured LA loss of 24%. Soundness testing indicated a low potential for reactivity and good weathering resistance with a mean soundness loss of 3.14%. The modified Proctor compaction testing found the slag to possess a maximum dry density (24.04kN/m(3)) greater than conventionally used aggregates and WTE BA. The LBR tests demonstrated a substantial bearing capacity (>200). Mineralogical analysis of the HTAG suggested the potential for self cementing character which supports the elevated LBR results. Preliminary material characterization of the HTAG slag establishes potential for beneficial use; larger and longer term studies focusing on the materials possibility for swelling and performance at the field scale level are needed.

Evaluation of Drilled Shaft Capacity Using Embedded Sensors and Statnamic Testing

AbstractThis paper presents an application of the embedded data collector (EDC) approach using strain and acceleration measurements at the top and bottom of a pile (drilled shaft) during dynamic loading (Statnamic) for estimation of static side and tip resistance. For assessment of the skin friction, wave propagation along the pile was modeled as a one-dimensional (1D) wave equation with nonlinear static skin friction and viscous damping. The soil–pile system was divided into segments, and each segment was characterized with independent multilinear skin friction. The skin friction of each segment was determined by least-squares fitting of computed particle velocities to the measured data at the top and bottom of the pile. For assessment of the tip resistance, the pile tip was modeled as a single—degree-of-freedom nonlinear system. A nonlinear stiffness–displacement relationship was determined by balancing force and energy from inertia, damping, and stiffness against the measured tip data. The technique wa...

Shear Wave Velocity Profiles of Roadway Substructures from Multichannel Analysis of Surface Waves and Waveform Tomography

Assessment of roadway subsidence caused by embedded low-velocity anomalies is critical to the health and safety of the traveling public. Surface-based seismic techniques are often used to assess roadways because of data acquisition convenience and large depths of characterization. To mitigate the negative impact of closing a traffic lane under traditional seismic testing, a new test system that uses a land streamer is presented. The main advantages of the system are the elimination of the need to couple the geophones to the roadway, the use of only one source at the end of the geophone array, and the movement of the whole test system along the roadway quickly. For demonstration, experimental data were collected on asphalt pavement overlying a backfilled sinkhole that was experiencing further subsidence. For the study, a 24-channel land streamer and a propelled energy generator to generate seismic energy were used. The test system was pulled by a pickup truck along the roadway and the data were collected with 81 shots at every 3 m for a road segment of 277.5 m, with a total data acquisition time of about 1 h. The measured seismic data set was analyzed by the standard multichannel analysis of surface waves (MASW) and advanced two-dimensional (2-D) waveform tomography methods. Eighty-one one-dimensional shear wave velocity (VS) profiles from the MASW were combined to obtain a single 2-D profile. The waveform tomography method was able to characterize subsurface structures at a high resolution (1.5- × 1.5-m cells) along the test length to a depth of 22.5 m. Very low S-wave velocity was obtained at the repaired sinkhole location. The 2-D VS profiles from the MASW and waveform tomography methods are consistent. Both methods were able to delineate high- and low-velocity soil layers and variable bedrock.

Evaluation of LRFD Resistance Factors and Risk for Mechanically Stabilized Earth Walls

The use of Mechanically Stabilized Earth (MSE) walls is very common in congested urban areas. AASHTOs current LRFD resistance values were established from Allowable Stress Design Factors of Safety. Variability of soil friction angle, unit weight, cohesion, etc. is not considered. This study investigates the influence of soil property variability on MSE wall sliding and bearing stability and compares Capacity Demand Ratio (CDR) distributions from conventional analytical approaches with laboratory centrifuge model results. Next, the probability of failures (CDR < 1.0) and associated variability is applied in risk assessment of two MSE walls used in existing transportation infrastructure subsystems. The risk assessment was used to develop recommended probability of failures in design to meet the associated cost of repair if catastrophic failures of the walls are to occur.