Time filter

Source Type

Midland, TX, United States

Lin C.,Terracon Consultants Inc. | Zhu W.,Hohai University | Han J.,University of Kansas
Journal of Materials in Civil Engineering | Year: 2013

Production and disposal of sewage sludge have raised increasing concerns due to their poor mechanical properties and negative environmental effect. Cement-based solidification/stabilization can improve the properties of sewage sludge so that it can be used either as an earth-construction material or landfills. To achieve this goal, a large amount of cement should be used, thus increasing the treatment cost and CO2 emission arising from cement production. To reduce cement usage, three inorganic additives (e.g., calcium-bentonite, fly ash, and kaolinite) were used and investigated in this study to improve the effectiveness of solidification/stabilization of sewage sludge with cement. The benefits of these additives to the treated sewage sludge were evaluated in terms of unconfined compressive strength and leaching of pollutants including alkalinity, chemical oxygen demand (COD), and heavy metals (e.g., copper, lead, and zinc). X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) were conducted to examine the mechanisms associated with the behavior of the treated sludge resulting from these additives. The test results show that calcium-bentonite was a favorable additive to improve the effectiveness of cement to solidify/stabilize the sewage sludge. As the ratio of sewage sludge, and cement, to calcium-bentonite by weight reached 1:0.2:0.2, the unconfined compressive strength of the treated sewage sludge could meet the requirement for landfilling at seven days and that of a construction material at 28 days. © 2013 American Society of Civil Engineers.

Tan Y.,Tongji University | Lin G.,Terracon Consultants Inc.
Journal of Performance of Constructed Facilities | Year: 2014

This paper introduces a comprehensive full-scale pile load test program on 457-mm (18-in.) square prestressed concrete (PSC) piles in Savannah, Georgia. The program consisted of pile driving analyzer testing during initial pile driving and restrikes, Statnamic tests, static axial compression load tests, and reciprocal lateral load tests. On the basis of the interpretation of the test data, some important findings were obtained: (1) the alluvial clays in Savannah can only provide very limited resistance; (2) the time-dependent pile capacity gain after pile driving (i.e., setup effect) was approximately proportional to the pile embedment length into the Marl formation; (3) the estimated equivalent static pile capacities from the Statnamic tests were comparable to those from the static axial load tests; (4) the Marl formation is a competent bearing stratum for piles; (5) the potential degradation of pile concrete stiffness caused by pile driving should be accounted for in pile capacity analysis; and (6) the piles exhibited stiffer response under the monotonic lateral loading condition than the cyclic lateral loading condition. Finally, predictions on both axial and lateral pile capacities, using the soil parameters derived from the instrumentation data and back-analysis of the pile load tests, were compared with the corresponding pile load test results. The comparisons demonstrate that in combination of the static-bearing capacity formulas and the LPILE program, the developed soil models can make reliable predictions on both the vertical and lateral behaviors of the PSC piles driven through the soft alluvial clays to end bearing in the Marl formation. © 2014 American Society of Civil Engineers.

Lamichhane S.,Terracon Consultants Inc. | Luke B.,University of Nevada, Las Vegas
International Journal of Geotechnical Engineering | Year: 2016

Earthquake ground motions (GMs) are developed for input to structural response analyses of a highway bridge in Las Vegas, Nevada (southwestern US), an area of arid climate and moderate seismicity. A target response spectrum for rock-outcrop ('bedrock') motions at the site is produced from a probabilistic seismic hazard analysis and GMs are found that are compatible with the target. Three approaches to generate input GMs are tested: a set of unscaled real (natural) GMs, a set of scaled real GMs, and a single, spectrally-matched GM. The input motions are filtered through a representative sediment column, nearly 400 m deep, to produce surface GMs. Both nonlinear and equivalent-linear analyses are conducted. The sediment column tended to deamplify short-period motions while amplifying long-period motions and shifting peak response to longer period, as expected. For nonlinear analysis, all three approaches to generating the input GMs yielded acceptable results. The single, spectrally-matched GM yielded the highest spectral accelerations. To explore effects of a heavily cemented layer (caliche) on site response, an alternative profile is tested. The 30-m depth-averaged shear wave velocity is unchanged, but a thick caliche layer is inserted just beneath it. In a third test, the caliche profile is truncated at the stiff inclusion. Only the nonlinear analyses showed effects of the caliche. The shallow profile predicted the highest amplification by far, demonstrating how consideration of only the upper 30 m of a sediment column can significantly overpredict short-period response. © 2016 Taylor & Francis.

Han J.,University of Kansas | Bhandari A.,University of Kansas | Bhandari A.,Terracon Consultants Inc. | Wang F.,Nanjing Southeast University
International Journal of Geomechanics | Year: 2012

The geosynthetic-reinforced pile-supported embankment is one of the favorable ground improvement techniques used in the construction of earth structures over a compressible soil when limited construction time is available and limited deformation is permissible. Various methods are available for the design of the geosynthetic-reinforced platform basedon various load transfer mechanisms from the embankment to the piles and the compressiblesoil. The existence of the geosynthetic layer makes the mechanisms more complex. This study focuses on the behavior of geogrid-reinforced embankments over piles compared with thebehavior of unreinforced embankments. The numerical simulations of the unreinforced and reinforced pile-supported embankments were conducted using the discrete element method (DEM). The embankment fill was simulated using unbonded graded aggregates of diameters ranging from 9.2 to 20.8 mm and the geogrid was simulated using bonded particles. This study investigated the changes of vertical and horizontal stresses and porosities, the vertical displacements within the embankment fill, and the deflection and tension in the geogrid. The simulation results showed that the coefficient of lateral earth pressure in the embankment fill changed from an initial at rest condition to a passive condition at certain locations after the compression of the compressible soil. The embankment fill dilated during the development of soil arching. The embankment load was transferred to the piles owingto the reorientation of the principal stresses. The results also showed that the geogrid reinforcement significantly reduced the total and differential settlements at the top of the embankment. © 2012 American Society of Civil Engineers.

Tetrachloroethene (PCE) releases at a former dry cleaner resulted in impacts to soil and shallow groundwater beneath and adjacent to the building. Subsurface impacts led to vapor intrusion with PCE concentrations between 900 and 1,200 micrograms per cubic meter (μg/m3) in indoor air. The migration pathways of impacted soil vapor were evaluated through implementation of a helium tracer test and vapor sampling of an exterior concrete block wall. Results confirmed that the concrete block wall acted as a conduit for vapor intrusion into the building. A combination of remediation efforts focused on mass reduction in the source area as well as mitigation efforts to inhibit vapor migration into the building. Excavation of soils beneath the floor slab and installation of a spray-applied vapor barrier resulted in PCE concentrations in indoor air decreasing by over 97.9 percent. Operation of an active ventilation system installed under the floor slab and groundwater remediation via injections of nano-scale zero valent iron (nZVI) further reduced PCE concentrations in indoor air by over 99.8 percent compared to baseline conditions. While significant reductions of PCE concentrations in groundwater were observed within two months after injection, maximum reductions to PCE concentrations in indoor air were not observed for an additional 12 months. © 2014 Wiley Periodicals, Inc.

Discover hidden collaborations