Midland, TX, United States
Midland, TX, United States

Time filter

Source Type

Thakur J.K.,Terracon Consultants Inc. | Han J.,University of Kansas | Parsons R.L.,University of Kansas
Journal of Materials in Civil Engineering | Year: 2017

A significant amount of recycled asphalt pavement (RAP) material is produced from flexible pavement rehabilitation projects. RAP can be used as a base course material for sustainable pavement construction. Performance of a pavement largely depends on the strength of its foundation, which consists of the subgrade and base course layers. Geocell was used in this study to increase the strength of RAP bases. Nine large-scale laboratory cyclic plate loading tests were conducted on unreinforced and geocell-reinforced RAP bases with three different thicknesses (150, 230, and 300 mm) over weak and moderate subgrades to investigate the influence of geocell confinement, base course thickness, base course strength, and subgrade strength on permanent and resilient deformations of RAP bases. The subgrade was prepared by mixing Kansas River sand with kaolin and compacted at weak [target California bearing ratio (CBR)=2%] and moderate (target CBR=5%) strengths. The test results showed that geocell confinement improved the performance of reinforced RAP bases by reducing permanent surface deformations and increasing resilient deformations and percentages of resilient deformation as compared with those of unreinforced bases. The RAP bases over the moderate subgrade performed better than those over the weak subgrade. Subgrade strength had a more pronounced effect than geocell confinement on the properties of RAP bases. Geocell confinement was more beneficial for the bases over the weak subgrade than those over the moderate subgrade. The relative improvement factors (RIFs) of the reinforced bases with respect to the unreinforced bases and the bases over the moderate subgrade with respect to the bases over the weak subgrade ranged from 1.1 to 11.4 and 1.2 to 17.2, respectively. The permanent deformation increased with the number of loading cycles and the RIFs increased with the permanent surface deformation of RAP base sections. © 2016 American Society of Civil Engineers.

Swaminathan “Vasan” Srinivasan has been elevated to president of Terracon Consultants Inc. from chief operating officer. In the new role, Srinivasan succeeds David Gaboury, who continues as chairman and CEO. An environmental and geotechnical consultant, Terracon ranks at No. 30 on ENR’s list of the Top 500 Design Firms, with $602 million in revenue and 3,500 employees. Vanderbilt University, Nashville, has re­appointed Philippe Fauchet to a second five-year term as dean of its school of engineering, beginning on July 1. The school says undergraduate enrollment rose 15% since 2012, and graduate enrollment is up 11%. It had about 2,000 students enrolled as of fall 2015, says its website; about 30% of undergraduates are women. The school also says it is experiencing “negative attrition,” contending that more students are earning undergraduate engineering degrees than the cohort that declared the major as freshmen. U.K.-based contractor Laing O’Rourke plc has named Sir John Parker chairman, effective later this year. He is set to succeed firm founder Ray O’Rourke, who remains CEO. Parker is former president of the Royal Academy of Engineering and a visiting fellow at Oxford University. He also held senior roles in several business sectors, including chairman of global mining firm Anglo-American plc, which he left in February. Richard McKinney has joined AECOM as vice president of IT strategy in its management services group’s systems engineering and information solutions business. He had been chief information officer of the U.S. Transportation Dept. and a senior adviser to the secretary of transportation on IT issues.

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.

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.

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.

Sallam A.M.,Terracon Consultants Inc | Casey K.G.,Ford Motor Company
Geotechnical and Structural Engineering Congress 2016 - Proceedings of the Joint Geotechnical and Structural Engineering Congress 2016 | Year: 2016

The new Florida Hospital for Women is located on the main campus and will provide a new era of high tech care for the women of Central Florida. The twelve story building includes a full basement and is situated on a tight urban site. A cast in place reinforced concrete flat plate structural framing system was selected. Column loads varied from 1800 to 3900 kips. The geotechnical field explorations included SPT borings and CPT soundings to about 100 feet deep. The subsoil consisted of medium dense sand followed by medium stiff clays and silty to clayey sands underlain by the Hawthorne Group soils. Iterative foundation design process was developed and executed between the structural and geotechnical engineers to design the most economical foundation system to support the building. Settlement analysis was performed utilizing numerical modeling to provide accurate subgrade reaction modulus. A soil mat foundation was selected which offered better stress distribution and minimized differential settlement; however total estimated settlements were in the order of 3 inches. The design team along with the owner agreed to take the risk of approving the building total and differential settlement and account for it in the final design. Few columns were instrumented and monitored for settlement throughout the construction process. Recorded settlements were in the order of 50% of the estimated settlements. This paper summarizes the structural components, the geotechnical aspects, foundation design, and construction challenges of the project. © ASCE.

Robinson J.D.,Terracon Consultants Inc. | Robinson J.D.,Mississippi State University | Vahedifard F.,Mississippi State University
Climatic Change | Year: 2016

California is currently suffering from a multiyear extreme drought and the impacts of the drought are anticipated to worsen with climate change. The resilience of California’s critical infrastructure such as earthen levees under drought conditions is a major concern that is poorly understood. California maintains more than 21,000 km of urban and nonurban levees which protect dry land from floods and deliver two-thirds of the state’s drinking water. Many of these levees are currently operating under a high failure risk condition. This essay argues that California’s protracted drought can further threaten the integrity of these already at-risk levee systems through the imposition of several thermo-hydro-mechanical weakening processes. Pertinent facts and statistics regarding California’s drought and current status of its levees are presented. Lessons from previous catastrophic levee failures and major damages which occurred under similar events are discussed. Weakening processes such as soil-strength reduction, soil desiccation cracking, land subsidence and surface erosion, and microbial oxidation of soil organic carbon are comprehensively evaluated to illustrate the adverse impacts that the ongoing California drought can have on levees. This essay calls for further research in light of these potential drought-induced weakening mechanisms to support adaptation and mitigation strategies to possibly avert future levee failures. These weakening processes can threaten any drought-stricken infrastructure interfacing with soil, including embankments, roads, bridges, building foundations, and pipelines. © 2016 Springer Science+Business Media Dordrecht

Rollins K.M.,Brigham Young University | Jessee S.J.,Terracon Consultants Inc.
Journal of Bridge Engineering | Year: 2013

The passive force-deflection relationship for abutment walls is important for bridges subjected to thermal expansion and seismic forces, but no test results have been available for skewed abutments. To determine the influence of skew angle on the development of passive force, laboratory tests were performed on a wall with skew angles of 0, 15, 30, and 45. The wall was 1.26 m wide and 0.61 m high, and the backfill consisted of dense compacted sand. As the skew angle increased, the passive force decreased substantially, with a reduction of 50% at a skew of 30. An adjustment factor was developed to account for the reduced capacity as a function of skew angle. The shape of the passive force-deflection curve leading to the peak force transitioned from a hyperbolic shape to a more bilinear shape as the skew angle increased. However, the horizontal displacement necessary to develop the peak passive force was still between 2 and 4% of the wall height. In all cases, the passive force decreased after the peak value, which would be expected for dense sand; however, at higher skew angles, the drop in resistance was more abrupt. The residual passive force was typically 40% lower than the peak force. For nearly all skew angles, the transverse shear resistance exceeded the applied shear force on the wall so that transverse movement was minimal. Computer models using the plane strain friction angle were able to match the measured force for the no skew case as well as for skewed cases when the proposed adjustment factor was used. © 2013 American Society of Civil Engineers.

Tan Y.,Tongji University | Tan Y.,WPC Inc. | Lin G.,Terracon Consultants Inc.
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2013

Although many studies have been done to investigate the axial behaviors of open-ended piles in sands, few studies have been reported for weak clayey silts. To develop reliable models for the design of open-ended steel-pipe piles driven into 29-m-thick varved clayey silt deposits, a series of full-scale field load tests including large-strain dynamic tests and static cyclic axial-compression-load tests was conducted on two groups of instrumented piles. Through analysis of the test data, soil parameters were back-calculated for estimation of pile capacities using the static-bearing-capacity formulas and cone-resistance-based methods. The comparisons between the calculated results and the field load test data demonstrated that the following considerations can be adopted in the design of static compression capacities of an open-ended pipe pile penetrating through thick varved clayey silts to end-bearing in dense cohesionless soils: (1) a fully plugged condition can be assumed, (2) cone resistance with an upper limit of 4,788 kPa (100 ksf) can be used for unit base resistance on the soil plug, and (3) exterior unit shaft resistance can be estimated using two-thirds of the total unit shaft resistance. © 2013 American Society of Civil Engineers.

Sebastian Bryson L.,University of Kentucky | Ortiz R.,Terracon Consultants Inc
Geotechnical Special Publication | Year: 2016

Cementitous grout is often used in permeation grouting applications, such as in seepage cutoff. However, ordinary Portland cement can be ineffective for permeation grouting of fine-grained sands or in sands with significant amounts of fines. Ultrafine cement grout thus becomes a viable alternative material for grout applications in these types of soils. While a major benefit of ultrafine grout is its penetration ability into the soils with relatively low hydraulic conductivity, the strength of the ultrafine grouted soil mass is not thoroughly discussed in literature. This study investigated initial conditions that could affect grout application effectiveness. An apparatus was developed so that a controlled volume of grout could be injected into a soil specimen. This study found that increases in water-To-cement ratio have a significant effect on the unconfined compressive strength of the neat grout. Grout penetration rates through the samples decreased as matric suction increased. The observed grout penetration rates were observed to be an inverse function of the unsaturated hydraulic conductivity. Also, the strength of the grouted sand was observed to increase as the matric suction increased. The results of this study suggest that knowledge of matric suction may be useful for estimating injection penetration rates and strength of ultrafine grouted sand. © ASCE.

Loading Terracon Consultants Inc. collaborators
Loading Terracon Consultants Inc. collaborators