Construction and Long-Term Performance of Transportation Infrastructure Constructed Using EPS Geofoam on Soft Soil Sites in Salt Lake Valley ,
The Utah Department of Transportation (UDOT) and the Utah Transit Authority (UTA) have made extensive use of EPS embankment for several major interstate, light rail, and commuter railway embankments in Salt Lake Valley, Utah. Constructed between 1998 and 2001, the Interstate 15 Design Build Reconstruction Project involved the widening of interstate embankments within a 27 km narrow corridor and limited right-of-way. Approximately, 100,000 m of EPS fill was placed at various locations to minimize post-construction settlements of deep, compressible lake deposits. This paper presents results of long-term monitoring of EPS fills and comparison with other geotechnologies. Geofoam embankments had the best overall settlement performance of the technologies monitored. Gap closure and deformation of the geofoam embankment due to placement of the load distribution slab and overlying roadway materials was about 1% of the embankment height. In addition, at 3300 South Street, the foundation soil settled about 15 mm due to placement of the embankment and overlying loads. The face of the embankment settled an additional 25 mm in a 5-year period due to additional pressure of a 1.5m toe berm placed at the base of the tilt-up wall. Total post-construction settlement (foundation settlement and geofoam creep) is expected to be about 50 mm at the wall face for a 10-year postconstruction period. The trend of post-construction settlements suggest that geofoam embankments are performing as designed and will meet the 50-year post-construction deformation limit of 1% creep strain. Overview of the I-15 Reconstruction Project The Utah Department of Transportation (UDOT) togeth er with Wasatch Constructors finished the $1.6 billion reconstruction of Interstate 15 (I -15) that runs through Salt Lake City, Utah in 2001 just prior to the start of the 2002 Winter Oly mpics. The interstate embankment was widened from eight lanes to ten general-purpose lan s, plus two high occupancy vehicle lanes, within an existing north-south alignment that runs through the middle of the densely populated Salt Lake Valley. In this area, parts of the I-15 a lignment are located atop extensive deposits of relatively compressible lake sediments. Collateral consolidation settlement along this widened alignment had to be minimized to prevent differenti al settlement damage and subsequent
Numerical Modeling of Geofoam Embankments
In 2001, the Utah Department of Transportation completed a 4-year $1.4 billion I-15 reconstruction project in Salt Lake City, Utah. This project included widespread use of expanded polystyrene geofoam as lightweight embankment at important utility crossings and where close proximity to existing buildings necessitated minimizing consolidation settlement. This paper presents construction and long-term monitoring results for some of these embankments with numerical modeling of the field measurements. Fast Lagrangian Analysis of Continua, a finite-difference program, was used to estimate the complex stress distribution and the displacements (i.e., strain) that developed in select geofoam embankments. The writers used a bilinear elastic model to produce reasonable estimates of gap closure, block seating, and the subsequent elastic compression of the geofoam embankment at higher stress levels. Such estimations are important for modeling and designing geofoam embankments and potential connections with other systems. The calculation of the complex stress distribution and displacements that develops in a geofoam embankment has application to settlement, lateral earth pressure against retaining and buried walls, slope stability, and seismic design of geofoam embankments.
Storage of Natural Gas as Frozen Hydrate
The formation of natural gas hydrates is a well-known problem in the petroleum and natural gas industries. Hydrates are solid materials that form when liquid water and natural gas are brought in contact under pressure. Hydrate formation need not be a problem. On the contrary, it can be an advantage. The volume of hydrates is much less than that of natural gas. At standard conditions, hydrates occupy 150 to 170 times less volume than the corresponding gas. Typically, natural gas hydrates contain 15% gas and 85% water by mass. It follows that hydrates can be used for large-scale storage of natural gas. Benesh proposed using hydrates to improve the load factor of natural gas supply systems. The author suggested that hydrates could be produced by bringing liquid water into contact with natural gas at the appropriate temperature and high pressure. The hydrate then would be stored at a temperature and pressure where it was stable. When gas was needed for the supply system, the hydrate would be melted at low pressure. The stability of a natural gas hydrate during storage at atmospheric pressure and below-freezing temperatures was studied in the laboratory. The gas hydrate was produced in a stirred vesselmore » at 2- to 6-MPa pressure and temperatures from 0 to 20 C. The hydrate was refrigerated and stored in deep freezers at [minus]5, [minus]10, and [minus]18 C for up to 10 days. The natural gas hydrate remained stable when kept frozen at atmospheric pressure.« less