Dawit Negussey

Preparation of Reconstituted Sand Specimens

Review and assessment of sand sample preparation techniques from both theoretical and experimental viewpoints are presented. Sample densities obtained by air pluviation are shown to be sensitive to rate of pouring and drop height. Terminal velocity is reached at a very small drop height, and homogeneous samples of the same initial density tend to be formed by pluviation of uniform sand in water. Uniformly dense samples obtained by vibration of loose pluviated samples show no detectable difference in behavior when compared to samples densified by control of drop height only. Effective confinement during densification by vibration appears to prevent formation of a loose top layer. A loose top layer in an otherwise dense sample leads to a marked decrease in liquefaction resistance. Preparation of triaxial sand samples by pluviation in water is recommended because it results in initially saturated specimens, and homogeneous samples of desired densities can be replicated without difficulty.

Stabilization of embankment slope with geofoam

A case history is presented describing the use of expanded polystyrene (EPS) geofoam blocks to treat an unstable roadway embankment slope involving clayey soils. The selection of the geofoam treatment was based upon its ability to be constructed and have the least impact on both the environment and adjacent homeowners. The site subsurface conditions, engineering properties of EPS, design analysis, and construction phases are reviewed. Potential traffic safety problems associated with differential icing of roadways caused by the presence of geofoam blocks beneath the pavements were minimized by using a thicker subbase layer in the geofoam-treated area. Data from an instrumentation program consisting of an inclinometer, extensometers, and thermistors are presented. Pavement temperature readings collected from areas with and without geofoam treatment are compared to investigate potential differential icing on the roadway.

An Investigation of Geofoam Interface Strength Behavior

Use of EPS (expanded polystyrene) geofoam as an ultra lightweight fill for construction over areas of soft ground has increased in recent years. An investigation of the interface friction between geofoam and construction materials that are commonly used with geofoam are presented in this paper. The interfaces studied included geofoam to geofoam, in dry and wet conditions. Geofoam to cast in place concrete as well as geofoam to geomembrane interfaces were also tested. Interface strengths between geofoam and HDPE as well as PVC geomembranes were determined. The effect of geofoam surface degradation due to extended exposure to sunlight on interface strength and adhesion bonding with cast in place were evaluated using field samples and samples degraded by accelerated weathering in the laboratory. The results indicate material density; sample size, stress level and surface moisture do not have significant influence on geofoam to geofoam interface strengths. A strong adhesion bond developed between geofoam and cast in place concrete. Both the peak and residual strength for geofoam and cast in place concrete surfaces were much greater than for geofoam to geofoam interfaces. Degradation due to exposure to sunlight and accelerated weathering in the laboratory reduced the strength of adhesion bonding between geofoam and cast in place concrete. The interface strength between geofoam and geomembranes was found to be much lower than any of the geofoam interfaces.

Sample size effects on the behavior of EPS geofoam

Expanded polystyrene (EPS) geofoam has now been used around the world as a remarkable lightweight soil substitute for a variety of geotechnical applications in soft ground construction. Property characterizations of EPS for determination of design parameters have relied on laboratory testing of small samples. For the most part much of what is commonly known is based on data derived from unconfined compression testing of standard 50 mm cube samples. Performance observations suggest that Youngs modulus values derived from laboratory tests when used in analysis tend to overestimate deformations. Available information on Poissons ratio values widely varies. Little is known about the influence of sample size on desired elastic parameters. Studies of EPS behavior under unconfined compression were conducted on both cubic and cylindrical samples of different material densities. Both axial and lateral deformations were monitored to enable simultaneous evaluation of Youngs modulus and Poissons ratio. The results indicate significant sample size influence on elastic parameters. Youngs modulus and Poissons ratio values tend to ,.be underestimated. The cause for the under estimation is attributed to be due to non uniformity and end effects in the proximity of the rigid loading platens. Introduction The use of Expanded Polystyrene (EPS) as a lightweight material is growing rapidly in the United States and elsewhere. Various geotechnical applications use geofoam. Among these are embankments, retaining walls, slope stabilization and bridge abutments. . . . . . . . . . . . . . . . . . . . . . . . lResearch Assistant, Geofoam Research Center and ESF, Syracuse, NY 13244 2Director, Geofoam Research Center, Syracuse University, Syracuse, NY 13244 3prof. Chairman, CMWPE Dept. SUNY-ESF, 403 Baker Lab, Syracuse, NY 13210

Effect of confinement on creep behavior of EPS geofoam

Time-dependent deformation under sustained loading or creep is an important consideration in the long-term performance of expanded polystyrene (EPS) geofoam. The design of EPS geofoam fills is mainly based on limiting working stresses to produce tolerable deformations. Results from unconfined uniaxial creep tests have provided justification for such design criteria. With different types of applications involving submergence and higher surcharge loads, creep deformations under confining pressures have been occurring. A series of creep tests were performed on different densities of EPS geofoam with and without confining pressures. The results showed confining pressures can significantly affect the creep responses of EPS geofoam. Effects of confining pressures on creep deformations were more pronounced at lower densities.

Modulus of Subgrade Reaction for EPS Geofoam

Expanded polystyrene (EPS) geofoam has been used as lightweight subgrade for rigid pavement construction over weak soils. Design methods require modulus of subgrade reaction as input parameter for characterizing subgrade materials underlying rigid pavement structures. Designs of structural foundations over EPS geofoam also utilize modulus of subgrade reaction. Available information related to estimation or appropriate test methods for evaluation of modulus of subgrade reaction of EPS is very limited. A series of plate load and California Bearing Ratio (CBR) tests were performed on different densities of geofoams. Effects of plate size and geofoam density were examined. Both plate load and CBR tests resulted in low design parameters for all geofoam grades. Plate load test results were used to calibrate a numerical model. Estimates of k values for concrete slabs over geofoams, assuming composite subgrades, were obtained from the calibrated numerical models. The equivalent k values for the combined concrete slab and geofoam subgrade layers were higher than for geofoam subgrades without concrete cover. The equivalent k values also indicate significant differences between low and high-density geofoam grades for the same thickness of concrete slab. Estimates of k for concrete slab and geofoam composite subgrades agree with previously reported assessments from field surveys and back calculations.

Use of EPS Geofoam for support of a bridge

In much of reported geofoam applications in roadway construction, innovative uses featured approach fills and light weight embankments below rigid or flexible pavement structures. This paper describes a bridge construction that represents a marked departure from conventional practice. EPS geofoam was used to support pre-stressed concrete box beams and composite concrete deck of a single span bridge. The bridge is a replacement of a shorter, steel-girder single-span bridge on spread footings across Oatka Creek in Warsaw, NY. Criteria for the new bridge included a larger span and increased load and hydraulic capacities. Soil borings showed very weak strata extend to large depths, initially suggesting the need for deep foundations to support the new bridge. As an alternative to piles, excavation and replacement of the underlying soil with EPS geofoam was selected to provide a compensated foundation system. This paper describes the construction and post-construction performance monitoring of the bridge. The instrumentation included stress cells, settlement plates, and piezometers. Heat dissipation in the thick early strength concrete of the abutment slabs was monitored, and was inferred as the source of thermally-induced creep. Periodic surveys of the roadway profile were also taken. Subsequent to completion, the bridge and the approaches were inundated during a period of intense rainfall, and successfully withstood the uplift due to buoyancy. Following 10 years of service, the bridge continues to be rated with the highest NYSDOT bridge performance ranking in 2012.

Gold cylinder fiber biosensor

We have fabricated and tested Gold Cylinder Fiber (GCF) bio sensors. The sensor fiber has a thin, approximately 3 nm to 5 nm thick, Gold alloy film layer at the glass core glass cladding boundary. One end of the fiber is etched to let the gold alloy cylinder protrude about 10 m. A Single Mode Fiber (SMF) is connected to the other end of the GCF. Light propagates through the SMF to a short section of GCF. The etched end of the GCF is dipped into the fluid to be analyzed. The reflected light from the sample returns back through the SMF to a spectrum analyzer.

Single eye and camera with depth perception

It is possible that each light sensor pixel in the eye has the capability of measuring the distance to the part of the object in focus at the pixel. One can also construct an electronic camera where each pixel can measure the distance to the portion of the object in focus at the pixel. That is, these devices have depth perception

Resilient Modulus for EPS Geofoam

Most of the current design methods for geofoam used in pavement structures adopt the allowable working stress concept. These design methods do not fit rationally in conventional pavement design practice such as the AASHTO pavement design guide. To design flexible pavement structures according to AASHTO, the resilient modulus, M r , for EPS geofoam would need to be estimated. The standard test method for estimating resilient modulus is not suitable for geofoam. Reinforced concrete slab is commonly poured over geofoam subgrades and below the pavement structure. The beneficial contribution of the concrete slab to improving the performance of the geofoam subgrade is not quantified in current design practice. Modified tests were performed to determine resilient modulus values for geofoam. Equivalent resilient modulus estimates were obtained considering the combined response of geofoam subgrade and concrete slab. The estimates were derived from finite element models, reported back calculations from FWD surveys and by correlations. The resilient modulus values obtained for the combination of geofoam and concrete slab are in a range that enables use of conventional pavement design by AASHTO methods.