Use of Ultra-Lightweight Geofoam to Reduce Stresses in Highway Culvert Extensions

OBJECTIVES: 1) Examine alternative lightweight materials when roadways are widened and culverts must be extended. 2) Develop guidelines to use ultra-lightweight geofoam in highway culvert extension design. BACKGROUND: Foamed concrete has been used in the past to reduce stresses on the culvert extensions. This study will concentrate mainly on using geofoam as an alternative material to foamed concrete. At some older sites, the culvert size was stepped-down when portions of the culvert was under the slopes of the embankment. In this situation, the part of the culvert positioned under the embankment slopes was made less strong because the stresses under the portions of the slopes were much smaller than the stresses acting on the culvert located under the main portion of the embankment. However, when roadway widening occurs much larger stresses are imposed on the less strong portions of the culvert. To accommodate the increased stresses on the downsized portion of the culvert, lightweight material, such as foamed concrete, has been used. This is a fairly expensive approach. The objective of this study is to examine the use of ultra lightweight geofoam as an alternative to the use of foamed concrete. Geofoam has a unit weight of about 1.5 1bs/ft3while the unit weight of foamed concrete is typically 35 Ibs/ft3• Geofoam per unit volume is about half the cost of foamed concrete. Comments: Two or three culverts sites will be selected that were actually designed and constructed using foamed concrete. Theoretical analysis (using a finite difference computer program referred to as FLAC 4.0) will be performed using foamed concrete and the proposed alternative, geofoam. In both cases, the imposed stresses using both materials will be calculated. If geofoam is more economical, then a test site(s) will be built using geofoam, monitored, and evaluated. FY 2006 ACCOMPLISHMENTS: Plans have been obtained for a site where foamed concrete and geofoam are to be used as lightweight fill to reduce stresses. Stress analyses have been performed comparing the effectiveness of foamed concrete and geofoam. Theoretical analyses of stress distribution on culverts that have been or are going to be extended have been performed. Sections where strain gages and pressure cells will be installed have been selected. Two strain gages were installed at a planned section. Analyses using FLAC 4.0 software show the most effective location of the lightweight materials relative to the culverts. Two other culverts have been analyzed. Comparisons and suggests were sent to the Division of Bridges and Geotechnical group. FY 2007 PROPOSED WORK: Stress analysis will continue on culverts where lightweight fill is being proposed. Stresses obtained for three different scenarios will be compared. The cases are: no lightweight material is used; foamed concrete is used, and geofoam is used. An economical analysis will be performed to determine if geofoam is more economical than foamed concrete. Concurrently to performing the theoretical analysis, a site will be sought where the use of geofoam may potentially be used. Preliminary theoretical analysis will be performed using foamed concrete and the proposed alternative, geofoam. The culvert where foamed concrete or geofoam are scheduled to be used will be instrumented to measure actual strains and stresses. A review of how other state transportation agencies treat the culvert extension problem will also be conducted. PROJECTED COST THROUGH FY 2006: PROGRAMMED COST FY 2007: TOTAL ESTIMATED COST: $229,000 $100,000 $325,000