Guidelines for Geofoam Applications in Slope Stability Projects (2013) / Chapter Skim
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NAtioNAl CooperAtive HigHwAy reseArCH progrAm Responsible Senior Program Officer: David A Reynaud January 2013 C O N T E N T S Introduction, 1 Problem Statement, 2 Solution Alternatives, 3 Research Objective, 4 Key Research Products, 4 NCHRP Project 24-11(02)
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2reduced inertial forces during seismic shaking. Thus, the lower density of EPS-block geofoam may alleviate the costs of soft soil removal (which include the attendant disposal problems and costs)
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3the current and future highway capacity problem. As noted by Spiker and Gori (2003)
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4The simplest solution to reducing the driving forces within a slope is simply to reduce the slope inclination. This reduces the shear stress on the material in the slope, making the entire slope more stable.
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5ment that provides design guidance to engineers, owners, and regulators for the use of EPS-block geofoam for the function of lightweight fill in slope stability applications.
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7embankment walls, the exposed sides should be covered with a facing. The facing does not have to provide any structural capacity to retain the blocks because the blocks are self-stable, so the primary function of the facing is to protect the blocks from environmental factors.
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8Table 1. Summary of failure modes and mechanisms incorporated in the proposed design procedure for EPS-block geofoam as a lightweight fill in slope stability application.
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9mechanisms shown in Table 1 are also included in the Japanese design procedure that Tsukamoto (1996) provides.
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10 ensure that water from seepage or surface runoff will not accumulate at or above the bottom of the EPS blocks is part of the design, then analyses for the hydrostatic uplift (flotation) and translation due to water failure mechanisms that are included in the NCHRP Project 24-11(01)
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11 material due to static loads and seismic loads and/ or a decrease in the shear strength of the foundation material (as shown in Figure 8) ; and earthquakeinduced settlement of the existing foundation material (as shown by Figure 9)
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12 driving force within the EPS-block fill mass causing instability. The driving force is small because the horizontal portion of the internal failure surfaces is assumed to be along the EPS-block horizontal joints and completely horizontal while the typical static loads are vertical.
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13 Pavement System Failure Mode. The objective of pavement system design is to select the most economical arrangement and thickness of pavement materials for the subgrade provided by the underlying EPS blocks.
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14 1 Background investigation including stability analysis of existing slope 2 Select a preliminary type of EPS and assume a preliminary pavement system design (if necessary) 3 Optimize volume & location of EPS fill or assume a preliminary fill mass arrangement 5 Static slope stability (external)
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15 the roadway as shown in Figure 14 (b)
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16 to the existing or proposed new roadway. Level IV indicates the location of the roadway in relation to the existing or anticipated slide mass.
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17 analysis based on various locations and thicknesses until a cross section that yields the minimum volume of lightweight fill at the desired level of stability is obtained. However, other factors will also impact the final design volume and location of EPS blocks such as •• Construction equipment access to perform excavation work, •• Ease of accessibility for EPS-block delivery and placement, •• Impact on traffic if lightweight fill will be incorporated below an existing roadway, and •• Right-of-way constraints and/or constraints due to nearby structures.
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18 In addition to the technical aspects of the design, cost must also be considered. Because EPS-block geofoam is typically a more expensive material than soil on a cost-per-unit-volume basis for the material alone, it is desirable to optimize the design to minimize the volume of EPS used yet still satisfy the technical design aspects of the various failure mechanisms.
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19 the production of EPS. Arellano et al.
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20 issues typically contribute to the cause of the failure in the first place. •• The volume of EPS placed within the overall slope cross section may be relatively limited.
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21 blocks and, in some cases, incorporated a drainage system between the adjacent upper slope material and the EPS blocks to collect and divert seepage water, thereby alleviating seepage pressures. Therefore, these case histories substantiate the recommendation included in the proposed design procedure of EPS-block geofoam slope systems that all EPS-block geofoam slope systems incorporate drainage systems to alleviate the need to consider and design for hydrostatic uplift (flotation)
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22 decade of actual project use and experience using the standard for stand-alone embankments included in NCHRP Report 529 and NCHRP Web Document 65, the standards developed for the past and current NCHRP studies are reasonable when implemented properly in practice. Proper implementation includes MQC/MQA laboratory testing performed in accordance with well-established ASTM protocols for test-specimen conditioning prior to testing, numerical correction of all stress-strain curves for machine compression, and graphical correction of stress-strains for initial concavity as necessary.
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23 or stockpiled at the site for immediate use. Thus, the use of EPS blocks in slope application projects can easily contribute to an accelerated construction schedule.
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24 with recycled EPS exists. The use of recycled EPS blocks would be an attractive "green" product that reduces waste by recycling polystyrene scrap and would also reduce the raw materials costs in the production of EPS (Horvath 2008)
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25 roadway embankments. NCHRP Web Document 65 includes the background and analyses used to develop the recommended design guideline and material and construction standard as well as a summary of the engineering properties of EPS-block geofoam and an economic analysis of geofoam versus other lightweight fill materials.
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26 in Urban Environments." Soil and Rock America, 12th Pan-American Conference on Soil Mechanics and Geotechnical Engineering and 39th U.S. Rock Mechanics Symposium, 2003, 6.
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Transportation Research Board 500 Fifth Street, NW Washington, DC 20001 These digests are issued in order to increase awareness of research results emanating from projects in the Cooperative Research Programs (CRP)
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