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13-1 CHAPTER 13 FUTURE RESEARCH AND DEVELOPMENT Contents General ...................................................................................................................................................... 13-1 Material Properties .................................................................................................................................... 13-1 Analytical Issues ....................................................................................................................................... 13-2 Conceptual Issues...................................................................................................................................... 13-5 References ................................................................................................................................................. 13-5 ______________________________________________________________________________ GENERAL Although this report presents a comprehensive design methodology for geofoam and EPS-block geofoam has been successfully used as lightweight fill, this NCHRP study did identify three main areas where further research would enhance the current state of knowledge of geofoam. These areas can be divided into material properties, analyses, and general conceptual issues. The recommendations included herein are primarily based on literature reviewed prior to April 2000. MATERIAL PROPERTIES Issues related to geofoam material properties that require further study are: ⢠Determining the minimum time required for seasoning EPS blocks to outgas the blowing agent to an acceptable level. ⢠Quantifying interface friction angles for EPS/EPS interfaces at large displacements and displacement reversals for use in static and seismic internal stability analyses. ⢠Quantifying interface friction angles for EPS/dissimilar materials, such as a variety of widely used geotextiles and geomembranes.
13-2 ⢠Comparison of the stress-strain behavior of full-size EPS blocks versus small test specimens routinely used in practice for engineering property and quality control/assurance testing. ⢠Development of a laboratory test procedure to define the small-strain stiffness of EPS blocks. ⢠Development of an accurate small-strain creep model so creep strains can be reliably estimated for lightweight fills. This should include correlations between laboratory and in-situ creep data. ⢠Development of a non-invasive testing device such as a sonic-wave device for routine on-site evaluation of the average density, initial tangent Young's modulus of an EPS block, and, if possible, average elastic-limit stress. ⢠Development of a standardized manufacturing quality assurance (MQA) procedure for EPS blocks to provide greater guidance to end users. Additionally, development and passage of an ASTM standard that is specific to the use of geofoam in geotechnical applications. The provisional AASHTO specification presented herein can serve as the framework for development of the ASTM standard. ⢠Development of reliable correlations between Youngâs modulus as measured in small laboratory test specimens and the behavior of full-size EPS blocks in situ. ANALYTICAL ISSUES Analytical issues requiring further research using numerical modeling, physical testing, and/or observation of full-scale structures are: ⢠Determine whether an external slope stability failure induces failure through individual EPS blocks or whether the blocks remain intact and displace as
13-3 individual elements as a result of the slope instability. This is important for the modeling of geofoam embankments in slope stability analyses. This would also include a consideration of how an EPS-block geofoam embankment behaves under large and rapid settlements such as associated with seismic liquefaction. ⢠Develop a more realistic procedure for evaluating the potential for basal translation (sliding) due to wind loading especially under Atlantic hurricane conditions that can affect the east coast of the U.S. This is required because the current procedure is conservative because it treats a trapezoidal embankment as a vertical embankment and thus the wind is assumed to act on a vertical face instead of a sloped embankment. An evaluation of the applicability of roof design shapes and procedures to side-sloped EPS-block geofoam embankments is recommended. This assessment would also consider whether the current AASHTO or ANSI/ASCE 7-95 code values for wind loading are appropriate for use in routine design practice. ⢠Determining the effectiveness of using geogrid or geocell reinforcement in the unbound layer(s) of a pavement system above a geofoam fill. ⢠Quantifying the effects of significant changes in ground water level, and the concomitant buoyancy of EPS blocks. In particular, development of strategies for securing the EPS blocks that do not rely on gravity loads, such as vertical ground anchors. Alternatively, evaluating the effectiveness of open-cell geosynthetic lightweight fills (termed geocombs) in synergistic combination with EPS geofoam to resist buoyancy. ⢠Development of a procedure to determine the types of pavement materials and thicknesses of such materials that are required over the EPS blocks to minimize the potential for differential icing of the pavement surface over the EPS. Such a
13-4 procedure may require the development of a rational method for quantifying the amount of heat energy (BTUs or joules) required from a pavement system to prevent differential icing. This would replace the current empirical methodology that is difficult to implement in routine design practice. ⢠A more detailed assessment of the potential for flexible pavement deterioration over the EPS due to solar heating and development of a procedure to determine the types of pavement materials and thicknesses of such materials that are required to minimize the potential for solar heating deterioration. ⢠Develop a better understanding of the seismic behavior of EPS-block geofoam fills, particularly their interaction with bridge abutments. ⢠A detailed assessment of the interaction between the thermally stable geofoam mass and integral-abutment bridges (also known as jointless bridges, integral bridge abutments, and U-frame bridges) that undergo complex combined rotation and translation due to seasonal thermal changes. ⢠Develop a rational methodology for determining when mechanical connectors, e.g., barbed plates, are required between EPS blocks, as well as a methodology for selecting the number and placement location. In addition, development of a new connector that can be copied and reproduced inexpensively to reduce the cost of using mechanical connectors instead of the proprietary designs currently available. Recent Japanese research indicates that the effectiveness of barbed- plate connectors is limited especially under seismic loading because it involves strain reversals and accumulated cyclic strains. ⢠Investigation of the seismic behavior of relatively tall and slender EPS-block geofoam fills is needed to assess the rocking mode of behavior. This mode of
13-5 behavior has been observed in recent full-scale shake-table tests performed in Japan. CONCEPTUAL ISSUES Two conceptual issues that require further consideration are: ⢠Revise the design methodology presented herein for EPS-block geofoam in roadway embankments to utilize Load and Resistance Factor Design (LFRD) instead of Allowable Stress Design (ASD). This may be desirable given the use of LFRD in other AASHTO codes. However, a review of (1) suggests that there are still some difficulties in using LFRD for non-foundation geotechnical elements, such as earth retaining structures and earthworks, and thus the provisional design guidelines included herein are based on the traditional ASD methodology. ⢠Develop standardized design details for facing systems (shotcrete, precast panels or blocks, EIFS coating, etc.) for geofoam walls. REFERENCES 1. Goble, G., âGeotechnical Related Development and Implementation of Load and Resistance Factor (LRFD) Methods, NCHRP Synthesis of Highway Practice 276.â Transportation Research Board, Washington, D.C. (1999) 69 pp.
