Design and Evaluation of Seismic Stability of Free-Standing EPS Embankment for Transportation Systems

Abstract

This paper summarizes a simplified method for evaluating the interlayer sliding potential of free-standing, rectangular, prismatic-shaped EPS geofoam block embankments subjected to strong ground motion associated with major earthquakes. The steps of the method are: (1) estimate the fundamental period of the embankment, (2) determine the design horizontal acceleration for the design earthquake, (3) determine the horizontal inertial force acting at each interface (4) estimate the sliding resistance and factor of safety against sliding at each interfaces and (5) evaluate the need for countermeasures, if necessary. The methods and evaluations summarized herein suggest that interlayer sliding may initiate if free-standing embankments are exposed to pulses of horizontal acceleration exceeding about 0.5–0.6 g. They further suggest that sliding is generally initiated at the lowermost interlayer and propagates upwards through the embankment to its crest. In severe cases, shear keys, adhesive bonding or other restraint mechanical mechanisms may be appropriate to locally disrupt potential sliding planes as a preventative countermeasure against interlayer sliding or excessive block movement near the outer edges of the embankment. Also, results of numerical modeling suggest that the basal edges of the EPS embankment may begin to experience overstressing due to horizontal sway of the embankment when the design horizontal acceleration values are large. For such cases, consideration should be given to using higher modulus EPS blocks at the outer edges of the basal layer to reduce the potential for overstressing.