Nonblocked Midwest Guardrail System for Wire-Faced Walls of Mechanically Stabilized Earth

Abstract

Wire-faced walls of mechanically stabilized earth (MSE) provide an economical method for building vertical structures for supporting roadways where local topography or high land costs preclude the use of conventional fill slopes. W-beam guardrail systems are often used for shielding high vertical drop-offs associated with MSE walls. For this study, the Midwest Guardrail System (MGS) was modified to decrease the overall width of the MSE wall structure. Dynamic component testing was used to determine the post–soil behavior of steel and wood posts embedded in compacted soil materials used for constructing wire-faced MSE walls as well as to evaluate the effects of sloped terrain and different installation methods. Twenty-six dynamic tests were performed to evaluate the propensity for MSE wall damage, to select post length, and to determine the preferred post material and section. The standard MGS was modified by removing the wood spacer blocks 12 in. (305 mm) deep and by incorporating W-beam backup plates. All other MGS features—including the W6 × 8.5 (W152 × 12.6) steel posts 6 ft (1.8 m) long, rail splices at midspan locations, the 31-in. (787-mm) top-mounting height, and the 75-in. (1,905-mm) post spacing—were maintained. The nonblocked MGS was installed with the posts driven at the slope break point of a 3H:1V fill slope. The modified MGS was successfully crash tested with both 1100C small car and 2270P pickup truck vehicles in accordance with Test Level 3 safety performance guidelines in the Manual for Assessing Safety Hardware. The MSE wall was not damaged during the testing programs. The nonblocked MGS is recommended for use with wire-faced MSE walls when they are placed at the slope break point of a 3H:1V fill slope. The modified MGS reduces the required width of the MSE wall, resulting in decreased construction costs.