Development of an Economical Guardrail System for use on Wire-Faced, MSE Walls
Mary McGhee, Ronald Faller, John Rohde, Karla Lechtenberg (Polivka), Dean Sicking, John Reid
Wire-faced, mechanically-stabilized earth (MSE) walls provide an economical method for constructing vertical structures for supporting roadways where local topography or high land costs preclude the use of conventional fill slopes. Corrugated guardrail is often used for shielding high vertical drop-offs associated with MSE walls. The Midwest Guardrail System (MGS) was modified to decrease the overall width of the MSE wall structure. Dynamic component testing was utilized 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, select post length, and determine post material and section. The standard MGS was modified by removing the 12-in. (305-mm) deep wood spacer blocks and by incorporating W-beam backup plates. All other MGS features were maintained, including the 6-ft (1.8-m) long W6x8.5 (W152x12.6) steel posts, rail splices at mid-span locations, 31-in. (787-mm) top mounting height, and 75-in. (1,905-mm) post spacing. The non-blocked 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 using both 1100C small car and 2270P pickup truck vehicles according to Test Level 3 (TL-3) safety performance guidelines provided in the Manual for Assessing Safety Hardware (MASH). The MSE wall was not damaged during the testing programs. The non-blocked MGS is recommended for use with wire-faced, MSE walls when placed at the slope break point of a 3H:1V fill slope. The modified MGS reduces the required width of the MSE wall, thus resulting in decreased construction costs.
Mechanically-Stabilized Earth, MSE, Midwest Guardrail System, MGS, Slope Break Point, SBP, Test Level 3, TL-3
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