Evaluation of Hybrid Micropile A-Frame-Geosynthetic-Reinforced Wall with Steel Guardrail Barrier for MASH Loading

US Transportation Collection2021PDFTech ReportPak, Ronald Y SZhang, ZhichaoUniversity of Colorado at Boulder. Dept. of Civil, Environmental and Architectural EngineeringColorado. Department of TransportationUnited States. Department of Transportation. Federal Highway AdministrationColorado Department of Transportation. Applied Research & Innovations BranchUnited StatesBarriers (Roads)DesignEarth wallsEvaluation and assessmentFinite element methodGeosyntheticsMechanically stabilized earthRoad constructionSlope stabilityGuardrailsThrie beamsgeosynthetic reinforced soilmicropilesMASH TL-4roadside guardrailW-beamLS-DYNACDOT-2021-11R.218-02FinalThis report presents the result of the evaluation of the adequacy and ability of a hybrid geosynthetic reinforced retaining wall in a truncated configuration for steep terrains to support steel bridge guardrails under the American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH)\u2019s Test-Level 4 impact loading. Intended to provide an engineering option particularly for marginal site or slope conditions, the hybrid design involves the installation of multiple pairs of vertical and inclined micropiles in the form of a structural A-frame through the backfill of a highway GRS wall into the foundation base, with a level of embedment that can strengthen the stability of both the wall and the slope. To determine the wall\u2019s ability to resist the more severe level of impact load-transfer from the roadside guardrail expected from MASH, use was made of the finite deformation and nonlinear modeling capability of finite element code LS-DYNA for the assessment. Using a combination of elastoplastic constitutive material models, a computer simulation platform was developed for modeling the hybrid soil-micropile-geofabric-guardrail design. To achieve a realistic representation of collision impact conditions pursuant to MASH on guardrails, compact modules of the finite element models originally developed by National Crash Analysis Center (NCAC) for a passenger car and single-unit truck vehicles were employed and integrated into the finite element W-beam and thriebeam guardrail-micropile-reinforced soil-wall analysis. From the analysis, the hybrid micropile-truncated GRS wall design was found to be capable of supporting the guardrail system under MASH TL-4 collision impact condition and a lateral design impact load of 88 kips for a 40\u201d guardrail was recommended. Parallel to the computational synthesis, a laboratory scaled-model study was conducted to ascertain possible preferences of the geotextile type and soil condition for effective micropile installation, analytical-physical correlation and improving the construction procedure. The possibility of an equivalent-frontal collision impact condition to facilitate design iterations for MASH was also explored.127