Evaluation of Geofabric in Undercut on MSE Wall Stability

摘要

Compaction of granular base materials at sites with fine grained native soils often causes unwanted material loss due to penetration at the base. In 2007, ODOT began placing geotextile fabrics in the undercut of MSE walls at the interface of the native soil and aggregate fill to facilitate construction. It is probable that the sliding resistances of the MSE retaining walls are affected by this practice. At this time, it is unknown if shear parameters at the base of the MSE walls are altered due to the presence of geotextiles at the soil/stone (granular backfill) interface and, if the factor of safety (FS) against sliding failure is compromised. To address this issue, a systematic investigation of the shear parameters at the geotextile/stone interface and native-soil/stone interface was conducted by Large Scale Direct Shear tests. It was observed that the shear strength between the geofabric/stone interfaces were lower than those of the soil/stone interfaces. The extent of the shear reduction depended on the properties of the base soil. For the same stone, the shear parameters at the geofabric interface changed from those of the cohesive soil interface such that friction angle slightly increased and the adhesion slightly decreased. However, the net shear strength at the geofabric interface, calculated with 25 psi normal stress, was generally lower. In case of cohesionless base soil, the shear parameters at the geofabric/stone interface reduced noticeably from those of soil/stone interface. This, in turn, produced a significant (up to 30%) reduction in shear strength at the geofabric/stone interface, calculated under 25 psi normal pressure. The findings of this research indicate that the design of MSE walls with geofabric at the undercut may require modification of the sliding safety factor to reflect the reduced shear strength at the interface.