Exhumation of a Coated Polyester (PET) Geogrid from a Masonry Block Retaining Wall after 20 Years of Service

Abstract

The technology of mechanically stabilized earth (MSE) retaining walls using masonry block facing with geosynthetic reinforcement is one of the fastest growing segments of the geosynthetic industry. Due to their excellent aesthetics, low costs, ease of constructability and usually good performance, these structures are seen throughout the world. However, some of these systems are being challenged for having very high alkalinity (particularly between rows of masonry blocks) which is unsuitable for some PET resins. The focus of this paper is to present field data from such a masonry block wall which was built using three different masonry block types. The wall was built as a test wall, but it is full size and serves a dual purpose of replacing a failed timber wall. Alkalinity (as measured by pH) measurements are taken directly between the block surfaces at the contact of the geogrids to the block units. Data and trends from twenty years of monitoring are presented. We had the opportunity to disassemble the wall and exhume a section of geogrid that was subsequently tested for wide width tensile strength. These tension test results shed some light on actual reduction factors for Installation damage and chemical degradation.