Design and Installation Considerations of Geocomposite Drains in Soil Nail Walls

Abstract

Permanent and temporary soil nail walls are gaining widespread acceptance as a cost-effective subsurface soil retention system. Conventional soil nail wall designs generally include geocomposite drain boards behind the soil nail wall to drain subsurface water and dissipate hydrostatic pressures behind the wall. It is the authors experience that the design and installation of these geocomposite drain boards is based on local experience and practice with little consideration given to the actual conditions under which the drains will be required to perform. The current Federal Highway Administration manual on the design and construction of soil nail walls provides limited technical discussion on the design of these geocomposite drain boards. However, similar drainage elements used as pavement edge drains have received attention lately with some failure case histories documented. The performance of these geocomposite drain boards is critical to the performance of the soil nail wall since it is assumed that these elements dissipate any hydrostatic pressures behind the wall. Unaccounted hydrostatic pressures behind the wall could lead to distress of the wall and the need for costly remedial efforts. This paper presents a discussion of the key design and installation considerations relevant to these geocomposite drain boards.