Cost and Schedule Savings from Directly-Driven Soil Nail and Innovative Fascia Systems: Fid-Bau Portal

Cost and Schedule Savings from Directly-Driven Soil Nail and Innovative Fascia Systems

Aziz, Enayat S. / Stephens, Tyler J.

A directly-driven soil nailing system has been developed recently for a full spectrum of natural and constructed soils in a wide range of in-situ conditions. After more than a decade in development, its applications include reinforcement of cut and fill slopes, stabilization and drainage of slope failures, repair and rehabilitation of existing mechanically stabilized earth walls, and reinforcement of permanent compound walls and steepened-slopes for road widening projects. This soil nail, termed the spiralnail, is a hollow tube with twisted, square-section, high-pitch helix shape, manufactured by a cold-rolling process from steel pipe, often hot-dip galvanized after fabrication. Spiralnails are directly driven, or occasionally driven into pre-drilled pilot holes. Using a hollow spiralnail as casing, it can be filled with grout to encase an internal reinforcement for extra corrosion protection. They form a frictional and mechanical bond with the surrounding soil along their full length in the absence of cement grout. In this manner the spiralnails improve internal stability of the soil mass in which they are installed. Spiralnails are immediately capable of carrying internal and external loads to which they are subjected. Therefore, they offer potential efficiency in project sequencing. They are installed using manufacturer-supplied, specialized percussion hammers which can be mounted to conventional excavators or a variety of other equipment, and used by non-specialized earthwork crews. The fascia design most commonly used with this system is known as "wiretruss", and is composed of welded-wire cellular paneling backfilled with coarse rock. This fascia is free-draining, self compensating in settlement, immediately confines the soil between the nails, and is quickly constructed. Another fascia, known as the "spider" system, has been used to stabilize steepened slopes, and is typically combined with existing or planted vegetation to form a bio-mechanical fascia. The spiralnail systems have provided substantial cost and schedule savings on completed projects. This paper presents case history-based cost and schedule data to support this claim.