Design and Installation of Horizontal Wick Drains for Landslide Stabilization

Abstract

One of the most effective options to stabilize landslides is to reduce the amount of water they contain by installing horizontal drains. A new type of horizontal drain material, geosynthetic wick drains, and a new installation method, driving drains rather than drilling them, were evaluated. Horizontal wick drains offer several advantages over conventional horizontal drains: They resist clogging, are inexpensive, may be deformed without rupture, and may be installed by unskilled laborers with a minimal investment in equipment. More than 100 drains were installed at eight sites in Missouri, Colorado, and Indiana using bulldozers, backhoes, and standard wick drain-driving cranes. Drains have been driven 30 m through materials with standard penetration test values as high as 28. Both experience and research indicate that drains should be installed in clusters that fan outward, aiming for average spacing of 8 m for typical clayey soils. As with drilled drains, initially some drains are expected to be dry, although these drains often become active during wet periods and serve as an important part of the overall slope stabilization scheme. Drain effectiveness is expected to build over the first few years as the effects of soil smear during drain installation are removed, peaking at 3 to 6 years after installation. The effectiveness is then expected to decrease as fine particles slowly clog the drain pores. From published tests, clogging appears to occur slowly enough in typical clay soils that the drain life is comparable with the project life.

Demonstration Projects Using Wick Drains to Stabilize Landslides

“…Pipe sections may be added and driven until the desired drain length is reached or until the driving resistance causes refusal. Once the total length has been driven, the pipes are pulled from the ground while the drive plate anchors the wick in place (Santi et al, 2001b).…”

“…A new method has been developed to stabilize slopes and landslides using driven, geotextile (polypropylene) wick drains rather than drilled polyvinyl chloride or steel drains (Santi, 1999;Santi et al 2001a). Compared to drilled horizontal drains, wick drains can be significantly stretched (as much as 60-100 percent) without rupturing, and they resist clogging (American Wick Drain Corporation, 2002;Nilex Corporation, 2002).…”

“…Compared to drilled horizontal drains, wick drains can be significantly stretched (as much as 60-100 percent) without rupturing, and they resist clogging (American Wick Drain Corporation, 2002;Nilex Corporation, 2002). Furthermore, they can be installed very rapidly, at rates in excess of 15 to 18 m/hour (50-60 ft/hour) (Santi et al, 2001b), and very economically, at costs of $8 to $13 per meter ($2.50-4.00 per foot) (Santi et al, 2001b). They may be installed by unskilled laborers with a minimal investment in equipment, which the authors estimate at less than $2,000.…”

“…They may be installed by unskilled laborers with a minimal investment in equipment, which the authors estimate at less than $2,000. Drains more than 30 m (100 ft) in length have been installed through materials with standard penetration test values as high as 28 (Santi et al 2001b). …”

“…Five of these sites were considered to be experimental installations, where the equipment and technique were developed and optimized for various geologic materials (Santi et al, 2001b). Three of the sites were considered to be full-scale installation efforts, where the density and layout of drains was considered to be sufficient to significantly enhance the stability of the slopes (Santi and Crenshaw, 2002).…”