HORIZONTAL DRAINS AND HORIZONTAL DRILLING: AN OVERVIEW

Subsurface water may act in many ways to reduce the stability of cuts and embankments. Among these are decrease in cohesion, subsurface erosion, lateral pressure in fractures and joints, and excess pore-water pressure. One way of removing subsurface water is to use horizontal drains, which are holes drilled into an embankment or cut slope and cased with a perforated-metal or slotted-plastic liner. The equipment, materials, and procedures used in the drilling and installation of horizontal drains have been improved and refined considerably since the California Division of Highways first introduced the Hydrauger in 1939. The development of polyvinyl chloride pipe, improvements in drill bits and drill stem, and the development of drilling machines capable of producing high thrust and torque have made subsurface drainage a significant and economical alternative in the repair and prevention of some types of landslides. (Author)