Drain pipes within a retaining wall are designed to remove incidental water that may collect at the base of the wall. The primary water management happens above and below the wall where grading and surface materials are designed to efficiently remove water before it saturates the retaining wall system.
A toe drain pipe should be located at the back of the wall rock behind the wall as close to the bottom of the wall as allowed while still maintaining a positive gradient for drainage to daylight, or a stormwater management system.
For site configurations with bottoms of the base on a level plane it is recommended that a minimum one percent gradient be maintained on the placement of the pipe with outlets on 50 feet (15 m) centers, or 100 feet (30 m) centers of pipe is crowned between the outlets. This would provide for a maximum height above the bottom of the base in a flat configuration of no more than 6 inches (150 mm).
You can use rigid or flexible drain pipe. For rigid pipes position the holes a down. Allan Block does not require that toe drain pipes be wrapped when installed into base rock complying with the specified wall rock material.
On sites where the natural drop in grade exceeds the one percent minimum, drain pipes outlets should be on 100 foot (30m) centers maximum. This will provide outlets in the event that excessive water flow exceeds the capacity of pipe over long stretches.
When the drain pipe must be raised to accommodate outlets through the wall face, refer to the Allan Block Spec Book.