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Thread: Retaining Wall drainage

  1. #1

    Retaining Wall drainage

    I'm an ME with a background in HVAC & light residential construction. I'm in the process of planning a retaining wall with a height of approximately 26 inches above finished grade in northern NJ (morris county). The soil type is listed as "RkgBc" Ridgebury Stony Loam (extremely stony) sloped, slow draining. My questions are regarding the perforated drainage pipe behind the wall.

    The foundation base trench will be approximately 10-12 inches deep & 36 inches wide. The bottom of the trench will be leveled & compacted (plate compactor). Approximately 6 inches (depth) of foundation base material (3/4 inch angular crushed clean gravel) will be then be added to trench, then leveled & compacted. The first course of wall stone will sit on this gravel base below grade. Behind the wall will be filled with 3/4 inch clean gravel (same as base) for the entire length of the with a minimum depth of 12+ inches from the rear wall. The trench does have an overall pitch since property is sloped. The finished area behind the wall will be back filled with the native soil & 3/4 inch gravel, then graded level for a pea gravel at finish. Fabric will be installed beneath the finshed pea-gravel layer. The drain pipe behind the wall will be perforated with holes down.

    OBSERVATION: The soil is definitely very slow draining & stony with many various size angular rocks from golf ball size to that of a shoe box.

    My questions are;

    1. Shall the drain pipe be covered with a pipe sock/sleeve or shall the entire gravel foundation base & drainage gravel area behind the wall be enclosed in a Geo-filter fabric similar to a burrito style to keep debris out?

    My research has revealed conflicting opinions regarding wrapping the drain pipe in a sleeve/sock or enclosing the entire gravel & pipe area with geo-filter fabric similar to a burrito. I'm sure the site and soil conditions would dictate which course of action to pursue since different soils perform differently regarding clogging up the pipe or fabric holes.

    Any guidance is highly appreciated. thank you

  2. #2
    New Member
    Join Date
    Sep 2023
    Hy there i can see your post and i must say

    Backfill Material: Use well-draining backfill material, such as gravel or crushed stone, behind the retaining wall. Avoid using compacted soil that could hinder water movement.
    Weep Holes: Incorporate weep holes or drainage pipes at the base of the wall to allow water to escape. These openings should be designed to prevent clogging while facilitating water drainage.

    Thanks and regards

  3. #3

    Given your soil type and drainage concerns, I'd suggest opting for both the pipe sock on the drain pipe and enclosing the gravel foundation base in a geo-filter fabric. The pipe sock will help prevent silt and fine particles from entering the pipe, while the fabric wrap around the gravel will provide an additional layer of filtration, which seems necessary in your soil conditions. This dual approach should maximize drainage efficiency and longevity of the wall structure.

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