Foundation System

Retaining walls can be provided with a variety of different foundation support systems depending upon the soil conditions and local topography.  The geologist and soils engineer must evaluate site conditions and provide the structural engineer with a recommendation of the foundation system to use and the bearing material which is to provide support for the foundation system.

    Conventional Foundations - The most common form of support of retaining walls is conventional footings.  The geologist and soils engineer must determine the foundation bearing material and the minimum depth of embedment.  The structural engineer will determine the actual depth of embedment and the width of the footing needed to support the wall.  A keyway is also sometimes employed in a conventional retaining wall foundation.

    Deepened Foundations - Deepened foundations, consisting of either friction piles or caissons are commonly used to support hillside retaining walls.  Deepened foundations are necessary when retaining walls are located over or near descending slopes or when necessary to penetrate deep unsuitable earth materials.  Deepened foundations are also sometimes used to avoid surcharging lower walls or structures.

    Tie Back Anchors  - Tie back anchors are sometimes employed to resist lateral forces imposed on retaining walls.  Tie back anchors are drilled at an angle into the slope and spaced at pre-determined intervals. Tie back anchors are commonly used in construction of temporary shoring for high excavations.  The Los Angeles Department of Building and Safety does not allow the use of tie back anchors in the permanent design and construction of retaining walls.

Subdrainage System

Several methods can be utilized to prevent the building up of hydrostatic (water) pressure behind the retaining wall.  Water pressure will exert 62.4 pounds per cubic foot of pressure on a retaining wall.  Typical retaining wall designs employ a 30 to 43 pound per cubic foot equivalent fluid pressure.  If water pressure is allowed to develop behind the wall, most walls will experience rotation or failure.  To prevent this condition from developing, several methods can be employed which include weepholes, open headers in concrete block and subdrains.


  Subdrains are a commonly used method of providing subsurface drainage control behind retaining walls.  A subdrain typically consists of a 4-inch diameter perforated PVC pipe.  The subdrain pipe must conform with ASTM standards.  Flexible subdrain pipe is normally not used due to its susceptibility to crushing when the wall backfill is placed.  The approved subdrain pipe is laid on a bed of 3/4 inch gravel at the base of the retaining wall.  The subdrain pipe is placed with the perforations pointing down, allowing the small trough at the bottom of the pipe to conduct drainage.  The perforated pipe is connected to solid drain pipe which discharges to an approved location (street).



      A commonly employed method to allow subsurface water to drain through the retaining wall is the use of weepholes.  This image shows 3-inch diameter weepholes installed into the base of the retaining wall. Weepholes can be installed at the time of wall construction or can be provided later.


Open Headers:

  When retaining walls are constructed from concrete blocks, the bottom course of block can have the joints between the blocks left ungrouted.  This allows drainage to seep through the open grout spaces, often referred as "open headers". Open headers are considered to be less effective than conventional weepholes or subdrains.


    Filter Fabrics:

In some applications, use of conventional subdrain systems is not possible.  MiraDrain Company offers a variety of filter fabrics which can be used to provide some degree of drainage behind retaining walls which have not been provided with enough free space behind the wall to employ a standard drainage system.  Filter fabrics are not as effective as conventional subdrains and weepholes, but in special circumstances, filter fabrics represent an alternative which can provide some degree of protection.

    Drainage Media:

Retaining walls must be properly backfilled.  The backfill material must be selected and approved by the geologist or soils engineer.  Typically, the subdrain pipe or weepholes must be covered with a minimum of 12 cubic inches of 3/4 gravel to allow free drainage to the subdrain pipe and to help prevent clogging of the pipe with finer drained silt and clay particles.  The remaining height of wall is typically backfilled with compacted fill.  Compaction testing must be performed on the wall backfill to ensure the require degree of compaction.  In some circumstances, gravel is placed the entire height behind the wall to within 2 feet of the top of the wall to provide better drainage conditions.  The upper 2 feet must consist of a compacted fill blanket to reduce surface drainage infiltration into the wall backfill.


   This exterior concrete block retaining wall has been constructed at the base of a compacted fill slope and has not been provided with waterproofing.  As a result, a significant amount of moisture penetration has occurred through the face of the wall.


 Surface Drainage System

  This picture illustrates several surface drainage control features of a typical retaining wall constructed at the base of an ascending slope.  The wall has been provided with a concrete drainage swale or "V" drain, to intercept upslope drainage. The drainage swale is designed to collect and discharge slope drainage to an approved location, usually the street or storm drain system.  The retaining wall has also been provided with freeboard, which is the portion of the wall which extends above the drainage swale.  The purpose of freeboard is to prevent upslope drainage and debris from overtopping the wall.  The height of freeboard is determined by the geologist, but typically is 2 feet.

Proper drainage behind the wall is critical to the performance or retaining walls. Drainage materials will reduce or eliminate the hydraulic pressure and increase the stability of the fill material behind the wall (assuming of course, that this is not a retaining wall for water...).

CCall Designer Properties Now for an Appointment!

Call 24/7 TOLL FREE 1-877-879-0989

Staying in Touch a Courtesy call/email From Designer Properties From Us. We will automatically call you in 1 week after you contact us, Only if we have been unable to contact you, Just to check and see if you are still interested in us discussing your project.


CUMBERLAND COUNTY Ardulusa★ Beard★ Beaver Creek★ Bethany Crossroads★ Bones Ford★ Bonnie Doone★ Carlos★ Cedar Creek★ Clifdale★ Colonial Heights★ Cumberland★ East Fayetteville★ Eastover*★ Elease★ Falcon*★ Fayetteville*★ Fenix★ Godwin*★ Grays Creek★ Haymount★ Hope Mills*★ Judson★ Lakedale★ Lane★ Lena★ Linden*★ Manchester★ Owens★ Pine Knoll★ Roslin★ Shaws★ Skibo★ Slocomb★ Spring Lake*★ Stedman*★ Vander★ Wade*★ Williams Village★ Anzio Acres★ Ardennes★ Arran Hills★ Arran Lakes★ Arran Lakes North★ Arran Lakes West★ Ascot II★ Bastogne Gables★ Bataan★ Belair★ Bizza Ridge★ Bluesprings Woods★ Bonair Place★ Bordeaux★ Borden Heights★ Bougainville★ Breezewood Acres★ Brentwood★ Bridle Creek★ Broad Acres★ Broadell★ Cade Hill★ Cambridge★ Casablanca★ Cherbourg★ Chestnut Hills★ Clairway★ Clifton Forge★ Corregidor★ Cottonade★ Country Club North★ Creekbend★ Crossgates★ Crystal Park★ Decker Heights★ Dogwood Acres★ Ducks Landing★ Eaglewood Forest★ Eccles Park★ Edenroc★ Emerald Gardens★ Englewood★ Eureka Springs★ Eutaw★ Evergreen Estates★ Fairview Park★ Fairway Forest★ Forest Hills★ Foxfire★ Glenbrook★ Glendale Acres★ Glenhaven★ Golfer Acres★ Green Valley Estates★ Greenwood Homes★ Hammond Hills★ Heritage Heights★ Hermitage★ Hickory Grove★ Highland Acres★ Highland Village★ Hillendale★ Holiday Park★ Holly Springs★ Hollywood★ Hollywood Heights★ Howard Acres★ Huntington Park★ Kingsford★ Kirkwood★ Kornbow★ Lake Shores★ Lake Valley★ Lakecrest★ Legion Park★ Loch Lommond★ Lockwood★ Longview Acres★ Mayfair★ McPherson Estates★ Montclair★ Murray Hills★ Myrtle Hill★ Nijmegen★ Normandy Heights★ North Point Village★ Northwood★ Oakdale★ Oakland★ Peters Creek★ Phoenician Woods★ Pinet Knoll★ Pinewood Lakers★ Pleasant Acres★ Quail Ridge★ Queensdale★ Rivercliff★ Riverview Estates★ Rollingwood★ Sadie Heights★ Saint Mere Eglise★ Savoy Heights★ Scotty Hills★ Seabrook Hills★ Shadowlawn★ Shenandoah★ Sherwood Park★ South Hills★ Southview Townhouses★ Stoney Point★ Stradford Hills★ Summer★ Summertime★ Talleywood★ Tanglewood Estates★ The Greens★ The Lakes The Oaks★ Timberlake★ Tokay★ Tranquil Acres★ University Estates★ University Hills★ Vanstory Hills★ Village Green★ Vineland Park★ Warrenwood★ Waters Edge★ Westchester★ Westwood★ Winter Park★ Woodbridge★ Woodfield★ Woodlea★ Woods Edge★ Yadkins Acres★28331★ 28301★ 28301★ 28301★ 28312★ 28342★ 28301★ 28302★ 28303★ 28304★ 28305★ 28306★ 28307★ 28308★ 28309★ 28311★ 28312★ 28314★ 28307★ 28310★ 28348★ 28356★ 28308★ 28308★ 28390★ 28391★ 28395★Harnett County  Anderson Creek NC★ Angier NC★ Barbecue NC★ Barclaysville NC★ Boone Trail NC★ Buies Creek NC★ Bunnlevel NC★ Cape Fear NC★ Chalybeate Springs NC★ Coats NC★ Cokesbury NC★ Duncan NC★ Dunn NC★ Erwin NC★ Fonville NC★ Hairtown NC★ Harnett NC★ Johnsonville NC★ Kipling NC★ Lakeside Village NC★ Lillington NC★ Luart NC★ Mamers NC★ Norrington Crossroads NC★ Olivia NC★ Overhills NC★ Pineview NC★ Rawls NC★ Ryes NC★ Seminole NC★ Senter NC★ Shawtown NC★ Spout Springs NC★ Turlington NC★ Twin Lakes NC★ Walkertown NC★Lee County Blacknel NC★ Broadway NC★ Colon NC★ Cool Springs NC★ Cumnock NC★ Jonesboro Heights NC★ Lemon Springs NC★ Murchisontown NC★ Northview NC★ Osgood NC★ Quail Ridge NC★ Rosser NC★ Sanford NC★ Swann NC★ Tramway NC★ White Hill NC★Moore County Aberdeen NC★ Addor NC★ Cameron NC★ Carthage NC★ Dover NC★ Eagle Springs NC★ Eastwood NC★ Edgewood Terrace NC★ Elberta NC★ Foxfire NC★ Garners Store NC★ Garren Hill NC★ Glendon NC★ Harris NC★ Haw Branch NC★ Hill Crest NC★ Hog Island NC★ Jackson Hamlet NC★ Jackson Springs NC★ Jugtown NC★ Knollwood NC★ Lakeview NC★ Lincoln Park NC★ Lobelia NC★ Manly NC★ McConnell NC★ Midtown NC★ Monroetown NC★ Mount Pleasant NC★ Murdocksville NC★ Narrow Ridge NC★ Niagara NC★ Parkwood NC★ Pine Hill NC★ Pinebluff NC★ Pinehurst NC★ Pleasantville NC★ Putnam NC★ Robbins NC★ Roseland NC★ Samarcand NC★ Seven Lakes NC★ Silver Springs NC★ Southern Pines NC★ Spies NC★ Taylortown NC★ Thomas Crossroads NC★ Vass NC★ West End NC★ West Philadelphia NC★ Westmore NC★ Whispering Pines NC★ Zion Grove NC★Johnston County Bagley NC★ Benson NC★ Beulahtown NC★ Blackmon Crossroads NC★ Brogden NC★ Clayton NC★ Coats Crossroads NC★ Creeches Mill NC★ Crockers Nub NC★ Crumplers Crossroads NC★ Dixie Crossroads NC★ Earpsboro NC★ Edmondson NC★ Emit NC★ Flowers NC★ Four Oaks NC★ Glenwood Crossroads NC★ Hardee Cross Roads NC★ Hares Crossroads NC★ Harper NC★ Heflin NC★ Hickory Crossroads NC★ Hocutts Crossroads NC★ Johnson Crossroads NC★ Jordan NC★ Kenly NC★ Lees Mill NC★ Lowell Mill NC★ McGee Crossroads NC★ McGee Mill NC★ McKoy NC★ Micro NC★ Moores Chapel NC★ Moores Crossroads NC★ Oak Forest NC★ Oak Grove Inn NC★ Ogburn Crossroads NC★ Oliver NC★ Overshot NC★ Peacocks Crossroads NC★ Pine Level NC★ Powhatan NC★ Princeton NC★ Radford Crossroads NC★ Rains Crossroads NC★ Selma NC★ Smithfield NC★ Spilona NC★ Stancils Chapel NC★ Strickland Crossroads NC★ West Smithfield NC★ Whitley Heights NC★ Willow Springs NC★ Wilsons Mills NC★ Woods Crossroads NC★