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| The outward movement of the upper part of this retaining wall can be halted only by structural reinforcement. Simply patching the crack will not solve the problem. |
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Retaining walls more than two feet in height should be backed with drainage material, such as gravel. There should be drains at the bottom of the drainage material. The drains should discharge water either at the end of the wall or through pipes set in the wall itself. These drains and the drainage material behind the wall relieve the pressure of ground water on the wall.
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| Inspect: If possible, weep holes and related drains should be examined closely following a reasonably heavy rain to make sure they are working properly. If they are not discharging water, the drains should be cleaned out and observed again in the next rain. |
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Failure to drain should be remedied by excavating behind the wall, replacing the drainage material and dam-aged drainage piping, and backfilling. In all but the driest climates, improper drainage of water from behind a retaining wall can cause the wall to fail.
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| Inspect: Check for bowing (vertical bulges), sweeping (horizontal bulges), and cracking in retaining walls that can be caused by water pressure. |
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Bulging can also be a result of inadequate strength to resist the load of the earth behind the wall. Bowing and sweeping failures may be correctable if found early enough and if the cause is poor drainage. Check for other failures of retaining walls. Failure by overturning (leaning from the top) or sliding may be caused by inadequate wall strength. In addition, water behind a wall can create moist bearing, especially in clay soils, and con-tribute to sliding.
Retaining walls also fail due to settling and heaving. The former occurs whenever filled earth below the wall compacts soon after the wall is built, or when wet earth caused by poor drainage dries out and soil consolidates at any time in a wall's service life. Poor drainage contributes to failure in cold climates by creating heaving from frozen ground. Both overturning and sliding may be stabilized and sometimes corrected if the amount of movement is not extreme.
Settling may be corrected on small, low walls of concrete or masonry, and heaving may be controlled by proper drainage. Significant failure of any kind usually requires rebuilding or replacing all or part of a wall. Failing retaining walls more than two feet in height should be inspected by a structural engineer.
Related stories: Site drainage issues | Site improvements
