Bulging, bowing and cracking

The Old House Web
Editor's note: This story is adapted from theU.S. Department of Housing and Urban Development's Residential RehabilitationInspection Guide, 2000. Clickhere for other stories in this series.

retaining wall

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.

Retaining walls more than two feet in height should be backedwith drainage material, such as gravel. There should be drains at the bottom ofthe drainage material. The drains should discharge water either at the end ofthe wall or through pipes set in the wall itself. These drains and the drainagematerial behind the wall relieve the pressure of ground water on the wall.

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.

Failure to drain should be remedied by excavating behind the wall, replacingthe drainage material and dam-aged drainage piping, and backfilling. In all butthe driest climates, improper drainage of water from behind a retaining wall cancause the wall to fail.

Inspect: Check for bowing (vertical bulges), sweeping (horizontal bulges), and cracking in retaining walls that can be caused by water pressure.

Bulging can also be a result of inadequate strength to resist the load of theearth behind the wall. Bowing and sweeping failures may be correctable if foundearly enough and if the cause is poor drainage. Check for other failures ofretaining walls. Failure by overturning (leaning from the top) or sliding may becaused by inadequate wall strength. In addition, water behind a wall can createmoist bearing, especially in clay soils, and con-tribute to sliding.

Retaining walls also fail due to settling and heaving. The former occurswhenever filled earth below the wall compacts soon after the wall is built, orwhen wet earth caused by poor drainage dries out and soil consolidates at anytime in a wall's service life. Poor drainage contributes to failure in coldclimates by creating heaving from frozen ground. Both overturning and slidingmay be stabilized and sometimes corrected if the amount of movement is notextreme.

Settling may be corrected on small, low walls of concrete or masonry, andheaving may be controlled by proper drainage. Significant failure of any kindusually requires rebuilding or replacing all or part of a wall. Failingretaining walls more than two feet in height should be inspected by a structuralengineer.

Related stories: Sitedrainage issues ~~ Siteimprovements

About the Author
The Old House Web

Search Improvement Project