Weep Holes in Gravity Retaining Walls

Finally, a subject to which I can contribute!

The purpose of weep holes is to avoid the build up water behind the wall. A build up of water has two negative consequences. The first is it acts as a lubricant for stone and soils that may be locked into place by their friction with adjacent particles. This can lead to increased soil loads the wall has to carry. The second, and definitley related, is the addition of a hydrostatic pressure on the backside of the wall.

Contrary to some of the post I read here, a gravity wall does not have to be a segmental wall. Though, to be fair, that is what is usually interpreted. A gravity wall relys solely on the moment created by the weight of the wall and the width of the wall to counteract the overturning force caused by the soil pressure and the wall height.

A segmental wall could relieve water through the joints in the segments. Depends upon the design. But this can be unsightly. A sub-grade drainage system that collects water and discharges it at designed locations can greatly improve aesthetics.

A solid gravity wall definitely needs a point to discharge accumulated water.

Typicall, the subgrade drainage system is perforated pipe. Thus, the weeps also tend to be circular. But if you are utilizing open graded rock as your collection and conveyance medium to transport and discharge water that may be behind the wall, the shape of the weep is immaterial.

There is really no rule-of-thumb as to how frequently weep holes should be spaced. But, obviously, the more frequent, most likely, the better your "back-wall" system of collecting, conveying, and discharging water from behind the wall will perform.

If your wall is a segmental wall, it seems likely that you will have a geotextile on the backside of the segments. This fabric prevents soil and rock particles from being transported away from the backside of the wall with the flow of water. This geotextile fabric can, over time, start to blind by the many pores in the facric being filled in by small soil particles. Thus, the reason to have the behind the wall water collection, conveyance, and discharge system. In other words, weeps are still a preferred design option.

Not so important is the spacing. What is important is the elevation of the weeps. Try to keep them near the toe of the wall. This is the best location to avoid the build up of water behind the wall.

A lot to cover here. But I hope this gives you enough information to decide for yourself what the correct answer. The best answer, I think, is one that gives you the tools to think through to a solution best suited to you (Something I think this site is great at). A cookie-cutter answer is almost as bad as no answer at all.

Thank you for giving me the opportunity to post.