Retrofitting weep holes after the fact
Retrofitting weep holes after the fact
(OP)
I'm seeing more and more instances recently of poured concrete retaining walls without weep holes, which are coming under hydrostatic load from rising groundwater tables, and then leaking through cracks to damage floor level condos and the like. I understand that normally you'd install a weep hole to tie in to porous backfill behind the retaining wall that collects water and helps convey it to the weep hole without pulling sediment / backfill from behind the wall. In cases where a weep hole does not exist at all, and a maintenance contractor needs to drill one to relieve hydrostatic pressure behind the wall and dry the backfill out, what's the best procedure? I worry that if I tell a maintenance contractor to simply drill a hole through the wall, that the weeping might advect sediment through the hole and create a problem. Is there a standard practice used for retrofitting weep holes that handles this? Any advice on weep hole spacing?
Thanks in advance.
Thanks in advance.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com





RE: Retrofitting weep holes after the fact
RE: Retrofitting weep holes after the fact
RE: Retrofitting weep holes after the fact
RE: Retrofitting weep holes after the fact
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Retrofitting weep holes after the fact
RE: Retrofitting weep holes after the fact
RE: Retrofitting weep holes after the fact
I've attached a photo of the wall on the exterior of the unit. Here it serves as a retaining wall, then it extends back under the building, behind the point of view of the photo, and becomes more of a foundation wall.
I can't put a monitoring well on the back side of the wall because there's a horizontal slab there serving as the sidewalk for the ground level unit. You can see staining from water leaking through the seam between the upper horizontal slab and the foundation wall. I've given the owner a laundry list of means to prevent surface water from accumulating behind the wall, but I'm not convinced the back side of the wall has dried out fully, and need a way to promote that.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Retrofitting weep holes after the fact
RE: Retrofitting weep holes after the fact
seal the slab joints and especially the joint between the slab and wall
I dont see where you could use bentonite if the ground is already covered with concrete slab
RE: Retrofitting weep holes after the fact
RE: Retrofitting weep holes after the fact
Lots of small problems. Roof drain leaders were put underground by a prior contractor. They enter the ground as black corrugated HDPE and daylight in the curb as PVC, so who knows how they were spliced together. Also the PVC is at an adverse slope, so the thing actually catches water from the curb instead of draining freely, which could be a big deal if the connection between the HDPE and PVC isn't water tight. Some slabs are cracked above the wall. Some gutters drain to the surface at the adjacent building and then drain through landscaping to the back side of the wall at an area not pictured, which traps the water up against the wall, and needs to be regraded. The slab outside the problem unit is flat, so needs a slot drain or trench drain. Some other stuff. Our soils are silty clay here, so I'm not that concerned with soil addenda.
I suspect the list of site improvements I gave will ameliorate the problem, but it'd be nice to provide relief otherwise, as well as have an easy way to test if the soil behind the wall is wet. I included oldestguy's suggestion in the writeup as part of an overall plan, so we'll see how it goes.
It's possible the wall was originally built with weep holes and appropriate backfill, but that the holes were covered over by some kind of surface treatment. Look closely at the image, you can see where it looked like someone had resurfaced the wall a while back.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Retrofitting weep holes after the fact
As to an observation well or two, coring of slabs is no big job and later filling can be barely visible. The observation well might even be as small as slotted electrical conduit, set in an augered hole. A piece of 2 conductor wire and an ohmeter is the measuring device if you can't read it with a tape measure.
If slabs have to be removed to change grades, think about a layer below them of a mix of 10% bentonite, at the most. Otherwise heaving can occur. That layer need only be 4 to 6 inches thick, and can be done with a garden rototiller.
I've cleaned out joints in slabs and have dribbled in bentonite. I'm leary of contractors that will "waterproof" walls by injecting bentonite. It can be vicious stuff if in a thick layer.
RE: Retrofitting weep holes after the fact
In the photo, you can see two important clues. The vertical crack itself is where the bulk of the water intrusion occurred during the lateral break, but you can also see staining of the wall from light water intrusion from above. That's from the seam between the foundation wall and the horizontal slab, which is hidden behind the stud wall in this photo, but visible in the prior photo further up the thread. My hope is that weep holes or similar, in conjunction with my "laundry list" of site improvements, will keep the groundwater below this upper seam.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Retrofitting weep holes after the fact
I'd concentrate on fixing up surface drainage and surface infiltration first. Handing the owner a list of work items may well not do it if the contractor is not well experienced or closely supervised by an experienced person. Blending of bentonite with on-site soil can be done wrong, especially if granulated bentonite is used vs powdered. Using laborers to do the mixing needs someone to say "OK that's good", etc. or a half a$$ job results. Will settling of new slabs result?
Buildings appear rather modern. Was there a building code requiring a footing drainage system? It's quite common in my area (Wisconsin).