We were able to determine that the cause of the rather dramatic movement was excess hydro-static pressure behind the walls, which had been occurring for many years.
Unfortunately for the homeowners, the ground surface below the wood deck adjacent to the damaged wall had promoted surface water drainage towards the foundation wall (i.e., negative drainage) instead of away from it (positive). This condition allowed the back-fill soils to be regularly saturated, which dramatically increases the lateral pressure on the wall. In this case, it was well beyond what the CMU bock wall could resist and it slowly started to move inward and begin to fail.
To add to their problems, a “waterproofing contractor” had sold the homeowners on an interior drainage system, who incorrectly informed them that this would relieve the hydro-static pressure on the exterior face of the foundation wall. Believe it or not, we see this far too often and it wastes thousands upon thousands of homeowner dollars.
The solution was to relieve the pressure from behind the wall and at the same time reinforcing and moving it back into a plumb position. The following order of construction was used:
1. Remove the saturated back-fill soils
2. Place bracing on the wall and hydraulically push it back into a plumb condition.
3. Reinforce the wall with carbon fiber straps and steel pins inserted into the wall.
4. Install a wall and footing drainage system to eliminate hydro-static pressure and tie it into the interior sump pump.
5. A waterproofing membrane was also applied to the below-grade wall face.
6. Re-grade the ground surface along the foundation wall to promote positive drainage away from the home.
7. Extend the sump pump discharge pipe away from the foundation wall so water was not reintroduced into the drainage system.
The end result was a completely restored and stabilized foundation wall with a 20-yr transferable warranty… and a happy and satisfied client!
Does your exterior basement area way drain easily clog with soil or other debris? Then it’s time for a drainage analysis by one of our engineers.
This picture is from a drain at the bottom of the exterior steps to the basement and regularly fills up with sand and silt. We will be sending a camera probe through the pipe to determine where the soil is entering the exterior footing drain and then design a solution to fix the problem.