mikeCTE
Structural
- Feb 21, 2014
- 42
A client of mine (City) has a retaining wall that we inspected (as part of a larger inspection program) that is failing. The wall ranges from 2-6ft tall and supports a 2-lane road. The wall appears to be L-shaped CIP concrete and there is undermining/washout that has occurred in multiple spots along the wall.
My company did an inspection 5 years prior, and the extent of the undermining has increased. The road is now showing signs of settlement through cracking of the asphalt - getting more significant as it approaches the wall. I'm assuming the soil is doing its best to arch and provide stability, but the vibration of the wall from traffic along with heavy precipitation events which likely funnel into the retained side of the wall are working against us.
As a short term, relatively cheap fix, I am recommending that they do a polyurethane foam injection to remove the dip in the road (currently 2-3" x 20ft long x 1 lane wide) and am also considering using the same foam to inject into the undermined voids along the exposed face of the wall (these voids are up to 5ft under the road). I am certain that the walls are not properly drained and that has led to this issue, so I don't want to make it any worse by blocking the flow of water and increasing the retained hydrostatic height.
The contractor we're working with for the foam suggests to use some pipes that would be inserted prior to foaming (while keeping the ends clear from the foam that will fill the voids). I'm open to this idea and would think that we'd probably want 2" pipes at 1ft OC for all void locations to try to provide a near continuous outlet to reduce the water pressure. However, I am not positive this will work because the water will be forced to find these little openings and could, instead, just decide to undercut the foam and create more problems.
The street is heavily used by both car and heavy truck traffic, so shutting things down to rebuild a wall is kind of the last resort vs this $15k fix.
Does anyone have thoughts on a good way to handle this situation? Ways to improve the drainage?
Should we try to wedge in a perforated pipe with a filter fabric and foam around it? <- this doesn't seem like it would work...
I'm confident in the foam's ability to provide the structural support needed, but the drainage is the failure mechanism at work, and without fixing that, we will only exacerbate the problem.
My company did an inspection 5 years prior, and the extent of the undermining has increased. The road is now showing signs of settlement through cracking of the asphalt - getting more significant as it approaches the wall. I'm assuming the soil is doing its best to arch and provide stability, but the vibration of the wall from traffic along with heavy precipitation events which likely funnel into the retained side of the wall are working against us.
As a short term, relatively cheap fix, I am recommending that they do a polyurethane foam injection to remove the dip in the road (currently 2-3" x 20ft long x 1 lane wide) and am also considering using the same foam to inject into the undermined voids along the exposed face of the wall (these voids are up to 5ft under the road). I am certain that the walls are not properly drained and that has led to this issue, so I don't want to make it any worse by blocking the flow of water and increasing the retained hydrostatic height.
The contractor we're working with for the foam suggests to use some pipes that would be inserted prior to foaming (while keeping the ends clear from the foam that will fill the voids). I'm open to this idea and would think that we'd probably want 2" pipes at 1ft OC for all void locations to try to provide a near continuous outlet to reduce the water pressure. However, I am not positive this will work because the water will be forced to find these little openings and could, instead, just decide to undercut the foam and create more problems.
The street is heavily used by both car and heavy truck traffic, so shutting things down to rebuild a wall is kind of the last resort vs this $15k fix.
Does anyone have thoughts on a good way to handle this situation? Ways to improve the drainage?
Should we try to wedge in a perforated pipe with a filter fabric and foam around it? <- this doesn't seem like it would work...
I'm confident in the foam's ability to provide the structural support needed, but the drainage is the failure mechanism at work, and without fixing that, we will only exacerbate the problem.
