CanuckPE
Structural
- Apr 14, 2021
- 21
I'm working on a project for a mat foundation under train rails for some rail equipment. The area we've excavated is traditionally wet, and we specifically designed a drainage system that would mitigate the typically wet surface. I've attached an image with a depiction of our proposed weeping tile location(drainage path is purple, top image) and the proposed weeping tile location from the contractor (drainage path is purple, bottom image). For reference in the images, the black rectangle is a rail loadout facility, the black parts with the hatch is the rail, the blue rectangle is our newly placed mat foundation with 30" of clean granular fill below, and red arrows depict the natural slope (which is about 1% from top of the image to the bottom). The water traditionally runs off of an adjacent road and towards the rails per the red arrows. The contractor "forgot" to place the weeping tile, and now has ground prepared, and reinforcing steel placed for the mat. I caught this on the field review.
I did soil mechanics training in a master's degree, but never really focused heavily on hydrology. I'm hoping there are some experts out there to provide some guidance.
The fact of the matter is that surface water from precipitation will likely hit the gravel, dive under the mat through the permeable clean gravel layer, and make its way into the weeping tile as proposed by the contractor. I would have preferred our original arrangement to the contractor's proposed alternative such that ground water was conducted under the mat via the weeping tile rather than through the gravel under the foundation. It's a more direct path.
Questions:
1) Should I capitulate and allow the contractor to place the weeping tile as proposed? Are there any technical drawbacks to this approach? The bearing pressure on the ground is minimal (in the 1000 to 1500 psf range), so the additional ground water shouldn't have a substantial drawback on strength/stiffness of the granular fill.
2) Would the granular fill conduct the water just as well/quickly as the weeping tile?
I did soil mechanics training in a master's degree, but never really focused heavily on hydrology. I'm hoping there are some experts out there to provide some guidance.
The fact of the matter is that surface water from precipitation will likely hit the gravel, dive under the mat through the permeable clean gravel layer, and make its way into the weeping tile as proposed by the contractor. I would have preferred our original arrangement to the contractor's proposed alternative such that ground water was conducted under the mat via the weeping tile rather than through the gravel under the foundation. It's a more direct path.
Questions:
1) Should I capitulate and allow the contractor to place the weeping tile as proposed? Are there any technical drawbacks to this approach? The bearing pressure on the ground is minimal (in the 1000 to 1500 psf range), so the additional ground water shouldn't have a substantial drawback on strength/stiffness of the granular fill.
2) Would the granular fill conduct the water just as well/quickly as the weeping tile?