I have a problem concerning very heavily loaded pipe-arch culverts under which normal assumptions appear rather conservative. This is based upon comments from a researcher who tested large span culverts with shallow cover. He related a test on a 24 ft span culvert with 16" cover supporting a 108 kip axle load without failure or serious deformation.
I have a 6 ft pipe-arch, 55" rise with 2 ft of cover and 110 psi tire pressure (46"x70" contact area, 4 tires) and a total axle load of 1406 kips. At the top of the culvert, using 2:1 footprint spread of the load, the resulting pressure is about 7.7 ksf uniformly distributed over the full span and length of the culvert. I am looking for a way to better determine pressures at the soil-structure interface using a concrete mat over the culvert area at the surface. It works fine if I use a slab-on-elastic foundation linear analysis, but to start I have just used a simple approach to determine the spring constants and done some bounding of the problem. I have varied the K's over the culvert from 5-10 ksf/in above the culvert to 67 ksf/in at a diameter away from the culvert, using 30 ksf/in in between.
Pipe-arch manufacturer's are not inclined to deviate from their normal approach of adding cover depth. This is not a practical option in this case, therefore the concrete mat approach. Additionally, a worst case scenario has 2 of the pipe-arches side-by-side with about 3 ft of space between them.
I have found reference to CANDE, a culvert analysis and design program, which is much more rigorous theoretically and appears to have some value for my analysis. I purchased the user's manual from McTrans and it will work for the single culvert case. With appropriate boundary conditions, I believe that it will suffice for the double culvert case as well. My question is: does anyone have comments pro or con about the software and experience with the somewhat esoteric soil and interface elements (for a stuctures type) used? Also, is there something out there that is better either for a manual solution or computer solution. Thanks for any help.
Barry Santana
I have a 6 ft pipe-arch, 55" rise with 2 ft of cover and 110 psi tire pressure (46"x70" contact area, 4 tires) and a total axle load of 1406 kips. At the top of the culvert, using 2:1 footprint spread of the load, the resulting pressure is about 7.7 ksf uniformly distributed over the full span and length of the culvert. I am looking for a way to better determine pressures at the soil-structure interface using a concrete mat over the culvert area at the surface. It works fine if I use a slab-on-elastic foundation linear analysis, but to start I have just used a simple approach to determine the spring constants and done some bounding of the problem. I have varied the K's over the culvert from 5-10 ksf/in above the culvert to 67 ksf/in at a diameter away from the culvert, using 30 ksf/in in between.
Pipe-arch manufacturer's are not inclined to deviate from their normal approach of adding cover depth. This is not a practical option in this case, therefore the concrete mat approach. Additionally, a worst case scenario has 2 of the pipe-arches side-by-side with about 3 ft of space between them.
I have found reference to CANDE, a culvert analysis and design program, which is much more rigorous theoretically and appears to have some value for my analysis. I purchased the user's manual from McTrans and it will work for the single culvert case. With appropriate boundary conditions, I believe that it will suffice for the double culvert case as well. My question is: does anyone have comments pro or con about the software and experience with the somewhat esoteric soil and interface elements (for a stuctures type) used? Also, is there something out there that is better either for a manual solution or computer solution. Thanks for any help.
Barry Santana
