Situation:
I recently had a 10-inch sanitary sewer line installed by directional bore. The depth of the line ranged from 21 to 30 feet, so I specified a DR-9 thickness smooth-wall HDPE (which actually gives an inside-diameter of about 8 inches, but that is the design I needed for my flow-line). The bore length was 470 feet with a plan slope of 1.50%, but the specified minimum for the pipe was 0.50%. The pipe would also be in the water table.
During the bore, the directional bore crew had to redo their bore 3 times because they were losing the signal on their drill string in about the same location -- apparently due to a nearby radio tower. During the 3rd redo on drilling the pilot hole, we had the crew dig a hole to find the drill string to where we were going to set a manhole for the line. An elevation shot indicated that the installed pipe would likely lay at a 0.80% slope, which was within specification. After finding the pipe, the crew proceeded with the back-ream and pipe-pull.
After a televising was done on the newly installed pipe, 3 sags in the pipe were found: Two sags at 1" deep and one sag at 2" deep. Maintenance personnel examining the televising had concerns, but indicated that extra cleaning would need to be done on the line once in use and didn't feel strongly about digging down 25-30 feet to make corrections. Another engineer and I agreed that the risks of digging the pipe up and breaking the bentonite seal after installation were not prudent given the opinion of our maintenance staff. After further deliberations with the contractor, we finally settled on a 5-year $200,000 maintenance bond on the pipe should the pipe fail while in service.
Questions:
1) Anyone have experience with this scenario? Have you heard of signal interferance from neighboring radio towers?
2) Is the radio tower interference considered an unforeseen condition that the engineer is responsible to disclose in the contract? (For background, the contractor did do some signal testing on the ground prior to bidding on the job.)
3) Ideally, no sag would be the best, but what should be tolerated in terms of sags in the pipe installation?
4) Would you specify a steeper plan slope than a 1.50%? My understanding is that a 1.50% for HDD installations is industry minimum.
5) What are your thoughts on the bond, versus corrections on the pipe?
Your opinions are appreciated! Thanks!
I recently had a 10-inch sanitary sewer line installed by directional bore. The depth of the line ranged from 21 to 30 feet, so I specified a DR-9 thickness smooth-wall HDPE (which actually gives an inside-diameter of about 8 inches, but that is the design I needed for my flow-line). The bore length was 470 feet with a plan slope of 1.50%, but the specified minimum for the pipe was 0.50%. The pipe would also be in the water table.
During the bore, the directional bore crew had to redo their bore 3 times because they were losing the signal on their drill string in about the same location -- apparently due to a nearby radio tower. During the 3rd redo on drilling the pilot hole, we had the crew dig a hole to find the drill string to where we were going to set a manhole for the line. An elevation shot indicated that the installed pipe would likely lay at a 0.80% slope, which was within specification. After finding the pipe, the crew proceeded with the back-ream and pipe-pull.
After a televising was done on the newly installed pipe, 3 sags in the pipe were found: Two sags at 1" deep and one sag at 2" deep. Maintenance personnel examining the televising had concerns, but indicated that extra cleaning would need to be done on the line once in use and didn't feel strongly about digging down 25-30 feet to make corrections. Another engineer and I agreed that the risks of digging the pipe up and breaking the bentonite seal after installation were not prudent given the opinion of our maintenance staff. After further deliberations with the contractor, we finally settled on a 5-year $200,000 maintenance bond on the pipe should the pipe fail while in service.
Questions:
1) Anyone have experience with this scenario? Have you heard of signal interferance from neighboring radio towers?
2) Is the radio tower interference considered an unforeseen condition that the engineer is responsible to disclose in the contract? (For background, the contractor did do some signal testing on the ground prior to bidding on the job.)
3) Ideally, no sag would be the best, but what should be tolerated in terms of sags in the pipe installation?
4) Would you specify a steeper plan slope than a 1.50%? My understanding is that a 1.50% for HDD installations is industry minimum.
5) What are your thoughts on the bond, versus corrections on the pipe?
Your opinions are appreciated! Thanks!
