Pipeline Trench Backfill Specifications
Pipeline Trench Backfill Specifications
(OP)
My question is can anyone point me to some previous specifications for backfilling the pipe's trench. I have not overseen many pipeline installations in my time, but the few that I have have mostly been for gravity / stormwater pipes (pond outlets / inlets).
I've taken over as the field QC for my company's project in southern Ohio. Part of the work is to install at 12-inch PVC raw water line and construct a sediment pond for the future landfill. I'm currently baby-sitting the water line installation and I believe the specifications are too restrictive / not producing the quality that they want to get. Currently, for the backfilling, we are required to backfill, with sand, in 6" lifts up to 9-in above the pipe. From there we will backfill with the excavated spoils (clay material) and compact in 4-in loose lifts and testing for 95% density test (ASTM D6938). The testing starts with the 2nd clay lift. Due to the depth of the pipe the clay fill will be approximately 3.5 ft to 4 ft thick.
This water line is not within any road ROWs, rather just out in the country-side.
One idea I have is to take a test area (roughly 50 LF) and try compaction at different thicknesses (8-in or 12-in) and test these areas to prove they will achieve the desired density.
My other is to try and present what others are doing / requiring for backfilling.
I've taken over as the field QC for my company's project in southern Ohio. Part of the work is to install at 12-inch PVC raw water line and construct a sediment pond for the future landfill. I'm currently baby-sitting the water line installation and I believe the specifications are too restrictive / not producing the quality that they want to get. Currently, for the backfilling, we are required to backfill, with sand, in 6" lifts up to 9-in above the pipe. From there we will backfill with the excavated spoils (clay material) and compact in 4-in loose lifts and testing for 95% density test (ASTM D6938). The testing starts with the 2nd clay lift. Due to the depth of the pipe the clay fill will be approximately 3.5 ft to 4 ft thick.
This water line is not within any road ROWs, rather just out in the country-side.
One idea I have is to take a test area (roughly 50 LF) and try compaction at different thicknesses (8-in or 12-in) and test these areas to prove they will achieve the desired density.
My other is to try and present what others are doing / requiring for backfilling.
--morgwreck243





RE: Pipeline Trench Backfill Specifications
8 inch thick might be acceptable, 4 inch thick loose lifts seems a bit excessive
95% seems high, but not unreasonable
so, are you working for the contractor?
suggest you request the engineer of record to review your proposal unless you wish to take responsibility for his design.
RE: Pipeline Trench Backfill Specifications
Is the pipe going to be adopted as public infrastructure ? In that case you may just have to stick to the local building authority codes.
RE: Pipeline Trench Backfill Specifications
EireChch - This is part of the new landfill for the DOE, which I imagine will be under their control in perpetuity.
--morgwreck243
RE: Pipeline Trench Backfill Specifications
MINIMUM TRENCH COMPACTION DENSITIES
type I (Under any existing or proposed pavement, curb, gutter, attached sidewalk, roadway
shoulders, and other areas within right-of-way subject to vehicular traffic, or when any part of the trench excavation is within 2-feet of the existing pavement, curb, or gutter.) - 95%
type II (On any utility easement or right-of-way outside limits of Type I backfill.) - 85% and 90% for the bedding
type III (Around any structures (manholes, etc.) or exposed utilities outside limits of Type I
backfill.) - 95%
RE: Pipeline Trench Backfill Specifications
RE: Pipeline Trench Backfill Specifications
RE: Pipeline Trench Backfill Specifications
RE: Pipeline Trench Backfill Specifications
RE: Pipeline Trench Backfill Specifications
1. This is a trench, so nuclear methods must be checked for trench effects.
2. You might consider that the in-place density should be slightly higher than the natural density of the area (for bedding purposes), so you might check the actual density of the material adjacent to the trench (I would suggest a drive sleeve method for this) and then set the in-place density to be about 10% higher than the natural density....forget the Proctor value in this case.
RE: Pipeline Trench Backfill Specifications
RE: Pipeline Trench Backfill Specifications
This seems to be, now, at odds with work done by Spangler back a half century ago . . . if you can find Leonards Foundation Engineering book, Spangler has an article on conduits and their backfill. He was addressing the deformation of the pipes. In his work, he stressed to leave a loose zone above the pipe - will reduce the weight of the soil on the pipe due to arching effects. PENNDOT as I referenced above wants high compaction to 4 ft above the pipe obvert and then 100% standard MDD in the upper 3 ft (presumably they are referring to where the drainage pipes cross the road.
I've seen contractors loosely backfill above conduits crossing the road and then place a bit extra for a "bump" - with time and with the traffic, the bump will settle a bit. Top it up if needed or after a season, cut it down. Not that I like this - but I saw one box culvert - about 3 m deep backfilled by a Malaysian contractor for a gov't road in less than a day . . . no layers/no tests and to date, after two monsoon seasons, there is no noticeable depression. Of course they could have just gotten lucky! There are plenty of other culverts crossing the same road (earlier construction) that definitely show depressions and growing each season.
RE: Pipeline Trench Backfill Specifications
I've seen too many cases of piping failure.
f-d
ípapß gordo ainÆt no madre flaca!
RE: Pipeline Trench Backfill Specifications
RE: Pipeline Trench Backfill Specifications
I guess I'll let the op let me know if I was helpful. . .
f-d
ípapß gordo ainÆt no madre flaca!
RE: Pipeline Trench Backfill Specifications
RE: Pipeline Trench Backfill Specifications
I've used PVC in a steel carrier pipe in similar installations. If the embankment's not too high, I just use PVC with mechanical joints.
What would you use?
RE: Pipeline Trench Backfill Specifications
Finally, the client has accepted my proposal for the test section. We performed the test section (8-inch loose lifts) and the compaction tests passed with flying colors (99% relative compaction). I am now waiting for test results to be processed through the client's bureaucracy before changing the specifications.
fatdad: Some of the raw water line (estimated 500 LF) runs through the sediment pond's embankment, but the areas that I was speaking of was where the raw water line is running through undeveloped areas (no roads or structures near the pipe's location).
--morgwreck243