Haunches of pipe? 3

[nutbutter]

This is a very silly question, but nobody is around to ask. What is meant by the haunches of a pipe? I've got to extend the pipe bedding to the haunches. Is it the centerline?

 

[cvg]

below the centerline - in the part of the pipe which is difficult / impossible to properly compact the backfill.

 

[nutbutter]

OK, so if one was required to extend the bedding to the haunches of the pipe, what would that mean? Would it have to extend all the way to the centerline?

 

[cvg]

bedding is typically placed below the invert 3 - 6 inches thick (minimum) unless you are installing very large pipe. Pipe zone material up to the springline might also be specified as granular bedding material instead of native soil, depending on the geotech or owners requirements. Since haunches don't exist above the springline and placement of bedding material above the springline doesn't do much for improving the strength or reducing settlement in the trench, I would have to assume you are correct to stop there.

 

[LHA]

In the US, bedding is spec'd by Class I-IV. Here's typical guidelines. cvg is correct, usually the geotech will recommend one.

Pipe Bedding: Unless otherwise specified or noted on the Plans the following bedding classes are as commonly required and shall also conform to Section C of the AWWA Standards: Bedding (R.61-58.4.D.(11)(b)).
When granular material embedment is required, the Contractor will backfill above the granular bedding as specified for Type I bedding to an elevation one (1) foot above the top of the pipe bell.
Stones, other than crushed bedding, shall not come in contact with the pipe and shall not be within 6 inches of the pipe.
a. Type I - Shaped Bottom Bedding: Shaped bottom bedding shall be such that the pipe bears uniformly upon undisturbed native earth. Soil is then backfilled by hand around the pipe and completely under the pipe haunches in uniform layers not exceeding six (6) inches in depth to an elevation one (1) foot above the top of the pipe bell.
Each layer shall be placed; then carefully and uniformly tamped so that the pipe is not damaged nor the alignment disturbed.
b. Type II - Granular Material Embedment: For Type II bedding, the trench bottom shall be undercut a minimum of six (6) inches below the pipe barrel grade and filled with an approved stone to an elevation such that the pipe will be completely and uniformly bedded to a vertical height of one-third the outside diameter of the pipe for the pipe’s entire length and the entire width of the ditch. Type II embedment shall be used as directed by the Engineer.
c. Type III - Granular Material Embedment: For Type III bedding, the trench bottom shall be undercut a minimum of six (6) inches below the pipe barrel grade and filled with an approved stone to an elevation such that the pipe will be completely and uniformly bedded to vertical height of one-half the outside diameter of the pipe for the pipe’s entire length and width of the ditch. Type III Granular material embedment shall be used as directed by the Engineer.
d. Concrete Encasement and Cradles: Concrete encasement or cradles will be used only as designed for individual cases or as directed by the Engineer and will be noted on the plans and in the Special Provisions when applicable.
e. Stone Stabilization: Stabilization stone shall be used when the trench must be undercut in excess of the six (6) inches required for Type II or Type III bedding, either due to excessive ground water or the existence of unsuitable material incapable of adequately supporting the pipe.
The Contractor shall undercut the trench as necessary and shall place the compact the stone stabilization material required to establish a stable bottom to receive either the Type Ii or Type III granular bedding and pipe.
2. Depth of Pipe Installation: Unless otherwise indicated on Plans, or required by existing utility location, all pipe will be installed with the top of the pipe at least 3.0' below the edge of adjacent roadway pavement or 3.0' below the ground at the pipe, whichever is greatest. The Contractor is instructed to check the construction plans and blow-up views for additional requirements.
The maximum depth of cover for the previously specified pressure classifications shall be as follows:
Type I Bedding 10 feet
Type II Bedding 15 feet
Type III Bedding 20 feet
The Contractor may be required to vary the depth of pipe to achieve minimum clearance from existing utilities while maintaining the minimum cover specified whether or not the existing pipelines, conduits, cables, mains, etc. are shown on the Plans.


Engineering is the practice of the art of science - Steve

 

[cvg]

note that the spec provided by LHA is for waterlines per AWWA standards. For RCP, American Concrete Pipe Assoc (ACPA) provides standards which are published in the "Concrete Pipe Design Manual". They also specify 4 types of installation, but bedding requirements are different than those published by the AWWA. Requirements are a bit less stringent, presumably because RCP is intended for low pressure or gravity flow situations. You need to evaluate the type of pipe, as well as the geotechnical conditions before establishing a trench bedding and backfill specification.