Backfill material and concrete encasement for Piping Trenches
Backfill material and concrete encasement for Piping Trenches
(OP)
Dear All ,
While we are excavating the trenches for 12" Ductile Iron water main transmission line , we faced a very hard type of rocks ( like granite stones) and it was very difficult to dig deeper to reach the required depth of excavation for the trench ( 140 cm ). As per the design drawings details ,The trench depth should be about 140cm ,and to be backfilled with 65cm soft bedding msterial ,55 cm of single size aggregate ,and 20 cm of compacted top basecourse layer. Due to the problem in axcavation and the difficulty to reach deeper than 80 cm , the contrcator proposed to fill the 80 cm depth trench and to encase the pipe with B-300 PLAIN CONCRETE . I believe the concrete is very strong comparing to the backfill material , is it OK to go for this choice or you have different ideas ?????
My concern is that the datasheets for the pipe manufacturer call for " minimum allowable depth of cover is 3ft (0.9m)" , But concrete is very strong ..... so if you think it is OK please let me know ....
Thanks in advance
While we are excavating the trenches for 12" Ductile Iron water main transmission line , we faced a very hard type of rocks ( like granite stones) and it was very difficult to dig deeper to reach the required depth of excavation for the trench ( 140 cm ). As per the design drawings details ,The trench depth should be about 140cm ,and to be backfilled with 65cm soft bedding msterial ,55 cm of single size aggregate ,and 20 cm of compacted top basecourse layer. Due to the problem in axcavation and the difficulty to reach deeper than 80 cm , the contrcator proposed to fill the 80 cm depth trench and to encase the pipe with B-300 PLAIN CONCRETE . I believe the concrete is very strong comparing to the backfill material , is it OK to go for this choice or you have different ideas ?????
My concern is that the datasheets for the pipe manufacturer call for " minimum allowable depth of cover is 3ft (0.9m)" , But concrete is very strong ..... so if you think it is OK please let me know ....
Thanks in advance





RE: Backfill material and concrete encasement for Piping Trenches
This flowable fill is just barely concrete (but you cannot stick a shovel into it), I think of it as "engineered dirt" and it doesn't generate much heat in curing so you don't have to worry about heat like you would with high-strength concrete. I would definitely use the flowable fill and definitely dye it a bright non-natural color.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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RE: Backfill material and concrete encasement for Piping Trenches
Its normally not required to fill the entire trench with this concrete. Ask if it is acceptable for him to fill the trench with the backfill material to 12" above the top of pipe, then a layer of only 4 to 6" thickness for placement of the red concrete slurry, then top off the remainder of the trench with the surface layer backfill materials. I think he will go for it.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Backfill material and concrete encasement for Piping Trenches
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Backfill material and concrete encasement for Piping Trenches
RE: Backfill material and concrete encasement for Piping Trenches
see #11 & #12
http://www.nbtexas.org/DocumentView.aspx?DID=406
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Backfill material and concrete encasement for Piping Trenches
If you are somewhere that traffic at speed is a reasonable possibility then you get deep enough (even if you have to blast) and/or case the crossing. I was talking about normal ROW that may see a tractor, ATV, or a deer.
David
RE: Backfill material and concrete encasement for Piping Trenches
RE: Backfill material and concrete encasement for Piping Trenches
Use of any casing is not preferred by gas & petroleum PL companies, but may be installed in special circumstances, ie. very high traffic load (plant roads, etc.) & reduced clearances. Casings are often a condition of RR crossings due to the age-old wars between them.
Some amount of full strength concrete (filled in trench, or placed as preformed slab in top layers) is typically required under road and highway traffic, with any granular backfill material placed to 95% proctor density, if clear cover is reduced below 3, 4, 5, or 6 feet for subdivision street, county, state and interstate highways respectively (as a rule of thumb only). Check the traffic load and add full strength concrete (w/ wwf or bars) as needed.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Backfill material and concrete encasement for Piping Trenches
I have always been under the further impression that DIP is buried all over at least the southern sections of the USA at such depth of cover or maybe at least a little less, and may be actually preferred over other types of pipe due to their dependable, long-term strengths and moduli in such areas.
The only standard exception that I am aware of with regard to use at 2.5 feet cover e.g. is only for absolute minimum Pressure Class 350 thickness pipes (the very lightest available in the USA) installed with the poorest quality (meaning just "dumped" native soil) "Type 1" trench assumed by the AWWA standards/manuals. I suspect few if any Engineers would actually approve installation of a transmission pipe trench under a roadway with such installed as a sub-base! Of course also, four standard trench types better than Type 1 are also illustrated in the standards/manuals, and many Special Class thicknesses of 12" DIP thicker than minimum PC350 may also be available.
Beyond this, I believe DIPRA also has a "...Shallow Cover..." paper that talks about aspects, including examining loadings etc., at depth of cover situations even less than 2.5 feet or 0.75 m (that I believe you can obtain from them upon request.) [Of course also, there may have to be very good reason or justification before many Engineers would design (against any applicable codes or consensus guidelines?) the installation of any pipe materials extremely shallow in very cold regions, due to freezing etc.]
RE: Backfill material and concrete encasement for Piping Trenches
RE: Backfill material and concrete encasement for Piping Trenches
I just want to know one thing .. as we are goint to encase the ductile pipes with concrete , do we need to wrap the ductile pipes with the polyethylene sheets , or no need !!
RE: Backfill material and concrete encasement for Piping Trenches
DIPRA's Installation Guide for Ductile Iron Pipe does mention in the context at least of thrust blocks, "...a sheet of polyethylene film is sometimes placed between the fitting and the block to aid in later removal as desired."
RE: Backfill material and concrete encasement for Piping Trenches
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/