Sant. Sewer & Watermain over culvert 2

[Sully03]

Does anybody know of any recommended clearances or procedures when constructing a sanitary sewer and a watermain above a concrete culvert(750mm). What vertical separation would you recommend between the services and the top of culvert? The recommended depth for frost protection in my area is 1.2m.

Cory

 

[KRSServices]

When you reference the term culvert, is the pipe exposed to the elements in a similar fashion that a road access culvert would be? Is the gradient of the sanitary main the determining factor as to the consideration of the pipes crossing the 750 mm pipe? What is the depth of cover over the existing 750 mm pipe and is it within the frost zone?

Based upon the answers, there would then be a number of different options that could be considered.

KRS Services

http://www.krs-services.com

 

[yogibear1]

Here, in west central Florida, there are statutory requirements from the State Health Dept regarding the horizontal and vertical separation of water lines from wastewater and stormwater. Our Health Dept. regards stormwater and sewer as the same class of risk for horizontal and vertical separations from potable water. I assume the concrete culvert you mention is for stormwater. Our required vertical separation for the water from stormwater is 18 inches O.D to O.D. I would not see the need for any vertical separation between wastewater and stormwater other than considerations for piping materials and any bedding requirements. We try to keep 3 ft of cover over all pipes if possible, but that is not always practical.

 

[RWF7437]

Frost penetration 1.2 meters ???? !!!! Really ?

Is this in Alaska or within the Arctic Circle ?

 

[KRSServices]

RWF,

I hate to break it to you, but a frost depth of 4 feet (1.2 m) is fairly common. In Southern BC (Cranbrook area, 5 feet of frost was considered normal. In Edmonton, 5 to 6 feet is also considered normal. In Alaska and the Yukon (Whitehorse) the frost depth was about 8 to 9 feet. It's all relative to the soils and the winter.

KRS Services

http://www.krs-services.com

 

[RWF7437]

Thanks for the information KRS Services....WoW !

Does mean then that you normally burry water and sewer mains and services at 1.2 meters? Or do you install utilidors as they do in Alaska ? Can you encase and insulate this water and sewr line at the culvert crossing perhaps at reasonable cost ? Arbitraty seperation rules seem to have little to do with this case but a practical solution which protects all the facilities from damage or contamination seems possible, although hardly cheap.

Good luck

PS

Do you, as I often do, wish people would say in this forum where they are from? I live and work in Oregon, USA and many others seem to be from Florida. Still others are from land outside North America. I feel very foolish trying to advise someone in Saudi Arabia about how to milk a camel.

RWF

 

[KRSServices]

RWF,

I don't know whether your comments were directed at myself or Sully. In any event, up here in Central Alberta we bury our watermains at about 8 feet or so. In the Yukon they were between 9 to 10 feet, depending on the soils.

Typically, the water and sewer mains are required to have a separation as well, and yes, if required they can be insulated.

I quite enjoy reading threads from those whom enjoy the warmer climates whereby the depth of bury for a water or sewermain is more focused from a soils loading than the risk of freezing. Up here the risk of freezing dictates the average depth. One of the reasons I enjoy this forum so much is that there is a vast wealth of different perspectives and experiences concerning a interest.





KRS Services

http://www.krs-services.com

 

[RWF7437]

My apologies to Sully.

Thanks to KRSS Services for the insight.



Let's all hope that Sully finds an answer in all this and that we all broaden our view of the world.

As always,

Good luck.

Russ

 

[TVE]

1) 1.5m cover requirement for watermains here in south-western Ontario, since we are comparing bury depths.

2) If you normally need 1.2m cover for frost penetration, then that is what you should have between the outside of your culvert and the sewer and watermain. That said, you can always look into the old standby of putting insulation (in this case on the bottom and sides of the trench)to reduce the cover requirement. I'd talk to the local authority to determine how much insulation they would be comfortable with/require for whatever separation you want to end up with.

3) As for separation requirements, again, check with your local authority. In Ontario, the "guideline" (which is treated as a "rule" these days) is that if a watermain goes above a sanitary or storm sewer, you just need enough cover to handle the structural issues. If it goes at the same depth or below, you need either 2.4m horizontal separation or 0.5m vertical separation. (Crossing or parallel installation doesn't matter for this "guideline".)

David Dietrich
Thames Valley Engineering

 

[RJLDesign]

Sully03

With u.P.V.C. you would not want less then the 1000mm. But make you have the cover at the closest point to the base slab. If this does have a base slab dont forget you want cover to the underside of the base slab and not to the invert of pipes.

How ever you could go down to 750mm if you used a D.I.C.L. pipe. What loads are you going to have on your R.C.B.C./R.C.P. ? you dont want to have any verticle movment from large trucks etc crossing over the pipe.

If you are particully worry try a D.I.C.L. pipe that is concrete incased. Bit of over kill but if this is going to be a major road it maybe a factor to take onto consideration.

You want details on a concrete incased pipe i can dig up a std. detail i have and give you the inforamtion

Regards

Rj

 

[rcrouse]

ok... so how about some tips on ways to combat Watermain that is shallow, besides replacing it. Any thing to put on top of it to insulate it? We are in Michigan, with a 5' min requirement for depth over watermain, but due to a reconstruction project, we have 4-4.5' of cover. Hate to rip it out and replace it. Any ideas?

 

[KRSServices]

rcrouse,

You may not be required to do anything. Before rushing into a whole forray of solutions, you should first determine whether there is a problem in the first place. You will need to perform an analysis on the area of the utility that has been shallowed. I suggest you contract someone whom is experienced in this field and can proceed throught the various stages of the analysis. You will need to evaluate the R condistions of the soils, the maximum frost penetration, and ambient tempurature of those soils, and the R values of the pipe and ratte of heat loss in the flowing fluid. Then you will have to perform a check calculation on no flow conditions to determine time to complete freeze of the fluid.

After this analysis is performed, then viable options to prevenet freezing (if necessary) can then be developed. There are several different solutions, but each carry a cost, which is most certainly less than getting the analysis completed. I have plenty of experience in this field as a result of my tenure in the north and therefore can assist you where required.

KRS Services

http://www.krs-services.com

 

[cr1973]

Here in WI we keep 6 feet of COVER over our watermains. Larger diameter, like 30" or 48", we go with less cover.

 

[wolfhnd]

Missouri 36" of cover was standard for years but some are going to 42".

 

[TKF]

Need to install sewer next to water main. Can not get 10 foot horizontal or 18 inch verticle separation. Sewer will be C900 pipe. Specifications call for pressure test of 150 psi.

How do we test when we have manholes and house laterals?

What alternatives do we have?

 

[KRSServices]

TKF,

Did I read that correctly? The sewer main is to be C-900 and pressure tested to 150 psi? Is it a forcemain perhaps (although I doubt it with manholes and gravity services)? Is it possible that someone has made a mistake and has incorrectly specified C-900 and/or inadvertantly copied water pipe installation specifications? Maybe the QA/QC review missed it? I dunno, but you should be asking questions.

If everything is correct (and I doubt it) then you will have to have test the pipe prior to connection to services and manhole installation. If this is not possible, then the spec writer should be requested to provide the solutions...because I will guarantee, your unit prices (estimated) will be very much lower than the contractor bid prices.

KRS Services

http://www.krs-services.com

 

[rconner]

With regard to the original inquiry, if depth of bury of cover of the new lines was not necessarily an issue (re freezing etc.), and if one or both of the new lines were ductile iron pipe, several passages of ANSI/AWWA C600, INSTALLATION OF DUCTILE-IRON WATER MAINS AND THEIR APPURTENANCES could arguably be applicable. They include,
<<<4.2.1.3 Clearance. When crossing existing pipelines or other structures, alignment and grade shall be adjusted as necessary, in accordance with the specifications, to provide clearance as required by federal, state or provincial, and local regulations or as deemed necessary to prevent future damage or contamination of either structure.>>> and,
<<<4.2.2.5 Rock conditions. When excavation of rock is necessary, all rock shall be removed to provide a clearance below and on each side of all pipe, valves, and fittings of at least 6 in. (150 mm) for nominal pipe sizes 24 in. (610 mm) or smaller and 9 in. (230 mm) for nominal pipe sizes 30 in. (762 mm) and larger. When excavation is completed, a layer of appropriate backfill material (see Sec. 4.2.5) shall be placed on the bottom of the trench to the appropriate depths, then leveled and tamped.
4.2.2.5.1 These clearances and bedding procedures shall also be observed for pieces of concrete or masonry and other debris or subterranean structures, such as masonry walls, piers, or foundations that may be encountered during excavation.
4.2.2.5.2 This installation procedure shall be followed when gravel formations containing loose cobbles or boulders greater than approximately 8 in. (200 mm) in diameter are encountered.
4.2.2.5.3 In all cases, the specified clearances shall be maintained between the bottom of all pipe and appurtenances and any part, projection, or point of rock, boulder, or stone of sufficient size and placement that could cause a fulcrum point or pointload.
4.2.2.6 Previous excavations. If the trench passes over a previous excavation, such as a sewer, the trench bottom shall be sufficiently compacted to provide support
equal to that of the native soil or conform to other regulatory requirements in a manner that will prevent damage to the existing installation.>>> (I guess it could of course be argued that the culvert, one would think a sort of “subterranean structure”, may be no less firm than an outcropping of rock.)

With regard to the comment/question of KRS concerning the apparent sort of high pressure testing requirement of the sewer here, I am not particularly surprised by this requirement either as I think I have seen such requirements in tight quarters in the past, I guess by the designers or regulatory agencies as further insurance versus leaks or contamination. e.g. , pg 30-11 “Section 38.3 Relation to Water Mains 38.31 Horizontal and Vertical Separation” of the “Recommended Standards for Wastewater Facilities” (Ten States Standards) includes, “…If it is impossible to obtain proper horizontal and vertical separation as described above, both the water main and the sewer must be constructed of slip-on or mechanical joint pipe complying with public water supply design standards of the agency and be pressure tested to 150 psi (1034 kPa) to assure watertightness before backfilling.” (it probably should be explained that this same passage of the Ten States Standards precedes this with other separation requirements, including, “so the bottom of the water main is at least 18” (460 mm) above the top of the sewer.”)

 

[pittsig]

TKF,
In North Carolina, state regulations require both water main and sanitary sewer main to be ferrous material if 10-foot horizontal and/or 18" vertical separation cannot be obtained and that the sanitary be tested to water main standards. Similarly, if a sanitary main is within 100 feet of a well, the sanitary must be ferrous tested to water main standards.

For example if your project were in NC, the sanitary would need to be ductile iron instead of C-900. (There is an option to not use ferrous pipe if the design engineer can justify it, however I'm not aware of anyone trying that route.) If your project were in the jurisdiction of the local government I work for, we would additionally require that the ductile iron pipe (DIP) used for sanitary sewer have an internal lining appropriate for sanitary sewer, not standard cement-lined DIP used for water mains.

Check with whatever regulatory agency oversees sanitary sewer in your project area and also the utility that will be accepting the new mains and/or flow for their requirements for pipe material.

This situation has occurred on a few recent projects in the jurisdiction I work for. I believe the contractors purchased special plugs in order to perform the hydrostatic test to 150 psi (water main standards) on the DIP sanitary sewer main. The tests were run from manhole to manhole. Test procedures and allowable leakage were based on AWWA water main testing procedures. Service wyes were plugged so that laterals were not tested, but the wyes were. Alternatively the mains could be installed and tested and taps for the services could be made after the main has passed testing.

We generally try to have the design engineer locate manholes at least 10 feet away from the water mains, so the only manhole testing is standard vacuum testing. However, on a recent project where a there was not alternative to placing a manhole within 100 feet of a well, the state reviews agency required the manhole to be tested to water main standards. Long story short, the contractor fabricated a ductile iron manhole rather than using a pre-cast concrete manhole and was able to pressure test it.

 

[KRSServices]

pittsig,

Thank you for the insights into your experiences. I have not been exposed to a juridiction wherein the specifications, particularly the testing parameters, you cited have ever been required. I would be interested in learning more about the costs and how the contractors solve the issue of testing the main inside a manhole, and how reactive thrusting is achieved.

KRS

KRS Services

http://www.krs-services.com