Manhole Frame and Lid Details

[deeman]

I am looking for a solution to a problem I am having with new manhole construction. The lid frames are being knocked off of the new manholes by grading equipment. This is occuring after we have inspected and approved the new sewer line and manhole construction in many of the new developments that are springing up in the area. Infiltration is starting to become a major problem at our wastewater treatment plant and this is one of the major causes. I do not have the manpower to go and re-inspect all of these developments and then send crews out to repair them. I have been looking for details on ways to permanently mount the frames to the manholes. I have a concern with bolting the frames to the concrete cones as the heavy equipment may damage the manhole when it hits the lids. I know that many cities use concrete slab collars around manhole lids for protection in pavement and have thought of using this method in all locations, paved and unpaved, but am not sure how effective it would be in protecting from a direct hit of a dozer blade. Any ideas or suggestions?

 

[RWF7437]

If you have the authority to do so, require the Contractor to repair or replace any damaged frames or covers. The concrete slabs work well in most places. Also, vacuum test the manholes after the street has been paved. Usually only takes about ten minutes per MH and here in the US there are many testing companies who can do the work.

good luck

 

[deeman]

Thanks RWF7437

We require vac test of all manholes before we accept them. The problems are occurring after sewer lines are installed and earthwork and other construction has started. In some situations we still have a bit of leverage with the developer to go back and fix any problems, but this is rarely the case. In most instances the problems are not found until the contractors have pulled out and lots are sold and housing construction has started. By that time it is too late to force the contractor or developer to fix the problem. Alot of this could be solved if I had the manpower to have full-time inspection at every jobsite in town, but this is impossible.

Any other ideas? Shear bolts or breakaway designs that would prevent shifting of manhole covers up to a certain force, but would break away if large forces were encountered is another idea I had. Has anyone seen this type of design used?

 

[RWF7437]

Note:

The key is to vacuum test the manholes AFTER paving is done. No frame which is not securely mortared in place could possibly pass a vacuum test, in my experience. You don't need full time inspection but you do need to be able to witness the required tests and enforce your standards by refusing to accept work which has not passed the tests. You may also want to consider a i year warranty period be required on all new constrcution.

At least, that's the way things are done around here.

good luck

 

[saxon]

deeman, It sounds as if you've got your inspection schedule out of sequence. Can you do your final system and site inspection after completion of construction (thats the way we do it in Chicago)? Also, in order to reduce your repair costs, require all repair to damages done by developers and contractors to be paid by them. You'll find that once they have to start picking up the repair tab, the damage drops off significantly.

Make something Dozer proof? Good luck!

Hope this helps.
saxon

 

[deeman]

Saxon, Thanks for your reply.

Maybe I should explain a little better how our development process is here. A developer will be required to obtain certification from the utility companies in the area that the property in question has water and sewer facilities available before either a subdivision plat is approved or a building permit is issued. Therefore, our inspection and acceptance of the utility improvements must be performed before we can sign off on the certification. It is after we sign off on the plat that the building contractors move in and start work. This is when the damage occurs and it is usually not in paved areas but field areas where it occurs most often. Needless to say, if and when the problems are found, it is not until long after the contractor has moved out and the developer has sold all of the lots. We do include a one year warranty period in our plat certification, but it is difficult to enforce once you've lost all leverage with a developer/contractor, i.e. he doesn't need any "favors" from you. I know that the warranty could be enforced through litigation but could get expensive if it got that far.

I guess what I'm looking for is a way to prevent most of the damage from happening by way of construction methods. Not necessarily a way to withstand the total force of a dozer, which I know is impossible, but some way of protecting it from glancing blows that otherwise would easily knock the lid from its perch.

 

[RWF7437]

You can enforce a warranty through the method of requiring a bond for say, 10 percent of the construction cost. This is often done. If manhole testing is the last thing on your inspection list you should be able to catch these problems before the contractor moves on.

It sounds like a very strange system and procedure. Can you tell us where this is and what kind of organization you work for ?

 

[RDK]

Is this for grading during road construction?

If so then why don’t you put the sewer in the boulevard? That way there will be no interference with the manholes during road construction and no risk of trench settlement after the sewers are installed.

If you are referring to road grading for snow removal, simply put the frame about 20 to 30 mm lower tan the pavement. That way the snow removal equipment will not hit the frame. (It would still be better if it was in the boulevard.)



Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[semo]

I've never seen a manhole ring that will remain in place if hit by a dozer, grader, front end loader, etc.

Do you have an inspection program for the developer? Even if its the local building inspector. He can check before and after to see that the manholes are in good condition before he signs off on the building.

Don't know the circumstances; but, one reason the contractor may hit the manholes is he doesn't know they're there. He probably didn't put them in and some may be invisible to him under the grass.

Can the utility contractor install some type of marking post. There are several fiberglass type of posts that are labeled and easy to install. Another kind is a regular metal t-post. We use that in our rural systems to mark valve boxes along the ditch banks so the county road grader or bush-hog doesn't hit them.

 

[dicksewerrat]

The bond process is probably your best bet. Also require the developer to put up a certain amount of actual cash to pay for an independent inspection after the houses are built and roads and lots finished. But you hire the inspection company. Or hire more people on their dime. The first project you find with damage, attach the bond and fix everything you can find. Publicize this action. The bonding companies really hate to pay for anything and the word will travel faster than a courthouse rumor.

 

[cajunj]

In the area that I work in, the city does require a bond or LOC to be placed on sewer as well as streets. This bond is held (but is subject to reduction) for one year after final inspection and start-up of the sewer occurs. However an additional inspection is conducted by city inspectors before the final release of responsibility and bond ammounts. All damaged manholes, service boxes, or anything else of concern is adressed at that time. This may not be the quickest way to insure a sound system, but it is by far the most effective way I've found. Afterall, the city has their money, and your not going to get any more leverage than that.

P.S. if you know anyone that has info on sodium nitrate and its uses to prevent H2S in a collection system please help!

 

[KRSServices]

MAy I inquire as to why the MH frame and covers are in place while the road base is being constructed?

I have been in the business for years and we always insiste the grading/paving contractor remove any covers, rings, etc and place steel sheets over the cone. They are marked and the bases is then constructed. Prior to paving the steel is removed and replaced with the frame and covers, compacted and paving is undertaken. No problems.

KRS Services

http://www.krs-services.com