×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Determining Restraint Length for a 24-inch Ductile-Iron Water Main Encased in Concrete

Determining Restraint Length for a 24-inch Ductile-Iron Water Main Encased in Concrete

Determining Restraint Length for a 24-inch Ductile-Iron Water Main Encased in Concrete

(OP)
Hi all,

I am new to the forum and I tried to use the search at the top of the page to find what I am looking for but could not come across anything useful. If I missed it please kindly direct me to the source. Also, HI!

I am currently working on a design of a 24-inch ductile-iron water main. The water main is to be no less than 5 feet below ground surface. The soils are very stiff to hard clay. Test pressure is to be 150 psi. Factor of safety is to be 1.5. I need to determine restraint lengths for various angles (22.5, 45, and 90 degrees).I have been messing around with the calculators provided by EBAA Iron and DIPRA to get a feel for the restraint length required however I am not sure if these can be applied to an concrete encased water main (per client request). I also tried a hand calculation using AWWA M41, and got in the same ballpark with my length as compared to the programs. However this is my first time really trying to do these calculations and would appreciate a reality check.

Basically can I apply equations for normally restrained joints (slip on / mechanical) to that which will be encased with concrete?

Thank you in advance for any help!

Nick

RE: Determining Restraint Length for a 24-inch Ductile-Iron Water Main Encased in Concrete

Am curious is the entire main to be encased, or just some or all of the restrained joint pipes?

RE: Determining Restraint Length for a 24-inch Ductile-Iron Water Main Encased in Concrete

(OP)
The client wants it encased where ever a bend of 22.5 degrees or greater is used.

Also, I talked with a few other engineers I work with and agree that my approach is okay because it will yield a more conservative restraint length.

RE: Determining Restraint Length for a 24-inch Ductile-Iron Water Main Encased in Concrete

Concrete encasement will likely provide greater resistance to thrust than any soil embedment condition described by DIPRA or AWWA Manual M41, and stiff clay has normally good bearing resistance. Consequently, I suspect your determinations are adequate. It may not be a bad idea to locate the transition between encased and non-encased pipe with a flexible joint at or just outside the concrete encased structure.

RE: Determining Restraint Length for a 24-inch Ductile-Iron Water Main Encased in Concrete

(OP)
Thanks rconner I will make a note of this. I appreciate your input

Nick

RE: Determining Restraint Length for a 24-inch Ductile-Iron Water Main Encased in Concrete

Just a suggestion: encase the pipe in concrete, but leave the pipe joints exposed for future inspection for leaks and future maintenance or disassembly. If possible, instead pour thrust blocks on the backside of the bends, with the block surface area bearing on undisturbed earth. Calculate thrust force vector and magnitude. Bearing area (sqft) should be equal to soil resistance (lbs/sqft) needed to equal thrust force (lbs).

RE: Determining Restraint Length for a 24-inch Ductile-Iron Water Main Encased in Concrete

better yet, wrap everything in poly; encase with 1/2 sack mix which is "diggable". blockout just the valves. no need for thrust blocks, but if you must, is probably better to restrain the joints near the bends, valves, tees and blinds than pour more concrete.

RE: Determining Restraint Length for a 24-inch Ductile-Iron Water Main Encased in Concrete

(OP)
Unfortunately the Client has been very adamant about the encasements for all bends 22.5 degrees and greater. We, the Consultant, tried to use typical restrained joints but they said no and if the Contractor proposes the change during construction they may accept it.

I agree with everyone that there are better ways of doing this, I was more or less seeing if my theory was sound for the calculation of the lengths.

I appreciate everyone input and will consider these issues during the design and meetings.

Nick

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources