Utility Trench Settlement- acceptable tolerances 3

[RochesterEngineer]

Could someone help me out on a problem we have with some utility trenching settlement under a roadway.
We have a sanitary sewer project that has experienced settlement from 1/8" to 4"+/- over a 6 month period. The Contractor will return to sawcut, re-compact and repair.
The Contract required 95% compaction by Standard Proctor for backfill compaction.

My question is: Is there an acceptable tolerance off of the straight line (1/4"/ft side slope), measured by a 10' straight edge that is a cut off for what needs to be replaced and/or repaired. Paving standards usually state a 1/4" variation off of straight line side slope is OK, but I can't seem to find a Standard Acceptable tolerance for settlement. One firm I worked at required all settlement to be brought back to 0". Varying from 0, 1/4" and 1/2" would mean the difference is hundreds of feet of repair. We want to be fair and not ask the contractor repair hundreds of feet of road uneccessarily, but also want to make sure anything that needs to be repaired, gets repaired.
Thanks for any help or input.

 

[GeoPaveTraffic]

I would have the contractor repair any pavement that is out of the 1/4" requirement. The cause of the deviation is not your problem just the result. Remember, whoever owns this pavement in the future is going to have to maintain it forever. Why start with a problem?

By the way, the kind of settlement that you are seeing likely indicates that the backfill was not compacted to anything like 95% standard.

 

[cvg]

If the pavement over the trench has settled, it will trap water and allow it to soak into the subgrade. this will weaken and eventually destroy the pavement. The contractor should repair to prevent this future (but certain) damage. I would require that it all be brought up even or higher to prevent the ponding.

 

[zabrab]

If the accepted paving practice is 1/4", that is what I would follow. You should also be sure of what is considered the maximum dropoff from a traffic safety standpoint.

If you are not going to follow a definitive 0", 1/4", 1/2" or whatever, observe the project after a rain. Any birdbaths or other areas traping water should be repaired regardless of the depth of settlement.

 

[LCruiser]

Depends on if it's a freeway or residential street. ZERO deflection is not an engineering standard, as anyone who has taken mechanics of materials knows. 4" is indicative of shoddy backfill. Keep an eye on that contractor from now on.

 

[DRC1]

Trenches cn be difficult to compact and pave with out some settlement. For a narrow trench 4" here and there is not unheard of. Most towns and DT's have standards for acceptable tolerances. The contractor is either working under a permit that will by reference require those standards or is building a new road, that if accepted by the town orstate. For major roads we will often patch by hand, compacting with a walk behind drum, and let the trench settle. Then about 6 months later, we have either half or the whole road milled. (depends on authority's preference) and machine pave the milled area. If this was not specifed, the contractor may balk (maybe not) but even if the owner has to pick up some costs, (which he would have if it were specified) it will give a good finished product at a reasonable price.

 

[emmgjld]

I do not see the truly important information in this discussion.

What were the actual specifications?
Did the contractor meet those specifications?
Was there a performance standard?

If the contractor met the specifications and met any performance standards, how is he responsible for what appears to be an improperly specified job? I have personally witnessed and retested a project with 10' to 14' deep backfills, which was exhumed and found to meet 95% of Standard and the client wished the settlements were only 4".

To be rendering opinions without knowing the soil types and depths of fills may not be prudent. We really need a little more information before a proper opinion can be rendered.

I practice in an area with some extreme conditions. In my area, for some soil types and conditions, the use of the Standard Proctor is a setup for settlement.

 

[cvg]

after re-reading - the original post does not question the compaction specification, only a reasonable limit for settlement. Pavement over trenchs that has settled can probably not be acceptable ever unless the surface is higher than the surrounding insitu pavement. If it is lower, causing a bird bath, then that is a problem and will probably lead to a shorter service life for the roadway. Regardless of whether it is a contractor error, lack of inspection, or design error, it should be repaired. In my experience, 4" of settlement is indeed indicative of both poor compaction and also probably poor inspection or testing. A good inspector should have cought the problem before the AC was placed.

 

[TDAA]

First I agree that it should be repaired, and I don’t think anyone argues that issue. I also agree that the repair should be at or slightly higher than the surrounding, to allow for some settlement of the repair.

However, I agree with emmgjld points, and also feel that cvg only refers to a portion of the original question in his second post. The question boils down to one item - How much do we make the contractor repair? Although not in question form, it was stated: "We want to be fair and not ask the contractor repair hundreds of feet of road uneccessarily, but also want to make sure anything that needs to be repaired, gets repaired." This is what emmgjld referred to, and is truly dependent on the spec. If the contractor met your specs, and your QA passed his work, and the settlements are within tolerance allowed in the contract, then technically the contractor met his obligation, and the owner should repair at their dime.

So, what does your contract say? Does it need some upgrades before the next project goes out the door? I have often seen this type of thing where the lack of specifics in an often-used specification is not noticed until there are contractual issues. To be fair, make the contractor repair the items not meeting spec, and pay them for the items that you want fixed that did meet spec. Then, be prepared to take it form an upset client.

 

[cvg]

Good points TDAA and to add one more, check your specs / contract for the length of warranty. Around here it is typically 1 year. Let it continue to settle and then at the end of 1 year, evaluate and make any necessary repairs at that time.

 

[DRC1]

How much of the road should be repaired is not a question of specification, it is a question of what work is needed to make the raod acceptable for the driving public. How much the contractor pays and how much the owner pays is a matter of the specifications. It always irks me when something is not accepatable it has to be fixed at the contractor's expense and no matter what it has to be fixed, until he points out that the repair is not in the contract, then suddenly it is okay. Review the contract, Talk to the owner, then talk to the contractor. There are often two sides to every story. Go back to the owner and set up a meeting between the three of you to decide what should be done and who should pay for it.

 

[LCruiser]

We only pay for work that meets specs. If the work is substandard, they have to remove and replace it at their specs because they are the ones who screwed up.

 

[dicksewerrat]

Did anyone take any compaction tests? What were the results? What did the spec. say about testing?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com