Surveying/Earthwork: Benchmark Adjustments

[usaedy]

Hello to all!

I just wanted to start up a conversation about benchmark adjustments. Does anyone have any experience with these at all?

I am looking at constructing a final, approved set of plans where the site was found to be extremely heavy. To achieve a balance the site design grades would have to be raised 9".

I would typically take the approved plans to our surveyor who performs our stakeout and contract him to redesign the site grading according to our houseline needs and give him the recommendation to raise the grades. We have been very succesful with this in the past. It works very well because we can send the redesigned grading plan to the excavator who will make the adjusments to his scheudule and the total dirt moved in the contract.

In this instance, I am going to use a benchmark adjustment. What this means is that instead of going through with the redesign by the surveyor, I have asked the surveyor to lower the benchmark by 9". This serves to make all the stakout higher by making the existing grade lower. Of course we got approval to do this by the township engineer...

In this instance though, I am running into a problem. The excavator is using GPS to grade the site. The existing topo in the cad file is based on the unadjusted benchmark. The will need to have the proper surface in order to make the correct cuts and fills. With the benchmark adjustment in place, we can't agree on how to get the site balanced correctly. I have to get the excavator to trust that the benchmark adjustment is going to create a balanced site and then get him to perform the work to the adjusted BM elevation.

Has anyone run into problems with benchmark adjustments in the past? What are your experiences?

 

[cvg]

in reality, you aren't adjusting any benchmark, you are simply adding 9" to all grades on the plans. This can cause a multitude of complications, especially on larger sites as you will still need to daylight at the edges. How will the daylights be adjusted? Will that cause other problems? with drainage? with driveway slopes? etc. How will you tie into the existing street, sewer, water - will these elevations / slopes also need to be adjusted? It seems you are leaving a lot of design work up to the grading contractor who must do it by the seat of his pants. Better to stop and re-do the grading plan.

 

[divad41]

I concur with cvg... someone (you or the owner or the contractor or all 3) will pay for a redesign, whether it gets done or not... and may be paid for many times over if no redesign. You'll discover things during the redesign that you hadn't thought about... and will say "boy am I glad we found that before we started construction"... probably several times.

Design by contractor's pant seats is asking for headache and heartache... it is probably not legal (as builts?) and not a professional ending of a professional design project. It is likely that the financing group would want to know about such an approach, and should / would squash it.

Tough position, but take the high (professional) road.

 

[usaedy]

Good feedback... Thanks.

Of course we did have the engineer look at the tie in points where roads and sewers meet existing and made the adjustments to the profiles. The entire job was raised so there would be no issues with driveway slopes because no driveways tie into existing roads. And as far as grades tieing in to existing, the site contractor would have to rely on stakeout rather than GPS. Stakout is paid for by us anyway so it would not cost them. Then the lot work contractor would be able to fine grade to daylight without a problem during houseline. Good relationships also help in this area...

Do you really think it is unprofessional to perform a benchmark adjustment? We went through proper channels. The township engineer approved it so as builts will not be a problem. The surveyor is informed and is making the adjustments where stakeout is needed, and we are up front with the excavator, not hiding anything.

How does the finance group fit in to this? What would their concerns be?

I think you have both brought up the major issues with a benchmark adjustment and I appreciate that. Thanks for helping me to think about both the positive and the negative aspects of the benchmark adjustment. As with any project, change management is the most difficult issue but these things can be managed none the less.

I would welcome more feedback...

 

[civilperson]

Benchmarks can be set any height you desire, with the datum adjustment shown prominently on the first sheet of plan set. Many cities have their own datum and the conversion to USGS is listed on the General Notes or on the the Site plan along with a list of monuments and the elevation/ coordinates of each. This method of achieving a fill/borrow balance is probably more work than just changing the grades on the plans and the tie in to boundary elevations will never reflect as-built conditions.

 

[sam74]

I've been involved in a project that this happened to. At the time I was in the field on the survey crew. It did add some confusion as the project was a large residentail apartment complex with 10 or 12 buildings and was constantly mud covered.

One half of the project was raised 3 or 4 feet. The slack was made up in the road that transitioned between two halves of the project. Once the engineer determined the increased slope still met city standards he was fine with it. Around here the engineer must stamp and sign an asbuilt stating that all civil design aspects will function as designed before the contractor can claim his bond upon completion of the project. I don't think we had to resubmit, redesign, or anything else with the city as we still were meeting local standards. I'm sure we updated the plans in the effected areas and adjusted TCs accordingly for the contractor since our site was not a total adjustment but its not really a total redesign.

 

[ml10950]

usaedy, I am a licensed surveyor with over 28 years experience. I seen this method applied a number of times, and I don't think I ever seen it succeed. It sounds simple, but you are openning yourself up to a number of problems, and when they do occur (which they will) you will not have a foot to stand on. Your excavator is right by not wanting to proceed using this method, he has probably seen it before.

Before you gamble, compare the cost of rippng out and replacing a few hundred feet of curb, or dranage pipe, with the cost of redoing the grading plan. I think you will find planning ahead is the better option.

Good luck

 

[divad41]

Regarding professionalism: I inaccurately assumed that such an effort would not be known by all.

Regarding Financing: If they know their business (granted, often a bif "if"), they want to know if any 'unusual' circumstances do or will exist on the project, including during construction. Plans that don't accurately reflect what is "really" going to be built could fall into this category. If there're any snags, they may be unacceptably at risk for receiving additional interest payments and potential major proejct risk. Who does everyone point the finger at when proejcts go bad? The PE, has been my experience.

Somewhere there is / are boundary condition(s) waiting to trip someone up.. It's way more fun to find them on paper than in dirt.