definition of LF 2

[cvg]

Specs read as follows for measurement and payment of storm drain pipe installed in public right of way:

"Shall be the number of linear feet of pipe laid as measured along the pipe axis."

Is the pipe length measured horizontally (plan dimension) or along the slope of the pipe?

My opinion is that it is generally measured in a horizontal plane at the ground surface, but the debate here in the office is that it is actually supposed to be measured along the alignment of the pipe. I have not seen this alternative method of measurement done and don't believe this is the commonly used method of measurement.

 

[RWF7437]

"Shall be the number of linear feet of pipe laid as measured along the pipe axis."

This clearly means along the centerline of the pipe as laid; whether horizontally, vertically, or on a slope. The Contractor must buy and install X feet of pipe, NOT Y horizontal feet of pipe.

Does any other interpretation make sense ?

 

[bimr]

"For payment purposes, the length of sewers installed shall be measured along the centerline. No deductions in length will be made for tees, fittings, or manholes. Where a change in sewer size is involved, it shall be assumed for measurement purposes that each sewer entering the manhole extends to the center of the manhole. Where sewers are connected to inlets or special structures, the length of sewer for measurement purposes shall extend to the nearest inside wall of the inlet or special structure.”

Piping is measured along the center line, not the horizontal plane. It would not make any sense to measure on the horizontal plane.

The Contractor would object when he has to buy lengths of pipe off the shelf at X feet long and then sell it for X- feet long when it is installed on a slope.

 

[gbam]

In most cases the horiz. length is ample to approximate the length of pipe. Typically SD and culverts are laid on flat slopes (<10%). The slope length increases 0.5' for every 100-feet of planar length for a slope of 10%. I typically do not provide slope lengths until the slope exceeds 10% or the length is "long". For quantifying purposes we also "round up" the length of pipe needed to nearest foot or two feet depending on client.

 

[cvg]

GBAM's comments agree with my past experience. I have not observed inspectors measuring along the axis of the pipe for payment purposes. Always along the horizontal plane as in from one station to another.

As stated by bimr, most specs I have seen say to measure to centerline of manholes, even though that clearly adds an extra 4 or 5 feet at each manhole. However, this spec does not say that, it says only that the measurement is to include that portion of pipe embedded within the structures.

I have a designer who is calculating pipe slope lengths for each pipe which in my opinion should just be measured horizontally off the plans and rounded up. This seems to be a tremendous waste of time and I don't expect our contractor to do it any different. Any other opinions?

 

[bimr]

In practice, most people probably do estimate the pipe lengths off the one dimensional plan drawings, although this is slighty inaccurate as you are pointing out.

Most Contractors are probably somewhat unsophisticated and do not notice the difference. However, if you showed a Contractor that he would be able to invoice for more footage, I am sure that he would take the opportunity.

Much of the piping seems to be sold with line item bids, in which case the difference in footage is not something that comes up for discussion. However, it is another reason to pad the line items totals so that the project costs do not go over the budgeted costs.

The bottom line is that the Contractor is due the actual pipe lengths that he installs.

Perhaps as CAD transitions into 3 dimensions, this problem will go away.

 

[RWF7437]

"one dimensional plan drawings" ??????

"Most Contractors are probably somewhat unsophisticated ..."
?????

 

[GoldDredger]

I think gbam is correct. Storm sewers in particular are fairly flat, so the difference between actual length and horizontal length is minimal for any given run of pipe. I would think for practical purposes the payment should be based on stationing length.

Also, remember that pipes are usually sold in prefabricated lengths, I've heard them refered to as 'sticks' of pipe. At the end of a pipe run, the last pipe segment is cut to fit into the structure and the excess is discarded.

That being said however, cvg's post says 'the pipe axis' for this specific contract. I interpret that to mean along the actual pipe, not the horizontal stationing difference (the hypotenuse rather than y axis if you will)

I would be curious to know what the difference actually is. My guess is not much at all, few feet maybe if it is a large project.

It also brings the question of actual installation vs. design. What if they install slightly greater or lesser slope, or the junction/manhole moves horizontally a few feet. Also, stationing is typically to manhole centerline, would you propose to void the space from centerline to outside of the barrel? If we are splitting hairs here these make a difference too.


I'd be curious to know what you decide to do, hope you'll post your decision.

 

[cvg]

so far we have agreed that:

for mainline
length is measured using plan stations without any deductions for manholes or other structures. The slope is very flat and lengths are to be rounded up to the nearest foot.

for laterals
1) we are "padding" the estimate for each lateral by a couple of feet by measuring from the centerline of the mainline to the inside face of the catch basin

2) the measurement is to be horizontal and then rounded up to the nearest foot

3) there was discussion of then rounding each one up to the nearest "even" integer

4) where the profile is steeper to duck under existing utilities, collars are used and these laterals will be flagged for a more accurate calculation of the length

5) currently collars are included in the unit prices for the pipe, but there is discussion of making them a bid item

 

[bimr]

One would think the correction for pipe slope is somewhat irrelevant. If you assume that for an 8”sewer pipe, that the maximum practical slope is about 7% (velocity = 9ft/sec), then the correction for distance is only 1 additional foot of pipe length per 400 foot section (typical distance between manholes). Unless you are talking about a huge project, the difference is miniscule.

“Service sewers shall be measured along the pipe from the outside surface of the main sewer to the extreme end of the last pipe or fitting placed. Measurement shall be to the nearest one (1) foot without deduction for fittings. Each size or type shall be measured separately. Tees, wyes, and bends of each type and diameter shall be measured on a per each basis. “

Regarding "one dimensional plan drawings" ??????”, the firm that I am associated with draws line segments “flat” using an AutoCAD program, so the line segments are one dimensional. There are 3 dimension cad programs available, but I am not familiar with how widely that the programs are used.

Regarding "Most Contractors are probably somewhat unsophisticated ...", I don’t work with any contractors that are familiar with geometry and/or trigonometry and that would be available to figure out the difference in length.

 

[coloeng]

When you really think about it, trying to get the exact length of the pipe, whether it is just horizontally along the center line or through the center of the pipe, isn't really all that important. The contractor purchases pipe in given lengths and unless the design is such that at every manhole, tee, valve, etc. ends up at the end of a full length of pipe, the contractor will have to cut the pipe. Chances are they won't use every piece of pipe that is cut off as waste. Most contractors estimate a certain percentage of waste when they bid, knowing that there will be some.

I agree with cvg that it is a waste of time to try to get the linear footage of pipe to the exact foot. I have yet to find any contractors that use every foot of pipe that is purchased for the project, unless the pipe is specifically fabricated for that project.

 

[tnboy82]

As a pipe estimator, I interpret that spec verbage to mean "as measure along the pipe centerline", NOT the horizontal (plan) or station distance.

In the case of a storm sewer, I would conceed that it is probably "ok" to do the estimate based on the horizontal (stationing) distance.

But, if I'm writing up an estimate, the slope are going to get checked. Because, it always seems that everyone's estimate can be a little bit sloppy, except when it comes to yours! It burns me up when a contractor starts complaining about us being 4-5% over our quote estimate. But ir really gets me hot is this instance. I look at the amount of pipe that I have on my estimate if 12,000 lf and the bid form says 15,000 lf. I call to discuss with the engineer, and they say "yeah, we just threw some extra pipe in there."

 

[cvg]

tnboy82
I have to say that I have never padded my pipe estimates by 25% nor have I ever seen an estimate that far off, so I'm not sure I understand your concerns. If I did work that sloppy, I would not get any repeat business and besides I pride myself on trying to do a good job. If the engineer really wants a contingency in the bid for his sloppy work, than I agree there is a problem - with that engineer. That is not the case I am looking at as we will have estimated the installed quantity of pipe to within less than 1% for the job. I don't consider this to be "sloppy" work. And as previously stated, the contractor will definitely add in another 2 or 3 percent additional length of pipe to account for all the wastage. I understand the language well, I am looking for opinions on the actual practice and it appears that it is quite common for plan dimensions to be estimated and provide accuracy sufficient for the project.

 

[Hoagie]

I believe the expression, LF, is lineal foot and not linear. By definition of a lineal foot is: "..A measure of one foot, in a straight line, along the ground..."

 

[cvg]

Hoagie - do you have a reference for the definition? It appears that this would muddy the waters a bit further.

 

[GoldDredger]

I'm not sure I agree with Hoagie on the last post. Lineal refers to a line of decent from an ancestor or in the context of direct heredity

Lineal: in a straight unbroken line of descent from parent to child

Linear: of or relating to length

 

[DRC1]

Pipe for payment is measured by tape along the axis that it is installed. How you estimate it is up to the estimator. Slope correction is done by the contractor for layouts of structures, which will probably be computed by the contractor and laid out to the nearest 1/4 to 1/8 inch.
Good site contractors are more than sufficently sophisticated to handle such lay out.
Unless you have slope pipe (pipe moving water down an embankment to a collector main) the typical correction will be small.
Pipe should be estimated based on each run, not on the total length, for 2 runs of 20 feet are not the same as one 40 ft run.
Finally adding 15 or 25% to the bid forces the owner to pay more for the project if it is built in accordance to the plans. Accurate take offs from accrurate plans will give the owner the best price.

 

[bimr]

"Lineal" just means that the poor fellow is older than you are and using an colloquial expression. See:

the measure of length; - usually written linear measure.

See also: Lineal

Webster's Revised Unabridged Dictionary, published 1913 by C. & G. Merriam Co.

 

[Hoagie]

CVG,

Sorry. I didn't mean to add to your woe or incite any additonal, useless commentary.

If you check any common, legal dictionary, you should find the definition that I posted. It's an expression taken from the civil venacular, so it won't show up in a common dictionary. I used Answers.com to find a down-n-dirty definition last week for the sake of speed.

Good luck, cheers--
h.

 

[rbulsara]

If a contractor measures the actual pipe lengths along the axis and bills for it and an inspector challanges him by relying only on "horzintal" measurements, the contractor will win the case in a court.

The spec as written is very fair. Trying to find a way to underpay is not.