Power Pole Installations...and Ethics 5

[tch549]

Are the installation of power poles typically monitored by a geotech? If so, what are the concerns?

The reason I am asking is because I am currently working as a geotech in northern Canada on a drill monitoring job which requires me to classify the soil in the base of the drilled hole. This is supposed to determine whether or not the power pole needs a bearing plate installed (which I assume increases surface area = decreasing bearing pressure caused by the butt of the pole). I have past experience with soil identification and geotech monitoring in other settings, but this is new to me - and I think the contractors might be trying to give me the run-around!

They claim to be well experienced, and I have no reason to believe they are not. They say "the engineers tried to apply the process for a multi-storey bldg to a @&#*$% wooden pole!". This could be a valid point, but contractors have a reputation for trying to bamboozle testers/techs to bend the rules for them, so I wanted to get some other opinions on what level of monitoring - if any - should be done with installation of power poles.

Also on a side note, when I become the bearer of bad news for contractors, i've had people tell me "once your in this career for a bit longer you will lose those ethics!", and then have a hearty laugh at my apparent "naivety". Are some rules meant to be broken in engineering? Or have I just been lucky enough to work with jackasses so far? lol

Geology of the Area: at the pole foundation depths ive encountered silt and clay based glacial tills (hard to very hard) and fluvial sand (fine to very fine grained, clean, moist-saturated, loose to dense)

Thanks for reading my lengthy post, all!

 

[Ron]

For typical wood poles, there is usually no regard given to bearing pressure as being a significant consideration. Lateral loading, thus fixity depth is a greater concern.

For very large steel or concrete poles/structures, foundation principles often apply.

 

[oldestguy]

This sounds really "way out there". I wonder if this is a joke question, since in my career of umteen many years this has never come up. Usually it is important to be sure you have good lateral support, but minor settlements that may occur for power poles, even those on caissons, is not in the picture of what is important out there.

Are there any elevation requirements for some reason? In other words at each site is there some fixed elevation for each pole? I would doubt it. If so, get from the designers how much settlement they can tolerate away from that figure. Then do an estimate of that settlement "with the vertical load they give you" for typical soils found there. I'll bet they won't have an answer.

By the time you drop that pole once, it probably will never have a static vertical load effect exceeding that under the base What about side friction support? In the long run that will be significant.

Final questions: How are you inspecting? Looking down to see if it is loosened soil there? Driving a rod? Spoon sampling? Has there been a spec. on how much loose soil can remain?

 

[tch549]

Sorry, I should have specified the size of the poles. They are for a 240kV line. They are they big two or three pole structures having poles with lower diameter of approximately 2 feet and a height of approximately 90 ft. Boreholes are done using a solid stem 30" auger. Sampling is done by hand off the auger with attention focused on the bottom 1 ft of material.

There is no spec on how much loose soil remaining. The only specifications given to me were soil classes ranked from 0 (most dense=bedrock) to 8 (least dense - organics..etc.). Anything between classes 4 and 8 need a bearing plate installed according to the specs.

There are also specs involving over excavation and placement of 70 inch minus gravel underneath the pole...on every pole regardless of soil conditions! This kinda of racks my brain, cause most of the holes are founded in very dense in-situ material...which shouldn't settle at all, correct?

It's not a joke either btw. I am just trying to figure out if these guys over engineered this and the construction crew is right...or are they wrong.

 

[paddingtongreen]

The rule of thumb for wood poles (usually distribution poles) is that the bottom 1/7th of the pole goes into the ground. For steel pole transmission lines, normal rules apply, except that, if utilities are putting up the line, they will often use reduced safety factors because it is less costly to fix the odd one that doesn't hold up, failure being self limiting.

I had a boss who came to us from a utility company, and he kept complaining that we were too conservative. We explained that if he worked for the utility company, he just fixed a pole that leaned a little, but if we designed one that leaned, the utility would make us pay for the fix, and that would use up the profit.

A little off track but i want to give you some feel for the nuances.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[SlideRuleEra]

housetim - You have received good advice, so I'll just add a couple of websites for reference:

http://www.usda.gov/rus/electric/bulletins.htm

and

http://www.woodpoles.org/EngineeringDesignInfo.htm

Concerning your other question:

Are some rules meant to be broken in engineering?

Having worked as both an Engineer and a Bridge Contractor, my answer is a qualified "yes", I'll explain my qualification in a simplified statement:

Sometimes it is more cost effective (material, labor, schedule, acceptable final product) for a Contractor to intentionally OVERBUILD than it is to precisely execute a carefully (and correctly) prepared design. I won't bore you with specific examples, but will be happy to discuss if requested.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[hokie66]

It wasn't a wood pole, but I once saw a concrete pole which just kept going down when it was released. So in that case, a bit of geotech advice would have been good to have.

 

[tch549]

Here is a scenario: The contractor is installing fairly large power pole structures (240kV, l=90' d=2.0') and I am working as a geotech monitor for the soil conditions in the foundations of the wooden pole structures. The engineering specs state that ALL pole foundations must be backfilled with a well graded sandy gravel.

The contractor says, "The design engineers don't have a clue! We have been doing this for 30+ years! Help us out would ya!? Just write on your sheet that we put gravel in the base of the hole!" (in a more subtle way than that of course). In the back of your mind you think, "hmm...I am very inexperienced, and not sure if these guys are trying to bamboozle me, but maybe they know what they are talking about...because now that I think about it: If the base material is already quite firm and un-disturbed, wouldn't the placement of a compacted gravel fill settle more than the in-situ material beneath it anyway?". I always learned that any re-worked fill can never be as throughly compacted as a very dense in-situ material.

So I decide to document the gravel being placed in what I deemed as competent foundations (based on the spec of course), while I knowingly allowed the contractor to omit the placement of gravel in these foundations.

IS THIS WRONG? I was always told throughout education that you learn the most once you are out in the field...I feel, and fear, that I am coming to a realization of how things are really done in the construction industry behind the backs of engineers. I want to know if what I decided to do was terribly unethical, or was I going with the norm? Also, I am questioning whether these guys have good intentions or bad (i.e. do they really know what they are doing? can I trust them? or are they just trying to swing in and make a buck while pinning the liability on me?).

Here is another example scenario: 98% compaction must be met. After much tamping and water added, material can not get higher than 96.5% from the densometer. On visual inspection, the material is very hard packed and you believe that its the hardest its going to get. Rather than waste the contractors money (and also hurt your relationship with them) by making them dig up, replace and repack the material, is it ethical to pass the area desipte the inadequate density reading? Especially if you are dealing with highly variable native material.

I guess in a nutshell the question is "as a monitor, is it okay to intentionally allow the contractors to disregard aspects of the engineering specs that are held by the experienced construction workers to be unnecessary or too conservative?"

 

[Qshake]

housetim - It's not uncommon for us in the midwest to require full geotech analysis, drilled shaft inspection and coring, if not full cross-hole sonic logginf for foundations of high mast lighting poles. These poles get up to about 150' so a little more than the 90 you're dealing with. However, your electrical lines will impose loads on the poles and consequently the foundations that lighting poles don't get. Lastly, the high mast lighting is usually on highway right of way and so failure puts the public at risk. In your application this may not be the case.

In the end, i'm just trying to point out that for the right collection of factors, yes, your work may actually be more important than the contractor's crew is allowing for.

Good Luck, stay warm! I hear the summers in Northern Canada can be brutally cold!

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[paddingtongreen]

If a pole structure fails and there is an investigation, guess who's career is in the toilet when they find that the documents were falsified. The Contractor will walk away unscathed because you made the decision that he was in compliance, not him.

The Contractor agreed to do certain things for a given amount of money, he agreed with the backfill and the density requirements. The Engineer has made calculations and determined the strength he needs to provide the mandated factors of safety, the Contractor is trying to eat some of those factors without checking if there is extra capacity there.

He sold the Owner, and is being paid for, a Cadillac and wants you to okay the delivery of a Chevrolet.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[cntw1953]

For your dilemma in between the design spec and the contractor, I suggest to follow the no-clue engineering document rather than the experienced contractor, to whom you have no contractual obligation. The ethic is simply carry out the project by spec to maintain the owner's interest at no fault of your own.

However, you may form your own judgement, then discuss with the designer and the owner. Change could be in the order, but not by you (filed engineer).

 

[ishvaaag]

I certainly agree with the last two post. Only if you find something wrong with the project should you object. By reasons that may escape both you and the contractor, the designer and maybe the owner have decided to build all their poles to some standard; as cntw1953 says, you are not paid to ease the earning problems of the contractor; and, except that you say otherwise, neither is your task ask or allow any unneeded modification. As well, this provides unwarranted earnings to the contractor to the risk of everyone else, you included.

In short, I would understand that in the difficulty of making the works, the contractor would ask easement from you; but if ethical, the decision should be taken by the director of the works with full knowledge and acquiescence of the owner and its management, whilst, of course, the standing diminished cost, go to the purse of the owner, and not of the contractor.

 

[hollowstemhead]

Make no mistake about it, you are certainly dealing with some significant structures with significant loads. As a field engineer, you are the eyes and ears of the designers. You have an obligation to make sure their design is being properly implemented AND you have the obligation to report when the conditions they assumed in their design (soil and groundwater in this case) are changing. Your observations and thoughts may very well be warranted, but convey them to the designer and let them check what is going on. Remember we are all to some point trying to model something as black and white that is very, much gray, especially along the entire length of a power line.

Your duties ethically are to do your best to ensure safety and a quality final product for the owner. Unfortunately this often times means delivering the bad news to the contractors. Remember, their mental conception of the project is not neccesarily wrong, but is based on a different thought process.

Discuss the design with the engineer so you can give some competent, reasonable responses to the contractors. The more consistent you are with your emotions and explanations, the more you will be respected in the field.

 

[ishvaaag]

What always makes me remember those baffling parables of the gospels on the "smart serf". Certainly there are owners that are wolves in legal wolf skin, but there are also as well contractors playin the poor lame sheep. Yet it is practical to make note anyway that an ethical decision needs not be (even if it should be the case) one purportedly supported by the law. Have zillions films on it.

 

[cntw1953]

Agree with steamhead.
Be consistent and persistent throughout, the good contractors respect that, the lousy ones do not deserve your helping hand.