I am sure that any surveyor that has had to pull up a sewer man hole cover and string through the 4 cup hooks to get a centerline intersection to the surface has had better experiences surveying. Many times the only thing left of the cup hooks are just stubs because of the 60+ years of being in a corrosive environment. At other times, one will not find hooks at all (city employees complained the hooks would rip their shirts when working in the manholes)and only nails would be in the leads. Nails create more work because you have to somehow get a cup tack or blue lath nail into the lead in line with the nail in the lead, or a cup hook shank, so a string could be strung through the four points for the centerline intersection...not a simple task.
OK, I was shown a much better way of dealing with hooks/nails that are in SMHM's and would like to pass it along..this is the way I do it.
After the man hole cover is lifted out of the way, we eyeball a chalk line through two leads. Line does not have to be perfect, within a few tenths. I extend the chalkline approx 6 feet or so beyond the man hole rim edge. This is done twice.
Set the gun up +/- on the chalk line and about 4' +/- above the surface. Fine leveling is not needed, I just target bubble level. Using the laser I target the cup hook, shank or nail in the chimney, then fine tune the sight optically.
The gun is rotated up and we check the existing punch marks in the rim for line. If those are off we set a new DEEP punch mark in the rim. If you set a new punch, please cut two angled side cuts on the rim on either side of the new punch mark to help the next guy. This is repeated four times.
The City of LA has been installing hooks in SMH's for years. The hooks are set in lead plugs which were drilled into either brick of concrete sewer chimney walls. The hooks were always placed on the street centerlines or whatever reference line is shown on the city field notes, very stable monuments. A following surveyor would open the man hole up, string through the four hooks, and tie out the string intersection with a bob and swing ties, or some other method. Cumbersome and time consuming and doing the intersection this way does not allow one to check existing punches for c/l alignment and definitely does not allow anyone to set new punches that will match the hooks.
Interesting and a pretty good source of evidence.
Ralph
Ralph
It's a fast method. Yesterday, we pulled up 5 man holes. The punch marks on four of the man holes were dead centered, quite amazing considering they were set back in the 50's or so. The punches in the fifth were off line, cover was lifted after some construction that rotated their positions, so we set four new punches on line with side cuts.
/.
Ralph
> It's a fast method. Yesterday, we pulled up 5 man holes. The punch marks on four of the man holes were dead centered, quite amazing considering they were set back in the 50's or so. The punches in the fifth were off line, cover was lifted after some construction that rotated their positions, so we set four new punches on line with side cuts.
>
> /.
It's a very good way to monument the Street Lines.
Someone in L.A. was thinking.
Ralph
Paul,
Very interesting procedure. What is the purpose of the procedure? I don't grasp the concept of why the manhole would need to be located to that degree of accuracy. Is this for some type of control?
It is pretty neat to see how things are done in other parts of the country.
Thanks or sharing.
Jimmy
City of Los Angeles - Jimmy
> Paul,
>
> .... What is the purpose of the procedure?
To transfer below surface control to the surface and to check or provide additional
control, i.e., punch marks in the man hole rim.
>I don't grasp the concept of why the manhole would need to be located to that degree of accuracy. Is this for some type of control?
It's not the manhole that is being located, it's the reference points inside the chimney that are being located.
This picture will help. The hooks/nails in the chimney are on the street centerlines and the intersection of the two reference lines forms the centerline intersection of the streets
City of Los Angeles - Jimmy
Interesting. I had not heard of that.
City of Los Angeles - Jimmy
One of the few things I like about working in LA was the control available for boundary work and how well it fit other boundary monuments.
City of Los Angeles - Jimmy
never seen anything like that in Arizona - interesting.
City of Los Angeles - Paul
good on safety, too. now you have eliminated confined space entry. oxygen depletion or carbon monoxide can put you down before you realize it.
how many surveyors have an o2 sniffer, body harness, big tripod and winch set?
City of Los Angeles - Jimmy
Thanks for the explanation. The second drawing explained it.
That is a pretty neat idea. Nothing like that here in the greater Memphis area that I am aware of. It's mostly locating curb and gutter and property corners along the right of way to reestablish rights of way.
Ralph
Here's another thought, don't place the SMH at the centerline intersection in the first place.
:gammon:
City of Los Angeles - Jimmy
Paul,
Thanks for posting this and the Beverly Hills stuff last week.
Good info.
And I agree with Ruel's comment.
Thanks,
Ryan.
City of Los Angeles - Jimmy
Thanks for posting Paul.
I will say that the City of LA and So cal in general has been on of the best places I've ever had the pleasure of surveying for finding previous controlling monuments or in this case controlling hooks. I miss that fact dearly. The framers of that system were pretty smart to document as much as they did.
Sadly they obviously lost the battle of SSWR manhole placement with the engineering department at the time.|-)
Manholes
Roger, 10-4. It amazes me that any City would let anyone who wants to open their utility structure and do anything they want.
Ralph
“Here's another thought, don't place the SMH at the centerline intersection in the first place.”
After eons of griping at them several of the larger engineering firms (and some smaller ones too) that don’t have a survey department have finally started offsetting SMH’s from PI’s.
For the manholes that do fall on an intersection straddlers are set. No manhole cover removal necessary!
Have a great week!
Manholes
> Roger, 10-4. It amazes me that any City would let anyone who wants to open their utility structure and do anything they want.
Not just anyone Jim..just surveyors and sanitary facility engineers!
City of Los Angeles - 1937 work
IMHO...hooks in SHM's are one of the best monuments there is. Stable and virtually indestructable...
Here's the cover page of the city field book that did that work. Eight man crew, 1937, calibrated chain..
City of Los Angeles - 1937 work
Those guys did some good work!:good:
Ralph
City of Los Angeles - 1937 work
Thanks for the post, Paul. I found the lead plugs and corroded remainders of hooks inside a manhole in LA recently. I just scratched my head and went with the punch marks of record on the rim.
