City of Los Angeles - Paul
> 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.
Glad to help. Never trust punch marks. Always check them. Rims do get rotated.
Nice diagram, is that from a book of standards.. I do, however, have a couple issues with the methodology (not necessarily a terrible method, though). I notice a plum line drawn from the hooks to the rim. I might disagree with the chalk line being ok to be within a few tenth's however. I am confident a surveyor is capable of "eyeballing" line within 'one tenth' in the 6 feet prescribed. My main concern is setting up the gun 6 feet from the manhole, where this will put you in the traffic lane. Looking at the tie sheet you posted, the tie distance is 3.25' to the C/L INT. I like to use large rubber bands and when the hooks are missing, bending a hub nail (not cup tack) is very easy. While one man is perpetuating the monument, the other is watching the traffic.
> Nice diagram, is that from a book of standards.. I do, however, have a couple issues with the methodology (not necessarily a terrible method, though). I notice a plum line drawn from the hooks to the rim. I might disagree with the chalk line being ok to be within a few tenth's however.
Why would he be off a tenth? Are we looking at the same diagram? It looks to me like he's plumbing it up on the same plane. This technique has been used by City Surveyors for at least 100 years.
Ralph
Pretty neat that they would monument that. In Pittsburgh they at one time had a very active survey department, and they established a high accuracy triangulation network, then 18,000 traverse points off of that, many of which were monuments inside cast iron boxes on street corners. They also created beautiful maps using planetable methods. In the mid 60's they tossed all the data because someone told them photogrammetry had made it all obsolete.
Here is a link to digital copies of these old maps:
Wouldn't it be possible to shoot the hooks with a dual prism pole? The rod can be at any angle, not plumb. That is how we now shoot inverts. It is especially applicable when the invert is several feet back from the rim. That gives us a very accurate horizontal position as well. Here I am shooting the invert on a storm pipe high up on a wall:
I apologize to Paul, and the readers, if I sounded critiquing in the first half of my earlier post where using an instrument to transfer the centerline to the surface.
I have, however, transferred many hooked smh's over the years and my concern was having the gun and i/o exposed to traffic.
City of Los Angeles - 1937 work
I always find it interesting the work done during the Great Depression.
We are letting it all slip away via neglect because we can't afford to budget that work any longer. They did it somehow during the Great Depression, though.
>..Wouldn't it be possible to shoot the hooks with a dual prism pole? The rod can be at any angle, not plumb.
Probably. However, it wouldnt be as fast for transfering the hook location to the surface and the human error of positioning the dual prism would be introduced.
Timely post John. I had the opportunity to do another set of transfers and I did some checking on the horizontal position of the leads/hooks inside the chimney to the center of the SMH rim at the surface. The chimney is on a batter and the hooks are always what seems to be a certain depth below the surface. It seems like the depth and the batter was taken into consideration for where the reference points would be placed. The rim center is directly above the hooks inside the chimney.
Here's a couple of pictures I snapped..
A city inspector was overseeing the operation disguised as an albino roach.
We repunched this rim with side cuts for the next guy /.. As you can see, that hook is located where the access ladder is, the rung may be a problem with placing a dual prism rod on it.
City of Los Angeles - Kan
> Nice diagram, is that from a book of standards.. I do, however, have a couple issues with the methodology (not necessarily a terrible method, though). I notice a plum line drawn from the hooks to the rim. I might disagree with the chalk line being ok to be within a few tenth's however. I am confident a surveyor is capable of "eyeballing" line within 'one tenth' in the 6 feet prescribed. My main concern is setting up the gun 6 feet from the manhole, where this will put you in the traffic lane. Looking at the tie sheet you posted, the tie distance is 3.25' to the C/L INT. I like to use large rubber bands and when the hooks are missing, bending a hub nail (not cup tack) is very easy. While one man is perpetuating the monument, the other is watching the traffic.
Kan..since the hook location inside the chimney is directly below the SMH rim center the transfer is going to be very accurate. For discussion, if I was offline two tenths in 6 feet, how far off would I be doing a vertical lift? Pretty minor.
City of Los Angeles - Kan
No apology necessary Kan 🙂
Try this method one time if you get the opportunity.
I like the albino roach!
as for the dual prism method, as long as the rod can be held steady (one option is to use another rod to stabilize it, or rig up a bipod stand), the method is very accurate, I would say to the couple of millimeter level (depending on the toal station angular and edm accuracy)
City of Los Angeles - John
Ok, say you use the dual prism to locate the hooks..then what?
City of Los Angeles - Kan
I've seen chiseled lines on manhole rims but never hooks inside the chimney riser.
For the most part up here manholes are offset 6 feet from the centerline. They are supposed to be out of the wheel track.
Paul Plutae, post: 134990, member: 12 wrote: 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..
I second this. A block with 4 hooked manholes will close within hundredths of the City tie notes nearly every time (and 60 years later!). Best type of monument hands down. The extra work and time to string the hooks (or lead) is more than worth it for me.
Can someone repost a picture or sketch of what these hooks are? The old links no longer work and we all know curiosity killed the cat. Thanks!
Will do when I get in from the field!
Here you go!
If the hooks are really deep, you can hand the string line to the locals (shown hereon) for assistance.
NC Hansen, post: 450207, member: 13086 wrote: If the hooks are really deep, you can hand the string line to the locals (shown hereon) for assistance.
I opened a couple of MHs today that looked just like that in terms of the denizens. They don't bother me much, but my wife absolutely freaks out at the sight of them.
Holy thread resurrection, nearly 5.5 years old and its back to life. Main reason why I love this site is all this data and information and knowledge stays pretty relevant. I wish we had CL ties, and CL tie sheets, and mh hooks up here in the pacific northwest. I miss that awesome framework of control that surveying in LA has to offer.
I set a lot of those lead and tacks when I was a grunt there (hooks were usually torn out by the sewer maintenance people because they would catch their overalls on them and cause rips). It amounted to laying on your stomach to reach down and drill the hole for the lead always fun on a busy street. Lucky the brick was soft or the mortar lining was thin for drilling with a star drill (no electric hammer drills in those days).
Probably one of the best reasons to get promoted was so someone else had to reach into those manholes.
As for the denizens, we would pour paint thinner on the insides and throw a match into it. Sometimes manhole lids in all directions would pop up.
Like a Cash boy, we would hope for a manhole that happened to be in a crosswalk. When the pedestrians got close was when we popped the lid and the critters scattered in every direction. You never heard so many girly screams, and from the guys, too.
By the way, I don't see the punches in the manhole rim. Were there any? Are you going to set some?
