Design of Manhole >6m depth 3

[BrianIreland]

I am designing a manhole with a depth of 8m. Is there any special considerations I should be aware of?
does it have to be a huge chamber (& what is a rest chamber)?

 

[gbam]

Depending on the diameter of the riser you may need to provide a safety cage around the ladder for fall protection.

 

[bltseattle]

Check you govt standards, for the U.S., a quick glance at the OSHA website resulted in the following:

Per OSHA Standards 29 CFR 1910.27

Cages or wells (except as provided in subparagraph (5) of this paragraph) conforming to the dimensions shown in figures D-7, D-8, and D-9 shall be provided on ladders of more than 20 feet to a maximum unbroken length of 30 feet

applications.


1910.27(d)(2)

"Landing platforms." When ladders are used to ascend to heights exceeding 20 feet (except on chimneys), landing platforms shall be provided for each 30 feet of height or fraction thereof, except that, where no cage, well, or ladder safety device is provided, landing platforms shall be provided for each 20 feet of height or fraction thereof. Each ladder section shall be offset from adjacent sections. Where installation conditions (even for a short, unbroken length) require that adjacent sections be offset, landing platforms shall be provided at each offset.


..1910.27(d)(5)

1910.27(d)(5)

"Ladder safety devices." Ladder safety devices may be used on tower, water tank, and chimney ladders over 20 feet in unbroken length in lieu of cage protection. No landing platform is required in these cases. All ladder safety devices such as those that incorporate lifebelts, friction brakes, and sliding attachments shall meet the design requirements of the ladders which they serve.

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9719

 

[Ginger]

If you are looking to use precast concrete manhole rings then look in the manufacturer's literature (ARC, Hanson etc). the rings are precast and so are the landing slabs, chimneys and cver slabs. Most good precasters list the allowable chamber depths for the UK i their data manuals.

You should take care when placing the landing slabs that the opening to the chamber below is about 90 degrees from the opening you have just climbed through. That is, looking on plan, if you go down a hole at 12 o'clock position, the opening on the landing should be around the 3 o'clock or 9'o'clock position ideally.

 

[pba]

A manhole of this size will present a serious problem as a confined working space. Consider not only how acess can be gained but how you could recover an unconcious (or dead)person.

Such a deep manhole is quite rare and you are clearly uncomfortable with the design issues. If it was me I'd be looing for someone with the relevant experience to assist in the design. I wouldn't take the risk without it...

 

[Ginger]

Anything below ground, whether 8m deep or not is a confined space, and therefore brings with it a risk. You therefore need to assess the risks (so far as you are reasonably able) in the design. You can't always design out the risks but you can minimise them. If you tried to carry out risk-free designs you would never build anything.

So, for a deep manhole you would expect operatives entering the confined space to have gas detectors, be carrying self-saver air supply kits, be fully trained and possibly wearing a body harness connected to a lanyard which is in turn connected to a winch on the surface. The winch operator is on the surface and can haul out an unconscious operative should the need arise. Your design should allow them to do this. You may need to chat to those who are using it before completing the design.

It is incumbent upon the operatives to have a safe system of work in place prior to entering the manhole.

If you don't want to consider the risks.........don't build the manhole.

 

[chicopee]

since the excavation is deeper than 20', A PE must stamp the prints to comply w/ OSHA excavation standard.

 

[dicksewerrat]

Just install Manhole barrel sections to the top and vacuum the soil out of the manhole. the sections will go down. don't put any steps or ladders in the manhole. if you do, rescue may be more of a problem. When maintenance persons need to go into the manhole, use a small crane to put them in and out.

 

[chicopee]

DOT projects all require steps inside their manholes.

 

[RJLDesign]

All the above comment are quiet good and important. But do not forget about ground water at those depths. You dont want it to float. Hows your skin friction to the sounding soils ?

Diplomacy Has Failed Time For Some Action

 

[zoomi]

Try and made the entrance/exit circular. It's the only shape of cover that won't fall down the hole.

 

[rconner]

I do not profess to be much experienced in this subject, but I believe I've have seen/heard some debates in various forums/locations an whether or not at least permanent "steps" are a good idea in manholes. I think where steps have not been employed, any required person access would probably have to be done with appropriate harnesses/lifts/hoists and/or temporary ladders (and of course with all other due testing and other safety precautions etc.). If ladders are employed, a couple things that haven't yet been said in this thread are (I guess some could additionally argue) perhaps that if permanent steps are not there they are not there to corrode where this is a concern or otherwise need to inspect for strength etc., quite a bit of exertion might be required to climb down and up the "steps" of an 8 m. ladder, and in this day of "vulnerability assessments" etc. at least permananent ladders may additionally more invite unauthorized access to the underground sewer system).

 

[rossmail]

at one time a platform was required to make it easier for a man to climb in ,a resting point ,stageing area for tools and such and shorten the fall if he did so but now with the confined space requirements the platforms are considered an obsitcal for man retreval from the top .go figure have you ever climbed into a deep manhole like that with out a safety platform or 2 along the way ,,gives me the creeps .some of the people who make this stuff up dont do the work .ventalation and a sniffer being manditory would make better sence ,i liked those platforms.but answer is no dont put it in ,new rules now .

 

[Hoagie]

IrishBrian..

Two weeks to St Pats Day, mate. Slainte...

I'd be weary of infiltration via the sidewalls. I'd eiher manage the infiltration or lock it out. Alike RJLDesign's suggestions, if you lock out the infiltration, you many need to beef up the joints and may need to add ballast if friction alone can't overcome bouyancy.

I agree with DickySewerRat...don't encourage entry by specifying steps or ladders. Yes, standard specifications will indicate this-that...however, this is not a standard manhole...this is more like a mine shaft. Don't forget to specify lockable access. I'd work with a GC to look at constructibilty, constraints, etc..

Good luck,

H.

 

[dicksewerrat]

An RCP manhole should not float out of the ground. I've installed them in sand, water and slimy clay. They all stayed right where I put them.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[rossmail]

the manhole will have to have a locking lid ,i have used bolt down casting,if frost heave or flotation is a concern strap the manhole recast vertical sections together.

 

[DRC1]

A 25 ft deep manhole is not uncommon in urban settings. Generally the manholes are precast with a precast slab or castin place slabs. Knock outs allow instalation of the pipes. Most DOT's & cities have standard designs for manholes. Most precasters can engineer details for specific situations. Ladder rungs are nearly always provided. They are currently made out of synthetic materials. Having been down in many sewer manholes, I would not worry about ladders inviting entry. There is nothing inviting about a live manhole. Joints at the precast sections are sealed with a tar like subbstance.Excavation can be accomplished bty driven sheeting or vertical wood sheeting that is dug down. Prior to excavating, Utilities must be marked out and any conflicting utilities relocated. Marking out the utilities and test pitting the proposed location in the design phase can avoid large delay claims in the contract.

Entry into a manhole requires blowers for ventilation, a four gas meter,body harness and life line attached to a retrival system, training in confined space entry, a top man a competent person, a written confined space entry permit and a written confined space entry plan

 

[rconner]

I hope my use of the word "invite" in my initial post was not misinterpreted! In general, I would not accept the "invitation" of unlocked manhole covers, ladder rungs or for that matter hoists any more than I need to! I am aware what is down there is not as glamorous as the Paris "float" tours, Teenage Mutant Ninja Turtles, and the "Penguin" of Batman fame have advertised!; however, I think I am aware of at least one manhunt where a "perp" actually used an underground system accessed by manhole rungs to evade capture (and seen criminals and terrorists at least in the movies sort of instructed to use them for many other purposes) -- also, to pardon the blunt analogy the availability of a suicide vest does not invite me to strap one on, but this obviously does not mean at least a few others with whatever motivation won't.

 

[DRC1]

Just a poor attempt on my part to interject a little dry hummor.

 

[Ginger]

There has been a fair bit of debate in the UK regarding the access into manholes, particularly amongst the water companies. The trend in the UK for deeper manholes is to NOT provide "step irons", ladders or rungs in the manhole wall.

The philosiphy is that any unauthorised person gaining access to a manhole incorporating step irons or ladders will have a readily available means of entry down to the bottom. Once there, they can become asphyxiated or swept away in the flow at their leisure. By not providing any means of entry, your average undesirable will not attempt to jump in as there is clearly no way out. those who should be entering the manhole will turn up with ladders winches, harnesses and gas detectors and enter the manhole in a safe and controlled manner.