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The Idiots' Guide to Highways
STREET IRONWORK ( INSPECTION COVERS & GULLYS ) INSTALLATION
|A practical example of resetting failed ironwork||General notes to lifting ironwork|
|Specifications relating to street ironwork||Personal Note|
A PRACTICAL EXAMPLE OF RESETTING FAILED IRONWORK
|Road ironwork should not fail to the degree
it does as long as the work is carried out in accordance with the
works drawings, and this series of photographs will show a simple
yet correctly performed method of resetting a major item of road
The actual chamber has been rebuilt with engineering quality bricks, these happen to be red, not all engineering bricks are blue.
The bed for the manhole casing has been laid with 60mm. layer of "fast-set" mortar with a two hour strength of 10kn., this is because the road will need to be opened before the evening "rush hour".
|It is clear to see that the
surround to the inspection cover has been cut back to sound
material with a vertical face in good quality material.
The manhole is placed at the correct level to ensure its cover will be at the same level as the surrounding road surface.
You are just able to see the end of the piece of timber that was used as the straight edge to set the cover in the mortar bed, none of this is rocket science just simple procedures that should be adhered to every time ironwork is placed.
material is prepared and is used to completely incase the manhole
casting, making sure it is fully compacted to ensure maximum
Sufficient depth is left to accommodate the placing of a bituminous material similar to that of the surrounding wearing course surface.
When the mortar has fully set and the wearing course has been replaced it is unlikely that this particular manhole will "move" for some considerable time.
RELATING TO STREET IRONWORK
BS 497 : Specification for manhole covers, road gully gratings & frames for drainage purposes :
Part 1 : Cast iron and cast steel
N.B. THIS SPECIFICATION WAS WITHDRAWN WITH EFFECT FROM 30th JUNE 1995, and is superseded by,
BS EN 124:1994:Gully tops and manhole tops for vehicular and pedestrian areas : Design requirements, type testing, marking, quality control
The specification includes such criteria as loading, design and dimensions.
BS EN 124:1994 was so difficult to understand BS 7903 was introduced to help make things a little less confusing.
BS 7903:1997:Selection and use of gully tops and manhole covers for installation within the highway
Highways Agency Guidance Document - HA 104/2 - Chamber Tops and Gully Tops for Road Drainage Services
GENERAL NOTES TO LIFTING IRONWORK
The term ironwork used in relation to highways maintenance and construction means gulleys (drains), manholes, stop-tap covers, inspection chamber covers, etc. etc..
All these products will be manufactured to the appropriate British Standard with regards to approved designs, dimensions and strength.
The actual specification and testing of ironwork items is a separate issue to the setting or lifting of such products, but without the correct setting of manholes covers and gully gratings they will be subject to unnecessary high levels of loading that may be above their design criteria and therefore will be the cause of early failure.
To achieve maximum effectiveness with regards to load carrying ability (traffic) and durability the ironwork must be lifted / installed / bedded in the correct way, poor workmanship in installation is a big cause of ironwork failure.
Ironwork that has been lifted poorly will "move" and settle, making the road unsafe, and cause premature failure of the pavement construction / surfacing / overlay.
Obtain a copy of the scheme design or overseeing organisation specification for full details of how the particular piece of ironwork should be lifted.
However, the basic requirements amount to good practice, the chamber shall be soundly constructed and pointed (if brickwork), some chambers / gulley pots are pre-made in concrete.
The gully pots that are preformed in plastic must be completely surrounded with fresh concrete, according to the specification, if the gully is to achieve the correct load carrying strength.
Ironwork in general shall be bedded on an approved mortar, quite often a rapid setting mortar,
e.g. a strength of 10n. per square mm. at 2 hours.
At the time of lifting it is not always known what will be required to successfully raise the ironwork to the new level, so a broad selection of materials and items should be carried by the lifting gang, e.g. fast set mortar, engineering bricks, engineering quality "tiles", steel strips to support ironwork, etc..
The frame of whatever item of ironwork you are lifting must be completely supported by the method of lifting/setting you have adopted.
Ironwork can be lifted before or after the wearing course has been laid, but it is usually preferred to lift before final surfacing if possible as this allows more thorough inspection of the ironwork lifting, and it avoids extra joints in the surfacing material and allows better compaction of the bituminous surface course.
Safety of operatives and the public shall be paramount at all times, during the lifting of ironwork and while the ironwork may be in a lifted condition before surfacing, and especially while other parts of the highway are still open to live traffic.
Correct signing and guarding must be in place during work, and until such time as the work is complete and able to successfully carry traffic.
try to refer to as few commercial sites as possible in compiling
my site, but when a site offers useful or interesting information
about a subject I make an exception.
Useful information on the manufacture and specification of inspection covers and gratings can be found, HERE.
It is sad to state that in my experience when I have been asked to investigate the failure of road ironwork, which usually means nothing more than the lifting of the grating and sticking your head down the chamber to have a good look, it has been the standard of workmanship that has been to blame for the failure.
This lack of workmanship seems especially prevalent when road gullys are raised to allow for an overlay of bituminous surfacing.
In this situation it is often the case that the ironwork is raised correctly to the right level, i.e. the surface level of the finished wearing course, but with a minimum of effort.
When you look at the standard of "lifting" it leaves a lot to be desired in terms of correctly placed and mortared in brick work and quarry tiles ( quarry tiles are used for small lifts ) to form a strong load transferring bed for the gully.
The finished bituminous surfacing will look fine for a while, but then you will see the tell tale cracking start to appear around the gully showing that the gully chamber was not correctly constructed when raised.
Again as I have said many times in the pages of this website there is no substitute for good site supervision to ensure work is correctly carried out.
Contractors who perform the work correctly, and there are some excellent, conscientious gangs who specialise in this type of work have nothing to fear, in fact they will benefit because contractors with poor working practice when gully lifting will be exposed by good site supervision and should be removed from the tender list.
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