hinekadon (13-02-21)
I have long held the belief that the Australian Standards are fundamentally flawed when it comes to pipe class/depth of fill.
I do not have access to the current Standards but the theory goes like this:
"The numeric classification system adopted to identify the load carrying capacity of concrete pipes is based
on the rationale that any particular pipe class is able to carry approximately the same proportionate height
of fill. For example, a class 10 pipe can carry five times the height of fill of a class 2 pipe, under the same
installation conditions. See Section 2 – Test load data, further information on test loads for each size class.
The required strength of a concrete pipe depends on both the load to be carried by the installed pipe, and the
supporting ground installation conditions.
The load transmitted onto the pipe depends on the height and the type of fill material. Also, when installed
in a trench, the width of the trench at the top of the pipe is important. Generally the wider the trench, the greater
the load for any height of fill over the pipe.
The load class for concrete pipes can be determined by consulting AS/NZS 3725: Design for Installation
of Buried Concrete Pipes which provides methods for determining the installed load on concrete pipes from
the earth fill over the pipes as well as any induced live (vehicle) load effects."
I do not have the ability to test this under real world construction conditions - I no longer work on projects that have large pipes and high fills.
I believe that for pipes with high fills and constructed correctly the pipe is mainly for hydraulic reasons only i.e. to prevent the fill from being washed away.
The Standards are based on theory published in the 1950's(?) - I have seen the original book but the chance of finding a copy now would be somewhere between nil and zero I would think. The premise was that the greater the depth of fill the greater the load on the pipe. A circular pipe completely surrounded by compacted fill and proper bedding would have close to zero stress hence my suggestion of a PhD research topic.
The Standards also go on about induced live (vehicle) load effects - any pavement designer can easily prove that vehicle load effects diminish to effectively zero at a very low pipe cover (pavement depth).
If Australia is a democracy why, then, is voting compulsory?
"What has changed between the arrival of the First Fleet and today?"
"Wearing leg irons is now not required."
hinekadon (13-02-21)
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