Attachment 4b - Engineering Report Part 2 · MCU18/0015

Michael Colnan

Subject:                            FW: Sewer Construction in Steep Sands
Attachments:                        20180515165709393.pdf




From: Adam Shayler [mailto:[email protected]]
Sent: Tuesday, 15 May 2018 4:48 PM
To: Pamela Davidson <[email protected]>; Justin Walsh <[email protected]>
Cc: James Brownsworth <[email protected]>
Subject: RE: Sewer Construction in Steep Sands

Hi Pamela/Justin,

I have reviewed the information provided and had a quick site inspection of the development area in question.

Installing Gravity sewers via horizontal Directional Drilling (HDD) is possible however highly dependent on the grade
and geology.

In this case as the overall grade of the sewer is quite steep (calculated around 8%), achieving this should not be a
problem.

However you need to note using HDD as an installation methodology there may be some variance in the grade along
the line however with a 8% overall grade there should be no issues with any backfalls.

I understand the geology is sand. This should not pose a problem unless it is very loose.

Depth of cover is another consideration that needs to be considered. Generally greater than 2m would be prefered
for a DN180mm pipe (ID Approx. 150mm). This will ensure the possibility of Frac‐out of drilling fluid is kept to a
minimum.

Based on the site layout provided a drill rig could set up on the building pad for units 1 & 2 and drill through to the
second manhole in a curve (Drill 1). Then the drill rig could reset up on the building pad for units 3 & 4 and drill the
remainer of the line (incorporating a big curve) through to adjacent the existing connection manhole at the
downstream end (Drill 2). (Refer marked up drawing).

Access for the drill rig, pipe (Drill 1) etc can be along Attunga Heights Road.

Pipe will need to be strung out at the exit end of each drill, however the impact is relatively minor. Pipe stringing for
Drill 2 may need to be assessed in more detail due to the length required.

The major impact will be the construction of the manholes shown, as well as connecting up the properties.

Obviously the above are only high level comments however utilising HDD appears feasible.

A more detailed site inspection, information on geology, grades etc will be required to make a final assessment.

A trust the above helps, however feel free to give me a call to discuss.

Kind regards,
Adam Shayler
Manager - Trenchless


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