ACCESS TO DRAINS
Access must be provided to drainage installations to allow for periodical
maintenance, inspection and testing. Manholes, inspection chambers
and shallow access chambers allow a system to be rodded in both
directions whereas rodding eyes allow for only a downstream operation.
Basic principles state that every length of drain should be accessible
for maintenance and rodding without the need to enter buildings.
Access should be provided at the following points:
Table 3 indicates the maximum recommended spacing between various
types of access points, based on standard rodding techniques and
the necessity to clear blockages.
Where two drains join together via a branch junction and no provision
of access is made on that junction then access should be provided
no more than 12m from this point.
TABLE 3
MAXIMUM SPACING OF ACCESS POINTS
| Distance to |
From acess
fitting |
From junction or branch |
From inspection chamber |
From Manhole |
| |
1 |
2 |
|
|
|
| Start of External drain |
m |
m |
m |
m |
m |
| Rodding eye |
12 |
12 |
- |
22 |
45 |
| Acess fitting(1)min. 150mm x 100mm or
150mm dia |
22 |
22 |
22 |
45 |
45 |
| Acess fitting(2)min. 225mm x 100mm |
- |
- |
12 |
22 |
22 |
| Inspection Chamber |
- |
- |
22 |
45 |
45 |
| Manhole |
22 |
45 |
22 |
45 |
45 |
| Start of External drain |
22 |
45 |
45 |
45 |
90 |
|
The depth of any inspection chamber or manhole is determined by
its minimum internal dimensions, since
there must be adequate access or entry for rodding and maintenance.
Details listed on Table 4.
TABLE 4
MINIMUM DIMENSIONS FOR ACCESS FITTINGS & CHAMBERS
Type |
Depth
to invert (m) |
Internal
Sizes |
Cover
Sizes |
Lenght
x width (mm x mm) |
Circular
(mm) |
Length
x Width (mm x mm) |
Circular
(mm) |
| Rodding eye |
- |
As drain but min
100 |
- |
- |
- |
| Access fitting |
|
|
|
|
|
small |
0.6 or less |
150 x 100 |
150 |
150 x 100 |
0.6 or less |
Large |
|
225 x 100 |
- |
225 x 100 |
- |
| Inspection chamber |
0.6 or less |
- |
190º |
- |
190º |
| |
0.1 or less |
450 x 450 |
450 |
450 x 450 |
450º |
| Manhole |
0.1 or less |
1200 x 750 |
1050 |
600 x 600 |
600 |
| |
over 1.5 |
1200 x 750 |
1200 |
600 x 600 |
600 |
| |
Manholes
over 2.7m deep should have a chamber 2m deep accessed
by, a shaft 900 x 840mm or 900mm in diameter. |
|
* drains up to 150mm diameter
† for clayware or plastic chambers the clear width may be
reduced to 430mm to provide support for cover and frame
|
