Environmental Engineering Reference
In-Depth Information
concrete or steel conduit
slope not steeper than 1h:8v
concrete for full length of
earthfill zones (preferably
for full length of conduit)
(a)
dam foundation
steel conduit
slope not steeper than 1h:8v
(b)
concrete for full length of
conduit
dam foundation
Figure 13.18.
Concrete support for (a) concrete or steel conduit strong enough to withstand earth pressure
from the dam (b) steel conduit requiring concrete surround to withstand earth pressure from
the dam.
slope not steeper
than 1h:8v
slope flatter than 1h:1v
to prevent arching
concrete culvert
1
width sufficient
to allow proper
compaction
1
Figure 13.19.
Trench and culvert details for cast-in-situ or pre-cast concrete culvert.
enough to allow for compaction and the batter slopes should be no steeper than
1H:1V so arching does not develop and lead to low stresses in the trench, conducive
to hydraulic fracture and cracking.
(e) Care should be taken to prevent desiccation cracking in the base and sides of any
trench into which a conduit is placed and any cracked soil should be removed imme-
diately prior to backfilling.
(f ) Where the only earthfill available is dispersive (Pinhole D1 or D2, Emerson Class 1 or
2), it would be wise, even with all of the above factors, to add 2% or 3% lime (by
weight) to the backfill soil, carefully mixed, to render it non dispersive.
(g) Care should be taken to provide joint details in the conduit and between conduits and
other structures, such as intake works, which will accommodate the likely longitudi-
nal and vertical deformations and prevent erosion of soil into the conduit or flow of
water out of the conduit.
(h) Consideration should be given to the potential for corrosion of conduits and whether
it is wise to rely on steel or corrugated steel pipes for long term operation.
