Note:If the intermediate pile (pile 2, D) is shallower than the end pile (pile
3, d), i.e. Dd and b 1 ' 2 d (12.50 m) the mutual interference correction is
negligible. The corrected pressures behind (E) of the pile 3,
PE/H36.00 1.67 0.07334.26≈34% and PD/H26%.
The actual pressure distributions are summarized in the following table:
Pressures Behind pile 1 Middle pile 2 Middle pile 2 Ahead of pile 3
Ahead Behind
P/H C71% E65% C56% E34%
D77% D64% D64% D26%
Bligh’s theory suggests linear pressure distribution with a safe exit gradi-
ent (see equation (9.1)),
Ge(Bligh)6/(50.502(7 7 7.5))1 in 15.6.
The actual exit gradient (after Khosla et al.– see equation (9.8))1 in
7.75.
9.2 Intakes
9.2.1 Introduction
The intake structure (or head regulator) is a hydraulic device constructed
at the head of an irrigation or power canal, or a tunnel conduit through
which the flow is diverted from the original source such as a reservoir or a
river. The main purposes of the intake structure are (a) to admit and regu-
late water from the source, and possibly to meter the flow rate, (b) to mini-
mize the silting of the canal, i.e. to control the sediment entry into the
canal at its intake, and (c) to prevent the clogging of the entrance with
floating debris.
In high-head structures the intake can be either an integral part of a
dam or separate; for example, in the form of a tower with entry ports at
various levels which may aid flow regulation when there is a wide range of
fluctuations of reservoir water level. Such a provision of multilevel entry
also permits the withdrawal of water of a desired quality.
The layout of a typical intake structure on a river carrying a heavy
bedload is shown in Fig. 9.16. The following are its major appurtenances:
392 DIVERSION WORKS
