23. In block work seawalls what is the purpose of slip joints?
Joints which are formed from the cope level to the toe level of seawalls through
a complete vertical plane are known as slip joints. Such joints are designed so
as to handle the differential settlements between the seawalls adjacent panels.
In the slip joints the aggregates inside the half-rounds channels enables some
vertical movements. These vertical movements are induced by differential
settlements. This enables in the interlocking of the adjacent panels of the
seawalls to link the panels in one unit against the earth pressure ( lateral )
which is exerted on the seawalls.
24. For a washout valve why are two gate valves required in normal practice?
The washout valves are primarily used for normal maintenance works such as that
of water main. This can be like to allow water to flow out during the cleaning
of the water main. The junctions at which a pipe branches out to a washout
point usually a gate valve is installed so that the two pipelines are
separated. The gate valve installed above usually remains open during normal
operation. Another gate valve is installed further downstream and this remains
closed during normal operation of the washout valve. In case this valve is not
installed then the pipe section of the branched out pipe would remain dry
during normal operation and high chances of damage and leakage can take place.
When the downstream valve is installed the branched out water main contains
water under normal operation. With two gate valves installed a leakage can be
25. What are the different approaches in designing the floors of the service
In general there are two main approaches of designing the reservoir floors to
prevent leakage of water due to seasonal and shrinkage movements:
> In this approach the movement joints of the reservoir floor panels are
such that the free expansion and contraction of the panels takes place. Every
panel is isolated from the other panels and two panels have a sliding layer
between them to help in sliding.
> The second method does not provide any room for free movement. With
seasonal and shrinkage movements, some cracks are designed to voluntarily occur
on the floors of the service reservoirs. These tiny cracks are spread
throughout the floor and are simply too minute to cause any leakage or
corrosion of the floors. But the difference also in this method is that the
amount of reinforcement used is much more than the first approach.