GRAVITY GOODS ROPEWAY
7.4 Construction of Gabion Wall
Gabion walls are usually provided for slope
protection at upper and bottom stations. The
standard slope of the gabions should be in the
ratio of at least 1:2 in horizontal. The gabion
should be filled from strong and solid rock laid
very closely and packed without gaps to maximise
the weight. The gabions should be firmly anchored
into the ground by founding the gabions below the
expected scour depth and should be tied together
to give a monolithic finish.
7.5 Mixing, Placing and Curing Concrete
7.5.1 Placing steel reinforcement
Following points should be kept in mind while
placing the reinforcement:
Steel will bond well with concrete only if it
is clean and free of grease and scaling rust.
The reinforcement should be cleaned using
wire brush to remove any scaling rust.
Ensure the minimum lap length, as
recommend by the IS code. The minimum
lap length ensures that the steel bars join
and perform as continuous bars in load
transmission.
The steel reinforcement bars should be
tied as shown in the working drawings. The
reinforcements should be tied and placed
by a qualified or experienced person. The
site in charge should inspect the quality
of all the steel fixings before the concrete
is placed.
The vertical reinforcement should
be provided with L shaped toes on
construction joints to ensure the stability
of the steel cage during the pouring of
the concrete and also to ensure proper
anchorage of the steel in the concrete.
Specifications
Reinforcement steel should comply with the
following IS codes:
IS 1786-1986
High strength deformed
steel bars for concrete
reinforcement
IS 456-1978
Plain and reinforced
concrete
Steel grade, Fe 415, High yield strength
Deformed Bars.
7.5.2 Concrete constituents
Concrete is composed of four constituents: cement,
sand, aggregate and water. The cement creates
adhesion between the concrete components as
well as fills the voids between them. The aggregate
forms the main body of the concrete, whilst water
acts as a catalyst and allows the mix to be worked.
The aggregate and cement together provides the
concrete strength.
Cement
Cement must meet requirement of the Nepal
standard (NS). The commonly used cement is
Portland cement of grade 55. It should neither
be exposed to moisture nor be stored for a lengthy
period to keep the strength of the cement intact.
Aggregates
The aggregate made of parent rock quality is
suitable for concrete but it should be approved
by the site engineer. The aggregates from rock
like mica, sandstone, marl, conglomerates,
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