Grameen Sampark Final April 0... - pmgsy

10
Construction of Sub grade
This is the foundation layer over which the block
pavement is constructed. Like in conventional
pavements, the depth of water table should not be at a
level of 600 mm or higher, below the subgrade level. It
should be compacted in layers of 150 mm thickness.
The prepared subgrade should be graded and surface
dressed to a tolerance of ± 20 mm of the design levels,
and its surface evenness should have a tolerance of
within 15 mm under a 3 m straight edge [7].
Construction of Base and Sub-base Layers
Base course and Sub-base course are constructed in
accordance with the standard procedures contained in
relevant IRC specifications like IRC:37-2001; IRC:50-
1973; IRC:51-1993; IRC:63-1976; IRC:19-1997. When
cement treated bound base is proposed it may be
constructed using rolled dry lean concrete as IRC:SP-
49-1998. The quality control methods, as specified in
IRC: SP-11-1988 shall apply. Constructing these layers
to the proper level and grade is very much essential to
maintain the top surface level and surface regularity of
the block pavement surface.
Grameen Sampark
Edge Restraint Blocks and Kerbs
Concrete blocks subjected to traffic tend to move
sideways and forward due to braking and maneuvering
of vehicles. The tendency to move sideways has to be
counteracted at edges by provisions of special edge
blocks and kerbs. The edge blocks should be designed
and anchored to the base such that the rotation or
displacement of blocks is resisted [7]. These blocks are
to be made of high strength concrete for withstanding
the traffic wheel-loads without getting damaged. These
members should be manufactured or constructed in-situ
in order to have at least a 28-days characteristic
compressive strength of 30 MPa or flexural strength of
3.8 MPa. As far as possible, the edge blocks should have
vertical face towards the inside blocks. Where the space
does not easily permit the use of plate vibrators,
dhurmut or manual compactor using small size plate
rammer may be used. The road kerbs provided on edges
of roads also serve the purpose of edge blocks. In case
the kerbs are not provided, it has to be replaced by the
edge strips. In case of heavy traffic, 150 mm x 150 mm
(height x width) plain cement concrete (M-25) may also
be provided over dry lean concrete to give further
confinement to the blocks. In-between the edgerestraint
blocks, cement mortar (1: 6, cement: coarse
sand) may be used in place of sand for sealing of blocks.
Placing and Screeding of Bedding Sand
The thickness of sand bedding after compaction should
be in the range of 20-40 mm, whereas, in the loose form,
it should be 25 to 50 mm. It is preferable to restrict the
compacted thickness to about 20-25 mm to reduce the
risk of any localized over-compaction, which would
affect the final block surface level. Bedding sand should
not be used to fill-up local depressions on the surface of
base or sub-base layers. The depressions, if any, should
be repaired with same base or sub-base material in
advance before placing the sand. The sand of specified
gradation, should be uniformly in loose condition, and
should have uniform moisture content. Optimum
moisture content is when sand is neither too wet nor too
dry and has moisture of about 6 to 8 percent.