Banded Stone Masonry Wall in Hilly Terrain as a slope protection measures, In Himalaya, India
Cut slope protection (slope stability) is a most important part of a newly constructed or widening of a existing highway in hilly area. But the designer or executors is not much concentrate on this topic due to direct high execution cost, even they are not follow the basic rules during cut slope excavation and they are executed the work as a Lehman in most of causes. In hilly area if you are not paying for protection measures then you must be ready to pay double in cut slope maintenance work in future. it is advised to execution contractor to follow basic rule of cut slope excavation as top to bottom method of excavation with proper safety.
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| Excavation of hill slope for widening of Existing Highway in Indian Himalaya |
Here I am taking about only the Banded dry stone masonry wall which is very helpful for protection of an excavated slope in hilly terrain due to easy availability of major raw material as a stone. It is most cheaper than other works. The water is easily peculate between the stone so no water pressure developed behind the wall. It is a cost effective as well as performed better in earthquake condition. It is repaired very quickly as compared to reinforced wall and other option.
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| Sketch for bonded stone masonry wall as a slope protection for 2-lane highway |
we can use a Cement Banded dry stone masonry wall to protect hill side slope, median side as well as valley side slope due to easily availability of raw materials.
Design criteria of banded stone masonry wall:
There are mainly four types of load and pressure should be considered to
built a
banded stone masonry wall which are as
follow-
• Self weight of banded stone masonry wall (SBC)
• Earth pressure acting on wall (Cut Slope soil/rock pressure)
• Water pressure (water pressure if any)
• Seismic load (seismic zone of the area where wall is to be built)
• Earth pressure acting on wall (Cut Slope soil/rock pressure)
• Water pressure (water pressure if any)
• Seismic load (seismic zone of the area where wall is to be built)
After
assessment of the above given point the design should be as follow based
on codal provision-
• Width of wall
foundation should be B= 0.5*H + 0.3
(where H=Height of wall) to get
desired SBC, top width should be 0.6 m up to 4 m
height and 0.5 m more than 4 m
height of wall.
• Foundation should be
inclined inward 1:3 to 1:6 to safe
against overturning
• keep the front better
1:2 to 1:6, keep back front straight up to 4 m, back front
reduced more than 4 m to 8 m height.
• Coping placed 0.50 to 0.75 mm. sloping towards valley side.
• There is no need to provide horizontal PVC pipe for drainage as there
is sufficient space between dry stone to flow the water.
Construction Methodology for site:
• First we should
ensure the desired excavation of cut slope is satisfactory or not
than SBC must be ensure before laying PCC by
Geo technical expert.
• Check the Line and level as per drawing for PCC. PCC done
100mm to 300mm thick
as per
strata.
• Wall foundation must be slopping inward 1:3 to 1:6 to escape
overturning.
• Construction materials as Cement mortar should be used 1:4
and size of stone should not be 20*15*10 cm approximately and stone should be
clean and clay free.
• Depth of foundation must be 1000 mm when rest on soil and
500 mm if rest on rock strata, depth generally should be 0.1*H + 0.3 .
• The wall should be constructed with 8 meter construction
joint up to the coping as per the
given figure.
• Compacted back fill
should be done simultaneously as the height of wall increase, back fill materials should be granular or stone chips (well drained). The back fill layer
should be place in such a manner that the back fill load on wall should be Zero.
Top surface of back fill to be sealed by impervious 300 mm layer to prevent
ingress of rain water.
•
Drainage PVC pipe within the wall is not required as space between dry stone is
sufficient to release the water pressure behind the wall.
• Coping should be done with 1:4 mortar 50-75 mm sloping
towards valley side.
• Road side drainage
should be provided as per discharge quantity of water during monsoon.
• Cement sand mortar ratio should be 1:4
The following points should be remember:
• The foundation area should be compacted properly before
laying the PCC.
• If water surcharge is more than proper weep holes should be
provided to release ground water.
• Back filling should be placed properly.
• Mortar quality should be checked at regular interval and
curing must be done as per standard.
• Man power should be well experienced in stone masonry works.
1.IRC:SP: 48,1998
2.IRC:40-2002
3. IRC:78-2014
4.IS:14458, Part3
