STONE Masonry Wall

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.

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.

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)

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