Introduction:-
Keystone is a mechanical stabilized earth wall MSEW which used to retain soil from one side, it's less cost than concrete walls.
Material
1-Keystone Blocks
2-Fiberglass Pins
3-Geo-grids
4- Back-filling Material
5-Concrete pad
Different type of Geogrid:
- TT045 can carry load till 45KN/m.
- TT060 can carry load till. 60KN/m.
- TT090 can carry load till 90KN/m.
- TT120 can carry load till 120KN/m.
- TT160 can carry load till. 160KN/m.
Method Statement
1) Place HDPE Geogrids on top of the compacted soil. HDPE Geogrids are installed from the front on top of the fiber glass pins (which penetrates the grid) and from to back, Geogrids are fixed horizontally using a steel bars.
2) Lay down the precast concrete units on top of a PC foundation at a level that is a Minimum of 5% from the wall height and reach 10% (buried height) to prevent any lateral movement .
3) Put the layers of Geotextile.
4) Backfilling using fine gravel behind the wall for a distance of 50 cm, max size of 20mm.
5) The sand for the rest of the reinforced backfilling area.
6) Layers are compacted to 95 Standard Proctor. Compacted layers are 30 cm in thickness or less.
7) Repeat the above steps (1-6).
Notes:
•Gravel size should not exceed 20 mm behind the wall, and depth behind the wall is not less than 30 cm and layers should be compacted 20-30 cm thick.
• Sand used for backfilling should be clean and free of any foreign materials & the percentage of fines should not exceed 10% and the size of gravel should not exceed 20mm.
• The concrete pad under the blocks should be smooth & leveled.
• Keystone blocks should not be thrown from top of the loaded Trucks. Blocks should be moved by pallets. Pallets of blocks should be handled using a fork lift and stored near the working area avoid double handling of the blocks.
• After installation of a row of blocks, block surfaces should be carefully cleaned using plastic brushes, before installing a new row of blocks.
• During block installation, blocks have to be pushed from the back to the front. • The wall has to be aligned properly using normal engineering practices.
• Fiberglass pins have to be in place inside the block before any backfilling activity to prevent blockage of the pin holes.
• Geogrids should be very well stretched to the back & should be laid horizontally & fixed at the end of its length by a steel bar or Wooden Edge then remove bars or edges from soil after finished backfilling.
• No equipment should be directly moving on top of the gerogrids. Equipment should be moving on a min of 10 cm of sand layer on top.
• Compaction should be implemented using a plate compactor for 1 m behind the wall and be used for all the section or use the largest compactor possible after 1 m horizontal distance behind the wall to avoid any block movement.
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