Stepwise repeated destabilization and stabilization of highly collapsible soil mass by ‘soil nailing technique’ used for construction of railway/road underpass

摘要

The excavations of side vertical walls for building and underpasses must be shored so that the excavations adjacent to the neighboring properties do not cave in during the constructions. A Soil Nailing system has been used for stabilization of excavations and natural slopes for the last few decades in India and Abroad. Soil Nailing Technique used steel anchor rods inserted directly into the soil mass as a driven nails and when Nails are placed in pre-drilled holes to form grouted nails. In both the cases, it restrained load and the side deformations. In the present study, an innovative technique of ‘Soil Nailing’ has been developed for stepwise vertical de-stabilization and stabilization of compacted collapsible sandy soil for the construction of railway underpasses in live railway loading conditions. This technique is successfully implemented first time in the world for controlled destabilization of vertical cut slope and again stabilization for creating a space for pushing of box for railway underpasses for the length of 22 m and 50 m at two sites, namely Yamuna Bazzar and Apsara border, respectively, in Delhi, India. This Soil Nailing Technique of controlled destabilization of soil and again stabilization in steps has proved a superficial method of stabilization with the other methods for such kind of dynamic loading situations.

主权项

1. A process for making an underpass through a railway track or road without service interruption by stepwise destabilization and stabilization of a collapsible soil mass by a soil nailing technique, the process comprising the steps of:
(i) marking a position of a box on a vertical face of a first retaining wall or an embankment; (ii) dismantling the retaining wall above the marked position of the box and providing temporary support by shuttering plates having holes for pre-decided positions of nails to be driven in the vertical face; (iii) nailing the soil mass by using grouted nails and driven nails above the marked position of the box; (iv) again dismantling the first retaining wall, placing the shuttering plates with pre-drilled positions of nails and inserting only the driven nails from the top to the bottom of a box pushing area; (v) leaving a complete nail system for a period in the range of 8 to 12 hrs to mobilize the friction of the nails; (vi) bringing the box close to the soil-nailed, wall face; (vii) loosening one top row of shuttering plates, and excavating the soil to a 30 to 40 cm depth; (viii) repeating step (vii) until the entire rows of the nails are covered for a 30 to 40 cm depth followed by pushing the box into the excavated area of 30 to 40 cm depth; (ix) pushing the nails into the soil mass and again tightening of the shuttering plates; (x) repeating steps (vii) to (ix) until 50% of the box pushing length; (xi) cutting the nails in the range of 25 to 35 cm to create a space for box pushing wherein first/pointed ends of the nails will touch a second retaining wall, followed by placing vertical nails in order to increase the stability of the cut slope; and (xii) again repeating steps (vii) to (ix) until complete insertion of the box for making an underpass.