Sunday, 27 January 2013



Soil nailing is a procedure to reinforce and strengthen ground adjacent to an excavation by installing closely spaced steel bars called nails, as construction proceeds from top down. It is an effective and economical method of constructing retaining wall for excavation support, support of hill cuts, bridge abutments and highways. This process is effectively in cohesive soil, brocken rock, shale or fixed face conditions.
Soil nail technology was first used in France to build a permanent retaining wall cut       in soft rock. The project undertaken in 1961, was the first where steel nails were used to reinforce a retaining wall. The first soil nail wall to use modern soil nailing  techniques was build near Versailles in 1972. The technique included installing high density,  grouted soil nails into 160-ft-high wall and facing it with reinforced    concrete. Germany was the next country to investigate soil nailing. From 1975-1981 the University of Karlsruhe and the construction company Baur collaborated to establish a research program. This program conducted full scale testing of experimental walls with different configurations and developed analysis procedures for use in design. The United States first used soil nailing in 1976 for the support of a 13.7 m deep foundation excavation in dense silty sands. Soil nailing was implemented in the expansion of The Good Samaritan Hospital in Portland, Oregon. This retaining system was produced in approximately half the time at about 85% of the cost of conventional retaining systems
Soil nail walls can be used for a variety of soil types and conditions. The most favorable conditions for soil nailing are as follows: The soil should be able to stand unsupported one to two meters high for a minimum of two days when cut vertical or nearly vertical. Also all soil nails within a cross section should be located above the groundwater table. If the soil nails are not located above the groundwater table, the groundwater should not negatively affect the face of the excavation, the bond between the ground and the soil nail itself. Based upon these favorable conditions for soil nailing stiff to hard fine-grained soils which include stiff to hard clays, clayey silts, silty clays, sandy clays, and sandy silts are preferred soils. Sand and gravels which are

dense to very dense soils with some apparent cohesion also work well for soil nailing. Weathered rock is also acceptable as long as the rock is weathered evenly throughout(meaning no weakness planes). Finally, glacial soils work well for soil nailing]. A list of unfavorable or difficult soil conditions for soil nailing can include dry, poorly graded cohesion-less soils, soils with a high groundwater table, soils with cobbles and boulders, soft to very soft fine-grained soils, highly corrosive soils, weathered rock with unfavorable weakness planes, and loess. Other difficult conditions include prolonged exposure to freezing temperatures, a climate that has a repeated freeze-and-thaw cycle, and granular soils that are very looses.


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