2017年04月02日

Best soil nail system



Soil nailing is an economical technique for constructing retaining walls from the top down as well as stabilizing slopes. When applying the soil nailing process relatively small, closely spaced steel tendons are drilled and grouted into the soil. The soil nails significantly increase the apparent cohesion of the soil through their ability to carry tensile loads. A construction facing is also usually required, and is typically shotcrete reinforced by welded wire mesh. A shotcrete facing is typically applied, although more astatically pleasing options such as precast panels, cast-in-place concrete or revegetation are available for permanent structures. Typical applications of soil nailing are in the construction of new slopes in cuttings and remedial works for unstable slopes. Soil nailing can be used in any natural ground.
Soil nailing system is possible in a wide range of materials including: clays sandy soils, weathered rock, tallus slope deposits, heterogeneous and stratified soils. Soil nailing can be seen as unpractical under the following conditions: soft, plastic clays, organics/peat, loose, low density and/or saturated soils and fills (rubble, cinder, ash, etc.). Soil Nailing Drainage Systems are also a key consideration in design. Drainage systems are integrated into the nailed wall, minimizing liquid pressure and preventing erosion of the reinforced ground.

Soil nailing is used primarily for excavation support or slope stabilization. This process involves the installation of closely spaced soil nails drilled near horizontal and the application of a facing material such as reinforced shotcrete or structural mesh. The soil nails themselves tend to be small in diameter, typically 4″ to 6″, and consist of a center reinforcing bar surrounded by grout. Soil nail spacing usually ranges from 4′ to 6′ on center vertically and horizontally with the top row of soil nails generally being placed in the upper two feet of the excavation or slope.
From a design standpoint, soil nailing is a passive system attempting to place enough anchorage into the adjacent soil so it acts as a “reinforced block” to resist overturning. The load demand on each nail tends to be fairly low as they are intended to act as a group. In the case of excavation support, the facing is usually designed to take little load but more so tie the system together. In the case of slope stabilization, the facing may be designed to take more load and the nails may be post tensioned.
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