Soil nails may be installed at various inclinations to the horizontal for different practical purposes. Different inclinations result in different effects on behaviour of nailed slopes. The orientation of soil nails plays an important role in the development of axial forces. When a soil nail is placed in the direction of tensile strain of soil, tensile forces will be developed. Consequently, there is an increase in shear resistance of the reinforced soil. When the soil nail is oriented in the direction of compressive strain of the soil, compressive forces will be developed. This leads to a decrease in shear resistance of the reinforced soil....[ Read more ]

Soil nails may be installed at various inclinations to the horizontal for different practical purposes. Different inclinations result in different effects on behaviour of nailed slopes. The orientation of soil nails plays an important role in the development of axial forces. When a soil nail is placed in the direction of tensile strain of soil, tensile forces will be developed. Consequently, there is an increase in shear resistance of the reinforced soil. When the soil nail is oriented in the direction of compressive strain of the soil, compressive forces will be developed. This leads to a decrease in shear resistance of the reinforced soil.

In order to investigate the effects of nail inclinations on the stability of a densely compacted completely decomposed granite (CDG) slope, four centrifuge tests were conducted with soil nails inclined at 10°, 20°, 45° and 55° to the horizontal together with nail head size of 600 mm x 600 mm (in prototype). Each CDG filled slope was compacted to a relatively density of 95% and every slope was inclined at 65° to the horizontal. For each test, soil nails were installed in nine rows and in five columns with horizontal spacing of 2.0 m (in prototype) and vertical spacing of 1.5 m (in prototype). The thickness of each nail head was 0.2 m (in prototype). At 30g, each model slope was equivalent to 15 m in height and it was destabilized by both transient and quasi-steady state seepage conditions in flight. Particle image velocity method was used to analyze deformation of soil developed in the centrifuge modelling. In addition, three dimensional coupled finite element (FE) analyses of slopes with nails inclined at 10°, 20°, 45° and 55° were carried out to assist in the interpretation of results from the centrifuge model tests.

Centrifuge test results reveal that cracks were observed at the crest in slopes with nails inclined at 45° and 55°. However, no crack was observed at the crest in slopes with nails inclined at 10° and 20°. It is evident that an increase in the nail inclination could not prevent the formation of crack on the crest. Both centrifuge test results and FE analyses show that no continuous slip plane and no yielding of any nail were observed in each nailed slope at the end of the quasi-steady state. Measured settlements increased with angles of nail inclination since smaller tensile forces were mobilized to restrain slope movements in the slopes. FE analyses reveal that horizontal displacements increased with an increase in angles of nail inclination. Both centrifuge test results and FE analyses show that greater tensile forces were mobilized in slopes with a small inclination angle of nails. On the other hand, greater compressive forces were mobilized in slopes with a large inclination angle of nails. Greater measured and computed contact pressures were observed in slopes with small inclination of nails. It is evident that the loads were substantially carried by the nail heads. Small loads were carried by nail heads in slopes with a large inclination angle of nails.