Influence of Nail Properties on the Performance of Soil Nail System
摘要
Soil nailing application has become one of the popular methods of deep excavation and ground improvement techniques used for stabilization of vertical or nearly vertical cuts. Soil nails are installed in ‘top-down’ construction sequence, which is suitable for many ground conditions and is cost effective. The nails are installed at each excavation stage followed by initial face shotcreting. The Soil Nail Reference Manual [FHWA (2003)] gives charts to calculate the normalized length of nail and normalized tensile force (theoretical) based on bond resistance, diameter of drill hole, height of cut, unit density of ground and spacing parameters. But, the methods of considering nail-hole diameter, nail tendon diameter are not well defined. In addition, the manual specifies the nail installation at an angle of 10–20° from horizontal. The reason behind this is also not mentioned. In this paper, efforts are made to study the effect of various nail properties (Nail length, Nail inclination, Vertical spacing of the nails and Stiffness and rigidity characteristics of nail) on the performance of the soil nail system. Using PLAXIS 2D, soil model with plate elements idealizing nails was analyzed. The nails were considered to have uniform length. It was inferred that the length of nail has less effect on the overall performance. However, from displacements consideration, it is better to provide a length more than the assumed pullout length. Inclination of the nail shows less effect on the performance. However, for easy flow of grout and easy slide of nail, the soil nails can be installed at an angle of 15° to horizontal as recommended by FHWA (2003). Lesser vertical spacing is preferred to achieve good bond strength.