Laboratory and field investigation on improved soil nails

ABSTRACT: The stabilisation of underground excavation faces is often achieved by soil nailing, that represents an efficient and economic method for their temporary support. The paper first focuses on a preliminary series of laboratory tests on injections in a sand box, in both dry and saturated conditions, that permit highlighting the characteristics of the grout columns. Then a traditional and an improved technique of soil nailing are described and compared, on the basis of the strength measured from pull out tests on nails grouted in a sandy gravel natural deposit and in a poor quality clay shale mass. In general, the improved technique offers higher strength and a better control on the volumes of injected grout. In addition, its performance is less dependent on the conditions of the site and on the quality of grout and injection, thus leading to a more reliable result of the treatment.