Laboratory study of a new screw nail and its interaction in sand

Experimental results of a series of laboratory pullout tests on a new screw soil nail are presented. A review of the literature for the screw soil nails as well as a comparison of its performance with other conventional types of soil nails is discussed. The present investigation also examines the fundamental interface mechanism and attempts to define the associated rupture zones in cohesionless material with the aid of thin vertical bands of coloured sand cast in a large distinctly fabricated pullout box. The philosophy behind the design and development of the new screw nail is briefly described first followed by presentation of the laboratory testing procedure and its instrumentation. The results of the testings indicate that the slip mechanism, which controls the pullout behaviour, is rather different to the conventional soil nails and the resultant pullout capacity is higher when compared to this type soil nails. This effect is attributed to the geometry of the screw nail and the installation processes that result in the development of different soil stresses around the soil nail. In addition, the experimental pullout results demonstrate, contrary to the conventional soil nail, that the screw nail pullout capacity is dependent on the overburden pressure and that the failure planes extends out a certain radial distance from the soil-nail interface. From the test results, it is shown that the failure of the screw nail satisfies the Mohr-Coulomb failure condition, which is similar behaviour seen in the conventional soil nail tests.