Laboratory investigation of pullout behavior of hollow and solid shaft helical nail in frictional soil
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RESEARCH PAPER
Laboratory investigation of pullout behavior of hollow and solid shaft helical nail in frictional soil Pankaj Sharma1 • Saurabh Rawat1
•
Ashok Kumar Gupta1
Received: 24 October 2019 / Accepted: 20 July 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Helical soil nails are passive elements installed in the soil which attains its bond strength through skin friction and bearing from helices. The present study examines the behavior of helical soil nail installed in cohesionless soil subjected to pullout force under varying parameters such as helical nail configuration (shaft diameter, helical diameter, helical pitch, number of helices), nail shaft types (roughness and stiffness), installation torque, and overburden pressure. The installation torque and corresponding nail pullout capacity can be established using a torque correlation factor (Kt). Kt value decreases with increasing embedded nail area and is inversely proportional to the nail shaft diameter. From pullout tests result, it is found that pitch in the range of 24.5–35.5 mm shows better pullout capacity. Also, results show that additional helices will only contribute to pullout capacity if located outside the region of soil mobilized in the failure mechanism of lower helix. Moreover, higher axial strains are found for hollow shaft nail, which alters with the increase in number of helices. Test results also indicate that various hollow shaft helical nails have nearly equal interaction friction angle to solid shaft helical soil nails with lesser shaft diameter. Therefore, it is concluded that solid shaft helical nails can be replaced by hollow nails without compromising on pullout capacity adding to reduction in construction cost. Tests results show linear correlation between maximum pullout shear stress and overburden pressure following a Mohr–Coulomb failure for different helical nail types. Keywords Helical soil nail Hollow and solid shaft Interaction factor Pullout capacity Torque correlation factor
1 Introduction Conventional soil nailing technique of drilling boreholes and placing a passive element along with cement grout has been widely used for stabilizing excavations, tunnels, slopes, and highway embankments [4]. However, during installation of conventional soil nails, drilling and grouting operation causes disturbance to the in situ soil properties. During bore hole drilling, soil settles down and causes local slope failure. Similarly, due to grouting pressure, loose soil & Pankaj Sharma [email protected] & Saurabh Rawat [email protected] Ashok Kumar Gupta [email protected] 1
Department of Civil Engineering, Jaypee University of Information Technology, Solan, HP 173234, India
undergoes fracturing which hampers the soil–nail and soil– soil interactive bonding. In order to overcome the difficulties associated with conventional soil nailing technique, researchers have attempted to develop passive elements which can mobilize better interac
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