Experimental Study on the Influence of Drillhole Roughness on the Pullout Resistance of Model Soil Nails
Publication: International Journal of Geomechanics
Volume 16, Issue 2
Abstract
Pullout resistance of cement-grouted soil nails is a key factor affecting the safety conditions of retaining walls, slopes, and excavations. The mobilized frictional resistance at the interface between soil nails and surrounding soils depends on various parameters such as saturation ratio, water content, grouting under gravity or pressure, etc. The interface roughness condition between soil nail and soil is a critical factor but difficult to control in both laboratory and field owing to technical difficulties in creating a rough drillhole surface. The present study focuses on the pullout behavior of model soil nails with different interface roughness conditions in the laboratory to establish quantified correlations between frictional resistance and roughness angles of internal drillhole surface. Cross-sectional shapes of internal drillhole surfaces were created using four plastic rods with various shapes of external threads (four different values of roughness angles). Measured peak values of pullout resistance of soil nails with rough drillhole surface were compared with the soil nails with smooth drillhole surface. The present test results were verified with a previous analytical model, which considered the soil dilation to be an important factor influencing the pullout resistance of soil nails. Test results also indicate that the peak pullout resistance increases almost linearly with an increase in roughness angles. In addition, the pullout resistance values decrease approximately linearly with an increase in pullout displacement after peak pullout resistance is approached. The soil-nail diameter values of the soil nails with rough drillhole surfaces expanded substantially after being pulled out of the ground. This leads to a substantial increase in pullout resistance of soil nails.
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Acknowledgments
The authors acknowledge the financial support from the Seed Grant Scheme of the Technological and Higher Education Institute of Hong Kong (Program Code: 99424), STU Scientific Research Foundation for Talents (SRFT) (Project No. NTF12015), State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration (Project No. LED2013B01), and National Natural Science Foundation of China (NSFC) (Project Nos. 51378303 and 51378462). Kind help and support from undergraduate students at Shantou University, namely, Yu Meng-Meng, Li Wen-Xin, Huang Zhi-Li, and Huang Chen-Rui, is also gratefully acknowledged.
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Published In
International Journal of Geomechanics
Volume 16 • Issue 2 • April 2016
Copyright
© 2015 American Society of Civil Engineers.
History
Received: Apr 14, 2014
Accepted: Jan 14, 2015
Published online: Jun 25, 2015
Discussion open until: Nov 25, 2015
Published in print: Apr 1, 2016
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