Limit analysis of ground anchor forces

An anchored sheet wall is commonly used in retaining deep excavations. Anchor force is one of the critical design parameters in practice. Based on the kinematical admissible failure mechanism, a limit analysis approach to determine the anchor force is presented. The explicit formula for the anchor force is given, which makes it easy to calculate using a simple calculation program such as MS Office Excel. Anchor force is mainly influenced by seven parameters: the internal friction angle; cohesion of the soil; wall friction angle; surcharge on the ground surface; dip angle of the anchor; penetration depth of the wall; and depth from the anchor force action point on the wall to the ground surface. The relevant quantitative calculation can be performed by the proposed method. In addition, the design anchor force under a specified design safety factor and the anchor forces of multiple rows of anchors are also illustrated in this paper. To verify that the method is reasonable, the predicted and measured anchor forces are compared in two classical soil-nailed wall experiments. The result shows that the presented method is applicable. Disciplines Engineering | Science and Technology Studies Publication Details Xiao, S. & Guo, W. (2017). Limit analysis of ground anchor forces. Proceedings of the Institution of Civil Engineers: Geotechnical Engineering, 170 (2), 175-185. This journal article is available at Research Online: http://ro.uow.edu.au/eispapers1/57 Limit analysis of ground anchor forces Shiguo Xiao PhD Professor, State-Province Joint Engineering Laboratory of Spatial Information Technology of High-Speed Rail Safety, Chengdu, P. R. China; Key Laboratory of High-speed Railway Engineering, Ministry of Education, Southwest Jiaotong University, Chengdu, P. R. China; School of Civil, Mining and Environmental Engineering, University of Wollongong, NSW, Australia (corresponding author: [email protected]) Wei Dong Guo PhD Associate Professor, School of Civil, Mining and Environmental Engineering, University of Wollongong, NSW, Australia An anchored sheet wall is commonly used in retaining deep excavations. Anchor force is one of the critical design parameters in practice. Based on the kinematical admissible failure mechanism, a limit analysis approach to determine the anchor force is presented. The explicit formula for the anchor force is given, which makes it easy to calculate using a simple calculation program such as MS Office Excel. Anchor force is mainly influenced by seven parameters: the internal friction angle; cohesion of the soil; wall friction angle; surcharge on the ground surface; dip angle of the anchor; penetration depth of the wall; and depth from the anchor force action point on the wall to the ground surface. The relevant quantitative calculation can be performed by the proposed method. In addition, the design anchor force under a specified design safety factor and the anchor forces of multiple rows of anchors are also illustrated in this paper. To verify that the method is reasonable, the predicted and measured anchor forces are compared in two classical soil-nailed wall experiments. The result shows that the presented method is applicable. Notation CP calculation coefficient of work rate of lateral resistance on penetration part of wall c cohesion of soil cr mobilised cohesion of soil considering shear strength reduction coefficient Ec internal energy dissipation rate F anchor force; subscripts 1, 2, 3 represent the first, second and third row of anchors, respectively Fp passive resistance acting from the left side (see Figure 1) of the penetration part of sheet wall Fs factor of safety or shear strength reduction coefficient fi derivation coefficient of gravity work rate, i= 1, 2, 3 h total height of anchored sheet wall i index of number kp coefficient of passive earth pressure n total number of anchor rows q surcharge on ground surface r radius of any point on a log-spiral slip line, where subscripts 0, h stand for the starting and ending points, respectively SH horizontal spacing between adjacent soil nails SV vertical spacing between adjacent soil nails s distance from intersection between the slip line and ground surface to the wall W work rates of external forces, where subscripts F, G, P, q stand for anchor force, gravity, passive earth pressure and surcharge on ground surface, respectively z depth of anchor force action point on the wall (below ground surface); subscript i stands for the ith row of anchors zp penetration depth of anchored sheet wall zs sum of depth z of each row of anchors β dip angle of anchor; subscript i stands for the ith row of anchor γ unit weight of soil δ wall friction angle θ rotation angle of any point on a log-spiral slip line, and subscripts 0, h denote the starting and ending points, respectively ξi ratio of anchor force of the ith row over the row nearest to the ground surface φ angle of internal friction of soil φr mobilised internal friction angle of soil considering shear strength reduction coefficient ω angle acceleration of kinematical soil body