Assessing the Relative Quality of Rock Bolt Grouting in Weak Rock Mass Based on In Situ and Numerical Pull-Out Tests

• Published in: Rock mechanics and rock engineering Vol. 58; no. 9; pp. 10497 - 10522
• Main Authors: Thirukumaran, Sivanathan, Oliveira, David, Ariza, Leo
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01.09.2025; Springer Nature B.V
• Subjects: Acceptance criteria; Anchor bolts; Bonding strength; Boring machines; Civil Engineering; Earth and Environmental Science; Earth Sciences; Fixtures; Geophysics/Geodesy; Grout; Grouting; Interfaces; Interfacial properties; Investigations; Laboratories; Lifting; Load transfer; Original Paper; Pull out tests; Rock; Rock bolts; Rock masses; Rocks; Sensitivity analysis; Shear; Shear stiffness; Shear strength; Strain gauges; Tensile stress; Weak rock; Grouting; In situ pull-out test; Numerical modelling; In-tunnel anchorage; Rock bolt
• ISSN: 0723-2632; 1434-453X
• DOI: 10.1007/s00603-025-04647-w

Grouted rock bolts anchor various in-tunnel fixtures, such as jet fans, TBM launch frames, heavy-lifting pullies or chain blocks, and abutment and corbel supports. In such applications, rock bolts are mainly subject to direct axial tensile loads rather than combined axial shear as and when working as reinforcement elements. The axial tensile load transfer between bolt and rock depends on the strength and stiffness of the grout–rock or grout–bolt interface parameters, which strongly depend on grouting quality along the bonded length. Assessing grouting quality in situ conditions is challenging, and a limited number of studies have focused on this. This paper proposes a potential method to evaluate the relative quality of grouting. The proposal is based on the limited in situ pull-out tests on short and long-grouted rock bolts compared with three-dimensional numerical simulations using the Itasca 3DEC program. Therefore, further investigation and studies are required before it is taken into practical application. However, the calibrated rock–bolt interface shear stiffness correlated well with grouting quality in this instance. It was, therefore, used as an input to assess the relative quality of grouting. A threshold value of the relative quality of grouting may be proposed as an acceptance criterion for in-situ pull-out tests. Finally, the present study investigated the sensitivity of the rock–bolt interface shear stiffness and bond strength to the load transfer between the bolt and the rock. This investigation was done through an actual application where grouted rock bolts were used to anchor lifting points for a large-scale energy project. Highlights Detailed review of the load transfer mechanism for rock bolts in situ pull-out conditions. Development of an approach to assess the grouting quality for rock bolt in situ pull-out tests. Proposal of additional acceptance criteria for analysing rock bolt in situ pull-out test results. Sample sensitivity analysis of the grouted rock–bolt interface properties for an actual application.