Contents lists available at ScienceDirect Tunnelling and Underground Space Technology journal homepage: www.elsevier.com/locate/tust Effect of grout strength on the stress distribution (tensile) of fully-grouted rockbolts Ahmet Teymen a, ⁎ , Alaettin Kılıç b a Niğde Ömer Halisdemir University, Mining Engineering Department, 51240 Niğde, Turkey b İstanbul University, Mining Engineering Department, 34320 Istanbul, Turkey ARTICLE INFO Keywords: Rockbolt Strain gauge Stress Strength Deformation ABSTRACT The paper deals with and axial stress distribution (ASD) obtained from pull-out tests of strain gauged rockbolts in high strength rock media. For this purpose, an experimental research was conducted considering the only axial forces acting on fully grouted rockbolts (FGR). Strain gauges were used to observe the behavior of rockbolts and to determine the load transfer mechanism of the bolts to rock mass. In the test, five grout mixture having different properties was prepared and stress–strain mechanism of the bolt-grout interface was investigated for these conditions. ASD was demonstrated elastic load transfer behavior from the rockbolt to the outlying rock under the applied load (for each grout type) and stress concentration was rather a high level at 70 mm distance from rock surface. Axial stress curves drawing with the aid of strain readings were showed the regular dis- tribution with increasing of grout stiffness. The test results of strain gauged rockbolts show that the shear stress distribution (SSD) is uniform and, the style of the distributions along the rockbolt was similar under various loading levels for all grout types. Shear stress was rather a small amount at the pulling end of rockbolt but it reached the peak after a short distance away from the pulling end of rockbolt and subsequent to peak value decayed rapidly with the load increase. The results were showed that strength properties of grout played an important role in SSD and ASD along the rockbolt. The increase in grout strength and rigidity made the stress distributions regular along the rockbolt. 1. Introduction Bolting provides stability by increasing the anchorage capacity of rock mass at the confines of an underground excavation. Rockbolts can combine support effects (shotcrete, steel mesh-arches) with reinforce- ment effects (bolting). Their use is usually the unrivalled way of sup- plying stability to excavations in problematic rock formations, before final concrete lining. Rockbolts are widely used as the main support instrument to stabilize the decoupled rock blocks around tunnels, dams, mines, slopes and other engineering construction apropos of rock masses. Yet another duty of rockbolts is restraining the deformation therein the rock masses. It is important to understand how rockbolts behave in deformed rock masses to improve bolting design. This can be accomplished by studies (laboratory tests, numerical and analytical studies and field modeling) to be conducted by researchers. For a better understanding of rockbolt performance and interaction between rock- bolts and rock mass, several studies have been carried out using la- boratory and in-situ test results. A significant part of literature related rockbolts was focused on analytical methods and numerical analysis (Stille et al., 1989; Indraratna and Kaiser, 1990a, 1990b; Stillborg, 1994; Li and Stillborg, 1999; Cai et al., 2004; Carranza-Torres, 2009; Martin et al., 2011; Ma et al., 2013, 2016; Nie et al., 2018). In practice rockbolts are exposed to axial and shear loads. From this point of view, many researchers were attending to rockbolt performance under shear loading and different grout (Bjurstroem, 1974; Spang and Egger, 1990; Holmberg, 1991; Reed et al., 1993; Kılıç et al., 2003; Jalalifar and Aziz, 2010; Martín et al., 2013; Spearing et al., 2013). Another study issue was stress distributions along the bolt length. Some researchers have examined the deformation and stress distributions using either pull or shear conditions by laboratory tests and analytical methods (Farmer, 1975; Stjern, 1995; Hyett et al., 1996; Grasselli, 2005; Ivanović and Neilson, 2009; Chen, 2014). Taking account of softening, elastic and debonding rock zones, Li and Stillborg (1999) presented three analytical model of the shear stress distribution (SSD) along with a full contact rockbolts in tension. The purpose of their analytical model was to explain the mechanical cou- pling at the interface of bolt-grout for fully grouted rockbolts (FGR) or https://doi.org/10.1016/j.tust.2018.04.022 Received 28 July 2017; Received in revised form 10 October 2017; Accepted 10 April 2018 ⁎ Corresponding author. E-mail address: ateymen@ohu.edu.tr (A. Teymen). Tunnelling and Underground Space Technology 77 (2018) 280–287 0886-7798/ © 2018 Elsevier Ltd. All rights reserved. T