Effects of steel fiber grout on the mechanical performance and failure characteristics of fully grouted bolts
Introduction
Fully grouted bolts, as an economical and effective rock reinforcement technique, have been widely used in coal mine roadway support [1], [2]. With the gradual deterioration of coal mining geological conditions in China [3], [4], bolt support is required to have higher bearing capacity to achieve the stability control of the roadway surrounding rock [5], [6]. Therefore, it is very necessary to improve the bearing performance of bolt support.
The fully grouted bolt support system is a typical Continuous Mechanically Coupled (CMC) system [7]. Generally, the bolt is boned to the rock by grout. The grout plays an important role in the bearing characteristics and load transfer of fully grouted bolts [8]. In recent years, many studies have been conducted to investigate the influence of the mechanical properties of grout on the bearing performance of fully grouted bolts. Yazici et al. [9] found that the bond strength of bolts increases with the increase of grout strength. Hyett et al. [10] illustrated that the bearing capacity of bolts most depends on the water-cement ratio of grout. The grout with low water-cement ratio has high uniaxial compressive strength and high Young’s modulus and can increase the peak bearing capacity of bolts by 50–75%. Kılıc et al. [11] studied the influence of cement grout strength on the pull-out bearing capacity of fully grouted bolts. The pull-out bearing capacity is positively related to the tensile strength, shear strength and Young’s modulus of the cement grout. Li et al. [12] experimentally studied the bond strength of grouting bolts with different water-cement ratios. The results showed that the bond strength of bolts is proportional to the uniaxial compressive strength of the cement grout. Teymen et al. [13] explored the influence of grout with different properties on the bearing characteristics of bolts. The bond strength of bolts increases with the increase of the shear strength of grout. According to their results, improving the mechanical properties of grout helps to increase the bearing capacity of bolts. However, considering the widespread use of resin grout at present, only by reducing the water-cement ratio of grout to improve the bearing capacity of bolts is limited [14].
In a fully grouted bolt, the bearing capacity of the bolt depends on the shear behavior of the anchoring interface [15]. Moosavi et al. [16] reported that grout shearing is the key factor determining the bearing capacity of bolts under tension, and the failure mode of the anchoring interface also illustrates this reality. The shear behavior of the anchoring interface is composed of chemical bonding, mechanical interlocking and friction [17]. Thus, any enhancement of the shear behavior of the anchoring interface will affect the bearing capacity of bolts. He and Liu et al. [18], [19] found that fiber grouting materials can improve the bearing performance of bolts. You et al. [20], [21] explored the influence of sand content in grout on the bearing capacity of bolts. The higher the sand content in the grout, the greater the bearing capacity of bolts. Cao et al. [22], [23] studied the influence of introducing metallic granules into grouting on the anchoring force of bolts. Teymen [24] discussed the influence of different mineral admixture in grouting materials on the bearing capacity of bolts. These studies provide useful guidance for effectively improving the shear behavior of the anchoring interface. Combined with the existing research status and based on the idea of steel fiber reinforced concrete, the steel fiber grout may effectively improve the bearing performance of fully grouted bolts. However, the understanding of the mechanism and effect of steel fiber grout on the bearing performance of bolts is limited. Therefore, it is necessary to study the effect of steel fiber grout on the mechanical behavior and failure characteristics of fully grouted bolts.
The focus of this paper is to investigate the effect of steel fiber grout on the bearing performance of fully grouted bolts. Generally, factors such as content, length-diameter ratio, shape of steel fiber are the key to determining the effect of steel fiber reinforcement. Many scholars have discussed the influence of content, length and shape of steel fiber on the reinforcement effect of bearing performance [25], [26], [27]. However, there are few studies on the effect of steel fiber diameter on the reinforcement effect of bearing performance. Thus, the steel fiber diameter is used as the research variable in this study. Three steel fibers with different diameters were selected to be added to the grout, and a series of laboratory pull-out tests were conducted. The mechanical behavior, acoustic emission (AE) response and failure characteristics of the anchored specimens during the whole bearing process were thoroughly analyzed. In addition, the mechanism of steel fiber reinforcement was also discussed. It is hoped that this study can provide a useful reference for the support design of fully grouted bolts.
Section snippets
Materials and properties
The experimental materials used in this study included bolts, anchoring agents, steel pipes and steel fibers, as shown in Fig. 1. A threaded bolt with a diameter of 20 mm and a length of 200 mm was used. The bolt rib height is 1.22 mm and the bolt rib spacing is 11.05 mm. The elastic modulus of the bolt is 200 GPa and the yield strength is not less than 500 MPa. A slow resin grout with a uniaxial compressive strength of 45 MPa and a shear strength of 35 MPa was used. The slow resin grout is
Experimental results and discussion
In this section, the experimental results of different anchored specimens are presented. The mechanical behavior, AE response and failure characteristics are comprehensively analyzed to reveal the effect of steel fiber grout on the bearing performance of fully grouted bolts.
Conclusions
This study aims to investigate the effect of the steel fiber grout on the bearing characteristics of fully grouted bolts. Three steel fibers with different diameters (0.5, 1.0 and 1.5 mm) were selected. Fiber specimens and fiber-free specimens were prepared and a series of pull-out tests were conducted. The main conclusions can be summarized as follows:
- (1)
The steel fiber grout can effectively improve the bearing capacity of the anchored specimens and significantly affect the post-peak bearing
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This research work was financially supported by the Joint Funds of the National Natural Science Foundation of China (U1710258), the Distinguished Youth Funds of National Natural Science Foundation of China (51925402). This research work was also funded by the Ten Thousand Talent Program of China for Leading Scientists in Science, Technology and Innovation and the Shanxi Science and Technology Major Project (20201102004). Yunlou Du would like to thank the Chinese Scholarship Council for
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