Influence of Water-Grout Ratio and Curing Time on Pull-Out Load of Rock Bolt Systems

Williams, Sally (2020) Influence of Water-Grout Ratio and Curing Time on Pull-Out Load of Rock Bolt Systems. [USQ Project]

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Rock bolts are widely used to strengthen and support rock walls and tunnels in mining and civil engineering. A typical rock bolt system comprises of a steel bolt installed in a drill hole encapsulated by cement or resin grout. Debonding and/or failure of the system usually occurs at the bolt-grout interface.

According to literature there appears to be limited research and experimental data on pull-out load testing of rock bolts, encapsulated by different water-grout ratios. Furthermore, there is also limited research and data on the influence of different curing times on different water-grout ratios, and its influence on the pull-out load of rock bolt systems. This project is intended to address the above-mentioned gaps in the literature by contributing data to the field of rock bolt systems.

Experimental samples were designed to simulate the real-world rock bolt system. This was achieved by using a steel pipe, steel rebar, and Stratabinder HS grout. Twelve variations formed from a matrix of water-grout ratios and curing time were investigated as part of this thesis, with three repeats per condition. Samples were cured under dry conditions to simulate real-world, worst case conditions. Pullout testing was conducted on each sample using a tensile testing machine at a rate of 1 mm/min. A smaller sample set of Uniaxial Compression Strength (UCS) tests were also conducted on grout cubes. The data collected as part of this thesis includes pull-out and compressive loads, displacement, time, and photographs of the test samples.

Results from the pull-out tests show a clear distinction between the different water-grout ratios. As expected, samples with a higher water content have a reduced ultimate load. An unexpected outcome is the low influence of curing time on pull-out loads. The difference in ultimate load at different curing times is however not significant. Another interesting finding is in the photographic documentation of the test samples. At day 7, there were no visible microfractures in the samples prior to testing. Conversely, samples that were cured for longer showed surface microfractures prior to testing.

In conclusion, the testing method developed and used in this thesis produced quality data on rock bolt systems. Furthermore, this study determined that shrinkage of the grout created microfractures, which in turn reduced the strength of the rock bolt system, thereby reducing the influence of curing time on pull-out load of rock bolts. As future work, it is recommended that further testing ne carried out to confirm this proposition.

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Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying (1 Jul 2013 - 31 Dec 2021)
Supervisors: Mirzaghorbanali, Ali; Nourizadeh, Hadi
Qualification: Bachelor of Engineering (Honours) (Civil)
Date Deposited: 09 Aug 2021 01:40
Last Modified: 26 Jun 2023 04:57
Uncontrolled Keywords: civil engineering, mining, rock walls, tunnels, rock bolt systems, water-grout ratio, curing time, pull-out load

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