The authors acknowledge that the issue of the critical embedment length was studied by others in conjunc- tion with individual engineering projects, but little information about it can be found in the literature.The rebar bolt is 20 mm in diameter, and it is widely used in underground excavations in Norway.
It was discovered that the critical embedment length of the rock bolts was approximately 25 cm for the water-cement ratio 0.40 (the corresponding uniaxial compressive strength (UCS) of the grout is 37 MPa), 32 cm for the ratio 0.46 (UCS 32 MPa), and 36 cm for the ratio 0.50 (UCS 28 MPa), for the specific type of cement, Rescon zinc rock bolt cement. It was found that the bond strength of the rock bolt is not a constant but is related to the embedment length. The bond strength was linearly proportional to the UCS of the grout. Number of rock bolt specimens for every water-cement ratio and for every embedment length. Pull load-displacement curves of the bolts grouted with water-cement ratio 0.40 for embedment lengths (a) 100 mm, (b) 150 mm, (c) 200 mm, and (d) 300 mm. Pull load-displacement curves of the bolts grouted with water-cement ratio 0.46 for embedment lengths (a) 100 mm, (b) 200 mm, (c) 250 mm, and (d) 300 mm. Pull load-displacement curves of the bolts grouted with water-cement ratio 0.50 for embedment lengths (a) 100 mm, (b) 200 mm, (c) 300 mm, and (d) 400 mm. UCS values of the grouts, measured with cubic specimens, for different water-cement ratios after 7-day curing. Figures - uploaded by Charlie Li Author content All figure content in this area was uploaded by Charlie Li Content may be subject to copyright. Calculate Anchor Bolt Embedment Length For Free Public FullDiscover the worlds research 17 million members 135 million publications 700k research projects Join for free Public Full-texts 2 2016Li, Kristjansson HienTUSTCritical Embedment Length and Bond Strength of Fully Encapsulated Rebar Roc kbolts.pdf Content available from CC BY 4.0: 2016Li, Kristjansson HienTUSTCritical Embedment Length and Bond Strength of Fully Encapsulated Rebar Rockbolts.pdf 2016Li, Kristjansson HienTUSTCritical Embedment Length and Bond Strength of Fully Encapsulated Rebar Rockbolts.pdf Content uploaded by Charlie Li Author content All content in this area was uploaded by Charlie Li on Dec 19, 2016 Content may be subject to copyright. Li, Kristjansson HienTUSTCritical Embedment Length and Bond Strength of Fully Encapsulated Rebar Roc kbolts.pdf Content available from CC BY 4.0: 2016Li, Kristjansson HienTUSTCritical Embedment Length and Bond Strength of Fully Encapsulated Rebar Rockbolts.pdf 2016Li, Kristjansson HienTUSTCritical Embedment Length and Bond Strength of Fully Encapsulated Rebar Rockbolts.pdf Content uploaded by Charlie Li Author content All content in this area was uploaded by Charlie Li on Dec 19, 2016 Content may be subject to copyright. Li, Gunnar Kristjansson, Are Hvard Hien Department of Geology and Mineral Resources Engineering, The Norwegian University of Science and Technology (NTNU), Norway article info Article history: Received 9 November 2015 Received in revised form 7 June 2016 Accepted 8 June 2016 Available online 17 June 2016 Keywords: Rockbolt Embedment length Pullout test Bond strength abstract A series of rock bolt pull tests were carried out in the laboratory to determine the critical embedme nt length of a specic type of fully cement-grouted rebar bolt. It was discovered that the critical embedment length of the rock bolts was approximately 25 cm for the water-cement ratio 0.40 (the corresponding uniaxial compressive strength (UCS) of the grout is 37 MPa), 32 cm for the ratio 0.46 (UCS 32 MPa), and 36 cm for the ratio 0.50 (UCS 28 MPa), for the specic type of cement, Rescon zinc rock bolt cement. The bond strength was linearly propor- tional to the UCS of the grout. The wide use of this type of rock bolt is predominately owed to its high load-bearing capacity. In such a test, a rock bolt grouted in a borehole is either pulled out to measure the bond strength in the case of a short embedment length ( Hyett et al., 1995; Benmokrane et al., 1992; Benmokrane et al., 1996; Zhao and Yang, 2011 ) or pulled until failure of the rock bolt shank ( Stillborg, 1994; Stjern, 1995; Chen and Li, 2015 ). Pull tests may be conducted in the eld ( Franklin and Woodeld, 1971; Franklin et al., 1974; Bjurholt, 2007; Soni, 2000 ) or in laboratories ( Ito et al., 2001; Li et al., 2014 ). The performance of a fully grouted rebar rock bolt is very much affected by the bond at the rock bolt-grout interface. The bond strength directly determines the critical embedment length of the rock bolt, which refers to the longest encapsulated length at which the rock bolt is pulled out of the borehole. The rock bolt will fail in the shank if the grouted section is longer than the critical embedment length. For instance, in order to stabilise a loosened rock block with fully grouted rock bolts, the length of the rock bolt portion that is installed in the stable stratum must be longer than the critical embedment length. The quality of grouting and the load-bearing capacity of grouted rock bolts are often examined through pull tests in the eld. One of the concerns with such a pull test is whether the performance of the rock bolt is negatively affected by the pull test.
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