Abstract
The short encapsulation pull-out test (SEPT) is extensively used in rockbolting research or engineering. The field SEPT is time-consuming and labor-intensive, and its result is only applicable to the tested in situ. The laboratory SEPT is usually employed in theoretical rockbolting research due to its easily controlled variables. However, the design of laboratory SEPT is quite different, as there is no standard testing method, resulting in the applicability and limitations of each study not being clear. Accordingly, the aim of this paper is to bridge the gap between laboratory SEPT research and field application. On the basis of thick-walled cylinder theory, a mechanical model of a rock bolt subjected to axial load was established under consideration of the deformational behavior of confining materials around the bolt. Plane stress analysis was introduced to derive the analytical relationship between the axial force of the bolt and the deformation of the confining materials. A new approach of laboratory SEPT sample design was established, namely, equivalent radial stiffness theory, to simulate anchorage performance in a specific in-situ geocondition. Consequently, the field SETP could be replaced by laboratory testing using properly designed bolting samples with a certain level of accuracy. In addition, the application scope of previous laboratory SEPT research could be accurately defined. Laboratory SEPT was carried out to study the anchoring performance of right spiral rebar bolts under different confining materials. Poly Vinyl Chloride (PVC) tubes with a thickness of 31 mm, #60 aluminum (Al) tubes with a thickness of 5.8 mm, and #20 steel tubes with a thickness of 5.5, 7.0 mm were used in sample preparation to simulate soft, medium, and hard surrounding rocks in the field. The anchorage performance of the bolt under different geoconditions was systematically proposed, which provides a technical approach for similar research using different anchoring materials. A negative exponential expression formulating the axial load capacity of the right spiral bolts for the full spectrum of the surrounding rocks’ strength was derived on the basis of theoretical analysis and data regression. It can be used for preliminary reinforcement design, as well as the accurate key parameter setting in the numerical calculation of roadway deformation using right spiral bolts. The theoretical prediction is highly consistent with the testing results in the literature, which confirms the validity and reliability of this research. This study contributes to the establishment of a laboratory SEPT standard in rock mechanics.
Highlights
IntroductionRockbolts are characterized by highly effective reinforcement and simple creativecommons.org/licenses/by/ 4.0/)
Microcomputer-controlled servo-testing modified dextral bolt, the peak anchorage force of the Al tube andelectrohydraulic the steel tube specimens machine was used to conduct the test, and loading displacement was controlled at a speed increased by 22.5%, 89.6%, and 99.8%, respectively, compared to that of the Poly Vinyl Chloride (PVC) tube
Axial load capacity the bolt increased an increase in the radial stiffness of the confining materials; anchorage performance may be quite different for the same dextral bolting support system but in the different surrounding rock
Summary
Rockbolts are characterized by highly effective reinforcement and simple creativecommons.org/licenses/by/ 4.0/). The bolting system consists of four components, namely, surrounding rocks, bolts, and internal and external fixtures [7,8]. External fixtures are trays and nuts, which connect the reinforcing elements at the roadway surface. The reinforcing effect is based on load transfer from unstable surrounding rock to stable rock mass through the bolt. The load-transfer capacity of the bolt is one of the most important indicators of the bolting effect. The accurate estimation of the bolting force is fundamental for reinforcement-system design and an important parameter in the numerical modeling of the deformation of underground roadways
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have