A Critical Review on Development of Laboratory Testing Technologies of Tendons Applied to Stabilize Underground Structures

A Critical Review on Development of Laboratory Testing Technologies of Tendons Applied to Stabilize Underground Structures

The paper reports on different methods and techniques developed, over the past several decades, to characterize axial and shear strength of various tendons used for ground reinforcement in mining and civil engineering operations. Most of axial loading methods are carried out by pull testing, with very few tests reported on push load tests. Based on an extensive literature survey of more than 80 scientific documents, published between 1970 and 2023, it was shown that a significant number of apparatuses have been developed for testing tendons axially with a limited number being developed for shear testing. The majority of axial testing is undertaken by pull testing tests. The type of tensile strength test selected is dependent on the test purpose and tendon type. The short encapsulation pull test is used mostly for testing solid rebar bolts, while double embedment can be used for the pull testing of both solid rebar and cables, preventing unwinding. A new reverse pull test rig is now available to undertake both the static and dynamic testing of tendons. The single shear and double shear test methods are discussed concerning the different purposes of testing and tendon tool design for the different ground conditions. Several factors and parameters, which influence the effectiveness of bolting, concerning rock reinforcement, are discussed. These factors or parameters include: the medium type and strength, the host medium shape and size of confinement, and the frictional resistance. Particular emphasis is placed on frictionless shear testing of joint faces using the Lateral Truss System (LTS) that prevents shearing faces from coming in contact with each other. The findings from the double shear test indicate that the type of medium, shape and size, and the sheared joint surface of the medium along the applied loading rate all played a prominent role in the determination of the shear test results to achieve effective reinforcement design of the reinforcement system, based on sound calculated parameters for effective ground reinforcement designs and construction. Finally, shear testing of tendons at various angles with respect to rock formation discussed is angle shear testing of tendons installed in large concrete blocks. The paper provides an opportunity for future tests to include the testing and further assessment of tendons studied dynamically to consider reinforcement in seismically active ground.