Abstract
Cable bolts help surrounding rock masses of underground excavations to form internal rock structure and thus self-stabilize through effective load transfer between rock masses and cable bolts. The load transfer characteristics of cable bolt play the most significant role in cable selection for support design. There are many factors potentially affecting the load transfer characteristics of cable bolt via strengthening or weakening load contributors such as cable bonding, mechanical interlocking, frictional resistance at cable-grout interface and grout-rock interface, and shearing of grout anchorage. Double embedment pull test (DEPT) is an effective, reliable, and repeatable test method of investigating the load transfer characteristics of cable bolt and thus was selected in this study. With DEPT, the influence of factors such as cable rotation, grout age, grout anchorage annulus thickness, cable wire profile, and failure mode on the load transfer characteristics of cable bolt were investigated in terms of tensile strength and stiffness in different loading stages. Conclusions drawn from the study can be used to improve cable installation quality and to select appropriate cable bolting technique.
Highlights
Bolting is currently the most commonly accepted rock reinforcement method of dealing with rock strata instability in both surface and underground mines as well as in civil engineering
A Double embedment pull test (DEPT) test apparatus comprises two embedment moulds, with each embedment mould consisting of two half blocks of steel mould with semicircular holes carved out in the middle. e two half blocks are butted together and bolted tightly using allen socket head bolts to form one embedment mould. e embedment mould has a central hole of designed diameter and length. e internal surface of the central hole has 2 mm deep grooves at a spacing of 10 mm. e objective of designing these internal grooves is to allow effective anchorage of grout to the steel mould. e two embedment moulds were connected by a cable bolt in tension to form a DEPT sample
As cable bolt has a spiral structure, its load transfer characteristics are expected to be different from rock bolt
Summary
Bolting is currently the most commonly accepted rock reinforcement method of dealing with rock strata instability in both surface and underground mines as well as in civil engineering. Bolts are installed in fractured rock mass to build composite beams in weak strata and/or to attach weak excavation surfaces to deeper and competent rock layers to achieve stability [1]. Multiple solid rock bolts are connected by connecting sleeves to form a long solid rock bolt. This type of connected long solid rock bolt is not popular due to its complexity in installation when used in narrow underground roadways [2, 3]. Due to the structural difference, the cable bolt and rock bolt behave differently in reinforcing rock masses
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