Stabilization of Deep Roadways in Weak Rocks Using the System of Two-level Rock Bolts

Large rock mass deformation around deep roadways in the weak rocks was a significantproblem in mining activities in Vietnam and other countries. The excavation of roadways leads to highreleasing stress, which exceeds the peak strength of spalling surrounding rock and causes it to enter thepost-failure stage. Tensile failures then initiate and develop around the roadways, which causes thefragmentation, dilation, and separation of surrounding rock. The capacity of the primary support systemis low, which results in a severe contraction in the whole section of roadways, which requires findingsolutions to prevent the deformation of rock mass around roadways and technical solutions fromstabilizing for deep roadways. To stability analysis of roadways can be applied analytical, experimental,semi-experimental, and numerical methods. This paper introduces the prevention mechanism of largedeformation of rock mass around roadways using 2-level rock bolts. The research results show that usingthe system of two-level rock bolts can reduce the values of tensile stress on the boundary of roadwaysrange from 10 to 15% compared with only one. The importance of the total displacement of rock mass onthe boundary of roadways will be reduced from 3.47 to 13.85% using six long cable bolts.

Failure Characteristics of W Straps Based on Field Observations and Laboratory Tests

W straps are important surface supporting components. When they cooperate properly with inner supporting components, such as rock bolts and cable bolts, they can enhance the supporting effects and bridging bolting units with integrity. Unfortunately, relevant studies regarding this topic have not been extensively reported. In this study, the failure characteristics of the W strap in the field are discussed and different types of distortion are proposed. Followed by the detailed failure patterns of the strap, a possible mechanism and solution are hypothetically put forward, which are then both numerically and experimentally verified. Afterwards, a loading apparatus capable of examining the mechanical behaviours of the strap is designed, which can similarly recreate the loading environment of the strap to the situation in the engineering field. By virtue of the designed loading device, a series of failure patterns of the bolting system are presented, and the distortion degree of the strap is evaluated using a 3D scanning method. The major findings in this study are as follows: 1) a domed face plate is better than a square domed face plate; 2) the existence of a hole beneath the strap in engineering applications can easily induce failure; and 3) cracked but compacted gravel-like roof strata beneath the strap may not cause damage to the strap-bolt supporting system. These ideas present new understandings in terms of the working conditions of W straps in coal mine roadway supporting systems, and the results can be referred to by practitioners.