Behavior Of Rock Bolts Research Articles

Modeling of grout crack of rockbolt grouted system

This paper presents a numerical study on the pullout behavior of the rockbolt grouted system. Among the complicated failure modes of the rockbolt grouted system, the crack of the grout is concerned here. A tri-linear cohesive zone model (CZM) is used to simulate the interfacial behavior of rockbolt–grout interface; and a plastic damaged model is adopted for the grout materials. The feasibility of the numerical method is verified by comparing the calculated results with the test observations. The numerical results indicate that two types of cracks of the grout materials can be identified as the inclined crack and the horizontal crack. The inclined crack forms firstly and then the horizontal crack. Both cracks can reduce the interfacial shear stress and thus reduce the load transfer efficiency. Further analysis indicates that the crack of the gout material can induce the obvious drops of load capacity, which is not a safe failure mode. This study leads to a better understanding of the mechanism for rockbolt grouted system.

Simulation of fully grouted rockbolts in underground roadways using FLAC2D

A numerical modelling approach of a mine roadway reinforced with fully encapsulated rockbolts is proposed to study the interaction between rockbolts and the rock mass. The rockbolt bond–slip relationships defined by conducting push tests of short rockbolts are implemented in the rockbolt elements used in the two-dimensional Fast Lagrangian Analysis of Continua (FLAC2D) model for precise simulation of the rockbolt behaviour. The performance of rockbolts installed in the roadway model under various conditions is discussed and compared with previous research. This paper provides a numerical modelling methodology to study the interaction between rockbolts and the rock mass subject to a variable stress state, rock mass quality, and the presence of rock fractures or joints. It was found that the bearing plates can improve the reinforcing performance of rockbolts.

Analytical model for rock bolts reaching free end slip

This paper presents the difference of behaviour between fully grouted bolts with and without free end slip when loaded in tension. An analytical approach is proposed for fully encapsulated bolts when the free end of the bolt slips. This model is based on the existing bond–slip relationship of bolt–grout interface with no free end slip. The derived analytical solutions of load–slip relationship, slip distribution, the shear stress and strain distributions presented in this paper are all connected with free end slip. The analytical approach is validated by experimental results. Free end slip has a significant influence on rock bolt behaviour and should not be ignored.

Development of Rock Bolt Elements in Two-Dimensional Discontinuous Deformation Analysis

Computer modeling can be used to explore and gain new insights into the impacts of rock bolt intersecting joints in rock masses, and to estimate the effectiveness of the rock reinforcement system. In order to achieve this goal, we couple a rock bolt element into the two-dimensional discontinuous deformation analysis (DDA2D) program. The coupling algorithm is based on the analytically-derived interface behavior between a rock bolt and the rock material for grouted rock bolts. The shear force generated by slippage along the interface is assumed to have a linear relationship with respect to the relative slipping distance between the rock bolt and the rock. The linear elastic criterion is applied to determine the material behavior of rock bolts before the axial stress reaches the yield value. The pullout tests are simulated to verify the coupling algorithm and the effects of the proposed rock bolt elements. Parametrical studies are also carried out to analyze the effectiveness of the rock bolts under various end conditions, joint locations and bond stiffness. In addition, the performance of the rock bolt during the interface debonding is analyzed using two types of constitutive laws, i.e., the friction law and the reduction law. The simulation results show that the proposed rock bolt models can predict the shear forces and axial loading along the rock bolts.

Computer Aided Understanding for Interaction between Stratified Slope and Bolt

Slope excavations are often constructed in stratified host rock masses in practice. The stratification in a rock mass is generally characterised by its planar geometry and persistence. The mechanical properties of the joints dictate both the deformation and strength characteristics of the stratified rock mass. Thus, it is imperative that the influence of the joints be incorporated in any type of load-deformation analysis of slope excavations in layered rock masses. Rock bolts have been widely used as the primary support system to stabilize the rock masses of slope. In general, rock bolts reinforce rock masses through restraining the deformation within rock masses and reduces the yield region around the excavation boundary. In order to improve bolting design, it is necessary to have a good understanding of the behaviour of rock bolts in deformed rock masses. In the present paper, the numerical analysis method is adopted to built the three springs bolt element; then the excavation in the stratified rock slope is simulated to improve the understanding of the slope deformation and bolt mechanical characteristic.

Instrumentation for monitoring the dynamic and static behaviour of rock bolts in tunnels : A. A. Rodger, G. S. Littlejohn, H. Xu & D. C. Holland, Proceedings — ICE: Geotechnical Engineering, 119(3), 1996, pp 146–155

Instrumentation for monitoring the dynamic and static behaviour of rock bolts in tunnels : A. A. Rodger, G. S. Littlejohn, H. Xu & D. C. Holland, Proceedings — ICE: Geotechnical Engineering, 119(3), 1996, pp 146–155

Rockbolt behaviour under dynamic loading: field tests and modelling : D. D. Tannant, R. K. Brummer & X. Yi, International Journal of Rock Mechanics & Mining Sciences, 32(6), 1995, pp 537–550

Rockbolt behaviour under dynamic loading: field tests and modelling : D. D. Tannant, R. K. Brummer & X. Yi, International Journal of Rock Mechanics & Mining Sciences, 32(6), 1995, pp 537–550

Rockbolt behaviour under dynamic loading: Field tests and modelling

Knowledge of rockbolt response under dynamic loading conditions is important when rockbolts are used to support ground subjected loads from blasts, earthquakes or rockbursts. Dynamic strain measurements from strain gauges mounted on end-anchored rockbolts and velocity measurements from geophones mounted on the rock surface were recorded during two different blasts. These blasts caused peak particle velocities in the rock exceeding 1 m/sec but maximum dynamic stresses in the bolts were well below the yield point of the steel. The measurements were analysed by analytical methods and a numerical model which was developed to explain the measured rockbolt variations resulting from the dynamic loading caused by the blasts. The numerical model developed for this study is a one-dimensional finite difference representation of a mechanical system involving the following components: the wave source, the rockmass, the mechanical rockbolt, and the anchor and head connections. The measured strains on the rockbolts and the dynamic movement of the rock surface were closely simulated by the numerical model. Both axial and lateral free vibrations were excited in the rockbolts by the dynamic loading and the vibrations persisted much longer than the ground motions. Damping at the connections between the rockbolt and the rockmass at the anchor and the plate influence the transfer of the stress wave from the rock to the bolt and the resulting frequency of vibrations in the rockbolt.

BEHAVIOR OF ROCKBOLTS FOUND IN THE EXPERIMENTS OF TWO LOWERING PANELS

Although the rockbolts are used very often as a main member of supports in NATM, the fact is that there are various understanding of the effects of rockbolts and that there has been no specified way of design. It is because the effects of rockbolts have been recognized mainly through experiences and also because there is no good way of investigation of them.This study of rockbolts by two lowering panels is a method of examining more positively the mechanical properties of rockbolts presented by our authors, following the previous study by one lowering panel. This series of the experiments by two lowering panels were made to examine the mechanical properties of a group of rockbolts while the experiments by one lowering panel were made to examine the effects of a rockbolt.This report describes the behavior of rockbolts found through the experiments of two lowering panels including theoretical consideration. And it also describes our view of design of rockbolts.

Behaviour of rock bolts in stratified ground and resulting specifications (in German) : Gluckauf-forschungsh V46, N2, April 1985, P69–75

Behaviour of rock bolts in stratified ground and resulting specifications (in German) : Gluckauf-forschungsh V46, N2, April 1985, P69–75