Laboratory studies of a high-strength roof bolting by means of self-extending mixtures

Abstract

Purpose is to analyze parameters of a new method to fasten roof bolts with the help of nonadhesive mixtures extending while hardening along with the development of high expansion pressures.Methods. The research, concerning forces applied while fastening roof bolts by means of self-extending mixtures, has been carried out under full-scale laboratory conditions using pressing-in method. Rock mass was simulated by means of concrete in plastic and metal forms, and steel pipes. The latter simulated ultimate rigidness conditions. Roof bolts were simulated by means of reinforcement steel fragments. In the context of the research, bolt diameters varied from 8 to 32 mm, and borehole diameters varied from 26 to 43 mm. Hydraulic 50-ton press was used for the tests. The testing results were applied to obtain regressive dependences of bolt fastening efforts in terms of different ratios between roof bolt diameter, borehole diameter, and incapsulation depth. Mine experiments concerning efforts to fasten Rockbolt System AG roof bolts of J64-27 type to strengthen chamber 1 of level 3 in Velychka mine were performed using a method of static bolt extraction. Hydraulic extraction device was equipped by ZEPWN CL 18T sensor and CL 162z-DW recorder.Findings. It has been proved experimentally that operation mechanism of the roof bolts, fastened by means of selfextending mixtures during hydration hardening, is close to the modern energy absorbing bolts. Bolt diameterborehole diameter ratio range, when ultimate effort of bolt fastening by means of extending mixtures is achieved, has been determined. Functional connection between the efforts to fasten roof bolts, using extending mixtures, and diameters of borehole and the roof bolt has been identified as well as linear connection between incapsulation depth and bearing capacity of the roof bolt. Originality.A new concept to fasten roof bolts with the help of nonadhesive technique owing to their quazistatic compression between borehole walls, taking place as a result of hydration self-extension of mixtures which can achieve 30 -50 MPa pressures under the conditions of zero deformations, has been developed. Regularities in the variation of efforts to fasten bolts, using the technique, depending upon roof bolt -fastening mixture -rock mass system geometry have been determined. Practical implications.The results can be used to calculate parameters of roof bolting with high bearing capacity under the conditions of large deformations. The proposed fastening method may be implemented in mine workings.

Influence of adhesion on stress-strain condition alongside of a full column resin cartridge rock bolt

“…The occurrence of high stresses in the anchor bolt and even the danger of its destruction with resins with high adhesion are confirmed by laboratory experiments under the guidance of Prof Korzeniowski (Skrzypkowski et al 2020). The presented results of numerical modelling in terms of the effect of the elastic modulus of the resin on the nature of stresses and failures arising in it are consistent with the results of laboratory tests of the effect of resin properties on the peak pullout forces mentioned in the work of Shen (Shen 2021), as well as in the works of Sakhno (Sakhno et al 2018;Sakhno et al 2019). 2) at 1 MPa pressure on the detaching part of the block, at rock interface: (for 17a) 1 -0.6 unit; 2 -1 unit; 3 -2 units; 4 -5 units; 5 -10 units; (for 17b) 1-5 minimum principal stresses (S 3 ) at rock interface: 1 -0.6 unit; 2 -1 unit; 3 -2 units; 4 -5 units; 5 -10 units; 6-10 maximum principal stresses (S 1 ) at rock interface: 6 -0.6 unit; 7 -1 unit; 8 -2 units; 9 -5 units; 10 -10 units…”

Integrated research into the stress-strain state anomalies, formed and developed in the mass under conditions of high advance velocities of stope faces

“…In addition to these factors, it is also necessary to take into account the processes of weakening the rock layers (occurrence of tension cracks, partitioning into blocks and their partial caving into the mined-out space). More intense fracturing [37] and the occurrence of the so-called thrust-block systems in the roof increases their deformation capacity for more significant displacements, and rocks caved into the mined-out space radically change their mechanical characteristics [38][39][40]. These factors have been sufficiently tested using modern methodologies for modeling geomechanical processes [41,42].…”

Research on Double-Layer Support Control for Large Deformation of Weak Surrounding Rock in Xiejiapo Tunnel

“…Ref. [37] conducted laboratory testing on expansion shell rock bolts with deformable components to investigate their stress-strain and displacement characteristics. They quantified the contributions of each component to the overall displacement and provided essential design data that enhance the performance of rock bolt support systems in underground excavations under static loads.…”