Rostov State Transport University, Rostov-on-Don, Russia:

M. S. Pleshko, Professor, Doctor of Engineering Sciences, mixail-stepan@mail.ru
Yu. V. Vcherashnyaya, Post-Graduate Student

Shakhty Institute (Branch), South Russian State Technical University, Shakhty, Russia:
A. A. Nasonov, Associate Professor, Candidate of Engineering Sciences

One of the key approaches to improvement of rigid support is replacement of multibunton storeys by cantilever, cantilever–spacer and modular reinforcement elements. On the other hand, the currently known designs of bunton-free reinforcement are meant for shafts with monolithic concrete or precast lining. With a view to enhancing technical and economic efficiency of construction and operation of deep ventilation shafts with shotcrete lining, the authors have developed designs of rigid support with anchoring of guides on rock bolt cantilevers directly on the shaft walls. Such design allows using both rail and box guides. The efficiency of the reinforcement grows when rock bolt cantilevers overhand by a minimized value relative to the shaft wall. The description is illustrated by the design of cross-section support in a ventilation shaft of Obukhovskaya Mine-1, where the length of the cantilevers is 290–430 mm. The mathematical modeling and bench testing of the developed rock bolting design showed that maximum shearing force was generated in cross-section of a rock bolt at a distance of 4–6 cm from the hole mouth. The comparison of the mathematical modeling and bench test data exhibited their agreement at a deviation of not more than 16%. The maximum principal stresses arose in rock bolt embedment at the hole mouth and intensively reduced depthward the hole. The basic factors determining values of the maximum principal stresses in embedment material are the value of horizontal dynamic load, rock bolt cantilever length, rock bolt diameter, as well as the quality of concrete and embedment material. Based on the data of the experimental research, a nomogram has been plotted to determine the safety factor of the loadbearing capacity of a rock bolt unit with the embedment made of different quality concrete manufactured from cement and sand. The research findings make a background for the wider introduction and application of the resource-saving designs of soreyless reinforcement and lightweight support for vertical shafts. The optimal application domain are the vertical shafts 1000 m in length, with the inside diameter of 4.5–6 m, drilled in rock mass of categories I and II as per Code 91.13330.2012 and equipped with auxiliary low-capacity cage hoists.

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