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Li S.-C.,Shandong University | Wang H.-T.,Shandong University | Wang H.-T.,Shandong Jianzhu University | Wang Q.,Shandong University | And 6 more authors.
Journal of Central South University | Year: 2016

In deep underground mining, the surrounding rocks are very soft with high stress. Their deformation and destruction are serious, and frequent failures occur on the bolt support. The failure mechanism of bolt support is proposed to solve these problems. A calculation theory is established on the bond strength of the interface between the anchoring agent and surrounding rocks. An analysis is made on the influence law of different mechanical parameters of surrounding rocks on the interfacial bond strength. Based on the research, a new high-strength bolt-grouting technology is developed and applied on site. Besides, some helpful engineering suggestions and measures are proposed. The research shows that the serious deformation and failure, and the lower bond strength are the major factors causing frequent failures of bolt support. So, the bolt could not give full play to its supporting potential. It is also shown that as the integrity, strength, interface dilatancy and stress of surrounding rocks are improved, the bond strength will increase. So, the anchoring force on surrounding rocks can be effectively improved by employing an anchoring agent with high sand content, mechanical anchoring means, or grouting reinforcement. The new technology has advantages in a high strength, imposing pre-tightening force, and giving full play to the bolt supporting potential. Hence, it can improve the control effect on surrounding rocks. All these could be helpful references for the design of bolt support in deep underground mines. © 2016, Central South University Press and Springer-Verlag Berlin Heidelberg.

Jiang B.,Shandong University | Wang Q.,Shandong University | Wang Q.,China University of Mining and Technology | Li S.C.,Shandong University | And 6 more authors.
Tunnelling and Underground Space Technology | Year: 2016

In this study, we use the upper-bound method to develop a collapse failure mechanism of the roof surrounding rock of semicircle arched roadway, with a consideration of the water pressure in the stratum and the support from anchor cables. We consider a cavern with a semi-circular roof and straight walls in a water-rich stratum as a case study. A design method is presented for the required length of and the pre-tightening force of anchor cables on the cavern roof, based on the Hoek-Brown criterion. We analyse the effects of factors such as the cavern width, the pore-water pressure coefficient and the specific weight and the compressive and tensile strengths of the rock mass using established sensitivity indexes for the factors that affect the design parameters of anchor cables. We provide recommendations for controlling the surrounding rock in practical engineering applications for actual scenarios. The design method is used to determine the parameters of anchor cables for the roof of a primary drainage pump station in a mine. The designed anchor cables are used to effectively control the deformation of the surrounding rock. The results show that at the early stage of the excavation of a cavern, the collapse of the surrounding rock of the roof can only be effectively controlled using anchor cables with lengths that meet the design requirements and to which a sufficient pre-tightening force has been applied. In addition, the required length of anchor cables increases with the cavern width, the pore-water pressure coefficient and the specific weight of the rock mass and decreases as the compressive strength of the rock mass increases. The cavern width has the highest sensitivity among the influence factors for the length of anchor cable. Furthermore, the required pre-tightening force for anchor cable for the roof decreases as the tensile and compressive strengths of the rock mass increase and increases with the pore-water pressure coefficient, the cavern width and the specific weight of the surrounding rock. The cavern width also has the highest sensitivity among the influence factors for the pre-tightening force. Finally, the cavern shape and width should be carefully selected for the design and construction of a cavern with weak surrounding rock in a water-rich stratum. The intactness of the surrounding rock should be improved by using high-strength and high-toughness anchored supporting components, applying a high pre-tightening force to the anchored supporting components and using grouting reinforcement to mitigate the effect of water. In this way, relatively good control of the surrounding rock can be realised. © 2016 Elsevier Ltd.

Wang H.-T.,Shandong University | Wang Q.,Shandong University | Wang Q.,Yankuang Group Company Ltd | Wang F.-Q.,Yankuang Group Company Ltd | And 6 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2015

In order to study the control effect of different anchoring lengths on surrounding rock in roadways, the stress distribution laws of bolt were deduced, and the mechanical analysis model concerning different anchoring lengths was established through theoretical method. Different factors, such as bolt diameter, surrounding rock strength, anchorage length, pre-tightening force, bolt spacing, etc., were analyzed, engineering measures on bolt designing were also recommended, and the correctness of theoretical results was verified through filed test. The results show that the inner force of rock bolt concentrates in the 1/3 range of anchoring section mainly, and damps to the root along the length of bolt. In softer rock mass, anchorage effect is better to be exerted. Adopting high pre-tightening force and setting a certain length of free-segment can help pre-tightening force to spread in surrounding rock, form effective bearing structure in anchored rock mass, and achieve a supporting potential of bolt. When bolt spacing increases, a better control effect of surrounding rock can be achieved through applying high pre-tightening force and reducing anchorage length appropriately. ©, 2015, Meitan Xuebao/Journal of the China Coal Society. All right reserved.

Wang H.-T.,Shandong University | Wang Q.,Shandong University | Wang Q.,Yankuang Group Company Ltd | Li S.-C.,Shandong University | And 6 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2015

To investigate the support of semicircle arched roadway, the roof failure mechanism, considering surrounding rock stress and bolting support, was constructed based on nonlinear Hoek-Brown failure criterion, and a simplified method for designing the pre-tightening force of roof bolts at the early stage after roadway excavation was proposed based on upper bound method. In addition, the recommended engineering measures were also provided accordingly, and the supporting effect of bolts with high strength and high pre-tightening force was verified through a field application. The results show that only imposing enough pre-tightening force after roadway excavation can effectively prevent roof falling. With the improvement of the strength parameters of rock mass, the required pre-tightening force of single rock bolt decreases, while increases with the increases of bolt spacing and surrounding rock stress. Adopting bolting support components with high strength, high tenacity and imposing high pre-tightening force, or adopting grouting reinforcement in soft, loose and broken surrounding rock can obtain more ideal control effects. ©, 2015, China Coal Society. All right reserved.

Wang H.-T.,Shandong University | Jiang B.,Shandong University | Wang D.-C.,Shandong University | Wang D.-C.,Longkou Coal Electrical Company Ltd | And 5 more authors.
Electronic Journal of Geotechnical Engineering | Year: 2014

In order to study the mechanical properties of bolting support failure in soft surrounding rock, the calculation theory of the maximum interfacial shear stress of the anchorage body in soft surrounding rock was established by considering factors including the strength and stress of surrounding rock, bolt design parameter, and interface dilation effect of the anchorage body. The influence law of the interfacial shear capacity of the anchorage body affected by different factors was analyzed; corresponding engineering suggestions and measures were proposed; the enhancement effectiveness of the bolt-grouting support technology on the control effect of soft surrounding rock and anchorage support was verified through certain engineering example; the control difficulties in field surrounding rock were resolved. The results showed that there was a positive correlation between the interfacial shear capacity of the anchorage body in soft surrounding rock and the elastic modulus, cohesion, internal friction angle, dilatancy angle, and surrounding rock stress while there was a negative correlation between the interfacial shear capacity and the anchorage body diameter; improving the anchorage technology on the anchored section and employing grouting reinforcement technology were two effective ways to improve the anchorage support boltability in soft surrounding rock; after the bolt-grouting supporting scheme was adopted in field 4606 material roadway, the largest deformation of surrounding rock was reduced by an average of 30.3% and the bolt force was increased by an average of 103.6%, which could provide references for roadway control in soft surrounding rock. © 2014 ejge.

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