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Pretension is a key factor affecting the performance of rock bolt. It is usually applied on the bolt by tightening the nut. The efficiency of the torque-to-pretension conversion is significantly influenced by the thread rolling accuracy. In this study, the influence of the thread rolling accuracy upon the pretension is investigated. Factors influencing the thread rolling efficiency, i.e., rock bolt material quality, rolling technic and equipments, are examined. To study the relationship between torque and pretension, a laboratory table was specially designed and a series of tests were carried out on the rock bolts with different thread accuracy. The result indicates that the higher the thread rolling accuracy, the higher the coefficient of torque-to-pretension conversion. And the coefficient can be improved by daubing lubrication oil on the thread. In China, the rock bolt thread encounters the issue of low rolling accuracy which results in coarse thread surface. As a result, the efficiency of the torque-to-pretension conversion is greatly reduced. In addition, the rock bolt is susceptible to break at the thread end. Essential approach to resolve these issues is to significantly improve the thread rolling accuracy by adopting advanced equipment.

By analyzing the stability factors and deformation characteristics of wall rock of dynamical pressure roadway in coal mine, the basic support form of dynamical pressure roadway was summarized. Combined with the geological conditions and the roadway damaged condition of two tape head chamber in ChengZhuang colliery No.2 area, the reinforcement approach was put forward, which adopting the composite grouting of cement and unsaturated polyester chemical pulp, then strengthened by prestressed grouting anchor. Comparing the supporting effect of prestressed grouted anchor with not grouted, it was obviously found that the effect is great improved. The strong deformation of dynamic pressure roadway can be solved effectively in this way.In recent years, with the development of mining technology and high-gas coal mining, the roadway layout that can meet the requirements of production and ventilation is increasingly complicated. The area of roadway increases as equipment have been expanding. The pressure has been apparently increasing because the thickness of mining and the height of caving face increase. The difficulty level of roadway support is also added since the surrounding rock condition become more and more complex [1-3].