Anchoring mechanism and application of hydraulic expansion bolts(1)

Anchoring mechanism and application of hydraulic expansion bolts used in soft rock roadway floor heave control

1. Introduction
In a soft rock roadway, the floor heave is one of the major deformation forms of the surrounding rock, and its control is also one of the problems which blocks the mine production. For a long time, many domestic and overseas scholars and mining technology staff have done much research on the mechanism of the floor heave and proposed some methods such as reinforcing method,releasing method, reinforcing combined with releasing method and so forth, to control floor heave. Among these control methods, the reinforcing method using the resin bolt, which is the most frequently-used reinforcing method, is making use of increasing the strength of the floor rock and preventing plastic flow of the floor rock to control floor heave. However, when drilling the bolt hole, the fact that the rock powder cannot be easily blasted out of the hole seriously, affects the control effect of the resin bolt in the soft rock roadway. Fortunately, the hydraulic expansion bolt can overcome this problem because it does not use the resin in the process of its application. And the anchoring form is full-size anchoring, which makes the anchoring force large. In this paper,firstly the research reveals the anchoring mechanism of the hydraulic expansion bolt. Then, the mechanism of floor heave in a soft rock roadway in Jinbaotun Coal Mine of Liaoyuan Group is analyzed. Finally, we design the reasonable parameters of the hydraulic expansion bolts and apply the hydraulic expansion bolts to the mining roadway.

2.Anchoring mechanism of hydraulic expansion bolt

2.1 Components of hydraulic expansion bolt

The hydraulic expansion bolt is manufactured from a seamless steel pipe to a rod body with a double-deck bizarre section, as shown in Fig. When the pressure of the injected water in the rod body is larger than the yield strength of the seamless steel, the rod body will be expanded along the radial direction.Then the extrusion force is imposed on the surface of the surrounding rock of the roadway. The accessory equipments include end sleeve, retainer ring, liquid injection mouth, pallet, etc.

2.2 Anchoring force of hydraulic expansion bolt

According to the failure characteristics of the hydraulic expansion bolt, its anchoring force is expressed in four forms, namely support anchoring force, tension anchoring force, expansion anchoring force and tangent anchoring force.

2.3 Anchoring mechanism of hydraulic expansion bolt

The support anchoring force of the hydraulic expansion bolt can be considered to be the confining pressure imposed on the surrounding rock. This makes two-direction forced rock change to three-direction forced rock, then helps to enhance the strength of the surrounding rock. The tangent anchoring force improves the mechanical property of the weak plane, and can enhance the strength of the surrounding rock. The tension anchoring force can deliver the vertical tension in the tensile strain compression area to limit the movement of the tension strain rising area in floor rock. The expansion anchoring force can increase the confining pressure of the floor rock, and then enhance the strength of the floor rock. Especially for the soft rock, this expansion anchoring force makes the bolt tightly combine with the rock, which makes the support effect more obvious.