Mining Roof Bolts Case Introduction
The mine engineering design annual production capacity is 1.8 million Ton, due to the complex geological structure in the minefield. In the design and construction of mining roof bolts support, support forms and parameters are selected based on experience or engineering analogy, so there are some problems, such as difficult roadway maintenance, low coal production rate and tight mining replacement. In order to solve these problems, take project mine roadway as the engineering background to carry out solutions based on the analysis of roadway deformation mechanism and support technical effect. The successful application of mining roof bolting, netting and cable combined support has important significance and practical application value for improving coal production rate, reducing support cost of mining roadway, and realizing high yield and high efficiency in mining roadway roof support.
In the construction and production of high-efficiency mines, the common mining roof bolts support has not been able to meet the requirements of mechanized large-scale production due to the fast construction speed. In order to solve the contradiction between the rapid excavation and the lagging of support, the combined support of high strength anchor bolt and anchor cable has been popularized and applied as the main support method. Mine roadway and semi-coal rock roadway are mainly mining rock bolted-net shotcrete, it is mainly bolted-net and anchor rock bolt + steel belt (or reinforced beam) support, general chamber also adopts rock bolt-net shotcrete + anchor cable support, only in special places (such as large ground pressure roof broken area) shed support. High strength roof bolt and cable combined support has the advantages of fast supporting speed, good effect and low cost.
Dimensions and Allowable Deviations of Hot-rolled Roof Bolts
| Size | Inner diameter | Rib Height | Rib Width | Out of roundness | Rib space | |||
|---|---|---|---|---|---|---|---|---|
| nominal size | allowable deviations | nominal size | allowable deviations | nominal size | allowable deviations | |||
| Φ16 | 16 | +0.5 +0.1 |
1.5 | +0.4 | 1.0 | ≤0.4 | 11.5 | +0.5 |
| Φ18 | 18 | +0.5 +0.1 |
1.5 | +0.4 | 1.3 | ≤0.4 | 13.3 | +0.5 |
| Φ20 | 20 | +0.5 +0.1 |
1.5 | +0.4 | 1.3 | ≤0.4 | 13.3 | +0.5 |
| Φ22 | 22 | +0.5 -0.4 |
0.8 | +0.3 -0.2 |
1.1 | ≤0.4 | 12 | +0.8 |
Main Factors Affecting Mining Roof Bolts Support
- The design method of mining roof bolts support is not scientific. Although its specification for coal roadway has been formulated, engineering analogy method is adopted in most of the design, and the support form and parameters are not reasonably determined. It is possible that the support strength is too much higher than the required level, the roof support structure cost is too much, for mining roof bolts are wasted. In soft, and other special geological conditions under the support strength may be insufficient, there is a possibility of danger, as roof collapse and other accidents may occur.
- The supporting material quality of mining roof bolt fails to reach the requirement. There might be various reasons, such as steel quality, thread quality of processing, resin coil quality are directly affected by the quality of support.
- The monitoring instrument and technology of mining roof bolts have high accuracy. The accuracy and practicability of the commonly used instruments are not perfect, which can not reflect the effect of bolt support completely.
- Under the existing technical conditions, the construction factor is the key link that directly affects the reliability of mining roof bolts support. The construction personnel does not have enough knowledge of the rock bolting support theory, or skills to install rock bolt properly, and the installation and operation quality management of the rock bolting cannot meet the design requirements. Such as sometimes only do the mining roof support and ignore the roadway side and floor, or some workers are not skilled enough and lacks sense of responsibility resulting in bolt and cable support strength reduction.
- In the construction of roadway uneven rock bolt anchor plate is not close to the rock surface, resulting in the failure of the mining rock bolt installed with no prestress. Different machines, tools and techniques used in the installation process lead to different pre-tensioning forces and different growth of support resistance after the installation of adjacent mining roof bolts, which will affect the support effect.
Mining Construction of Roof bolts
During the installation of the resin bolt, the bolt must be pushed to the bottom of the hole to achieve the anchoring force. The agitator should be gently pushed vigorously, in order to quickly coagulant and resin stir evenly. When installing the nut of bolt support plate, the resin should reach a certain strength. The curing rate of resin and the growth rate of strength are accelerated with the increase in temperature. Practice shows that when the construction temperature is above 5 ℃, the supporting plate can be installed within minutes after mixing.
When the construction site temperature is below 5 ℃, the installation time should be postponed appropriately. The construction sequence is as follows: firstly construct the middle bolt, then construct the side bolt, dig a row spacing for each row, install a row of bolts, and make the jacking bolt and the side bolt work in parallel as far as possible.
- According to the design requirements to excavate the roadway section, and then laid roof net, steel belt.
- Use a single bolt drill to push the anchor hole to the design depth, place resin coil inside the hole, super-fast coil at the bottom of the hole, medium-fast coil at the outer part of the hole, and then use the assembled bolt to send the coil to the bottom of the manhole.
- Lay the side net, set up the steel bar and the tray, tighten the nut with the plank hand, that is, complete the installation of a side bolt.
How to Install Roof bolts for Underground Mining
Construction tips for roof bolts install: from top to bottom, from back to front in turn.
- Clean the coal side to make it reach the design section size, and then determine the anchor hole position according to the design requirements.
- With the first hit the upper of the coal electric drill for bolt holes to design depth pack resin cartridge, the drill with connector and bolt, and start the drill, stirring side, until the bolt head to the bottom of the manhole, time is about 20 a 30 s, and then stop waiting for medicine curing, constraints, 30 s and then start the drill to tighten the nut, bolt installation. Lay the side net, set up the steel bar and the tray, tighten the nut with the plank hand, which is, complete the installation of a side bolt.
Anchor Cable Construction Tips
- Cut the steel hinge line according to the design length, remove rust and sludge (especially the internal anchoring section), install burr and retaining ring in the anchoring head section.
- Fix anchor cable hole position according to design requirement, use single anchor bolt drill, drill pipe and rotary bit to drill anchor cable hole to design depth.
- To hole placed resin cartridge, cartridge of super fast on the hole bottom, the medium cartridge placed outside the hole section, and then gently with the prepared steel strand pushing resin cartridge to the bottom of the hole, with stirring connector connect steel strand and drill, start the drill, stirring edge ahead, until to push resin cartridge to the bottom of the hole, such as back drill after 2 min, mixing connector, complete anchor cable anchorage.
- After resin anchoring and curing for 30 minutes, install jostles, trays and locks, and make them cling to the roof, hang tensioning, open the pump for tensioning, and observe the blasphemies of the pressure gauge, until pretension is designed, tension is stopped, jack is removed, and anchor cable is installed.
Test shows that rock bolt for mining roof with low initial anchor force cannot effectively control the displacement and deformation of surrounding rock. After the deformation, it only relies on the bracket of the net, beam and steel belt to prevent it from falling, which will increase the support cost. So by simply increasing the strength of roof bolt rebar, and neglecting to increase the primary anchor force, the strength of rock bolt rebar cannot be effectively exerted. Strictly control the mixing, solidification and waiting time of anchoring agent to ensure that the anchoring force meets the requirements of setting a standard, and the roles of composite beams and reinforced effect.
To make the anchorage rock bearing structure form as one structure, improves strata bearing capacity through changing the lower strata stress, effectively reduce the deformation of surrounding rock of roadway surrounding rock control early abscission layer, to improve the reliability of roadway roof support. After roadway excavation, the failure of surrounding rock gradually develops from the bottom to the roof, which shows that strengthening the support of the side walls plays an important role in the stability of the mining roof support. Prestressed rock bolt can effectively control the displacement of coal roof and the side walls. The higher initial anchor force of the rock bolt is main force to form “rigid” beam and “rigid” wall structure.
