FUNDAMENTALS

strata control

 

Strata Reinforcement

   

Cement and Resin Reinforcement
 

Strata Reinforcement

Cement and Resin Reinforcement

The reinforcement of strata by injecting various types of resin or cement material into it is now routinely adopted in adverse ground conditions. It is usually quite a slow process and some resins can be a health hazard requiring personnel access to be restricted during pumping. Therefore their use cannot be incorporated into the normal mine development process.

The main use of this type of reinforcement is to pre-grout strata where stability problems are predicted e.g. where geological structures are expected, or to grout around areas where a major failure has already occurred to assist in recovery of control. The latter method is quite common where the roof has been lost on a longwall face.

The reinforcement process involves drilling into the strata then pumping the resin or cement material into the hole under pressure, forcing the material into any spaces in the strata and gluing it together. Some of these materials form a high expansion foam which also creates its own pressure thereby improving penetration of the strata.

At times these materials are used to fill a cavity where a major failure has occurred. In such cases they are not being used so much to reinforce the strata as to replace the strata so that operations can recommence.

Care is need in the use of these materials as:

  • The pressure applied during injection of grouts can itself cause strata failure.

  • Resins generally are a two part mix and the chemical reaction is exothermic. Fires have occurred during placement. There are usually restrictions on the amount of resin which can be pumped into any one hole and they are not suitable for placing in bulk in cavities.

  • Some resin materials are carcinogenic before the reaction has taken place so access to work sites and on the downstream ventilation side is restricted.