1. Field of the Invention
This invention relates to a method for installing a rock bolt in geological strata and to a package containing resinous material for practicing the method.
2. Description of the Prior Art
Rock bolts of roof bolts are employed in mining operations and elsewhere to maintain geological strata in alignment and to support such geological strata. Such rock bolts are installed in a bore hole which is drilled into and through the geological strata, usually at an angle with respect to the geological fault lines of the strata. Some rocks bolts are provided with mechanically expandable anchoring devices at the forward end, within the bore hole, for retaining the rock bolt rigidly within the bore hole. Sometimes an inorganic cement has been introduced into the bore hole to assist in retaining the rock bolt, U.S. Pat. No. 2,682,152. Rupturable packages containing inorganic cementitious materials have been employed in the bore hole, U.S. Pat. Nos.: 4,126,003, 4,126,005, and 4,127,001. Packages containing the cementitious material are ruptured by the rock bolt which is agitated to mix the cementitious ingredients; thereafter the rock bolt is retained in place until the cementitious material hardens and retains the bolt. Organic polymerizable resinous materials such as epoxy resins, polyurethane resins, unsaturated polyester resin syrups have been employed in rupturable containers in a similar fashion, U.S. Pat. Nos.: 3,618,326; 3,302,410; 4,211,681; and 4,136,774. These hardenable materials are generally identified as grouting materials in the rock bolting art. The organic polymerizable resins are preferred because of the speed with which they gel and harden to secure the rock bolt in its bore hole; because of their ease of mixing within the bore hole; and because of their acceptable storage life prior to use. Such compositions customarily include two reactive ingredients which are provided in a common package having two compartments separaed by a rupturable barrier. The organic polymerizable resinous materials are considerably more expensive than the inorganic cementitious materials. The organic polymerizable resinous materials are customarily blended with inexpensive, inert finely divided filler substances such as sand, silica and the like. The organic polymerizable resinous materials normally experience a shrinkage upon cure which can be a disadvantage in their use. Use of expandable resinous compositions has been proposed to overcome the disadvantage of the characteristic shrinkage. For example, in U.S. Pat. No. 4,136,774, the use of ammonium bicarbonate and sodium bicabonate is proposed for the purpose of generating a carbon dioxide gas to foam the resinous material. Low boiling point liquids have been considered but rejected. The combination of unsaturated polyester resin with diisocyanate and polyalcohol or castor oil is described for generating expandable resinous compositions. A need for significant expansion of the grouting material upon cure is recognized in the same U.S. Pat. No. 4,136,774 where geological faults or fissures can result in an unstable anchoring for the rock bolt.
What is required in a roof bolt grouting composition is expansion of the composition during cure; suitable shelf life; relatively low cost; adequate structural properties after expansion in order to retain the rock bolt in a firm anchor; and facility in usage.