Anchor bolt installation method
An improved method of installing tensional anchor bolts or cable bolts into a geological or man made formation by preheating anchor bolts or cables prior to inserting them into a borehole, mixing the bonding material within the borehole by rotating the bolt and allowing curing of the bonding material prior to the cooling of the bolt, thereby placing the bolt under tension and the formation into compression, is provided. 1. A method for anchoring a bolt under tension in a borehole comprising the steps of:(a) introducing a curable bonding material into a borehole wherein said material is compartmentalized prior to introduction to prevent curing;
(b) heating a bolt to a temperature at least 40กใ C. above ambient temperature prior to insertion into said borehole;
(c) inserting and rotating the heated bolt into the borehole thereby mixing the components of said bonding material; and
(d) keeping the bolt stationary for a time sufficient to allow the bonding material to reach minimum cure strength; said time sufficient for the curable bonding material to reach minimum cure strength being less than the time needed for the bolt to cool by 15% of the temperature above ambient temperature to which it had been heated prior to insertion into the borehole.
2. The method of claim 1 where the bolt is an anchor bolt or a cable bolt.
3. The method of claim 1 wherein the curable bonding material is selected from cementitious grout and crosslinkable multi-component organic systems.
The present invention relates to an improved method for installing a resin-grouted anchor bolt in a borehole, and, more particularly, to an improved method of quickly securing an anchor bolt or cable in a borehole using a settable bonding material. The improvement comprises heating the bolt to a temperature at least approximately 40กใ above ambient temperature prior to contacting the bolt and bonding material during the installation procedure whereby curing is accelerated, and the bolt is placed under tension without mechanical torquing.
In the art of bolt anchoring systems, and especially in mine roof support, it is well known how to tension bolts by the use of a shell-type, plastic or metallic-sleeve mechanical expansion system with and without resin. Non-mechanical anchor bolts of the type which are installed with a settable bonding material are normally placed under tension after the bonding material has reached a predetermined initial cure strength by torquing a nut or a bolt on the exposed bolt end. Popular bonding materials; e.g., polyesters, epoxies, and other known commercially available synthetic resins, are typically provided in packages in which the resin and a catalyst for the resin are separated by a package film or reacted zone of the resin. During normal installation when the anchor bolt, or anchor bolt assembly, is forced into a drilled borehole which already contains the resin/catalyst package, the bolt breaks the package and then mixes the resin and catalyst as it is rotated from 30 to about 100 revolutions at a rate of 150 rpm to 1200 rpm. At ambient mine temperatures, which can range from 3กใ to 35กใ C., the elapsed time from insertion of the bolt until the resin reaches a satisfactory cure strength and can be torqued into tension can range from 14 seconds up to about 60 seconds.
Another method of securing a bolt or cable utilizes cementitious materials. Cementitious materials, packaged for water soaking or pumpable, are used in securing bolts and cables in various geological strata.
Packaged cementitious materials are soaked in water prior to inserting into the borehole. The bolt or cable is then installed through the cementitious material. Alternatively, the bolt or cable is installed first followed by pumping the cementitious material into the hole to grout the system.
U.S. Pat. No. 4,353,463, issued Oct. 12, 1982 to R. W. Seemann, discloses a cartridge assembly of a multicomponent curable system for use in anchoring bolts into solid structures wherein preheating the cartridge and/or the bolt can reduce reaction time. In such a system, the resin curing time is less than the bolt warming time and, therefore, the bolt goes into compression and the solid structure goes into tension. There is a need to achieve the opposite effect, that is, for the bolt to go into tension and the solid structure to go into compression. To achieve that, there is a need for a system where resin curing time is less than bolt cooling time.
