MEASUREMENT OF STRESS OF ROCK BED BY BOTTOM-HOLE STRAIN METHOD

摘要

PURPOSE:To enhance the analytical accuracy of stress, by making the bottom- hole of a bore hole spherical and constituting a gauge from 16 elements. CONSTITUTION:A bore hole 2 is formed to a rock bed by drilling the same by a large caliber bit 1 through a rod 1' and the bit 1 is withdrawn from the bore hole at the point of time reaching scheduled depth. Next, a centering guide 3 is inserted into the bore hole 2 and a small caliber bore hole 5 is further drilled by a small caliber bit 4. Subsequently, when the small caliber bore hole reaches the scheduled depth, the bit 4 is pulled off and a convex pin 6 is inserted into said bore hole 5 to polish and shape the bottom-hole into a concave spherical surface shape. Then, the convex pin 6 is removed and a 16-element strain gauge 9 is adhered to the bottom-hole through an adhering machine 8 having a rotary degree measuring instrument 7 mounted to the rear part thereof. After the adhering machine 8 and the centering guide 3 are withdrawn from the bore hole, the large caliber bore hole 2 is extended by the large caliber bit 1 to perform over-boring.