INTRODUCTION

ABSTRACT:

This paper traces the evolution of rock reinforcement design in mining and tunneling. In the late 1940's and early 1950's, the first true design methods -as opposed to simple pinning of loose materials -used suspension load carrying concepts. Next, the beam and friction approach to optimize fiber stresses in roof beams was developed. Later methods, in the middle to late 1950's and 1960's, relied upon rock arch development, confining stress maintenance and shear reinforcement, and rock arch thrust capacity. Theoretical approaches were developed, beginning in the 1930's but peaking in the 1960's and 1970's, such as the "ground reaction curve," using the changing stiffness with time of the deforming rock mass and the supplied reinforcement or support to optimize the reinforcement effort. Empirical methods arose as more experience was gained and the subsequent methods used ratios of span to bolt length, ratios of mined height to bolt length, calculation of the equivalent support pressure, and rock mass ratings with stand-up time and bolting needs estimation from pure empirical findings or through roof loosening estimates. Physical models were also used. Numerical modeling was developed in the late 1960's which allowed incorporation of rock reinforcement elements in twoand three-dimensional models of excavations. In the early 1980's, the keyblock concept evolved for identifying and reinforcing the "keystone" block in an arch or wall of fractured rock, minimizing reinforcing requirements. The evolution of rock reinforcement design from early suspension and beam and friction concepts, to rock arch maintenance and modeling all have the common thread of helping the rock mass to help itself as a support. Future challenges lie in characterizing the rock mass appropriately and realistically.

The construction and excavation of mines and tunnels was practiced in antiquity, and the tendency of the rock mass to collapse upon excavation or some time after was well-appreciated, with timber supports or rock block supports being used to minimize roof collapses. Mine and tunnel timbering became a well-developed technology, with texts on the subjects such as Peele & Church (1918) in mining and Prelini & Hill (1901), going into great detail as to how to size and proportion timbers or steel members based upon expected loosening loads. This has persisted to modem times, with the author himself as a management-trainee miner being part of a crew setting 12-inch by 12-inch timber sets in a mine in 1971.

The importance of tensile reinforcement in brittle materials was understood in ancient times with the Biblical Book of Exodus account of "you can not make bricks without straw." Modem reinforced concrete was developed by Lambot about 1850 in France, exhibited in the Paris Exposition in 1855, and patented the same year (Tumeaure & Maurer, 1907). The clever, well-traveled, and well-read mining engineer, it can be speculated, may have realized the benefits of this technology in rock. For, in 1918, the first known published report of rock bolting was made in Prussia for coal mining in Silesia (now Poland) (cited in Thomas, 1959(.9)). Woodruff (1966) reports un-published applications in the United States in 1917 in the Sangamore Coal Mine of Pocahontas Fuel Company in Illinois, in the 1920's at the Homestake Gold Mine in South Dakota, and in the 1920's in the Gilman Zinc Mine in Colorado.

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