The significance of in situ tests on large rock specimens

Abstract This paper reviews large scale in situ tests on rock conducted throughout the world. Based on the authors' experience of 8 years of in situ testing involving 66 large coal speciments (up to 2 m in width and height and with width-to-height ratios from 0·5 to 3·4 ), the value and meaning of large scale in situ tests in compression are discussed. Practical guidelines are given for performing the tests, preferred testing techniques are described and typical data to be expected from the tests are listed. Empirical formulae are derived for the presentation of strength results and application of large scale test data to engineering design is demonstrated. It is also shown how the results of such tests can be directly applicable to predicting the behaviour of full size rock structures. Finally, the costs of large scale tests are considered, in terms of both time and money, and actual figures are quoted. It is concluded that large scale in situ tests can be an invaluable aid in engineering design and that their costs constitute a very small percentage of the value of production from an average mine and that the costs of tests are more than offset by the financial returns and technical gains obtained from large scale in situ tests.