ABSTRACT:

High horizontal stresses can cause numerous ground control problems in mines and other underground structures ultimately impacting worker safety, productivity and the economics of an underground operation. Mine layout and design can be optimized when the presence and orientation of these stresses are recognized and their impact minimized. A simple technique for correlating the principal horizontal stress direction in a sedimentary rock mass with the preferential orientation of moisture induced expansion in a rock sample was introduced in the 1970s and has since gone unused in practice. This procedure was reexamined at a proposed mine site near the original White Pine Mine in White Pine, Michigan in order to validate the original research and to consider its usefulness in mining and civil engineering applications in high horizontal stress conditions. This procedure may also be useful as an economical means for characterizing regional stress fields.

1. INTRODUCTION
1.1. The importance of horizontal stress in underground structures

The importance of horizontal stresses in the stability of underground structures was first reported in the mid 20th century. Horizontal stresses were found to be the cause of numerous and otherwise poorly understood ground control issues in mines and quarries throughout the world [1]. Sudden fracturing, rock bursting, floor heave at shallow depths, compressional roof failures, roof falls in consistent directions, cracking of concrete tunnel linings and wall movement of unsupported excavations at depth [2] were seen as evidence that high horizontal stresses, when present played an equal, if not greater role in mine stability than the vertical force of overburden alone. It has also been shown that high horizontal stresses remain at depths greater than any that are currently mined today [4] but that the ratio of horizontal stress to vertical stress is largest within the first 450m (1,500’) of depth [5].

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