This work explains the development of a so-called rock mass system performance map, that provides a backdrop to assist in performance interpretation. The rock mass system performance maps presented in this paper are 2D graphical devices prepared using Sammon mappings, Learning Vector Quantisation, Self-Organising Topological Maps and combinations of these mathematical techniques. Using supervised or unsupervised learning methods, these algorithms project and partition high-dimensional vector spaces, of a dimension equal to the number of environmental and rock mass condition parameters considered, into 2D categories of rock mass condition. In providing 2D renderings, the techniques aim to preserve properties of the characterising vector space such as adjacency of states and topology. The condition of a rock mass can be ‘plotted’ on that map by identifying its k-nearest neighbours and interpreted relative to stability metric categories. Should the defining vector space include rock mass properties or environmental parameters that are repeatedly measured, or possibly continuously monitored, then the rock mass condition marker traces out a performance trajectory across the performance map. An example of rock mass performance map synthesis and use is presented.
The ultimate objective of the work reported in this paper is to show how the performance of rock engineering systems may be characterized with an instance of a state vector formed from the values of rock mass properties and geomechanical environmental factors. It will then show how these may be plotted on partitions of complete real valued vector spaces with dimension equal to that of the defining state vector, mapped or projected into a 2D charts of practical utility.
By ‘rock engineering system’ we refer to specific application domains of geomechanics for engineering purposes in the same sense conveyed by Hudson [1], exemplified by rock slopes, rock foundations, and underground excavations in rock masses, whether these be created for civil or mining engineering or other similar purposes. In using the term ‘rock properties’ we do not necessarily refer only to mechanical properties of the rock material, but take the term to generalize to mechanical properties applying to rock masses incorporating the DIANE concepts articulated by Hudson and Harrison [2] at varying engineering scales, as well as those mechanical properties resulting from introduction of stabilizing elements that render a composite rock mass engineering material. By geomechanical environmental factors we refer to the physical fields the rock engineering systems may be subjected to, depending on location, time and application. More specifically these could be exemplified by the stress field, water flow field, and temperature field, represented in the coupled thermo-hydro mechanical conceptual frameworks formulated by Hart & St John, [3].