A good understanding of the subsurface distribution of rock properties and its uncertainties are important elements in the development of safe and economical geo-engineering projects. The aim of this paper is to describe the steps to be followed in order to construct a comprehensive model of the rock mass. A brief review of the main elements of 3D geological and geomechanical modeling is presented followed by a discussion of the main tools available for applications to rock engineering. One case history that describes the evaluation of rock mass conditions for a powerhouse excavation in a metamorphic environment is presented. Geostatistical techniques were used to construct a model of rock fracturing and rock mass strength throughout the building area. After the excavation the rock model was compared with conditions displayed by the actual rock mass.
The study and understanding of a complex environment of difficult access, the subsurface, has always been a challenge and the objective of geoscientists and some related fields, like geotechnical, mining and petroleum engineering. Engineering works are designed and investments are secured based primarily upon site characterization. Therefore, good site characterization, with distribution of rock properties and its associated uncertainty, is of fundamental importance for the decision process and management of geo-engineering projects. Traditional geotechnical engineering works are usually based on 2D representations of data between boreholes (the so-called geotechnical cross-sections). These cross-sections are not able to fully represent the global distribution of properties on the subsurface though carried out by highly skillful geologists. Industries like oiland- gas and mining, on the other hand, use sophisticated 3D modeling techniques to predict subsurface property distribution and its associated uncertainties, a process called 3D geological characterization . The geological characterization comprises actions for the acquisition and interpretation of data from different sources and scales combined with a 3D representation and hierarchical importance for developing a model. The modeling procedure was first used in the mining industry and later was adapted and improved by the oil-and-gas industry, which introduced the concept of Common Earth Model or Shared Earth Model. The construction of these models depends very much upon the existence of cross-disciplinary teams in order to unite the knowledge of different areas . Following the examples of these industries, the geotechnical community has made some efforts to change the traditional practice. Recently, many studies that employ this technique to develop 3D models for site characterization have been published [3–7]. This process, however, has evolved slowly, because civil engineers argue that the costs to develop these models are too high . An explanation about geological and geomechanical elements involved in the model build up process is presented and one case history is described to illustrate the proposed workflow.
The first step during the development of a 3D earth model is to define the final objective, i.e., what are the models for? Who are they for? . Once the final objective of the model has been defined, data requirements and their collection procedures can be established.