Abstract
Rock mass classification is important in preliminary design of geotechnical engineering projects. Using the columnar jointed basalt at the foundation of Baihetan Hydropower Station as an example, this paper presents a classification scheme of the columnar jointed rock. Unlike many common rock masses, an obvious characteristic of columnar jointed rock is that it is discontinuous in geometry while continuous in mechanics. Due to the inapplicability of existing rock mass classification systems, a classification scheme, combined with rock mass integrity, weak plane tightness, and permeability, is proposed. The new classification system has five grades with quantitative factors, which takes into account the features of columnar joints. As an easy-to-use scheme and case study, it would be helpful as a reference in the rock mass classification of similar problems.
Highlights
Columnar jointing is a typical fracture pattern, best known from such locations as the Giant’s Causeway or Fingal’s Cave, in which cracks self-organize into a nearly hexagonal arrangement, forming an ordered colonnade [1, 2]
Due to the cuts of joints, the value of rock quality designation (RQD) is quite low, and it will be identified as fragmentized rock mass using existing rock classification methods [19, 20]
The objective of this paper is to propose a classification scheme for columnar jointed basalt based on a comprehensive understanding of its properties
Summary
Columnar jointing is a typical fracture pattern (shown in Figure 1), best known from such locations as the Giant’s Causeway or Fingal’s Cave, in which cracks self-organize into a nearly hexagonal arrangement, forming an ordered colonnade [1, 2]. As a kind of adverse geologic condition, a reasonable and suitable rock mass classification is extremely important for engineering projects. With the booming development of the water conservancy and hydropower projects, more and more complicated engineering geological conditions, such as columnar jointed rock, are encountered. The seismic velocities Vp are high and the rock strengths are high in certain stress states. It has typical characteristics of discontinuity in geometry and continuity in mechanical properties. A case study on columnar jointed basalt is conducted; the results may be extended to other similar cases or used as reference for other engineering projects
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