Ingenieurgeologie aufgelockerter Granite Verwitterung und Auflockerung — Einführung und Versuch einer Klassifikation

Summary

The degree of disintegration of rock masses and rock materials defines their use in construction foundations, excavations, underground cavities as well as the extraction of construction materials. Within the framework of the research programme “Engineering Geology” of the German Research Society (Deutsche Forschungsgemeinschaft), an interdisciplinary working group at Karlsruhe University investigated various aspects of weathering and disintegration of granitic rocks. One of the primary objectives of this research project was to quantify disintegration and its effect on the geotechnical properties of such rocks.

In light of the results obtained, it seems necessary to distinguish between mechanical disintegration and chemical alteration. In addition, it is appropriate to differentiate mechanical disintegration in regard to its macro- and micro-scale features, that is the system of discontinuities in a rock mass as opposed to the fabric of micro-fractures in the rock material.

Two tables of characteristics, used to determine the extent of mechanical disintegration and chemical alteration of rocks, are proposed for a general field Classification. These tables allow Classification on the basis of 10 characteristics for both the rock mass (table 1) and the rock material (table 2) with average numerical values between zero (indicating no sign of disintegration or decomposition) and five (representing completely disintegrated and decomposed material). Certain stages of weathering (“W 0” to “W V”) D are also recommended for usage in conjunction with these numerical values.

In addition the degree of weathering or disintegration of granites can be expressed quantitatively using three diagnostic characteristics:

• a) frequency of joints in rock mass

• b) frequency of micro-fractures in rock material

• c) extent of chemical weathering (proportion of newly formed clay minerals in rock material)

The relative importance of these three characteristics may vary depending on the application. Therefore a general system, classifying degrees of weathering with a quantitative scale based on a), b) and c), seems not very useful. Such a general Classification system should be restricted to a more qualitative and general description of a rock mass, as previously described.