The triassic and jurassic layers in the Jura Mountains show often a heavy swelling potential. They contain clays and sulphates as a reason for swelling. It is the intention to simulate the swelling processes with cores out of the Belchen Tunnel (N2) in the laboratory for a better understanding of the phenomenon and their geological conditions as well as the possibility to influence the swelling by technical means.
The crucial objective of the project is to detect the operations on swelling of clay minerals and sulfate rocks depending on the geological situation and comparing the results with practical experience from the underground.
Further objectives of the project are:
- to understand the phenomena of swelling,
- to understand the dependency between sulphates clays
- to compare the laboratory results with the results obtained on the ground in tunnels Jura taking into account the regional geology.
Following basic conclusions arised of the project:
In rocks containing a sizable amount of clay minerals, swelling is due to the incorporation of water in the crystal lattice of specific clay minerals. The partial amount of these minerals in the total rock determines the degree of swelling or,alternatively, the pressure potential which may amount to up to 2.5-3MPa. This process is reversible.
If the rock, in addition, contains anhydride, swelling is considerably augmented because of the crystallization of gypsum. As a result, pressures of up to 7 MPa may be attained. Rocks consisting of pure anhydrite that is devoid to clay, as a rule, do not exhibit swelling. If, however, clay minerals are present, their swelling may crack the otherwise dense anhydrite with the ensuing accessibility for water capable of dissolving the sulfates. Moreover, due to their ability to retard water percolation because of their adsorptive power they help increase gypsum crystallization. Gypsum swelling is irreversible under natural conditions and in experiments performed in rock mechanics laboratories.