A Case Study of Thaumasite Sulfate Attack in Tunnel Engineering
Table 5
Identification results of core samples of the surrounding rock.
No.
Test items
Test results/descriptions
1
Name of rock sample
Anhydrite rock
2
Naked-eye observation on color
Grey-white
3
Sample preparation
Thin slice
4
Structure
Fibrous structure, metasomatic residual structure
5
Tectonics
Bedded
6
Identification basis
GB/T17412.1
7
Essential mineral
90% gypsum
8
Secondary minerals
4–6% dolomite and 4–6% anhydrite
9
Accessory mineral
Zircon
10
Microscopic observation
The rock has a bedded tectonics, a fibrous structure, and a metasomatic residual structure. Gypsum is fibrous. The protrusion is low and negative, and the highest interference color is first-order yellow and white, and is arranged in a directional arrangement. Anhydrite is columnar, and most of it is converted into gypsum, and a small amount of residue can be seen in the center of the crystal. The protrusion is middle and positive, the highest interference color reaches third-order green, and it exhibits parallel extinction and polysynthetic twin development with a directional arrangement. Dolomite has an allotriomorphic granular structure with a particle size distribution of 0.005–0.02 mm, and it has a prominent twinkling and high-order white interference color.
