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Infrared Thermography and Fracture Analysis of Preferential Flow in Chalk

The Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK 1350 Copenhagen K, Denmark

View larger version (73K): [in a new window]   Fig. 1. Location map of the Sigerslev site with location of walls for infrared thermography (IRT) and wells for detailed IRT investigation. Additionally, a water table elevation map of the study area is presented.

View larger version (115K): [in a new window]   Fig. 2. (a) The tectonic setting in the Danish Basin. The dextral (right lateral) displacement along the faults delineating the tectonic block where Sigerslev is situated is indicated with red arrows. (b) Tectonic model showing the expected fractures formed within the given stress regime prevailing in the Stevns block (Hobbs et al., 1976): two sets of conjugated shear fractures, one set of extensional fractures, and one set of extensional fractures related to stress release.

View larger version (29K): [in a new window]   Fig. 3. Relative water table fluctuations and water temperature in Well I and Well II while injection tests are performed in Well I and Well II, respectively. The reference level for the water column is approximately 10 m below sea level.

View larger version (26K): [in a new window]   Fig. 4. Fracture analysis of vertical fractures. (a) Rose diagram (showing orientation and frequency) of all vertical fractures measured in the Sigerslev Chalk Quarry. (b) Rose diagram of vertical fractures with estimated trace length, grouped into multilayer fractures and single-layer fractures. (c) Rose diagram of vertical fractures registered for staining, with staining, and without staining. (d) Diagram showing orientation of hydraulic active fractures in the bottom of the quarry.

View larger version (28K): [in a new window]   Fig. 5. Image logs from Well I and Well II, indicating fractures, flint layer, and the water table in the two wells. The strike/dip of the fractures in the two wells are represented in Wulff nets.

View larger version (51K): [in a new window]   Fig. 6. Thermographic images of two corners in the chalk quarry seen from southeast. The upper image shows Level A (5 to 20 m), and lower image shows Level B (–20 to 0 m). The images are taken on a cold winter morning with the relatively warm groundwater seeping out on the cold wall surface.

View larger version (110K): [in a new window]   Fig. 7. Thermographic image series illustrating the temperature changes with time of the south-facing wall by the lake in the quarry (Level B, Fig. 6) under injection of cold water in Well I (Test 1, upper image series) and Well II (Test 2, lower image series).