GEOMETRIES OF ROCK DEPOSITS
Geomtetries are presented with air photos of the surface and three dimensional illustrations of the three dimensional complexity. The photos are grouped by rock type and structure (for sedimentary rocks). The air photos show the surface variability better than a graphical description or an autocorrelation function. Shapes and context of the deposits can be seen directly in the photographs. Three dimensional sketches demonstrate the vertical geometry that , while not visible from the photograph, is intimated from the surface landform and its association with a particular geologic transport process.
To enhance the visibility of the differences in rock type and depositional geometry, the photos will be presented in both single photo and stereo pair. The stereo pairs are colored and offset so that use of blue and red filter lenses will display the images in 3D as anaglyphs. These glasses are inexpensive. They cost less than $0.50 and single pairs are available from the GeoEnvironmental Source for free after registration. For larger quantities please contact American Paper Products, (800) 767-8427. They send out free sample packages for consideration.
Initially many of the photos have been taken from the collection at Northwestern University that remains from the time that the Cold Regions Research Engineering Laboratory was located on campus. It is the intention of this project to add geologically significant photographs from other collections. These photos are almost all at a scale of 1 to 20,000. To eliminate any confusion, eventually each photo will carry a bar that is 30 m (100 ft) long. It should be recalled that 30m is a typical horizontal autocorrelation distance for soils as reported in Table B4 in the discussion of variability. By comparing the size of the features with the bar, it is possible to gain some sense of the scale of the change in properties.
In addition and where possible, cases will eventually include reports of boring logs, RQD, etc. to demonstrate the spatial variability of the parameters within relatively homogeneous strata. While not all cases are complete, it is anticipated that over the next few years the collection can be expanded through contribution. The scheme for contribution will be discussed in a separate section.
Most importantly the air photos, stereo pairs, 3D illustrations, and property measures should be integrated to establish a "prior" geologic model of a site. In the context of this module, the prior model is that of the location of the subsurface boundaries of layers, lenses, veins, strata, etc. Variability of properties within these homogeneous zones is discussed in detail in the geostatistics module.