Many sites have geologic structures (plutons, karst geology, sand channels, etc.) that do not lend themselves to description within the context of hierarchical layers. For these sites, GIK offers the ability to build extremely complex models with a minimum of effort (and virtually no interpretation) on the part of the geologist. GIK can also be a useful check of geologic hierarchies developed for sites that do lend themselves to a model based upon hierarchical layers.
GIK uses the raw, uninterpreted 3D borings logs in the form of a .pgf (pre-geology file) as the input. Consecutive integer values (e.g. 0 through n-1, for n total observed materials in the site) are used to describe each material observed in the entire site.
NOTE: It is recommended to start your material ID numbering at zero (0) instead of 1.
Usually, materials are numbered based upon a logical classification (such as porosity or particle size), however the numbering can be arbitrary as long as the numbers are consecutive (don’t leave numbers out of the sequence). For the example given above, we could number the materials as shown in the figure below (even though it is not a numbering sequence based on porosity or particle size).
For a .pgf file, borings that do not see the clay (material 1 in the figure) would not need to consider the sand as being divided into upper and lower. Rather, every boring is merely a simple ASCII representation of the raw borings logs. The only interpretation involves classification of the observed soil types in each boring and assigning an associated numbering scheme.
As an example, we have taken the five material geologic data and created a model using both methods. This is a moderately complex site with geology that can be represented reasonably well with hierarchical layering. However the complexity at this site does require a significant amount of interpretation (by a geologist or analyst) that lends a subjective element to the resulting model.
The interpretation was performed interactively using the make_geo_hierarchy module in EVS/MVS. A display of 5_material_complex_geology.pgf using post_samples is shown in the figure below.
The application that was used to display the borings is shown in the figure below.
Note that there is a significant difference in the depths of some of the borings. Most notably, AW-3 (right foreground) is much shallower than the rest and is located quite a distance from any neighboring borings. With both techniques, extrapolation of the geology to the region below AW-3 will be low confidence and we expect that the two methods (Geologic Hierarchy and Geologic Indicator Kriging) will yield different results.
However both techniques should (and will) result in the same layering in the vicinity of the borings. This is a common theme in EVS for both geology and chemistry data. EVS will honor your measured data.