Geognostic tests database

The project of a geognostic database concerning the whole regional territory of the Plain has been accomplished in order to make available underground geological data. These data are aimed to support the preparation of the new Geological Maps of the Plain to the 1:50,000 scale, which the Emilia-Romagna Region is realizing as assigned by the National Geological Survey (CARG Project). A huge amount of technical-geological data was already available in many and fragmented files of both public and private properties. They were collected to support investigations of different nature.

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Fig.1 Distribution of the geognostic tests (click on the image to enlarge it)

The first phase of work was to begin a large collection of existing data disseminated all around the regional territory of the plain, meanwhile organizing a database framework suitable for the storage of collected data.

The collection of the already existent data and their loading in numerical files have been done by geologists directly selected by the Emilia-Romagna Region or by single Provinces, some of those have been actively participating to the project through agreements of collaboration.

The Database implementation is always in progress, since the Emilia-Romagna Region directly make continuous core drillings and penetrometric tests in all the territories presently under study for the Plain Geological Map.

These tests are also included into the same files and contextually managed.

The Geognostic Database covers the whole regional territory of the plain. The distribution of the data already available within the regional territory of the plain is shown in fig. 1.

Reliability and validation

In general, the reliability of each retrieved datum cannot be defined a priori. In fact, a poor descriptive detail of an underground log does not necessarily involve a low reliability of the stratigraphic definition. Only the underground stratigraphic model and an integrated geologic study can allow a real and reliable action of Database validation on the whole.

The superficial and subsurface maps realized since now made a large use of these data showing their internal coherence, even though with some obvious and unavoidable deficiency or wrong usage.

It is important to underline that the new tests realized by the Emilia-Romagna Region confirm the overall geological setting inferred by the study of data retrieved from other files.

Assuming as highly reliable the lithologic descriptions made by the geologists of the Geological Office on continuous core logs directly realized by the Emilia-Romagna Region, and having by now a large amount of case studies in the different geographic and sedimentologic contexts of the Emilia-Romagna Plain, some general considerations can be done about the terminology used in the well logs descriptions retrieved from other files:
- for coarse deposits there is a substantial terminological correspondence among all types of tests;
- for fine deposits there are evident differences between water wells and soundings. Generally, the distinction between different lithologies is arduous.
The terms "clay" and "earth" are generically used in the water wells to include most of sediments with fine granulometry; in both continuous core and destruction logs the term "clay" is used properly, but the silty fraction is almost never distinguished.

There are no doubt that the primary objective of a water well is the detection of the groundwater intervals (therefore those with coarse grain size), and that the distinction in a working site between clay and silt is not so easy for technicians who are not geologists.

In conclusion, the tests retrieved from other files (which are about 80% of total amount) allow underground stratigraphic reconstructions more detailed and homogeneous concerning the coarse bodies, while leaving an uncertainty margin even quite large in recognizing and correlating bodies with finer lithologies.

For detailed geologic studies of the first meters of subsurface water wells are often not utilized; they become important for the recognition and the cross-section correlation of the main sedimentary bodies of marine origin.

Concerning the penetrometric tests retrieved from other files, the resistance curves of the first meters of subsurface result hardly interpretable, thus rarely used to recognize shallow or semi-outcropping bodies.

In general, the penetrometric tests allow to recognize the main textural contrasts within the crossed layers and to detect their different physical state as far as the consolidation. This information is often useful to recognize the different depositional environments.

Database content

Since November 2011 the Database includes 62.561 tests, subdivided as in the following table:

There are two necessary conditions to be satisfied since that the test could be included in the Database:

- the possibility of a reasonable precise localization on the Regional Technical Map;
- for all wells and soundings: the presence of an original lithological description;

for all penetrometric tests: the presence of original logs.

A paper file parallel to the numerical file is organized. It is composed by the Regional Technical Maps with all the localized tests and by the copies of original documents retrieved or available for each test (logs for the penetrometric tests, lithological description for wells and soundings, laboratory tests eventually available, excerpts of cartography used for localization).

As general orientation, during data loading, most indications deducible from paper data have been included into the files, avoiding any interpretations.

Geognostic tests made by SGSS are available for download in the Webgis cartographic website.