Video Log of Soil Boring

Narrated video log of soil boring. To understand how ground water flows through the sequence of deposits beneath the site, it is essential that I - the field geologist - understand the site geology. It's the same for understanding the nature and distribution of the geotechnical properties. Why? Because it is the geology that determines the what the sequence of deposits is beneath our site and what properties the deposits have.

Understanding the site geology requires more than just identifying clay, silt, and gravel. It requires more than just identifying the permeability intervals.

Understanding the site geology requires me to understand how and why the clay, silt, and sand were deposited, which is dependent on my ability to recognize sedimentary processes and depositional environments in the soil core.

As I examined the core, I'm able to interpret the depositional environments based on consideration of the (1) the nature of the sedimentary structure (bedding, grading, or lack of it) of the deposits, (2) landscape position relative to a nearby stream, (3) geomorphic setting, and (4) soil classification (which is an indicator of grain size and grain-size distribution), (5) the regional geologic model (which identified the kinds of depositional environments that occurred in this area through time). Knowing the depositional environments of the sedimentary sequence has enabled me establish the site-specific stratigraphy in the core. From that, I can now evaluate a number of questions that will lead to establishing a creditable Conceptual Site Model.

Here are questions regarding my understanding of the depositional environments for the different deposits underlying the site based on the primary depositional properties of the deposits:

- Can deposits of particular depositional environments be subdivided because of differences in important properties?

- What does understanding the depositional environments indicate about the geometry, thickness, scale, and probable lateral continuity of individual units across the site? Are they likely to be sub-horizontal or dipping? If dipping, what do we need to be aware of in correlations between borings? Were any deposits made in channels and only present where a channel was located beneath the site? Are any deposits just lenses rather than laterally continuous units? What bounds any lenses below, above, and to the side?

- What does the sedimentary structure tell me about bedding patterns and preferential lateral ground water movement?

- What does understanding the depositional environments indicate to us about the lateral uniformity or variability of particular deposits across the site?

- What unit(s) could serve as marker beds in the sequence?

- What coarser grained deposits are present in the sequence? Is there any evidence that they laterally continuous or are they lenses?

- What coarser grained deposits in the sequence are likely to have lateral ground water flow whereas what finer grained deposits in the sequence are likely to exhibit vertical groundwater seepage?


Weathering causes secondary changes to the properties of deposits. Is there evidence that some of the deposits underlying the site have been weathered after they were deposited? What secondary changes have taken place and what is their significance on ground water flow?

- What weathering zones are present?

- What do the oxidized colors of OU weathering zone tell me about the water table and dominant ground water flow direction?

- What do the reduced colors of the RU, MRU, and MRJU weathering zones tell me about ground water occurrence and movement?

- What does the color of the unoxidized UU weathering zone indicate about the diamicton and underlying glaciolacustrine facies?

- Do the secondary carbonate accumulations along some bedding planes impact small- or large-scale preferential ground water flow?

- Sediments are not deposited with joints and fractures. Fracturing is the result of secondary processes. Fracturing occurs during the weathering of finer grained deposits above the water table by desiccation. Desiccation (shrink-swell) causes the sediments to shrink and develop secondary fractures, joints. My analogy is my garden when it dries out in the summer and the surface cracks that develop in the shrinking mud. Those are the kind of fractures. The fractures that develop in finer grained sediments as they weather above the water table have the same geometry and develop by the same process as mud cracks. Are there weathering zones in the site sequence where desiccation and joint (fracture) development occurred?


How has my determination of the site stratigraphy and the evaluation of the primary sedimentary structures and secondary weathering effects helped establish a creditable Site Conceptual Model? How can I best illustrate the Conceptual Site Model with stratigraphy that gives context to soil classifications, unit scale and orientation, unit uniformity or heterogeneity, and depict the effects of secondary weathering?

Any and all insights/suggestions are welcome.