Chapter 4: Soil and Bedrock Logging
Anchor: #CIHBDBDFSection 1: Logging
Anchor: #i1020355Material Order of Description
Keep core descriptions as simple as possible. The order of description is as follows:
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- Material Anchor: #FMODBRNK
- Density or consistency, hardness Anchor: #YHJIBYNR
- Moisture Anchor: #AKOJXJJT
- Color Anchor: #AMHTLUXL
- Cementation Anchor: #ILEIRNQU
- Descriptive adjectives Anchor: #VPGVMGLP
- Unified Soil Classification System Anchor: #WITIJELV
- Rock Quality Designation (RQD), percent recovery
Material
Keep the number of strata to a minimum. Remember that every small variation in a soil—such as a change in clay from “slightly sandy” to “sandy”—does not necessarily warrant a strata change. The logger must define strata that have significance to designers and contractors who will use the core log information. Designers and contractors are mainly interested in the primary and secondary soil or rock constituent and whether ground water is present.
Anchor: #i1019832Density or Consistency, Hardness
Use the following charts to determine the density or consistency and hardness of material encountered.
Density (Cohesionless) |
Consistency (Cohesive) |
TCP Values |
Field Identification |
---|---|---|---|
Very loose |
Very soft |
0 to 8 |
Core (height twice diameter) sags under own weight |
Loose |
Soft |
8 to 20 |
Core can be pinched or imprinted easily with finger |
Slightly compact |
Stiff |
20 to 40 |
Core can be imprinted with considerable pressure |
Compact |
Very stiff |
40 to 80 |
Core can be imprinted only slightly with fingers |
Dense |
Hard |
80 to 5 in./100 |
Core cannot be imprinted with fingers but can be penetrated with pencil |
Very dense |
Very hard |
0 in. to 5 in./100 |
Core cannot be penetrated with pencil |
Mohs’ Hardness Scale |
Characteristics |
Examples |
Hardness |
Approximate TCP Values |
---|---|---|---|---|
5.5 to 10 |
Rock will scratch knife |
Sandstone, chert, schist, granite, gneiss, some limestone |
Very hard |
0 in. to 2 in./100 |
3 to 5.5 |
Rock can be scratched with knife blade |
Siltstone, shale, iron deposits, most limestone |
Hard |
1 in. to 5 in./100 |
1 to 3 |
Rock can be scratched with fingernail |
Gypsum, calcite, evaporites, chalk, some shale |
Soft |
4 in. to 6 in./100 |
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Moisture
If any moisture exists, note the extent present. The samples will be assumed dry if the degree of moisture is not indicated. If free water is present, describe the soil as wet or water-bearing.
Anchor: #i1020214Color
Describe the primary color, and restrict description to one color. If one main color does not exist in a sample, call it multicolored.
Anchor: #i1020239Cementation
Identify the degree of cementation if any is present.
Anchor: #i1020271Descriptive Adjectives
Use any descriptive adjectives that might further aid in the description.
Anchor: #i1020302Unified Soil Classification System (ASTM D2487)
This soil system is based on the recognition of the type and predominance of the constituents considering grain size, gradation, plasticity index, and liquid limit. It contains three major divisions of soil: coarse-grained, fine-grained, and highly organic. See ASTM D2487, Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System), for the procedure for determining soil classification. TxDOT test procedures, Tex-141-E, Manual Procedure for Description and Identification of Soils and Tex-142-E, Laboratory Classification of Soil for Engineering Purposes may also prove useful in the determination of soil type.
Anchor: #i1021391Rock Quality Designation (RQD) and Percent Recovery
Determine the RQD for rock core samples following ASTM Test Procedure D6032, Standard Test Method for Determining Rock Quality Designation (RQD) of Rock Core. Always note the RQD and percent recovery on logs of borings where rock is encountered.
Anchor: #i1016631Log Form
For uniformity, use the standard log form 513, Drilling Log. Group the materials encountered into strata consisting of the same or similar constituents.