ANSWERS TO “TEST YOUR KNOWLEDGE” ON PAGE 40 Answers:


1. The answer is choice “b” or “lopolith.” See the table and sketch below.. Pluton


Batholith Stock Dike


Laccolith Lopolith


Sill


Massive X X


X X


X


Tabular Discordant Concordant X X X


X


X X


X Comments


Area > 100 km2. Area < 100 km2.


Cuts across bedding.


Lenticular shape; Intruded between sedimentary layers; Dome-up the overlying strata.


Lenticular shape; Depressed central region. Parallel to bedding.


2. The answer is choice “c” or “Quartzite being tested under unconfined compression at a high strain rate.” Under these conditions, quartzite should deform in brittle fashion, as indicative from our given stress-strain curve.


Key terms related to stress-strain curves


Elastic versus ductile or plastic behavior 3. The answer is choice “c” or “CL” or clay of low plasticity (such as kaolinite).


The “Unified Soil Classification System” (based on particle size, plasticity, and overall engineering behavior) is a useful tool in geology and civil engineering, as it describes various soils and sediment types and their related and expected properties. A helpful summary of key soil/sediment types under this system is shown below:


SW Well graded sand SP Poorly graded sand SM Silty sand SC Clayey sand ML Inorganic silt of low compressability CL Clay of low plasticity OL Organic silt of low compressability MH Silt of high compressability CH Clay of high plasticity OH Organic clay of medium to high plasticity


Casagrande’s plasticity chart is helpful in the classification of silts and clays. Silts lie below the “A line” and clays above it. To the right of the “B line” we find silts and clays of high compressibility or plasticity. In contrast, silts and clays of low compressibility or plasticity are found to the left of the “B line.”


46 TPG • Jul.Aug.Sep 2024


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