SCEBs - University of Colorado Boulder

transported sealed in airtight five gallon buckets to prevent moisture loss during
transport. Samples that contain too much or too little natural water content will need to
be amended before use in SCEB production.
3.4. Soil Classification
A grain size analysis is required to classify a soil. A proper classification will
correctly identify a soil, thus providing insight to the soil‟s properties. Soils are tested
and classified as per the Unified Soil Classification System – USCS (ASTM D2487).
Clay and silt are commonly referred to as fine grained soils, while sand and clay are
referred to as coarse grained soils. A sieve test (ASTM D422) is performed to determine
the soil grain size distribution. For fine grained soils, a Liquid and Plastic limit tests
(ASTM D4318) is carried out (also known as the Atterberg limit test). The Atterberg
limit test provides a method for quantifying a soil‟s plasticity, providing information
regarding the amount of clay present. Using the information obtained from the grain size
distribution and Atterberg limit tests a soil classification is determined using the process
provided by the USCS. Any soil found to contain organic material is unacceptable. The
sand used for aggregate must have angular particle characteristics and its gradation must
be compatible with that of the clayey soil to be used.
Current literature and applicable building codes do not offer guidelines for
selecting an optimal soil for earthen construction based on the soil‟s USCS classification.
The case studies presented in Chapter 4, offer some goals for optimal soil classifications.
The sand aggregate used is ideally well-graded with a USCS classification of SW. The
clayey soil used contains a significant amount of clay minerals with a USCS
classification of CL. In addition, the clayey soil should achieve a plasticity index which
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