General
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Fine-grained soil is tested in compression using
constant rate of strain (CRS) testing to determine volume change behavior
under load. When a saturated soil mass is subjected to
an increase in load (such as a new building), it is carried initially by increased pore
water pressure. The resulting "excess hydrostatic pressure" causes water
to drain from the soil pores, shifting the load to the soil structure. The volume of the
soil also decreases (equivalent to the volume of water drained) causing settlement. The
process is known as consolidation.
Three important soil properties found using a consolidation test are:
- The coefficient of consolidation, Cv, obtained from deformation-time
curve data and an equation. It indicates the rate of compression under a load
increment.
- The preconsolidation stress, s'p, obtained
graphically from a log stress-void ratio curve. It indicates the maximum past
effective stress the soil has been subjected to.
- The compression index, Cc, also obtained graphically from the log
stress-void ratio curve. It indicates the compressibility of the specimen.
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