ABSTRACT

The pore and bulk volume compressibilities of unconsolidated sands and clays were determined using both triaxial and uniaxial compaction apparatuses.

The bulk compressibilities of unconsolidated sands ranged from 7.4 10-⁴ to 3 10-⁵ psi^-1 at effective pressure range of 0 to 3,000 psi (FOOTNOTE 2), whereas the pore volume compressibilities ranged from 1 10-³ to 1 10^-4in the same pressure range using triaxial compaction apparatus. These values are greater by about 55 to 100% than those obtained on using uniaxial compaction equipment.

The bulk compressibilities obtained on compacting montmorillonite clay saturated in sea water using the triaxial apparatus (5 10-⁴ to 2.9 10^-5 psi^-1) were found to be about 300 to 500% higher than those obtained on using uniaxial loading (1.8 10^-4 to 5.4 10^-6 psi^-1) in the applied pressure range of 400 to 20,000 psig.

A graph is presented comparing the compressibilities of various clays, sands, sandstones, shale, and limestone. Compressibilities of unconsolidated sands appear to be very close to those of clays. Compressibilities of the consolidated sandstones, shales, and carbonates range from 10^-5 to 10^-7 psi^-1 in the 500 to 15,000 psi pressure range.