MINERALOGY AND CHEMISTRY, AND THEIR CORRELATION WITH THE GEOTECHNICAL INDEX PROPERTIES OF BANGKOK CLAY: COMPARISON WITH ARIAKE CLAY

MASAMI OHTSUBO, KAZUHIKO EGASHIRA, TATSUYA KOUMOTO and DENNES T . BERGADO

ABSTRACT The mineralogy and chemistry of two marine alluvial deposits with different parent materials, Ariake clay with pyroclastic origin and Bangkok clay with non-pyroclastic origin, were compared and their correlation with geotechnical index properties was discussed. The predominant clay mineral in both clay deposits was smectite , but the smectite in Bangkok clay was found to be of the high-swelling type while that in Ariake clay is of the low-swelling type from the sediment volume determination. The range of the liquid limit and activity was mostly 100 to 140% and 1.25 to 1.90 for Bangkok clay, and 60 to 140% and 0.75 to 1.25 for Ariake clay. A positive correlation existed between the activity and the smectite content for each of Bangkok and Ariake clays, where the greater increasing ratio of the activity for Bangkok clay was attributed to the high-swelling nature of the smectite. The liquid limit of an Na-saturated sample for Bangkok clay increased with increasing NaCl concentration and when substituting Ca for Na in a similar manner to Ariake clay, but the extent of the liquid limit change by such treatments was much smaller for Bangkok clay than for Ariake clay.

Key words: alluvial deposit, clay mineral, consistency limits, marine clay, salt concentration, smectite (IGC: B1O/D2)