Top and base California bearing ratio behaviour of soaked gypsum-rich roadbed soils

Abstract

The effect of long-term soaking on the California bearing ratio (CBR) of the top (CBRT) and base (CBRB) of both gypsum sand and clayey gypsiferous soil was obtained. The gypsum contents of gypsum sand and clay were about 28ṡ9% and 25·6%, respectively. For each soil, CBR specimens were compacted at optimum moisture content and 95% of the modified American Association of State Highway and Transportation Officials (AASHTO) maximum dry density. For each soil, two specimens were soaked for periods of 0, 4, 7, 15, 30, 60, 120 and 180 d with 50 lb (222ṡ5 N) surcharge load. For each soil specimen, the CBR load–penetration test was carried out at the top (during soaking) and the inverted bottom (base) of the specimen, yielding CBRT and CBRB, respectively. The paper reveals that there is a significant drop in CBRT and CBRB with increasing soaking period. This effect is more pronounced in CBRT than CBRB for both soils. There is a strong correlation between CBRT and CBRB for each soil tested and the difference between CBRT and CBRB increases with increasing soaking period.