Predicting long-term soaked CBR of gypsiferous subgrade soils Available to Purchase

Thirty-two laboratory California Bearing Ratio (CBR) tests were carried out on a CH gypsiferous subgrade soil with an initial gypsum content of 34%. The soil samples were prepared according to ASTM D 1883-99 at 95% of the maximum modified AASHTO dry density. For each 40 lb (178 N) and 70 lb (311·5 N) surcharge load, eight pairs of CBR samples were prepared, and soaked for periods of 0, 4, 7, 15, 30, 60, 120 and 180 days respectively. To develop a general empirical formula for predicting long-term soaked CBR from unsoaked CBR, use was made of available results on CH soil with a gypsum content of 15%, on granular gypsiferous soils of the SW-SM group with a gypsum content of 64%, and on SM soils with gypsum contents of 34% and 61%. The empirical equation developed in this paper enables the soaked CBR to be determined from the unsoaked CBR for all types of gypsiferous soil and for any surcharge load and soaking period. The equation's validity was examined using six different gypsiferous soils (eight case studies) including both granular and fine-grained soils. This paper also shows the invalidity of Fekpe's empirical equation in modelling the long-term behaviour of gypsiferous soils.