Geotechnical Properties of Bangkok Clay Mixed Gypsum

Abstract

This paper described the results of a study which was primarily directed to the determination of geotechnicalproperties of Bangkok Clay - Gypsum admixtures at 0%, 5%, 10%, 15% and 20% by weight of air-dry clay. Sampleof Bangkok Clay was taken from a rural-highway construction project SP.4100 located at Ban Klongsuan-BanKlongkaom, Prasamuthjadee district, Samuthprakarn province where as Gypsum from Gypsum mine atDoungchalearn district, Pijit province. The physical and engineering properties of studied admixtures such asGrain size distribution, Specific gravity, Atterberg limits, Standard compaction, California Bearing Ratio (CBR)and Undrained shear strength are tested.

The testing results can be concluded as follows. As the variety of admixture proportions, the specificgravity decreased when the quantities of Gypsum in admixture increased. The plastic index decreased when thepercentages of Gypsum increased. According to standard compaction test, the results showed that the maximumdry unit weight decreases until the quantity of Gypsum reach at 5% and then continue to increase to themaximum dry unit weight of 1.42 g/cm3 at 20% Gypsum content. The California Bearing Ratio test whichsamples soaked at curing time 7 days and unsoaked at curing times 7 and 14 days were carried out. The resultsindicated that the CBR value of admixture at 5% Gypsum has lower value compared to CBR value of pure clayand the CBR value increase continuously where as the percentage of Gypsum increases. The swelling index fromswelling test decreased while the ratio of gypsum increased. Finally, the undrained shear strength from unconfinedcompression test of samples at curing time 1, 3, 7, 14 and 28 days were carried out. The test results revealed thatthe undrained shear strength continuously decrease until the amount of Gypsum reach at 10% and then theundrained shear strength increase regularly as the amount of gypsum increase to 15% and showed tendency todecrease when Gypsum content over 15%. All of various curing time samples showed the similar curves andsample at curing time 28 days gave the maximum value of undrained shear strength of 1.578 kg/cm2 at 15%gypsum content. Conclusion and recommendation also were presented.