Abstract
A fine-grained gypsum-rich clayey soil having a gypsum content of 33% is subjected, in CBR moulds, to modified American association of state highway and transportation officials compaction at optimum moisture content. Two sets of samples were prepared. The first set remained unsoaked, while the second was soaked in fresh water for 120 days. From each CBR sample, three specimens were extracted for unconsolidated undrained triaxial test and the Mohr–Coloumb failure envelopes were obtained for soaked and unsoaked conditions. Soaked samples suffered a significant drop in both cohesion and angle of internal friction. The ultimate bearing capacity of a strip footing was calculated for each of soaked and unsoaked conditions revealing the critical region. For important structures on gypsum-rich soil, the paper shows that the allowable bearing capacity should be based on soaked condition. Based on unsoaked conditions, a safety factor of 8 is required to assure a safety factor of 3 based on soaked condition. For less important structures in regions of hot dry climate with low probability of soaking, safety factors of 4 and 3, based on unsoaked conditions, are required to give safety factors of 1.5 and 1.1 based on soaked conditions, respectively.
Highlights
Gypsum-rich soils in the form of gypsum sand and finegrained gypsiferous soils as well as gypsum rocks are of wide occurrence in the Middle East, especially in areas peripheral to the Red Sea and Arabian Gulf [1,2,3,4]
For gypsum sand having a gypsum content of 28%, Razouki and Ibrahim [15] reported a significant increase in California bearing ratio (CBR) value for both soaked and unsoaked conditions due to increase in compaction effort (10–70 blows/ layer) for soil samples compacted at the optimum moisture content of the modified AASHTO compaction
To avoid any possible bearing capacity failure, the aim of this paper is to study the decrease in both soil strength parameters and in ultimate bearing capacity of strip footings on gypsum-rich soil subjected to long-term soaking in fresh water
Summary
Gypsum-rich soils in the form of gypsum sand and finegrained gypsiferous soils as well as gypsum rocks are of wide occurrence in the Middle East, especially in areas peripheral to the Red Sea and Arabian Gulf [1,2,3,4]. James and Lupton [5] studied the problems of gypsum rock in foundations of hydraulic structures, while Salih [6] studied thoroughly the stability of Mosul earth dam constructed on gypsum rocks in northern Iraq. In the United Kingdom, Cooper and Saunders [7] pointed out that gypsum problems caused difficult conditions for bridge and road construction. Harris et al [8] recommended stabilization of high-sulphate soils in Texas and Hunter [9] measured pavement heaves in Las Vegas, USA as high as 300 mm and wide cracks on pavement surface up to 150 mm width
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