Geotechnical behaviour of a lime treated expansive soil

Abstract

In this research, geotechnical properties of a selected lime treated expansive soil have been investigated. For this purpose, initially, index and swelling properties of untreated samples collected from six different locations of Rajendrapur Cantonment, Gazipur were determined. The relative degree of expansion of the six soil samples has been evaluated in order to select the most expansive soil used for subsequent lime stabilisation. On the basis of the recommended criteria of expansive soil, the soil sample collected from POL store area of Rajendrapur Cantonment, Gazipur was found to be the most expansive soil. Samples of this soil (liquid limit = 56, plasticity index = 43) were stabilised with five different lime contents of 3%,6%,9%, 12% and 15%. Index, swelling and engineering properties ofthe lime treated expansive soil were evaluated in order to examine the effect oflime stabilisation on geotechnical properties of this expansive soil. Compared with the untreated sample, liquid limit of the stabilised samples initially decreases with the increment of lime content up to 6% and then increased with increasing lime content. Plastic limit and shrinkage limit of the treated samples increased considerably with increasing lime content. Compared with the untreated sample,. plasticity index, linear shrinkage, volumetric shrinkage and shrinkage ratio of lime treated expansive soil decrease markedly due to increase in lime content. Swelling test results show that free swell and free swell index of the stabilised samples decrease significantly with increasing lime content. Swelling pressure and swelling potential of the treated samples also reduce markedly. Compared with the untreated sample, volume change of the stabilised samples from air-dry to saturated condition decreased considerably. The experimental results on the influence of lime stabilisation on swelling properties clearly demonstrate that lime can be considered a very effective additive to reduce various swelling properties of an expansive soil. It has been found that with the increase in lime content, maximum dry density reduces while optimum moisture content increases. Compared with the untreated sample, unconfined compressive strength of the treated samples increases significantly, depending on the lime content and curing age. It was found that unconfined compressive strength of samples of this expansive soil treated with 6%, 9%, 12% and 15% lime fulfilled the requirements for its use for upgrading heavy clays to sub-base material quality type, as proposed by Ingles and Metcalf (1972). It was found that strength development index increases with increasing curing age and lime content. It has been observed from the present investigation that long-term curing has profound influence on the gain in strength. The effect of long-term curing on the increase in unconfined compressive strength has been found to be more pronounced when samples were treated with higher lime contents. Unconfined compressive strength of sample treated with 15% lime and cured for 16 weeks was about 8.4 times higher than the strength of the untreated sample. It was also found that unconfined compressive strength of samples treated with different lime contents and cured for different ages increased with the increase in moulding water contents. Unconfined compressive strength was found to be the maximum and minimum at moulding moisture contents of wet side of optimum and dry side of optimum, respectively. CBR tests performed on treated and untreated samples indicated that CBR-values of the treated samples at all levels of compaction increase considerably with increasing lime content. At any particular lime content, CBR increases significantly with the increase in compaction energy. Compared with the untreated sample, CBR-values of treated samples increased by 4.75 to 8.75 times due to increase in lime content from 3% to 15%. The flexural stress versus deflection curves has been found to be approximately linear. Compared with the untreated sample, flexural strength and flexural modulus of the stabilised samples increase significantly, depending on the lime content and curing age. Flexural strength and flexural modulus of samples of the expansive soil cured for 8 weeks increased by about 66% to 209% and 37% to 76%, respectively, due to increase in lime content from 3% to 15%.