In this study, the effects of calcium sulfate contaminated soil treatment methods on the index properties, compacted soil properties, free swelling and compressive stress strain relationship of a CL soil obtained from the field was investigated. Calcium sulfate concentration in the soil was varied up to 4 % (40,000 ppm) and the soil samples were cured for seven days at 25 °C and 100 % humidity before testing. With 4 % sulfate contamination the liquid limit and plasticity index of the soil increased by 44 and 81 % respectively. The free swelling increased from 7 to 18 % and the compressive strength decreased by 65 % with 4 % of calcium sulfate, Also the study investigated the effects of fly ash (class C) and hydrated lime treatment on the behavior of treated sulfate soils. X-ray diffraction (XRD) was used to characterize the soil and the reaction products of lime and fly ash treated soils. Based on XRD analyses, major constituents of the CL soil were calcium silicate (CaSiO3), aluminum silicate (Al2SiO5), magnesium silicate (MgSiO3) and quartz (SiO2). Addition of calcium sulfate resulted in the formation of calcium silicate sulfate [Ternesite Ca5(SiO4)2SO4] and aluminum silicate sulfate [Al5(SiO4)2SO4]. Treatment with lime resulted in the formation of ettringite [Ca6Al2(SO4)3(OH)12·26H2O]. Treating with fly ash resulted in the formation of calcium silicate hydrate (CaSiO3H2O) and magnesium silicate hydrate (Mg3SiO3H2O), cementing by products. Contaminated soil treatment with lime and fly ash reduced the index properties and free swelling and increased the short-term compressive strength of the soil. Behavior of the compacted sulfate soils, with and without treatment, has been quantified using a unique model that was used to represent both linear and nonlinear responses. Also the model predications were compared with other published data in the literature. Compressive stress–strain relationships of the sulfate soil, with and without lime and fly ash, have been quantified using a nonlinear constitutive model. The constitutive model parameters were sensitive to the calcium sulfate content and the type of treatment. Compared to the fly ash treatment, the lime treatment reduced the strain at peak stress making the lime treated soil more brittle.

Testing and Modeling the Short-Term Behavior of Lime and Fly Ash Treated Sulfate Contaminated CL Soil

In the present scenario, with much focus on sustainable development worldwide, Microbially Induced Calcite Precipitation (MICP) is a promising biological soil improvement technology. However, only ...

Engineering behaviour of MICP treated marine clays

The detection of the plastic limit of clays is subject to human error. Several attempts have been made to correlate across studies the geotechnical properties of fine-grained soils (water content, liquidity index, shear strength, etc.). Based on the premise that the liquidity index and water content ratio can be correlated directly, an alternative method to obtain indirectly the plastic limit is suggested here. The present study investigated 40 natural clayey samples of various mineralogies and origins and other publicly available data, where Atterberg limits and undrained shear strength values obtained with the vane shear tests were given. The liquidity index and water-content ratio correlate very well for defined undrained shear strength values of the clays. Solving the liquidity index equation for the plastic limit, estimated plastic limit values obtained by the liquidity index/water-content ratio relationship were compared with laboratory plastic-limit values. Preliminary results based on 62 values show an exponential trend with a multiple regression coefficient of 0.79. The data need to be confirmed on a larger database, however.

Relationship between measured plastic limit and plastic limit estimated from undrained shear strength, water content ratio and liquidity index

Kuttanad clay from Kerala, India is a soft soil with associated problems of low shear strength and compressibility. An attempt is made to characterize the soil in terms of its mineralogy, fabric, organic matter, and pH in order to understand its geotechnical behavior and suggest a suitable ground improvement technique. It was found that the soil has a unique combination of minerals such as metahalloysite, kaolinite, iron oxides, and aluminum oxides. The diatom frustules present in the soil indicate biological activity during the sediment formation, and this also accounts for the nature of organic matter predominantly present in the soil, which is mostly derived from planktonic organisms. A considerable amount of organic matter is present in the soil, and the magnitude measured accounts to about 14 % by mass. The soil is found to be acidic and the low pH to some extent can be connected to the partial oxidation of pyrite. The aggregated-flocculated fabric, as deduced from the scanning electron microscopy images, is supported by comparison of liquid limit with plasticity index and the shrinkage limit. Low specific gravity, high liquid limit, and relatively low plasticity index are explained due to presence of organic matter, silica frustules, and fabric. The influence of soil fabric and composition on the index properties of the soil is likely to bear a direct link to the corresponding influence on the engineering behaviour of the soil.

P.K. Mathews

Papers

Physico-chemical and mineralogical studies on cochin marine clays