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The organic matter within clay soil is one of the important factors affecting its engineering characteristics. In this study, the influence of organic matter on the strength evolution of cement-stabilized marine soft clay is evaluated by scanning electron microscopy (SEM) and unconfined compressive strength (UCS) testing. The experimental results show that the after-curing clay water content of the specimens increased with the organic matter content. However, the after-curing unit weight decreased with the organic matter content. The strength decreased with the increase in the amount of organic matter. The strength loss (SL) increased with the organic matter content. A new mathematical model was determined and then used to quantitatively analyze the strength of the investigated samples. A relationship between the strength and organic matter content was established. The evaluation of the accuracy of this new strength model was carried out by comparing the predicted values and measured values, and the results indicated that the deviation was mostly within 10%. Finally, the microscopic changes of the sample surface and influencing mechanism of the organic matter were revealed through SEM. A high soil strength is mainly due to a relatively low porosity, a dense microstructure and the formation of hydration products. [ABSTRACT FROM AUTHOR]

Marine soft clay with a high salt concentration is widely distributed in coastal areas. In this study, cement-based composites consisting of cement, silica fume, plant ash and NaOH were used as a substitute for ordinary Portland cement, and the effect of salt (sodium chloride) on the strength development of clay was investigated by unconfined compressive strength (UCS) testing and scanning electron microscopy (SEM). With the addition of sodium chloride (NaCl), the amount of cementitious materials decreased, and the salt (sodium chloride) was considered to consume the cement-based composites. The consumption effect could be quantitatively evaluated by the consumption index of salt (CIS) and the clay-water/cement ratio hypothesis. The relationship between the CIS and curing period and an UCS prediction model of clay stabilized with cement-based composites with different salt contents and curing times were established. The CIS gradually decreased with increasing curing time and cement-based composites content. The accuracy of the prediction model was evaluated by a comparative analysis between the measured strengths and predicted strengths; the deviation was mostly within 10%. SEM analyses were employed to describe the changes in the microstructure of the specimens and the influencing mechanism of salt on clay stabilized with cement-based composites. [ABSTRACT FROM AUTHOR]