Geotechnical Evaluation of Diesel Contaminated Clayey Soil

Soil contamination by different hydrocarbons has rapidly expanded worldwide, surpassing the self-purification capacity of soils and increasing the number of contaminated sites. Although much effort has been devoted to study the effects of diesel contamination on the geotechnical properties of soil, there is still limited available information about it. Moreover, there is no available information about the maximum diesel retention that soil can have and its effect on the geotechnical behavior of the soil. Thus, in this paper, we determined the maximum diesel retention by an unsaturated clayey soil and evaluated the impact of diesel contamination on its geotechnical properties. The results showed that the soil could only retain 12.6% of the added diesel and the excess was expulsed. At such a diesel concentration, the saturation rate of the soil was lower than 80%. Diesel contamination increased the plasticity and the internal friction angle of the soil, while its cohesion was considerably decreased. It should be noted that the matric suction of contaminated soil was lower than the one obtained for natural soil. However, its osmotic suction was considerably higher. This indicates that osmotic suction must be considered to evaluate the shear strength of contaminated soils.

Effect of osmotic suction on the stability of microaggregations and aggregations in a lateritic soil

It has been established that the matric suction is the portion of the total suction that affects, more directly, the mechanical behaviour of unsaturated soils, being less considered the effects of the osmotic suction. Considering that in the deeply weathered soils will occur, depending on its chemical-mineralogical characteristics, more or less ionic exchange between the soil particles and the chemical products to which the soil has been exposed to, the study of the osmotic suction and its impact on the soil textural and structural stability becomes relevant. In natural terrain and slopes, the chemical products come mostly from agricultural inputs, while in road constructions they come from additives such as lime and cement that are incorporated to the soil with the objective of enhancing its mechanical behaviour. In the case of cast in situ concrete foundations, part of the concrete’s chemical compounds migrates to the surrounding soil. In all of the above mentioned cases, the matric suction acts on the chemical compounds’ migration process, affecting soil’s osmotic suction. Aiming at assessing the impacts of these chemical compounds on the soil properties and behaviour, soil-water characteristics curves of a lateritic soil mixed with a dolomitic limestone and a fertilizer were evaluated. The results show that, in the case of the fertilizer mixture, the variation of osmotic suction contributed to the disaggregation of the soil.

Preliminary study on the contribution of osmotic effects for the electrical resistivity of sands

Electrical resistivity of soils can be used to evaluate the level of contamination in soils in geophysical prospection tests. The chemical composition of pore fluid also corresponds to a given water potential, named as osmotic suction. Therefore both electrical resistivity and osmotic suction can be related when soil is saturated. This paper investigates their relationship when the soil is not saturated. The osmotic suction and electrical resistivity were measured for uniform grading size samples of sand prepared with different concentrations of an ionic leachate from a real landfield. Both were measured also for the fluid with the different concentrations. Suction was measured for different degrees of saturation using the ionic fluid for the different concentrations. The soil osmotic suction is similar to the osmotic suction of the pore fluid independently from the degree of saturation, and the differences in electrical resistivity in the saturated samples and pore fluid alone as function of osmotic suction are related by a constant. Although pore fluid composition affects electrical resistivity, when evaluating the electrical resistivity considering the degree of saturation one should pay attention to factors that are related with matric suction instead of osmotic suction.