Study On Water-physical And Mechanical Properties Of Oil-contaminated Soils

Soil is the main natural resource that the mankind depended on for existence, and it's one of the important components of the ecological environment, too. With the rapid development of the petroleum industry and mass use of petroleum and its products, a large quantity of crude oil and its products enter into the environment. Worldwide oil pollution and disposal of oil-contaminated soil have drawn general concern of people. So, further investigation should make on transportation of oil. And new or better disposal of oil-contaminated soil should be discussed, which may offer scientific choice for remediation or disposal of oil-contaminated soil and has a value of practical application.The sorption-retention and transport process of oil in soil were studied systemically in this research. And then, water-physical and mechanical properties of oil-contaminated soil were discussed. First, experiments were carried out to simulate the transferring process of oil pollutants through different soil columns and the sorption-retention behaviors of them were concluded. The oil pollution range and the distribution law in the soil layer have been confirmed. Second, the water-physical properties related to remediation were investigated, which mainly include water holding characteristics, capillary and permeability, the factors that are unfavorable to remediation have been found. Finally, geotechnical engineering properties such as Atterberg limits, compaction and direct shear were tested on clean and oil-contaminated soils to determine the action of oil pollution types and levels on soils. At the same time, the possible application of oil-contaminated soils as construction material was put forward. In addition, the moisture content of oil-contaminated soils was corrected and empirical formula was proposed. On the basis of these investigation and experimental tests, some new understanding and conclusion drawn in this paper can be summarized as follows: (1) The oil evaporation and water evaporation does not interfere with each other in the experiment when the oil-contaminated soil samples were put at 105℃for more than 16h. The evaporation increases with decreasing soil particle size. The lose proportion of volatile oil is linear well with oil content in the same oil- contaminated soil and the correlation coefficient≥0.99. On this basis, the corrected and empirical formula is proposed and empirical coefficients are provided.(2) The results of diesel seepage in sands and overflowing in loamclay and sands indicate that the appearance oil content in sands up to 12% and can also reach about 9% in loamclay, which in seepage tests are greater than overflowing tests. The infiltration speed increases with the increasing of the moisture content of soils. However, the critical moisture content exists, when the moisture content is greater than the critical moisture content, the infiltration speed decreases with the increasing of the moisture content of soils. Then the column-leaching tests were carried out. The diesel moves and spreads in columns, which leads to uniform distribution of retention oil along the height of sands columns. The stable oil content of sands is about 25% of the appearance oil content while its up to about 75% in the loamclay columns. The oil content is between 1% and 14% in the soil samples.(3) The water holding capacity reduces with the increasing of oil content. The water retaining capacity decreases with the increasing of diesel content and the decreasing of water bearing capacity and drainable porosity are relatively light. While, all of them reduce notably with the increasing of crude oil.(4) Capillary water height of soils drops because"Lotus Effect"produced by hydrophobicity of oil. The relation between capillary water height of sands and time at different oil contents fits well with the logarithm equation and R2 > 0.92, which of loamclay accords with the power relation highly and R2 > 0.99. Empirical formula for capillary water up speed is power equation and the experience coefficients reduce with the increasing of oil content. The capillary water height of sands is negatively linear with oil content and R2=0.9956. The capillary water height and up speed of loamclay is also reduced with the increasing of diesel oil content. When crude oil content up to 1%, capillary water doesn't rise.(5) The permeability coefficients of diesel contaminated sands are in 10-3 magnitude, which of crude oil contaminated sands reduces to 10-4 magnitude. The permeability coefficient of oil-contaminated soils reduce from 10-5 to 10-8, and then <10-8 while crude oil content is greater than 8% for the layer of bitumen preventing the seepage of water. It is that the oil blocks pores and medium fluid viscosity increase act on together result in weakened permeability.(6) Atterberg limits results indicate that, Atterberg limits of diesel contaminated loamclay reduce with increasing of oil content and the plasticity index changes lightly. The"false viscosity"caused by crude oil leads to reducing of plastic limit and rising of liquid limit, which makes the plasticity index increase.(7) Optimum moisture contents of loamclay decrease with increasing of oil content, but trend of maximum dry density varies with oil characteristics. Dry density of oil-contaminated sands is larger than which is in equal moisture content, and it can raise to 1.8g/cm3 under the viscosity and lubricated function of crude oil.(8) Direct shear tests indicated that shear strength parameters of loamclay reduce lineally with increasing of oil content at natural dry density. Influence of oil on shear strength obviously is smaller than water. Although maximum dry density of oil-contaminated loamclay decreases with the increasing of crude oil and diesel content, the cohesion is 1.5 times and 2 times lager than that of clean soils'separately. For unsaturate sands, oil pollution has no prominent influence on shear strength.