Evolution Of Mechanical Properties Of Oil Contaminated Soil Solidified With Inorganic Materials And Its Influence

Being as one of the essential society developing engines,oil has induced directly and indirectly environmental problems with its demand and consumption increased.Physical and mechanical properties of soil changed as it contaminated by oil,and secondary pollution with environmental existed simultaneously.Thus the reasonable disposal of oil contaminated soil has become an inevitable demand for the harmonious development of economic construction and ecological environment in oilfield area.From the perspective of environmental geotechnical engineering,this paper took the comprehensive utilization of environmental special soil engineering as orientation,and takes into consideration the green development strategy and engineering mechanics,solidition/ stabilizaion method was applied for treating oil polluted saline soil,which lime and fly ash were chosen as solidified materials.Tests of unconfined compressive strength and triaxial shear strength were used to study the mechanical strength variation,and then response surface method(RSM)was employed to analyze the interaction and soilidited mechanism of various factors,and also the sensitivity from oil pollution level,the amount of solidified material and curing days.Micro-mechanism explored cooperatively to obtain the evolution of micromorphological characteristics Research results and perspectives were as followed:(1)The change of mechanical strength of oil contaminated soil solidified jointly with lime and fly ashCompressive strength of solidified soil was improve greatly,and met to the requirements in Specifications for Design of Highway Subgrades(JTG D30-2015),and especially as oil pollution level was within 8%,it can meet the requirements of highway and first-class highway.Stress-strain curve of solidified contaminated soil included linear load,nonlinear rising and decline phase,it presented strain softening damage.With the increase of oil pollution level,the plastic deformation was partially enhanced and strength decreased.The presence of oil contamination in soil can slow the solidified rate and weakens the fuction among lime,fly ash and soil particles.Lime and fly ash contributed to increasing cohesive force(c),which was much higher than internal friction angle(?).With the extend of curing periods,the deformation modulus and ratio of deviator stress were gradually increasing,and failure was from hardening to softening.Under light pollution level(?4%)condition,oil had less influence on curing reaction,and the suitable amount in 28 d was 6% of lime and 20% of fly ash.Oil characterhad higher impact on c and ? at the beginning curing and the increasing of materials amountcan cause swelling and slide bead function.Under heavy polluting condition(8%<pollution level? 12%),oil viscosity decreased with the increasing of lime amount.Physical package action of oil delayed the reaction rate,and then caused less crystallization and persistence increase of strenght.Suitable amount in 28 d was 8% of lime and 25% of fly ash.(2)Factor interaction effect and solidified mechanism analysisInteraction between lime content,fly ash content and oil pollution level was discussed by RSM and formation development and solidification mechanism were analyzed.Results indicated that: in early curing stage(less than 7 days),there was positive effect on improving solid integrity by increasing oil contaminated level and decreasing material amount,and excessive amount was easy to cause soil expansion and water entry.In mid-stage(7~14 d),solidified reaction was mainly chemical,and the amount of lime and fly ash increased.In last stage(14~28 d),there was still large growth on strength.As to severe contaminated soil,the degree of crystallization was reduced as loose aggregate structure.Oil contamination had negative effect on the shear strength,and the solidified reaction and fly ash absorption were the key to improve mechanical properties.Oil was not involved in chemical reaction and the control effect of lime fly ash on oil is mainly derived from the good adsorption of fly ash and the sealing effect of solidified products.For heavy oil contaminated soil,it was necessary to extend the curing and increase amount of solidified materials so as to stabilize its strength and take advantage of material performance fully.On the other hand,it will help to curbe the hindrance functionoil from oil to materials and water flow.Increasing the amount of fly ash moderately to adsorb oil contribute to solve the problem of difficult contact caused by physical inclusion from oil.(3)Constructive suggestionAs to light contaminated soil,the increase density had a great influence on the resistance of lubrication and softening for humidity,and the increase of fly ash content had limited effect on the enhancement of strength.To moderate contaminated soil(4% <contaminated level < 8%),the water displacement caused the strength evolution was retarded by oil,and then its growth rate increased in later.Collaborative increasing of material amount and density was more beneficial to strength development as to single chang.To heavy pollution,physical package of oil was more pronounced under the high density,humidity increasing can promote the solidify action,and meanwhile,it enhancedby the micro expansion and flocculant coagulation from lime under low humidity.It was recommended that the corresponding working conditions and solidification materials should be selected for different oil pollution levels in the subsequent tests and related specifications...