Effect Of Acid Rain On Stability Of Engineering Properties Of Foamed Light Soil With River Sludge

In China’s Jiangnan water network area,a large amount of river sludge is produced every year along with the river management and dredging works.Based on the purpose of comprehensive and effective use,the development and utilization of river sludge has become an important issue of all walks of life.The river sludge can be processed to meet the engineering requirements of the geotechnical materials,which will not only make extensive use of river silt and improve the efficiency of use,but also can save a lot of geotechnical materials and reduce project costs.At the same time,it is also beneficial to improve the environmental quality of the river and reduce the cost of sludge treatment.It is a new way to make foamed light soil with river sludge(FMLSS)with the river silt as the raw material,which is mainly reflected in the simple process,simple construction technology and strong applicability.When the river silt is used as geotechnical materials for practical engineering,in addition to the need to examine its physical and mechanical properties to test the applicability of the project,the durability or stability in the course of use is also an important aspect of its performance.In recent years,with the progress of industrialization and the use of a large number of fossil fuels,the scope and extent of acid rain is still expanding.Considering the effect of acid rain on the performance of FMLSS is an important aspect of evaluating its durability.For this reason,the experimental study was carried out to study the acid resistance and failure mechanism of FMLSS:(1)The stability of the FMLSS in the acid rain environment is closely related to its leaching characteristics.The leaching characteristics of the FMLSS in the acid rain environment are investigated by simulated acid rain test.Experimental results show that the H+ ions in the acid rain will react with the cementitious materials such as hydrated silicate of FMLSS,and the result is that the cementitious materials dissolve in the form of Ca2+ ions resulting in the neutralization of FMLSS.The stronger the acidity of simulated acid rain and the smaller the solid to liquid ratio,the greater the intensity of reaction with the mixed soil,the more the amount of Ca2+ ions dissolved in the acid solution,the higher the degree of neutralization.After 60 days of immersion in stronger acidity acid rain pH2.5,The progress of the neutralization of FMLSS is obviously increased under the experimental conditions.(2)With the continuous action of acid rain and dissolution process,it will lead to the change of physical properties of FMLSS.Experimental results show that effect of simulated acid rain causes the leaching of Ca2+ ions in FMLSS.The leaching of Ca2+ ions makes the permeability of the mixed soil better,so the acid solution is easier to penetrate into the mixed soil and reacts with it and the physical properties of FMLSS will change.Compared with the conventional gas conservation,the volume of FMLSS samples by the action of acid rain increases,water content and wet density increase significantly,and dry density decreases.Especially at the initial stage,the change of physical properties is obvious.The change of physical properties is also related to the ratio conditions of FMLSS,acidity of acid rain,solid-liquid ratio,infiltration amount and so on.(3)The change or deterioration of the mechanical properties caused by acid rain will result in the decrease of the strength and stiffness of FMLSS and the decrease of the bearing capacity.The simulated acid rain test results show that the acid rain can lead to the gradual neutralization of FMLSS,weakening the mixed soil skeleton formed by cement as the curing agent,and the mechanical properties of the mixed soil change.Compared with the conventional gas condition,the strength and peak failure strain of FMLSS decrease after the the action of acid rain,making FMLSS into a brittle failure mode.Besides the decrease of strength and the increase of brittleness degree become more obvious with the increase of acidity of acid rain.The change of mechanical properties is also affected by the conditions of FMLSS ratio,the duration of acid rain,the ratio of solid to liquid,and the amount of infiltration and so on.(4)The erosion of acid rain causes the deterioration of properties of FMLSS,which is due to the weakening of cementation between soil particles caused by chemical reaction and the reaction degree is closely related to the change of the mineral composition.In order to study the correlation between the physical and mechanical properties of FMLSS and the change of the mineral composition,the crystal phase changes of quartz,gypsum,two calcium silicate ettringite and albite in FMLSS were analyzed by X-ray diffraction test.After the acid rain erosion,the content of main minerals such as quartz,albite,gypsum and so on in FMLSS decreases,so that the acid solution is easier to penetrate,leading to the increase of moisture content and wet density of mixed soil and the decrease of dry density;the increase of ettringite causes the volume of mixed soil to increase by comparing with that in the air.Effect of acid rain erosion leads to the hydrolysis and dissolution of cement hydration products from solidified soil skeleton,decrease of main mineral quartz and albite,and increase of expansibility mineral ettringite.As a result,the overall gelling property of the FMLSS becomes worse and the whole structure is damaged,which results in the decrease of strength and the transformation of FMLSS specimen failure mode from ductile to brittle.