Study On Strength Attenuation Law OfRed Clay Subgrade Under The Action Of Acid Rain

The red clay can be reconstructed and its mechanical performance may change dramatically due to the effect of acid rain.As the results,the many geotechnical issues,such as ground damage,subgrade damage and slope sliding,may happen.In literature,almost of studies of red clay with respect to Calcium,Magnesium,Aluminum and other cementing structure damage degree are based on qualitative analyses.While,the seepage characteristics and the strength evolution patterns of red clay under acid rain have not been systematically studied.To this end,this thesis focused on the residual red clay of Guilin tuff in Guangxi,and analyses the microstructural changes of the red clay by electron microscopy scanning test and agglomeration meter.The depth of the influence of acid rain on the red clay has been explored with the instrumentation developed by the author.The ion loss with chemical total analysis test was conducted,accordingly.In addition the strength decay model with triaxial test was established to describe the stress-strain damage relationship of the red clay with consideration of the influence of acid rain.The stress-strain damage relationship was built.The detailed conclusions are as follows.1.Using scanning electron microscopy,the characteristics of microstructure of the remodeled red clay with different degrees of compaction were analyzed.Some majors remarks was as: under the same compaction of the red clay soil,when the p H value of acid rain decreases,thesoil microstructure damage increased;in contrast,structure gap decreases with the increase of the p H value of acid rain.With a fixed p H value,as the red clay's compaction degree grows,the soil's damage decreases.It was concluded that a strong acid makes the internal red clay cements corrode rapidly.And the higher p H action on the undisturbed red clay,it resolves into smaller grains,which reduced aggregation degree.In addition,it also makes the structure loosen,the chemical elements loss,and strength impaired.2.the acid rain leaching device was developed and used to test the influence of the depth of red clay.For the leaching experiments in the same sample control,with the increase of the leaching liquid p H,the value became closer to the soil p H value,and gradually reaches a certain depth leaching liquid p H itself.When the p H value of acid rain remain the same level,the higher the degree of compaction of soil is,a smaller value of depth affected by acid rain is.Likewise,under a fixed soil compaction degree,the greater the intensity of acid rain,the smaller soil depth affected the by acid rain.When subgrade's degree of compaction is over 95%,the damage from acid rain is mild.When this value increase to 98%,at the each of p H value,there is no change for the loss of each ion in red clay subgrade.After reaching a certain depth,the acid rain action can be neglectable.The possible reason is that the red clay expanded under the action of water,resulting in the blocking of the downward channel of soil moisture,so that the water flow channel is blocked,resulting in the suspension of damage.Another reason is that the acid in the acid rain is completely reacted after a certain depth,so the damage is terminated.3.A acid rain leaching equipment is developed and used to simulate the acid rain leaching of the remolded red clay.The proposed testing model has compared the variation characteristics of mineral composition before and after the effect of acid rain.Some insightful findings are listed as below: free oxides(e.g.,Al2O3,Fe2O3,etc.)are the main structural elements of the bonded red clay;after acid erosion,red clay of Al,Si,K,Ca,Fe and other elements of the content decreased significantly.The ion release amount and leaching solution p H were correlated,and the red clay compaction exhibits a reverse correlation;when the subgrade compaction degree is 85% or 90%,the red clay shows highly distinct characteristics with the effect of acidity acid rain.The roadbed with a compaction degree higher than 95% might be a well buffing zone to acid rain;and when the roadbed compaction degree reaches 98%,the red clay subgrade under the effect of the acidity of each ion release quantity showed slightly different behavior.4.The undisturbed red clay with different p H value of acid and the mechanism of the permeability were obtained: the action of acid rain can cause red clay soil permeable,the permeability coefficient is correlated to p H value in a power function.The value decreases exponentially with the increase of dry density.The influence of acid rain on the permeability of remolded soil is higher than that in the undisturbed soil.Under the same degree of compaction,the stronger the acidity is,the greater degree of permeability coefficient can be achieved.Acid dissolution of soil mass in the soil pore expanded,while the undissolved salt dissolution and cementation of soil structure resulted in the damage,formation and seepage channel.The soluble substances with the seepage flow process caused the the permeability of soil.On the red clay subgrade,when the compaction degree reaches more than 95%,the stability of the red clay subgrade can be guaranteed under the condition of acid rain.5.The triaxial test was conducted;and the stress-strain curve relationship and strength damage law of red clay under different p H value and compactness after acid rain leaching were obtained.Moreover,for undisturbed soil and remolded soil in different degree of compaction,the principal stress of the shear failure and peak bubble acid p H value of soil samples increased.For the undisturbed soil samples,the strength of grain group structure has been greatly improved compared with the strength of the structure of the undisturbed soil samples.The results of disturbance,and remolded soil samples by cementation structure destruction showed that the strength of the remolded soil sample shear is low.Normalized equation of acid rain on red clay foundation is not consolidated undrained shear.The corresponding stress-strain relationship shows a good predictability.The deviation of the stress as the normalization factor can be used to predict the acid rain.6.The damage model of acid rain on red clay is established.With the decrease of p H value,the damage variable increases continuously till a stable state was reached.It is consistent with the decreasing trend of red clay with the increase of acid rain concentration.Most of the damages and failure process of red clay involved plasticity.At the initial stage of damage,the sample was damaged rapidly.With the increase of strain,the damage rate started to slow down and finally tended to a stable state.Under the same degree of compaction,the cementation of free oxides between each particle is destroyed and formed up "gullies".The number and size of holes increase significantly with the decrease of p H value,and the increase of the porosity.Therefore,the mechanical strength of red clay under the action of acid rain decays.