A Study On Road Performance Of Carbonate Saline Soil Improved By Lime

With the development of economy,both personnel and goods exchange between different regions have became more frequent,and this puts forward higher requirements on China's transportation capacity.Roads and railway play an important role in the whole transportation system,as space linear structures,both of them are directly exposed to the nature,and as a result,they are easily affected by natural environment which finally weakened their service ability.Most parts of Jinlin province in the west is covered by large amounts of carbonate saline soil,and as a special kind of soil,it easily corrodes buildings and causes damages to roads and railway,such as collapse,salt expansion,frost heave and frost boiling,etc.so it is very important to improve saline soil to make its performance indicators meets the relevant requirements.In this thesis,we choose some carbonate saline soil that collected from Nong'an,Jinlin province as research object,and we improved it by adding different proportions of lime to it.We conducted the following experiments on both unimproved and improved carbonate saline soil,such as compaction test,unconfined compression test and CBR test,etc.And we explored the mechanism,finally,we get several achievements listed below:(1)We test the samples and get its soluble salt content in each layer by mass method.Except that part of topsoil reaches strong saline soil degree and even ultra-intense degree,all of the other layers'soluble salt content ranges from 0.5%to1.0%which belongs to middle saline soil.We conducted a particle analysis of the soil samples by particle test,at the same time,we measured the samples'liquid and plastic limit in each depth degree by liquid-plastic limit combined measurement,and according to its plasticity chart it can be classified as high liquid limit clay.(2)The soil samples'maximum dry density and optimum water content is measured by compaction test and the value is 1.89g/cm~3 and 14%.And after been improved by separately adding 3%,5%,7%,9%and 11%percent of lime to it,the corresponding maximum dry density and optimum water content is measured,and the value is 1.82g/cm~3,1.80g/cm~3,1.80g/cm~3,1.79g/cm~3 and 1.76g/cm~3 which is the corresponding maximum dry density and the corresponding optimum water is 14.5%,14.7%,14.0%,13.8%and 14.3%.The maximum dry density of the soil samples decreases with the increasing percent of lime,but the optimum water content was unaffected by it.(3)By conducting unconfined compression test,we found that adding lime to carbonate saline soil has a great improvement to its water stability and carrying capacity.But one point need to notice is that when the lime's proportion that added to carbonate saline soil less than 5%,it has no significant effect on its stability and carrying capacity,when the percent is greater than 5%,both water stability and carrying capacity increase with the increase of line's amount that added to carbonate saline soil.When control the increase of moisture content during specimen making progress,the effect of lime gradually appeared.And within a certain range,its water stability and unconfined compression strength increase greatly.(4)After comparing the CBR test results of unimproved saline soil and improved saline soil which has been added different proportion of lime,we found that with the increase of lime,the value of CBR increase greatly at first,and then continue increase,but the growth rate slow down and the turning point is about at 7%~9%.For the swelling capacity,it decreases with the increasing of lime's proportion,but its water absorption is much bigger than before.What needs to be noticed is that when adding 3%proportion lime to the samples,the value of CBR is 2.6 and it is smaller than 3 which is the minimum requirement for embankment filling.What's more,its water stability is very poor when water immersed.In our experiment,the specimens that added only 3%proportion lime damaged seriously,and only when the proportion is bigger than 5%,its CBR value can meet the specification requirement,and it has good water stability.