Experimental Study On Modification Of Expansive Soil In Heilongjiang Province

Expansive soil is a kind of disastrous clay which forms in natural geological processes.It has the special property with multiple fracture and obvious swell-shrink characteristic.The expansive soil is improved by two methods of replacement and modified expansive soil.Most studies improve the expansive soil by mixing lime,cement,efflorescent sand,HEC curing agent,but there are still many difficulties.In this paper,the study on the modification of fly ash and straw ash by extracting the expansive soil in the area of the Nenjiang River diversion project in the north of Heilongjiang.The ash-doped rate of modified soil is 5%,10%,15%,20%.Through the specific gravity test,grain analysis test,boundary moisture content test,consolidation test,compaction test,free expansion rate test,free load swelling rate test and the loaded swelling rate test,shrinkage test,direct shear test,unconfined compressive strength test,the main conclusions are as follows:(1)Fly ash and straw ash have significant effects on the basic physical properties of expansive soil.The proportion of modified expansive soil decreases with the increase of content of fly ash and straw ash,and the coefficient of uniformity of soil particles also decreases.The liquid limit and plasticity index of the modified expansive soil also reduce,and the change of plastic limit is not obvious.The optimum moisture content of the modified expansive soil is continuously reduced due to the increasing proportion of ash.The maximum dry density of the modified expansive soil increases firstly and then decreases,and the compressive characteristic of the expansive soil is also improved.(2)The swell-shrink characteristics of expansive soil are affected by fly ash and straw ash.As the content of ash increases,the free expansion ration,free load swelling rate and the loaded swelling rate of the expansive soil decrease.The shrinkage characteristic index of the modified expansive soil is generally improved as the content of ash increases.(3)With the increase of content of ash,the shear strength and unconfined compressive strength of the modified expansive soil show a tendency of increasing firstly and then decreasing.(4)It is similar that the reaction mechanism of fly ash and straw ash on expansive soil,but its specific effects are different.In the same mixing amount,the comprehensive modification effect of fly ash is better.