Study On Engineering Mechanical Properties Of Saline Soil Improved By Industrial And Construction Wastes

Saline soil is widely distributed in Xinjiang,China.In the natural environment,saline soil will produce engineering diseases such as salt heave,frost heave,settlement,corrosion and so on.Its use as roadbed and pavement base filling will seriously affect the stability and durability of roads and other infrastructure.With the development of economic construction in Xinjiang,industrialization,urbanization and the improvement of infrastructure have led to the production of a large number of industrial and construction wastes,and leaving them idle will have a certain impact on the environment.Therefore,the engineering mechanical properties of saline soil are improved by industrial and construction wastes such as cement kiln dust(CKD)and recycled fine powder of waste concrete(RFP),so that the improved saline soil can be used as filling material for highway roadbed and pavement base in saline land area of Xinjiang,which has certain engineering significance,economic and environmental protection value.In this paper,through unconfined compressive strength test,direct shear test,dry-wet cycle test and freeze-thaw cycle test,the effects of test factors on the mechanical properties and road properties of industrial and construction wastes such as cement kiln dust and recycled fine powder of waste concrete were studied,and the engineering mechanical properties of improved saline soil were evaluated comprehensively.The purpose of this paper is to provide a reference for the improved saline soil to be used as the filling material of highway roadbed and pavement base in Xinjiang saline soil area.The main conclusions are as follows:(1)The mechanical properties of improved saline soil under various test factors were studied by unconfined compression test and direct shear test.The results show that the initial moisture content,curing age,content and improver ratio have significant effects on the compressive strength and shear strength of saline soil and improved saline soil.The index of compressive strength and shear strength of saline soil improved by adding CKD and RFP is obviously better than that of unimproved saline soil.The indexes of compressive strength and shear strength of saline soil improved by single addition of CKD and RFP increased with the increase of content.The compressive strength of improved saline soil increases with the increase of curing age.When the curing age of RFP modified saline soil is 21d-28 d,the compressive strength of RFP modified saline soil with an initial water content of 9.9% is better than that of other RFP improved saline soil.The compressive strength of saline soil improved by CKD,the shear strength index of CKD and RFP decreased with the increase of initial water content.The compressive strength and shear strength of improved saline soil will increase with the increase of the proportion of RFP,indicating that the ability of RFP to improve the strength of saline soil is better than that of CKD.Among them,the test factors are curing for 28 days,the initial water content is 9.9%,and the compressive strength of 30%RFP improved saline soil is the highest,reaching 3227.40 k Pa,which is higher than that of unimproved saline soil under the same test factor 2849.78 k Pa.The test factors are that the initial water content is 5%,and the cohesion and internal friction angle of 30%RFP improved saline soil are the highest,reaching 91.95 k Pa and 20.48°respectively,which is higher than that of unimproved saline soil under the same test factor by 52.04 k Pa and4.71°,respectively.After CKD and RFP were added into saline soil,gel material was formed in saline soil,and ion exchange and granulation occurred in saline soil.Part of CKD and RFP,which did not participate in hydration reaction,were filled in the overhead pores of saline soil.Together,soil particles formed soil masses,pores decreased greatly,and agglomerated spatial network structure was formed,which was more dense and stable than that of unimproved saline soil.(2)The road performance of improved saline soil under various test factors was studied by dry-wet cycle and freeze-thaw cycle tests.The results show that the initial moisture content,the ratio of modifiers,the number of dry-wet cycles and freeze-thaw cycles will affect the dry-wet and freeze-thaw durability of improved saline soil.After 10 dry-wet cycles,the dry-wet and freeze-thaw residual compressive strength and the coefficient of dry-wet and freeze-thaw residual compressive strength of RFP modified saline soil are higher than those of saline soil,CKD improved saline soil and CKD+RFP modified saline soil,indicating that the dry-wet and freeze-thaw durability of saline soil is remarkable.Judging from the residual compressive strength coefficient of improved saline soil after 10 dry-wet cycles,when the initial water content is 15%,the dry-wet durability of 30%RFP improved saline soil is the best,and the dry-wet residual compressive strength coefficient is 98.34%.Judging from the residual compressive strength coefficient of the improved saline soil after 10 freeze-thaw cycles,the initial moisture content is 9.9%,the freeze-thaw durability of 30%RFP improved saline soil is the best,and the freeze-thaw residual compressive strength coefficient is 69.51%.