Experimental Study On Improved Expansive Soil Properties Of Composite Materials

Expansive soil is a kind of special clay with high liquid limit,which is rich in hydrophilic minerals.Montmorillonite,illite,kaolinite and so on,the granularity is mostly clay particles.The general expansive soil has high strength and high bearing capacity.It is often mistaken for good foundation filling material,but the idea is biased.That's because expansive soil has a very unfavorable property.It has great water absorption,making water volume larger in damp climate and shrinking volume in dry climate.The volume expansion makes repeated expansive soil cracks,the soil instability collapse,it may cause major engineering accidents and huge economic property losses.A lot of ways to improve the expansive soil to increase the strength of the expansive soil to reduce the expansion rate.In this paper,the optimum admixture of weathered sand is obtained through the study of the improved expansive soil of weathered sand.Then the mechanism of expansive soil improved by fly ash and weathered sand composite material was studied.Finally,basalt fiber was added to analyze the improvement effect of composite material to expansive soil.The test results show that:(1)In the expansive soil,0%,8%,16%,24% and 32% weathered sand was added.Through comapction test,no load expansion test and three axis test,it was determined that when the amount of weathered sand is 16%,the swelling property is the most obvious and the strength is the largest.(2)The mixture of fly ash and weathered sand makes the sum of fly ash and natural sand accounted for 16%,and 5 compound improvement ratios are selected.Expansive soil: natural sand: fly ash,respectively 84:16:0;84:12:4;84:8:8;84:4:12 : 84:0:16,The optimum mixing amount of fly ash and weathered sand composite is determined by compaction test,unconfined compression test and three axis test——Fly ash 12% weathered sand 4%.(3)On the basis of the optimum mixing amount of fly ash and weathered sand,0.1%,0.3% and 0.5% basalt fibers are added to a series of laboratory tests:Consolidation test,free expansion rate test,expansive force test.The test results show that basalt fiber can effectively restrain expansion of expansive soil,and the effect is most obvious when the amount of admixture is 0.3%.(4)In order to further study the effect of basalt fiber on the strength of the improved soil,0.1%,0.3% and 0.5% basalt fibers were added to two different dry density 1.7g/cm3 and 1.8g/cm3 respectively consolidation undrained three axis test.The test shows that the fiber can improve the strength in a small degree and improve the ductility of the expansive soil obviously.When the fiber content is 0.3%,the improved effect is best.