Experimental Study On Physical And Mechanical Properties Of Lignin And Cement Composite Improved Expansive Soil

For the improvement of expansive soil,cement,lime and fly ash are often used to improve the soil properties.But these modifiers have a great impact on the underground environment.Therefore,it is very important to seek more environmental friendly and pollution-free modifier to replace or reduce the use of cement and lime.In this paper,lignin and cement are selected as modifiers,and expansive soil in Nanyang area is taken as test soil sample.Based on the basic physical and mechanical tests,the physical and mechanical properties of improved soil with different content,moisture content,compactness and curing age were studied.The dynamic shear modulus and damping ratio of improved soil with different content,moisture content and confining pressure were studied by resonant column test.The main conclusions are as follows:Through the liquid plastic limit test and compaction test,it is found that cement and lignin can be used to reduce the liquid plastic limit and plasticity index of expansive soil.When the content of lignin is more than 1%,the influence of lignin on liquid plastic limit and plasticity index of expansive soil is greater.The optimal moisture content of expansive soil improved by 4% cement increases,while the maximum dry density decreases.Under the condition of 4% cement content,the optimal moisture content gradually decreases with the addition of lignin,while the maximum dry density is on the contrary.Through the unconfined compressive strength test and direct shear test,it is known that the strength of the composite improved expansive soil first increases and then decreases with the increase of lignin.When lignin is 1%,the strength of improved soil reaches the maximum.The unconfined compressive strength increases with the increase of curing age and compactness,and the strength is mainly concentrated in the first 7 days of curing age.In the direct shear strength index,the increase of cohesion is greater than the internal friction angle.The dynamic shear modulus and damping ratio of expansive soil improved by lignin and cement under different modifier content,water content and confining pressure were obtained by resonance column test.Among them,the dynamic shear modulus of improved soil is greater than that of plain soil,and the damping ratio is less than that of plain soil.Under the same confining pressure,the dynamic shear modulus and damping ratio of improved soil decrease with the increase of water content.At the same moisture content,the dynamic shear modulus and damping ratio of improved soil increase with the increase of consolidation confining pressure.