| Although the traditional expansive soil improvement method improves the swelling-shrinkage and strength characteristics of expansive soil,some modifiers may cause secondary pollution of the environment and increase the cost of engineering construction.Using solid waste to improve expansive soil not only implements the concept of green sustainable development,but also saves the cost of expansive soil improvement.In this paper,oyster shell powder is used as an soil conditioner.Through the limit water content test,particle analysis test,expansion rate test,expansion force test,shrinkage test,and direct shear test,SEM test and crack test under dry-wet cycle were carried out,the influence of oyster shell powder on the physical characteristics,swellingshrinkage characteristics,strength characteristics,microscopic mechanism and crack characteristics of expansive soil in Ningming area of Guangxi was studied.The following research results are obtained:(1)The liquid limit,plastic index,clay content,silt content,free expansion rate,24 h unloaded expansion rate,loaded expansion rate,expansion force,shrinkage rate and shrinkage coefficient of expansive soil decrease with the increase of oyster shell powder content,while the plastic limit and shrinkage limit increase with the increase of oyster shell powder content.The addition of oyster shell powder changed the clay particle content and particle size distribution of expansive soil,and effectively improved the swelling-shrinkage characteristics of expansive soil.(2)The shear strength and cohesion of expansive soil increase first and then decrease with the increase of oyster shell powder content,and reach the maximum value when the oyster shell powder content is 9%.The shear strength and cohesion of expansive soil with different oyster shell powder content decrease with the increase of dry-wet cycle times,and tend to be stable at 4 times of dry-wet cycle.The internal friction angle has no obvious change rule with the number of dry-wet cycles and the content of oyster shell powder.However,the internal friction angle of expansive soil with oyster shell powder is larger than that of expansive soil without oyster shell powder.The addition of oyster shell powder effectively improves the shear strength and cohesion of expansive soil,and enhances the structure and stability of soil.However,adding too much oyster shell powder will lead to accumulation between particles,which will destroy the stability of soil structure.(3)The expansive soil with oyster shell powder content of 0%,3%and 6% will heal after the main crack appears under the dry-wet cycle,and the crack rate will reach the maximum value when the dry-wet cycle is 4 times.The expansive soil with oyster shell powder content of 9% and 12% only has edge cracks,and the crack rate reaches the maximum value when the dry-wet cycle is5 times.By comparing and analyzing the variation law of the maximum crack characteristics of expansive soil with the content of oyster shell powder,it can be seen that 9 % oyster shell powder has the best inhibitory effect on the crack development of expansive soil. |
