Experimental Study On Mechanical Properties Of Cement Soil With High Content Fly Ash

Cement soil mixing pile method is one of the foundation treatment techniques that have both technical practicable and economic reasonable. In view of there is rich resources of fly ash and magnesium slag in Yinchuan, and the mechanical properties of cement soil has certain regional features, aiming at these practical problems that lake deposits soft clay around Yinchuan is widely distributed, low strength, high compressibility, can be used as the foundation of the building after treatment, and less accumulation of relevant information about the mechanical properties of fly ash cement soil, took typical soft soil as object, cement content, fly ash content, magnesium slag content, soil moisture content, soil particle size and age as main factors, the effects of cement content, fly ash content, magnesium slag content, soil moisture content, soil particle size and age on mechanical properties and change regulation of cement soil wore studied by mechanical experiments and microcosmic structure analysis, the orthogonal test design and the related mathematical statistical analysis.According to the current specification, cube test specimen with70.5mm length of a side prepared by mixing method, standard curing condition, the strength and deformation of cement soil specimens is tested using the universal material testing machine, microstructure is analyzed by SEM, mechanical properties of cement soil with high fly ash content wore studied, revealed the role law of fly ash, magnesium slag and sand on strength of fly ash cement soil, to clarify the mechanism of soil strength of fly ash cement, determined the optimal combination program of cement and fly ash, established relational model of cement soil with high fly ash content. Research results are as follows.(1)Cement soil with low compressive strength shows the plastic damage obviously. σ-ε curves of specimen which compressive strength is slightly higher can be divided into six stages, there are a like yield stage which like yield strength approximately1.0MPa.The constitutive relation model of cement soil with high fly ash content is established on the basis of σ-ε curves.(2) Fly ash has great contribution to the strength growth of cement soil, especially the later strength growth up to8times. When the cement content>8%, the ratio of fly ash and cement was2-3, fly ash has good filling effect and hydration effect. Filling effect and hydration of fly ash is intrinsic factor that significantly increase the strength of cement soil.(3)The relationship between strength, strain and fly ash content, cement water ratio, water content is approximately linear. The linear correlation between strength and cement water ratio is the best. The linear correlation between strain and water content is the best.(4) The optimal combination of Water content, cement content, fly ash content is that water content is25%, cement content is12%, and fly ash content is20%. Significant sequence is cement content, water content and fly ash content, and increases with age.(5) The strength of cement soil approximately linear increase with the magnesium slag content increase, magnesium slag and fly ash composite mutual enhancement effect, and the effect is significant when activity coefficient is greater than0.37.(6) Cement soil strength increase with the increase of the sand content increase first, decrease later after reached the peak, sand content has a best value. The thicker the sand particle size is, the higher the skeleton effect, and the greater the optimal content.The research results provide a theoretical basis for the reinforcement of soft soil foundation in Yinchuan, has some guidance and reference value to actual project.