Study On Unconfined Compressive Strength Characteristics And Micro Mechanism Of Composite Fiber Cement Soil

At high water content and low cement mixing ratio,the ability of fibers to solidify soil is limited,but the addition of fibers can significantly increase the residual strength of the soil.So it is necessary to explore a kind of composite fiber cement soil which has both high strength and fiber crack resistance for soil reinforcement.Based on the study of the mechanical properties of fiber-reinforced cement soil,this paper further adds fly ash,nanoclay,and nano-magnesium oxide to the fiber cement soil to obtain fly ash composite fiber cement soil(FPCS)and nanoclay composite fiber.Cement soil(abbreviated as NPCS),nano-magnesia composite fiber cement soil(abbreviated as MPCS).Unconfined compressive strength test and microstructure test were performed on the composite fiber cement soil.Based on the IPP image processing software,the SEM images were analyzed,and the microstructure parameters of the composite fiber cement soil were quantitatively analyzed.The solidification mechanism of the external materials was discussed.The main work and results of this article are as follows:(1)By comparing different data processing methods,a "normalized weighted average algorithm" data processing method is proposed.In this method,the weight of each peak point is used to represent the weight of each curve,and the original five values are determined by determining the standard value,deviation,deviation,average weight coefficient,average weight,initial weight,weight function,weight,weighting factor,weighting stress and other steps The set of data is normalized into a set of typical data.The comparison between the original data and the typical fitting curve verifies that the algorithm is feasible for data processing.(2)Use the algorithm in(1)to calculate the weighted average UCS parameters of each group,and analyze the unconfined compressive strength of the cement soil with 10% and 15% of the two types of cement content and single-fiber cement with the fiber Than the impact.The compressive strength,residual strength,peak strain,brittleness index,failure mode,etc.were compared and analyzed,and it was found that the fiber blending ratio of 0.6% can make the best mechanical properties of fiber cement soil.(3)Based on fiber cement with a fiber blending ratio of 0.6% and cement blending ratio of 15%,blending materials such as fly ash,nano-clay,and nano-magnesium oxide.Influence of mechanical properties of cement soil.The unconfined compressive strength test of 4 kinds of composite fiber cement soil under the ages of 7d,14 d,and 28 d found that the addition of fly ash,nanoclay,and nanomagnesium can improve the composite fiber to varying degrees.Compressive strength of cement soil.Among them,fly ash has the best effect,followed by nanoclay,and nanomagnesium oxide is inferior.(4)Take the composite fiber cement soil samples after 7d and 28 d damage for micro test,and use the SEM picture as the carrier to analyze the micrograph of the composite fiber cement soil with the aid of Image-Pro Plus image analysis software.The results show that the porosity of each composite fiber cement soil at 28 d is smaller than that of 7d,which is consistent with the law of compressive strength at the macromechanical level.At 7d and 28 d,the porosity of the four composite fiber cement soils: FPCS <NPCS <MPCS <PCS;the order of unconfined compressive strength in macromechanics is: FPCS> NPCS> MPCS> PCS.That is,the larger the compressive strength,the denser the structure and the smaller the porosity,so the microstructure conforms to the macromechanical properties.(5)Based on the characteristics of the stress-strain curve of the composite fiber cement soil,summarize the shortcomings of the traditional constitutive model and establish a 4-parameter composite sine-exponential constitutive model(referred to as "FCSE model").By analyzing the mathematical characteristics of the constitutive model and the stress-strain curve fitting,the applicability of the constitutive model is verified.Based on this,an empirical formula based on the change of composite fiber cement soil with different ages was proposed,and the stress-strain curves of composite fiber cement soil samples under different ages were fitted,and 3d,10 d,and 20 d curing were predicted.Stress-strain curve at the age.