Study On The Improvement Of Silty Sand And The Variation Regularity Of Microstructure Parameters In The Yellow River Flooding Area

In history,the Yellow River flooded and changed its course several times,forming a belt-like alluvial plain from west to East.In this area,there are a large number of surface silty sand distributed in layers.This kind of silty sand which mainly composed of sand and silt,with little clay content,no cohesion and low strength,can not be directly used.Under the action of external vibration and load,it is easy to be damaged or even liquefied,which affects the bearing capacity of the foundation.Therefore,the treatment of topsoil is an urgent problem to be solved.In this paper,the silty sand soil from Kaifeng area was taken as the research object,and the relationship between the change of soil strength was revealed by combining the macro mechanical properties and micro perspective of silt soil modification.To start from the Macro-view,the changes of the compressive strength of the remold compaction samples were studied with the addition of the single liquid of ultrafine cement and MC-S liquid as modifiers under various factors.The microstructure of some samples was analyzed by SEM.The binarization of SEM images was processed by Matlab2016 a operation code,and the particle size,shape,orientation of arrangement and structural parameters of pore changes were quantitatively analyzed.The main research results are as follows:(1)According to the XRF experiment,the mineral composition of the silty sand in Kaifeng area is mainly Ca O and Si O2,accompanied by a small amount of Al2O3,Mg O,Fe2O3 and SO3.Through SEM experiments,based on the SEM images of the original silty sand in Kaifeng area under four different magnification of 50 ×,200 ×,500 ×,1000 × the microstructure of the original silty sand is observed.It is found that the structure of the original silty sand is single grain structure as a whole,and a small part of it has agglomerated structure,mainly with micro pores.The contact mode between particles is mainly in the form of face-face,point-face,and edge-edge.It is more dispersed and the cementation between particles is not obvious.(2)The failure modes of unconfined compressive strength test of single liquid cement and MC-S double liquid consolidated silty sand are mainly brittle tensile failure and plastic shear failure.With the increase of the amount of admixture and the extension of the curing age,the brittle fracture is more significant.(3)With the increase of curing age and content of cement,the compressive strength of the sample is gradually increased.When the content is 2%,the effect of ultra-fine cement on the strength and deformation modification of silty sand is not obvious.When the content is about 6%,the performance of ultra-fine cement on silty sand is significantly improved.When the content of ultra-fine cement is 8%,the strength of modified silty sand will not increase with the extension of curing age.(4)From the longitudinal point of view,under the same curing age,with the increase of mc-s double liquid content,the compressive strength and peak strain of the solidified silty sand increase,but the growth rate is declining as a whole.The growth rate of compressive strength and peak strain slows down after 14 days,and basically stops growing after 28 days.When the content of MC-S less than 2%,0.7%,the strength and deformation modification effect of silty sand is not good enough,which is similar to the modification of ultra-fine cement.Generally speaking,the effect of MC-S double liquid reinforcement is better than that of superfine cement single liquid.Through the analysis of compressive strength and peak strength deformation curve and the range analysis of orthogonal test data,it is determined that the optimal scheme is that the MC-S double liquid content is 8%,0.4%,and the curing period is 28 d.(5)Based on the 12 SEM images of 200 × power,the corresponding microstructure parameters are extracted and measured,and the change rule of each parameter is analyzed.As a whole,the change of particle size is from small particles to aggregate.With the increase of curing age,the colloidal particles are neutralized by particles with opposite charges,resulting in colloidal agglomeration,the clay particles and the surrounding large particles without cementation ability gather together,and the integrity of soil structure tends to be stable.The roundness of particles is concentrated between 0.4 and 1.0,especially between 0.4 and 0.8.On the whole,with the increase of curing age,the roundness of particles develops from long strip in narrow state to more regular ellipse and circle.The crystal of cemented material is affected by hydration temperature,and the activation energy changes during the crystal growth process,resulting in the change of crystal structure and the increase of cohesion between particles.The orientation angle of particles approximately presents normal distribution under a certain curing age,mainly concentrated between 70 ° and 150 °,and the orientation of particles changes slightly.The internal force produced by extrusion will force particles to develop into aggregates.During this period,the difficulty of adjust the degree and speed of particle gradually increased,which lead the directional probability entropy fluctuated around 0.949,showing a trend of earlier decline and later rise.The orientation angle is basically the same.With the increase of curing age,the change of small pore is opposite to the change of micro,medium and large pore,showing an upward trend.Generally speaking,the pores change from big pores to small pores and medium pores,and the soil structure becomes more dense.