Analysis On The Influence Of Reactive Magnesia On Grouting Reinforced Soft Foundation

Grouting technology has been widely used in soft soil improvement projects.The main research focuses on improving the grouting technology,creating new construction processes,improving the grouting slurry formulation and discovering new grouting materials.The mechanism of grouting slurry has been insufficiently analyzed.This paper is based on the reconstruction project of Provincial Highway203,K9 + 900-k33 + 877 section from Qipanzhou to Fuchi,in Yangxin County.The cement slurry has been used as the grouting material to strengthen the soft foundation,and the reactive magnesia has been used as an admixture to explore the reactive magnesia injection the effect of slurry reinforcement on soft foundation.A variety of testing and characterization methods has been used to perform performance testing and composition analysis on the undisturbed soil;an indoor unconfined compression test was used to test the strength of the cement-solidified soil sample;an indoor triaxial test was used to detect the shear strength of the cured soil at various ages Parameters;Scanning electron microscope(SEM)and X-ray diffractometer(XRD)were used to analyze the microstructure of the cured soft clay.The main work and conclusions are as follows:1)In order to obtain the macroscopic physical properties and microstructure of the undisturbed soil,the undisturbed soil taken in the target section had been subjected to an indoor direct shear test and a liquid-plastic limit test,and an X-ray diffractometer,a fluorescence spectrometer and a scanning electron microscope had been used to compare the undisturbed soil Characterize and analyze the mineral composition and microstructure of the soil.The test results show that the undisturbed soil contains 14% of clay minerals,the main mineral phase is kaolinite,and this mineral composition is the main reason why the undisturbed soil is in a soft plastic state.The natural water content of the soil is 31.66%,resulting in lower strength of the undisturbed soil.The microstructure of undisturbed soil is as follows: the soil particles are fine,and the microscopic crystals have no framework structure,resulting in a small cohesion and internal friction angle of the undisturbed soil.2)In order to obtain the effect of the reactive magnesia incorporation on the soft foundation strengthened by grouting,the strength test had been carried out by unconfined compression test,and the grouting material had been studied based on the composition analysis of the grouting material and the mineral composition and crystal structure of the undisturbed soil.A chemical reaction that occurs during the curing of soft clay.The test results show that the incorporation of reactive magnesia improves the early strength of the sample,mainly because the active magnesium oxide can promote the hydration reaction of cement.When the added amount of reactive magnesia is 3% of weight of the cement mass,the compressive strength of the sample is the largest.In addition,reactive magnesia improves the cohesiveness of cement cured soil.3)In order to obtain the stress-strain relationship of the samples mixed with active magnesium oxide,indoor triaxial tests had been carried out on the samples with the optimal mix ratio.Three different age periods of 7 days,14 days and 28 days had been selected,and four groups of different confining pressures of 100 KPA,200KPa,300 k Pa and 400 k Pa had been taken to obtain the relevant triaxial test results.The test results show that the confining pressure has a direct effect on the peak strength of the sample.The greater the confining pressure,the higher the strength of the sample;as the curing period increases,the strength of the sample increases significantly;the grouting slurry made with the optimal mix ratio It can effectively improve the cohesion and internal friction angle of the soil,and enhance the strength of the soil.4)In order to obtain the mechanism of reactive magnesia mixed with grouting slurry in the process of strengthening soft foundation,X-ray diffractometer and scanning electron microscope had been used to characterize and analyze samples with different mixing ratios.The evolution explains the reason for the increased strength of samples at different ages.The test results show that the addition of solidifying agent generates a layer of gelling substance on the surface of the soil particles,which causes the size of the soil particles to increase continuously.The magnesium hydroxide formed after the hydration of activated magnesium oxide has weak cementing properties and promotes the granulation of soil particles,resulting in an increase in the particle size of the sample.The hydration,carbonization and ion exchange reaction of active magnesium oxide to form fine flaky crystals can fill the pores between large-volume crystals and enhance the micro-skeleton structure of the solidified soil.5)In order to obtain the action mechanism of active magnesia incorporation on grouting to strengthen the soft foundation,and to establish a structural model of solidified soil of various ages.Based on the micro-test results of undisturbed soil and cement solidified soil of various ages,the microstructure model of the soil body was established,and the reason why the shear strength parameters of the solidified soil increased with the increase of curing period was revealed according to the model changes.