| The Pisha sandstone region is one of the most fragile ecological area that soil erosion and sediment deposition are very serious and have become one of the major sources of coarse sand in the middle reaches of the Yellow River as well.In this research,W-OH(hydrophilic polyurethane material)was used to consolidate and reshape the pisha sandstone,and the ability to resist drying-wetting cycles was an important indicator to test the durability of solidified soil.After the soil has undergone multiple drying-wetting cycles,It showed that strength decreased significantly and the deformation enlarged.This had important influence on the long-term stability of building foundations,road slopes,and embankment engineering in the sandstone-sandstone region.Therefore,it had great theoretical and practical significance to study the strength and microstructure changes of consolidation under drying-wetting cycles.In this paper,the sandstone samples were taken from the Erhu dtich in the Huangfuchuan basin of Zhungeer Banner,Inner Mongolia.Through the indoor physical and mechanical tests and microscopic structural analysis,The unconstrained compressive strength and triaxial compression properties of the plastic consolidated body with different concentration of W-OH and drying-wetting cycles are analyzed.After that,the weight loss,microstructure and elemental composition of the drying-wetting cycles were analyzed by weighing method,SEM and EDS.The research results are as follows:(1)Based on the unconfined compressive strength test,the relationship between the unconfined compressive strength,elastic modulus and the number of drying-wetting and W-OH concentration of the W-OH pisha sandstone consolidated body were studied.Using the triaxial unconsolidated undrained test,the strain-softening characteristics of the stress-strain curves of the sandstone consolidation bodies with W-OH after different drying-wetting cycles were obtained.The results show that unconfined compressive strength,elastic modulus,and cohesion of the W-OH solidified Pisha sandstone increase after drying-wetting cycles of 1?3 times,since some W-OH still continue to solidify in water during drying-wetting cycles of 1-3 times.During drying-wetting cycles of 3?9 times,the mechanical strength of the W-OH solidified Pisha sandstone decreases,since the W-OH consolidate totally and some solidified W-OH with low cohesive force disengage due to the increasing times of drying-wetting cycles.After 9 times,the rest solidified W-OH with high cohesive forces remains on the surface of the Pisha sandstone particles and the mechanical strength tends to be stable.The internal friction angle fluctuates up and down from 1?9 times drying-wetting cycles and stabilizes after 9 times,since in the early stage W-OH has not been completely solidified with destruction and the loss process of solidified W-OH,and after 9 times consolidation process was stabilized.(2)Based on the analysis of the mechanical properties of W-OH pisha sandstone consolidated weight-plastic samples(remodeled after 12 times of drying-wetting cycles),the unconfined compressive strength test and the triaxial unconsolidated undrained test were found to be heavy at the same moisture content.It is found that the mechanical properties of the remoldeled W-OH pisha sandstone consolidation are much lower than those before the remolding.This is because the particles are directly connected together by the W-OH cement body before remodeling;After the plastic remodeling,the connection between the particles relies on the adhesion of the W-OH cement body.Thus,the adhesion force is obviously smaller than the binding force of the W-OH cement body which results in the consolidation of W-OH sandstone and the decrease of mechanical properties of soil significantly.The unconfined compressive strength,cohesive force,and internal friction angle of the plastic solidified body gradually increased with increasing W-OH concentration.This was because the W-OH cements were encased on the surface of the sandstone particles,and the high concentration of W-OH cements enabled higher adhesion between the sandstone particles.Even after remodeling(complete destruction of soil particles),it still showed high macro mechanical strength.(3)Based on the analysis of the microstructure of sandstone consolidation at 5%W-OH under different times of drying-wetting cycles,it was found that W-OH was wrapped on the surface of pisha sandstone to increase the adhesion between soil particles.Its macroscopic performance shows the increase of compressive strength and cohesion of soil samples.After drying-wetting cycles,the W-OH cement bodies were detached from the surface of the soil particles,resulting in a decrease in the adhesion between the soil particles.The macroscopic performance shows the decrease of the compressive strength and cohesion of soil samples.Considering that the content of C in the soil sample was from W-OH,the macro-mass loss and the loss of meso-W-OH were analyzed by weighing method and EDS spectrometer(testing C element).It was found that the decrease in strength of the W-OH pisha sandstone consolidation after drying-wetting cycles were mainly due to the destruction and loss of the W-OH cement entrapped on the surface of the sandstone.Finally,it stabilized after 9 times drying-wetting cycles.This was similar to the above-mentioned variation of the unconfined compression strength,elastic modulus,and cohesion with increasing number of cycles.It could be judged that the W-OH pisha sandstone solidified body would form a stable microstructure after times drying-wetting cycles and W-OH would no longer lost.Therefore,the strength,elastic modulus and cohesion should be regarded as important parameters for the later soil evaluation. |
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