深圳全风化花岗岩加固土力学与微观特性

Mechanical and microscopic properties of reinforced soil of completely decomposed granite in Shenzhen

为揭示注浆加固后全风化花岗岩力学及内部微观结构的变化特征,基于直剪试验和电镜扫描观测,分析水泥质量分数对全风化花岗岩加固土的抗剪强度、剪胀性和微观结构的影响规律.直剪试验结果表明,随着水泥质量分数上升,全风化花岗岩加固土抗剪强度和剪胀性显著增大,由应变硬化型材料逐渐转变为应变软化型脆性材料;水泥质量分数从0增加到16%,最大剪胀角增加了6°~10°,黏聚力从7 kPa提高到203 kPa,内摩擦角在31°~38°间波动,水泥加固全风化花岗岩主要通过增加黏聚力的方式提升抗剪强度.电镜扫描结果表明,随着加固水泥质量分数的增加,水泥结晶物越来越密集,相互胶结形成连续的空间网状甚至团聚状结构,改变了土颗粒间的相互作用方式,使加固土由以摩擦为主的材料向以胶结为主的材料转化.研究可为评估全风化花岗岩加固土物理力学特性及深圳地区的工程建设提供参考.

The influence of cement mass fraction on shear strength,shear dilatancy,and microstructure of completely decomposed granite cemented soil is examined through direct shear tests and scanning electron microscope observations to uncover the alterations in mechanical properties and internal microstructure of completely decomposed granite after grouting reinforcement.The experimental findings indicate that the shear strength and shear dilatancy of completely decomposed granite cemented soil experience significant increase as the cement mass fraction increases,transitioning progressively from a strain-hardening material to a strain-softening brittle material.As the cement mass fraction rises from 0 to 16%,the maximum shear dilation angle expands from 6°to 10°,and the cohesion increases from 7 kPa to 203 kPa.The internal friction angle fluctuates between 31°and 38°.Cement reinforcement primarily enhances the shear strength of completely decomposed granite by augmenting the cohesion.Scanning electron microscopy findings demonstrate that with an increase in cement mass fraction,cement crystallites become denser and bond with one another,forming a continuous spatial mesh or even agglomerate structure.This alters the interaction mode between soil particles,transforming the cemented soil from a friction-based material to a cementation-based material.This research can be applied to assess the physical and mechanical properties of completely decomposed granite cemented soil and engineering construction in the Shenzhen area.