轻量砂变形及强度特性三轴试验研究

Triaxial test for deformation and strength characteristics of light weight sand

通过三轴试验系统研究了新型土工材料——轻量砂的变形及强度特性。结果表明,不同的配比、龄期使轻量砂具有不同的原生结构强度,围压使不同原生结构强度的土样处于剪胀或剪缩状态,导致发生应变硬化、应变软化以及相应状态下孔压的3种对应形态变化。变形模量随EPS(发泡聚苯乙烯)球粒掺入比的增大而线性减小,随水泥掺入比、龄期增大而线性增大,相同配比的土样变形模量与围压关系不大;三轴抗压强度随EPS球粒掺入比增大而呈负指数关系减小,随水泥掺入比、龄期、围压增大而线性增大,存在水泥掺入比阀值;土骨架转换效应对于土样强度的影响很大,造成了土体单轴、三轴抗压强度分带,高水泥掺入比能够大大弱化EPS颗粒的土骨架效应。结合前人成果,系统地研究了轻量砂密度、无侧限抗压强度的影响因素,引入材料学中比强的概念,提出了单价比强图结合配方公式的方法,对轻量土砂进行配方优化。分析了轻量土砂应力-应变关系转型问题,提出采用无侧限抗压强度来表征不同配比、龄期轻量土砂的原生结构强度。通过试验与数理统计,建立临界围压与原生结构强度的关系,为数值模拟计算与建立本构模型奠定了基础。

In order to research a new type of geotechnical material——light weight sand,its deformation and strength characteristics were researched by triaxial test.The results show that light weight sand have different primary structural strength because of different mixed ratio and age,soil samples of different primary structural strength are in the state of shear dilatancy or shear contraction under different confining pressures,these lead to strain hardening,strain softening,and three corresponding pore pressure states.Deformation modulus decreases linearly with increase of EPS（expanded polystyrene beads） mixed ratio,increases linearly with increase of cement mixed ratio and age;and there is little relation between deformation modulus and confining pressure for the same mixed ratio soil samples.Triaxial compressive strength decreases according to negative exponential relation with increase of EPS mixed ratio,increases linearly with increase of cement mixed ratio,age and confining pressure.There is a threshold for cement mixed ratio.Transformation effect of soil framework has an important effect on soil strength,and that leads to strength zoning under uniaxial and triaxial compression states.When cement mixed ratio reaches to a high value,it can weaken transformation effect of soil framework of EPS beads.Combining precursors＇ research production,influence factors of density and uniaxial compressive strength of light weight sand are researched;then the concept of specific strength is recommended.Prescription of light weight soil-sand can be optimized by combining unit price-specific strength figure and recipe formula.Stress-strain relation transformation of light weight soil-sand is researched,uniaxial compressive strength is recommended to be metewand of primary structural strength.The relation between critical confining pressure and primary structural strength should be built according to test and mathematical statistics;these can make contribution for numerical simulation and establishment of constitutive model.