塑性状态对冻结原状黏性土的抗拉与抗压特性影响研究

Effect of plastic states on tensile and compressive properties offrozen undisturbed clays

基于现场详勘,以三亚某河口通道工程推荐采用管幕冻结法施工为背景,考虑到不同塑性状态黏性土分布深度的不确定性,采用径向劈裂试验和单/三轴压缩测试,系统地研究了冻结原状流塑状、硬塑状黏土及可塑状粉质黏土的抗拉与抗压特性。结果表明,无论是拉伸还是压缩应力-应变行为,三种冻结土体的弱应变硬化和弱应变软化行为都可采用偏差应力与轴向应变的双曲线型修正表达式描述,而强应变软化行为可用二次抛物线模型描述。同一负温下,流塑状黏土的抗拉能力最弱,抗变形能力最强;可塑状粉质黏土次之;硬塑状黏土的抗拉能力最强,抗变形能力最弱。三种冻结原状土体的初始切线模量分布范围基本满足可塑状粉质黏土>流塑状黏土>硬塑状黏土,它们的抗剪强度特性都可用线性摩尔-库伦准则描述。三种冻结土体的黏聚力和内摩擦角基本随温度的降低而增大;同一温度下,流塑状黏土的黏聚力最小,可塑状粉质黏土与硬塑状黏土的黏聚力大小接近,而内摩擦角则表现为:硬塑状黏土>流塑状黏土>可塑状粉质黏土。

The artificial ground freezing method is widely used in underground engineering in soft soil areas and has been rapidly developed.However,the complex stratigraphic distribution in soft soil areas and the rheologi-cal properties of frozen soil materials also bring challenges to the program design and engineering construction of the artificial ground freezing method under large-scale conditions.Based on the field surveys and the context of an estuary access project in Sanya with pipe curtain freezing method construction,considering the complexity of distribution depth on clay with different plastic states,the tensile and compressive properties of frozen fluid-plas-tic clay,hard-plastic clay and plastic-silty clay were studied by radial splitting and uniaxial or triaxial compres-sion tests.The results show that the tensile properties of frozen undisturbed clays with three different plastic states are different under the radial splitting.The fluid-plastic clay and plastic-silty clay display weak strain-hard-en at-5℃,and weak strain-soften at-10℃and-15℃,while hard-plastic clay exhibits strong strain-soften at three negative temperatures.The frozen undisturbed clays with three different plastic states show weak strain-soften under compression tests.For both the tensile and compressive stress-strain behaviors,the weak strain-harden and strain-soften behaviors of the frozen undisturbed clays with three different plastic states can be de-scribed by a modified hyperbola model of deviator stress and axial strain,and the strong strain-soften behavior can be described by a quadratic parabola model.Under the same negative temperature,the tensile strength of the fluid-plastic clay is the weakest and the deformation resistance is the strongest,the plastic-silty clay is second-ary,and the hard-plastic clay has the strongest tensile resistance and the weakest deformation resistance.In the distribution range of initial tangential modulus on the frozen undisturbed clays with three different plastic states,it is largest for the plastic-silty clay,secondary for the fluid-plastic clay and smallest for the hard-plastic clay.However,the initial tangential modulus tends to increase with the decrease of temperature.The failure strain of hard-plastic clay has a tendency to increase with the increase of confining pressure,while the failure strain of flu-id-plastic clay and plastic-silty clay is relatively discrete and irregular.The shear strength of fluid-plastic,hard-plastic clay and plastic-silty clay can be described by the linear Mohr-Coulomb criterion.The cohesion and inter-nal friction angle of the three soils basically increase with the decrease of temperature.At the same temperature,the cohesive force of fluid-plastic clay is the smallest,the cohesive force of plastic-silty clay is close to that of hard-plastic clay,and for the internal friction angle,it is largest for the hard-plastic clay,secondary for the fluid-plastic clay and smallest for the plastic-silty clay.In this paper,the influence of plastic state on the tensile and compressive properties of frozen undisturbed clay is studied so as to provide data support and reference for the de-velopment of underground artificial freezing projects.