常 在, 杨 军, 程晓辉. 砂土强度和剪胀性的颗粒力学分析[J]. 工程力学, 2010, 27(4): 95-104.
引用本文: 常 在, 杨 军, 程晓辉. 砂土强度和剪胀性的颗粒力学分析[J]. 工程力学, 2010, 27(4): 95-104.
CHANG Zai, YANG Jun, CHENG Xiao-hui. GRANULAR MECHANICAL ANALYSIS OF THE STRENGTH AND DILATANCY OF SANDS[J]. Engineering Mechanics, 2010, 27(4): 95-104.
Citation: CHANG Zai, YANG Jun, CHENG Xiao-hui. GRANULAR MECHANICAL ANALYSIS OF THE STRENGTH AND DILATANCY OF SANDS[J]. Engineering Mechanics, 2010, 27(4): 95-104.

砂土强度和剪胀性的颗粒力学分析

GRANULAR MECHANICAL ANALYSIS OF THE STRENGTH AND DILATANCY OF SANDS

  • 摘要: 砂土强度和剪胀性一直是土力学强度和变形研究的难点和重点,对其进一步认识的关键取决于对砂土颗粒状微观结构的洞察。砂土的颗粒性和散碎性使其适合采用颗粒力学来研究。该文从颗粒力学角度出发,利用平面离散元模拟砂土变形,建立并标定了砂土单元实验的一个颗粒力学模型。在此基础上,通过颗粒力学参数影响分析,研究了砂土无侧限双轴试验的三种表观强度指标(临界状态强度、峰值强度和特征应力强度)、剪胀性及剪切模量的颗粒力学影响因素。研究结果表明:砂土临界状态强度仅受砂土颗粒摩擦系数的影响,是材料属性,符合临界状态土力学理论;砂土峰值强度和特征应力强度不但与砂土颗粒摩擦系数相关,还与围压水平和相对密实度有关。峰值强度不受砂土颗粒自身刚度性质的影响,而特征应力强度受颗粒刚度性质的影响较大,但后者的影响规律不是简单的正比或反比的关系。砂土剪切模量主要受其颗粒自身刚度性质的影响,就目前研究来看,它与砂土相对密实度的关系并不显著。用颗粒力学方法对剪胀性的深入研究比较困难,主要是因为诸多颗粒力学参数(砂土颗粒摩擦系数和刚度、砂土样品的孔隙率及围压水平)均与之相关。该文尝试研究了砂土剪胀性与其颗粒转角的关系。最后,用该文标定的颗粒力学模型,研究了无重地基极限承载力普朗德尔-瑞斯纳问题,通过颗粒力学计算结果与普朗德尔-瑞斯纳解的对比,深化了对砂土地基极限承载力的理解,也为计算颗粒力学方法在岩土工程尺度上的应用提供了参考。

     

    Abstract: The strength and dilatancy of sands are continuously the research focus of soil mechanics. Further understanding of these mechanical properties depends on the insight view of the granular fabric of sands. The granular and discrete properties of materials make sands feasible to be studied by granular mechanics. Three strength indices including the critical state strength, the peak strength and the characteristic stress strength, dilatancy and shear modulus of sands in unconfined biaxial tests were investigated using the approach of granular mechanics. Micromechanical insights were obtained for the phenomenological behavior of sands observed in 2D discrete element simulations. The results presented in this paper indicated the friction coefficient of sand particles was crucial to the critical state strength of sands. This conformed to the theory of critical state soil mechanics. The other two strength indices correlated not only to the friction coefficient of sand particles but also the confining stress that sands were subject to and the relative density. The peak strength of sands was found to be irrespective of the stiffness of sand particles. A definite correlation of the characteristic stress strength with the stiffness of sand particles was unable to determine. The shear modulus of sands primarily correlated with the stiffness of sand particles, but its correlation with the relative density of sands was insignificant as far as the present situations were considered. The dilatancy of sands remained difficult to be understood as it correlated with many parameters such as the friction coefficient of sand particles, the mean stress that sands were subject to, the relative density, the Poisson’s ratio of sand particles as well as the stiffness of sand particles. At last, the calibrated model of granular mechanics developed was employed to investigate the Prandel problem in which a limit equilibrium solution was obtained for the bearing capacity of weightless foundations subject to surcharges. Agreements and disagreements of these two solutions were observed which enriched the understanding of bearing capacity of foundations.

     

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