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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。
Sandy soil strength and dilatancy have always been the difficulties and focuses of soil mechanics strength and deformation research. The key to further understanding of sand and clay depends on the insight into the granular microstructure of sand. The granularity and fragmentation of the sand make it suitable for studying with particle mechanics. Based on the particle mechanics, this paper uses the plane discrete element to simulate the deformation of sand, and establishes and calibrates a particle mechanical model of sand cell experiment. Based on the analysis of the influence of particle mechanics parameters, three kinds of apparent strength indexes (critical state strength, peak strength and characteristic stress strength), dilatancy and shear modulus The particle mechanics influence factors. The results show that the critical state strength of sand is affected only by the friction coefficient of sand particles, which is the material property and meets the critical mechanics theory. The peak sand strength and the characteristic stress intensity are not only related to the friction coefficient of sand particles, Pressure level and relative density. The peak strength is not affected by the stiffness properties of the sand particles, while the characteristic stress intensity is strongly influenced by the properties of the particles. However, the influence of the latter is not simply proportional or inversely proportional. The shear modulus of sand is mainly affected by its own stiffness properties. For the current study, the relationship between the shear modulus and the relative density of sand is not significant. The in-depth study of dilatancy using particle mechanics is more difficult because of the correlation between the mechanical parameters of many particles (the friction coefficient and stiffness of sand particles, the porosity of sand samples and the confining pressure). This paper attempts to study the relationship between the dilatancy of sand and its particle angle. Finally, by using the particle mechanics model calibrated by this paper, the problem of the Prandre-Reisner problem of the ultimate bearing capacity of heavy foundations is studied. By comparing the results of particle mechanics with the Prandtl-Reisner solution, The understanding of the ultimate bearing capacity of foundation also provides a reference for calculating the application of particle mechanics to geotechnical engineering.