DEM-FDM coupled simulation of cone penetration tests in a virtual calibration chamber with sand
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摘要: 静力触探是岩土工程最重要的原位测试手段之一,然而静力触探不能直接测出土体参数,需借助标定罐试验或数值模拟中已有的锥尖阻力与土体参数的经验关系来确定土体参数。本研究利用离散元(DEM)与有限差分法(FDM)耦合数值方法实现了砂土中标定罐静力触探贯入全过程的高效模拟,探究了影响锥尖阻力的主要因素。模拟中,首先根据砂土单元体宏观力学特性标定了砂土颗粒接触模型参数,并进一步分析了标定罐尺寸、砂土密实度、围压等对锥尖阻力影响,最后建立了归一化锥尖阻力Q和峰值内摩擦角φpeak的关系。研究结果表明,在离散-连续模型径向尺寸比Rdf为0.67且标定罐归一化径向长度Rd为20的情况下,模拟的尺寸效应可忽略。同时,锥尖阻力的模拟结果与小孔扩张理论计算结果吻合良好,验证了数值模拟的可靠性。归一化锥尖阻力Q和峰值内摩擦角φpeak之间呈指数关系,与原位测试结果接近,进一步验证了耦合模拟方法的准确性,其结果可为砂土静力触探锥尖阻力与土体参数经验关系的建立提供重要参考。Abstract: The cone penetration test, considered one of the most crucial in-situ testing methods in geotechnical engineering, is unable to directly measure soil parameters. Generally, the empirical relationship between the penetration resistance and the soil parameters is established through tests or numerical simulations. In this research, a coupled numerical approach of the discrete element method (DEM) and the finite difference method (FDM) is employed to simulate the entire cone penetration test process within a calibration chamber and unveil the mechanisms that influence the penetration resistance. Firstly, the microscopic parameters of the sand are calibrated based on its macroscopic behaviors. Additionally, the effects of calibration chamber size, sand density and confining stress on the penetration resistance are thoroughly analyzed. Finally, a relationship is established between the normalized penetration resistance Q and the peak internal friction angle φpeak. The findings indicate that the size effects in the simulation become negligible when the continuous-discrete model size ratio Rdf reaches 0.67 and the normalized radial length Rd of the calibration chamber is set at 20. Furthermore, the simulated penetration resistance closely matches the results obtained by the cavity expansion methods, confirming the reliability of the numerical simulation. An exponential relationship is observed between Q and φpeak, which closely aligns with the in-situ test results. This further validates the accuracy of the coupled simulation method. These outcomes offer valuable insights for establishing empirical relationships between the cone penetration resistance in sand and the soil parameters in geotechnical engineering.
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表 1 砂土颗粒接触模型参数
Table 1 Microscopic contact parameters of sand
参数 数值 颗粒密度(ρ) 2650 kg/m3 刚度系数(k0) 8×108 N/m2 刚度比(αs) 0.15 颗粒摩擦系数(μ) 0.45 颗粒抗转动系数(μr) 0.35 颗粒法向刚度(kn) kn = k0×r 颗粒切向刚度(ks) ks = αs×kn 表 2 莫尔-库仑模型参数取值
Table 2 Parameters of Mohr-Coulomb model
相对密实度Dr/% 杨氏模量E/ MPa 泊松比 内摩擦角φ/(°) 剪胀角ψ/(°) 70 60.6 0.3 36.5 10.3 40 36.3 0.3 31.9 3.2 10 30 0.3 30.1 0 表 3 模型边界及锥体参数
Table 3 Model boundary and cone parameters
参数 数值 耦合墙法向刚度 4×106 N/m 耦合墙切向刚度 6×105 N/m 耦合墙摩擦系数 0.45 耦合墙抗转动系数 0.35 边界墙法向刚度 1×1010 N/m 边界墙切向刚度 1×1010 N/m 边界墙摩擦系数 0 边界墙抗转动系数 0 锥体法向刚度 1×1010 N/m 锥体切向刚度 1×1010 N/m 锥体摩擦系数 0.2 锥体贯入速度 0.1 m/s 表 4 莫尔库仑本构模型模拟三轴试验的参数
Table 4 Parameters of Mohr-Coulomb model for simulating triaxial test results
Dr/% p0/kPa qpeak/kPa E/MPa ψpeak/(°) ϕpeak/(°) 10 100 205 20.3 0.23 3.9 30.4 40 100 224 36.3 0.25 6.1 31.9 70 100 311 56.5 0.25 18.1 36.5 10 200 405 21.2 0.24 5.1 30.2 40 200 448 38.4 0.26 4.8 31.9 70 200 580 56.7 0.25 16.8 36.3 10 400 801 26.3 0.21 2.9 30.1 40 400 874 40.1 0.27 5.9 31.5 70 400 1132 56.3 0.25 16.1 35.9 -
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