Discrete element numerical simulation of the accumulation process of wave-induced pore water pressure in the seabed
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摘要: 海床土层在波浪的循环荷载作用下会逐渐累积孔压，降低土层的稳定性，并威胁海上工程。为了研究孔隙水压力的累积机制，本文提出离散元孔隙密度流方法，并改进研发离散元分析软件MatDEM，实现了海床沉积物孔压的累积过程模拟。基于现场试验装置及土体力学参数建立离散元模型，通过对比试验和数值模拟结果发现：对海床沉积物施加波浪荷载后，表层土体中产生较高孔压，并逐渐向深层传递；在循环波浪荷载作用下，土颗粒间孔压累积范围逐渐增加；当孔压累积时间足够长时，土层中孔压收敛于所施加最大荷载与最小荷载的平均值，此时若孔压达到初始有效应力，土体将发生液化，内部土颗粒成为再悬浮沉积物；在周期性波浪荷载作用下，土颗粒液化悬浮后发生移动，浅层颗粒位移量大，土体整体表现为圆弧形移动。Abstract: The seabed soil layer will gradually accumulate pore pressure under the action of wave cyclic load, reduce the stability of the soil layer, and threaten offshore engineering. In order to study the accumulation mechanism of pore water pressure, the discrete element pore density flow method was proposed, and the discrete element analysis software MatDEM was improved to realize the simulation of the accumulation process of seabed sediment pore pressure. Based on the field test device and the mechanical parameters of the soil body, a discrete element model was established. By comparing field test and numerical simulation results, it was found that after applying the wave load to the seabed sediment, a higher pore pressure was generated in the surface soil body and gradually transferred to the deep layer. Under the action of cyclic wave load, the cumulative range of pore pressure between soil particles gradually increased. When the pore pressure accumulation time was long enough, the pore pressure in the soil layer converged to the average of the maximum and minimum loads applied. As the number of load cycles increased, the pore pressure at all depths increased cumulatively until the soil body liquefied and the internal soil particles became resuspended sediments. Under the action of periodic wave loads, the soil particles moved after being liquefied and suspended, and the shallow particles had a large displacement, and the overall performance of the soil was circular arc movement.
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Key words:
- discrete element /
- numerical simulation /
- wave action /
- pore water pressure /
- MatDEM
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图 1 离散颗粒堆积模型（a）、颗粒间法向弹簧力（b）和颗粒间切向弹簧力（c）
Fig. 1 Packing model of discrete element (a), normal spring force between particles (b), and shear spring force between particles (c)
图 2 离散元堆积颗粒（a）、孔隙流体域（b）和颗粒−孔隙系统（c）
Fig. 2 Discrete element stacked particles (a), pore fluid domain (b), and particle and pore system (c)
图 6 荷载循环1次（a）、10次（b）、20次（c）、40次（d）孔压分布
Fig. 6 Pore pressure distribution of load cycle 1 (a), 10 (b), 20 (c), 40 (d) times
图 7 循环荷载40次孔压累积
Fig. 7 Pore water pressure accumulation process under cyclic loading 40 times
表 1 海洋土体宏观力学性质
Tab. 1 Macro mechanical properties of ocean soil
力学性质 测试值 杨氏模量E/MPa 5.00 泊松比v 0.14 抗拉强度Tu/kPa 1.00 抗压强度Cu/kPa 10 内摩擦系数μi 0.5 
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表 2 离散元微观力学参数
Tab. 2 Micro mechanical parameters of the discrete element
力学参数 平均值 法向刚度 Kn/(kN·m−1) 123 切向刚度 Ks/(kN·m−1) 48.7 断裂位移 Xb/m 1.40×10−6 抗剪力 Fs0/N 0.898 摩擦系数 μp 0.121
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表 3 数值模拟与现场试验孔压数据对比
Tab. 3 Data comparison of pore pressure between numerical simulation and field test
深度/m 现场孔压/kPa 模拟孔压/kPa 0.05 0.585 0.652 0.12 0.799 1.513 0.20 1.890 1.858 0.30 1.635 1.814
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