# 基于离散元法的水合物沉积物双轴压缩试验模拟分析Simulation Analysis of Biaxial Compression of Hydrate-Bearing Sediments Based on Discrete Element Method

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Hydrate-bearing sediments can be regarded as a class of mixed granular material forming with sand and hydrate particles, which is a typically discontinuous problem. The discrete element method is an effective way to solve the problem. The DEM samples of hydrate-bearing sediments with saturation of 15%, 25%, 35% and 45% were prepared by discrete element numerical simulation software PFC
2D, and the biaxial compression discrete element simulation experiments were carried out. The strength and deformation characteristics of saturation and effective confining pressure on the mechanical properties of hydrate-bearing sediments were studied. The experiments results show that there is strain softening phenomenon appearing under low saturation condition, and with the increase of the saturation, the stress-strain curve would transit from strain softening to strain hardening. The peak stress and initial elastic modulus of the hydrate-bearing sediments increase upon the increased saturation and effective confining pressure. The cohesion and friction angle of the sediments are affected by the hydrate saturation, but the strength of the sediments is mainly affected by cohesion.

1. 引言

2. 离散元双轴试验模拟

2.1. 试样制备

Figure 1. Grain gradation curve and DEM numerical specimen

${{S}^{\prime }}_{mh}=\frac{{S}_{mh}}{{S}_{v}}$ (1)

$N=\frac{S\rho {{S}^{\prime }}_{mh}}{\text{π}{r}^{2}}$ (2)

Figure 2. The filling process of hydrate particles

Table 1. Material properties used in DEM simulations

2.2. 试验过程

Figure 3. The simulation process of biaxial compression of hydrate-bearing sediments

2.3. 应力–应变曲线

Figure 4. Deviator stress-axial strain relationship under different confining pressure for hydrate-bearing sediments

Figure 5. Deviator stress-axial strain relationship under different MH saturation of hydrate-bearing sediments

3. 试验结果分析

3.1. 峰值应力

Figure 6. Curve of peak strength and saturation of hydrate-bearing sediments

Figure 7. Curve of peak strength and effective confining pressure of hydrate-bearing sediments

3.2. 初始弹性模量

Figure 8. Curve of initial elastic modulus and saturation of hydrate-bearing sediments

Figure 9. Curve of initial elastic modulus and effective confining pressure for hydrate-bearing sediments

3.3. 摩擦角和内聚力

Figure 10. Mohr’s envelopes of hydrate-bearing sediment

Table 2. The internal friction angle and cohesive of hydrate-bearing sediments

4. 结论

1) 水合物沉积物在饱和度较低(小于25%)的条件下会表现出明显的应变软化现象，而在饱和度较高(大于25%)的情况下则会表现出应变硬化现象。

2) 水合物沉积物的峰值应力随着水合物饱和度的增加而呈非线性增长，且增长速率是逐渐增大的；而其初始弹性模量随着饱和度的增加成线性增大。

3) 水合物沉积物的峰值应力随着有效围压的增大是成线性增大的；而其初始弹性模量随着有效围压的增大也是成线性增大的。

4) 水合物饱和度对沉积物的内聚力和摩擦角都有影响，但由于对摩擦角的影响是十分微小的，所以可以忽略摩擦角对沉积物强度的影响，所以沉积物的强度主要是由内聚力的变化影响的。

NOTES

*通讯作者。

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