饱和破碎砂岩压实过程中粒度分布及能量耗散

Particle size distribution and energy dissipation of saturated crushed sandstone under compaction

分别对不同级配(Talbot指数为0.2,0.4,0.6和0.8)侧向受限饱和破碎砂岩进行压缩,利用显微CT观察了试样内部孔隙结构的变化规律;基于分形理论,定量研究了粒度分布特征;通过计算应变能密度,分析了能量耗散特征。结果表明,在16 MPa轴向应力下,轴向应变为0.304 5~0.324 1;在压实初期,试样结构松散,颗粒间接触不稳定,孔隙尺寸较大且联通性好;而在压实后期,试样密实,孔隙形状多为稳定的三角形。粒度分布具有分形特征,分形维数范围为1.733 1~2.561 0。当轴向应力为0~4 MPa时,颗粒破碎发生急剧,分形维数快速增大;而在4 MPa后,颗粒破碎发生较少,分形维数缓慢增大。变形引起的能量耗散随着轴向应变和分形维数的增大而加速增大,当轴向应变大于0.17或分形维数大于2.1后,应变能密度急剧增大。初始粒径配比对粒度分布和能量耗散均有影响,相同轴向应力下,Talbot指数越大,分形维数越小;相同轴向应变下,Talbot指数越大,应变能密度越小。

Compaction tests on saturated crushed sandstone with lateral constraint and different initial gradation （Talbot exponent is 0.2, 0.4, 0.6 and 0.8, respectively） were conducted. And Micro-CT system was adopted to observe the changing process of the pore structures. Meanwhile, the characterization of the particle size distribution was quantitatively obtained based on the fractal theory. The properties of energy dissipation were analyzed through calculating the strain energy density. Results indicate that the axial strain ranges from 0.3045 to 0.3241 when the axial stress is 16 MPa. At the early stage of compac- tion, the samples are loose, the contact among particles is unstable, and the pore size is large with good connectivity. However, at the later stage, the samples are dense with most pores being relatively stable triangle. The particle size distribution of saturated crushed sandstone under compaction satisfies fractal condition well, and the ffactal dimension ranges from the particle crushing occurs extensively and the fractal dimension increases rapidly during compaction. In contrast, while the axial stress is more than 4 MPa, the particle crushing occurs slightly and the fractal dimension increases slowly. With the increase in axial strain and fractal dimension, the energy dissipation caused by deformation increases at an accelerated rate. After the axial strain exceeds 0.17 or the fractal dimension exceeds 2.1, the strain energy density increases rapidly. It should be pointed out that the initial gradation affects the evolution of particle size distribution and energy dissipation. Under the same axial stress, the fractal dimension decreases with an increase in the Talbot expo- nent. While under the same axial strain, the strain energy density declines with an increase in the Talbot exponent