碎屑砂岩三轴压缩下强度和变形特性试验研究

基于碎屑岩组织结构疏松、含水率较高、物理力学性能较差、呈孔隙式胶结接触等特点,对碎屑砂岩首先开展了物理特性试验分析,认为其微、细观结构复杂、内部破坏严重,矿物成分为石英、长石、绢云母等,化学成分以SiO2为主,属微透水、小孔隙率砂岩,且渗水化学侵蚀并不显著。其次,开展了静水压力、单轴压缩和三轴压缩试验,研究了碎屑砂岩的强度和变形破坏特性。最后,初步探索了物理特性与强度变形特性的关系。结果表明,静水压力为2.6 MPa时,岩样内部微缺陷压密完成;单轴压缩曲线呈明显6阶段特征,峰值应力达0.98 MPa,属脆-延性破坏;三轴压缩条件下,岩样呈压缩为主的延性扩容破坏,轴向压缩和环向体积扩容达6%和4%;曲线无明显破坏荷载,呈现非线性、塑性硬化、存在屈服平台和体积由压缩向扩容过渡等特性。且体积扩容破损应力与屈服应力基本相同,扩容转折点随围压增加而增大,围压可增强岩样抵抗变形破坏的能力。试验结果旨在为岩石工程稳定分析及本构模型构建提供可靠的依据。

Experimental investigation on strength and deformation properties of clastic sandstone under triaxial compression

Based on the characteristics of loose organizational structure, high moisture content, poor physical mechanical properties and pore cementation contact, the basic physical properties tests on clastic sandstone were carried out first. It's considered that the rock which belongs to small porosity sandstone as micro-permeability is extremely complex microstructure and that internal structure is damage seriously. The main mineral compositions are quartz, feldspar, sericite and so on; mainly chemical constituent is SiO2 and the chemical erosion is not significant. Secondly, the hydrostatic pressure tests, uniaxial and triaxial compression tests were carried out for clastic sandstone to study the strength and deformation failure properties. Finally, the correlations between mechanical properties and physical properties are preliminary discussed. The results show that the internal micro-defect of rock is compaction completed when hydrostatic pressure reaches 2.6 MPa. The uniaxial compression curve shows the characteristics of six distinct stages; and that the peak stress is 0.98 MPa. Moreover, brittleness and ductility are shown. Under triaxial compression test, clastic rock shows significant characteristics of mainly compressed and ductility dilatancy failure. In the action of deviatoric stress, the axial and lateral strains of rock reach 6% and 4% respectively. The curve has no significant damage load, which shows the mechanical properties of nonlinear, plastic hardening, yield platform and volume strain from compression to ductility dilatancy and so on. And the volume dilatancy damage stress is almost the same as the yield stress. The dilatancy turning point increases with an increase of confining pressure, and moreover, the confining pressure enhances the rock resistance to deformation and failure. The results provide dependable reference for the establishment of rock constitutive model and stability analysis.