渗透压–应力耦合作用下砂岩渗透率与变形关联性三轴试验研究

为了探讨渗透压–应力耦合作用下岩石渗透率与变形的关联性，采用岩石伺服三轴试验系统，在不同围压和渗透压条件下，利用稳态法对砂岩全应力–应变过程进行渗透率试验研究。根据试样渗透率变化与其破坏过程的对应关系，分析全应力–应变过程中试样渗透率随其脆性、延性变化的特点及渗透率–轴向应变和渗透率–体积应变之间的关联性。试验结果表明：(1) 在渗透压–应力耦合作用下，试样初始渗透率、峰值强度随着围压与渗透压的改变而改变。(2) 在渗流场–应力场耦合作用下连续加载的全应力–应变过程中，渗透率先随着轴向应变的增大而逐渐减小，进入弹塑性阶段后，渗透率变化曲线随围压变化呈现增大、持平及减小3个不同趋势。其中，渗透率曲线持平的现象为三轴渗透试验研究中的新现象。(3) 围压较高时，若形成局部压缩带，则试样进入弹塑性阶段后，渗透率的变化趋势是由岩石微裂隙的萌生、扩展与岩石骨架颗粒压碎这2个主要因素共同决定的。(4) 岩石微裂隙的萌生、扩展对渗透率增大起积极作用，岩石骨架颗粒压碎形成的压缩带对渗透率增大起抑制作用。(5) 岩石进入塑性阶段后，随围压增大，渗透率由上升趋势转变为下降趋势的现象先于脆–延转换的临界状态发生。(6) 岩石的体积应变对渗透率有一定影响，在脆–延转换阶段存在体积应变增大而渗透率减小的现象，这需要其他能够更精确地测量体积应变变化的试验进一步验证。

TRIAXIAL EXPERIMENTAL STUDY OF ASSOCIATED PERMEABILITY-DEFORMATION OF SANDSTONE UNDER HYDRO-MECHANICAL COUPLING

In order to understand the relationship between rock permeability and deformation under hydro- mechanical coupling，a servo-controlled triaxial rock mechanics test system is employed to investigate the steady-state permeability of sandstone under various confining stresses and osmotic pressures. Permeability characteristics(associated with brittleness and ductility) and the relationship(associated with permeability，stress and strain) are analyzed based on permeability-strain curves of sandstone samples. The results show that：(1) The initial permeability and peak strength of sandstone vary with the confining stress and osmotic pressure under hydro-mechanical coupling. (2) In the complete stress-strain process under hydro-mechanical coupling，the permeability decreases with the increase of axial strain in the beginning. However，at the elastoplastic stage，the curves of permeability vary with different confining pressures，i.e. dropping，constant，and rising. A new phenomenon in the horizontal curve of permeability is observed in rock seepage triaxial test. (3) Under high confining pressure，if local compaction band is formed，the trend of permeability is determined by coalescence of microcracks and skeleton crushed after the elastoplastic stage. (4) Coalescence of microcracks plays a positive role in increasing permeability，but the formed compaction band resultant from crushed skeleton will decrease the permeability. (5) After the plastic stage，the permeability changes from increase to decrease prior to the critical state of brittle-ductile transition when confining pressure increases. (6) Volumetric strain of rock has certain influences on the permeability. For the phenomenon that permeability decreases when the volumetric strain increases in the brittle-ductile transition stage，further study is needed where more accurate measurement of volumetric strain is required.