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为了揭示深部软弱地层开挖卸荷后围岩流变力学特性,开展砂质泥岩恒轴压逐级卸围压三轴卸荷蠕变试验,研究软岩轴向、侧向和体积蠕变规律和卸荷流变过程中偏应力–应变关系特性。主要结论有:(1)每卸除一级应力(10 MPa)产生的瞬时变形、蠕变变形、蠕变变形相对该级荷载下的瞬时变形的比值、蠕变变形占总变形量百分比均随偏应力的增加而增大,围压越低蠕变变形增加的幅度越大;(2)随着围压逐级卸荷,岩石内部产生竖向张性微裂纹,微裂纹的萌生和扩展使得卸围压瞬时产生较明显的侧向变形,且蠕变过程中微裂纹将发生与应力水平相应的时效扩展,产生黏塑性变形;(3)岩石在时效条件下的渐进破坏的本质是损伤随时间的逐渐累积,并伴随着裂纹的时效扩展,统称为时效损伤破裂;(4)随着围压逐级卸荷,偏应力增大,历史上经历的卸荷级数多、蠕变时间长,试样内部积累的不可恢复应变和损伤越多,时效损伤破裂越剧烈,在该级荷载条件下轴压低的试样其流变速率越大,蠕变变形量越大,卸荷效应和流变特征更加明显,同时伴随显著的侧向扩容,导致蠕变扩容;(5)卸荷和蠕变所产生的损伤和塑性变形对后续力学行为影响非常显著。
In order to reveal the rheological mechanical properties of surrounding rock after excavation and unloading in deep weak strata, creep tests of unloading and unloading with constant axial pressure of sandy mudstone are carried out to study creep regularity of axial, lateral and volume of soft rock And unloading stress during the process of stress-strain relationship. The main conclusions are as follows: (1) The ratio of creep deformation to instantaneous deformation, creep deformation and creep deformation relative to the instantaneous deformation at this level of load, (2) With the gradual unloading of confining pressure, vertical tensile microcracks are generated in the rock, and the initiation and propagation of microcracks make the dumping The pressure transiently produces obvious lateral deformation and the microcracks will undergo age-dependent expansion corresponding to the stress level during the creep process, resulting in viscoplastic deformation. (3) The progressive destruction of rocks under aging conditions is due to the damage (4) With the gradual unloading of the confining pressure, the deviatoric stress increases, the number of unloading history experienced in history and the creeping time are long, so the test The more non-recoverable strain and damage accumulated in the specimen, the more severe the damage was. In the specimen with lower axial load, the higher the rheological rate, the larger the creep deformation, the unloading effect and the rheological characteristics More obvious, accompanied by significant lateral expansion, leading to creep (5) The damage and plastic deformation caused by unloading and creep have a significant impact on the subsequent mechanical behavior.