砂岩蠕变特性试验及其影响因素研究

发布时间：2019-04-09 15:58

【摘要】：在荷载作用下,岩石不仅表现出弹性和塑性,而且具有与时间相关的性质,即岩石的流变性。工程实践中,岩石流变现象随处可见,岩石流变所造成的危害也不容忽视。如隧道、矿山洞室掘进后,围岩随时间产生变形甚至破坏;地基在附加荷载作用下随时间逐渐沉降,最终导致建筑物变形破坏。多年来,岩石流变特性研究取得了丰富的成果。但岩石作为一种特殊的工程材料,其流变特性受到包括岩石本身性质(如矿物组成、节理等)和外部环境(湿度、地应力等)等诸多方面的综合影响,以致目前为止岩石流变理论仍不甚完善。为了预测复杂应力环境中岩石工程长期稳定性,本文采用YSJ-01-00岩石三轴压缩流变试验仪和YZJL-300岩石直剪流变仪对完整砂岩和预制裂隙砂岩开展三轴压缩和剪切蠕变试验,基于试验结果并结合理论分析和数值计算,研究了岩性、围压、轴压、含水率、裂隙长度等因素与砂岩蠕变特性的关系。具体研究内容及结论如下:(1)通过常规单轴压缩试验和三轴压缩试验,测得细砂岩和粗砂岩抗压强度、内聚力和内摩擦角。(2)通过三轴压缩蠕变试验,获得细砂岩和粗砂岩在三向应力作用下的蠕变规律。随轴压增加,细砂岩表现出减速和等速两阶段蠕变过程,粗砂岩则表现出减速、等速和加速三阶段蠕变过程。由于时效性,岩石长期抗压强度降低。细砂岩长期强度参数内聚力随时间降低,而内摩擦角基本无变化;粗砂岩内聚力和内摩擦角同时随时间减小。通过不同含水率粗砂岩三轴压缩蠕变试验,发现岩石含水率越高,瞬时应变越大、蠕变速率越高、长期强度越低,瞬时应变与含水率呈线性关系,长期强度与含水率呈对数关系。(3)通过剪切蠕变试验获得完整砂岩和预制裂隙砂岩蠕变规律。结果表明,正应力增加,岩石抗剪长期强度增加,剪切破裂面越光滑且接近预制裂隙平面;剪应力增加,岩石表现出减速蠕变、等速蠕变和加速蠕变三个过程;裂隙长度增加,岩石长期抗剪强度快速降低,瞬时剪切应变增加。(4)采用Cvisc模型对砂岩三轴压缩蠕变和剪切蠕变全程曲线进行了成功辨识,得到Cvisc模型参数。在数值计算中调用Cvisc模型对砂岩三轴压缩蠕变规律进行模拟,数值结果与试验数据较吻合,验证了该模型对于描述砂岩蠕变性质的适用性。将研究成果应用于砂岩地基在建筑物附加应力下蠕变沉降分析,在应力较低时,地基蠕变速率小,且快速降低至零;在较高应力情况下,地基蠕变速率先降低,随后保持不变,地基变形随时间逐渐增加。该研究可为工程实践提供参考。
[Abstract]:Under loading, rock not only shows elasticity and plasticity, but also has the property of time-dependent, that is, the rheology of rock. In engineering practice, the phenomenon of rock rheology can be seen everywhere, and the harm caused by rock rheology can not be ignored. For example, after excavation of the tunnel, the surrounding rock will deform or even destroy with time, and the foundation will gradually subside with time under the action of additional load, which will eventually lead to the deformation and failure of the building. Over the years, a wealth of achievements have been made in the study of rock rheology characteristics. However, as a special engineering material, the rheological properties of rock are influenced by many aspects, such as the properties of rock itself (such as mineral composition, joint, etc.) and the external environment (humidity, in-situ stress, etc.). So far, the theory of rock rheology is still not perfect. In order to predict the long-term stability of rock engineering in complex stress environment, In this paper, YSJ-01-00 rock triaxial compression rheometer and YZJL-300 rock direct shear rheometer are used to carry out triaxial compression and shear creep tests on intact sandstone and prefabricated fractured sandstone. Based on the test results, combined with theoretical analysis and numerical calculation, The relationship among lithology, confining pressure, axial compression, moisture content, fracture length and creep characteristics of sandstone is studied. The concrete research contents and conclusions are as follows: (1) the compressive strength, cohesion and internal friction angle of fine sandstone and coarse sandstone are measured by conventional uniaxial compression test and triaxial compression test. (2) through triaxial compression creep test, the compressive strength, cohesion and internal friction angle of fine sandstone and coarse sandstone are measured. The creep law of fine sandstone and coarse sandstone under three-dimensional stress is obtained. With the increase of axial pressure, the fine sandstone exhibits two-stage creep process of deceleration and constant velocity, while the coarse sandstone shows deceleration, constant velocity and accelerated three-stage creep process. Due to time-effectiveness, the long-term compressive strength of rock decreases. The cohesion of the long-term strength parameter of fine sandstone decreases with time, but the angle of internal friction basically does not change, while the cohesion and angle of internal friction of coarse sandstone decrease with time at the same time. Through triaxial compression creep tests of coarse sandstone with different moisture content, it is found that the higher the water content of rock is, the greater the instantaneous strain is, the higher the creep rate is, the lower the long-term strength is, and the linear relationship between instantaneous strain and moisture content. There is a logarithmic relationship between long-term strength and water content. (3) the creep law of intact sandstone and prefabricated fractured sandstone is obtained by shear creep test. The results show that with the increase of normal stress, the shear strength of rock increases and the shear fracture surface becomes smoother and closer to the prefabricated crack plane, and the rock exhibits three processes: deceleration creep, constant velocity creep and accelerated creep when the shear stress increases. With the increase of fracture length, the long-term shear strength of rock decreases rapidly and the instantaneous shear strain increases. (4) the triaxial compression creep and shear creep curves of sandstone are identified successfully by using Cvisc model, and the parameters of Cvisc model are obtained. In the numerical calculation, the Cvisc model is used to simulate the triaxial compression creep law of sandstone. The numerical results are in good agreement with the experimental data, and the applicability of the model to describe the creep properties of sandstone is verified. The research results are applied to the creep settlement analysis of sandstone foundation under the additional stress of the building. When the stress is low, the creep rate of the foundation is small and the creep rate is reduced to zero rapidly. Under the condition of high stress, the creep velocity of the foundation decreases at first, then remains unchanged, and the deformation of the foundation increases gradually with the time. This study can provide reference for engineering practice.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU45

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