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冰川冻土 ›› 2022, Vol. 44 ›› Issue (6): 1853-1862.doi: 10.7522/j.issn.1000-0240.2022.0161

• 寒区工程与灾害 • 上一篇    

不同冻结条件下砂岩冻胀特性试验研究

董西好1,2(), 叶万军1(), 刘帅1   

  1. 1.西安科技大学 建筑与土木工程学院,陕西 西安 710054
    2.西部矿井开采及灾害防治教育部重点实验室,陕西 西安 710054
  • 收稿日期:2021-12-11 修回日期:2022-04-26 出版日期:2022-12-25 发布日期:2023-01-18
  • 通讯作者: 叶万军 E-mail:dongxh@xust.edu.cn;yewanjun2004@126.com
  • 作者简介:董西好,工程师,主要从事低温软岩物理力学性质与工程应用研究. E-mail: dongxh@xust.edu.cn
  • 基金资助:
    国家自然科学基金项目(41272340);陕西省重点科技创新团队计划资助项目(2016KCT-13)

Study on frost heaving characteristics of sandstone under different freezing conditions

Xihao DONG1,2(), Wanjun YE1(), Shuai LIU1   

  1. 1.College of Architecture and Civil Engineering, Xi’an University of Science & Technology, Xi’an 710054, China
    2.Key Laboratory of Western Mine Exploitation and Hazard Prevention, Xi’an 710054, China
  • Received:2021-12-11 Revised:2022-04-26 Online:2022-12-25 Published:2023-01-18
  • Contact: Wanjun YE E-mail:dongxh@xust.edu.cn;yewanjun2004@126.com

摘要:

人工冻结法由于能够阻止地下水的移动,限制围岩的变形,目前已经成为煤矿井筒穿越富水软岩地层的有效方法之一。为了研究不同冻结条件下砂岩的冻胀特性,结合现有的冻土物理力学性质理论,采用GCTS(Geotechnical Consulting & Testing Systems)电液伺服控制低温高压岩石三轴测试系统对饱和、干燥白垩系红砂岩进行不同冷却速度(10 ℃·h-1、5 ℃·h-1、2 ℃·h-1、1 ℃·h-1)和不同围压(5 MPa、10 MPa、15 MPa、20 MPa、25 MPa)下的冻胀试验,研究不同冻结条件下砂岩的冻胀规律,探索冻胀机理。研究结果表明:在降温的过程中,干燥岩样始终产生冷缩变形,饱和岩样先产生冷缩变形,后产生冻胀变形,最后趋于基本稳定,且饱和岩样变形量远大于干燥岩样。当冻结温度一定时,岩样所处的应力水平越大,冻胀变形越小,两者呈线性负相关,这主要是由于高围压限制了岩样内部孔隙水相变成冰时体积的膨胀。岩样的冻胀变形量主要受围压、含水率的影响,而冷却速度主要影响岩样的冻胀速率,本试验条件下,砂岩的冷却速度越大,冻胀速率越大,且二者近似呈线性关系。对于饱和岩样,围压主要通过限制冰水相变时的膨胀变形而减小岩石的冻胀变形,温度主要通过影响孔隙水的冻结率和岩石骨架的热胀冷缩而影响岩石的冻胀变形,而干燥岩样变形主要是由于热胀冷缩效应导致岩石矿物颗粒体积收缩,且温度变化越大,变形越大。结合试验结果,运用理论分析方法,建立了考虑围压影响的岩石冻胀变形计算公式。通过对不同围压下冻结稳定后的砂岩冻胀变形进行计算,发现计算结果与试验结果具有较好的吻合度。此外,由冻胀变形计算公式可知,降温过程中岩石的冻胀变形影响因素大致可分为内因和外因两大类,内因包括岩石的孔隙度、饱和度、冰和岩石骨架的体积模量,外因主要是温度、围压。对于饱和岩石,冻胀变形主要受围压、温度、孔隙度等因素影响。饱和度、孔隙度和冻结率决定了岩石是冻胀还是冻缩,当这些指标较小时,岩石可能只产生冻缩变形。内因和外因相互影响、相互制约,加之冻胀过程中岩石微观结构及力学性质的动态变化,导致岩石冻胀机理十分复杂。研究结果可为深厚煤层矿井建设冻结法施工方案设计提供理论参考,也可为冻土地区软岩物理力学性质及其工程应用研究提供理论基础。

关键词: 砂岩, 冻胀变形, 冷却速度, 围压

Abstract:

At present, artificial freezing method has become one of the effective methods for coal mine shaft to pass through water-rich soft rock strata, which can stop the movement of groundwater and limit the deformation of surrounding rock. In order to study the frost heaving characteristics of sandstone under different freezing conditions, frost heaving tests of saturated and dry Cretaceous red sandstone samples under different freezing rates (10 ℃·h-1, 5 ℃·h-1, 2 ℃·h-1, 1 ℃·h-1) and different confining pressures (5 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa) were carried out by using GCTS (Geotechnical Consulting & Testing Systems) servo-controlled low temperature and high pressure triaxial rock testing system. In this paper, based on the existing theory of physical and mechanical properties of frozen soil, we studied the frost heaving law of sandstone under different freezing conditions and explored the frost heaving mechanism. The result shows that in the process of cooling, the dry rock sample always produce cold shrinkage deformation, while the saturated rock sample first produce cold shrinkage deformation, then produce frost deformation, and finally the deformation tends to be stable. The deformation of saturated rock samples is much larger than that of dry rock samples. The larger the stress level of rock samples at the same temperature is, the smaller the frost deformation is, which shows a linear negative correlation, mainly because the high confining pressure limits the volume expansion of the water phase in the pore inside the rock samples when it becomes ice. The frost deformation of rock samples is mainly affected by confining pressure and water content, while the frost heaving rate is mainly affected by cooling rate. Under this test condition, the higher the cooling rate of sandstone is, the higher the frost heaving rate is, and the relationship between them is approximately linear. For saturated rock samples, the confining pressure reduces the rock frost heaving by limiting the expansion during the phase transformation of ice water, and the temperature affects the rock frost heaving by affecting the freezing rate of pore water and the thermal expansion and cold contraction of rock skeleton. For dry rock samples, the deformation is mainly due to the volume contraction of rock mineral particles caused by thermal expansion and cold contraction effect, and the greater the temperature change, the greater the deformation. Based on the experimental results and theoretical analysis method, a calculation formula of rock frost heaving considering the influence of confining pressure was established. By calculating the frost heave of sandstone samples under different confining pressures, it is found that the calculated values are in good agreement with the experimental results. Moreover, according to the calculation formula of frost heaving, the influence factors of rock frost heaving during freezing can be divided into two categories: internal cause and external cause. The internal cause includes porosity, saturation, volume modulus of ice and rock skeleton, and the external cause includes temperature and confining pressure. For saturated rock, the frost heaving is mainly affected by factors such as confining pressure, temperature and porosity. When the saturation, porosity and freezing rate are low, the rock may only produce shrinkage deformation, because these indicators determine whether the rock produces frost heave or freeze shrinkage. The mechanism of rock frost heaving is very complicated due to the interaction and restriction between the internal and external factors and the dynamic changes of rock microstructure and mechanical properties during the process of frost heaving. The research results can provide theoretical reference for freezing construction scheme design of deep coal seam mine construction, and also provide a theoretical basis for the study of physical and mechanical properties and engineering application of soft rock in frozen soil area.

Key words: sandstone, frost heaving, freezing rate, confining pressure

中图分类号: 

  • P642.14