高应力环境下深部人工冻结黏土融沉的流变固结机制及模型研究

Freezing sinking is an important technology to exploit solid resources in loose water-bearing ground. In recent years, China has built many shafts in 400 ~ 800m deep alluvium. Due to the thawing of frozen soil wall, the shafts are generally affected by the thawing settlement disaster，which cannot be predicted now because the fundamental research on the thawing settlement of frozen soil wall is less. With regards to this situation, the project will study on the mechanism and model of thawing settlement for deep artificially frozen clay, which is the key scientific problems for thawing settlement disaster. The subject will closely focus on the special properties of deep soil and high stress conditions, considering the rheological consolidation effect, to study characteristics and relationships of thawing settlement deformation and pore pressure during the frozen clay thawing under high stress. The creep characteristics and theoretical model of thawed clay will be studied. We investigate the microstructural evolution of deep clay affected by freeze thawing under high stress, and study its influence mechanism on macroscopic deformation. The rheological thawing consolidation model of deep frozen clay is established and the numerical analysis is carried out to explore the rheological properties of thawing settlement. The research results will provide a scientific basis for the development of prevention and control technology for frozen soil wall thawing settlement disaster, which is of great value to protect mining safety and enrich the theory of frozen soil mechanics.

冻结法是深厚不稳定含水地层中凿井的主要方法。近年来，我国在400～800m厚表土层中建设的冻结井筒，因冻结壁解冻普遍出现了井壁下沉甚至破裂现象，对井筒安全运行构成重大威胁。由于基础研究较为匮乏，目前尚无法可靠地预测预报冻结壁融沉灾害。本项目将紧抓深部高应力环境、深土特殊物性、流变融化固结等特点，对冻结壁融沉灾害的关键科学问题——深部人工冻结黏土融沉机制和模型开展研究。首先，开展宏观力学试验，查明深冻土的融沉变形和孔压变化规律，掌握已融土的蠕变特征，建立蠕变理论模型，为后续研究提供模型与参数。其次，开展微观试验研究，弄清冻融过程微观结构演化规律，构建考虑流变效应的颗粒流模型，分析孔隙变化和土骨架粘滞性对宏观变形的影响。最后，建立流变融化固结模型，开展数值计算，根据试验结果优化模型和参数，为冻结壁融沉灾害防治提供理论依据和数据支持。研究成果对于保障矿井安全运营有重要价值，并可丰富冻土力学理论。

我国中东部地区深厚表土层中的立井井筒建设广泛采用冻结法凿井技术，对于400~800m厚表土层，为抵抗巨大的水土压力，冻结壁厚度需达10余米，平均温度低于-20℃。当冻结壁解冻时地层沉降常导致井筒装备变形过大，甚至井壁压坏，给矿井安全带来较大危害。深入认识高应力环境下冻融作用对深部土体工程特性的影响，是科学防治冻结壁融沉灾害的重要基础。为此本项目针对深部黏土的特殊物性和原位高应力冻融作用，开展了深部黏土融化固结特性和流变固结模型研究。通过本项目的实施，研制了系列适用于深土高压冻融作用研究的试验装置。掌握了封闭系统和开放系统下深部黏土有载冻融过程温度-变形-孔压动态关系，以及含水率、压力、融化温度对变形和孔压的影响。获得了不同孔隙比、围压 、冻融条件下，冻融作用对深部黏土瞬时强度、长期强度及蠕变性能的影响。从微观尺度上揭示了深部黏土经有载冻融作用后，其颗粒形态、空间方位，孔径分布、孔隙形态等微观结构特征的演变；构建了深部冻融黏土颗粒流模型，探讨了蠕变过程颗粒移动和力链变化。利用弯曲元声波测试技术，获得了深部黏土在固结-有载冻融条件下的动剪切模量变化规律。掌握了深部黏土无载冻融和有载冻融模式下的流变固结特性，建立了描述深部冻融黏土流变固结的元件模型，并对模型进行二次开发，数值计算结果表明模型能较好地反应冻融黏土的固结变形。上述成果将为进一步认识解冻后冻结壁-井壁耦合作用机制提供基础数据和理论模型，对于井壁破裂灾害防治有理论意义。