膨胀土边坡长期变形演化状态及力学机制

Deep primary fractures are universally found in the expansive soil layer,and engineering practices show that, its extension over time has a close relationship with long-term deformation of expansive soil slope. This program adopts these methods of field observation, theoretical analysis, and experimental study to research long-term deformation evolution characteristics of expansive soil slope, in which deep primary fractures are distributed, as well as the relationship between long-term deformation evoluting characteristics and the extension over time of primary fractures. Through field statistics, the spatial distribution characteristics of primary fractures are obtained, based on which primary fractures can be simulated in remolded expansive soil; using the cell model test method designed by ourselves, small plate loading tests on expansive soil with primary fractures are carrid out, so that the long-term deformation evolution categories of expansive soil under diffirent loads can be devided; Triaxial creep experiments of expansive soil with typical-dips primary fractures are as well carried out, during which the primary fractures are being scanned, so that the relationship beween long-term deformation evolution categories and extension over time of primary fractures can be revealed, then quantitative criterion to distinguish long-term deformation evolution categories of expansive soil with primary fractures is proposed, at last the deformation evelution state parameters are derived. Research achievements provide theoretical basis and experimental evidence for analysing and evaluating long-term deformation evolution states of expansive soil slope that considering durability.

深层原生裂隙在膨胀土地层中普遍存在，工程实践表明，开挖卸载导致深层原生裂隙随时间逐步扩展与膨胀土边坡变形长期发展的密切相关。项目采用现场考察、理论分析与试验研究相结合的研究方法，研究赋存原生裂隙膨胀土边坡长期变形演化特征，及其与原生裂隙扩展规律之间的关系。通过现场统计，得到膨胀土地区深层裂隙的空间分布特征，并在室内模拟原生裂隙；利用自行设计的单元模型试验方法，开展恒湿条件下赋存原生裂隙膨胀土模型试验，分析不同荷载条件下原生裂隙膨胀土长期变形演化的状态类别；采用CT三轴试验设备，开展赋存缓倾角原生裂隙的膨胀土三轴蠕变试验，并进行全程扫描，揭示膨胀土内部裂隙扩展规律与长期变形演化状态类别之间的关系，提出区分赋存原生裂隙膨胀土长期变形演化状态的定量判别方法，得到相应的偏应力阈值，推导裂隙膨胀土的变形状态参数。研究成果为建立考虑耐久性的膨胀土边坡长期变形状态分析与评价方法提供理论基础和试验依据。

深层原生裂隙在膨胀土地层中普遍存在，工程实践表明，开挖卸载导致深层原生裂隙随时间逐步扩展与膨胀土边坡变形长期发展的密切相关。项目采用现场考察、理论分析与试验研究相结合的研究方法，研究赋存原生裂隙膨胀土边坡长期变形演化特征，及其与原生裂隙扩展规律之间的关系。基于土体剪切蠕变变形随时间的三阶段发展规律，采用负幂函数作为第一阶段（蠕变衰减阶段）的时间函数，推到了衰减阶段蠕变基本方程，并确定了第一阶段蠕变收敛与发散以及发散快慢的负幂函数判别阈值，提出了基于短期衰减阶段的膨胀土长期变形状态划分及判别准则，结合现场原型试验，对该判别准则的合理和可靠性进行了验证；通过现场统计，得到膨胀土地区深层裂隙的空间分布特征，并在采用人工制配的手段，实现含非贯通裂隙的膨胀土试样；利用自行改装设计的直剪仪，开展不同裂隙率以及不同上覆荷载条件下膨胀土块直接剪切试验，得到峰值剪切强度随裂隙率的衰减规律，并采用复核指数函数推演不同裂隙率试样的剪切曲线；采用自行改装的剪切蠕变仪器，开展不同裂隙率膨胀土试样的剪切蠕变曲线，并得到了变形速率衰减的幂次值。研究成果为建立考虑耐久性的膨胀土边坡长期变形状态分析与评价方法提供理论基础和试验依据。