卸荷变形对黄土包气带水气二相驱替影响机理研究

Due to terrain fragmentation in loess hilly region in China, there are great differences in the thicknesses of unsaturated zones. Hence, the hydrogeological condition and engineering geological conditions are complex. Land creation can release the shortage of land for urbanization in loess hilly region. Large-scale excavation in the project of land creation causes significant soil rebound deformation, leading to changes in pore structure. These changes affect the existing conditions of pore water and pore air and water-air two-phase flow in unsaturated zones of loess. In this study, multiple disciplines and methods of unsaturated soil mechanics and hydrogeology have been comprehensively applied to the Q2 loess in Yan’an city. The objectives are to study the law of loess deformation and the evolution of pore water and pore air pressures in the field under unloading condition. In details, it is to study the law of loess deformation under unloading condition, the influence of pore structure change law on soil-water characteristics and the permeability and coupled flow and deformation. The major techniques have been used in this study include numerical simulation, laboratory physical modeling and field measurements. The impact mechanism of unloading deformation on the water-air two-phase flow in the unsaturated zones of loess has been determined. The results of this study enable a deeper understanding of the two-phase flow in unsaturated zones of loess subjected to unloading. The results also form a scientific basis for ascertaining the effect of unloading on hydrogeological and engineering geological conditions in disturbed unsaturated loess zones due to excavation.

我国黄土梁峁区地形破碎，包气带厚度差异大，水文地质条件、工程地质条件复杂。开展 “削山造地”工程可缓解该地区城镇化面临的土地紧缺局面。工程实施中大规模挖方卸荷使黄土发生不可忽略的回弹变形，引起孔隙结构变化，改变黄土包气带内水、气赋存条件，影响水气二相运移。为破解该科学问题，本项目拟综合运用非饱和土力学、水文地质学等多学科的理论与方法，选取延安地区Q2黄土为研究对象，以卸荷作用激发下黄土变形响应—孔隙结构变化对土水特征关系、渗透特性影响—卸荷变形与渗流耦合作用为研究主线，借助数值模拟、室内物理模型模拟及野外站点监测等研究手段，研究卸荷作用下黄土变形规律和包气带孔隙水压力场、孔隙气压力场演化模式，揭示卸荷变形对黄土包气带水气二相驱替的影响机理。以期深入理解卸荷作用下黄土包气带水气二相运移规律，研究成果为判明卸荷作用对挖方卸荷区水文地质条件和工程地质条件的影响提供科学依据。

黄土梁峁区开展“削山造地”工程可缓解该地区城镇化面临的土地紧缺局面，工程实施中大规模挖方卸荷使黄土发生不可忽略的回弹变形，引起土体应力-孔隙水压力-孔隙气压力变化。本项目以延安地区Q2黄土为研究对象，借助室内物理模型模拟、数值模拟等手段研究手段，研究卸荷作用下土体变形规律和包气带孔隙水压力、孔隙气压力演化。研制了卸荷扰动下非饱和土水气二相运移实验仪器，该仪器包括加卸荷系统、土应力监测系统、气相压力监测系统、水相压力监测系统。试验揭示了在荷载扰动下，固体骨架发生变化，进而影响非饱和土中水气二相的运移过程。针对蒸发条件下稳态渗流问题，推导均质/非均质非饱和土水力连续区液相运动方程解析解，揭示了蒸发对渗流过程的影响。针对定水头入渗条件，推导了相应的解析解，揭示了定水头入渗条件下水相迁移机理。推导了半正弦循环加、卸载作用下非线性渗流固结解析解，揭示了固结过程中，超静孔隙水压力、有效应力和平均固结度随时间变化规律；初始条件、间歇期和荷载频率的差异对固结过程影响规律。构建循环加、卸载作用下渗流固结的有限分析法格式。研究成果为判明卸荷扰动对土体内孔隙流体迁移的影响提供科学依据。