城市地下输水管道是城市供水系统的主要组成部分，对于保障城市居民的日常生活用水、工业用水和农业用水具有重要意义。在长期的使用过程中，地下输水管道因管道材料老化、交通荷载的振动波以及施工扰动等问题常常导致管道破损发生泄漏，引起黄土路基的水分迁移和湿化变形，甚至严重的地面塌陷事故，影响了城市居民的正常用水和交通安全。因此，开展城市地下输水管道泄漏对黄土路基湿化变形的影响研究对于科学预测城市道路灾害和保障城市稳定运行具有重要的应用价值。本文以西安地区城市道路黄土路基为研究对象，针对城市地下输水管道泄漏引起的路基湿化及变形灾害问题，采用室内试验、理论分析和数值模拟相结合的研究方法，开展压实黄土的水力特性试验和湿化变形特性试验，建立非饱和土水-力耦合模型，分析输水管道泄漏作用下黄土路基的水分迁移规律和增湿变形特性，探讨地下水位深度、泄漏位置、泄漏孔尺寸和管道覆土厚度等对黄土路基湿化变形的影响。获得的主要结论有：

（1）采用压力板仪进行土水特征曲线试验，获得试验黄土增湿与减湿阶段的土水特征曲线，分析并得出了非饱和黄土的基质吸力与体积含水率之间的关系。试验表明，在增减湿的循环过程中，体积含水率与基质吸力的平衡关系呈现非一一对应性，相同吸力条件下，增湿阶段含水率较减湿阶段存在明显滞后现象，滞回曲线幅度覆盖全含水率变化范围，且在孔隙水快速排出与吸收区域最为突出。

（2）采用应力应变式非饱和土三轴仪，开展多级净应力工况下土体湿化变形特性实验。通过孔隙结构变化与吸力变化联立分析，建立水-力耦合参数关联模型，进而得到土体结构和水的变形状态变量：以净应力和基质吸力为状态变量的水-力耦合本构方程。

（3）基于净应力-基质吸力对土体体积变形的影响，构建非饱和土水-力耦合本构模型，推导多应力路径下各体积模量的表达式；改进达西渗流理论，建立以孔隙水压力梯度为驱动势的渗流控制方程，实现饱和-非饱和渗流场的连续表征。

（4）基于COMSOL Multiphysics数值模拟软件，构建输水管道泄漏作用下的渗流-应力耦合模型，通过地下水位深度、泄漏位置、泄漏孔尺寸和管道覆土厚度等因素，分析路基的水分迁移与湿化变形的机理。研究表明：湿润锋几何形态从拟圆形演变为非对称水滴形，其前锋抵达区域饱和度迅速达到稳定，而路基湿化变形呈持续发展趋势；地表形变速率先急后缓，孔心轴线地表位移峰值始终存在，最终沉降形成“漏斗状”分布；管道埋深增大导致其上方地表沉降量显著上升；地下水位越深地表最大沉降量越大，管道中轴线区域位移变化最为显著；管道破损孔洞尺寸的扩大导致路基饱和区向下延伸，湿润锋水平扩展范围小幅增长，这种水力条件的变化加剧了路基的湿化与沉降。

Urban underground water supply pipelines are crucial components of urban water supply systems, playing a vital role in ensuring daily domestic water consumption, industrial water use, and agricultural irrigation for urban residents. During prolonged service, underground pipelines frequently experience leakage due to material aging, vibration waves from traffic loads, and construction disturbances. These leaks can induce moisture migration and wetting deformation in loess subgrades, potentially leading to severe ground collapse accidents that disrupt normal water supply and compromise transportation safety. Therefore, investigating the impact of underground pipeline leakage on wetting deformation of loess subgrades holds significant application value for scientifically predicting urban road hazards and ensuring urban operational stability.This study focuses on loess subgrades of urban roads in Xi"an region, addressing the wetting and deformation disasters caused by underground water pipeline leakage. Adopting an integrated research methodology combining laboratory experiments, theoretical analysis, and numerical simulations, it conducts hydraulic characteristic tests and wetting deformation tests on compacted loess. The research establishes an unsaturated soil hydro-mechanical coupling model to analyze moisture migration patterns and wetting deformation characteristics of loess subgrades under pipeline leakage conditions. It further investigates the influences of groundwater table depth, leakage location, leak aperture size, and pipeline burial depth on subgrade wetting deformation. Key conclusions obtained include:

(1) Soil-water characteristic curve (SWCC) tests were conducted using a pressure plate apparatus to obtain wetting and drying paths of the tested loess, establishing the relationship between matric suction and volumetric water content in unsaturated loess. The results revealed a non-unique correspondence between volumetric water content and matric suction during cyclic wetting-drying processes. Under identical suction conditions, moisture content during the wetting phase exhibited significant hysteresis compared to the drying phase. The hysteresis loops spanned the entire range of moisture content variation, with the most pronounced effects observed in zones of rapid pore water drainage and absorption.

(2) Wetting Deformation Characteristics under Multi-Stage Net Stress Conditions were investigated using a stress-strain controlled unsaturated triaxial apparatus. By jointly analyzing pore structure evolution and suction changes, a hydro-mechanical coupling parameter correlation model was established. This led to defining deformation state variables for soil structure and water, culminating in a hydro-mechanical constitutive equation with net stress and matric suction as state variables.

(3) Hydro-Mechanical Coupling Constitutive Model for Unsaturated Soil was developed based on the influence of net stress and matric suction on soil volumetric deformation. Expressions for bulk moduli under multi-stress paths were derived. Darcy’s seepage theory was enhanced by formulating a seepage control equation driven by pore water pressure gradients, enabling continuous characterization of saturated-unsaturated seepage fields.

(4) A seepage-stress coupled model under water supply pipeline leakage was developed using COMSOL Multiphysics software. By incorporating parameters such as groundwater table depth, leak location, leak aperture size, and pipeline burial depth, the mechanisms of moisture migration and wetting deformation in the subgrade were systematically analyzed. Key findings demonstrate:The geometric morphology of the wetting front evolved from quasi-circular to asymmetric droplet-shaped. Saturation rapidly stabilized in the advancing front region, while subgrade wetting deformation exhibited persistent progression; Surface deformation rates showed an initial abrupt phase followed by gradual deceleration. Persistent displacement peaks along the leak axis ultimately formed a "funnel-shaped" settlement distribution; Increased pipeline burial depth significantly amplified surface settlement above the pipeline; Deeper groundwater tables correlated with greater maximum surface settlements, with the most pronounced displacement variations observed along the pipeline central axis; The enlargement of pipeline breach apertures induces downward extension of the subgrade's saturated zone, resulting in a slight horizontal expansion of the wetting front. Such hydraulic modifications exacerbate wetting deformation and settlement in the subgrade.

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