黄土滑坡作为黄土地区的代表性地质灾害，具有孕灾时间长、发生突然等特点，给当地居民生命财产安全造成巨大威胁。经野外调查发现，受长期农业灌溉影响，泾阳南塬地下水位不规则抬升，导致斜坡坡脚土体中孔隙水压力升高，有效应力状态改变，进而造成土体形变引发液化。然而孔隙水压力上升速率对土体力学行为、微观结构及液化机理等影响尚不清晰。因此，本文以泾阳南塬Q₂黄土为研究对象，通过开展7种不同孔压增速下的常剪应力排水剪切（CSD应力路径）试验，查明孔压增速影响下黄土力学破坏过程及液化特性，并利用扫描电镜（SEM）测试，厘清液化破坏试样微观特征，在此基础上，采用Geo-Studio软件揭示不同灌溉作用和裂缝特征对黄土斜坡渗流场和稳定性的影响，阐释孔压增速影响下黄土滑坡机理。研究成果以期为水致黄土斜坡失稳研究提供一定理论借鉴。取得主要成果如下：

（1）CSD应力路径试验结果表明，随着孔隙水压力的增加，黄土试样的破坏过程可分为“平稳蠕动”和“失稳剧动”两个阶段。应力重分布和颗粒联锁结构的形成是“失稳剧动”阶段出现应变台阶的主要原因。随着孔压增速的增大，试样破坏的临界孔压比也随之增大，其范围在0.48~0.66；

（2）SEM测试结果表明，CSD试验后的黄土试样中出现了明显团粒化结构，大、中孔隙大部分转变为微小孔隙，黏粒聚团填充孔隙现象显著。随着孔压增速的增大，颗粒和孔隙定向性增强，孔隙的丰度和分形维数均降低；

（3）数值模拟结果表明，灌溉量、灌溉范围、裂缝深度和裂缝塬边距对黄土斜坡渗流场和稳定性存在显著影响。斜坡稳定性随灌溉范围和灌溉量的增大而减小，随裂缝深度的增加而减小，随裂缝塬边距的增加先减小后增大，在15m塬边距位置存在稳定系数临界值；

（4）灌溉水沿裂隙入渗，形成优势渗流通道，导致地下水位不断升高，引发黄土胶结弱化，颗粒旋转、错动并重新组合，大量黏粒滑移并填充至孔喉中造成渗流通道堵塞，促使坡脚土体中局部孔压快速增加，饱和软弱带形成，最终因排水不畅导致有效应力迅速降低，液化开始发生，此时微小的蠕动即可使土体沿潜在贯通滑动面快速滑动，形成黄土滑坡。

Loess landslide is a typical geological disaster in loess areas. It has the characteristics of long preparation time and sudden occurrence, which poses a huge security threat to the lives and property of local villagers. Field investigation shows that the loess landslides in the South Jingyang Platform are affected by long term agricultural irrigation, resulting in irregular increase of groundwater table. The increase of pore water pressure of loess at the slope toe causes the change of effective stress state, which further leads to soil deformation and even liquefaction damage. However, it is not clear about the influence of rise rate of pore water pressure on the mechanical behavior, microstructure and liquefaction mechanism of loess. Therefore, taking the Q₂ loess in the South Jingyang Platform as the samples, constant-shear drained (CSD) triaxial tests under different rates of increase in pore water pressure was carried out to find out the mechanical failure process and liquefaction characteristics of loess. In addition, the scanning electron microscope (SEM) tests were used to clarify the microscopic characteristics of the liquefied samples. On the basis of the above, Geo-Studio software was used to reveal the influence of different irrigation and crack characteristics on the seepage and stability of slope, and finally explain the mechanism of loess landslide under the influence of pore water pressure growth rate. The results can provide some theoretical reference for the study of water-induced loess slope instability. The main results include:

(1) The CSD triaxial tests results showed that with the increase of pore water pressure, the failure process of the samples can be divided into two stages of stable creep and sharply unstable deformation. The stress redistribution and the formation of interlocking structure were the main reasons for the occurrence of rapid-slow strain development state in the sharply unstable deformation stage. In addition, with increases in the rate of increase in pore water pressure, the critical pore pressure ratio u/σ_c increased ranging from 0.48 to 0.66.

(2) The SEM tests results showed that the samples after CSD triaxial tests had obvious clay particles filling the pores and aggregation structures, and macropores and mesopores were transformed into micropores. Moreover, with increases in the rate of increase in pore water pressure, the orientations of particles and pores increased, and the abundance and fractal dimension of pores decreased.

(3) The numerical simulation results showed that irrigation amount, irrigation area, crack depth and crack platform edge distance had significant effects on the seepage and stability of loess slope. Slope stability decreased with the increase of irrigation amount, irrigation area or crack depth. However, the slope stability decreased first and then increased with the increase of the distance the crack and the edge of the platform, and there was a critical value of the stability coefficient at the edge distance of 15m in platform.

(4) The infiltration of irrigation water along the cracks formed the dominant seepage channels, which led to the continuous increase of groundwater table. Therefore, it caused the weakening of cementation, the rotation and the recombination of particles. And a large number of clay particles slipped and filled into the pore throat, causing the blockage of seepage channel, leading to a rapid increase of local pore water pressure in the loess and the formation of saturated weak zones. Due to the obstruction of drainage, the effective stress was reduced, and liquefaction began to occur. Finally, small creep can make the slide rapidly along the potential sliding surface, forming a loess landslide.

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