深挖方膨胀土渠坡运行期存在失稳风险。以一长距离调水工程中的膨胀土渠段为例开展研究,该段渠坡共6级、坡高超40 m。通过安全监测数据分析、隐患地球物理探测和稳定性数值模拟等手段,考虑工程与水文地质、降雨与地下水位等内外因素,综合分析渠坡运行期的变形机制,评判渠坡稳定性以及处置措施效果。得到如下结论:表层改性土未能隔绝膨胀土与大气的水汽交换,汛期降雨补给渠坡上层滞水导致地下水位上升,旱季少雨地下水位下降,多个干湿循环后,膨胀土体反复胀缩引起渠坡裂隙发育贯通,因裂隙面影响和过水断面抗滑桩作用,二—四级渠坡沿裂隙面蠕变变形,渠坡局部抗滑稳定性不满足规范要求;潜在滑动面表现出前缘缓倾角和后缘陡倾角折线组合滑动面特征,潜在剪出口在一级马道;为降低地下水位,提高渠坡的稳定性,采取的排水沟和排水井措施较为有效。研究成果可为类似工程运行管理和加固治理提供参考。

Deeply excavated expansive soil canal slopes face the risk of instability during its operation period. This paper presents a case study of a moderately expansive soil canal slope, with a height exceeding 40 m, from a long-stretching water transfer project. The slope stability and the effectiveness of reinforcement measures were assessed. Multiple approaches, including safety monitoring data analysis, non-destructive detection, and numerical simulation analysis, were utilized. The deformation mechanism was evaluated by considering internal factors such as engineering geology and hydrogeology, as well as external factors like rainfall and changes in groundwater levels. The surface modified soil failed to prevent water vapor exchange between the expansive soil and the air. Moreover, during rainy season, precipitation replenished the stagnant water within the upper layer of the canal slope, resulting in a rise in groundwater levels. Conversely, the groundwater levels dropped during dry season. These cycles of drying and wetting led to the development and penetration of fissures in the canal slope. Additionally, creep deformation occurred along the fissure surface of the 2nd to the 4th slopes, influenced by both the fissure surface and the arrangement of anti-sliding piles in the water-passing section. As a result, the local slope stability did not meet specification requirements. The potential sliding surface exhibited characteristics of a combined sliding surface, with a gentle inclination angle at the leading edge and a steep inclination angle at the trailing edge. The potential shear outlet was identified at the first-level berm, although the exact location of the trailing edge of the landslide remains unclear. To enhance slope stability, a combination of drainage ditches and drainage wells proved effective as drainage measures. These findings offer valuable insights for the operation management and reinforcement governance of similar projects.