Analysis of Deformation Formation Causes and Reinforcement Disposal Effects in Deep Excavated Expansive Soil Canal Slope: Case Study

Deeply excavated expansive soil canal slopes can have instability risks during operations. The deformation mechanism is analyzed using internal and external factors, such as engineering geology, hydrogeology, rainfall, and groundwater levels in the middle expansive soil canal slope in the central line of the South-to-North Water Diversion Project, Taocha District, Nanyang City, Henan Province, China. The stability of the canal slope and the effect of the reinforcement and disposal measures are evaluated with a geological survey, manual inspection of the defects, safety monitoring data analysis, hidden danger geophysical detection, and stability numerical simulation. The following conclusions are drawn: (1) the surface-refilled cement-treated soil failed to isolate the water vapor exchange between the expansive soil and the atmosphere; and (2) the stagnant water in the upper layer is replenished by precipitation, leading to the increase in the groundwater level during the rainy season and the decrease in the groundwater level during the dry season. Shear creep deformation occurs along the fissure of the second to fourth grade canal slopes. The potential sliding surface consists of a gentle dip angle leading edge and a steep dip angle trailing edge. The arrangement of the antisliding piles on the water-passing section and the crack surface distribution had an effect, and the potential shear outlet is in the first grade berm, the deformed body is still developing, and the trailing edge is not apparent. The potential failure mode of the slope is deep sliding, and the current safety factor is 1.002. A combination of groundwater discharge and micropile reinforcement is required to improve the stability of the canal slope. After the drainage and reinforcement are implemented, the slope’s deep antislide stability safety factor increases to 1.462, which met the safety requirements. The results could provide a reference for the operation management and reinforcement governance of similar projects.