Causes and rectification of repeated slumping of canal slopes under high groundwater conditions: case study of SNWD, China

This work arises from investigations into repeated slump failures of the side slopes of canals of the middle route of the South-to-North Water Diversion project in China. Investigations centered on a 770 m long canal segment, located on the alluvial–proluvial plain east of the T’ai-hang Mountains, where the canal was constructed in a cutting in Quaternary superficial deposits containing water bearing, high permeability sands and gravels. The area has experienced several severe rainstorms since the canal was put into operation in December 2014, including those of July 9, 2016 and July 20, 2021, in which the studied canal segment was seriously damaged. The post-failure investigations included visual inspection, monitoring of groundwater levels, and geophysical detection of poor ground conditions. These showed that a permeable sandy gravel layer was present and the existing drainage measures system failed adequately to control groundwater levels during the rainstorms. The confined groundwater level was much higher than the design value and local defects adversely affected the stability of the fill soil zone. The high groundwater level and sudden drop of canal water level resulted in damage to the lining panels of the canal. A combination of emergency treatment, including lowering groundwater and raising canal water level, and permanent correction measures such as seepage control and drainage of canal foundation were carried out. This case study can provide a reference for dealing with instability in similar engineering situations and operation management.