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This study develops a coupled model of chemical clogging and permeability coefficient of geotextile envelope. Based on the distribution characteristics of crystal precipitates on geotextile envelope and their influence on the permeability coefficient, a permeability coefficient model of an actual geotextile envelope that considers the overlapping effect is developed. Then, the densification effects of geosynthetic fiber hypothesis and the filter cake effect hypothesis are proposed to simulate the processes of increasing fiber diameter after crystal precipitation and the accumulation of crystal precipitates on the surface of geotextile envelope. The crystal precipitation module and permeability coefficient module are coupled, and their experimental values are used to confirm the availability of the model. Results indicate the satisfactory performance of the model. In addition, the parameter sensitivity analysis and trend prediction show that the saturation index SI and solution flow rate V are the main factors that affect the chemical clogging and permeability of geotextile envelope. When the solution conditions are not considered, the sensitivity of geotextile envelope parameter d f increased with the amount of precipitation in crystal precipitation. When the pores of the geotextile envelope are completely clogged, the permeability coefficient of the geotextile envelope will drop sharply, then decline slowly. • A coupled model for chemical clogging and permeability coefficient of geotextile envelope is developed. • The densification effect of geosynthetic fiber and the filter cake effect are proposed to generalize chemical clogging. • The sensitivity of geotextile envelope parameter d f increased with the amount of precipitation. [ABSTRACT FROM AUTHOR]

Accurately assessing the clogging risk of the drainage pipe envelopes is a prerequisite for the reasonable design and proper management of subsurface drainage. However, the current assessment of clogging risk for subsurface drainage envelopes in arid areas mainly focuses on the impacts of single factors such as physical or chemical factors, with less attention given to combined physical–chemical clogging, which is more likely to occur and causes significant harm. Based on the evaluation indicators for physical and chemical clogging risks, this study utilized the entropy weight method to determine the weights of physical and chemical clogging risks, then proposed evaluation indicators for combined clogging risks and generated risk maps of physical, chemical, and combined clogging within the Xinjiang watershed. Furthermore, field excavation and sampling of subsurface drainage pipes were conducted to apply the proposed evaluation indicators for combined clogging risks and analyze the influencing factors. The results show that the combined clogging risk map based on the proposed combined clogging evaluation indicators is consistent with the actual clogging situation in the subsurface drainage system. Both physical and chemical clogging coexisted in the subsurface drainage system in Xinjiang, with a higher mass content of SiO 2 than CaCO 3 in the clogging substances. The combined clogging risk increased with rises in the drainage temperature and salinity. Under current conditions, the proportions of high, moderate, and low-risk areas of combined clogging risk are 22.10%, 30.37%, and 47.53%, respectively. The high-risk areas are mainly concentrated in Southern Xinjiang, which accounts for 91.7% of the high-risk area. This study can provide technical support for the prevention and control of clogging in subsurface drainage systems for saline-alkali farmland in arid areas. • Risk evaluation indicators for combined clogging of subsurface drainage were proposed. • Risk maps of physical, chemical, and combined clogging in Xinjiang were generated. • The combined clogging risk increased with rises of drainage temperature and salinity.. [ABSTRACT FROM AUTHOR]