Influence of clogging substances on pore characteristics and permeability of geotextile envelope of subsurface drainage pipe in arid areas

Geotextile envelope clogging is one major reason reducing the drainage efficiency during the operation of subsurface drainage pipes. Current studies generally concern physical clogging caused by soil particle invasion and chemical clogging in humid areas where own oxidizing environments to drive chemical reactions. In this study, experiments were conducted for investigating the clogging substances and its potential risk eval uation ind icators in Xinjiang regi on wh ere it is arid and suffered from soil salinity problem . Three kinds of geotextile envelope with different serving times (3, 7 and 15 years) were collected by excavating from the irrigated farmland in 2018 . The ultrasonic variation method was used to remove clogging substances on the three original geotextile envelopes for the pore characteristics and permeability of virgin ones . The pore size characteristics and permeability of three original and virgin ones were measured by the bubble point method and vertical permeameter . The X- R ay D iffraction (XRD) , S canning E lectron M icroscopy ( SEM ) , Energy Dispersion Spectrum ( EDS ) methods were used to analyze the pattern and composition of clogging substances in the geotextile envelope. The soil permeability coefficients were calculated by the Rosetta Lite embedded in the HYDRUS-1D. The content of chemical precipitation was measured by the gas content volume method. The saturation index (SI) of the possible mineral precipitation was calculated by geochemical software PHREEQC. The results show that the macropores (above 1 25 micron) of envelopes are obviously clogged while the smaller pore (50-100 micron) are still unblocked after serving for 15 years . And the permeability coefficients of geotextile envelopes after serving for 3 and 15 years are smaller than the minimum required permeability coefficients value after clogging. T he major clogging substances in the geotextile envelope are SiO₂ and insoluble calcium-magnesium precipitation. T he reduction of the permeability coefficient will increase the risk of insoluble salt precipitation. T he ratio of O ₉₀ size of envelope material over d₉₀ of soils (O ₉₀/d ₉₀ ) and SI can be used to assess the risk of physical and chemical clogging. This study provides a preliminary reference for investigating the clogging risks of geotextile envelope in arid areas.