Research progresses and frontiers in anti-seepage and anti-frost heave of canals in cold-arid regions

Abstract: Canals, as the preferred form of water conveyance, play an important role in the agricultural irrigation and long-distance water diversion projects in arid regions. However, the arid regions are mainly distributed in the seasonal permafrost regions in China, namely arid-cold regions. Due to the interaction between the canal seepage and frost heave, the freeze-thaw aging damages are more severe and common. The field investigation shows that the failure forms of canals include seepage, swelling, uplift, overhead, instability and collapse, and limit the safe operation and performance of canals seriously. In this study, the research progresses of the theories and technologies of anti-seepage and anti-frost heave for canals in arid-cold areas were summarized. Firstly, the mechanism of freeze-thaw failure and failure mode for canals was analyzed by indoor unit experiments, model experiments and field monitoring. Secondly, the engineering mechanical models of canal frost heaving failure were introduced based on limit equilibrium theory, such as material mechanics model and elastic mechanics model. Thirdly, multi-field coupling numerical models were developed including coupled heat-mechanics model, heat-water-mechanics model and the interaction model between frozen soil and canal lining. Lastly, the development processes of anti-seepage and anti-frost heave technologies for canals were expounded from four aspects: 1) the thermal insulation and preservation technologies against the external low temperature on soil and heat loss; 2) the anti-seepage and drainage technologies to reduce water content and water migration in soil; 3) soil replacement with sand or gravel technologies; 4) force release technologies by section structure optimization. With the increase of canal scale and upgrading demand for disrepair canals in harsh environment, the frost heaving failure mode was complex. The research frontiers and technical difficulties in this study mainly included: 1) the multi-field coupling failure mechanism and failure mode in the complex environment, such as solar radiation, freeze-thaw cycles and salinization, and operation conditions, such as water conveyance in winter with or without ice cover and water level dropping; 2) further development of multi-field coupling simulation model based on coupled heat-water-mechanics model covered the following aspects: canal thermal boundary with solar radiation and convective heat transfer model considering section form; canal damage model of freeze-thaw deterioration considering frost heaving and thawing of soil to analyze canal slope collapse; viscoplastic damage model for contact surface according to experiment on interfacial strength and stress-strain characteristics of lining-separated ice-frozen soil under freeze-thaw cycles; effects of salt on parameters of moisture field, thermal field and mechanical field and coupled heat-water-mechanics-salt model; 3) the canal failure criterion determination including strength, stiffness and stability of structures combined with field monitoring and numerical model, then modified the engineering mechanical model from the aspects of frost heaving force and adfreezing force distribution and foundation coefficient, and eventually formed a set of design method using engineering mechanical model to design and numerical model to check; 4) moisture, temperature and displacement changes under different anti-seepage and anti-frost heave measures of canals and standardization design combined with experiments, failure criterion and numerical model; 5) the dynamic disaster process and prevention and control technologies of canals determination by the following methods: classified variables such as environmental factors, operating conditions, section forms and failure forms of canals based on the field monitoring data and numerical simulation results, and then established the relationship between the variables by neural network and other algorithms. Finally, the future research directions were discussed and included: 1) complement of the design theory and method for anti-seepage and anti-frost heave; 2) establishment of dynamic evolution forecasting model for disaster chain in the whole life cycle. These may help to provide guidance to scientific design and efficient operation of water conveyance canals in arid-cold areas.