Study On The Adaptability Of Concrete Lining Of Mold Bag To Frost Heaving Under The Action Of Moisture-heat-stress Coupling

Mold bag concrete is widely used in north irrigation area because of its advantages of fast construction speed,good integrity and strong adaptability to the frost heaving of canal foundation soil.However,the research on the adaptability of mold bag concrete to frost heave of canal-based soil is still incomplete.Based on this,this paper mainly explores the influence of water migration in the canal foundation soil on the frost heave failure of concrete lining of mold bag,the adaptability of canal lining to the frost heave amount,and finds out the relatively optimal lining structure form.The water field,temperature field and displacement field of canal foundation soil are coupled and affect each other in the process of frost heave.The change of the temperature field forms a temperature gradient,which makes the water in the unfrozen area migrate to the frozen front,and generates a large amount of latent heat to affect the distribution of the temperature field.The water migrates under the action of temperature gradient and the ice lens is formed to block the water migration.Under the joint action of temperature field and water field,the characteristic parameters such as thermal conductivity,heat capacity,density and pore ratio of channel base soil all change with time,and finally the displacement field changes due to water icing.The distribution of temperature field,water field and stress field in canal foundation soil can be expressed by partial differential equation.The frost heave process of canal foundation soil can be simulated by solving three partial differential equations simultaneously by multi-field coupling software COMSOL.The thermal resistance formed by composite geomembrane can be realized by the thermal resistance layer in COMSOL,so as to explore whether composite geomembrane are installed on the lower side of the lining to influence the frost heave amount of channel based soil.On this basis,the simulation results of frost heave of canal foundation soil were input into the finite element software of ABAQUS to simulate the contact mechanical behavior between concrete lining and canal foundation soil.Finally,by changing the quantity of uneven frost heave of canal slope,the maximum quantity of uneven frost heave that ordinary concrete can adapt to and the adaptability of mold bag concrete to the quantity of uneven frost heave are explored.The results show that:(1)According to the prototype observation results,the concrete lining of mold bag has a good adaptability to the frost heaving of canal foundation soil,and can adapt to the frost heaving of canal foundation soil up to 11 cm.At the same time,the mold bag concrete integrity is good,the canal foundation soil because of frost heaving,thawing and sedimentation there is residual frost heaving rate,but the mold bag concrete lining still can ensure the relative stability of the lining structure.(2)When the concrete thickness of mold bag is 15 cm and 12 cm respectively,the improvement of the frost heaving amount of the composite geomembrane is more significant.The water migration in canal foundation soil mainly occurs at the shallow burial depth.The water transfer mainly occurred in the period from December 6,2017 to January 16,2018,and the water content reached the maximum during the period from January 16,2018 to February 26,2018.After that,the water content at the same location in the channel foundation soil gradually decreased over time.(3)The water-thermal three-field coupling simulation was carried out for the channel subsoil under the condition of composite geomembrane on the lower side of concrete lining.The effects of groundwater level change on temperature field and capillarity on water migration are considered.The simulation results are basically consistent with the measured results and reveal the distribution law of frost heaving in trapezoidal channels.According to the simulation results,the frost heaving amount of canal base soil reached the maximum value of 8.243 cm at the length of about one third of the slope from the canal bottom.At the bottom and top of the channel,there is less frost heave.(4)The setting of composite geomembrane has little influence on the water migration of channel subsoil,but it can change the temperature distribution in channel subsoil to a great extent.The addition of composite geomembrane reduces the frost heaving of the channel because it can form thermal resistance between the concrete lining and the canal foundation soil.At one third of the slope away from the bottom of the canal,the frost heaving at the top of the canal decreased by 14.3% and 15.5% respectively.(5)in the simulation of upper lining structure,the contact mechanical behavior between the channel foundation soil and the lining was considered,and the contact mechanical behavior between the foundation soil and the lining could be completely analyzed.Under the action of freezing force,the maximum frost heaving amount of concrete lining is about 1/3 slope away from the canal bottom.With the increase of frost heaving amount at this position,the lining gradually enters the plastic damage stage and causes damage.The maximum non-uniform frost heaving amount that concrete can adapt to is 2.98 cm.(6)when mold bag concrete lining is used,on the one hand,the addition of mold bag enhances the tensile strength of concrete,thus improving the adaptability of the lining to the frost heaving of canal foundation soil;On the other hand,the mold bag changes the contact constitutive structure between concrete and frozen soil,releases the freezing force,and can greatly reduce the stress of lining itself.The maximum stress is about 1/250 of that of ordinary concrete.Therefore,the adoption of mold bag concrete in seasonal permafrost area can significantly improve the adaptability to uneven frost heave.