Mechanical Model And Its Application Of Frostheave Damage Of Concret Lining Canal Under Open System Conditions

Water is the source of life,the key of production,the foundation of ecology and the basis for human survival.Particularly in arid and cold regions,water resource has important significance for development of industry,agiculture,society and economy.In order to reconcile contradiction between supply and demand of water,advance water conservancy modernization,and ensure sustainable development of regional economy and society,irrigated areas reconstruction for water saving and long distance inter-basin water diversion projects such as the south-to-north water diversion project are continuously advancing,in which main conveyance buildings are lining canal.But in winter,canals in cold regions can be easily damaged because of foundation soil frost heave,which influences safe operation of canals and performance of engineering benefits and is especially harmful to canals with high groundwater level under open system conditions.Most lining canals with high groundwater level are located in Mountains or Plains,such as Tarim irrigated areas in Xinjiang,Yellow irrigation areas downstream in Baiying city in Gansu province,and the middle and lower reaches of the inland river basin in Hexi corridor.At present,engineering design for preventing frost heave damage of concrete lining canal mostly depends on engineering experience and qualitative understanding without considering the influences by groundwater migration and recharge,so it is necessary to construct a reasonable and reliable quantitative design method.Taking concrete lining canal under open systems conditions in boreal arid and cold regions as research object,based on reasonable basic assumption and combination of multiple disciplines such as frozeon soil mechaics,material mechanics and elastic foundation beam theory,the study proposes a calculating method for mechanical analysis of frost heave damage of concrete lining canal under open system conditions,then constructs mechanical models of frost heave damage for different kinds of canal and presents corresponding judging criteria for canal lining frost heave damage.The results can provides technical guidance and theoretical basis for anti-freeze design and related engineering anti-freeze measures.Main research contents and relative results are outlined below:(1)Supposing that frozen soil of canal foundation is elastic foundation obeying Winkler assumption,and based on functional relations between frost heaving force,frost heaving strength and groundwater level,the study proposes a calculating method for distribution of normal frost heaving force acting on canal lining under open system conditions,then a basic framework of mechanical analysis of frost heaving damage is constructed by combining theories of material mechanics and frozen soil mechanics.On this basis,mechanical models of frost heave damage of cast-in-place lining canals,precast concrete lining canals and curved cross-section lining canals are established,respectively.Then judgment criterion of frost heave damage for different kinds of lining canals is put forward.(2)Combined related mechanical theory and field experimental results,calculating methods for frost heave strength and frozen depth of foundation soil are deduced,and analytic expressions to calculate the maximum bending moment of section and the position of the most vulnerable section are obtained.The unevenness of distributuion of frost heaving load is quantitatively analyzed from both the whole and the local level,based on which the reason of the good performance of wide and shallow cross-section trapezoidal canal under frost heave conditions is revealed.(3)By considering orthogonal anisotropy of frost heave deformation of frozen soil and frost heave reduction effect caused by overlying soil gravity,determined method of distribution of tangential frost heaving force on lining canal under open system conditions is proposed.In winter through regarding canal lining plates as uniform contraction rectangular beams with one dimensional tangential frozen constrait,the analytic expression of temperature stress in canal lining caused by canal frozen shrinkage is deduced.System of equations in which unknown quantities includes all external constraints acting on shade-slope lining plates,sunny-slope lining plates and canal bottom plates is established.(4)Through improving the theory of elastic foundation beam,the method which is widely applied to foundation settlement problem can be appied to frost heave problem now.Based on establishment of differential equations of flexure line of lining plate caused by foundation soil frost heave,the analytic expression of internal force and deflection of lining are obtained,and the judgment criterions rlating to lining plate frost heave displacement for frost heave damage of lining plates are estabilished.By taking a trapezoid canal in Tarim irrigation areas as prototype,frost heave displacements of lining plates are calculated.The comparative analysis between the results calculated by the article method,material mechanical and observed value is carried out.The results show that the results calculated by the article method are in accordance with observed value better,and are less than results calculated by material mechanical because of considering reduction of frost heave force.