Frost heave fracture mechanical model for concrete lining trapezoidal canal and its application

Abstract: As for rigid materials such as concrete there existing some invisible initial cracks which can propagate under the force of frost heave, leading to the decrease of water transportation efficiency and massive loss of precious transport water. That is to say, it is quite meaningful and necessary to analysis the damage of concrete lining canal with initial cracks from the perspective of fracture mechanics in seasonal permafrost zones. Based on the theory of linear elastic fracture mechanics and utilizing existing frost heave mechanical model for concrete lining canal, meanwhile through appropriate assumptions and simplifications and taking the consideration of frost heave force, a frost heave fracture mechanics failure criteria for concrete lining canal was proposed by taking the frost heave damage of lining concrete as a composite fracture problem ofⅠandⅡstyle fracture. In fracture criterion under the force of frost heave, the fracture toughness of concrete is regarded as the criterion on the judgment of whether the concrete is damaged or not. When the fracture strength factor is less than fracture toughness of concrete, the concrete lining plate remained compact. Simultaneously, there is a close relation between fracture toughness and temperature. Therefore, a relationship between frost heave parameters and fracture toughness was formed to solve the shortage of frost heave mechanical model. A frost heave fracture mechanical model for concrete lining channel regarding the reasonable and optimal thickness of lining plate was established for shady slope, sunny slope and channel bottom respectively. For the fracture mechanical model of frost heave concrete lining channel, the reasonable and optimal thickness of lining plate is determined, and the model presents a feasible and simple way for aided design for anti-frost heave of concrete lining channel. Results suggest that the most vulnerable parts with the highest moment and shear force is the middle in channel bottom and 1/3 lining plate length near the bottom in both sunny slope and shady slope. Under the assumption of extreme condition KfⅠ+KfⅡ=KfⅠc ，the thickness of lining plate in shady slope, sunny slope and channel bottom is determined. Shady slope has the highest thickness because it has highest frost heave force and is vulnerable to sunshine, followed by the channel bottom and sunny slope, which accords with the engineering practice.