Abstract:
Exploring the frost heaving effects of structures in cold regions is quite necessary, especially in Northern China, since frost heave will be a major cause of damage to some geotechnical structures there. The present paper takes the small U-shaped canal of splicing concrete lining with three arc-plates as a case study sample, which is a common structure type at the construction of canal in Yellow River irrigation area of Ningxia, and investigates the effects of frost heave on stress state of canal's concrete lining. At first, take 6 assumptions to simplify the complicated factors of frost heave. According to the superposition principle, we consider the frost heave action on the concrete linings as the combined result of gravity, tangential freezing stress, normal frost heaving stress and freezing stress, and give the equilibrium relationship between them both integrally and locally; then we analyze the force for each part of concrete lining subjected, and establish the mechanical model under frost heave according to the structure and failure characteristics of concrete linings and the site monitoring experiment data in Yellow River irrigation area of Ningxia during freeze-thaw period from 2013 to 2015. Thus, the simple computational formulas of internal force for linings' each part including the slabs of lining, the arc plates and the U-shaped bottom of lining are obtained. Using the above formulas, in one U-shaped canal with three arc-plates concrete lining with known size in the prototype observation region, the frost heave and the internal force are calculated. The calculating results show that: Firstly, the small U-shaped canal with three-plates bears compression and relatively uniform bending moment together, which is in accordance with actual engineering; Secondly, the most complicated stress situation of the concrete lining exists in the areas from the junction of slab and arc plate to the rigid seams with cement mortar of fine aggregate concrete, where the section easily cracks or is destroyed if the frost heaving and freezing stress are big enough; Thirdly, if the camber of the slab of lining is too small, it may lead to the fragility of concrete linings under frost heaving situation; Fourthly, the position of normal frost freezing stress decides the bending moment of canal's slope. At last, this paper further analyzes the effects of camber of slab and central angle of arc plate on normal heaving stress, discusses the position of normal frost freezing stress, and gives the following suggestions that the camber of the slab of lining ranges from 20 to 26 degrees, and meanwhile, normal frost freezing force actions at the position of 2/3 of slope from the top. Especially, the internal forces of rigid seam are researched by using the central angle of arc plate, which indicates the position of rigid seam. Results show that, due to great axial and shearing force, the rigid seam is weakness position of concrete lining, and thus, the central angle of arc plate should be greater than the half of the central angle of curved bottom slightly when it is designed in order to obtain lesser frost heaving force and damages. All these works are beneficial for the design of U-shaped canal with three-ace plates in frozen soil area.