U形混凝土衬砌结构冻胀性能离心模型试验研究

为了控制季冻区渠道混凝土衬砌结构的冻胀破坏程度,基于小型U形渠道混凝土衬砌结构的冻胀破坏特征及抗冻胀性能,通过取消衬砌结构的刚性接缝形成整体式大跨度U形混凝土衬砌结构,并利用冻胀离心模型试验研究该衬砌结构的冻胀效应。试验表明,土温在冻结前期降幅较大,渠坡两侧土体降温快于渠底。整体式大跨度衬砌结构呈偏心受力状态,坡板上部上表面受拉,底板上表面受压。变形性能良好,在持续负温作用下没有发生明显的破坏,冻胀变形从坡板变形开始,随着渠道底部土体温度的下降,引发结构整体变形,底板大幅抬起。结构以向上抬升为主,同时沿法向向衬砌结构中心收缩。底板和坡板的抬升最大分别可达16、4 mm。渠坡向内回缩约5 mm。整体式大跨度U型混凝土衬砌结构抗冻胀性能良好,能在一定程度上减轻衬砌结构的冻胀破坏。

Frost heave performance of U-shaped canal concrete lining based on centrifuge model test

Abstract: Small U-shaped canal concrete lining are easily destroyed because of frost heaving in seasonally frozen areas. Along the longitudinal and horizontal direction of concrete lining, rigid joints are formed of cement-sand mortar or fine aggregate concrete with same width as plate thickness. These joints exist between the plates or every two spans of lining. Previous research has founded that the destruction of concrete lining is always related to the rigid joints, because of the distinction between rigid joint and concrete lining on material and construction sequence, resulting in uneven distribution of water temperature along the canal longitudinal at the same time. So, canceled the rigid joint paralleling to the longitudinal channel, reduced the rigid joint paralleling to the cross section and enlarged the span of lining, eventually formed lining structure which with excellent performance in either longitudinal or horizontal direction. Aiming at controling the frost heave damage of the lining structure while still able to make full use of the U-shaped structure for compression performance, an integral long-span U-shaped concrete lining structure was proposed based on traditional small U-shaped concrete lining. Because centrifugal model test can reproduce the performance of the prototype in the model with great reality, freezing centrifugal model experiment of proposed lining was carried out to researchthe frost heaving characteristics. This study took a silty sandy soil based bucket canal concrete lining as a prototype in Yellow River irrigation area in Ningxia. According to the section size of the prototype canal and the space of the model box of geotechnical centrifugel, a model lining was made withthe similarity scale of 12.5 to perform centrifuge model test. The centrifugal acceleration was set to 12.5 times the acceleration of gravity, and model lining was unidirectional freezing from top to bottom with the target boundary temperature of -35 °C. Experiment showed that soil temperature decreased greatly in the early freezing stage, and decreased faster on both sides of canal slope than canal bottom. The integral long-span U-shaped concrete lining structure was eccentrically loaded, with upper surface of top slope in tension and the upper surface of bottom lining in pressure. Deformation of the structure began with canal slope. With the decrease of soil temperature of canal bottom, the integral deformation were caused, and then the lining bottom of canal was raised sharply. Comprehensively, the structure had good deformation performance , and no obvious damage occurred under continuous negative temperature. The structure was mainly uplifted upward, and meanwhile contracted to the lining center along the normal direction. The maximum uplift of canal bottom and canal slope could reach 16 and 4 mm respectively. The canal slope retracted about 5 mm inward. Therefore, integral long-span U-shaped concrete lining structure had good frost heaving resistance and the frost heaving damage could be reduced to a certain extent. Meanwhile, the frozen effect research of canal lining structure using centrifugal model experiment could be further understood and verified. This study could provide a reference for the design of U-shaped canal in frozen soil area.