模袋混凝土衬砌梯形渠道冻胀适应性研究

Research on adaptability of using molded bagged concrete to ameliorate heave in trapezoidal concrete channel

为探明开放系统条件下梯形渠道渠基土冻胀对混凝土衬砌结构破坏规律,该文在水热力三场耦合理论的基础上,考虑毛细作用及薄膜水迁移理论,采用动态变化的上下温度边界,利用多场耦合软件COMSOL模拟了渠基土67 d的冻胀过程,得出渠基土冻胀量。在此基础上,考虑模袋对冻土与混凝土间接触行为的影响,利用有限元软件ABAQUS模拟冻土与普通混凝土、冻土与模袋混凝土间接触力学行为,最终得出衬砌不同位置处应力场及位移场。结果表明:在距离渠底约1/3坡长处、渠底中心处冻胀量较大,渠顶处冻胀量最小;普通混凝土所能适应的最大不均匀冻胀量为2.98 cm;模袋混凝土的使用改变了冻土与混凝土间的接触行为,应力最大值约为普通混凝土的1/250,季节性冻土地区采用模袋混凝土可显著提高对不均匀冻胀量的适应性。该模拟结果与工程实际结果吻合度较好,研究结果可为开放系统下季节性冻土区梯形渠道的工程设计提供参考和依据。

Concrete channel could heave and even fail in winter under the combined impact of frozen-thawing, temperature fluctuation and mechanical stresses. Understanding the mechanisms underlying the failure of lining structure of the concrete channel is hence important. Taking trapezoidal concrete channel as an example, a numerical model was developed in this paper based on heat-moisture-stress theory, capillary force and water flow in soil to calculate the impact of these factors on concrete channel. In the model, the temporal change in temperature on the channel surface was treated as the top boundary and the groundwater table as the bottom boundary where the temperature remains stable. The multifield coupling software COMSOL was used to simulate potential occurrence of heaves in soil induced by frost. We simulated a 67-day heaving process induced by frost in the foundation soil and obtained the final heave simultaneously by solving the partial differential equations in COMSOL. Based on the results, the finite element software ABAQUS was used to simulate the nonlinear mechanical behavior of the contacts between the concrete lining and the soil, as well as the contacts between the molded bag concrete and the soil using different contact models. The stress and displacement at different location on the contacts were calculated using the ABAQUS. The result showed that: 1) the frost-induced heave varied spatially in the channel. The worst occurred at the center of the channel bottom and on the 1/3 the slope length(measured from the slope tip), and the least was on the top of the channel. 2) If the failure criterion was defined as when the concrete lining reached its plastic stage, the maximum non-uniform heave calculated by the ABAQUS was 2.98 cm for the traditional concrete lining. 3) Compared with traditional concrete lining, the molded bag concrete substantially reduced the force between the lining and the soil. This changed the mechanical behavior of their contact, thereby effectively reducing the stress on the molded bag concrete lining. The maximum stress on the top surface of the molded bag concrete lining was only 1/250 that in the traditional concrete lining, effectively improving its adaptability to uneven frost heave in seasonal frozen soil. The simulation results are in good agreement with experimental data and have implications for designing trapezoidal channels in seasonal frozen regions.