Research On The Thermal State Of Culvert In Deep Seasonally Frozen Region And It’s Optimized Design

The culvert in frozen region could improve transverse drainage condition of this area, and optimize the structure of transportation route. However, it changed the original states of water-heat balance, and had impact on the thermal stability of roadbed. In order to analysis its impact to the roadbed-culvert transition section, based on the existing monitoring data, we established a finite element model to simulate culvert’s temperature fields in consideration of latent heat, and judged the reliability through comparing the simulation results to the monitoring data, and then we simulated with different parameters or different sizes to obtain the influence on the maximum frozen depth caused by different intensity of foundation convection under the culvert, different water content of subsoil, different size of culvert. The results indicated that:1) The match between measured temperatures and simulated temperatures was shown to be very good, which demonstrated the accuracy of the numerical model.2) In the design of culvert in seasonally frozen region, foundation convection under the culvert in cold season could not be ignored. Some active measures should be taken to protect the subsoil from the effect of convective heat transfer.3) The culvert maximum frozen depth changing with water content is divided into three steps. At first, it decreased with increasing water content. And then, the reduction got slow, even the frozen depth increased slightly. At last, it decreases again;4) The diameter of culvert greatly affected the maximum frozen depth, while the size of clear height had little effect on it. Diameter is our first priority for the requirements of strength, stability, functionality, etc. and the clear height could be considered at last. In a word, finite element model is established to simulate different temperature fields, which could provide an available reference for designing, constructing and maintaining the culverts engineering in cold region.In deep seasonally frozen region, because of culvert changed the freezing process, the maximum depth of seasonal freezing in roadbed was much deeper than which in natural ground, a research report indicates that it is about2times. In order to ease the situation, we proposed the measure of laying thermal-protective coating under the culvert, calculated and decided the material of the layer by way of equivalent conversion. Based on the existing monitoring data of culvert in Harbin to Dalian passenger dedicated line, we established a finite element model to simulate the temperature fields of the culvert with thermal-protective coating. We simulated with different parameters or different sizes to obtain the influence on the maximum frozen depth caused by different depth, different modes and different thicknesses, so as to obtain the best measure. The results indicated that:The foam concrete is the ideal material to be used, and we could lay the19-cm-thick foam concrete on the top of the culvert foundation as thermal-protective coating, which is10cm broader than the foundation. In this way, the maximum depth under the culvert could be reduced, which could be adapted to the cold region engineering.