青藏铁路旱桥桥面遮阳对桥下及周边冻土太阳辐射影响

通过分析太阳辐射强度和旱桥桥面影子轨迹随时间的变化规律,建立时间、太阳辐射强度、太阳位置和影子轨迹关系的数学模型,并利用该模型对旱桥桥面遮阳效应进行研究。提出直射率概念表示周边冻土获得的太阳直接辐射能量的比例。研究发现旱桥的高度、走向、桥面宽度等因素对桥下及周边范围冻土的太阳直射率影响很大。随着旱桥高度的增加,桥面遮阳影响范围增大,遮阳中心直射率增大;随着旱桥宽度的增加,桥下及周边冻土的直射率降低;东西走向的旱桥桥下及周边冻土表面直射率非对称性最为明显。旱桥桥面的遮阳可以有效减少桥下及周边冻土的太阳辐射热量,同时也会引起桩基周边冻土表面非均匀太阳辐射受热,这种太阳辐射的非均匀性不可忽视,在旱桥长期稳定性分析中应予以考虑。

Effects of Sunshine-shield of Qinghai-Tibet Railway Land Bridge on the Solar Radiation of Underbridge and Surrounding Permafrost

Based on the change law of solar radiation intensity and shadow of land bridge variation with time, the mathematical model expressing of the relationship among time, solar radiation intensity,solar position and shadow track was established. The effects of the sunshine-shield of land bridge floor were studied using the model. Direct rate concept was proposed to define the proportion of solar direct radiation energy of the surrounding permafrost. The results show that height, direction and width of land bridge are the major influence factors on the solar radiation of underbridge and surrounding permafrost. With the increase of the height, shading scope and direct rate of sunshade center also increase; with the increase of the width, direct rate of the surrounding permafrost decrease; there was obvious asymmetry distribution of permafrost surface direct rate, especially for the east-west bridge. Sunshine-shield of land bridge can effectively reduce the sun radiation heat of the surrounding permafrost and also cause non-uniform distribution of solar radiation on permafrost surface around piles, which should be concerned in the stability estimation of land bridge.