寒区路基反射率及其对调控阴阳坡的应用研究

Most of embankments of the Qinghai-Tibet Railway have a northeast strike. The south-facing shoulder absorbs more solar radiation than the north-facing shoulder, a phenomenon called the Ying-Yang slope effect (YYSE). Eliminating the YYSE is crucial to thermally stabilize the permafrost under the embankments because the YYSE differs the solar absorption across the embankment and promotes embankment distresses. As solar irradiance is uncontrollable, it is critical to increase the embankment albedo and to vary the shoulder’s albedo to eliminate the YYSE. Measuring the albedos of the embankment and of the shoulders, however, is technically difficult because the embankment, in shape, is a trapezoid so multiple reflections occur between the shoulder and the ground near the shoulder. On the basis of these multiple reflections, we propose a physical model to calculate the albedos of the embankment and of the shoulders. We validate the model by using an albedometer to measure the albedo of a small-scale embankment model. We measure the albedos of stockpiled crushed rocks with different diameters and with whitish coatings, in order to evaluate the albedo of the shoulder with crushed rocks revetment. Using the measured shoulder’s albedo and the proposed physical model, we attempt to adjust the embankment shoulder’s albedo to eliminate the YYSE and to reduce the absorption of the embankment. Our works will lay scientific basis for varying embankment shoulder’s albedo to remedy the thermal imbalance across the embankments in cold region and for reducing embankment’s solar absorption. Our works will also provide engineered solutions to remedy the YYSE according to the geometry, striker, and shoulder materials of the embankment.

青藏铁路大部分路段接近东北走向，路基两侧存在阴阳坡效应，促使路基病害的发生。由于太阳辐射为不可控因素，平衡阴阳坡辐射吸收差异关键在于调节阴阳坡的反射率。路基呈梯形状且尺寸大，太阳辐射在路肩与附近地面处发生多重反射，很难实地测量整个路基、路肩的反射率。基于路肩与地面发生多重反射，建立路基、路肩反射率的综合计算模型，通过观测路基实体小模型的反射率验证反射率模型的准确性；现场实测路基表面反射率，实验测量不同粒径块碎石堆、涂白块碎石堆的反射率，查清块碎石路肩太阳辐射吸收量以及反射率可控范围, 阐明提高路肩反射率的具体工程措施；运用路基反射率的综合计算模型，建立阳坡反射率与阴阳坡辐射差的关系式，查明影响路基边坡热平衡的主要因子及其相互动态关系；查清与局地因素相适应的工程措施以减少阴阳坡效应。为依路基尺寸、走向、路肩材料调控路基表面反射率以减少路基的太阳辐射吸收量、消除路基阴阳坡效应提供技术支持。

青藏铁路大部分路段接近东北走向，路基两侧存在阴阳坡效应，促使路基病害的发生。由于太阳辐射为不可控因素，平衡阴阳坡辐射吸收差异关键在于调节阴阳坡的反射率。主要研究内容包括：(1) 测量了小比例路基模型反射率，提高路基模型阳坡反射率可提高路基模型整体反射率0-0.2。该发现可用于冷却寒区路基; (2) 模拟了边坡反射率对路基热不对称性的影响，当路基热不对称程度最大时，将阳坡吸收率从0.8降至0.4可消除热不对称性。该发现表明提高路基阳坡反射率可用于消除路基的热不对称性; (3)建立了包含反射率和热惯量等关键参数的多年冻土区路面温度变化预测新模型，模拟结果说明路面温度的振幅、最大值及最小值随路面吸收率、每日天顶入射太阳辐射量、热惯量倒数线性增大，其中提高反射率是降低路面温度最为有效的方法; (4) 观测了块碎石层反射率随其粒径的变化规律，结果表明多重反射效应导致块碎石层反射率较平面涂料反射率低0.1-0.2，且块碎石层反射率随其粒径增大而降低。该发现表明可在边坡喷涂非白高反涂料以提高其反射率，降低护坡的太阳辐射吸收量，提升其制冷效果; (5) 提出测量路基模型反射率的新方法，即黑白板法，测量结结果表明路基模型反射率较平面反射率低0.05-0.08，说明路基较原地表及周围地表吸收更多阳光。新方法可测量路基等曲面的反射率，进而量化工程建设所引起的冻土温度扰动的程度；(6) 建立了两种理论模型来评估路堤的太阳辐射吸收量，太阳捕获模型和表面粗糙度模型。吸收率为0.8的路堤宏观吸收率较其微观吸收率低0.01-0.05，说明边坡的太阳辐射捕获效应可以忽略，提高边坡反射率仍能有效地降低边坡的太阳辐射吸收。新模型无需考虑太阳位置、地面反射率、边坡反射率以及天空晴朗系数等参数，可直接模拟计算出路堤和边坡的宏观反射率。