冻土路基块(碎)石层反射率测量及应用

Theory and application of measuring the albedo of crushed-rock layer embankment in permafrost regions

通过测量平均粒径为1,2,3和5 cm的天然碎石层的反射率,以揭示影响碎石层反射率的主控因子。为了提高碎石层的反射率,将不同粒径骨料均匀涂上高反射率材料,并将实测碎石层表面的反射率与采用ASTM E1918A规范计算结果进行对比。研究发现:ASTM E1918A规范计算值是文中模型的一个特例。当太阳辐射瞬时强度值变化小于20 W/m2,模型计算的反射率与ASTM E1918A计算值的偏差在0.00~0.03。由于碎石层表面粗糙度,其反射率总比新鲜碎石平面的反射率低0.10~0.25,且随着骨料粒径的增大,天然碎石层的反射率逐渐降低。因为从表面散射反射的光子重新回到表面的概率增大,加剧了碎石孔隙间的多重反射,从而降低了反射率。经喷涂高反射率材料后,可将碎石层反射率从0.262提高至0.433,提高幅度在0.10~0.20。提高碎块路基的反射率可以有效地降低路基边坡温度,有利于保护冻土路基的稳定性。

A novel method for measuring the albedo of crushed-rock layer was proposed in this paper. The albedo of the crushed limestone layers with single-size aggregates of 1, 2, 3 and 5 cm sizes was measured respectively to reveal the main factors controlling the albedo of the crushed-rock layer. The layer was painted with the high-reflective pigment to increase the albedo of the crushed-rock layer and then the albedo of the painted layer was measured. The albedo of the crushed-rock layer was tested and compared against the albedo measured by the ASTM E 1918A. It was found that when the variation of the incident solar intensity was less than 20W/m2 （tolerant errors stated by ASTM E1918A）, the ASTM E1918A either underestimate or overestimate the albedo of the crushed-rock layer up to 0.00 - 0.03. The reflectivity of the crushed-rock layer decreases with the aggregate size, and the albedo of the crushed-rock layer is 0.10 - 0.25 lower than that of the fresh flat crushed-rock. This difference is because photons leaving the crushed-rock layer have a probability to return to the layer, reducing the albedo of the crushed-rock layer. Painting the crushed-rock layer with high reflective pigment raised the albedo of the layer from 0.262 to 0.433. Raising the reflectivity of the crushed-rock layer on slope of embankment reducesthe temperature of side slope and protects the permafrost stratum.