岩体化学风化的非连续性及其科学意义

The Discontinuity of Rockmass Chemical Weathering and Its Scientific Significance

岩体化学风化在空间上具有高度的非连续性,这种非连续性广泛存在于从宏观、细观到微观的所有尺度。宏观结构面是化学风化最主要的发生场所;风化岩体内,新鲜岩块被沿结构面内法线方向发育的腐蚀带包围,呈斑点状分散于腐岩中。微缝等细观损伤普遍存在于各类岩石中;化学风化从岩块内不同空间位置的水力有效空隙向三维空间扩展,决定了细观尺度上化学风化的非连续性。矿物溶解是在晶体中具有过剩表面能的缺陷位置优先发生的,因而具有显著的微观非连续性。由于非连续特性,化学风化可增大水岩界面,提升矿物溶解反应的规模及速率。通过对既有损伤的扩展及在损伤空间堆积残余物,化学风化具有分离—裂化岩体、岩块及造岩矿物的重要作用,这种作用可使以新鲜岩石为主的岩体大规模脱离母岩,而堆积于坡脚的岩石块体在化学风化的继续作用下,可裂解为更小的岩屑或矿物碎屑,为向水体搬运创造条件,从而极大地促进斜坡夷平及地貌重塑进程。

Chemical weathering is highly discontinuous and the discontinuity exists at the macro-scale, mesoscale and micro-scale. Macro-fractures are the main places of chemical weathering occurring. In weathering rockmass fresh rock blocks are surrounded and separated by corrosion zones. Water-rock reaction in Meso-fractures and pores between mineral particles determine the discontinuity of chemical weathering at the meso-scale. Mineral dissolution occurs preferentially in crystal defects and is discontinuous at the micro-scale. Because of discontinuity, chemical weathering can add water-rock interface and raise mineral dissolution rate. By way of spreading existing damages and accumulating weathering residue, discontinuous chemical weathering has the efficiency of separating, cracking rockmass, rock blocks and forming minerals, which may cause the rockmass mainly made up of fresh rock breaking away from the parent rock on a large scale. Chemical weathering affects rock blocks piling up the slope foot and brings them to split smaller rock and mineral debris that can be carried way by surface runoff. So, chemical weathering can promote remarkably slope planation landform evolution course.