Degradation and protection of cut slopes in weathered gneiss; a 40-year case study

IF 1.3 4区 工程技术 Q3 ENGINEERING, GEOLOGICAL
R.P. Martin, J.H. Howell
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Abstract

The retreat of two road-side cut slopes in weathered gneiss in the Middle Himalaya of east Nepal has been assessed by engineering geological mapping, sequential photography and slope profiling over a 40-year period from 1979 to 2018, allowing approximate degradation rates to be calculated. The rate of removal of completely weathered gneiss and residual soil was about twice that of highly weathered material, primarily reflecting increased micro-cracking and breakdown of feldspars and micas in the weathered fabric. Surface water erosion by rilling and gullying in the summer monsoon wet season was the dominant process affecting the slopes, with landsliding (mainly by soil falls and debris slides) playing a secondary role. Drainage and bio-engineering protection measures applied to the slopes within the first three to 12 years after excavation were effective in reducing the degradation rate by between one to two orders of magnitude once the slopes had developed a moderate vegetation cover. The total volume of material removed from the slopes over four decades is equivalent to average rates of ground lowering in the range of 150 to 320 mm a -1 and 2 to 4 mm a -1 , before and after protection works respectively. The latter range is similar to long-term denudation rates measured in drainage catchments in the region with similar settings. Supplementary material: https://doi.org/10.6084/m9.figshare.c.7005885
风化片麻岩切坡的退化与保护;40 年案例研究
从 1979 年到 2018 年的 40 年间,通过工程地质测绘、连续摄影和斜坡剖面测量,对尼泊尔东部喜马拉雅山脉中段风化片麻岩中两个路边切坡的退缩情况进行了评估,从而计算出大致的退化率。完全风化片麻岩和残留土壤的流失率约为高度风化材料的两倍,这主要反映了风化结构中长石和云母的微裂缝和分解增加。在夏季季风湿季,地表水通过碾压和沟壑造成的侵蚀是影响斜坡的主要过程,而滑坡(主要是土壤崩落和泥石流)则是次要过程。在开挖后的头 3 到 12 年内,对斜坡采取排水和生物工程保护措施,一旦斜坡形成适度的植被覆盖,就能有效地将退化率降低 1 到 2 个数量级。40 年来从斜坡上清除的材料总量相当于保护工程前后地面平均下降率,分别为 150 至 320 毫米/年和 2 至 4 毫米/年。后一范围与该地区环境类似的排水集水区测得的长期剥蚀率相似。 补充材料:https://doi.org/10.6084/m9.figshare.c.7005885
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来源期刊
CiteScore
3.40
自引率
14.30%
发文量
66
审稿时长
6 months
期刊介绍: Quarterly Journal of Engineering Geology and Hydrogeology is owned by the Geological Society of London and published by the Geological Society Publishing House. Quarterly Journal of Engineering Geology & Hydrogeology (QJEGH) is an established peer reviewed international journal featuring papers on geology as applied to civil engineering mining practice and water resources. Papers are invited from, and about, all areas of the world on engineering geology and hydrogeology topics. This includes but is not limited to: applied geophysics, engineering geomorphology, environmental geology, hydrogeology, groundwater quality, ground source heat, contaminated land, waste management, land use planning, geotechnics, rock mechanics, geomaterials and geological hazards. The journal publishes the prestigious Glossop and Ineson lectures, research papers, case studies, review articles, technical notes, photographic features, thematic sets, discussion papers, editorial opinion and book reviews.
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