Effects of Wooden Embers Cover on thermo-hydrological response of silty volcanic cover and implications to post-wildfire slope stability

IF 6.9 1区 工程技术 Q1 ENGINEERING, GEOLOGICAL Engineering Geology Pub Date : 2024-09-08 DOI:10.1016/j.enggeo.2024.107724
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Abstract

Wildfires striking vegetated hillslopes appear to increase the hazard towards rainfall-induced landslides. One mechanism little investigated in the literature consists in the formation of Wooden Embers Cover (WEC) following the wildfire. This layer has very peculiar thermohydraulic properties and may affect the interaction between the atmosphere and the subsoil. The paper presents an experiment conducted in an outdoor lysimeter filled with pyroclastic silt (SILT) up to 75 cm covered with 5 cm of WEC. Water storage in the SILT layer, soil water content, suction, and temperature were recorded for several years, initially under bare (no-WEC) condition (4 years), then vegetated (no-WEC) condition (5 years) and, finally, with a WEC placed on the top of the SILT (SILT+WEC condition; 3 years). The hydrological effect of the WEC was assessed by comparing the response of the SILT+WEC with the SILT under bare or vegetated conditions. The WEC reduces water losses by evaporation, thus increasing the average water content in the underlying SILT, an effect that is detrimental to slope stability. To discriminate whether the barrier effect was associated with the lower thermal or hydraulic conductivity of the WEC, a numerical simulation was carried out by considering the case of a WEC with its real thermal and hydraulic properties and the case of a fictitious top layer placed on the top of the SILT having the same hydraulic properties of the WEC but the thermal properties of the SILT. It is concluded that the barrier effect of the WEC is mainly associated with its hydraulic properties, i.e. the WEC acts as a capillary barrier. To demonstrate the practical implications of this findings, a case study of rainfall-induced landslide has been reanalysed by simulating the presence of a WEC layer having the same thermohydraulic properties as the material characterised in this study. It is shown that a WEC can substantially reduce the severity of the triggering rainfall event, thus increasing the vulnerability of the slope to rainfall-induced failure.

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木烬覆盖对淤泥质火山覆盖层热-水文响应的影响以及对野火后斜坡稳定性的影响
野火袭击植被丰富的山坡似乎会增加降雨引发山体滑坡的危险。文献中研究较少的一个机制是野火后形成的木烬覆盖层(WEC)。该层具有非常奇特的热水力特性,可能会影响大气与底土之间的相互作用。本文介绍了一项在室外渗滤池中进行的实验,该渗滤池中填充了高达 75 厘米的火成碎屑粉土(SILT),并覆盖了 5 厘米的木烬覆盖层。对淤泥层中的蓄水量、土壤含水量、吸力和温度进行了长达数年的记录,最初是在裸露(无 WEC)条件下(4 年),然后是在植被(无 WEC)条件下(5 年),最后是在淤泥层顶部放置 WEC 的条件下(淤泥层 + WEC 条件;3 年)。通过比较 SILT+WEC 与裸露或植被条件下的 SILT 的反应,评估了 WEC 的水文效应。WEC 可减少水分蒸发损失,从而增加下层 SILT 的平均含水量,这种效应不利于边坡稳定性。为了区分阻隔效应是否与 WEC 的热导率或水导率较低有关,我们进行了一次数值模拟,考虑了具有真实热导率和水导率特性的 WEC 的情况,以及在具有与 WEC 相同的水导率特性但具有 SILT 热导率特性的 SILT 上部放置一个虚构顶层的情况。得出的结论是,水环沉积物的阻隔效应主要与其水力特性有关,即水环沉积物起着毛细阻隔作用。为了证明这一研究结果的实际意义,我们对降雨引发的山体滑坡案例进行了重新分析,模拟了与本研究中的材料具有相同热水力特性的 WEC 层的存在。结果表明,水下蚀刻层可大大降低引发降雨事件的严重程度,从而增加斜坡在降雨引发的崩塌面前的脆弱性。
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来源期刊
Engineering Geology
Engineering Geology 地学-地球科学综合
CiteScore
13.70
自引率
12.20%
发文量
327
审稿时长
5.6 months
期刊介绍: Engineering Geology, an international interdisciplinary journal, serves as a bridge between earth sciences and engineering, focusing on geological and geotechnical engineering. It welcomes studies with relevance to engineering, environmental concerns, and safety, catering to engineering geologists with backgrounds in geology or civil/mining engineering. Topics include applied geomorphology, structural geology, geophysics, geochemistry, environmental geology, hydrogeology, land use planning, natural hazards, remote sensing, soil and rock mechanics, and applied geotechnical engineering. The journal provides a platform for research at the intersection of geology and engineering disciplines.
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