{"title":"Effects of Wooden Embers Cover on thermo-hydrological response of silty volcanic cover and implications to post-wildfire slope stability","authors":"","doi":"10.1016/j.enggeo.2024.107724","DOIUrl":null,"url":null,"abstract":"<div><p>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.</p></div>","PeriodicalId":11567,"journal":{"name":"Engineering Geology","volume":null,"pages":null},"PeriodicalIF":6.9000,"publicationDate":"2024-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Engineering Geology","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0013795224003247","RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ENGINEERING, GEOLOGICAL","Score":null,"Total":0}
引用次数: 0
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.
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.