Dankwerth, Lisa

Fuchs, Anna-Lisa

Kaitna, Roland

Nagl, Georg

Proske, Dirk

Reider, Lukas

Scheidl, Christian

Wernhart, Susanna

English

Berner Fachhochschule: ARBOR

EGU21-10777, updated on 29 Apr 2021https://doi.org/10.5194/egusphere-egu21-10777EGU General Assembly 2021© Author(s) 2021. This work is distributed underthe Creative Commons Attribution 4.0 License.A combined model approach for debris-flow impact forcesLukas Reider1, Anna-Lisa Fuchs1, Lisa Dankwerth1, Susanna Wernhart1, Roland Kaitna1, GeorgNagl1, Dirk Proske2, and Christian Scheidl11Institute of Mountain Risk Engineering (IAN), University of Natural Resources and Life Sciences, Vienna, Austria(lukas.reider@boku.ac.at)2Bern University of Applied Sciences, Bern, SwitzerlandFor the design of mitigation measures knowledge of debris-flow impact forces, usually estimatedbased on hydrostatic, hydrodynamic, or combined approaches, is essential. As these approachesare based on Newtonian fluids, they must be adjusted by empirical correction factors to accountfor the solid-fluid nature of debris flows. The values for the correction factors shown in theliterature vary over a wide range and several studies showed a clear dependence with the Frouderegime of debris flows.To better understand the correction factors and to be able to calculate them using parametersthat describe the flow behaviour a total of 32 experiments were conducted in the course of theproject “Debris flow impact forces on bridge super structures (DEFSUP)”, funded by the AustrianScience Fund (FWF). Two different material compositions, different water contents as well as atotal impact and a bypassing of the measuring block were tested.The experimental setup designed within the project consists of a 4 m long semi-circular channelwith a diameter of 300 mm and an inclination of 20°. The material is released from a rectangularreservoir in a dam-break scenario and accelerated with zero roughness on a length of 1.2 m andtransferred to the semi-circle profile. The subsequently introduced roughness with a graindiameter of 1-2 mm generates a stationary phenomenological debris flow until it hits themeasuring setup. With a starting volume of 50 kg, flow heights between 8 and 12 cm and velocitiesfrom 0.8 to 2.2 m/s were achieved according to the material composition and different watercontent. With these different mixtures a Froude-range from 0.6 to 3.6 was covered. In addition,normal stresses and pore water pressures were measured at the exact same point.A detailed analysis of the measured impact forces together with the above mentioned measuredparameters showed that the hydrodynamic correction factor is a constant mainly correspondingto the liquification ratio of the debris-flow mixture. Hence, the hydrodynamic correction factor canbe regarded as a drag coefficient and seems to depend mainly on the internal friction of theflowing medium. At low Froude numbers measured impact forces exceed even a full momentumtransfer if the mean bulk density is used for the calculation. This indicates that the impact forcescan no longer be described by the hydrodynamic approach alone. For this reason, an additionalpressure term based on a hydrostatic approach is considered in the combined concept. Thissource: https://doi.org/10.24451/arbor.14947 | downloaded: 12.10.2021additional pressure term depends on the dynamics of flow (Froude number) and can be modelledvia a dynamic earth pressure coefficient.The findings from these experiments contribute to a better prediction of debris-flows impactforces in terms of their material composition and flow behaviour.Powered by TCPDF (www.tcpdf.org)

A combined model approach for debris-flow impact forces

https://arbor.bfh.ch/14947/1/EGU%20Ver%C3%B6ffentlichung.pdf

A combined model approach for debris-flow impact forces

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