Bio-engineering Mitigation Debris of Flow

在气候变化的影响下，降雨引发的泥石流事件越来越多地被报道，这些事件导致了重大的社会经济损失。现有的缓解方法包括混凝土挡板，但这些方法含有大量二氧化碳，这将进一步促进气候变化。坡面生物工程，如灌木铺层[1]是一种替代的“绿色”和低碳技术(图1)。植物枝条可以用来减弱碎屑撞击能量，随后可以动员根部拔出阻力来抵抗对植物产生的阻力。然而，还没有研究评估这种土壤-植物-泥石流相互作用及其对泥石流流动性的影响。这个博士项目的目的是调查使用刷子分层来减少泥石流块体的流动性的有效性。该项目的目标是：(I)确定在泥石块运输过程中对植物地上部施加的阻力；(Ii)量化土壤-根部对阻力的机械拔出阻力；(Iii)量化由于生物工程缓解而降低的水流流动性；以及(Iv)评估灌木分层技术相对于刚性挡板方法的性能；将开发一种新的大型实验水槽来模拟不同的泥石流事件。刷子分层将通过3D打印一些有代表性的植物性状来模拟[2]，因此(I)消除了等待植物生长的需要，(Ii)实现了可重复的结果。已知泥石流体积的泥石流事件将在水槽上游触发。将监测泥石块在灌木层中的流动特征的任何变化，并将其与没有生物工程缓解的情况和通过刚性挡板缓解的情况进行比较。任何可以提高生物工程技术性能的有利植物性状和植物配置都将被确定。2015年。山坡失稳的生态缓解：研究人员和实践者面临的十个关键问题。植物与土壤，377：1-23。2014年。从单个根-土相互作用到整体边坡行为的有根边坡的地震性能模拟，岩土技术，65(12)：995-1009。

Under the impact of climate change, rainfall-induced debris flow events have been increasingly reported and these have led to significant socio-economic losses. Existing mitigation methods include concrete baffles, but these methods have high embodied CO2 that would further promote climate change. Slope bioengineering such as brush layering [1] is an alternative, "green" and low-carbon technique (Fig. 1). Plant shoot might be used to attenuate the debris impact energy, and subsequently the root pull-out resistance may be mobilised to resist against the drag force induced on the plant. There is, however, no study evaluating such soil-plant-debris interaction and its effect on debris flow mobility. The aim of this PhD project is to investigate the effectiveness of using brush layering to reduce the mobility of a debris flow mass. The objectives of this project are to(i) Determine the drag force exerted on plant shoot during the transport of a debris mass;(ii) Quantify the soil-root mechanical pull-out resistance against the drag force;(iii) Quantify the reduced mobility of a flow mass due to bioengineering mitigation; and(iv) Evaluate the performance of brush layering technique against rigid baffles method;A new large-scale experimental flume will be developed for modelling different debris flow events. Brush layering will be modelled by 3-D printing some representative plant traits [2], hence (i) removing the need to wait for the plant growth and (ii) enabling repeatable results. Debris flow event with a known volume of dry granular soil will be triggered at the upstream of the flume. Any changes of the flow characteristics of a debris mass across the brush layering will be monitored and compared with cases without bioengineering mitigation, and cases that mitigated by rigid baffles. Any favourable plant traits and plant arrangement that could enhance the performance of the bioengineering technique will be identified.References:Stokes, A., et al. 2015. Ecological mitigation of hillslope instability: ten key issues facing researchers and practitioners. Plant and Soil, 377: 1 - 23.Liang, T., et al. 2014. Modelling the seismic performance of rooted slope from individual root-soil interaction to global slope behaviour, Geotechnique, 65(12): 995 - 1009.