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，这些事件造成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，将进一步促进气候变化。坡面生物工程，如刷层[1]，是另一种“绿色”低碳技术（图1）。植物的茎部可以用来减弱碎片的冲击能量，随后可以调动根部的拔出阻力来抵抗对植物产生的阻力。然而，目前还没有研究评估土壤-植物-碎屑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研究使用刷状分层来降低泥石流块体流动性的有效性。本项目的目标是：(i)确定在碎片团块运输过程中对植物茎部施加的阻力；（ii）量化土根对阻力的机械拔出阻力；㈢量化因生物工程缓解而降低的流动质量的流动性；（iv）对比刚性挡板法，评价刷层技术的性能；将开发一种新的大型试验水槽，用于模拟不同的泥石流事件。刷层将通过3d打印一些具有代表性的植物特征[2]来建模，因此(i)不再需要等待植物生长，（ii）实现可重复的结果。在水槽上游将触发已知体积的干粒状土泥石流事件。将监测穿过灌木层的碎屑体流动特性的任何变化，并与未采用生物工程缓解措施的情况和采用刚性挡板缓解措施的情况进行比较。将确定任何有利于提高生物工程技术性能的植物性状和植物安排。参考文献：Stokes， A.等。2015。斜坡不稳定性的生态缓解：研究人员和实践者面临的十个关键问题。植物与土壤，2011,31(1):1 - 23。梁涛等。2014。从根-土相互作用到整体边坡行为的根状边坡地震性能建模，岩土工程，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.