Bio-engineering Mitigation Debris of Flow

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.