Abstract
Debris flow gullies have high potential energy and geomorphic characteristics including a steep longitudinal slope and abundant loose material sources. They often experience debris flow with a strong impact force and a large instantaneous flow. Drainage engineering measures are most commonly used for mitigation in these gullies. However, the abrasion of drainage channels with large gradients (DCLG) is complex and strong because of the high-speed flushing of debris. In this study, the abrasion behavior of debris flow in DCLG is analyzed based on the kinematic characteristics and the theory of composite abrasive wear. Energy dissipation and anti-wear measures are suggested, and their effects are summarized with reference to a case study and in situ observation. The results show that there are four main types of wear morphology in drainage channels. The abrasion system of drainage channels shows the characteristics of system dependency, time dependency and multidisciplinary coupling. Energy dissipation and anti-wear measures include prefabricated reinforced concrete boxes as substrate, transverse roughening belts, adding a wear-resistant admixture, etc. The flow velocity of the debris flow is reduced by 5.7–37.1% after passing through the energy dissipation section. The distribution of abrasion and the mud depth show that the variation trend of the flow velocity in the channel is ”acceleration → deceleration → reacceleration“. According to tracking observations during two flood seasons, the energy dissipation and anti-wear measures are the most effective.
Highlights
Debris flow gullies in earthquake-affected areas and mountain areas vary, with differences in the micro-geomorphic conditions, loose material conditions and hydrological conditions [1]
According to relevant research [3], there was a considerable amount of debris flow in the area affected by the Wenchuan MS 8.0 earthquake which occurred on 12 May 2008, which was observed in a large gradient gully with a watershed area of F ≤ 5 km2, a gully bed with an average longitudinal slope of I ≥ 300% and a basin integrity coefficient of δ ≤ 0.4
Typical cases are the mass debris flows which occurred on 13 August 2010 in Northwest Sichuan, China [5], the mass debris flows which occurred on 17 August 2012 in Mianzhu City, and the debris flows which occurred on 20 August 2019 in Wenchuan County, resulting in greater damage, loss and environmental impacts than those which occurred before the earthquake [6]
Summary
Debris flow gullies in earthquake-affected areas and mountain areas vary, with differences in the micro-geomorphic conditions, loose material conditions and hydrological conditions [1]. In terms of the mitigation strategies for debris flows with a high potential energy, the engineering measures are different from those of common debris flows [7]. The need to effectively reduce the abrasion damage of the debris flow to the bottom plate and side wall of the drainage channel and to ensure the set service life of the drainage channel are important issues in the design of drainage channels with large gradients (DCLG) [3,9]. The influencing factors of debris flow abrasion capacity, the composition of the abrasion system and features of abrasion morphology, the regulating effects of energy dissipation and anti-wear measures of the drainage channel and the design and construction methods should be included so as to expand the applicable range of the use of drainage channels as a mitigation measure and improve the service life and operational uses of drainage channels
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