Abstract
Abstract. A debris-flow catastrophe hit the city of Zhouqu, Gansu Province, western China, at midnight on 7 August 2010 following a local extreme rainfall of 77.3 mm h−1 in the Sanyanyu and Luojiayu ravines, which are located to the north of the urban area. Eight buildings damaged in the event were investigated in detail to study the characteristics and patterns of damage to buildings by debris flows. It was found that major structural damage was caused by the frontal impact of proximal debris flows, while non-structural damage was caused by lateral accumulation and abrasion of sediment. The impact had a boundary decreasing effect when debris flows encountered a series of obstacles, and the inter-positioning of buildings produced so-called back shielding effects on the damage. Impact, accumulation, and abrasion were the three main patterns of damage to buildings in this event. The damage scale depended not only on the flow properties, such as density, velocity, and depth, but also on the structural strength of buildings, material, orientation, and geometry. Reinforced concrete-framed structures can effectively resist a much higher debris-flow impact than brick-concrete structures. With respect to the two typical types of structure, a classification scheme to assess building damage is proposed by referring to the Chinese Classification System of Earthquake Damage to Buildings. Furthermore, three damage scales (major structural, minor structural, and non-structural damage) are defined by critical values of impact pressure. Finally, five countermeasures for effectively mitigating the damage are proposed according to the on-site investigation.
Highlights
Human lives and constructions in debris-flow prone mountain areas are regularly subject to debris-flow hazards
The most severe damage occurred to buildings that were located around the main streamline and impacted by proximal debris flows in which most of the mass and energy was concentrated (Fig. 3)
According to previous classifications (Toyos et al, 2003; Zanchetta et al, 2004; Jakob et al, 2011), the five classes were reduced to three damage scales that can be roughly quantified by the results of Zanchetta et al (2004) and Wei et al (2006)
Summary
Human lives and constructions in debris-flow prone mountain areas are regularly subject to debris-flow hazards. A large-scale debris flow occurred at Liziyida Ravine, a tributary of the Dadu River in Sichuan Province, China, on 9 July 1981 and destroyed a railway bridge, leading to the overturning of a moving train and 275 deaths (Wu et al, 1993) Another wellknown tragedy was in the Vargas State of Venezuela in December 1999 (Wei et al, 2000; Wieczorek et al, 2001). Jakob et al (2012) defined four damage classes, from minor sedimentation to complete building destruction, and related them with an intensity index represented by the impact force of debris flows These empirical relationships can be applied in practice to some extent, most of the previous studies have focused on empirical relationships between the hazard magnitude and the respective degree of loss that was caused by recent events. A classification scheme for assessing building damage is proposed with respect to brick-concrete and reinforced concrete structural buildings, which are the most common structures in the mountain areas of China
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