Report No. : GEO Report No. 370

Report Title : Review of Rockfall Incidents Occurring under Dry Weather (2024), 36 p.

Author : R.C.T. Wai, K.S.P Lam & R.W.H. Lee

Abstract

In Hong Kong, on average about 300 landslides are reported to the Government every year, among which rockfall incidents constituted about one-tenth of the reported landslides. The majority of rockfall incidents, similar to other types of landslides, are rain-induced. Meanwhile, rockfalls have from time to time occurred under dry weather with little tell-tale sign. Aggravated by the dense urban settings in Hong Kong, some of these incidents resulted in serious/significant consequence or rendered 'near-miss' events with the potentially severe consequence narrowly avoided. Along with the generally low alertness or perception to landslide risk by the public under dry weather, the respective risk of rockfalls should not be overlooked. An improved understanding on this type of event would therefore be useful for examination of the adequacy of the relevant slope engineering practice.

This report presents the findings of a review of the rockfall incidents occurring under dry weather between 2001 and 2020 to provide insights on their characteristics, in particular the probable triggers, causes and modes of failure when under dry weather. The notable incidents in recent years are presented to shed light on the lessons learnt. It is noteworthy that while the rockfalls are generally local and not sizeable, they could also be consequential. The adverse consequence of rockfall events could have been minimised should there be proper provisions to mitigate the risk concerned. The review findings reiterate the importance to have proper provisions to mitigate the landslide risk associated with rockfall events as a good practice in slope safety management.

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