关键词: 岩溶塌陷, 隐伏可溶岩, 溶洞和土洞, 触发因素, 夏茅村, 广州

Abstract:

Sinkholes are common geohazards in karst areas and often cause life and economic losses. Karst collapses are random, fuzzy, sudden, and concealed owing to the randomness of karst cave and karst channel development. On December 19, 2008, five karst collapses and one land subsidence occurred in Xiamao village. The center of this karst collapse is the Northwest street of Xiamao village and Huafu street of Shayuanfang, Baiyun District, Guangzhou (23°13′40″ N, 113°14′47″ E). Karst collapses cause wall cracking, building inclination, and subsidence of ground foundation, with a depth of 2-4 m. In August 2015, a karst collapse was induced by drilling of a bored pile at a residential building construction site. Sinkhole hazards in Xiamao village have greatly affected the safety and life of residents. To prevent karst collapses, it is important to investigate the formation mechanism of the sinkholes. Based on the geological exploration of the aforementioned karst collapse in Xiamao village, Guangzhou, we discuss the local geological environment conditions and characteristics of karst development, and causes of karst collapse. The results show that the soluble rocks in and around Xiamao village are Carboniferous Hutian Formation limestone (C₂ht) and Permian Qixia Formation marl and carbonaceous marl (P₂q), hence the frequent karst collapses in the area. The Quaternary overburden in the area is thick and unevenly distributed, with several soil caves at the bottom, and the concealed soluble rock has high water content and is rich in karst caves, providing a good geological environment background for karst collapse. Furthermore, there is a close hydraulic connection between the pore water in the overburden soil and the water in the underlying limestone fractured caves. The change of the groundwater level in the water-bearing sand layer directly causes the water level of the underlying limestone fractured cave water to fluctuate, thus enabling the hydrodynamic factors of karst collapse. During the construction of the aforementioned bored pile, the borehole penetrated the soil cover on the top of the soil cave in the overburden, causing the fine sand and silt on the upper part of the cover to flow into the soil cave, triggering karst collapse. Therefore, establishing a long-term monitoring network of groundwater dynamics in karst distribution areas and grouting the karst-collapsed areas are effective ways for remediation of karst collapse in Xiamao village. Additionally, we can provide technical support to the local government in implementing karst collapse prevention measures in urban planning and construction.

Key words: Karst collapse, Hidden soluble rock, Karst caves and soil caves, triggering factor, Xiamao Village, Guangzhou