Abstract
Karst landscape is a general term for earth surfaces and underground patterns that have been formed by the dissolution of soluble rock. Karst landscapes are widely distributed throughout China—particularly in the Guangxi and Guangdong provinces. The main features of karst landscapes are typically reflected in karst caverns, sinkholes, and other geographical phenomena. During tunnel construction in karst areas, various forms of karst caverns may appear on the construction route, and they can cause hazards—such as water inrush and collapse—during tunnel construction. These hazards affect the tunnel construction process. As such, it is necessary to propose a treatment for karst caverns. In this work, a case study of the tunnels on the Hechi‐Baise expressway is presented. A comprehensive pretreatment method suitable for this tunnel is proposed. On the premise of prioritizing the safety and timeline of construction, an optimized treatment scheme for the karst caverns of Hebai tunnel is followed. The optimized treatment scheme primarily includes calculation of safe thickness of tunnel face, strengthening the initial support and increasing the thickness of the second lining, increasing the reserved deformation, and grouting. The proposed scheme achieved favorable results in the treatment of a karst cavern in the Hebai tunnels.
Highlights
Karst landscapes are formed as a result of the dissolution of soluble rock— limestone. ey have a significant degree of unpredictability and heterogeneity, by which various hazards may be caused [1,2,3,4,5,6]
Water inrush, mud inrush, and collapse may occur due to karst caverns [8,9,10,11,12,13]
Safety and mitigation of hazards will be guaranteed during construction. erefore, it is essential to study karst geology and take effective countermeasures to mitigate geohazards during deep excavations in karst regions with caverns [14,15,16]
Summary
Karst landscapes are formed as a result of the dissolution of soluble rock— limestone. ey have a significant degree of unpredictability and heterogeneity, by which various hazards may be caused [1,2,3,4,5,6]. Karst caverns can be discriminated into two types, according to the internal filler content (with or without water), or three types, according to the cavern position (at the tunnel vault, arch waist, or bottom) Besides these characteristics, high permeability, variable shapes, and collapse are features of tunnel caverns in Guangxi Province. The most widely used methods include the clearance-filling and beam-bridge methods, dynamic compaction, jet grouting, and sleevevalve-pipe grouting [3, 4, 21] These methods have defects in construction and cannot be universally applied to tunnel caverns [14]. E objectives of this paper are as follows: (i) to describe the general situation of the tunnels on the Hechi-Baise (Hebai) Expressway in Guangxi Province, as shown, (ii) to discuss potential geohazards and pretreatment techniques for karst caverns during tunnel construction in karst regions, and (iii) to introduce a karst cavern treatment technique for the specific position of the tunnel.
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