Engineering Geological and Geotechnical Challenges of Lin Ma Hang Mine Revitalization – A Unique Community-based Educational Mining Heritage Project

Abstract

The revitalization of the 19th-century Lin Ma Hang Lead Mine cavern and surrounds provides a unique demonstration of innovative geotechnical investigation and design for conservation and educational purposes in country park. The restoration of the cavern complex and nearby area aimed to improve the safety of the old heritage mining complex for the public, whilst enhancing the recreational value of the newly designated Robin's Nest Country Park. The project is a unique example of historical and scientific preservation and safety-based enhancement for the public and community. From the outset, assessment of the engineering geological and geotechnical conditions of the natural terrain, drainage, anthropogenic influences and the rock mass related to the ore body were key for prioritizing the geotechnical works. Insights gained from the challenges encountered during the background study, investigations, design and construction phases will contribute valuable experience for future projects with similar sensitivity in Hong Kong and elsewhere. The design balanced safety and stakeholder issues with the goal of promoting the outstanding mining heritage and associated scientific value as a unique user-based educational facility showcasing the splendour of the remote environment, the outstanding mine geology and geomorphological setting within a palimpsestic framework of old anthropogenic activity ranging from several phases of mine activity, war intervention, and cycles of land management over many centuries. Technical challenges included: (1) methodology for assessment with limited access to the rock face; and (2) balancing robust geotechnical works with resultant visual impact. The NGI Q-system was utilized for rock stabilization along with analytical design through kinematic analysis. Enhanced access afforded by the construction stage refined geotechnical works for rock pillars and blocks formed as part of the historical and geological context of the mine, potentially blast-induced open apertures, a fault zone, and a galena vein found in association with highly decomposed materials. Construction challenges were numerous due to the remoteness of the site. Advanced techniques such as 3D point cloud model from laser scanning of the cavern complex helped develop an authentic record of the mining heritage in parallel with the works. Comprehensive planning was important to ensure timely project delivery with helicopter-lifts as the major means of material and machinery delivery. To ensure safety during drilling works, tensioned safety nets were used to protect workers from potential rock fall. Grouting the mostly vertical rock dowels in highly jointed / fractured rock required a multi-stage approach with control of grout viscosity. Coring was utilised to reduce vibration and noise impacts to minimize disturbance to the Site of Special Scientific Interest (SSSI) bat roosts nearby. Artificial rock cladding was employed for pillar buttresses and waste rock features, together with heritage-style brown finishes for dowel heads and wire meshes. All essential elements in helping establish a balance between making “safe for purpose” without compromising the integrity of the heritage and scientific character of the site. From an industrial mining perspective, the finished cavern works resemble features commonly associated with active mine environments and some original rusted steel structures.