Stability analysis of Cavern No. 5 with the largest span in Heidong large ancient underground quarry

Abstract

The Heidong Cavern Group of China includes 21 large-scale caverns that have remained stable for 1400 years. Cavern No. 5 of the Heidong Cavern Group is characterized by an unsupported span of up to 92 m, which is considered to be the largest span in a single underground artificial rock cavern. Cavern No. 5 may have gone through a period during which it was the only cavern and a period during which it had adjacent caverns; recent investigations have proved that Cavern No. 5 is suffering from considerably serious partial damage. The factors affecting the stability of Cavern No. 5, including waste rock accumulations, rock mass structures, surrounding rock quality, and cavern structures, were analyzed to prevent further damage and analyze the influence of the existence of adjacent caverns on the stability of Cavern No. 5. The numerical analysis software MIDAS GTS (Geotechnical and tunnel analysis system) was used to simulate and compare the stability of Cavern No. 5 under the single-cavern and adjacent-cavern cases. Research proves that when this cavern is independently considered and the remaining caverns are excluded, the arched roof structure is considerably favorable to ensure the cavern’s stability and the horizontal compressive stress of the roof becomes approximately equivalent to the vertical tensile stress. The horizontal forces generated by the cavern’s inclined roof contribute to the cavern’s stability. The horizontal compressive stress area of the roof and the effect of the arched structure decrease when adjacent caverns are present, causing the roof to become prone to tensile failure. These results provide a reference for modern underground engineering construction and a theoretical basis for long-term protection of the large and ancient Heidong Caverns.