SONG Zhang, JIANG Liangwen, XU Sheng, HU Qingbo, ZHANG Guangze, REN Jinlong
Journal of Railway Engineering Society. 2026, 43(6): 65-71.
Research purposes: The disease phenomena in the LSS Tunnel on the Nanning-Kunming Passenger Railway initially manifested as invert bulging, gradually developing into invert arch and filling layer cracking, concrete corrosion with sanding and siltation, as well as cracking and spalling of the parallel heading sidewalls. As time progresses, the lengths of the bottom bulges in each section tend to extend toward both ends, and the degree of concrete corrosion gradually becomes more severe, affecting railway operational safety.To investigate the causes of the hazards, the degree of the concrete corrosion, and its development trends, successive geological drilling, well television, geophysical surveys, in-situ stress testing, experiments, and specialized studies were employed. Through a method of elimination, it was determined that the primary controlling factors of the hazards were small deformations induced by high in-situ stress and concrete corrosion caused by sulfates.
Research conclusions: (1) The hazards in Sections 1-3 are primarily caused by the upward extrusion effect of gently dipping strata at tunnel invert under high geostress environments, and secondarily by the invert arching due to high groundwater levels and dynamic train loads, as well as by construction-related structural defects such as insufficient thickness and inadequate curvature of invert arch that failed to effectively resist and suppress initial structural deformation. (2) The hazards in Sections 4-11: During the initial phase (2017-2019), the primary cause is the upward extrusion effect of the fragmented rock mass at the tunnel bottom under high-stress environment, combined with local construction defects in the tunnel bottom structure failing to effectively resist and suppress initial deformation, resulting in micro-level deterioration of the tunnel bottom structure. Secondary factors include sulfate (SO42-) erosion from groundwater and expansion reactions from concrete containing gypsum aggregate upon water exposure, leading to concrete expansion-induced bulging and reduced strength. During the post-construction phase (2020-present), the primary cause of deformation is the continuous corrosion of concrete,producing large amounts of sulfate corrosion products such as gypsum, ettringite, and monosulfate, leading to concrete volume expansion and bulging. The presence of gypsum and anhydrite in concrete aggregates accelerate the corrosion rate and severity. Secondary causes include construction defects in tunnel base structures, reduced early-age concrete strength, and the upward extrusion effect of fractured rock mass under high geostress, all of which exacerbate deformation development. (3) Based on the causes of the diseases and the degree of concrete corrosion, it is recommended to consider engineering measures such as water drainage at the tunnel bottom, corrosion protection for concrete, and reconstruction of the invert arch. (4) The research methods and findings provide valuable references for the investigation and prevention and control of engineering hazards under similar geological conditions.
Just Accepted