ENGINEERING GEOLOGICAL PROBLEMS OF DEFORMATION AND DESTABILIZATION OF SURROUNDING ROCKS IN RAILWAY TUNNEL CONSTRUCTION

In recent years, Chinese railway construction technology has improved significantly. Number and length of tunnel engineering increase considerably and the engineering geological conditions are more complicated. Along with the significant technical progress, some major design changes and injuries also occurred in the construction process. During technology survey, the authors started with analyzing regional engineering geological conditions. Based on studying the usual geological factors, such as fracture structure, fold structure, rock strength, rock mass integrity, karst and special soil, apply petrology, mineralogy, structural geology and rock structural mechanics, etc. to deepen understanding some special engineering geological factors. Authors confirm that high in-situ stress squeezing action, extremely soft rock extruding and unloading effect, ancient metamorphic soft interlayer sliding action, dike (wall) body softening and bedding shearing deformation are the main geological factors to cause surrounding rock instability and collapse during tunnel construction. Due to understanding insufficiently and lack of the corresponding engineering measures before, it caused significant adverse impact to construction, investment and time limit for a project. Combing with 11 engineering examples, the paper analyses five types of surrounding rock deformation characteristics and causes and put forwards engineering countermeasures. Expect to draw lessons and reduce similar problems.