The Study Of Slate Tunnel Surrounding Rocks’deformation And Damage Mechanism And Stability Controlling Method

The safety and economy of tunnel construction have always been the two most concerned problems, of which the safety depends on the stability of tunnel surrounding rock and supporting structure when they are under construction and function, while the economy concerns the reduction of construction investment on the premise of safety guaranteed. To achieve those needs a thorough recognition of features of surrounding rock in the process of tunnel design and construction and selection of reasonable supporting parameters and constructive methods. The Guiguang railroad slate tunnels on which this paper relied are double-track railway tunnels, the particular stratified feature of slate may cause many construction issues such as the surrounding rock spalling, overbreak, even collapse, among which the problem of spalling affects safety, the overbreak affects the economy, and the collapse may seriously influence both safety and the economy. This paper takes the safety and economy of Guiguang railroad slate tunnel construction as a starting point, studies in detail the engineering properties of slate so as to probe mechanism of several engineering problems during construction, and thus the support parameters and construction methods can be further optimized detailedly. The research findings are as followes:(1) Through the investigation of the slate tunnels, this paper summarizes the factors causing common problems in the process of construction, such as large deformation、 spallings and tunnel collapses, and overbreaks. According to the investigation and study of Guiguang railroad slate tunnels, the collapses of slate tunnel are categorized into three types of buckling failure of strata、strata slide and instability of broken slate; the spallings are categorized into large-rock spalling, step-shaped spalling and peel-off spalling; the overbreaks are divided into step-shaped over-break, jagged over-break and fracture-leading over-break, and this paper also makes a detailed count on the situations under which kinds of construction problems occur.(2) To sum up the affecting factors of slate stability on the basis of the collection of factors that cause slate tunnel’s common engineering issues. To conduct sub-level classification of slate stability through rock’s laboratory experiment and the experiment of water-weakened degree of cement, and etc.(3) To deeply study the mechanism of collapses of buckling failure of Strata, strata slide and instability of broken slate on the basis of theoretical analysis. Analyze quantitatively or qualitatively the instability conditions of some slate tunnel collapses. Analyze the damaging mechanism of stratified rock by the elastic foundation beam theory; which provides the theoretical explanation for the damage and instability of medium thickness slate, step-shaped spalling, and Peel-off spalling.(4) Plenty of spot experiments have been conducted during tunnels construction concerning issues of surrounding rock stability control, and the calculation method of surrounding rock pressure suitable for slate tunnel is drawn through surrounding rock pressure experiments of kinds of surrounding rocks, and the distribution patterns of horizontal and vertical surrounding rocks pressure are analyzed. The paper studies the effect of anchor in the slate tunnels’ support through a combination of spot experiment and numerical simulation, the result shows that the anchor vertical to the slate bedding plane plays most important role, while the rest of anchor’s effect are not so obvious. The paper studies the role and effect of steel frame through a combination of spot experiments and convergence-confinement method, which puts an emphasis on the comparison of applicability between section steel frame and grid steel frame, the result shows that though section steel frame has larger safety stock, the grid steel frame has better mechanical properties and economic efficiency, and finally obtains the steel frame supporting form and parameters suitable for all levels of slate.(5) This paper summarizes the reasonable blasting schemes and auxiliary construction approaches for controlling slate tunnels’ overbreak through theoretical calculation and several spot experiments, studies the controlling methods of slate tunnel collapses by numerical analysis and theoretical analysis, and proposes specific excavation processing to address the issues of three types of collapses, which proves that it should take " reducing excavation span, short footage、advance reinforcement by small-diameter pipes " as a chief principle regarding to collapse of buckling failure of Strata and Instability of Broken slate; and as to collapse of Strata Slide, the chief principle should be controlling tunnel face.Reasonable supporting parameters and constructing methods for slate tunnels are finally drawn from the summarization and analyses of slate tunnels’ engineering problems, which guarantees the safety and the economy of the Guiguang railroad slate tunnels’ construction.