STUDY ON THE EFFECTS OF COMBINED SUPPORTS OF SEGMENTAL LININGS AND COMPRESSIBLE LAYERS IN DEEP-BURIED COMPOSITE GROUND

The surrounding rock pressure of deep buried shield tunnels is mainly the deformation pressure produced by large extrusion type deformation of the surrounding rock. Its main feature is that the deformation lasts for a long time with repeatability. The pressure of the surrounding rock will keep increasing after the support is completed. Because it is unfeasible to restrain the deformation of surrounding rock by increasing the support rigidity, yieldable supports become a solution for the problem. Meanwhile, due to the complexity and variability of the surrounding rock condition and the rock mass structure, it is inevitable to pass through composite strata in shield tunnel construction. Based on the inclined shafts in two deep buried shield coal mines, comparison and analysis on the mechanical properties of segment linings with the segment lining + compressible layer combined supports in different composite stratum conditions are studied by means of similarity model tests and the finite element numerical method. The results indicate that the finite element method results are in good agreement with the experimental results when the model is correctly established and the parameter values are reasonable. Under the uniform formation condition, the compressible layer brings about 12.5%~19.9% decrease to the maximum bending moment and 14.2% decrease to the maximum axial force. The composite stratum causes obvious changes in the value and distribution of the segment bending moment, but has little effect on the segmental axial force, indicating that the bending moment is more sensitive to the resistance of the composite stratum while the axial force is relatively insensitive. With the compressible layer, the distribution of the segment internal force is more uniform in the composite stratum and there is little change in the axial force. Furthermore, the relative thickness of the composite stratum influences the maximum positive bending moment stably. It also greatly influences the maximum negative bending moment, causing deviation to the relative soft side of its generating position. The larger the relative thickness of the composite stratrum, the more obvious is the deviation. In an upper hard and lower soft composite stratum, the segment bending moment is more easily affected by the relative stiffness of the stratum.