Study On The Underground Cavern Excavation Mechanics Characteristics And Reasonable Cross-section

During the construction of underground cavern, different construction methods anddifferent construction sequence would cause different displacements and stress results ofthe surrounding rock. And the section of cavern determines how difficult to constructsuch a cavern and also the stability of surrounding rock and supporting structure duringthe construction process: the longer the span is in the cavern section, the greater thedifficulty is in cavern construction and the more complex is to stable surrounding rockand supporting structure. Support lining parameters, section type and constructionprograms are the key and difficult points in a long-span section cavern construction. Inthis paper, based on the cavern tunnel section in Taiping Village Station-Hongqiao stationof the Kunming Rail Transit Line3, combining with the theories of rock mechanics andelastic-plastic mechanics, the paper takes the none-linear factors of rock and soil intoconsideration by introducing elastic-plastic mechanics and D-P yield criterion toestablish the finite element model by ANSYS, in which different classes of surroundingrock, different section forms with different ratio of height to span were simulatedrespectively. The following conclusions have been obtained:â‘ A comparison and selection to lining form of the section (one-center circle,three-center circle and five-center circle) was conducted, and reasonable lining contoursection form was obtained.â‘¡By detailed analysis and comparison of the convergence of the verticaldisplacement, initial lining stress, stress distribution of surrounding rock and the initiallining eccentricity, reasonable high span ratio of the cavern section was obtained underdifferent classes of surrounding rock.â‘¢By calculating and analyzing the standard section forms of two-lane tunnel, theresistance zone in the lining structure was obtained.â‘£The construction process of the benching tunneling method was simulated bynumerical modeling. By analysis and comparison of the vertical displacement of thecaverns under construction, the convergence value of the horizontal displacement afterexcavation, the initial lining stress, the rock stress distributions, the change rules of thevertical displacement, convergence value of horizontal displacement, the initial liningstress and the stress distribution in rock were obtained during the construction process of the benching tunneling method. Then by analysis and comparison with the on-sitemonitoring data, it was found that the deformation of surrounding rock in the actualopening excavation process was consistent with the results by simulation, whichindicates that finite element method can be used for effective simulation of tunnelconstruction.