Xue Kaixi

The Creep Properties of Fine Sandstone under Uniaxial Tensile Stress

A graduated uniaxial direct tensile creep test for fine sandstone is conducted by adopting a custom-designed direct tensile test device for rock. The experiment shows that the tensile creep of fine sandstone has similar creep curve patterns to those of compression creep, while the ratios of the creep strain to the total strain obtained in the tensile tests are substantially higher than those obtained for similar compression tests, which indicates that the creep ability of rock in the tensile process is higher than that in the uniaxial compression process. Based on the elastic modulus in the approximately linear portion of the obtained isochronous stress-strain curves of the tensile creep, the time dependence of the elasticity modulus for the Kelvin model is evaluated, and a revised generalized Kelvin model is obtained by substitution into the generalized Kelvin model. A new viscousplastic model is proposed to describe the accelerated creep properties, and this model is combined in series with the revised generalized Kelvin model to form a new nonlinear viscoelastic-plastic creep model that can describe the properties of attenuation creep, steady creep, and accelerated creep. Comparison of the test and theoretical curves demonstrates that they are nearly identical, which verifies the performance of the model.

Stability analysis of surrounding rock of unlined highway tunnel in Chongqing

Taking the Daxihe unlined tunnel located at Fuling-to-Pengshui section of 319 federal highway partly in Three Gorges Reservoir Region as project background and choosing its typical sections, numerical analysis for the stability of surrounding rock, based on coupled fluid-solid theorem, was done with Fast Lagrangian Analysis of Continua in three-dimension(FLAC3D). Meanwhile, effects of multiple factors such as unsymmetrical pressure, rock mass weathering degree, change of groundwater tables etc on the stability of surrounding rock were studied when considering fluid-solid coupled effect, resulting in obtainment of principal stresses, placements, plastic zones and pore water pressure distribution of the unlined tunnel under a variety of conditions during its open for trial service. The achieved results are expected to be applied successfully to guidance of the unlined tunnel disease treatment. Furthermore, the study results can also provide a theoretical basis for the disease management of similar tunnels containing water-rich strata.