Chunsheng Zhang

Laboratory tests and numerical simulations of brittle marble and squeezing schist at Jinping II hydropower station, China

Four 16.7 km-long tunnels with diameters ranging from 12.4 to 14.6 m are now under construction at Jinping II hydropower station along the Yalong River. The tunnels pass through Triassic rocks below Jinping Mountain. The tunnels are characterized with high overburden, long alignment and complex geological conditions. Brittle failure in marble and squeezing in schist are the primary problems in tunnelling. This paper introduces the studies of laboratory tests on Jinping II marble as well as numerical prediction of excavation damaged zone (EDZ) of tunnel section in brittle marble and determination of reinforced concrete lining thickness for restraining time-dependent deformation in the schist tunnel section. Laboratory tests indicate that Jinping II marble presents a complex brittle-ductile-plastic transition behavior of post-peak response with increasing confining pressure. Such behavior can be described numerically with the Hoek-Brown model. The EDZ was calibrated and predicted using both fast Lagrangian analysis of continua (FLAC) and particle flow code (PFC). The predicted result of EDZ in sections with different qualities of rock mass under various overburden pressures is quite helpful in understanding EDZ characterization and support design. A power-law creep model was used to support the lining design, especially in determining the lining thickness. Field convergence measurement data over 19 months were used to calibrate the creep model properties, followed by a sensibility analysis of reinforced concrete lining thickness that was launched to present the maximum lining compressive stress.

Time-Dependent Failure of Marble Under Long-Term Loading

Observations of marble brittle failure at the laboratory scale indicates that the failure process involves the initiation, growth and accumulation of micro-cracks. With the micro-cracks increasing, marble subjected to long-term loading will be damaged. The rate of cracking is sensitive to the magnitude of long-term loading. The static-failure tests were conducted and the test results indicate that the time-dependent is being. Process simulation tests have been conducted to investigate the time-dependent failure in JPII marble. The static-failure data were used to match the parallel-bonded stress corrosion (PSC) model parameters which based on PFC2D (Particle Flow Code in 2 Dimension). The time-dependent failure was simulated. The response was characterized by a creep curve. The damage mechanisms and deformation behavior of marble were discussed. The model exhibits damage mechanisms and deformation behavior that are similar to those of the rock.