Ground reaction curves for circular excavations in non-homogeneous,axisymmetric strain-softening rock masses

Fast methods to solve the unloading problem of a cylindrical cavity or tunnel excavated in elasto-perfectly plastic, elasto-brittle or strain-softening materials under a hydrostatic stress feld can be derived based on the self-similarity of the solution. As a consequence, they only apply when the rock mass is homogeneous and so exclude many cases of practical interest. We describe a robust and fast numerical technique that solves the tunnel unloading problem and estimates the ground reaction curve for a cylindrical cavity excavated in a rock mass with properties depending on the radial coordinate, where the solution is no longer self-similar. The solution is based on a continuation-like approach(associated with the unloading and with the incremental formulation of the elasto-plastic behavior), fnite element spatial discretization and a combination of explicit sub-stepping schemes and implicit techniques to integrate the constitutive law, so as to tackle the diffculties associated with both strong strain-softening and elasto-brittle behaviors. The developed algorithm is used for two practical ground reaction curve computation applications. The frst application refers to a tunnel surrounded by an aureole of material damaged by blasting and the second to a tunnel surrounded by a ring-like zone of reinforced(rock-bolted) material.

Analysis on the Cause and Forecast Deviation of an Extreme Rainstorm in Changsha Urban Area

Using NCEP reanalysis data,high-altitude and ground observation data,numerical model data,satellite and radar data,formation cause and forecast deviation of an extreme rainstorm process in Changsha urban area at night on June 9,2020 were analyzed.The results showed that(1)the extreme rainstorm process developed near the surface convergence line,with strong localization,short duration and large hourly rainfall intensity.(2)Under the high temperature and high humidity environment,the low-level cold advection and the hot low-pressure system interacted,and the potential con-vective unstable energy was released,and a strong convective weather was formed.(3)The convergence of water vapor in the lower layer and the strong upward movement provided sufficient water vapor for the rainstorm.The low-centroid thunderstorm was the main reason for the extreme rainstorm.(4)The forecast deviation of the numerical model to the low-level shear line and the mesoscale convergence line was an important reason for the forecast deviation of the heavy rainfall area.

Study on Mesoscale Circulation Characteristics of Heavy Rainstorm in Wangmo County in Qianxinan on June 6,2011

[Objective] The aim was to analyze the causes of '6.06' heavy rainstorm in Wangmo County in Qianxinan.[Method] By dint of NCEP/NCAR 1°×1° reanalysis data,FY-2E TBB data,seven ground elements and two elements from automatic station data,the main influential system and all kinds of physical quantity field features of heavy rainstorm in upper reaches of Wangmo County in Qianxinan from the evening on 5 June to 08:00 on 6 June in 2011 were studied.[Result] The rainstorm was the result of cold air,which was provided by 850 hPa cold shear line and ground radiation line,and warm and wet airstream on the northwest edge of subtropical high.MCS was the main reason for such heavy rainstorm.Southwest warm and wet airstream in middle lower part provided sufficient water vapor for the rainstorm.The 850 hPa water vapor flux divergence center moved from north to south along ground convergence line to Qianxinan.Rainfall location and water vapor flux as well as convergence center were corresponding.The rainfall intensity also was consistent with the amount of water vapor flux and water vapor convergence.[Conclusion] The study provided reference for the report of heavy rainstorm.