The stability of underground excavations is influenced by discontinuities interspaced in surrounding rock masses as well as the stress condition. In this work, a numerical study was undertaken on the failure behavior around a circular opening in a rock mass having non-persistent open joints using PFC software package. A parallel-bond stress corrosion(PSC) approach was incorporated to drive the failure of rock mass around the circular opening, such that the whole progressive failure process after excavation was reproduced. Based on the determined micro parameters for intact material and joint segments, the failure process around the circular opening agrees very well with that obtained through laboratory experiment. A subsequent parametric study was then carried out to look into the influence of lateral pressure coefficient, joint dip angle and joint persistency on the failure pattern and crack evolution of the rock mass around the circular opening. Three failure patterns identified are step path failure, planar failure and rotation failure depending on the lateral pressure coefficient. Moreover, the increment of joint dip angle and joint persistency aggravates the rock mass failure around the opening. This study offers guideline on stability estimation of underground excavations.
One of the major challenges during subsea tunnel construction is to seal the potential water inflow.The paper presents a case study of Xiang'an subsea tunnel in Xiamen,the first subsea tunnel in China.During its construction,different grades of weathered geomaterials were encountered,which was the challenging issue for this project.To deal with these unfavorable geological conditions,grouting was adopted as an important measure for ground treatment.The grouting mechanism is first illustrated by introducing a typical grouting process.Then the site-specific grouting techniques employed in the Xiang'an subsea tunnel are elaborated.By using this ground reinforcement technique,the tunneling safety of the Xiang'an subsea tunnel was guaranteed.
