Some factors affecting deep excavation in clay over gassy bedrock

Abstract

A study of excavations within normally to slightly over consolidated deposits over a gas source is presented with reference to the potential for gas venting from a bedrock aquifer. The effects of key design factors on excavation integrity and potential of inducing hydrofractures are examined. Based on the calculated gas distribution, the study introduces the gassy effect to the deepest 6 m of the clayey layer by: a) increasing pore fluid compressibility, b) reducing Young’s modulus of soil skeleton. The study illustrates the importance of considering hydrofracturing potential and gassy behaviour when assessing the stability of excavations in deposits overlying a gas source.