CAUSE OF SWELLING PHENOMENA IN TUNNELLING AND A PROPOSAL FOR A DESIGN PROCEDURE FOR A SWELLING TUNNEL

概要

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Swelling pressure often experienced in deep tunnels driven through soft mudstone or its fault clay has long been explained to be caused by swelling of clay minerals (such as Montmorillonite) due to their sucking up of water. This is the reason why the swelling test of clay is specified by "Standard design specification for tunnels" published by JSCE (Japan Society of Civil Engineers). Both Case study and experimental and analytical research based on Critical State Soil Mechanics' concept have been undertaken to investigate if this explanation is really correct. Incorporating shear strength parameters in terms of total and effective stress, for short-term and long-term problems respectively, into modified Kastner's classical approach, clear evidence has been given that the predominant cause of large earth pressure and convergence encountered in the so-called swelling tunnels is the plastic flow of the broken material and not the swelling of it, indicating that the competence factor and strength parameters are the decisive factors, the result obtained by swelling test of clay being of no use for designing purpose. Based on the result thus obtained, a smiple design procedure of a circular tunnel driven through mudstone or its fault clay is tentatively proposed.
社団法人地盤工学会の論文
1996-12-15