On July 29th 2006 at 1.30 A.M,an overall slope failure took place at eastern wall of a 28 m-depthmetro station shaft in Esfahan,Iran. The failure caused some serious damage to the city utilities and loss of oneman life. The instability occurrence was about 10 month after the shaft completion,where,the shaft walls hadbeen supported by a regular grid of grouted dowels,steel mash and shotcrete.According to the geotechnical investigation results carded out after the failure,the main cause of the rock massinstability at the shaft wall was a major shear joint existence in the rock mass,trending almost parallel to the slopeface and dipping towards the shaft bottom with about 60 degrees angle. This structural feature was unrecognizedbefore the failure incidence.In this paper,by describing the induced failure mechanism,the dominant role of the existing natural plan ofweakness on the rock instability is analyzed and the unsuccessful effect of the used rock supporting system isdiscussed. It has been concluded in this paper that the possibility of the structurally-controlled rock failuresshould be taken into account seriously in design and execution of any earth structures,especially in urban areas.
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