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Abstract The tunnel boring machine(TBM) performance is influenced by the joint spacing in a large extent. TBM penetration rate increases with decreasing joint spacing. But，too small joint spacing makes the tunnel face in stable that is not favorable to TBM excavation. The rock masses along the headrace tunnel of Jinping II hydropower station are composed of marble with different thicknesses of the layers. The thickness varies largely along the tunnel alignment from several centimeters to several meters. The layer surface is the main non-continuous face in these rock masses and the intersection angle between the tunnel axis and the layer is from 60°to 80°. The rock breakage process in the tunnel is influenced by the high in-situ stress and the layer thickness. TBM performance is analyzed in thin layer，thin to middle layers and thick layer marble rock masses under the high in-situ stress from the point view of rock breakage mechanism by TBM，respectively. The influence of the layer thickness on TBM penetration is studied.
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Received: 08 January 2010
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