The Mechanism of TBM Cutter Wear in Mixed Ground

Abstract

The TBM cutter wear causes not only low performance of tunneling but also the additional cost of cutter discs and potential safety hazard in construction. Excessive cutter wear and replacement were observed in tunneling with a TBM through sandy cobble stratum in Chengdu metro Line 1. Comparison with other geological layer, the ground has leaded to more cutter wear. Moreover, the form of wear is great varieties which include flat wear, multi-flat wear, eccentric wear and cutter bearing breakage etc. Based on the statistical analysis, general rule can be found that the number of cutter wear or replacement increases along the outer radial direction of the cutterhead. This paper has adopted the engineering analog method and theoretical research to study the mechanism of cutter wear. There are three forces acting on the cutter, namely the normal force, the rolling force and the side force. Thereinto, the high shock the normal force and random side force are primary causes of cutter wear. Putting the engineering geology and field survey into consideration, the immediate causes could be as follows: ①There are more hard cobble stone with high quartz contents in the layer; ②When the cutter traversed from soft soil to hard rock, very high shock loads can be imposed on the cutter assembly; ③The roller cutters sometimes were blocked and resulted in flat wear because of muck cake in the centre part of the chamber. In a word, the main causes of cutter wear are geological condition. By analyzing the TBM performance, the soil conditioning should be highlighted for the pebbles with sand matrix layers. Soil conditioning not only improves the flow of muck, control of earth pressure, face stability, but also reduces cutter, cutterhead and screw conveyor wear. The results are to be applied to a tunneling project where such ground condition was encountered