AbstractThis study aimed to solve the problem of setting and optimizing the driving parameters for shield tunneling in sand–clay composite strata. First, the strata composite ratio parameter (ξ) and the unit thrust (F¯) and unit torque (T¯) of the shield machine driving parameters were defined. The quantitative correlations of F¯ and T¯ with varying ξ were obtained. The results can help set the driving parameters of the shield machine. Second, the data point distribution space of F¯−T¯ was established and analyzed by mathematical statistics. The distribution area of the data recorded was classified as an abnormal Zone II when the cutterhead of the shield machine is obstructed by mud cakes, ground settlement occurs, and so on. The distribution area of the data recorded was classified as abnormal Zone III when the cutterhead of the shield machine encounters boulders, excessive jacking force leads to ground uplift, and so on. The remaining area was defined as normal Zone I. The developed zoning criterion can make a quality assessment for the shield driving status. Finally, the clustering theory was used to divide Zone I into six subregions. A composite strata identification method for shield tunneling was established. Combined with the research results, a systematic evaluation method of shield machine driving state was summarized. Through field verification, the evaluation method has guidance for the setting of shield machine driving parameters and the evaluation of driving state.

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