Research on the design method for uniform wear of shield cutters in sand-pebble strata

During shield tunneling in highly abrasive formations such as sand–pebble strata,nonuniform wear of shield cutters is inevitable due to the different cutting distances.Frequent downtimes and cutter replacements have become major obstacles to long-distance shield driving in sand–pebble strata.Based on the cutter wear characteristics in sand–pebble strata in Beijing,a design methodology for the cutterhead and cutters was established in this study to achieve uniform wear of all cutters by the principle of frictional wear.The applicability of the design method was verified through three-dimensional simulations using the engineering discrete element method.The results show that uniform wear of all cutters on the cutterhead could be achieved by installing different numbers of cutters on each trajectory radius and designing a curved spoke with a certain arch height according to the shield diameter.Under the uniform wear scheme,the cutter wear coefficient is greatly reduced,and the largest shield driving distance is increased by approximately 47%over the engineering scheme.The research results indicate that the problem of nonuniform cutter wear in shield excavation could be overcome,thereby providing guiding significance for theoretical innovation and construction of long-distance shield excavation in highly abrasive strata.

Wear mechanism and life prediction of the ripper in a 9-m-diameter shield machine tunneling project of the Beijing new airport line in a sand-pebble stratum

Tool wear is a noteworthy problem in the process of shield tunneling,and the degree of wear varies with stratum.The sand-pebble strata in Beijing are typically mechanically unstable.However,many subways are buried wholly or partially in sand-pebble strata.Taking the Beijing New Airport line tunneling project as research background,this study evaluated the wear characteristics of the multiconfiguration rippers of a 9-m-diameter spoke-type shield tunneling machine in a sand-pebble stratum.The wear values of five ripper teeth and ripper flanks were analyzed based on field-measured data from the Beijing New Airport line project.As the analytical results show,the wear value generally increases as the installation radius enlarges with the rise of cutting trace length.The wear of the 190-rippers was divided into five categories:pedestal wear,ripper teeth collapse,uniform wear,ripper teeth falling off and ripper flank wear.Uniform wear of the ripper teeth and ripper flank wear were the two abrasion types of the 190-rippers.The teeth of the 155-rippers mostly maintained their cutting capacity under the protection of the 190-rippers.A wear prediction model of linear fitting field data was developed for a 190-ripper face to obtain the optimum shield driving distance in the sand-pebble stratum.The average wear coefficients of the 190-ripper before and after replacement matched well,being 0.045 and 0.066 mm/km,respectively.The results of this study provide a theoretical reference for tool wear prediction in shield construction under similar geological conditions.