Study On Mechanism And Evaluation Method Of Shield Tool Wear In Beijing Waterless Sand-pebble Stratum

The sandy-pebble stratum with high gravel content,large particle size,poor grain distribution,high intensity and loose soil structure has high soil abrasivity.It is hard to tunnel a long distance because of severe cutting tool wear in earth pressure balance shield tunnelling.Cutting tool wear is a complex and interdisciplinary subject.It is of great significance to study on tool wear mechanism of sand-pebble soil for guiding the scientific construction of shield in sand-pebble stratum,extending the healthy service life of shield tunneling tools,and realizing the long-distance shield tunneling.In this paper,a lot of research work has been carried out through theoretical analysis,laboratory test and field investigation.The main research contents and findings are as follows:(1)The characteristics of Beijing’s waterless sand-pebble stratum,shield propulsion mode and cutterhead as well as cutters configuration,tool working mechanism and failure mode are analyzed.The results show that spoke type cutterhhead and cutting tool is the main combination form in sand-pebble stratum.Flake type cutting is the main cutting type in sand-pebble stratum.Abrasive wear and adhesive wear are the main abrasion mechanism of shield cutters.The tool wear mechanism caused by different size particles in sand-pebble stratum and the influence of various factors of tool wear were analyzed.(2)On the basis of analysis of sand-pebble fabric and dynamic tunneling characteristics of shield,a tool wear testing device which can be used for cutting tool wear test in sand-pebble soil with large displacement movement under the action of gravity is developed.Based on this device,the abrasion characteristics of sand-gravel mixetures and the law of tool wear were studied,the influence mechanism of sandgravel mixtures soil on tool wear was revealed from the perspectives of wear amount,surface wear form,particle breakage and action strength between soil particles and test cubes.Meanwhile,the effects of soil moisture environment,tool material and wear time on shield tool wear were also studied.(3)Soil conditioning could improve sandy pebble soil liquidity and reduce tool wear,the solid-liquid two-phase mud and gas-liquid two phase foam modifier were studied,the results shown that bubbles can reduce the impact wear and adhesive wear at the same time,however,mud can reduce impact wear while enhance the adhesion wear.It is better to mianly use foam agent in sand-pebble stratum and the mud could as a supplement modifier.Meanwhile,the influence of tool orientation and radius on tool wear were also studied.(4)For the parallel double shield construction situation,the abnormal wear could be quantitatively assessed.The service health evaluation method was put forward in consideration of different cutter types,the health service coefficient calculation process was put forward and it was applied to Beijing’s new airport line and the result is available.Meanwhile,the working mode of old and new tool and the reason of abnormal wear of new tool were also analyzed.