Abstract:

To evaluate the tunneling effect of the earth pressure balance(EPB) shield in typical strata in Nanchang, China, a case study is conducted on a shield tunnel from Shengjinta station to Liuyanjing station. The evolution patterns of the main tunneling parameters of the EPB shield in fullsection gravel sandstone stratum, fullsection argillaceous siltstone, and composite sandrock strata are investigated. Then, some characteristic parameters of the stratigraphic boreability including penetration degree, field penetration index, and tunneling specific energy are introduced to establish the relationships between the investigated key tunneling parameters. On this basis, the stratigraphic boreability of these three types of strata is evaluated. The research results indicate the following: (1) The main tunneling parameters are stable relatively when tunneling in gravel sandstone and argillaceous siltstone strata. The total thrust and the rotation speed of the cutterhead increase considerably in the composite sandrock strata. (2) The cutterhead torque decreases gradually when shield tunnels from composite sandrock strata to argillaceous siltstone strata. There is a satisfied positive linear relationship between the cutterhead torque and the total thrust in the argillaceous siltstone strata. (3) The value and oscillation of the penetration degree decline obviously when the shield tunnels from gravel sandstone to argillaceous siltstone strata. There are similar distributed characteristics of the field penetration index in the composite sandrock strata and argillaceous siltstone strata but exhibit an opposite variation trend. Nevertheless, the tunneling specific energies of shield in these three strata are close to each other. (4) Significant correlations between the field penetration index and the penetration degree are observed in both gravel sandstone and composite sandrock strata, but the correlation is weak in argillaceous siltstone strata. (5) The shield has a highest penetration degree and lowest field penetration index and tunneling specific energy in gravel sandstone strata, indicating the best tunneling effect of EPB shield in such strata. (6) On the whole, the gravel sandstone strata and the intermediatelyweathered argillaceous siltstone strata show a better boreability than composite sandrock strata.

Key words:  , earth pressure balance shield, tunneling parameters, penetration degree, field penetration index, tunneling specific energy