EVOLUTION LAWS OF EARTH PRESSURE BALANCE SHIELD ATTITUDE IN MEDIUM EXPANSIVE ROCK UNDERLYING GRAVEL-COBBLE LAYER

The Nanning metro line 1 partly passes through the complex strata of gravel-cobble and medium expansive rock. In order to obtain the evolution process of shield attitude when tunneling in this complex strata, the influence of water-swelling expansive rock on shield attitude is analyzed by measured data. The result shows that the mixture of water-swelling mudstone and synchronous grout can adhere under the shield when encountering water, and makes it difficult to control the shield attitude. The attitude in head part of shield can be descend by enlarge shield thrust in upper region when tunneling. But the attitude in postmedian of the shield can ascend. The water-swelling mudstone can raise the head part of shield when assembling shield segments. The thrust difference between upper and lower regions should be kept in a reasonable value when tunneling. Other control measures should be taken as well.