Abstract:Based on the shield tunnel construction in complex strata in Guangzhou second tunnel line, an idea of composite metro shield machine is brought forward,and the shield function and its technique parameter are studied and analyzed with the adaptability of cutterhead,cutter,geological condition. The excavation mode theory,the transition between different excavation modes and different excavation parameters are studied,and some technical problems,such as the excavation difficulties problem,the low efficiency problem,the high cost problem,the trouble in distortion control of the shield excavation,are solved. Furthermore,in order to control the excavation direction of the shield more effectively and avoid the cracking and the dislocation of segment,the reason of direction warp is analyzed;and some control methods are presented. In order to avoid mud in clay strata and water gushing in water-enriched geology,the technique of sediment improvement is studied. In order to guarantee the security of nearby building and the routine traffic condition of Beijing—Guangzhou Railway,some credible techniques,such as synchronous grouting technique,construction monitoring technique,the variation of excavation parameters to control tunnel deformation,are adopted.