Abstract:

In order to learn the distribution, content, diameter and strength of boulders and machine tool coefficient, nature intensity and hydrogeological characteristics of boulders and pebbles met on west extended section of Phase Ⅱ of Chengdu Metro Line No. 4, a series of methods, i.e. insitu well group dewatering, manual excavation of largediameter exploratory well, reinforced concrete retaining wall, underground geological compilation and measuring, site K30 test, intensity tests, sampling and hydrogeological tests of boulders, are carried out. The construction method selection, tunnel buried depth and shield type selection are analyzed; the potential geotechnical issues occuring during shield tunneling are predicted. Finally, some countermeasures and surveying method for boulders and pebbles are suggested.

Key words: Chengdu Metro, shield tunnel, special survey, features of boulders and pebbles, shield type selection