Abstract: The implementation of an open tunnel boring machine(TBM) for construction within highgeostress soft rock formations in western Yunnan, China, encounters various challenges, such as support failures, frequent equipment jamming, and tunnel intrusions, due to large deformation of surrounding rocks. Consequently, an analysis of the permissible deformation amount and deformation pattern of the surrounding rocks is conducted to propose spatiotemporal principles for controlling the surrounding rocks. These principles include initiating primary support construction within 15 days after excavation, spatial positioning within 30 m from the excavation face, and requiring a minimum daily TBM excavation rate of 2 m. Onsite tests on different types of support structures reveal that prestressed long anchor cables and Hshaped steel arches filled with concrete can effectively control the surrounding rock deformation. Several effective technologies have been developed for controlling surrounding rock deformation through open TBM construction practices at the Xianglushan tunnel within the central Yunnan water diversion project. These technologies encompass reserved allowable deformation during cutterhead expansion excavation at the face position, passive strong support of the surrounding rock shield pouring concrete box arch frames, automatic early sealing of the upper half circle of the tunnel with preinstalled shotcrete, active control of deep surrounding rock deformation using prestressed long anchor cables, and reinforcement of the bottom of the tunnel with selfadvancing anchor bolts.

Key words: large deformation of soft rock, surrounding rock deformation control, high geostress, water diversion tunnel, rock tunnel boring machine