Abstract
The receiving portal of a shield tunnel at an interval ventilation shaft for a subway project in the North China Plain is situated in strata that primarily consist of silty clay, clayey silt, and fine sand from top to bottom, characterized by a high groundwater table and high fluidity. For safety considerations, the receiving portal was reinforced using high-pressure jet grouting; however, horizontal probe holes indicated that risks of water and sand inrush persisted. Technical expert assessment determined that the shield machine's cutterhead was highly susceptible to triggering water and sand inrush through the portal gap during portal breakthrough. To ensure successful shield exit from the portal (breakthrough and exit), a design for shield idling through the station was implemented. Surface grouting was employed to perform targeted reinforcement of the water-rich fine sand formation at the receiving portal of the interval ventilation shaft, thereby ensuring project safety. Following this treatment, the shield machine successfully idled through the station without any water or sand inrush incidents.
Full Text
Preamble
Title: Grouting Reinforcement of Shield Machine Receiving End in Water-Rich Silty Sand Layer in the North China Plain
Authors: Li Qiaobin, Zhong Jiu'an, Zang Peng
Affiliation: Sichuan Gotone Geotechnical Technology Co., Ltd., Chengdu, Sichuan 610073, China
Abstract
The shield receiving end of a subway ventilation shaft in the North China Plain is located in a water-rich stratum composed primarily of silty clay, clayey silt, and silty fine sand, with high groundwater levels and strong mobility. Initial reinforcement using high-pressure jet grouting proved insufficient, as horizontal probe holes revealed continuing risks of water and sand inrush. Technical experts assessed that breakthrough of the portal by the shield machine's cutter head would likely trigger water and sand gushing through the portal gap. To ensure safe breakthrough and successful empty-propulsion through the station, targeted surface grouting was employed to reinforce the water-rich silty fine sand layer at the receiving end. This treatment enabled the shield machine to smoothly complete empty-propulsion without any water or sand inrush.
Keywords: subway shield; receiving end; sleeve valve pipe grouting; GX modified silicate grout material; reinforcement; water-rich silty sand layer