Abstract
The key to guaranteeing excavation face stability in slurry shield tunneling is the formation of an impermeable dynamic filter cake. At the same time, the effect of the cutter head and rotation speed should be taken into account. We studied the characteristics and formation mechanism of the dynamic filter cake using a newly developed experimental apparatus. The experiment results show that the hysteretic infiltration zone appeared in the curves of stepped loading filtration while the cutter head was rotating, and the volume of water filtration increased by 11.2% compared to when the cutter head stopped. The higher the rotation speed was, the lower the conversion rate of the effective stress was. Under the same rotation speed, the formation time of the 6-cutter arm was almost 5 s slower than that of the 5-cutter arm. As the cutter arms and the rotation speed increased, the stratum’s electrical conductivity increased and stabilized at a distance of 20 cm from the cutter head. The filter cake transited from ‘filter cake plus an infiltration zone’ to ‘an infiltration zone without a filter cake’ with the increase of the rotation speed. The thickness of the dynamic filter cake was smaller than that of the static filter cake, the thickness of 10 groups decreased significantly, and the average thickness decreased by 76.15% at 1.0 rpm. The mesoscopic formation process of the dynamic filter cake can be divided into six stages. This study revealed the slurry penetration mechanism and filter cake characteristics present under cyclic damage by the shield cutter head to the filter cake and soil and provided theoretical support on how to maintain the stability of the excavation face during slurry shield tunneling.
Highlights
In the past few years, due to their extensive range of geological applications, low disturbance to surrounding rock, and high excavation face stability, slurry pressure balance shield (SPB) technology has been widely used in shield tunnels [1–4], such as the fourth tunnel of the Elbe River in Germany, the Westerschelde tunnel in The Netherlands, the Eurasia tunnel in Turkey, the Tokyo Bay submerged highway tunnel in Japan, and the Nanjing Yangtze River and Hangzhou Qianjiang tunnels in China [5–8]
In the slurry permeation test, the water filtration volume at a certain time can reflect the quality of the filter cake: the less water filtration, the better the quality of the filter cake and the greater the stability of the excavation face [32,36]
The slurry permeation time was longer than the working duration of the cutter head, showing a hysteretic infiltration zone and indicating that there was a delay of about 10–20 s while the cutter head stopped
Summary
In the past few years, due to their extensive range of geological applications, low disturbance to surrounding rock, and high excavation face stability, slurry pressure balance shield (SPB) technology has been widely used in shield tunnels [1–4], such as the fourth tunnel of the Elbe River in Germany, the Westerschelde tunnel in The Netherlands, the Eurasia tunnel in Turkey, the Tokyo Bay submerged highway tunnel in Japan, and the Nanjing Yangtze River and Hangzhou Qianjiang tunnels in China [5–8]. When slurry shield tunnels are constructed in a stratum in which the water pressure is more than 0.5 Mpa and the permeability coefficient is more than 10−3 cm/s, the excavation face will become unstable, causing seawater backflow and slurry spillover if special measures are not taken. This can lead to major accidents, such as tunnel collapse [9,10]. Broere et al [18] established a mechanical model for excavation face stabilization He compared the calculated pore-pressure distribution with the actual results of the slurry shield in the sand stratum, indicating that the excess pore pressure had an important impact on the tunnel face stability. Zizka et al [19] applied a method for predicting an increase in pore water pressure in front of the tunnel face and concluded that the permeation of slurry is related to time and the pore water pressure transfer follows Darcy’s law
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
