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Min F.,Hohai University | Xu J.,Hohai University | Du J.,Hohai University | Xing H.,China Railway 14th Bureau Group Co.
Modern Tunnelling Technology | Year: 2015

The Yangtze River tunnel, which passes through a highly permeable gravel and sand stratum in Nanjing, was constructed by a slurry shield, and the slurry preparation and filter cake formation were important for a stable cutting face during tunnel excavation. In this paper, results from laboratory tests and field investigations indicate that as the content of clay particles in the slurry increases, the following are true: 1) less tackifier is used for slurry preparation; 2) the physical stability of the slurry is better; 3) there is less slurry filtration loss during the formation of the filter cake; and 4) the filtration coefficient of the filter cake is smaller. The content of clay particles in the slurry can be used as an important indicator of slurry adjustment during slurry shield tunnelling in the gravel and sand stratum. As the slurry shield passes through the gravel and sand stratum, the clay content in the slurry should be adjusted to greater than 20%. The study results provide a valuable reference for the construction of similar slurry shield tunnel projects in gravel and sand stratum. © 2015, Editorial Office of "Modern Tunnelling Technology". All right reserved. Source

Shi Q.,China Railway 14th Bureau Group Co.
Modern Tunnelling Technology | Year: 2014

In this paper, based on the underground traffic axis project for Nanjing 2014 Youth Olympic Games, the characteristics of foundation pit construction in floodplain area is analyzed and the affects of foundation pit construction on groundwater level in flood plain area are studied. Groundwater level monitoring holes are laid out around foundation pit to monitor variation of groundwater level. It is found that sharp ascending of groundwater level is closely related to atmospheric precipitation and substantial descending of groundwater level is caused by local seepage in retaining walls. ©, 2015, Editorial Office of "Modern Tunnelling Technology". All right reserved. Source

Hu Y.,China Railway 14th Bureau Group Co.
Modern Tunnelling Technology | Year: 2014

Using the handling of a collapse in a shallow-buried tunnel of the Beijing metro as an example, the topics of engineering geology, hydrogeology, and metro construction in Beijing are presented. The action mechanisms of the collapse incentives, such ashydrogeology, construction behavior, underground pipelines, and vibrating load are analyzed, deepening the understanding of the collapse-forming mechanism in shallow-buried tunnels. The countermeasures are summarized from the two aspects of collapse prevention and collapse treatment, providing a reference for similar projects. Source

Dewatering during deep foundation pit construction causes ground settlement around the pit. As for foundation pits in areas with rich groundwater, dewatering would largely result in worse ground settlement and have negative impacts on nearby underground utilities. This paper, based on the Meizizhou river-crossing passage of the Nanjing YOG transportation axis project, gives a profile of the foundation pit construction and a layout of measuring points and monitoring results for the Yangtze River floodplain area. Through an analysis of the monitoring data, it presents the causes and law of ground settlement and impacts to underground utilities around the foundation pit and addresses the countermeasures against these problems. ©, 2014, Editorial Office of "Modern Tunnelling Technology". All right reserved. Source

Zeng X.-H.,Central South University | Zeng X.-H.,Southwest Jiaotong University | Xie Y.-J.,Central South University | Deng D.-H.,Central South University | And 3 more authors.
Jianzhu Cailiao Xuebao/Journal of Building Materials | Year: 2011

The electrical conductivity and flowing characteristics of fresh cement-emulsified asphalt mortars (CA mortar) with different compositions were studied. The relation between the differences of density and electrical conductivity of slurries at different depth were also investigated. The results show that the electrical conductivity has linear relationship with the liquid volume fraction of the slurry. The viscosity of the solution is increased and the transferring speed of the free ions is decreased by adding thickening agent, so that the electrical conductivity of the mortar is decreased. The flowing time of the mortar from the "J" type funnel has exponential relations with its liquid volume fraction and electrical conductivity. The fluidity of the CA mortar can be designed by the liquid volume fraction method and the electrical conductivity method can be used to monitor the fluidity when preparing the CA mortar. Based on the liquid volume fraction, the relationship between the differences of density and conductivity caused by the segregation of slurry can be established. Source

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