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Shanghai, China

Xu Q.-W.,Shanghai JiaoTong University | Xu Q.-W.,Tongji University | Xu Q.-W.,University of Shanghai for Science and Technology | Zhu H.-H.,Tongji University | And 3 more authors.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering

The cutting torque is an important construction parameter during tunnelling process by use of shield machines. It not only determines the difficulty degree of construction but also influences other working parameters, such as thrust force, advancing speed, rotation speed and driving power. Based on the cutting mechanism of EPB shield machine, a new reasonable calculation model of cutting torque is presented by applying mathematical and mechanical theories, and its influence factors are then discussed. Subsequently, model experiments on the cutting torque during tunnel excavation with EPB shield machine under different conditions of buried depth, cutter head aperture ratio, rotation speed and advancing speed are carried out. The aforementioned theoretical studies are then verified, and satisfactory results are achieved. Source

Bai T.-H.,Tongji University | Bai T.-H.,Shanghai Shentong Metro Co. | Liu S.-J.,Tongji University | Liao S.-M.,Tongji University
Yantu Lixue/Rock and Soil Mechanics

In view of shield tunnel projects in soft soil area of Shanghai, the advancing speed of the shield machine is adjusted, and the water pressure, soil pressure and strata stability are observed in the whole process of the shield crossing the monitoring section. According to the measured soil consolidation ratio, the pressure of artesian water and other strata soil properties, the influences of the varied advancing speeds are comprehensively evaluated by the mechanisms of soil disturbance. The analysis indicates that the shield tunneling in soft soil area is approximately 4 times of the diameter (D=6.2 m). By keeping the chamber earth pressure and grouting amount invariant in the shield advancing process, the change of the hoisting speed of the jack to great extent influences the soil pressure and deformation. Reducing the advancing speed results in the decrease of the disturbance range of water and earth pressures and then the disturbance is generated by the pressure increment, but leads to more stable values of the induced surface heave. The corresponding change value is determined by the ratio of depth to the advancing speed. Experiment results provide a certain valid reference to ensure the effect from the shield speed of the jack at the depth of 4D. © 2016, Science Press. All right reserved. Source

Lou X.-M.,Tongji University | Yang J.,Tongji University | Li D.-N.,Tongji University | Liu J.-H.,Tongji University | Liu J.-H.,Shanghai Shentong Metro Co.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering

Based on the new understanding about rebound stress and deformation at the bottom of deep foundation pits and the generalized load transfer method considering the additional load or deformation of the soil around piles, an analytical method is proposed for the uplift of soldier piles due to excavation. It can take many factors into account, e.g., variable cross-section character of soldier piles, installation and stepped excavation of strut system and construction situation, and it can be employed to analyze the load transfer behaviors of soldier piles. Because the uplift displacement of the soldier piles is easily monitored, the calculated results are easily compared with the measured ones, which can improve the method itself and the parameters to be chosen more reasonably. Through two cases, the rationality of the proposed method to calculate the uplift displacement of soldier piles is validated. The difference between the calculated and the measured values is also discussed. Source

Xu C.,Zhejiang University | Wang H.-F.,Zhejiang University | Wang X.-B.,Shanghai Shentong Metro Co.
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control

This paper analyzes the problems in short-circuit calculation model of DC traction system, and presents a set of fault calculation process meeting the requirements of protection setting and validation by analyzing different fault calculation models. The reasons for producing calculation errors are analyzed. The method of reducing the calculation error in steady-state short-circuit calculation is presented from two aspects of rectifier unit equivalent and knee current. The optimized calculation process is given. Based on the calculation model of transient current of DC-side output short-circuit and remote short-circuit, the overshoot theory is applied to come up with a new method to identify the output short-circuit, close-up short-circuit, and far end short-circuit, and method of calculating the transient current of close-up short-circuit is proposed. Simulation examples confirm the feasibility and accuracy of the proposed models and methods in meeting the requirements of protection setting and validation. Source

Lou X.,Tongji University | Li D.,Tongji University | Liu J.,Shanghai Shentong Metro Co.
Tumu Gongcheng Xuebao/China Civil Engineering Journal

Rebound deformations were measured at different depths below the bottom of a strip excavation of 15m depth. According to the compression-swelling odometer test, the relationship between the rebound modulus and the ratio of unloading at depth below the bottom of the excavation was obtained. Based on the results, with respect to the impact of lateral net pressure, the magnitude of the rebound stress can be determined by the fact that the up-load applied to the bottom of excavation is equivalent to the weight of the removed soil. The rebound stress is reduced by the weight of the soil below the bottom of excavation and decreases linearly with increasing depth. Residual stress is just the effective overburden stress below the bottom of the excavation. In terms of the rebound stress, the rebound deformation can be calculated with high accuracy. Source

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