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Li Y.,China Aerospace Science and Technology Corporation | Lv X.,Beijing Urban Engineering Design & Research Institute CO. | Liu K.,Beijing Urban Construction Group Co. | Zhao S.,Nanjing University of Information Science and Technology
Acta Oceanologica Sinica | Year: 2014

The target on the sea surface is complex and difficult to detect due to the interference of backscattered returns from the sea surface illuminated by the radar pulse. Detrended fluctuation analysis (DFA) has been used successfully to extract the time-domain Hurst exponent of sea-clutter series. Since the frequency of the sea clutter mainly concentrates around Doppler center so that we consider to extract frequency-domain fractal characterization and then detect a weak target within sea clutter by using the difference of frequency-domain fractal characterization. The generalized detrended fluctuation analysis (GDFA) is more flexible than traditional DFA owing to its smoothing action for the clutters. In this paper, we apply the GDFA to evaluate the generalized Hurst exponent of sea-clutter series in the frequency domain. The difference of generalized Hurst exponents between different sea-clutter range bins would be used to determine whether the target exists. Moreover, some simulations with the real IPIX radar data have also been demonstrated in order to support this conclusion. © 2014, The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg.

Sun F.,Qingdao Metro Group Co. | Liu T.,Ocean University of China | Lei G.,Beijing Urban Engineering Design Research institute Co.
Modern Tunnelling Technology | Year: 2014

ADECO-RS, i.e. "toroidal horizontal jet grouting pile + advance grouting pipe", is adopted in the Qingdao metro for the reinforcement of a water-rich sand stratum characterized by being soft at the top and hard on the bottom. The pile-forming effect and problems regarding horizontal jet grouting piles for different sand layers are studied through field sampling and observation. The impact of ADECO-RS on construction and the surrounding environment is analyzed by field monitoring and measuring. The results show that the application of ADECO-RS has an obvious positive effect on settlement control, and there are many problems, such as water leakage induced by the misalignment of two piles and ground uplift caused by improper grouting pressure control. In order to overcome these problems encountered during construction, the pile body is controlled both horizontally and vertically, and tracking monitoring is used for the grouting process. The construction results prove the applicability of ADECO-RS for use in water-rich sand strata.

Liu T.,Ocean University of China | Huang Y.,Ocean University of China | Lei G.,Beijing Urban Engineering Design & Research Institute Co.
Modern Tunnelling Technology | Year: 2015

In tunnel construction, dismantling the temporary strut or steel support will break the original balance of the structural system, especially in shallow tunnels with large sections, which may cause a safety accident by excessive deformation of the primary support or the local overloaded internal force if dismantling of the temporary support is performed in an improper way and at an improper time. A large-span shallow bored subway station in a soil-rock compound stratum is used as an example in this paper to simulate the process of dismantling the longitudinal temporary support in a large-section tunnel by a 3D model, and the effects of different dismantling sequences and one-time demolition lengths on the tunnel structure are analyzed. The analysis results show that the effect of alternating the dismantling sequence and the one-time demolition length of 6 m on factors such as crown settlement and surface subsidence is comparatively small. Additionally, a recommended value for controlling standards of surface subsidence induced by dismantling is presented on the basis of numerical calculations, providing a reference to similar projects. ©, 2015, Editorial Office of "Modern Tunnelling Technology". All right reserved.

Peng Z.,Beijing Jiaotong University | Liu W.,Beijing Jiaotong University | Ding D.,Beijing Urban Engineering Design & Research Institute Co. | Yang X.,Beijing Urban Engineering Design & Research Institute Co. | And 2 more authors.
Zhongguo Tiedao Kexue/China Railway Science | Year: 2015

The axial force and critical moment envelope curves of the interfaces for partitioned key segment obtained from loading tests were taken as the risk control criteria for constructing metro station by enlarging shield tunnel with partitioned key segment. The risk control problem of applying partitioned segment to metro station constructed by enlarging shield tunnel was analyzed with the embedded depth, construction condition and the staggered distance of enlarging excavation as the key influencing factors. The results showed that the complex compression zone on the interface of partitioned key segment moved frequently from the top zone to the bottom zone, and then back to the top zone again. The effect of arch enlarging excavation was the greatest on the internal force of interface. The increase of staggered distance caused the internal force on the interface increase gradually. The arch excavation with staggered distance had great influence on the internal force of interface. By grading and analyzing the internal force of the interface under the interaction of three key factors, the relationship curve between embedded depth and staggered distance under different enlarging excavation conditions was obtained to judge whether the partitioned key segment could be used normally. Theoretical references have been provided for the risk control on metro station constructed by enlarging shield tunnel with partitioned segment. ©, 2015, Chinese Academy of Railway Sciences. All right reserved.

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