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Numerical investigation of the convex effect on the behavior of crossing excavations
Min Zhang, Xing-hua Wang, Guang-cheng Yang, You Wang
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2011, 12(10): 747-757.
https://doi.org/10.1631/jzus.A1100028
A 3D numerical model considering the soil-structure interaction is presented in this paper to examine the ground movement and internal force during the construction of Qingdao North Metro Station, China with a special focus on the convex effect of the crossing excavation. The influence of intersection angles and soil resilience characteristics on deformation behavior is discussed, and the suitability of two alternative constitutive models applied in excavation simulation is also considered. The analysis results show that a notable convex effect appears to be associated with the crossing excavation, and the intersection is the key area requiring special attention. The displacements at the corner decrease with increasing crossing angles. The axial loads of struts along the retaining pile wall are unequal, and the values near the cross section are generally larger than the average loads of the left-sided ones. The modified Cam-Clay (MCC) model, which is capable of describing the loading-unloading criterion and identifying the stiffness difference of strain hardening between loading and unloading, can yield a relatively high accuracy of estimation for the behavior of excavations in comparison to the Mohr-Coulomb (MC) model. Furthermore, slight soil deformation resilience after unloading can reduce the ground surface settlement and enhance the ground stability.
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Three-dimensional numerical simulation and earth pressure analysis on double-row piles with consideration of spatial effects
Zi-han Wang, Jian Zhou
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2011, 12(10): 758-770.
https://doi.org/10.1631/jzus.A1100067
As a new kind of technology in retaining structures, the characteristics of double-row piles are significantly affected by spatial effects. In this paper, double-row piles as a retaining structure are simulated numerically in three-dimension by finite element software PLAXIS 3D FOUNDATION. The behavior differences of piles in different positions around the foundation pit are analyzed. By changing the parameters, including the length-width ratio, the excavation depth, the distance between rows and the diameter of piles, the variations of the lateral deformation, the bending moment and the earth pressure around the piles are determined. The reasonable values of parameters and some suggestions with consideration of earth pressure are proposed for the design of double-row piles as a retaining structure. The results show that the lateral deformation and bending moment are the largest in the middle of long side of the foundation pit, which is identified as the most unfavorable position. It is indicated that the earth pressure between rows above pit bottom is close to active earth pressure, while the earth pressure between rows under pit bottom is close to static earth pressure. It is suggested that 1/2–2/3 of pile length, 0.6–1.2 m, 3d–6d, and 2d–2.5d be chosen as embedded depth of piles, diameter of piles, distance between rows, and distance between piles, respectively, where d is the pile diameter.
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Comparative study of static and dynamic parameters of rock for the Xishan Rock Cliff Statue
Jin Jiang, Jin-zhong Sun
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2011, 12(10): 771-781.
https://doi.org/10.1631/jzus.A1100003
Ultrasonic wave testing was applied to investigate the quality and weathering status of rock specimens obtained in two borings situated in the Xishan Buddha rock slope in Taiyuan, China. This paper pays special attention to the distribution of bulk density, dynamic parameters and static parameters of rock specimens as well as the relationship between static and dynamic parameters. The results illustrate that the distribution of both parameters is identical along the depth of two drilled holes in the rock slope. When the hole depth increases, the density of rock mass, saturated compression strength and static elastic modulus, dynamic elastic modulus and wave velocity also show increase tendency. The weathering degree in the rock mass ranging from the surface of cliff to the depth of 2.5 m is the highest while the rock mass is unsalted and more rigid when the depth is larger than 3.0 m. The relationship between dynamic elastic modulus, sonic wave velocity and horizontal depth indicates that dynamic elastic modulus is more sensitive than sonic wave velocity. Conversely, by comparing quantity relationship between static elastic modulus and sonic wave velocity, it is found that the composition of rock has a great influence on the relationship between static and dynamic parameters, that is, inequality of rock composition will lead to dispersion and abnormality of the distribution of static and dynamic parameters.
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Metro train-induced vibrations on historic buildings in Chengdu, China
Meng Ma, Valéri Markine, Wei-ning Liu, Yang Yuan, Feng Zhang
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2011, 12(10): 782-793.
https://doi.org/10.1631/jzus.A1100088
In this paper, the vibration influence on a monument caused by Chengdu Subway Line 2 is analyzed. Due to its elaborate and unique design, both structural and architectural damages should be avoided. First, the allowable root mean square (RMS) velocity at the foundation of the monument is derived and a site measurement is performed to obtain the background vibrations induced by road traffic. In addition, a train-track coupled model and 3D tunnel-soil-structure coupled finite element models are built to predict the dynamic response of the monument. Prediction models are checked by site measurement in Beijing Subway Line 5. Different kinds of fasteners and train speeds are compared and discussed as well. Results show that: (1) At a train speed of 72 km/h, all the traffic vibrations exceed the low limit no matter what kind of fastener is used, which is mainly due to the contribution of road traffic. Slowing down train speeds can cause effective vibration attenuation; (2) Vibrations drop dramatically with the train speed from 65 to 58 km/h. When the train speed is lower than 58 km/h, vibrations are lower than allowable value even if the contribution of road traffic is considered.
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Evaluating population exposure to N, N-dimethylformamide in a small industrial area accounting for population movement
Yu-mei Wei, Wei-li Tian, Qing-yu Zhang, Ying-yue Zheng, Yi-ke Yang, Zu-cheng Wu, Qi Zhu, Lei Zhou, Si-mai Fang
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2011, 12(10): 794-806.
https://doi.org/10.1631/jzus.A11b0381
Population exposure to pollutants is important for studies on the exposure-response relationship. However, it is difficult to evaluate population exposure to non-conventional pollutants due to limited data on concentration levels and the movement patterns of inhabitants. In this study, an air dispersion model was used to simulate N, N-dimethylformamide (DMF) concentrations, as a proxy to monitoring concentrations. A total of 1289 randomly selected household representatives were surveyed to obtain information on movement characteristics. Subsequently, population movement patterns were combined with DMF concentration levels on maps of 100 m×100 m resolution to calculate population exposure. During 2008, the estimated population exposure to DMF ranged from 0.002 to 0.64 mg/m3. The highest level of population exposure to DMF was found in the north and northwest sub-districts of the study area, ranging from 0.42 to 0.64 mg/m3. The population exposure to DMF for different occupational groups indicated that retired people and farmers were vulnerable subpopulations among people highly exposed to DMF. This was mainly because they spent most time at home where the DMF concentration was high. As pollutant concentrations were divided into small grids, we found that exposure levels were substantially impacted by population movement characteristics.
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7 articles
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