Guangyun Gao

Zoning of confined aquifers inrush and quicksand in Shanghai region

Groundwater inrush and quicksand from the underlying aquifers are two typical geological hazards during underground constructions in Shanghai region, China. The objective of this work is to give a zoning study on confined aquifers and quicksand geology in Shanghai region and provide helpful decision-making information for the government, urban planners and designers. The hydrogeological characteristics of the confined aquifers in Shanghai are collected, and two different criteria are then proposed for mapping the aquifers. The characteristics and distribution of the soil stratum, in which quicksand would occur, are then presented, and an index system for quicksand hazard and vulnerability assessment is proposed. Furthermore, the quicksand risk in different zones of Shanghai is evaluated using a semiquantitative approach, and the management zoning is developed by considering the urban planning of Shanghai. The zoning maps of confined aquifers and quicksand risk are obtained, and the high-risk zone can be directly identified from the zoning maps. This is greatly helpful for the future urban planning and underground constructions in Shanghai region. The proposed method for quicksand hazard and vulnerability assessment is also applicable for other cities undergoing geological hazards caused by confined water inrush and quicksand.

Dynamic Responses of Saturated Transversely Isotropic Ground Subjected to High-Speed Train Load

A u-p format 2.5D finite element method (FEM) is proposed to investigate the ground vibration and distribution of pore water pressure in transversely isotropic saturated medium subjected to high-speed train load. The governing equations are derived based on Biot’s theory in frequency domain by applying Fourier transform with respect to time. The Galerkin method is then employed to develop the 2.5D FE model. Verification of the model is carried out by comparing the predictions with published data. Effects of soil parameters on the dynamic responses of ground are investigated in detail. Results indicate that the increase in vertical elastic modulus contributes much more to the decrease in displacement amplitude of ground and maximum amplitude of pore water pressure in soil, compared to that of horizontal elastic modulus. Both horizontal and vertical Poisson ratios have insignificant effects on ground vibration, while the change of Poisson ratio lead to a great change in the maximum amplitude of pore water pressure. Effects of shear modulus on both ground vibration and maximum amplitude of pore water pressure are negligible.

Field Measurement and Analysis of Ground Vibration Induced by High-Speed Train

In situ test data for ground vibration of high-speed railways is valuable but scarce. Chinese researchers used to cite test results from European countries to verify their numerical model, owing to the lack of open access to in situ data. To remedy this shortage, this paper presents field measurements of ground vibrations induced by high-speed trains at a site on the Qin-Shen Line in China. The free field vibrations at different distances from the track center during the passage of a high-speed train at a speed varying from 230 to 250 km/h are measured. The recorded vertical accelerations are analyzed both in the time and the frequency domains. The periodic exciting action of the train wheel-set can be identified in the vertical acceleration time-history when the test site is close to (e.g. 3.5 m away from) the track centerline. Vertical acceleration generally attenuates with distance from the track centerline, but a vibration boom occurs at the distance of 12 m. The effect of both P and S waves cannot be neglected in the vicinity of the track, while R waves begin to dominant beyond the distance of 15 m. In addition, an important frequency in the acceleration spectrum of the ground vibration is the fundamental axle passage frequency (25.6–27.8 Hz). The test results could be available to peer researchers for verification of their numerical models, and meanwhile act as a complementary material to currently scarce in situ tests results.

Micro-vibration Measurement and Analysis of High-Tech Electronics Workshop in Guangzhou

High-tech electronics workshop typically has stringent requirements for micro-vibration control, so as to ensure the proper operation of the installed vibration-sensitive facilities. Based on a micro-vibration measurement on a high-tech electronics workshop in Guangzhou, China, this paper reports the test data, presents a systematic and detailed summary of issues related to vibration data processing, and analyzes the transformation of the vibration characteristics when the anti-vibration techniques enhances. The results show that, the one-third octave band spectral has great advantages in representing vibration data of high-tech buildings. With the enhancement of the anti-vibration techniques, the vibration amplitudes in all of the three directions decrease both in time-history and one-third octave band spectral and finally become roughly the same; and the dominant high-frequency component disappears, while the relative low-frequency component takes the leading role in all the three directions.

Analysis of ground vibration induced by trains on saturated layered foundation

Based on Biots wave propagation equations and boundary conditions, the Galerkin method is used to derive the u-p format finite element equation in the frequency domain by Fourier transform. The track and the attached sleepers are simplified as Euler beams resting on saturated half-space, the wave-number transform in the load moving direction is applied to reduce the three-dimensional (3D) dynamic problem to a two-dimensional (2D) problem. The dynamic problem is solved in a section perpendicular to track direction, and the 3D responses of the track and the ground are obtained from the inverse wave-number expansion. Combined a moving track-ground interaction model, a parametric study is given to evaluate the ground vibration induced by train moving loads on the saturated layered ground. The effect of the soil parameters (such as permeability coefficient, porosity and shear wave velocity) on the attenuation of ground vibration are investigated and discussed in detail. The results show that the saturated soils permeability coefficient, porosity and shear wave velocity have great influence on the ground vibration.