scholarly journals Dynamic Performance of Soil–Tunnel System under Transverse Sinusoidal Excitations

2021 ◽  
Vol 11 (11) ◽  
pp. 5097
Author(s):  
Shaohua Zhang ◽  
Yong Yuan ◽  
Yusheng Yang ◽  
Chong Li ◽  
Herbert A. Mang
Keyword(s):  
Fundamental Frequency ◽  
Dynamic Performance ◽  
Free Field ◽  
Excitation Frequency ◽  
Soil Layer ◽  
Shaking Table ◽  
Cross Sectional ◽  
Tunnel Model ◽  
Longitudinal Joints ◽  
Tunnel System

Input of sinusoidal excitation with specified frequency is an optimal way to capture the mechanism of soil-tunnel interaction. Focusing on the relationship between the frequency of input sinusoidal motions and the dynamic response of a system, this study carried out a series of shaking table tests on both a free-field model and soil–tunnel model in the background of the tunnel in soft ground. To detect the detailed deformation of segmental linings, a refined lining ring of the model tunnel was developed, and the stiffness ratio between the soil and tunnel was verified. Seven sinusoidal excitations were designated to cover the fundamental frequency of the model ground, with the input of transverse direction. Effects of frequency of sinusoidal excitations on soil-tunnel interaction can be evaluated by the detailed responses of segmental linings, such as cross-sectional deformations, extension/closure of longitudinal joints, dynamic normal earth pressures, and dynamic strains of segments. Results shows that the differences of the acceleration responses, on the respects of waveform, phase, and peak, between the upper soil layer and the lower soil layer are obviously increasing with the input frequency increasing. The presence of the tunnel induces a relatively high effect on acceleration responses of the ground within excitation frequency varying from 9 to 17 Hz. The maximum responses of the tunnel are highly influenced by both the fundamental frequency of the model ground and lower frequency of excitations.

scholarly journals Shaking Table Test Study on Flexible and Rigid Immersed Tube Tunnel in Liquefiable Soil Layer

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Zhiyong Ouyang ◽  
Peijie Li ◽  
Jie Cui ◽  
Ruofan Luo ◽  
Dandan Yuan
Keyword(s):  
Growth Rate ◽  
Pore Pressure ◽  
Water Pressure ◽  
Free Field ◽  
Soil Layer ◽  
Shaking Table ◽  
Liquefiable Soil ◽  
Tunnel Model ◽  
Immersed Tunnel ◽  
Surrounding Soil

To study the seismic response law of the immersed tunnel under different structural stiffnesses, three groups of shaking table models of immersed tunnel are carried out, including free-field model, flexible tunnel model, and rigid tunnel model. The similarities and differences of the pore water pressure and acceleration time-history between the free site and liquefiable soil layer around the flexible and rigid immersed tube tunnel are analyzed. The results show that, compared with the soil layer at the same position in the free-field, both the amplitude of acceleration and frequency component in the surrounding soil layer are affected by the stiffness of tunnel, and the influence comes greater with the larger stiffness of tunnel. When the input amplitude of seismic ground motion is small, the soil layer in the free field and the flexible tunnels share the same acceleration amplification law. The development law of pore pressure in the soil layer of test 1 was similar to test 2 but was quite different from test 3. Specifically, when the tunnel stiffness is smaller, the surrounding soil layer is easier to liquefy, with greater influence of the tunnel stiffness on the development law of pore pressure in the surrounding soil layer. The lower the soil buried depth is, the faster the pore pressure dissipates. The growth rate of tunnel strain is related to the stiffness of the structure. Generally speaking, the strain growth rate of the structure with smaller stiffness is higher under moderate earthquakes. The smaller the tunnel stiffness is, the more adaptable the tunnel is to the movement of the surrounding soil layer.

scholarly journals Experimental and analytical study of seismic site response of discontinuous permafrost

2016 ◽  
Vol 53 (9) ◽  
pp. 1363-1375 ◽  
Author(s):  
Behrang Dadfar ◽  
M. Hesham El Naggar ◽  
Miroslav Nastev
Keyword(s):  
Shear Wave ◽  
Site Response ◽  
Free Field ◽  
Frozen Soil ◽  
Shaking Table ◽  
Experimental Program ◽  
Small Scale ◽  
Seismic Site Response ◽  
Discontinuous Permafrost ◽  
Spectral Accelerations

Seismic site response of discontinuous permafrost is discussed. The presence of frozen ground in soil deposits can significantly affect their dynamic response due to stiffer conditions characterized by higher shear-wave velocities compared to unfrozen soils. Both experimental and numerical investigations were conducted to examine the problem. The experimental program included a series of 1g shaking table tests on small-scale models. Nonlinear numerical analyses were performed employing FLAC software. The numerical model was verified using the obtained experimental results. Parametric simulations were then conducted using the verified model to study variations of the free-field spectral accelerations (on top of the frozen and unfrozen soil blocks) with the scheme of frozen–unfrozen soil, and to determine the key parameters and their effects on seismic site response. Results show that spectral accelerations were generally higher in frozen soils than in unfrozen ones. It was found that the shear-wave velocity of the frozen soil as well as the assumed geometry of the blocks and their spacing have a significant impact on the site response.

Geotechnical Seismic Isolation System - Experimental Study

2010 ◽  
Vol 163-167 ◽  
pp. 4449-4453
Author(s):  
Wei Xiong ◽  
Hing Ho Tsang ◽  
S.H. Lo ◽  
Shou Ping Shang ◽  
Hai Dong Wang ◽  
...  
Keyword(s):  
Seismic Isolation ◽  
Dynamic Performance ◽  
Testing Procedure ◽  
Shaking Table ◽  
Isolation System ◽  
Isolation Technique ◽  
Sand Mixture ◽  
Seismic Hazard Mitigation ◽  
Constituent Material ◽  
Different Levels

In this study, an experimental investigation program on a newly proposed seismic isolation technique, namely “Geotechnical Seismic Isolation (GSI) system”, is conducted with an aim of simulating its dynamic performance during earthquakes. The testing procedure is three-fold: (1) A series of cyclic simple shear tests is conducted on the key constituent material of the proposed GSI system, i.e., rubber-sand mixture (RSM) in order to understand its behavior under cyclic loadings. (2) The GSI system is then subjected to a series of shaking table tests with different levels of input ground shakings. (3) By varying the controlling parameters such as percentage of rubber in RSM, thickness of RSM layer, coupled with the weight of superstructure, a comprehensive parametric study is performed. This experimental survey demonstrates the excellent performance of the GSI system for potential seismic hazard mitigation.

scholarly journals Influence of Structure on the Aseismic Stability and Dynamic Responses of Liquefiable Soil

2021 ◽  
Author(s):  
Pengfei Dou ◽  
Chengshun Xu ◽  
Xiuli Du ◽  
Su Chen
Keyword(s):  
Earthquake Engineering ◽  
Damping Ratio ◽  
Free Field ◽  
Shaking Table ◽  
Dynamic Responses ◽  
Seismic Stability ◽  
Geotechnical Earthquake Engineering ◽  
Liquefiable Soil ◽  
Porewater Pressure ◽  
Lateral Displacements

Abstract In previous major earthquakes, the damage and collapse of structures located in liquefied field which caused by site failure a common occurrence, and the problem of evaluation and disscusion on site liquefaction and the seismic stability is still a key topic in geotechnical earthquake engineering. To study the influence of the presence of structure on the seismic stability of liquefiable sites, a series of shaking table tests on liquefiable free field and non-free field with the same soil sample was carried out. It can be summarized from experimental results as following. The natural frequency of non-free field is larger and the damping ratio is smaller than that of free field. For the weak seismic loading condition, the dynamic response of sites show similar rules and trend. For the strong ground motion condition, soils in both experiments all liquefied obviously and the depth of liquefaction soil in the free field is significantly greater than that in the non-free field, besides, porewater pressure in the non-free field accumulated relately slow and the dissapited quikly from analysis of porewater pressure ratios(PPRs) in both experiments. The amplitudes of lateral displacements and acceleration of soil in the non-free field is obviously smaller than that in the free field caused by the effect of presence of the structure. In a word, the presence of structures will lead to the increase of site stiffness, site more difficult to liquefy, and the seismic stability of the non-free site is higher than that of the free site due to soil-structure interaction.

Saliency of Vowel Features in Neural Responses of Cochlear Implant Users

2018 ◽  
Vol 49 (6) ◽  
pp. 388-397
Author(s):  
François Prévost ◽  
Alexandre Lehmann
Keyword(s):  
Speech Recognition ◽  
Cochlear Implant ◽  
Fundamental Frequency ◽  
Mismatch Negativity ◽  
Free Field ◽  
Event Related Potentials ◽  
Oddball Paradigm ◽  
Aural Rehabilitation ◽  
Spectral Components ◽  
Related Potentials

Cochlear implants restore hearing in deaf individuals, but speech perception remains challenging. Poor discrimination of spectral components is thought to account for limitations of speech recognition in cochlear implant users. We investigated how combined variations of spectral components along two orthogonal dimensions can maximize neural discrimination between two vowels, as measured by mismatch negativity. Adult cochlear implant users and matched normal-hearing listeners underwent electroencephalographic event-related potentials recordings in an optimum-1 oddball paradigm. A standard /a/ vowel was delivered in an acoustic free field along with stimuli having a deviant fundamental frequency (+3 and +6 semitones), a deviant first formant making it a /i/ vowel or combined deviant fundamental frequency and first formant (+3 and +6 semitones /i/ vowels). Speech recognition was assessed with a word repetition task. An analysis of variance between both amplitude and latency of mismatch negativity elicited by each deviant vowel was performed. The strength of correlations between these parameters of mismatch negativity and speech recognition as well as participants’ age was assessed. Amplitude of mismatch negativity was weaker in cochlear implant users but was maximized by variations of vowels’ first formant. Latency of mismatch negativity was later in cochlear implant users and was particularly extended by variations of the fundamental frequency. Speech recognition correlated with parameters of mismatch negativity elicited by the specific variation of the first formant. This nonlinear effect of acoustic parameters on neural discrimination of vowels has implications for implant processor programming and aural rehabilitation.

scholarly journals Laboratory Tests for Subgrade Reaction Coefficient in Seismic Design of Underground Engineering Domain

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Kunpeng Xu ◽  
Liping Jing ◽  
Xinjun Cheng ◽  
Haian Liang ◽  
Jia Bin
Keyword(s):  
Seismic Design ◽  
Shaking Table Test ◽  
Free Field ◽  
Deformation Mode ◽  
Shaking Table ◽  
Subgrade Reaction ◽  
Underground Structures ◽  
Testing Methods ◽  
Underground Engineering ◽  
Reaction Coefficient

Subgrade reaction coefficient is commonly considered as the primary challenge in simplified seismic design of underground structures. Carrying out test is the most reliable way to acquire this intrinsic soil property. Owing to the limitations of experimental cost, time consumption, soil deformation mode, size effect, and confined condition, the existing testing methods cannot satisfy the requirements of high-precision subgrade reaction coefficient in seismic design process of underground structures. Accordingly, the present study makes an attempt to provide new laboratory testing methods considering realistic seismic response of soil, based on shaking table test and quasistatic test. Conventional shaking table test for sandy free-field was performed, with the results indicating that the equivalent normal subgrade reaction coefficients derived from the experimental hysteretic curves are reasonable and verifying the deformation mode under seismic excitation. A novel multifunctional quasistatic pushover device was invented, which can simulate the most unfavorable deformation mode of soil during the earthquake. In addition, the first successful application of an innovative quasistatic testing method in evaluating subgrade reaction coefficient was reported. The findings of this study provide preliminary detailed insights into subgrade reaction coefficient evaluation which can benefit seismic design of underground structures.

scholarly journals Polymeric Bearings as a new base isolation system suitable for mitigating machine-induced vibrations

2018 ◽  
Vol 211 ◽  
pp. 17001 ◽  
Author(s):  
Tomasz Falborski ◽  
Robert Jankowski
Keyword(s):  
Base Isolation ◽  
Excitation Frequency ◽  
Hysteresis Loops ◽  
Shaking Table ◽  
Damping Properties ◽  
Structural Vibrations ◽  
Isolation System ◽  
Equivalent Damping ◽  
Flexible Polymer ◽  
Base Isolation System

The present paper summarizes the preliminary results of the experimental shaking table investigation conducted in order to verify the effectiveness of a new base isolation system consisting of Polymeric Bearings in reducing strong horizontal machine-induced vibrations. Polymeric Bearing considered in the present study is a prototype base isolation system, which was constructed with the use of a specially prepared flexible polymer with improved damping properties. Dynamic oscillatory tests, during which a concrete base slab supported by four Polymeric Bearings was subjected to horizonal sinusoidal excitations characterized by different frequencies and amplitudes, were conducted in order to determine the damping properties of Polymeric Bearings and their effectiveness in mitigating structural vibrations. Equivalent damping ratios for every excitation frequency considered were determined using the experimentally obtained hysteresis loops. Final conclusions are presented and the results discussed.

scholarly journals Dynamic Response of an Inhomogeneous Viscoelastic Pile in a Multilayered Soil to Transient Axial Loading

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Zhiqing Zhang ◽  
Jian Zhou ◽  
Kuihua Wang ◽  
Qiang Li ◽  
Kaifu Liu
Keyword(s):  
Frequency Domain ◽  
Longitudinal Wave ◽  
Soil Layer ◽  
Axial Loading ◽  
Analytical Form ◽  
Sine Wave ◽  
Function Technique ◽  
Cross Sectional ◽  
Soil System ◽  
Single Defect

A quasi-analytical solution is developed in this paper to investigate the mechanism of one-dimensional longitudinal wave propagating in inhomogeneous viscoelastic pile embedded in layered soil and subjected to a transient axial loading. At first, the pile-soil system is subdivided into several layers along the depth direction in consideration of the variation of cross-sectional acoustic impedance of the pile or differences in soil properties. Then, the dynamic governing equation of arbitrary soil layer is established in cylindrical coordinates and arbitrary viscoelastic pile segment is modeled using a single Voigt model. By using the Laplace transform and boundary conditions of the pile-soil system, the vertical impedance at the top of arbitrary pile segment is defined in a closed form in the frequency domain. Then by utilizing the method of recursion typically used in the Transfer Function technique, the vertical impedance at the pile top can be derived in the frequency domain and the velocity response of an inhomogeneous viscoelastic pile subjected to a semi-sine wave exciting force is obtained in a semi-analytical form in the time domain. Selected numerical results are obtained to study the mechanism of longitudinal wave propagating in a pile with a single defect or double defects.

Dynamic Characteristics Analysis of Axle Box Spring by FEM

2013 ◽  
Vol 712-715 ◽  
pp. 1535-1540
Author(s):  
Li Liu ◽  
Wei Hua Zhang ◽  
Dong Li Song
Keyword(s):  
Dynamic Characteristics ◽  
Dynamic Stiffness ◽  
Dynamic Performance ◽  
Excitation Frequency ◽  
Railway Vehicle ◽  
Helical Spring ◽  
Working Stress ◽  
Characteristics Analysis ◽  
In Series ◽  
Spring Method

Axle box spring of railway vehicle is the structure of helical spring in series with rubber pad to reduce working stress of helical spring and absorb high-frequency vibration. Rubber pad model was built. Static and dynamic characteristics were researched in axial and radial directions. The results show that the static stiffness of rubber pad decreases with the increase of radial displacement and increases distinctly with the increase of the amount of compression; The dynamic stiffness of rubber pad increases with the decrease of the excitation force in the case of the same excitation frequency and decreases with the decrease of the frequency in the case of the same excitation displacement. Axle box spring method was established and the amplitude-frequency curve of dynamic stiffness of the spring was presented. The results provide a theoretical basis to research the dynamic performance of railway vehicle.

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