- Email: [email protected]
Reduction of metro vibrations by honeycomb columns under the ballast: Field experiments
Soil Dynamics and Earthquake Engineering 129 (2020) 105913
Contents lists available at ScienceDirect
Soil Dynamics and Earthquake Engineering journal homepage: http://www.elsevier.com/locate/soildyn
Reduction of metro vibrations by honeycomb columns under the ballast: Field experiments M. Gao a, X. Xu a, Q.S. Chen b, Y. Wang a, * a
Shandong Province Key Laboratory of Civil Engineering & Disaster Prevention and Mitigation (College of Civil Engineering and Architecture), Shandong University of Science and Technology, Qingdao, 266590, China b Department of Civil and Environmental Engineering, National University of Singapore, No.21, Lower Kent Ridge Road, 119077, Singapore
A R T I C L E I N F O
A B S T R A C T
Keywords: Environmental vibration Vibration generated by metro Duxseal-cement columns Isolation effect One-third octave spectrum
Environmental vibrations induced by subway operation are harmful to human health and structures when they exceed a certain value. Therefore, effective measures should be taken to reduce the noise and vibration generated by the metro. Therefore, a method to reduce the vibration by the installation of honeycomb Duxseal-cement columns under the ballast is presented in this paper. A honeycomb Duxseal-cement column was embedded in the subgrade of Qingdao Metro Line 13. A field test to measure the vibration of Qingdao Metro Line 13 was conducted. In addition, the time history curve of the vibration acceleration was obtained by processing the data and a Fourier transform was conducted for the test data to obtain a corresponding frequency spectrum curve. The spectrum curve was then converted into the one-third octave spectrum. Finally, the average value of the fre quency vibration levels was determined. The comparison between the vibration generated by the metro filling and non-filling Duxseal-cement columns was investigated in detail. The test results show that the subgrade of metro in-filled by the Duxseal-cement columns obtains a better isolation effect than that of non-filling Duxsealcement columns. The honeycomb Duxseal-cement columns present in the metros decrease their vibration ac celerations in three directions, the X-, Y-, and Z-directions, by 33%, 28%, and 40%, respectively, compared with the original.
1. Introduction In recent decades, urban subway traffic construction around the world has been vigorous. While urban subway traffic alleviates traffic congestion and improves resident travel conditions, the problem of environmental vibration generated by subway operation has become increasingly intense and frequent. For example, the noise and vibration due to the subway moving loads influence the normal performances of L’Opera de la Bastille [1] when the Paris Metro Line No.7 and No.13 passed its opera house. When the Beijing Subway DAXING Line passed through the Qingdao Jiayuan Community, there was an evident sense of shock in nearby high-rise buildings for 5 s, which caused the serious misplacement of furniture. Owing to the passing subway in Shenzhen, 30% of the electronic devices produced by an electronic chip factory were unqualified. In the Czech Republic [2], a few ancient buildings with masonry structures near the metro line were fractured by train-induced vibrations, and even collapsed due to the continuous
expansion of the cracks. The development of effective methods of vibration isolation is a significant measure for the prevention and control of vibration pollution from the subway moving loads. Starting from the late 1990s, various vibration mitigation solutions emerged as a focus for much of the literature. Using a 2D profile mathematical model, Yang et al. [3] investigated the effectiveness of three different wave barriers, i.e., the open trench, in-filled trench, and elastic foundation, to reduce the ground vibrations caused by trains. Aimed at mitigating the low-frequency vibrations from a train viaduct, Takemiya [4] developed an innovative honeycomb wave impeding barrier. Then, Sheng et al. [5] further researched its damping effect based on Takemiya’s work and built structures in the track direction. With et al. [6] built a lime-cement columns and a noise-embankment barrier to reduce the ground-borne vibrations inside nearby buildings. On the scattering of Rayleigh waves, Gao et al. [7] and Cao et al. [8] have devoted to this subject of vibration reduction and made some work. A theoretical research by
* Corresponding author. College of Civil Engineering and Architecture, Shandong University of Science and Technology, Qingdao, 266590, China. Tel.: þ8653286057646. E-mail addresses: [email protected] (M. Gao), [email protected] (X. Xu), [email protected] (Q.S. Chen), [email protected] (Y. Wang). https://doi.org/10.1016/j.soildyn.2019.105913 Received 23 July 2019; Received in revised form 22 September 2019; Accepted 21 October 2019 Available online 1 November 2019 0267-7261/© 2019 Elsevier Ltd. All rights reserved.
M. Gao et al.
Soil Dynamics and Earthquake Engineering 129 (2020) 105913
Francois et al. [9] showed that a higher isolation performance could have been achieved using a concrete isolating screen. In addition, Jones et al. [10] and Coulier et al. [11] investigated the efficiency of reducing the surface-propagating vibration from trains using earthworks next to the track. However, most of the previous methods of isolation vibration, as mentioned above, have certain applicable conditions and limitations for metro vibration reduction. For instance, the open and filled trenches are limited by the stability of groundwater and surrounding rock in the tunnel. The earthworks next to the track such as the concrete isolating screen will affect the width of the tunnel, resulting in high cost. Duxseal, a viscoelastic material, has been validated by the actual recordings by the Pak et al. [12]. Herein proposed, as a promising vibration mitigation measure, is an arrangement of Duxseal–cement columns with honey comb configurations in the horizontal plan view. Considering this, the present work attempts to establish the vibration reduction effectiveness of honeycomb Duxseal–cement columns on a rocky foundation through in-situ measurements together with Tromino, a vibration meter from Italy. First, experimental investigations were conducted at the Qingdao Metro Line 13 test site. The vibration responses were recorded in all three component directions and the vibration characteristics generated by the metro filling and non-filling Duxseal–cement columns were compared. In addition to the general vibration responses, the differential characteristics of the one-third octave band spectrum and vibration level were investigated, respectively. A key aim of this paper is to provide a series of vibration records that researchers can use for further investi gation and for the validation of numerical prediction models. The results obtained are of great significance to the study of subway vibration reduction.
Liqun station were monitored by the Tromino to evaluate the effec tiveness of honeycomb Duxseal–cement columns on the metro vibration reduction method. Tromino was arranged on the ballast approximately 2 m away from the track (see Fig. 2). 2.3. General remarks The test data could be saved and uploaded by the storage system of the vibration meter; the time history curves of the vibration accelera tions in the X-, Y-, and Z-directions of the May Fourth Square station, before and after addition of the damping material, the honeycomb Duxseal–cement columns, were then depicted by the drawing software ORIGIN, as shown in Figs. 3–5, respectively. By performing Fourier transform on the monitoring data, the spectrum curves of the vibration accelerations corresponding to Figs. 3–5 were obtained, as shown in Figs. 6–8, respectively. From Figs. 3–5, it is primarily observed that the vibration accelera tions in the X-, Y-, and Z-directions of the Liqun station are all greater than that of the applied honeycomb Duxseal–cement columns, although the acceleration trends are similar between application and nonapplication of the Duxseal–cement column; specified as follows. The maximum acceleration in the X-direction of the Liqun station was 3.3 � 10-2 m/s2, which is much larger than that after the damping vi bration with 2.2 � 10-2 m/s2. Similarly, the maximum accelerations in the Y- and Z-directions were 3.2 � 10-2 m/s2 and 4.0 � 10-2 m/s2, respectively, which are much greater than those using the damping material with 2.3 � 10-2 m/s2 and 2.4 � 10-2 m/s2, respectively. The honeycomb Duxseal–cement column presence in the metros decreases their vibration accelerations in three directions; the X-, Y-, and Z-di rections are reduced by 33%, 28%, and 40%, respectively, compared with the original. That is, an impressive reduction in the vibration ac celerations of all directions owing to the Duxseal–cement columns was observed. The diffusion of energy and the ability of the media to absorb vibrations surrounding the subway line are the main factors that affect the ground vibration subjected to a subway loading. For the same con ditions of the energy of the vibration source and the monitoring site, the energy diffusion with Duxseal is identical to that without Duxseal. For the absorption of the vibration energy, the characteristics of the sur rounding medium are closely related to it; that is, the materials of the reducible vibration have an effect on the attenuation of the vibration propagation. This indicates that the use of the honeycomb Duxseal–ce ment column led to a significant reduction of the Qingdao metro vi bration regarding its wave absorption capability. Figs. 6–8 present the spectrum curves for vibrations of the Liqun station in Qingdao, with and without damping materials, as a result of subway loading, respectively. A comparison shows that the main fre quencies move forward with the application of the honeycomb Dux seal–cement column for any direction. That is, the main frequencies in this context are much smaller than those without the Duxseal–cement columns. It must be emphasized that, for the vibration accelerations of
2. Project overview and floor vibration tests 2.1. Test details In this study, the exits of the metro depots at Liqun station of Qingdao Metro Line 13, the most representative site, were selected to perform the vibration measurements. A honeycomb Duxseal-cement column arrangement was proposed and embedded into the appro priate depth of the foundation of Qingdao Metro Line 13 before the tunnel is construction (as shown in Fig. 1). The in-fill material is a Duxseal column, dedicated to absorbing energy and reducing the vi bration amplitudes across it. The material properties for the homoge nous Duxseal column are: the density ρ ¼ 1650 kg/m3, the Young’s module E ¼ 8MPa, the Poisson’s ratio v ¼ 0.46. The geometry of Duxseal-cement columns with honeycomb configurations is shown in Fig. 1. 2.2. Setup of monitoring point After Qingdao Metro Line 13 runs, the vibration data of the exit of
Fig. 1. Plane layout of Duxseal-cement columns. 2
M. Gao et al.
Soil Dynamics and Earthquake Engineering 129 (2020) 105913
Fig. 2. In-field deployment of monitoring point: (a) Site layout; (b) Optimized sketch.
Fig. 3. Time history curves of vibration acceleration in X-direction.
Fig. 4. Time history curves of vibration acceleration in Y-direction.
the Liqun station with the vibration damping material, both the hori zontal and vertical directions appear lower compared with the original. This is highly consistent with the above observations regarding the distinction of the vibration acceleration with and without the Dux seal–cement medium, as in Figs. 3–5. The main reason for this result is that the honeycomb Duxseal–Cement columns have a notable absorbed energy as well as reducing reflection in its material behavior (see Pak et al. [12]). The measured data again substantiates the need and usefulness of coupling the honeycomb Duxseal–Cement material with the metro. Furthermore, there appears to be a wider range of frequencies in both the horizontal and vertical directions where multiple dominant fre quencies exist. The main cause of this is that the soil of the Qingdao area is primarily granite. Compared with a soft soil foundation, the soil layers
of the Qingdao metro are unevenly distributed in the horizontal and vertical directions, with less damping parameters and larger dynamic shear moduli, resulting in a relatively small attenuation of medium- and high-frequency vibration energy. Therefore, it is of critical importance to select a mitigation material with an excellent damping capacity to highly mobilize the vibration damping capacity for the Qingdao metro. 3. Ground and floor vibration analysis and comparison To further evaluate the environmental vibration by the moving subway loads, the spectrum curves were transformed into one-third octave spectrum curves. On the basis of the literature [13], the one-third octave spectrum on each direction is plotted in Fig. 9. From Fig. 9(a), it is clear that the one-third octave spectrum of the Qingdao 3
M. Gao et al.
Soil Dynamics and Earthquake Engineering 129 (2020) 105913
Fig. 5. Time history curves of vibration acceleration in Z-direction.
Fig. 6. Spectrum curve of vibration acceleration in X-direction.
Fig. 7. Spectrum curve of vibration acceleration in Y-direction.
Fig. 8. Spectrum curve of vibration acceleration in Z-direction.
metro has two peaks at 40 Hz and 200 Hz. Meanwhile, the correspond ing maximum vibration acceleration of 1.70 � 10-3g along the Y-axis and 1.12 � 10-3g along the Z-axis were noted for the case with the
honeycomb Duxseal–Cement columns. From Fig. 9(b), the maximum vibration acceleration of the Qingdao metro without the honeycomb Duxseal–cement columns at 50 Hz is along the Y-direction, of 4
M. Gao et al.
Soil Dynamics and Earthquake Engineering 129 (2020) 105913
Fig. 9. One-third octave band of subway vibration (a) with Duxseal–cement columns and (b) without Duxseal–cement columns.
2.32 � 10-3g. At 250 Hz, the maximum along the Z-direction is 2.0 � 10-3g. The one-third octave spectrum, shown in Fig. 9, demon strates that the frequency corresponding to the peak acceleration is significantly reduced after the application of the Duxseal–cement col umns. More interestingly, the vibration accelerations of the Qingdao metro without the Duxseal–cement columns subjected to a moving load is substantially higher than that with the honeycomb Duxseal–cement columns (peak around 1.8 times in this research), which is identical to the results of the acceleration versus time data and the spectrum ana lyses. This agreement validates the inarguably dramatic impact of the honeycomb Duxseal–cement columns presence on the damping prop erties of the metro vibration. Fig. 10 depicts the average values for the frequency vibration levels of the Qingdao metro. These figures illustrate that the maximum vi bration levels appeared at the dominant frequencies, and the vibration levels for the Qingdao metro without the Duxseal–cement columns, subjected to a moving load, are evidently higher than that with the Duxseal–cement columns. It is further noticed that the vibration level without the vibration mitigation exceeded the environmental standard of China, while that with the mitigation material is slightly lower than the standard. The upper limits for the standard of the vertical vibration level in day and night are 75 dB and 72 dB in a common urban residential-commercial neighborhood, respectively, according to the Standard of Vibration in Urban Area Environmental (GB 10070-1988) in China. However, the maximum vibration level without a mitigation measure is nearly 90 dB, physically affecting passengers and surround ing residents badly. Therefore, it is efficient and inevitable to employ the honeycomb Duxseal–cement columns to alleviate and isolate the vi bration of the Qingdao metro.
Qingdao Metro for providing researchers with an available dataset for modelling validation, and to provide a new method for the metro to reduce ground vibration. The experiments consisted of ground vibration monitoring to assess the vibration reduction effect of the honeycomb Duxseal–cement columns and the vibration level due to subway passage. The analysis of the field results revealed that: (1) The vibration acceleration subjected to the moving loads of the Qingdao Metro Line 13 in the absence of the vibration damping material is evidently larger than that in the presence, peaking at 1.8 times. (2) The main frequencies move forward with the application of the honeycomb Duxseal–cement columns for any direction, i.e., an impressive decrease in the dominant frequencies in the Qingdao Metro due to the material presence was observed. (3) The vibration data detected proves that the honeycomb Dux seal–cement columns could reduce the vibration due to moving loads and has good absorption for vibrational reflection. The ef fect of the vibration-alleviation materials, i.e., the honeycomb Duxseal–cement columns, is practical and the material should be popularized among the field of metro. Declaration of competing interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “Reduction of metro vibrations by honeycomb columns under the ballast: field experiments”.
4. Conclusion Field experiments were undertaken at the Liqun station of the
Fig. 10. Average frequency vibration levels of subway vibration (a) with Duxseal-cement columns and (b) without Duxseal-cement columns. 5
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Soil Dynamics and Earthquake Engineering 129 (2020) 105913
Acknowledgements
[5] Sheng X, Jones CJC, Thompson DJ. Prediction of ground vibration from trains using the wavenumber finite and boundary element methods. J Sound Vib 2006; 293(3-5):575–86. [6] With C, Bahrekazemi M, Bodare A. Wave barrier of lime-cement columns against train-induced ground-borne vibrations. Soil Dyn Earthq Eng 2009;29(6):1027–33. [7] Gao GY, Chen J, Gu X, et al. Numerical study on the active vibration isolation by wave impeding block in saturated soils under vertical loading. Soil Dyn Earthq Eng 2017;93:99–112. [8] Cao ZG, Cai YQ, Han Jie. Mitigation of ground vibration generated by high-speed trains on saturated poroelastic ground with under-sleeper pads. J Transport Eng 2014;140(1):12–22. [9] Francois S, Schevenels M, Thyssen B, et al. Design and efficiency of a vibration isolating screen in the soil. Soil Dyn Earthq Eng 2012;(39):113–27. [10] Jones CJC, Thompson DJ, Andreu-Medina JI. Initial theoretical study of reducing surface-propagating vibration from trains using earthworks close to the track. In: Proceedings of the Eighth international conference on structural dynamics. Leuven (Belgium): EURODYN; 2011. p. 684–91. 2011. [11] Coulier P, François S, Degrande G, et al. Subgrade stiffening next to the track as a wave impeding barrier for railway induced vibrations. Soil Dyn Earthq Eng 2013; 48(5):119–31. [12] Pak RYS, Mahdi S, Farzad A. Experimental synthesis of seismic horizontal free-field motion of soil in finite-domain simulations with absorbing boundary. Soil Dyn Earthq Eng 2011;31:1529–39. [13] Gao GY, Chen J, Yang J, et al. Field measurement and FE prediction of vibration reduction due to pile-raft foundation for high-tech workshop. Soil Dyn Earthq Eng 2017;101:264–8.
The research presented in this paper was supported by the Natural Science Foundation of China (No. 51808324) and Natural Science Foundation of Shandong Province (No. ZR201702160391). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.soildyn.2019.105913. References [1] Watts GR. Case studies of the effects of traffic induced vibrations on heritage buildings. Trrl. Res. Rep. 1988:1–22. [2] Bata M. Effects of buildings of vibrations caused by traffic. Build Sci 1971;6(4): 221–46. [3] Yang YB, Hung HH. A parametric study of wave barriers for reduction of traininduced vibrations. Int J Numer Methods Eng 1997;40(20):3729–47. [4] Takemiya H. Field vibration mitigation honeycomb WIB for pile foundations of a high-speed train viaduct. Soil Dyn Earthq Eng 2004;24(1):69–87.
6
Contents lists available at ScienceDirect
Soil Dynamics and Earthquake Engineering journal homepage: http://www.elsevier.com/locate/soildyn
Reduction of metro vibrations by honeycomb columns under the ballast: Field experiments M. Gao a, X. Xu a, Q.S. Chen b, Y. Wang a, * a
Shandong Province Key Laboratory of Civil Engineering & Disaster Prevention and Mitigation (College of Civil Engineering and Architecture), Shandong University of Science and Technology, Qingdao, 266590, China b Department of Civil and Environmental Engineering, National University of Singapore, No.21, Lower Kent Ridge Road, 119077, Singapore
A R T I C L E I N F O
A B S T R A C T
Keywords: Environmental vibration Vibration generated by metro Duxseal-cement columns Isolation effect One-third octave spectrum
Environmental vibrations induced by subway operation are harmful to human health and structures when they exceed a certain value. Therefore, effective measures should be taken to reduce the noise and vibration generated by the metro. Therefore, a method to reduce the vibration by the installation of honeycomb Duxseal-cement columns under the ballast is presented in this paper. A honeycomb Duxseal-cement column was embedded in the subgrade of Qingdao Metro Line 13. A field test to measure the vibration of Qingdao Metro Line 13 was conducted. In addition, the time history curve of the vibration acceleration was obtained by processing the data and a Fourier transform was conducted for the test data to obtain a corresponding frequency spectrum curve. The spectrum curve was then converted into the one-third octave spectrum. Finally, the average value of the fre quency vibration levels was determined. The comparison between the vibration generated by the metro filling and non-filling Duxseal-cement columns was investigated in detail. The test results show that the subgrade of metro in-filled by the Duxseal-cement columns obtains a better isolation effect than that of non-filling Duxsealcement columns. The honeycomb Duxseal-cement columns present in the metros decrease their vibration ac celerations in three directions, the X-, Y-, and Z-directions, by 33%, 28%, and 40%, respectively, compared with the original.
1. Introduction In recent decades, urban subway traffic construction around the world has been vigorous. While urban subway traffic alleviates traffic congestion and improves resident travel conditions, the problem of environmental vibration generated by subway operation has become increasingly intense and frequent. For example, the noise and vibration due to the subway moving loads influence the normal performances of L’Opera de la Bastille [1] when the Paris Metro Line No.7 and No.13 passed its opera house. When the Beijing Subway DAXING Line passed through the Qingdao Jiayuan Community, there was an evident sense of shock in nearby high-rise buildings for 5 s, which caused the serious misplacement of furniture. Owing to the passing subway in Shenzhen, 30% of the electronic devices produced by an electronic chip factory were unqualified. In the Czech Republic [2], a few ancient buildings with masonry structures near the metro line were fractured by train-induced vibrations, and even collapsed due to the continuous
expansion of the cracks. The development of effective methods of vibration isolation is a significant measure for the prevention and control of vibration pollution from the subway moving loads. Starting from the late 1990s, various vibration mitigation solutions emerged as a focus for much of the literature. Using a 2D profile mathematical model, Yang et al. [3] investigated the effectiveness of three different wave barriers, i.e., the open trench, in-filled trench, and elastic foundation, to reduce the ground vibrations caused by trains. Aimed at mitigating the low-frequency vibrations from a train viaduct, Takemiya [4] developed an innovative honeycomb wave impeding barrier. Then, Sheng et al. [5] further researched its damping effect based on Takemiya’s work and built structures in the track direction. With et al. [6] built a lime-cement columns and a noise-embankment barrier to reduce the ground-borne vibrations inside nearby buildings. On the scattering of Rayleigh waves, Gao et al. [7] and Cao et al. [8] have devoted to this subject of vibration reduction and made some work. A theoretical research by
* Corresponding author. College of Civil Engineering and Architecture, Shandong University of Science and Technology, Qingdao, 266590, China. Tel.: þ8653286057646. E-mail addresses: [email protected] (M. Gao), [email protected] (X. Xu), [email protected] (Q.S. Chen), [email protected] (Y. Wang). https://doi.org/10.1016/j.soildyn.2019.105913 Received 23 July 2019; Received in revised form 22 September 2019; Accepted 21 October 2019 Available online 1 November 2019 0267-7261/© 2019 Elsevier Ltd. All rights reserved.
M. Gao et al.
Soil Dynamics and Earthquake Engineering 129 (2020) 105913
Francois et al. [9] showed that a higher isolation performance could have been achieved using a concrete isolating screen. In addition, Jones et al. [10] and Coulier et al. [11] investigated the efficiency of reducing the surface-propagating vibration from trains using earthworks next to the track. However, most of the previous methods of isolation vibration, as mentioned above, have certain applicable conditions and limitations for metro vibration reduction. For instance, the open and filled trenches are limited by the stability of groundwater and surrounding rock in the tunnel. The earthworks next to the track such as the concrete isolating screen will affect the width of the tunnel, resulting in high cost. Duxseal, a viscoelastic material, has been validated by the actual recordings by the Pak et al. [12]. Herein proposed, as a promising vibration mitigation measure, is an arrangement of Duxseal–cement columns with honey comb configurations in the horizontal plan view. Considering this, the present work attempts to establish the vibration reduction effectiveness of honeycomb Duxseal–cement columns on a rocky foundation through in-situ measurements together with Tromino, a vibration meter from Italy. First, experimental investigations were conducted at the Qingdao Metro Line 13 test site. The vibration responses were recorded in all three component directions and the vibration characteristics generated by the metro filling and non-filling Duxseal–cement columns were compared. In addition to the general vibration responses, the differential characteristics of the one-third octave band spectrum and vibration level were investigated, respectively. A key aim of this paper is to provide a series of vibration records that researchers can use for further investi gation and for the validation of numerical prediction models. The results obtained are of great significance to the study of subway vibration reduction.
Liqun station were monitored by the Tromino to evaluate the effec tiveness of honeycomb Duxseal–cement columns on the metro vibration reduction method. Tromino was arranged on the ballast approximately 2 m away from the track (see Fig. 2). 2.3. General remarks The test data could be saved and uploaded by the storage system of the vibration meter; the time history curves of the vibration accelera tions in the X-, Y-, and Z-directions of the May Fourth Square station, before and after addition of the damping material, the honeycomb Duxseal–cement columns, were then depicted by the drawing software ORIGIN, as shown in Figs. 3–5, respectively. By performing Fourier transform on the monitoring data, the spectrum curves of the vibration accelerations corresponding to Figs. 3–5 were obtained, as shown in Figs. 6–8, respectively. From Figs. 3–5, it is primarily observed that the vibration accelera tions in the X-, Y-, and Z-directions of the Liqun station are all greater than that of the applied honeycomb Duxseal–cement columns, although the acceleration trends are similar between application and nonapplication of the Duxseal–cement column; specified as follows. The maximum acceleration in the X-direction of the Liqun station was 3.3 � 10-2 m/s2, which is much larger than that after the damping vi bration with 2.2 � 10-2 m/s2. Similarly, the maximum accelerations in the Y- and Z-directions were 3.2 � 10-2 m/s2 and 4.0 � 10-2 m/s2, respectively, which are much greater than those using the damping material with 2.3 � 10-2 m/s2 and 2.4 � 10-2 m/s2, respectively. The honeycomb Duxseal–cement column presence in the metros decreases their vibration accelerations in three directions; the X-, Y-, and Z-di rections are reduced by 33%, 28%, and 40%, respectively, compared with the original. That is, an impressive reduction in the vibration ac celerations of all directions owing to the Duxseal–cement columns was observed. The diffusion of energy and the ability of the media to absorb vibrations surrounding the subway line are the main factors that affect the ground vibration subjected to a subway loading. For the same con ditions of the energy of the vibration source and the monitoring site, the energy diffusion with Duxseal is identical to that without Duxseal. For the absorption of the vibration energy, the characteristics of the sur rounding medium are closely related to it; that is, the materials of the reducible vibration have an effect on the attenuation of the vibration propagation. This indicates that the use of the honeycomb Duxseal–ce ment column led to a significant reduction of the Qingdao metro vi bration regarding its wave absorption capability. Figs. 6–8 present the spectrum curves for vibrations of the Liqun station in Qingdao, with and without damping materials, as a result of subway loading, respectively. A comparison shows that the main fre quencies move forward with the application of the honeycomb Dux seal–cement column for any direction. That is, the main frequencies in this context are much smaller than those without the Duxseal–cement columns. It must be emphasized that, for the vibration accelerations of
2. Project overview and floor vibration tests 2.1. Test details In this study, the exits of the metro depots at Liqun station of Qingdao Metro Line 13, the most representative site, were selected to perform the vibration measurements. A honeycomb Duxseal-cement column arrangement was proposed and embedded into the appro priate depth of the foundation of Qingdao Metro Line 13 before the tunnel is construction (as shown in Fig. 1). The in-fill material is a Duxseal column, dedicated to absorbing energy and reducing the vi bration amplitudes across it. The material properties for the homoge nous Duxseal column are: the density ρ ¼ 1650 kg/m3, the Young’s module E ¼ 8MPa, the Poisson’s ratio v ¼ 0.46. The geometry of Duxseal-cement columns with honeycomb configurations is shown in Fig. 1. 2.2. Setup of monitoring point After Qingdao Metro Line 13 runs, the vibration data of the exit of
Fig. 1. Plane layout of Duxseal-cement columns. 2
M. Gao et al.
Soil Dynamics and Earthquake Engineering 129 (2020) 105913
Fig. 2. In-field deployment of monitoring point: (a) Site layout; (b) Optimized sketch.
Fig. 3. Time history curves of vibration acceleration in X-direction.
Fig. 4. Time history curves of vibration acceleration in Y-direction.
the Liqun station with the vibration damping material, both the hori zontal and vertical directions appear lower compared with the original. This is highly consistent with the above observations regarding the distinction of the vibration acceleration with and without the Dux seal–cement medium, as in Figs. 3–5. The main reason for this result is that the honeycomb Duxseal–Cement columns have a notable absorbed energy as well as reducing reflection in its material behavior (see Pak et al. [12]). The measured data again substantiates the need and usefulness of coupling the honeycomb Duxseal–Cement material with the metro. Furthermore, there appears to be a wider range of frequencies in both the horizontal and vertical directions where multiple dominant fre quencies exist. The main cause of this is that the soil of the Qingdao area is primarily granite. Compared with a soft soil foundation, the soil layers
of the Qingdao metro are unevenly distributed in the horizontal and vertical directions, with less damping parameters and larger dynamic shear moduli, resulting in a relatively small attenuation of medium- and high-frequency vibration energy. Therefore, it is of critical importance to select a mitigation material with an excellent damping capacity to highly mobilize the vibration damping capacity for the Qingdao metro. 3. Ground and floor vibration analysis and comparison To further evaluate the environmental vibration by the moving subway loads, the spectrum curves were transformed into one-third octave spectrum curves. On the basis of the literature [13], the one-third octave spectrum on each direction is plotted in Fig. 9. From Fig. 9(a), it is clear that the one-third octave spectrum of the Qingdao 3
M. Gao et al.
Soil Dynamics and Earthquake Engineering 129 (2020) 105913
Fig. 5. Time history curves of vibration acceleration in Z-direction.
Fig. 6. Spectrum curve of vibration acceleration in X-direction.
Fig. 7. Spectrum curve of vibration acceleration in Y-direction.
Fig. 8. Spectrum curve of vibration acceleration in Z-direction.
metro has two peaks at 40 Hz and 200 Hz. Meanwhile, the correspond ing maximum vibration acceleration of 1.70 � 10-3g along the Y-axis and 1.12 � 10-3g along the Z-axis were noted for the case with the
honeycomb Duxseal–Cement columns. From Fig. 9(b), the maximum vibration acceleration of the Qingdao metro without the honeycomb Duxseal–cement columns at 50 Hz is along the Y-direction, of 4
M. Gao et al.
Soil Dynamics and Earthquake Engineering 129 (2020) 105913
Fig. 9. One-third octave band of subway vibration (a) with Duxseal–cement columns and (b) without Duxseal–cement columns.
2.32 � 10-3g. At 250 Hz, the maximum along the Z-direction is 2.0 � 10-3g. The one-third octave spectrum, shown in Fig. 9, demon strates that the frequency corresponding to the peak acceleration is significantly reduced after the application of the Duxseal–cement col umns. More interestingly, the vibration accelerations of the Qingdao metro without the Duxseal–cement columns subjected to a moving load is substantially higher than that with the honeycomb Duxseal–cement columns (peak around 1.8 times in this research), which is identical to the results of the acceleration versus time data and the spectrum ana lyses. This agreement validates the inarguably dramatic impact of the honeycomb Duxseal–cement columns presence on the damping prop erties of the metro vibration. Fig. 10 depicts the average values for the frequency vibration levels of the Qingdao metro. These figures illustrate that the maximum vi bration levels appeared at the dominant frequencies, and the vibration levels for the Qingdao metro without the Duxseal–cement columns, subjected to a moving load, are evidently higher than that with the Duxseal–cement columns. It is further noticed that the vibration level without the vibration mitigation exceeded the environmental standard of China, while that with the mitigation material is slightly lower than the standard. The upper limits for the standard of the vertical vibration level in day and night are 75 dB and 72 dB in a common urban residential-commercial neighborhood, respectively, according to the Standard of Vibration in Urban Area Environmental (GB 10070-1988) in China. However, the maximum vibration level without a mitigation measure is nearly 90 dB, physically affecting passengers and surround ing residents badly. Therefore, it is efficient and inevitable to employ the honeycomb Duxseal–cement columns to alleviate and isolate the vi bration of the Qingdao metro.
Qingdao Metro for providing researchers with an available dataset for modelling validation, and to provide a new method for the metro to reduce ground vibration. The experiments consisted of ground vibration monitoring to assess the vibration reduction effect of the honeycomb Duxseal–cement columns and the vibration level due to subway passage. The analysis of the field results revealed that: (1) The vibration acceleration subjected to the moving loads of the Qingdao Metro Line 13 in the absence of the vibration damping material is evidently larger than that in the presence, peaking at 1.8 times. (2) The main frequencies move forward with the application of the honeycomb Duxseal–cement columns for any direction, i.e., an impressive decrease in the dominant frequencies in the Qingdao Metro due to the material presence was observed. (3) The vibration data detected proves that the honeycomb Dux seal–cement columns could reduce the vibration due to moving loads and has good absorption for vibrational reflection. The ef fect of the vibration-alleviation materials, i.e., the honeycomb Duxseal–cement columns, is practical and the material should be popularized among the field of metro. Declaration of competing interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “Reduction of metro vibrations by honeycomb columns under the ballast: field experiments”.
4. Conclusion Field experiments were undertaken at the Liqun station of the
Fig. 10. Average frequency vibration levels of subway vibration (a) with Duxseal-cement columns and (b) without Duxseal-cement columns. 5
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Soil Dynamics and Earthquake Engineering 129 (2020) 105913
Acknowledgements
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