3.1. Time domain analysis
From
Figure 10, it can be seen that the vertical vibration acceleration at the measurement points on the third floor of the Leisure Centre is much greater than the horizontal one, which is consistent with the findings of previous studies; while the difference between the horizontal and vertical vibration acceleration on the first and first floors is slightly smaller than that on the third floor. Comparing the acceleration time curves of the measurement points at the third level, it can be seen that the vibration acceleration in the slab is greater compared to the measurement points next to the columns, and the vertical vibration acceleration can reach 0.05m/s2.
The vibration duration of the underground in the throat area is about 25s, and the underground uses a 6-part B-type train. The operating speed of the underground train when passing through the test section can be deduced from the train length and passage time to be about 16km/h. Overall, the vibration intensity caused by the underground operation is greater than the background vibration.
From the acceleration time curve of the third floor column measurement point, we can see that the train shows a certain loading and unloading process when passing near the measurement point: when the first carriage is still some distance away from the measurement point, the loading process starts and the acceleration gradually increases; when the first carriage reaches a position closer to the measurement point, the loading process ends and the acceleration starts to stabilise; when the last carriage passes the building, the unloading process starts and the acceleration gradually decreases; when the last carriage passes the building, the acceleration gradually decreases. When the last carriage passes the building, the unloading process starts and the acceleration gradually decreases; when the last carriage leaves a certain distance, the unloading process ends.
According to the data obtained from the same column on the first, second and third floors, the acceleration of vibration caused by the operation of the metro train increases with the increase of the floor height, and the increase in the vertical direction is about 0.002 m/s2 per floor.
Looking at the vertical acceleration time curve in
Figure 10b, it can be seen that the acceleration values at measurement points K3, K4 and K5 and K6 (8.5m from the track), which are closer to the track where the metro is running, are slightly larger than those at K7 and K8 (18.9 m from the track), which are slightly further away from the track, and the peaks of loading and unloading are more obvious when the wheels are in contact with the track. This shows that the vibration caused by the operation of the metro train attenuates with the increase of distance in the process of propagation, reflecting a certain law of vibration propagation, which should be related to the geological structure of the soil layer, the driving characteristics of the metro train and other influencing factors.
The section 2 is at a certain distance from the track and is slightly less affected by vibrations than section 1. However, due to the high number of layers in this section, it is possible to study the propagation and variation of vibration due to train operation along the layer height direction. From
Figure 11, it can be seen that the duration of vibration in the throat area and the access line is about 20s, which can be inferred from the train running speed of 20.5km/h.
As can be seen from
Figure 11a, the vibration acceleration in the horizontal direction is within the range of -0.0015~0.0015m/s2 and tends to decrease with the increase of storey height. 1, 2 and 4 storeys do not differ significantly in vibration acceleration, and the vibration acceleration obtained from the measurement points at 13 storeys and above gradually decreases to two-thirds of that at 1 storey. Comparing
Figure 11b, the vibration in the vertical direction is much greater than that in the horizontal direction, in the range of -0.008~0.008 m/s2, similar in the horizontal direction, and tends to decrease with the increase of storey height, and the wave crest generated by the wheel is more obvious than that in the horizontal direction.
The vibration peaks at the middle floors, such as the 10th and 13th floors, are more obvious than those at the other floors. 1 floor is connected to the cover, so the vibration is relatively large.
As can be seen from
Figure 12, the section 3 times course curve is similar to the pattern reflected in the first two sections, with the train passing for approximately 30 seconds, inverse to the train speed of 13.68 km/h. As the train is running at a slower speed than the first two sections, it is easier to identify the 12 wave peaks generated by the front and rear wheels.
Comparing the horizontal and vertical vibration acceleration values reveals that the building is more affected by vertical vibration. The acceleration of vertical vibration at the same measurement point is generally greater than that in the horizontal direction by more than 0.005 m/s2. In the analysis of the vibration propagation law, vertical vibration is the main focus. Comparing the data from the measured points in the ground floor slab of the kindergarten with the data from the bottom of the column, the results are similar to those obtained in the Leisure Centre, where the vibration acceleration in the slab is greater than that in the column.
Near and far track room measurement points Y4, Y3 data compared, after nearly 6m of decay, can be seen from the track farther away from the measurement point Y3, the recorded vibration acceleration value than Y4 slightly smaller than 0.005 m/s2; with the increase in floor height, observation of different floors near the track at the room measurement points Y4, Y6, can be seen compared to the first floor vibration acceleration value has increased, the peak value is about one floor measured acceleration value The peak value is about twice the acceleration value measured on the first floor, close to 0.06 m/s2.
As can be seen from
Figure 13, the vibration in section 4 is also induced by the train running into the parking garage, the speed of the train is lower, the operation is smoother, the vibration induced is smaller, and the crest generated by the wheel-rail contact is not obvious; the horizontal vibration acceleration range is -0.0008-0.0008m/s2; the vertical acceleration is -0.005-0.005 m/s2; it can be seen that the vertical vibration acceleration is still much larger than the horizontal.
Comparing the ground floor measurement point G1 in section 2 with the two measurement points in this section, it can be seen that the vibration acceleration values differ at different speeds.
The speed of the train in section 2 is about 20.52 km/h, which is more than twice the speed of the train measured in section 4, causing a horizontal vibration acceleration in the range of -0.0015-0.0015 m/s2 and a vertical acceleration of -0.006-0.006 m/s2; it can be seen that as the speed of the train increases, the horizontal and vertical vibration acceleration increases, and due to the operation of the train The vertical vibration is much larger than the horizontal one, so the growth of vertical vibration is more significant.
As can be seen from
Figure 14, the section 5 times curve train passage time is approximately 32 seconds and the train speed is approximately 14 km/h, which is in line with the range of train operating speeds in the throat area and easily identifies the wave crests generated by the front and rear wheels. The vertical acceleration values are then in the range of -0.08 to 0.08 m/s2, with a peak acceleration of 0.077 m/s2.
The distance between the measurement point and the nearest track is known to be 5 m. Comparing the second level kindergarten measurement point Y6 in section 3, which is 15.6 m from the track, it is found that after about 10m of attenuation, the vertical acceleration of the vibration due to the operation of the metro train attenuates by about 0.02 m/s2. It can be seen that as the distance to the source increases, a corresponding attenuation of vibration occurs in the process.
3.2. Frequency domain analysis
In order to study in depth the frequency structure of the vibration triggered by the operation of the train in the vehicle section, reveal the vibration signal each frequency composition and the size of each frequency component, the measured time course data is fast Fourier transformed to obtain the vibration spectrum.
Figure 15 shows the spectrum corresponding to the time-domain graph of the car.
The horizontal ground vibration acceleration spectrum response band width in the 0-140Hz are distributed, the peak frequency band is mainly concentrated in the vicinity of 40-60 Hz; vertical band width is slightly narrower than the horizontal direction, distributed in the 0-120 Hz, the dominant frequency band is 40-60 Hz, the frequency band of the measurement point in the plate is mainly distributed in the 0-80 Hz, slightly narrower than the band width of the measurement point next to the column.
Comparing the measurement points K5 and K6, which are 8.5 m away from the track centre line, with the measurement points K7 and K8, which are 18.9 m apart, it is found that the vibration amplitude in the main response band of 20-60 Hz decreases as the distance from the track increases.
Looking at the frequency bands of the points in the plate and the points next to the column, it can be seen that the points next to the column have a peak vibration amplitude in the low frequency band around 10 Hz.
Similar to section 1, the measured acceleration time range of section 2 was fast Fourier transformed to obtain the corresponding Fourier spectrum,
Figure 16 shows the acceleration spectrum of a measured vehicle vibration at each measurement point.
From
Figure 16 can be seen, and section 1 is different, section 2 horizontal vibration response band width distribution is wider, covering 0-200 Hz, the main vibration frequency is not the same, there are high frequency components, in addition to the ground floor measurement point G1 location and vehicle section cover cover connected, the main frequency concentration in 40-60 Hz; the rest of the floor measurement point vibration frequency in the 40-120 Hz band near all There are peaks in the 40-120 Hz range. In the middle floors G13 and G16 there are large peaks in the low frequency region around 10 Hz.
In contrast, the response band width in the vertical direction is narrower and the peaks are more homogeneous. The vibration frequencies in the vertical direction are mainly concentrated in the low and medium frequencies from 20 to 60 Hz, with the peak condition generally occurring around 40 Hz. As the floor increases, the vibration frequency distribution gradually homogenises, the high frequency component decreases and the main frequency range is concentrated.
Figure 17 shows the horizontal direction of the ground floor measurement points Y1-Y4 vibration response band in the 0-120 Hz are distributed, the wave peak is mainly concentrated in the 20-60 Hz range, the wave peak more undulating; first floor measurement points of the frequency band distribution is significantly narrower, above 80 Hz high frequency significantly reduced, the peak in 40Hz and 60Hz near; and compare the first floor near the rail plate measurement point Y6 and the foot of the column measurement point Y5. It can be seen that the vibration amplitude in the plate is significantly greater than that in the foot of the column.
The acceleration spectrum in the vertical direction in
Figure 17b is also similar to that in the horizontal direction. The vibration response frequency band of the ground floor measurement points is distributed in the range of 0-160 Hz, and the vibration propagates vertically, and the high frequency component of the vibration decays after reaching the first floor. The vertical vibration amplitude peaks at 40 Hz, and the amplitude measured in the middle of the slab is much greater than that at the foot of the column.
In order to analyse the vibration attenuation pattern in the horizontal direction in the frequency domain, the spectra of Y3 and Y4 were compared. After the attenuation in the 6m range at ground level, as in the previous section, the high frequency component in the vibration response band of Y3 was reduced, and the vibration amplitude peak value was reduced. However, due to the limitation of the site area, the vibration propagation relationship at long distances (above 10 m) could not be further investigated.
The peak value of vibration amplitude is concentrated in the low frequency band near 0-20 Hz, and there are occasional small peaks in the middle and high frequency band of 80-100 Hz; the acceleration of vertical vibration is obviously reduced in the high frequency band, and the dominant frequency band and peak value are concentrated near 40 Hz, and the vibration amplitude is much larger than that in the horizontal direction, which proves that the train The vibration caused by the train is mainly in the vertical direction.
Compared with measurement point G1 in section 2, the peak amplitude of vibration response in the horizontal direction of measurement point G1 is around 50Hz, which belongs to the middle frequency band, indicating that the dominant frequency band of vibration generated by train operation at different speeds is different; the vibration amplitude of measurement point G1 is significantly larger than that of measurement point 4 in section; in the vertical direction, the dominant frequency of G1 is around 20-40Hz, and the vibration amplitude is significantly larger than that of measurement point 4 in section.
In order to facilitate the study of the frequency structure of the vibration triggered by the operation of the train in the vehicle section, the vibration signal is explored for each frequency component and the magnitude of each frequency component, and a fast Fourier transform is carried out on the measured time course data to obtain the vibration spectrum.
Figure 19 shows the spectrum corresponding to the time domain graph of this vehicle.
The vertical acceleration spectrum shows that within 5 m of the track in the throat area, the main frequency distribution of the vibration is in the low to medium frequency range of 20-60 Hz, with a peak in spectral amplitude near 40 Hz.