A pile foundation construction method for adjacent subway tunnel based on steel casing segmented replacement

Abstract

This invention discloses a construction method for adjacent subway tunnel pile foundations based on segmented replacement of steel casing, specifically relating to the technical field of guiding devices for pile foundation construction. It addresses the problem that existing guiding devices, being rigid structures, directly introduce the mechanical vibration of the casing into the surrounding strata, causing cyclic loads on adjacent shield tunnels. The method involves acquiring vibration acceleration signals at the interface between the casing and the guiding device using vibration sensors deployed on the guiding device, calculating the power spectral density, extracting the energy concentration within the half-power bandwidth of the first three natural frequencies of the tunnel lining structure as the resonant excitation potential, continuously sampling the resonant excitation potential and calculating the differential slope, and using the product of the differential slope and the current resonant excitation potential as a switching criterion to trigger the guiding device to switch from a rigid limiting state to a hysteretic damping energy absorption state. The method utilizes a built-in viscoelastic damping layer to dissipate the casing vibration energy and block the transmission of vibration to the surrounding strata via the guiding device.

Description

Technical Field

[0001] This invention relates to the field of guiding devices for pile foundation construction, and more specifically, to a method for pile foundation construction of adjacent subway tunnels based on segmented replacement of steel casing. Background Technology

[0002] When constructing pile foundations in areas adjacent to subway tunnels, a segmented replacement process with full casing is typically used to avoid borehole collapse and control disturbance to the tunnel boring machine (TBM) structure. During construction, steel casing sections are lowered to the design depth, grouted, and then pulled out in segments. To ensure the verticality of the casing and the alignment accuracy when connecting upper and lower segments, guiding devices, such as guide frames or guide hoops, are installed at the borehole opening and inside the borehole. These devices fit tightly with the outer wall of the casing, serving to limit and guide movement. The structural design of these guiding devices primarily focuses on lateral constraint and positioning under static conditions.

[0003] Existing guiding devices are mostly rigid structures. While they can maintain the geometric posture of the casing when transmitting jacking or downward pressure, they directly couple the mechanical vibrations generated by the jacking equipment during the segment replacement process to the outer wall of the casing. These vibrations are then introduced into the surrounding strata through the outer annular gap or contact surface of the casing. The micro-movement of the soil caused by this vibration will apply additional cyclic loads to the adjacent shield tunnel, causing changes in the stress state of the tunnel segment joints or lining, thus leaving hidden dangers for the long-term stability and operational safety of the tunnel structure. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, the present invention provides a construction method for adjacent subway tunnel pile foundation based on segmental replacement of steel casing to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A construction method for pile foundations of adjacent subway tunnels based on segmented replacement of steel casing includes the following steps:

[0007] S1: During the segmented replacement of the steel casing, vibration acceleration signals at the contact interface between the steel casing and the guide device are obtained by vibration sensors installed on the guide device.

[0008] S2: Perform power spectral density analysis on the vibration acceleration signal to obtain the power spectral density curve reflecting the frequency domain distribution of vibration energy;

[0009] S3: Extract the integral values ​​of the power spectral density within the half-power bandwidth of the first three natural frequencies of the adjacent subway shield tunnel lining structure from the power spectral density curve, and calculate the ratio of the sum of the integral values ​​of each order to the total power of the whole frequency band as the resonant excitation potential.

[0010] S4: Continuously sample the resonant excitation potential, calculate the differential slope of the resonant excitation potential in adjacent sampling windows, and when the product of the differential slope and the current resonant excitation potential reaches the preset switching sensitivity coefficient, output a switching command to the built-in electronically controlled damping adjustment unit of the guide device, so that the guide device is converted from the rigid limit state to the hysteretic damping energy absorption state.

[0011] S5: Under hysteretic damping energy absorption, the viscoelastic damping layer built into the guide device dissipates the vibration energy of the steel casing, blocking the transmission of vibration to the surrounding formation through the guide device.

[0012] Furthermore, during the segmented replacement of the steel casing, vibration acceleration signals at the contact interface between the steel casing and the guide device are acquired using vibration sensors installed on the guide device, including:

[0013] The vibration sensors deployed on the guide device are arranged in a multi-point contact manner. Each vibration sensor is arranged circumferentially at intervals on the annular contact surface between the guide device and the outer wall of the steel casing. The vibration acceleration components along the radial and tangential directions of the guide device are collected synchronously at each contact point. The radial and tangential vibration acceleration components collected by all vibration sensors are vector synthesized to obtain the vibration acceleration signal at the contact interface between the steel casing and the guide device.

[0014] Furthermore, the vibration sensors deployed on the guide device are arranged in a multi-point contact manner, including: the number of vibration sensors deployed on the annular contact surface between the guide device and the outer wall of the steel casing is not less than the minimum number required for circumferential arrangement, so that the central angle corresponding to the arc length between two adjacent vibration sensors is less than or equal to the central angle corresponding to the preset contact sensing resolution.

[0015] Furthermore, power spectral density analysis is performed on the vibration acceleration signal to obtain a power spectral density curve reflecting the frequency domain distribution of vibration energy, including:

[0016] After applying anti-aliasing filtering to the vibration acceleration signal, an analysis window is extracted at a preset sampling frequency. A window function is applied to the vibration acceleration signal within the analysis window, and a fast Fourier transform is performed to obtain a complex spectrum. The amplitude of each frequency point in the complex spectrum is squared and divided by the frequency resolution to obtain a power spectral density curve with frequency as the abscissa and power spectral density as the ordinate.

[0017] Furthermore, the window function applied to the vibration acceleration signal within the analysis window is the Hanning window.

[0018] Furthermore, the integral values ​​of the power spectral density within the half-power bandwidth of the first three natural frequencies of the adjacent subway shield tunnel lining structure are extracted from the power spectral density curve. The ratio of the sum of the integral values ​​of each order to the total power of the entire frequency band is calculated as the resonant excitation potential, including:

[0019] The power spectral density curve is smoothed by moving average to obtain a smoothed power spectral density curve. On the smoothed power spectral density curve, the spectral peaks corresponding to the first three natural frequencies of the adjacent subway shield tunnel lining structure are identified. With each spectral peak as the center, the frequency points where the power spectral density value drops to half the amplitude of the spectral peak are found in the low-frequency and high-frequency directions as the lower limit frequency and upper limit frequency of the half-power bandwidth. The half-power bandwidth interval of each order is numerically integrated on the power spectral density curve to obtain the integral value of each order. The power spectral density curve is numerically integrated over the entire frequency band to obtain the total power of the entire frequency band. The sum of the integral values ​​of each order is divided by the total power of the entire frequency band to obtain the resonant excitation potential.

[0020] Furthermore, the power spectral density curve is smoothed by moving average, including: selecting a sliding window with an odd number of frequency points spanning and moving the power spectral density curve point by point; averaging the power spectral density values ​​of all frequency points within the sliding window in each move and replacing the power spectral density value of the center frequency point of the sliding window with this average value.

[0021] Furthermore, the resonant excitation potential is continuously sampled, and the differential slope of the resonant excitation potential within adjacent sampling windows is calculated. When the product of the differential slope and the current resonant excitation potential reaches a preset switching sensitivity coefficient, a switching command is output to the electronically controlled damping adjustment unit built into the guide device, causing the guide device to switch from a rigid limiting state to a hysteretic damping energy absorption state, including:

[0022] A sampling sequence is formed by collecting resonant excitation potentials at fixed time steps. The resonant excitation potential of the current sampling window is subtracted from the resonant excitation potential of the previous sampling window to obtain the difference. The difference is divided by the time step to obtain the differential slope. The differential slope is multiplied by the resonant excitation potential of the current sampling window to obtain the product value. When the product value is greater than or equal to the preset switching sensitivity coefficient, a switching command is generated and sent to the electronically controlled damping adjustment unit built into the guide device to control the guide device to switch from the rigid limit state to the hysteretic damping energy absorption state.

[0023] Furthermore, the resonant excitation potential is collected at a fixed time step to form a sampling sequence, including: setting overlapping time periods between adjacent sampling windows so that the start time of the current sampling window is located inside the previous sampling window.

[0024] Furthermore, under hysteretic damping and energy absorption conditions, the viscoelastic damping layer built into the guide device dissipates the vibration energy of the steel casing, blocking the transmission of vibration to the surrounding formation via the guide device, including:

[0025] The viscoelastic damping layer built into the guide device is in contact with the outer wall of the steel casing under hysteretic damping energy absorption state. The viscoelastic damping layer converts the vibration energy transmitted from the steel casing to the guide device into heat energy through shear deformation, cutting off the transmission path of vibration energy from the guide device to the surrounding strata.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. By utilizing the integrated sensing and damping adjustment capabilities of the guiding device, the traditional rigid limiter is transformed into an energy-absorbing barrier that can actively switch according to vibration characteristics. By acquiring the vibration acceleration signal at the contact interface between the casing and the guiding device in real time and calculating the power spectral density, the energy concentration within the half-power bandwidth of the first three natural frequencies of the adjacent tunnel lining structure is extracted as the resonant excitation potential. This parameter can sensitively reflect the proportion of energy concentrated in the tunnel's sensitive frequency band during casing vibration. Furthermore, the resonant excitation potential is continuously sampled and the differential slope is calculated. The energy amplitude is multiplied by the trend of change to form a switching criterion. The state transition is triggered in the early stage of the accelerated rise of resonant energy, rather than waiting for the vibration amplitude to exceed the limit. Thus, intervention is completed before the disturbance is fully transmitted to the stratum, significantly reducing the risk of the tunnel structure bearing cyclic loads.

[0028] 2. Upon receiving the switching command, the guiding device transitions from a rigid limiting state to a hysteretic damping energy absorption state. The built-in viscoelastic damping layer adheres to the outer wall of the casing, irreversibly converting the mechanical vibration transmitted from the casing into heat energy dissipation through the shear hysteresis deformation of the viscoelastic material. This process is equivalent to inserting a high-energy-consuming link in the vibration transmission path, cutting off the rigid transmission of casing vibration to the surrounding strata via the guiding device. This transforms the previously almost unaffected elastic wave transmission into rapidly attenuating damped motion, effectively suppressing the micro-motion of the borehole wall soil and protecting the stress state of the adjacent subway shield tunnel segment joints and lining. The guiding device is upgraded from a positioning accessory to an active control node for track protection. Without changing the pile foundation construction process, the structural optimization and control strategy of the guiding device itself achieves safety assurance for the full casing segment replacement pile foundation construction in complex and sensitive areas. Attached Figure Description

[0029] Figure 1 This is a flowchart of a construction method for adjacent subway tunnel pile foundations based on segmented replacement of steel casing, according to the present invention.

[0030] Figure 2 This is a power spectral density curve of the present invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Example: Figure 1This invention presents a method for constructing pile foundations for adjacent subway tunnels based on segmented replacement of steel casings, comprising the following steps:

[0033] S1: During the segmented replacement of the steel casing, vibration acceleration signals at the contact interface between the steel casing and the guide device are obtained by vibration sensors installed on the guide device.

[0034] S2: Perform power spectral density analysis on the vibration acceleration signal to obtain the power spectral density curve reflecting the frequency domain distribution of vibration energy;

[0035] S3: Extract the integral values ​​of the power spectral density within the half-power bandwidth of the first three natural frequencies of the adjacent subway shield tunnel lining structure from the power spectral density curve, and calculate the ratio of the sum of the integral values ​​of each order to the total power of the whole frequency band as the resonant excitation potential.

[0036] S4: Continuously sample the resonant excitation potential, calculate the differential slope of the resonant excitation potential in adjacent sampling windows, and when the product of the differential slope and the current resonant excitation potential reaches the preset switching sensitivity coefficient, output a switching command to the built-in electronically controlled damping adjustment unit of the guide device, so that the guide device is converted from the rigid limit state to the hysteretic damping energy absorption state.

[0037] S5: Under hysteretic damping energy absorption, the viscoelastic damping layer built into the guide device dissipates the vibration energy of the steel casing, blocking the transmission of vibration to the surrounding formation through the guide device.

[0038] In the specific implementation of S1, during the segmented replacement of the steel casing, vibration acceleration signals at the contact interface between the steel casing and the guide device are acquired by vibration sensors deployed on the guide device. The guide device is located at the orifice, providing positioning and limiting for the segmented lowering and removal of the steel casing. The vibration sensors are fixedly installed on the body of the guide device. When the steel casing passes through the inner hole of the guide device, the sensing end of the vibration sensor makes contact with the outer wall of the steel casing. The vibration sensors deployed on the guide device adopt a multi-point contact arrangement, with each vibration sensor arranged circumferentially at intervals on the annular contact surface between the guide device and the outer wall of the steel casing. The annular contact surface refers to the circular area formed on the cross-section of the cylindrical mating surface between the inner wall of the guide device and the outer wall of the steel casing. The vibration sensors are sequentially deployed circumferentially along this annular area, maintaining an arc-length distance between adjacent vibration sensors, so that each vibration sensor can sense the vibration changes of the outer wall of the steel casing at different locations.

[0039] The number of vibration sensors arranged on the annular contact surface between the guide device and the outer wall of the steel casing is no less than the minimum number required for circumferential arrangement, ensuring that the central angle corresponding to the arc length between two adjacent vibration sensors is less than or equal to the central angle corresponding to the preset contact sensing resolution. The central angle corresponding to the contact sensing resolution is a preset angle value based on the diameter of the guide device's inner hole and the size of the vibration sensor's sensing end, used to ensure that two circumferentially adjacent vibration sensors can distinguish the vibration differences of the outer wall of the steel casing at different circumferential positions. For example, if the diameter of the guide device's inner hole is 1 meter and the diameter of the vibration sensor's sensing end is 10 millimeters, and the central angle corresponding to the contact sensing resolution is set to 2 degrees, then the number of vibration sensors arranged circumferentially on the annular contact surface is no less than 180, and the central angle corresponding to the arc length between two adjacent vibration sensors does not exceed 2 degrees. The central angle corresponding to the contact sensing resolution is determined by first measuring the circumferential length of the smallest possible local contact area between the outer wall of the steel casing and the inner hole of the guide device. This circumferential length is then converted into a central angle corresponding to the radius of the guide device's inner hole. The conversion method involves dividing the circumferential length by the radius of the guide device's inner hole in radians, then converting the resulting value to an angle. The calculated result is the central angle corresponding to the contact sensing resolution. The number of vibration sensors is calculated by inversely using the central angle corresponding to the contact sensing resolution and the full circumference angle of the annular contact surface. This inverse calculation involves dividing 360 degrees by the central angle corresponding to the contact sensing resolution and rounding up to ensure that at least one vibration sensor covers any arc segment on the annular contact surface whose length equals the circumferential length of the smallest local contact area.

[0040] The vibration acceleration components along the radial and tangential directions of the guide device are simultaneously acquired at each contact point. The vibration sensor is a biaxial sensor, with the two axes aligned with the radial and tangential directions of the guide device, respectively. The radial direction of the guide device refers to the straight line from the center of the cross-section of the guide device's inner bore to the outer edge of the bore wall. The tangential direction of the guide device refers to the direction perpendicular to the radial direction and extending along the tangent of the bore wall on the cross-section of the guide device's inner bore. At its respective contact point, each vibration sensor simultaneously records the radial and tangential vibration acceleration components. The radial vibration acceleration component reflects the radial impact strength of the steel casing at the contact point, while the tangential vibration acceleration component reflects the frictional and torsional load changes of the steel casing along the tangential direction of the bore wall. During the acquisition process, all vibration sensors are synchronously triggered by the same clock source to ensure strict time alignment of the radial and tangential vibration acceleration components at each contact point.

[0041] The radial and tangential vibration acceleration components collected by all vibration sensors are vector-synthesized to obtain the vibration acceleration signal at the contact interface between the steel casing and the guide device. The vector synthesis method involves combining the radial and tangential vibration acceleration components collected at the same contact point at each instant, using a parallelogram shape with a 90-degree angle between them. The amplitude of the synthesized vector is the synthesized vibration acceleration value at that contact point at that instant, and the direction of the synthesized vector is the principal vibration direction at that contact point at that instant. The synthesized vibration acceleration values ​​of all contact points at the same instant are sorted according to their circumferential position on the annular contact surface, forming an acceleration sequence representing the vibration state of the entire annular contact interface at that instant. This acceleration sequence is the vibration acceleration signal at the contact interface between the steel casing and the guide device. An acceleration sequence is generated at each sampling instant. Multiple acceleration sequences, as the sampling time progresses, constitute a time-series vibration acceleration signal for subsequent power spectral density analysis.

[0042] In the specific implementation of S2, power spectral density analysis is performed on the vibration acceleration signal at the contact interface between the steel casing and the guide device to obtain a power spectral density curve reflecting the frequency domain distribution of vibration energy. After obtaining the vibration acceleration signal at the contact interface between the steel casing and the guide device generated in S1, anti-aliasing filtering is first applied to the vibration acceleration signal. A low-pass filter is used for anti-aliasing filtering, with its cutoff frequency set to half of the preset sampling frequency to filter out high-frequency components in the vibration acceleration signal with frequencies higher than half of the preset sampling frequency, thus avoiding the influence of frequency aliasing on subsequent spectrum analysis. The preset sampling frequency is determined based on the vibration frequency range generated by the jacking equipment during the segmented replacement of the steel casing. The frequency components of the vibration acceleration signal during the segmented replacement of the steel casing are mainly distributed in the range of 0 Hz to 200 Hz, and the preset sampling frequency is set to no less than 400 Hz to meet the Nyquist sampling condition. A Butterworth low-pass filter is selected, with a filtering order of 4th order to balance the filtering attenuation rate and phase response characteristics.

[0043] After anti-aliasing filtering, a fixed-duration segment of the continuous vibration acceleration signal is extracted as an analysis window at a preset sampling frequency. The duration of the analysis window is determined based on the desired frequency resolution, which is defined as the frequency interval between two adjacent frequency points in the power spectral density curve. The frequency resolution is equal to 1 divided by the duration of the analysis window, and the unit of frequency resolution is Hertz (Hz). For example, when the desired frequency resolution is 1 Hz, the duration of the analysis window is set to 1 second. With a preset sampling frequency of, for example, 400 Hz, a 1-second analysis window contains 400 sampling points. The analysis window is extracted by tracing back one analysis window duration from the current acquisition time of the vibration acceleration signal and retrieving the corresponding sequence of sampling points.

[0044] The window function applied to the vibration acceleration signal within the analysis window is the Hanning window. The application process involves first generating a sequence of Hanning window function values ​​equal to the number of sampling points within the analysis window. The Hanning window function values ​​approach 0 at the beginning and end of the window, reaching their maximum value in the middle, forming an envelope shape that is high in the middle and low at both ends. Then, the vibration acceleration value of each sampling point within the analysis window is multiplied point-by-point by the corresponding function value in the Hanning window function value sequence to obtain the windowed vibration acceleration signal sequence. The amplitudes at both ends of the windowed vibration acceleration signal sequence are smoothly attenuated to near zero to suppress spectral leakage caused by truncating the analysis window.

[0045] A Fast Fourier Transform (FFT) is performed on the windowed vibration acceleration signal sequence to obtain a complex spectrum. The number of transform points in the FFT is the same as the number of sampling points in the windowed vibration acceleration signal sequence. The complex spectrum consists of a series of complex frequency components, each corresponding to a frequency point. The frequency value of a frequency point is determined by the number of transform points in the FFT and the preset sampling frequency. The frequency interval between adjacent frequency points is the frequency resolution. Each complex frequency component contains a real part and an imaginary part, and the amplitude at that frequency point is equal to the square root of the sum of the squares of the real and imaginary parts.

[0046] The power component value at each frequency point of the complex spectrum is obtained by squaring the amplitude. This power component value represents the power of the vibration acceleration signal at that frequency. Dividing the power component value by the frequency resolution yields the power spectral density value. The frequency resolution is the reciprocal of the analysis window duration. For example, when the analysis window duration is 1 second, the frequency resolution is 1 Hz. In this case, dividing the power component value by 1 Hz equals the power spectral density value. The unit of power spectral density is the square of the vibration acceleration unit per Hz. Plotting the power spectral density values ​​at each frequency point on a coordinate system with frequency as the x-axis and power spectral density as the y-axis, and connecting them forms the power spectral density curve. The power spectral density curve visually reflects the energy distribution of the vibration acceleration signal with frequency. A higher y-axis value indicates a more concentrated vibration energy at that frequency. This power spectral density curve is used in subsequent S3 extraction of the resonant excitation potential.

[0047] Figure 2 The power spectral density curve of this invention is given. The power spectral density curve is plotted with frequency on the x-axis and power spectral density value on the y-axis. The unit of frequency on the x-axis is Hz, and the unit of power spectral density value on the y-axis is (m / s). 2 ) 2 / Hz. The power spectral density curve shows a power spectral density value of 0.02 at 0Hz. The power spectral density value gradually increases with increasing frequency, reaching a peak near 32Hz with a power spectral density value of 0.85. After that, the power spectral density value drops, decreasing to 0.40 at 45Hz. It then rises again, reaching a second peak near 78Hz with a power spectral density value of 1.05. After that, the power spectral density value continues to decrease with increasing frequency, dropping back to 0.20 at 100Hz.

[0048] In the specific implementation of S3, the integral values ​​of the power spectral density within the half-power bandwidth of the first three natural frequencies of the adjacent subway shield tunnel lining structure are extracted from the power spectral density curve obtained from S2. The ratio of the sum of the integral values ​​of each order to the total power of the entire frequency band is calculated as the resonant excitation potential. First, the power spectral density curve is smoothed by moving average to obtain a smoothed power spectral density curve. The specific method of moving average smoothing is as follows: a sliding window with an odd number of frequency points is selected and placed on the power spectral density curve. Starting from the lowest frequency point of the power spectral density curve, the window is moved point by point towards higher frequencies, moving one frequency point at a time. After each movement, the power spectral density values ​​of all frequency points within the sliding window are statistically analyzed. The arithmetic mean of the power spectral density values ​​of all frequency points within the sliding window is calculated to obtain an average power spectral density value, which is then used to replace the original power spectral density value of the center frequency point of the sliding window. The span of the sliding window is set according to the frequency resolution of the power spectral density curve; the finer the frequency resolution, the narrower the frequency width corresponding to the span of the sliding window can be set. For example, when the frequency resolution of the power spectral density curve is 1 Hz, the span of the sliding window is selected to be, for example, 5 frequency points, corresponding to a frequency width of 5 Hz. The 5-frequency-point span ensures that the center frequency point is a uniquely determined midpoint of the odd-numbered span within the sliding window. By moving the sliding window point-by-point across the entire frequency band of the power spectral density curve and replacing the power spectral density values ​​at all center frequency points, a smoothed power spectral density curve is obtained. The smoothed power spectral density curve reduces the local jitter caused by random noise in the original power spectral density curve, highlighting the peak shape.

[0049] The spectral peaks corresponding to the first three natural frequencies of the adjacent subway shield tunnel lining structure were identified on the smoothed power spectral density curve. The first three natural frequencies of the adjacent subway shield tunnel lining structure were obtained in advance through on-site dynamic testing. The on-site dynamic testing method involved placing accelerometers on the adjacent subway shield tunnel lining structure and recording the vibration response of the adjacent subway shield tunnel lining structure under environmental excitation. The first three natural frequencies were extracted from the vibration response using modal parameter identification methods. The first three natural frequencies are denoted as the first natural frequency, the second natural frequency, and the third natural frequency, with their frequency values ​​increasing sequentially. On the smoothed power spectral density curve, a search interval was extended both towards the low-frequency and high-frequency directions, centered on the first natural frequency. The width of the search interval was set to, for example, ±10% of the first natural frequency value. Within this search interval, the frequency point with the largest power spectral density value was found; this frequency point is the spectral peak corresponding to the first natural frequency. Similarly, on the smoothed power spectral density curve, centered at the second natural frequency, the frequency point with the largest power spectral density value within the search interval corresponding to the second natural frequency is selected as the spectral peak corresponding to the second natural frequency. Likewise, centered at the third natural frequency, the frequency point with the largest power spectral density value within the search interval corresponding to the third natural frequency is selected as the spectral peak corresponding to the third natural frequency. The position of each spectral peak on the smoothed power spectral density curve is determined by the frequency value and the corresponding power spectral density amplitude.

[0050] Using each spectral peak as the center, frequencies where the power spectral density value drops to half the peak amplitude are identified as the lower and upper limits of the half-power bandwidth. For each spectral peak, starting from the peak's frequency, the curve is moved point by point towards lower frequencies along the smoothed power spectral density curve, comparing the power spectral density value at each frequency with half the peak amplitude. When a frequency with a power spectral density value less than or equal to half the peak amplitude first appears, that frequency is recorded as the lower limit of the half-power bandwidth. Similarly, starting from the peak's frequency, the curve is moved point by point towards higher frequencies, comparing the power spectral density value at each frequency with half the peak amplitude. When a frequency with a power spectral density value less than or equal to half the peak amplitude first appears, that frequency is recorded as the upper limit of the half-power bandwidth. The frequency range between the lower and upper limits constitutes the half-power bandwidth corresponding to that spectral peak. The power spectral density value within the half-power bandwidth represents the concentrated distribution range of vibrational energy near that natural frequency.

[0051] Numerical integration of the power spectral density curve across each half-power bandwidth interval yields the integral values ​​for each order. The numerical integration method is the trapezoidal integration method. Within the half-power bandwidth interval corresponding to the first natural frequency, starting from the lower limit frequency, the power spectral density values ​​between adjacent frequency points are averaged and multiplied by the frequency interval between these two frequency points. The sum of these multiplications is then used to obtain the first-order integral value. Similarly, the summation is performed segment by segment within the half-power bandwidth intervals corresponding to the second and third natural frequencies, respectively, to obtain the second-order and third-order integral values.

[0052] The total power across the entire frequency band is obtained by numerically integrating the power spectral density curve over the full band. The full band is the complete frequency range from the starting frequency to the ending frequency of the power spectral density curve, with the starting frequency at 0 Hz and the ending frequency at half the preset sampling frequency. The numerical integration method is consistent with that used within the half-power bandwidth, employing the trapezoidal integration method. Starting from the starting frequency, the product of the average power spectral density between adjacent frequency points and the frequency interval is accumulated segment by segment until the ending frequency is reached. The accumulated result is the total power across the entire frequency band.

[0053] The resonant excitation potential is obtained by dividing the sum of the integral values ​​of each order by the total power across the entire frequency band. The sum of the integral values ​​of each order is the result of adding the first, second, and third integral values. The resonant excitation potential is a dimensionless ratio that reflects the concentration of the vibration acceleration signal energy near the first three natural frequencies of the adjacent subway shield tunnel lining structure. The numerical range of the resonant excitation potential is between 0 and 1. The closer the value is to 1, the more concentrated the vibration energy is within the sensitive frequency band of the first three natural frequencies of the adjacent subway shield tunnel lining structure, and the higher the resonance risk. The resonant excitation potential is used for subsequent judgment and control decisions in S4.

[0054] In the specific implementation of S4, the resonant excitation potential obtained in S3 is continuously sampled, and the differential slope of the resonant excitation potential in adjacent sampling windows is calculated. When the product of the differential slope and the current resonant excitation potential reaches the preset switching sensitivity coefficient, a switching command is output to the electronically controlled damping adjustment unit built into the guide device, causing the guide device to switch from a rigid limiting state to a hysteretic damping energy absorption state. The resonant excitation potential is calculated by S3 in each analysis window. As the steel casing segment replacement process progresses, the analysis window slides forward continuously, and the resonant excitation potential is updated and output window by window.

[0055] A sampling sequence is formed by acquiring resonant excitation potentials at fixed time steps. The fixed time step refers to the time interval between two consecutive acquisitions of the resonant excitation potential. The fixed time step is set based on the rate of change characteristics of the resonant excitation potential, which is related to the operating cycle of the jacking equipment and the formation response during the segmented replacement of the steel casing. For example, a fixed time step of 0.1 seconds is set. During the segmented replacement process of the steel casing, the current resonant excitation potential value is recorded every fixed time step. The recorded values ​​are arranged chronologically to form the sampling sequence. Each sampling point in the sampling sequence corresponds to a sampling time and the resonant excitation potential value at that time.

[0056] An overlap period is set between adjacent sampling windows, ensuring that the start time of the current sampling window falls within the time interval of the previous sampling window. The sampling window is the time interval of the vibration acceleration signal intercepted when calculating the resonant excitation potential. The duration of the sampling window is determined by the duration of the analysis window in S2, and is denoted as T. The overlap period is set as follows: the start time of the previous sampling window is t0, and the end time is t0+T; the start time of the current sampling window is t0+Δt, where Δt is less than T. This ensures that the start time of the current sampling window falls within the time interval of the previous sampling window, and there is an overlap period of duration T-Δt between two adjacent sampling windows. Setting the overlap period improves the continuity of the resonant excitation potential sampling sequence's response to changes in the resonant excitation potential.

[0057] The difference is obtained by subtracting the resonant excitation potential of the previous sampling window from the current sampling window's resonant excitation potential. Dividing this difference by a fixed time step yields the differential slope. In the sampling sequence, two temporally adjacent resonant excitation potential values ​​are paired; the latter resonant excitation potential is the current sampling window's value, and the former is the previous sampling window's value, with a fixed time step. The difference reflects the absolute change in the resonant excitation potential between two sampling moments; a positive difference indicates an increase, while a negative difference indicates a decrease. Dividing the difference by the fixed time step yields the differential slope, which represents the rate of change of the resonant excitation potential per unit time, measured in seconds. The magnitude and sign of the differential slope reflect the evolution trend of the resonant excitation potential; a positive and large differential slope indicates a rapid increase in the resonant excitation potential, suggesting an accelerating increase in resonance risk.

[0058] The product value is obtained by multiplying the differential slope by the resonant excitation potential of the current sampling window. The calculation of the product value combines the rate of change of the resonant excitation potential with the amplitude of the resonant excitation potential itself. The product value represents a weighted measure of the growth trend of the resonant excitation potential; a larger product value indicates that the resonance risk is not only at a high level at the current sampling moment but is also continuing to worsen at a faster rate. The product value integrates both the static amplitude information and the dynamic change information of the resonant excitation potential, and is more effective at identifying the moment of accelerated increase in resonance risk than using the resonant excitation potential amplitude or the differential slope alone.

[0059] When the product value is greater than or equal to the preset switching sensitivity coefficient, a switching command is generated and sent to the built-in electronically controlled damping adjustment unit of the guide device, controlling the guide device to switch from a rigid limit state to a hysteretic damping energy absorption state. The preset switching sensitivity coefficient is a dimensionless threshold pre-calibrated based on the allowable vibration level of the adjacent subway shield tunnel lining structure and the permissible vibration transmission degree during the segmented replacement of the steel casing. The calibration method involves obtaining multiple sets of resonant excitation potential and differential slope data by test-pulling the steel casing at the engineering site, combined with vibration monitoring data from the adjacent subway shield tunnel lining structure, and determining the product value corresponding to the abnormal vibration monitoring data as the preset switching sensitivity coefficient. The preset switching sensitivity coefficient ensures that the product value is triggered when the resonance risk reaches the critical state requiring vibration interruption.

[0060] Once the product value reaches the preset switching sensitivity coefficient, a switching command is generated. This command is a set of electrical signals transmitted via wires from the signal processing terminal to the electrically controlled damping adjustment unit built into the guide device. Before receiving the switching command, the electrically controlled damping adjustment unit is in a rigid limiting state. In this state, the guide device and the outer wall of the steel casing transmit constraint force through rigid contact components, and the contact interface between them is rigidly connected. Upon receiving the switching command, the actuator within the unit actuates, retracting the rigid contact components between the guide device and the outer wall of the steel casing. Simultaneously, it pushes in the viscoelastic damping layer, bringing it into contact with the outer wall, thus switching the guide device from the rigid limiting state to the hysteretic damping energy absorption state. After the switch, the viscoelastic damping layer engages, initiating the vibration energy dissipation process described in S5 under the hysteretic damping energy absorption state.

[0061] In the specific implementation of S5, under hysteretic damping energy absorption, the viscoelastic damping layer built into the guide device dissipates the vibration energy of the steel casing, blocking the transmission of vibration to the surrounding strata via the guide device. The viscoelastic damping layer built into the guide device adheres to the outer wall of the steel casing under hysteretic damping energy absorption. The viscoelastic damping layer is made of a viscoelastic material, which possesses the mechanical properties of both viscous liquids and elastic solids. When subjected to alternating shear forces, it exhibits a hysteresis effect, with a phase difference between stress and strain, forming a hysteresis loop. The area enclosed by the hysteresis loop represents the energy dissipated per unit volume of viscoelastic material in one vibration cycle. The viscoelastic damping layer is made of a high-molecular-weight polymer viscoelastic damping material, such as polyurethane or butyl rubber. The damping loss factor of the viscoelastic damping layer is greater than 0.3 to ensure effective dissipation of the main vibration frequency components during the segmented replacement of the steel casing. The viscoelastic damping layer is arranged in the annular gap between the inner wall of the guide device and the outer wall of the steel casing. The initial thickness of the viscoelastic damping layer is determined according to the difference between the inner diameter of the guide device and the outer diameter of the steel casing, so that the viscoelastic damping layer can form a surface contact with the outer wall of the steel casing when it is pushed into the annular gap after switching.

[0062] When S4 generates a switching command and sends it to the electronically controlled damping adjustment unit built into the guide device, the actuator inside the unit actuates, pushing the retracted viscoelastic damping layer radially towards the center of the guide device, causing the inner surface of the viscoelastic damping layer to adhere to the outer wall of the steel casing. The adhesion between the viscoelastic damping layer and the outer wall of the steel casing is an interference fit; after being pushed out, the viscoelastic damping layer is pressed tightly against the outer wall of the steel casing under its elastic restoring force, forming a continuous annular contact surface. The actuator inside the electronically controlled damping adjustment unit is specifically an electromagnetically driven push rod or a piezoelectrically driven push rod. The actuator causes the viscoelastic damping layer to retract into the receiving groove inside the guide device in the rigidly limited state, and to extend out of the receiving groove and contact the outer wall of the steel casing in the hysteresis damping energy absorption state. The switching action is completed within the response time after receiving the switching command. The response time is determined based on the response characteristics of the actuator and is set to be less than a fixed time step to ensure that the state transition is completed before the next sampling time arrives.

[0063] The viscoelastic damping layer converts the vibrational energy transmitted from the steel casing to the guiding device into heat energy through shear deformation. The mechanical vibration generated during the segmented replacement process of the steel casing is transmitted to the viscoelastic damping layer through the contact interface between the outer wall of the steel casing and the inner surface of the viscoelastic damping layer. This vibration causes a slight reciprocating displacement of the outer wall of the steel casing relative to the inner wall of the guiding device, inducing alternating shear deformation within the viscoelastic damping layer. During this alternating shear deformation, the molecular chain segments of the viscoelastic material undergo conformational rearrangement and internal friction under alternating stress, irreversibly converting mechanical energy into heat energy. This heat energy dissipates from the viscoelastic damping layer to the guiding device body and the surrounding air through heat conduction. The vibrational energy is continuously consumed during the conversion and dissipation process, and the amplitude of the vibration is gradually attenuated along the transmission path.

[0064] The transmission path of vibration energy from the guide device to the surrounding strata is severed. The transmission path is a continuous mechanical path from the steel casing, through the viscoelastic damping layer, the guide device itself, and finally to the surrounding strata. Under rigid constraint, the steel casing and guide device are rigidly connected in the transmission path, and the vibration energy is transmitted to the surrounding strata in the form of elastic waves with almost no attenuation. Under hysteretic damping, the viscoelastic damping layer is inserted at the interface between the steel casing and the guide device in the transmission path, changing the local impedance characteristics of the transmission path from a rigid impedance region to a high-damping energy-dissipating region. Vibration energy is largely absorbed and converted into heat energy when passing through the high-damping energy-dissipating region of the transmission path. The vibration input in the latter half of the transmission path is significantly reduced, the vibration energy transmitted from the guide device to the surrounding strata is blocked, the micro-movements of the soil caused by vibration transmission in the surrounding strata are suppressed, and the cyclic load on the lining structure of the adjacent subway shield tunnel is eliminated.

[0065] The calculations involved in the embodiments are all dimensionless numerical calculations, and the preset parameters and thresholds in the calculations are set by those skilled in the art according to the actual situation.

[0066] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0067] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and inventive constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0068] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0069] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or modules may be electrical, mechanical, or other forms.

[0070] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0071] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A construction method for adjacent subway tunnel pile foundations based on segmented replacement of steel casing, characterized in that, Includes the following steps: S1: During the segmented replacement of the steel casing, vibration acceleration signals at the contact interface between the steel casing and the guide device are obtained by vibration sensors installed on the guide device. S2: Perform power spectral density analysis on the vibration acceleration signal to obtain the power spectral density curve reflecting the frequency domain distribution of vibration energy; S3: Extract the integral values ​​of the power spectral density within the half-power bandwidth of the first three natural frequencies of the adjacent subway shield tunnel lining structure from the power spectral density curve, and calculate the ratio of the sum of the integral values ​​of each order to the total power of the whole frequency band as the resonant excitation potential. S4: Continuously sample the resonant excitation potential, calculate the differential slope of the resonant excitation potential in adjacent sampling windows, and when the product of the differential slope and the current resonant excitation potential reaches the preset switching sensitivity coefficient, output a switching command to the built-in electronically controlled damping adjustment unit of the guide device, so that the guide device is converted from the rigid limit state to the hysteretic damping energy absorption state. S5: Under hysteretic damping energy absorption, the viscoelastic damping layer built into the guide device dissipates the vibration energy of the steel casing, blocking the transmission of vibration to the surrounding formation through the guide device.

2. The construction method for adjacent subway tunnel pile foundations based on segmented replacement of steel casing as described in claim 1, characterized in that, During the segmented replacement of the steel casing, vibration acceleration signals at the contact interface between the steel casing and the guide device are acquired by vibration sensors installed on the guide device, including: The vibration sensors deployed on the guide device are arranged in a multi-point contact manner. Each vibration sensor is arranged circumferentially at intervals on the annular contact surface between the guide device and the outer wall of the steel casing. The vibration acceleration components along the radial and tangential directions of the guide device are collected synchronously at each contact point. The radial and tangential vibration acceleration components collected by all vibration sensors are vector synthesized to obtain the vibration acceleration signal at the contact interface between the steel casing and the guide device.

3. The construction method for adjacent subway tunnel pile foundations based on segmented replacement of steel casing according to claim 2, characterized in that, The vibration sensors deployed on the guide device are arranged in a multi-point contact manner, including: the number of vibration sensors deployed on the annular contact surface between the guide device and the outer wall of the steel casing is not less than the minimum number required for circumferential arrangement, and the central angle corresponding to the arc length between two adjacent vibration sensors is less than or equal to the central angle corresponding to the preset contact sensing resolution.

4. The construction method for adjacent subway tunnel pile foundations based on segmented replacement of steel casing according to claim 1, characterized in that, Power spectral density analysis of the vibration acceleration signal yields a power spectral density curve reflecting the frequency domain distribution of vibration energy, including: After applying anti-aliasing filtering to the vibration acceleration signal, an analysis window is extracted at a preset sampling frequency. A window function is applied to the vibration acceleration signal within the analysis window, and a fast Fourier transform is performed to obtain a complex spectrum. The amplitude of each frequency point in the complex spectrum is squared and divided by the frequency resolution to obtain a power spectral density curve with frequency as the abscissa and power spectral density as the ordinate.

5. The construction method for adjacent subway tunnel pile foundations based on segmented replacement of steel casing according to claim 4, characterized in that, The window function applied to the vibration acceleration signal within the analysis window is the Hanning window.

6. The construction method for adjacent subway tunnel pile foundations based on segmented replacement of steel casing according to claim 1, characterized in that, The integral values ​​of the power spectral density within the half-power bandwidth of the first three natural frequencies of the adjacent subway shield tunnel lining structure are extracted from the power spectral density curve. The ratio of the sum of the integral values ​​of each order to the total power of the entire frequency band is calculated as the resonant excitation potential, including: The power spectral density curve is smoothed by moving average to obtain a smoothed power spectral density curve. On the smoothed power spectral density curve, the spectral peaks corresponding to the first three natural frequencies of the adjacent subway shield tunnel lining structure are identified. With each spectral peak as the center, the frequency points where the power spectral density value drops to half the amplitude of the spectral peak are found in the low-frequency and high-frequency directions as the lower limit frequency and upper limit frequency of the half-power bandwidth. The half-power bandwidth interval of each order is numerically integrated on the power spectral density curve to obtain the integral value of each order. The power spectral density curve is numerically integrated over the entire frequency band to obtain the total power of the entire frequency band. The sum of the integral values ​​of each order is divided by the total power of the entire frequency band to obtain the resonant excitation potential.

7. The construction method for adjacent subway tunnel pile foundations based on segmented replacement of steel casing according to claim 6, characterized in that, The power spectral density curve is smoothed by moving average, which includes: selecting a sliding window with an odd number of frequency points spanning and moving the power spectral density curve point by point; averaging the power spectral density values ​​of all frequency points within the sliding window in each move and replacing the power spectral density value of the center frequency point of the sliding window with this average value.

8. The construction method for adjacent subway tunnel pile foundations based on segmented replacement of steel casing according to claim 1, characterized in that, The resonant excitation potential is continuously sampled, and the differential slope of the resonant excitation potential within adjacent sampling windows is calculated. When the product of the differential slope and the current resonant excitation potential reaches a preset switching sensitivity coefficient, a switching command is output to the electronically controlled damping adjustment unit built into the guide device, causing the guide device to switch from a rigid limiting state to a hysteretic damping energy absorption state, including: A sampling sequence is formed by collecting resonant excitation potentials at fixed time steps. The resonant excitation potential of the current sampling window is subtracted from the resonant excitation potential of the previous sampling window to obtain the difference. The difference is divided by the time step to obtain the differential slope. The differential slope is multiplied by the resonant excitation potential of the current sampling window to obtain the product value. When the product value is greater than or equal to the preset switching sensitivity coefficient, a switching command is generated and sent to the electronically controlled damping adjustment unit built into the guide device to control the guide device to switch from the rigid limit state to the hysteretic damping energy absorption state.

9. A method for constructing adjacent subway tunnel pile foundations based on segmented replacement of steel casings according to claim 8, characterized in that, The sampling sequence is formed by collecting resonant excitation potentials at fixed time steps, including setting overlapping time periods between adjacent sampling windows so that the start time of the current sampling window is located inside the previous sampling window.

10. The construction method for adjacent subway tunnel pile foundations based on segmented replacement of steel casing according to claim 1, characterized in that, Under hysteretic damping and energy absorption conditions, the viscoelastic damping layer built into the guide device dissipates the vibration energy of the steel casing, preventing the transmission of vibration to the surrounding formation via the guide device, including: The viscoelastic damping layer built into the guide device is in contact with the outer wall of the steel casing under hysteretic damping energy absorption state. The viscoelastic damping layer converts the vibration energy transmitted from the steel casing to the guide device into heat energy through shear deformation, cutting off the transmission path of vibration energy from the guide device to the surrounding strata.

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