Underwater pile foundation void detection method based on transmission-reflection dual-mode broadband acoustic wave tomography

Abstract

The application discloses a transmission-reflection dual-mode wide-frequency acoustic wave tomography pile foundation disengaging detection method, and relates to the technical field of nondestructive testing of underwater engineering structures, and comprises the following steps: in the process of detecting the pile foundation disengaging, collecting wide-frequency transmission signal continuous propagation data and wide-frequency reflection signal continuous propagation data, synchronously recording time variation information of acoustic energy in the circumferential propagation process of the pile foundation, and forming a circumferential propagation record. The application builds a transmission and reflection dual-mode wide-frequency acoustic wave joint analysis mechanism, separates the circumferential cyclic propagation component and locates the abnormal cyclic position, avoids misjudgment of the annular disengaging, adjusts the acoustic wave excitation rhythm based on the energy distribution imbalance section, makes the excitation rhythm and the circumferential cyclic rhythm form a non-matching relationship, reduces the cyclic superposition interference, and improves the underwater pile foundation disengaging identification accuracy and the tomography reliability.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing technology for underwater engineering structures, specifically to a method for detecting voids in underwater pile foundations using transmission-reflection dual-mode broadband acoustic tomography. Background Technology

[0002] Transmission-reflection dual-modal broadband acoustic tomography for underwater pile foundation void detection refers to emitting a wide-bandwidth acoustic signal into the pile foundation structure in an underwater environment, while simultaneously acquiring two types of response data: transmitted and reflected signals after the acoustic waves propagate through the pile and its surrounding medium. The transmitted signal is used to analyze the propagation time, attenuation amplitude, and spectral variation characteristics of the acoustic waves along different paths after passing through the pile, while the reflected signal is used to identify the echo characteristics generated at the pile interface and abnormal cavity locations. Based on this, through comprehensive inversion and spatial reconstruction of multi-path, multi-angle acoustic propagation data, tomographic imaging results of the pile foundation interior and pile-soil contact area are generated. This allows for the identification of void sections, void ranges, and distribution patterns at the pile bottom or pile side, achieving non-excavation, fine-grained detection of the integrity and load-bearing safety status of underwater pile foundation structures.

[0003] The existing technology has the following shortcomings: In existing technologies, transmitted and reflected acoustic wave detection is mostly based on the echo intensity and spatial distribution characteristics to determine the condition of the pile perimeter structure. When a regular annular void exists around the pile, the reflected acoustic waves will repeatedly propagate circumferentially within the annular cavity and superimpose multiple times, easily forming a continuous, closed, and high-intensity annular echo image in the imaging results. Because this type of echo is stable and uniformly distributed, existing interpretation methods can easily mistake it for a continuous, dense solid interface structure, ignoring the actual annular void defect. This can lead to misjudgment of the actual stress state around the pile, affecting the accuracy of underwater pile foundation structure safety assessment.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a method for detecting voids in underwater pile foundations using transmission-reflection dual-mode broadband acoustic tomography, in order to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for detecting voids in underwater pile foundations using transmission-reflection dual-mode broadband acoustic tomography, comprising the following steps: During the underwater pile foundation void detection process, broadband transmission signal continuous propagation data and broadband reflection signal continuous propagation data are collected, and the time change information of sound energy during the circumferential propagation of the pile foundation is recorded simultaneously to form a circumferential propagation record, which is used to determine whether there is a circumferential propagation phenomenon. Based on the circumferential propagation record, time expansion processing is performed to extend the closed high-intensity echo formed in the circumferential propagation record along the time axis in segments, extract the continuous retention segment of sound energy, and generate the retention intensity record. Based on the retention intensity records, the propagation paths of the continuous propagation data of broadband transmitted signals and the continuous propagation data of broadband reflected signals are split, the recurring detour rhythms are screened, the circumferential loop features are extracted, and the abnormal loop locations are determined. By tracing back the changes in the continuous propagation data of the broadband transmission signal around the abnormal cycle location, comparing the synchronization relationship between the attenuation trend of the broadband transmission signal and the enhancement trend of the broadband reflection signal, the energy distribution imbalance section is determined, and the adjustment starting position is formed. The sound wave excitation frequency rhythm is adjusted around the starting position, the excitation interval is offset in a progressive manner, and the excitation time interval parameter is adjusted synchronously according to the changes in the sound energy residence time in the circumferential propagation record, so that the adjusted sound wave excitation frequency rhythm forms a non-matching relationship with the circumferential cycle rhythm corresponding to the abnormal cycle position.

[0007] Preferably, the steps for acquiring continuous propagation data of broadband transmitted signals and continuous propagation data of broadband reflected signals and forming circumferential propagation records are as follows: The system deploys sound wave transmitting positions and multiple receiving positions, transmits broadband sound wave excitation signals, controls the start time, duration and excitation interval of the excitation signals to form a fixed rhythm, and synchronously collects continuous propagation data of broadband transmitted signals and broadband reflected signals in each excitation cycle. Around each excitation cycle, the continuous propagation data of broadband transmission signal and broadband reflection signal are time-calibrated, the start time of acoustic excitation is set as a unified time zero point, and the time node of acoustic energy entering the circumferential path of the pile foundation and the energy change process along the circumferential path of the pile foundation are recorded. Based on the time calibration results, the continuous propagation data of broadband transmission signals and broadband reflection signals formed by multiple excitation cycles are arranged in chronological order to identify the time nodes when sound energy enters, the time intervals of residence, and the time nodes when it exits, thus forming a circumferential propagation record. Based on the circumferential propagation record, the acoustic energy residence segments with the same time interval in multiple excitation cycles are arranged accordingly, the repetitive propagation rhythm is extracted, and the circumferential cyclic propagation phenomenon is determined based on the repetitive propagation rhythm.

[0008] Preferably, the steps for performing time-expansion processing based on circumferential propagation records and generating retention intensity records are as follows: Traverse the excitation cycle in the circumferential propagation record to locate the echo entry time node, echo energy concentration time node and echo exit time node of the closed high-intensity echo, and extract the continuous propagation data of broadband transmitted signal and broadband reflected signal within the corresponding time interval. The time axis is segmented and extended around the time node from the echo entry point to the echo exit point, and the time interval between adjacent energy peaks is divided into propagation sub-segments, and the start time and end time of the propagation sub-segments are recorded. The acoustic energy retention segment is determined based on the start and end times of the propagation sub-segment, and the corresponding time range is marked in the continuous propagation data of broadband transmitted signal and the continuous propagation data of broadband reflected signal. Arrange the sustained acoustic energy retention sections sequentially, record the section number, start time, end time, and energy change data within the corresponding time range, and establish a retention intensity record.

[0009] Preferably, the steps for splitting the propagation path and determining the location of the abnormal cycle based on the retention intensity record are as follows: Based on the start and end times of the continuous lodging segment in the lodging intensity record, corresponding locations are made in the continuous propagation data of broadband transmitted signals and broadband reflected signals, and the corresponding time windows are extracted to form a propagation segment centered on the continuous lodging segment, thereby realizing the propagation path splitting. Arrange the propagation segments sequentially according to their internal time structure, align the propagation segments with the same continuous stagnation segment number within multiple excitation cycles, compare the time intervals of peak occurrences, and filter out recurring detour rhythms. Based on the recurring detour rhythm, the corresponding continuous lingering section is mapped to the time position in the circumferential propagation record. The synchronous time arrangement of the detour rhythm in the continuous propagation data of broadband transmitted signal and broadband reflected signal is recorded, and the circumferential loop feature is extracted. By sequentially sorting the persistent lingering sections by their numbers, persistent lingering sections that exhibit the same detour rhythm across multiple excitation cycles are identified as abnormal loop locations.

[0010] Preferably, the peak occurrence time intervals of propagation segments within multiple excitation cycles are arranged around the same continuous dwelling segment number. When the peak occurrence time interval remains consistent within consecutive excitation cycles and presents a synchronous time arrangement in the continuous propagation data of broadband transmitted signals and the continuous propagation data of broadband reflected signals, the corresponding continuous dwelling segment is marked as an abnormal cycle position.

[0011] Preferably, the steps for determining the energy distribution imbalance segment around the abnormal cycle location and establishing the adjustment starting point are as follows: Based on the serial number of the persistent lingering section corresponding to the abnormal cycle position, the start time node and the end time node are extracted from the circumferential propagation record to construct a complete time window. Within this time window, the continuous propagation data of the broadband transmission signal is traced back to form the attenuation trend. Based on the same time window, the continuous propagation data of broadband reflected signals are synchronously backtracked and extracted to form an enhanced change trend, so that the attenuation change trend of broadband transmitted signals and the enhancement change trend of broadband reflected signals are arranged correspondingly under a unified time reference. Based on a unified time reference, the amplitude change direction of continuous propagation data of broadband transmitted signals and continuous propagation data of broadband reflected signals at the same time nodes is compared point by point. Time segments in which continuous attenuation and continuous enhancement occur simultaneously are extracted to determine the energy distribution imbalance segments. The starting time node of the energy distribution imbalance section in the circumferential propagation record is marked, and this starting time node is determined as the adjustment start position. Corresponding positioning is then performed in the continuous propagation data of broadband transmitted signals and the continuous propagation data of broadband reflected signals.

[0012] Preferably, around the continuous stagnation section corresponding to the abnormal cycle position, the attenuation trend of the continuous propagation data of the broadband transmission signal and the enhancement trend of the continuous propagation data of the broadband reflection signal are synchronously arranged within multiple excitation cycles. Only when the attenuation trend and enhancement trend continue to correspond at the same time position is the time section determined to be the energy distribution imbalance section.

[0013] Preferably, the steps for adjusting the sound wave excitation frequency rhythm around the initial adjustment position are as follows: Around the time coordinate corresponding to the adjustment start position, determine the initial adjustment period, record the reference excitation time interval, and add a fixed time increment to the next excitation time node after the adjustment start position to form a new excitation time node; Based on the new excitation time node, the excitation interval is shifted in a progressive manner for subsequent excitation cycles, and the same time increment is accumulated in each excitation cycle to form a gradually staggered acoustic excitation time sequence. By focusing on the acoustic energy residence time corresponding to the abnormal cycle position in the circumferential propagation record, the acoustic energy residence time variation segment is extracted, and the time length that overlaps with the acoustic energy residence time and the circumferential cycle rhythm time interval is excluded when setting the excitation time interval parameter. The acoustic excitation time sequence formed by offsetting the excitation interval in a progressive manner is compared and arranged with the circumferential cyclic rhythm time sequence corresponding to the abnormal cyclic position, maintaining the non-overlapping state of the two on the time axis and forming a non-matching relationship.

[0014] The technical effects and advantages provided by the present invention in the above technical solution are as follows: This invention constructs a dual-mode broadband acoustic wave joint analysis mechanism for transmission and reflection, establishes circumferential propagation records under the same time reference, and performs time-expansion processing. This enables the separation and identification of multiple circumferential cyclic propagation behaviors formed inside the annular cavity in the time dimension, thereby distinguishing the cyclic propagation components contained in the closed high-intensity echo from the response of the real entity interface. By extracting the repetitive circumferential rhythm and circumferential cyclic features, the abnormal cyclic location is accurately located, so that the energy retention behavior caused by annular voids is no longer masked by simple intensity features, improving the judgment accuracy and imaging interpretation reliability of underwater pile foundation void identification.

[0015] After determining the location of the abnormal cycle, this invention identifies energy distribution imbalance sections by tracing the synchronization relationship between the attenuation trend of the broadband transmitted signal and the enhancement trend of the broadband reflected signal. It then progressively shifts and reconstructs the acoustic excitation frequency rhythm around the initial adjustment position, creating a mismatch between the acoustic excitation rhythm and the circumferential cycle rhythm. This alters the original cyclic superposition conditions and reduces the impact of circumferential propagation on the imaging results. This method achieves active control while maintaining the broadband acoustic wave coverage, helping to improve the tomographic imaging results' ability to reflect the true stress state around the pile and enhancing the stability of underwater pile foundation structure safety assessment. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0017] Figure 1 This is a flowchart of the underwater pile foundation void detection method using transmission-reflection dual-mode broadband acoustic tomography according to the present invention. Detailed Implementation

[0018] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that the description of this disclosure will be more complete and fully convey the concept of the exemplary embodiments to those skilled in the art.

[0019] This invention provides, for example Figure 1 The transmission-reflection dual-mode broadband acoustic tomography method for detecting voids in underwater pile foundations, as shown, includes the following steps: During the underwater pile foundation void detection process, broadband transmission signal continuous propagation data and broadband reflection signal continuous propagation data are collected, and the time change information of sound energy during the circumferential propagation of the pile foundation is recorded simultaneously to form a circumferential propagation record, which is used to determine whether there is a circumferential propagation phenomenon. In the specific implementation process, by continuously acquiring and synchronously calibrating the entire process of circumferential acoustic wave propagation of the pile foundation in the underwater environment, a complete circumferential propagation record is constructed, providing continuous time basis for subsequent determination of circumferential propagation phenomena. The specific implementation steps are as follows: In an underwater environment, acoustic wave emission points and multiple receiving points are deployed to ensure that the acoustic excitation signal covers both the axial and circumferential regions of the pile foundation. When emitting broadband acoustic excitation signals, the start time, duration, and excitation interval are controlled to maintain a fixed rhythm, ensuring each excitation forms a complete propagation cycle. After each excitation, continuous propagation data of the broadband transmission signal formed after the acoustic wave passes through the pile foundation are continuously acquired, along with continuous propagation data of the broadband reflection signal formed after the acoustic wave reflects at the pile foundation interface. The continuous propagation data of the broadband transmission signal and the broadband reflection signal corresponding to each excitation are independently time-calibrated, and the start time of the acoustic excitation is set as a unified zero point, ensuring a correspondence between the two types of continuous propagation data on the same time coordinate. During data acquisition, the time point at which the acoustic energy enters the circumferential path of the pile foundation is recorded, and the energy change curve of the acoustic energy propagating along the circumferential path is continuously recorded until the acoustic energy attenuates to a preset background value, thereby obtaining complete information on the circumferential propagation time change of the acoustic energy.

[0020] After obtaining continuous propagation data of broadband transmitted signals and broadband reflected signals formed by multiple consecutive excitation cycles, the data corresponding to each excitation cycle are arranged in chronological order, making each excitation cycle an independent time sequence. Around the circumferential propagation process of the pile foundation, the time nodes when sound energy enters the circumferential path, the time interval during which sound energy continuously propagates in the circumferential path, and the time nodes when sound energy exits the circumferential path are marked segment by segment. These time nodes are uniformly numbered within each excitation cycle, allowing direct comparison of similar time nodes in different excitation cycles. In this way, the continuous propagation data of broadband transmitted signals and broadband reflected signals are presented in a continuous arrangement on the same time axis, thus forming a complete circumferential propagation record including the sound energy entry time, residence time, and exit time.

[0021] After forming the circumferential propagation record, the time variation of acoustic energy during the circumferential propagation of the pile foundation is compared cycle by cycle within multiple consecutive excitation cycles. The dwell time of acoustic energy after entering the circumferential path in each excitation cycle is recorded one by one, and the corresponding dwell time is arranged in correspondence with the dwell time in the next excitation cycle. When acoustic energy dwelling segments with the same time interval appear in multiple excitation cycles, the time interval is marked as a repeating propagation rhythm. When identifying the repeating propagation rhythm, the signal intensity changes corresponding to the time segment in the continuous propagation data of broadband transmitted signals and the continuous propagation data of broadband reflected signals are extracted synchronously to maintain the correspondence between the two types of continuous propagation data at the same time node. When the repeating propagation rhythm appears continuously in multiple consecutive excitation cycles, the existence of a circumferential cyclic propagation phenomenon can be determined based on the circumferential propagation record, and the corresponding time segment is fixedly marked in the circumferential propagation record.

[0022] After determining the circumferential propagation phenomenon, the determined time segments are associated and stored with the corresponding broadband transmission signal continuous propagation data and broadband reflection signal continuous propagation data, so that the circumferential propagation phenomenon forms a traceable time tag in the continuous propagation data. The circumferential propagation time segments formed by multiple excitation cycles are arranged continuously, so that each propagation cycle corresponds to a specific time position. By continuously collecting new broadband transmission signal continuous propagation data and broadband reflection signal continuous propagation data, and adding the new data to the existing circumferential propagation record according to the predetermined time calibration method, the circumferential propagation phenomenon forms a continuous evolution trajectory on the time axis. Through the above steps, the broadband transmission signal continuous propagation data and broadband reflection signal continuous propagation data form a complete circumferential propagation record under a unified time reference, and the determination of the circumferential propagation phenomenon is completed based on the time change information in the circumferential propagation record, providing a continuous data foundation for subsequent time unfolding processing.

[0023] Based on the circumferential propagation record, time expansion processing is performed to extend the closed high-intensity echo formed in the circumferential propagation record along the time axis in segments, extract the continuous retention segment of sound energy, and generate the retention intensity record. After constructing the circumferential propagation record, the closed high-intensity echo is segmented and continuously decomposed along the time axis, transforming the originally concentrated superimposed acoustic energy response into multiple independent propagation segments arranged in time sequence. Based on this, a persistence intensity record is formed. The specific implementation steps are as follows: The circumferential propagation record is traversed cycle by cycle, and the closed high-intensity echoes appearing in each excitation cycle are located one by one. Specifically, under a unified time reference, the start time, peak formation time, and echo attenuation end time of the closed high-intensity echo are identified, and these three time nodes are marked as the echo entry time node, echo energy concentration time node, and echo exit time node, respectively. Around the complete time interval between the echo entry time node and the echo exit time node, the continuous propagation data of the broadband transmitted signal and the continuous propagation data of the broadband reflected signal within the corresponding time interval are simultaneously extracted, so that the closed high-intensity echoes form a completely consistent time range in the two types of continuous propagation data. In this way, each closed high-intensity echo has a clear time boundary in the circumferential propagation record, and provides an accurate time positioning basis for subsequent time axis segmentation extension.

[0024] After obtaining the complete time interval of the closed high-intensity echo, this time interval is continuously segmented and extended along the time axis. Specifically, starting from the echo entry time node, the energy peak change process inside the closed high-intensity echo is segmented in chronological order, and the time interval between two adjacent energy peaks is divided into an independent propagation sub-segment. Each propagation sub-segment maintains its original chronological order, and the start and end times of the propagation sub-segment are recorded separately in the circumferential propagation record. During the segmentation process, the temporal consistency between the continuous propagation data of the broadband transmitted signal and the continuous propagation data of the broadband reflected signal is maintained, so that each propagation sub-segment corresponds to the same time interval in both types of continuous propagation data. Through this time axis segmentation and extension method, the multiple superimposed propagation behaviors inside the closed high-intensity echo are divided into several continuously arranged propagation sub-segments on the time axis, thereby achieving temporal separation of superimposed energy.

[0025] After completing the division of the propagation sub-segments, the residence of acoustic energy in the circumferential path within each propagation sub-segment is continuously recorded. Specifically, starting from the start time of the propagation sub-segment, the time point at which acoustic energy enters the circumferential propagation path is recorded, and the duration of acoustic energy maintaining its propagation state within the circumferential propagation path is continuously recorded until the time point at which acoustic energy exits the circumferential propagation path is recorded. This time span is defined as the acoustic energy continuous residence segment, and the corresponding time range of the continuous residence segment in the broadband transmitted signal continuous propagation data and the broadband reflected signal continuous propagation data is synchronously marked. Within multiple excitation cycles, the acoustic energy continuous residence segments appearing at the same time position are arranged one by one, so that each acoustic energy continuous residence segment has a unique time number, thereby forming a set of continuous residence segments arranged in chronological order.

[0026] After obtaining multiple sustained acoustic energy retention segments, the energy change process within each segment is continuously recorded. The energy change curve from entering to exiting the circumferential propagation path is completely preserved, and this curve is correlated with the start and end times of the corresponding sustained retention segment. Around the set of sustained retention segments formed within multiple excitation cycles, each segment is arranged chronologically to establish a retention intensity record. The retention intensity record includes the segment number, start time, end time, and energy change data within the corresponding time range. Through these steps, the closed high-intensity echo formed in the circumferential propagation record is segmented and extended along the time axis into multiple propagation sub-segments with clear time boundaries. These sub-segments are then further extracted to form sustained acoustic energy retention segments, ultimately generating a complete retention intensity record. This provides continuous time and energy basis for subsequent propagation path decomposition based on the retention intensity record.

[0027] Based on the retention intensity records, the propagation paths of the continuous propagation data of broadband transmitted signals and the continuous propagation data of broadband reflected signals are split, the recurring detour rhythms are screened, the circumferential loop features are extracted, and the abnormal loop locations are determined. After constructing the retention intensity record, the continuous retention segments in the retention intensity record are used as time indices to segment the continuous propagation data of broadband transmitted signals and broadband reflected signals. Based on the segmentation, recurring circumferential rhythms are identified, and then circumferential cycle features are extracted and abnormal cycle locations are determined. The specific implementation steps are as follows: Using each numbered persistent lingering segment in the lingering intensity record as a reference time unit, the start and end times of this persistent lingering segment are precisely located in the broadband transmission signal continuous propagation data, and simultaneously located at the same time in the broadband reflection signal continuous propagation data, so that the same persistent lingering segment forms a completely consistent time window in the two types of continuous propagation data. Within each time window, all waveform changes within the corresponding time range are extracted, and the extracted waveforms are stored independently according to the persistent lingering segment number, so that the original broadband transmission signal continuous propagation data and broadband reflection signal continuous propagation data are divided into multiple propagation segments centered on the persistent lingering segments. During the division process, the original time order is maintained, so that each propagation segment has a clear start and end position on the time axis, thereby completing the propagation path splitting based on the lingering intensity record.

[0028] After the propagation path was decomposed, the temporal structure within each propagation segment was analyzed segment by segment. The time points when the acoustic energy began to increase, reached their peak, and decayed to the background value within each propagation segment were recorded sequentially. Propagation segments formed across multiple excitation cycles were arranged horizontally around the same sustained stagnation segment number, aligning segments with the same number in different excitation cycles on the time axis. By comparing the time intervals of peak occurrences in propagation segments with the same number across multiple excitation cycles, propagation segments with completely identical time intervals were categorized, and this categorization result was defined as a loop rhythm. When the same time interval recurred in multiple consecutive excitation cycles, this time interval was identified as a recurring loop rhythm. During the identification of recurring loop rhythms, the continuous propagation data of broadband transmitted signals and broadband reflected signals were simultaneously compared temporally, ensuring that the recurring loop rhythms maintained a consistent temporal arrangement in both types of continuous propagation data.

[0029] After identifying the recurring looping rhythms, the corresponding persistent lingering segment numbers are mapped to the time positions in the circumferential propagation records, allowing the recurring looping rhythms to be traced back to specific circumferential propagation time segments. For each recurring looping rhythm, its occurrence frequency across multiple excitation cycles is continuously recorded, forming a fixed repeating sequence on the time axis. Simultaneously, the amplitude variations of this fixed repeating sequence in the broadband transmitted signal continuous propagation data and the broadband reflected signal continuous propagation data are synchronously labeled, ensuring that the circumferential cyclic feature includes not only the time intervals of recurrence but also the synchronous changes of the two types of continuous propagation data at corresponding time positions. Through this method, a complete correspondence is established between the recurring looping rhythms, persistent lingering segments, and the two types of continuous propagation data, thus forming a complete circumferential cyclic feature.

[0030] After extracting the circumferential cycle features, all persistent retention segments are sequentially numbered. Persistent retention segments exhibiting the same circumferential rhythm across multiple consecutive excitation cycles are marked as candidate segments for abnormal cycles. The temporal position of these candidate segments in the circumferential propagation record is mapped to their specific spatial position in the circumferential propagation path, allowing them to be mapped to the specific circumferential propagation orientation of the pile foundation. When a persistent retention segment maintains the same circumferential rhythm across consecutive excitation cycles and exhibits synchronous temporal arrangement in both broadband transmission signal continuous propagation data and broadband reflection signal continuous propagation data, this persistent retention segment is ultimately determined as the location of an abnormal cycle. Through these steps, the retention intensity record serves as the basis for propagation path decomposition, the recurring circumferential rhythm as the screening criterion, and the circumferential cycle features as the judgment standard, achieving accurate determination of the abnormal cycle location. This provides a clear temporal and spatial positioning basis for subsequent comparison of transmission signal changes and adjustment of excitation frequency rhythm around the abnormal cycle location.

[0031] By tracing back the changes in the continuous propagation data of the broadband transmission signal around the abnormal cycle location, comparing the synchronization relationship between the attenuation trend of the broadband transmission signal and the enhancement trend of the broadband reflection signal, the energy distribution imbalance section is determined, and the adjustment starting position is formed. After determining the location of the abnormal cycle, the time coordinates of the abnormal cycle location in the circumferential propagation record are used as a reference. Synchronous backtracking and segment-by-segment comparison are then performed on the continuous propagation data of the broadband transmitted signal and the continuous propagation data of the broadband reflected signal. This ensures that the two types of continuous propagation data form a complete change trajectory under the same time reference. Based on this, the energy distribution imbalance section is determined, and the adjustment starting position is established. The specific implementation steps are as follows: Using the continuous loitering segment number corresponding to the abnormal loop position as the time index, the start and end time nodes of this continuous loitering segment in the circumferential propagation record are precisely extracted. The start time node is extended forward to the time position before the sound wave enters the circumferential propagation path, and the end time node is extended backward to the time position when the sound wave completely exits the circumferential propagation path, thus forming a complete time window containing the abnormal loop position. Within this time window, the continuous propagation data of the broadband transmission signal is continuously back-recorded, and the amplitude changes at each time sampling point are arranged in chronological order, so that the attenuation change trajectory of the sound energy from the beginning of entering the propagation path to the end of the abnormal loop position forms a complete curve. During the recording process, the time calibration method is kept consistent with the circumferential propagation record, so that the continuous propagation data of the broadband transmission signal forms a continuous and uninterrupted change sequence before and after the abnormal loop position, thereby obtaining the attenuation change trend of the broadband transmission signal corresponding to the abnormal loop position.

[0032] While maintaining the same time window, synchronous backtracking extraction is performed on the continuous propagation data of broadband reflected signals. The time range of the persistent stagnation segment corresponding to the abnormal cycle position in the continuous propagation data of broadband reflected signals is marked point by point, and this time range is extended forward to the time node when the sound wave begins to form a reflection response and backward to the time node when the reflection response completely decays, so that the continuous propagation data of broadband reflected signals forms a complete enhancement change trajectory within the same time window. The amplitude changes at each time sampling point are arranged in chronological order, so that the continuous propagation data of broadband reflected signals forms a continuous enhancement change sequence within the time segment of the abnormal cycle position. Through the above processing, the decay change trend of the continuous propagation data of broadband transmitted signals and the enhancement change trend of the continuous propagation data of broadband reflected signals have a directly comparable time series under a unified time reference.

[0033] After obtaining the attenuation trend of the broadband transmitted signal and the enhancement trend of the broadband reflected signal, the amplitude change direction of the two types of continuous propagation data at the same time node is compared point by point. Within the complete time window corresponding to the abnormal cycle position, the amplitude change state of the broadband transmitted signal continuous propagation data and the amplitude change state of the broadband reflected signal continuous propagation data at each time sampling point are arranged side by side, so that any time node on the time axis corresponds to a set of transmission and reflection amplitude change states. When the broadband transmitted signal continuous propagation data shows a continuous attenuation state and the broadband reflected signal continuous propagation data shows a continuous enhancement state in multiple consecutive time sampling points, the continuous time segment is marked as an energy distribution imbalance segment. The energy distribution imbalance segments appearing at the same time position in multiple excitation cycles are repeatedly marked so that the energy distribution imbalance segments form a stable interval on the time axis, thereby ensuring that the energy distribution imbalance segments have a continuous time characteristic.

[0034] After identifying the energy distribution imbalance section, the starting time node of the energy distribution imbalance section in the circumferential propagation record is extracted and determined as the adjustment starting position. Around the adjustment starting position, its corresponding time coordinates in the continuous propagation data of broadband transmitted signals and broadband reflected signals are uniformly identified, ensuring consistent time positioning of the adjustment starting position in both types of continuous propagation data. Simultaneously, the adjustment starting positions formed in multiple consecutive excitation cycles are arranged to form a recurring time sequence on the time axis, providing a clear time reference for subsequent adjustment of the acoustic excitation frequency rhythm around the adjustment starting position. Through these steps, the changes in the continuous propagation data of broadband transmitted signals are traced back around the abnormal cycle position, and the energy distribution imbalance section is determined by comparing the synchronous relationship between the attenuation trend of the broadband transmitted signal and the enhancement trend of the broadband reflected signal, ultimately forming the adjustment starting position.

[0035] The sound wave excitation frequency rhythm is adjusted around the starting position, the excitation interval is offset in a progressive manner, and the excitation time interval parameter is adjusted synchronously according to the change of sound energy residence time in the circumferential propagation record, so that the adjusted sound wave excitation frequency rhythm forms a non-matching relationship with the circumferential cycle rhythm corresponding to the abnormal cycle position. After establishing the initial adjustment position, the sound wave excitation frequency rhythm is continuously reconstructed, starting from the precise time coordinate of the initial adjustment position in the circumferential propagation record. This causes subsequent excitation behavior to gradually deviate from the circumferential cycle rhythm corresponding to the abnormal cycle position on the time axis. The specific implementation steps are as follows: The initial adjustment period is set as the excitation cycle number corresponding to the initial adjustment position. Before this initial adjustment period, the original sound wave excitation frequency rhythm remains unchanged. The sound wave excitation time nodes are rearranged starting from the initial adjustment position. The original fixed excitation time interval is recorded as the reference excitation time interval. A preset time offset is added to the next excitation time after the initial adjustment position, causing the new excitation time node to move backward on the time axis. This time offset is a fixed time increment, and its value is less than the circumferential cyclic rhythm time interval corresponding to the abnormal cycle position, thereby ensuring that the new excitation time node does not coincide with the circumferential cyclic rhythm time node corresponding to the abnormal cycle position. During implementation, the excitation cycle time coordinate corresponding to the initial adjustment position is marked separately, so that all subsequent time offsets revolve around this time coordinate.

[0036] After the first time offset following the adjustment of the initial position, the excitation time interval of each subsequent excitation cycle is offset in a progressive manner. Specifically, the excitation time of the second excitation cycle is increased by the same time increment as the first offset, so that the excitation time node of the second excitation cycle is offset by a time increment of twice the original rhythm. The excitation time of the third excitation cycle is further increased by the same time increment as the second offset, so that the excitation time node of the third excitation cycle is offset by a time increment of three times. By continuously offsetting the excitation interval in a progressive manner, the excitation time nodes of multiple excitation cycles are arranged in a gradually staggered structure on the time axis, thereby changing the time correspondence between the original sound wave excitation frequency rhythm and the circumferential cycle rhythm corresponding to the abnormal cycle position.

[0037] While implementing a progressive offset of the excitation interval, the excitation time interval parameter is synchronously adjusted based on the changes in acoustic energy residence time corresponding to the abnormal cycle positions in the circumferential propagation record. Specifically, the acoustic energy residence time recorded in the continuous residence segment corresponding to the abnormal cycle position is extracted point by point, and this acoustic energy residence time is used as a reference time scale. When setting a new excitation time interval, the new excitation time interval value is not equal to an integer multiple of the acoustic energy residence time, nor is it equal to an integer multiple of the sum of the acoustic energy residence time and the circumferential cycle rhythm time interval, so that the new excitation time node and the residence time rhythm of acoustic energy in the circumferential propagation path are misaligned. After each progressive offset, the positional relationship between the new excitation time node and the acoustic energy residence time on the time axis is re-compared, so that the excitation time interval parameter always maintains a non-overlapping arrangement with the changes in acoustic energy residence time in the circumferential propagation record.

[0038] After completing the progressive shift of the excitation interval and synchronous adjustment of the excitation time interval parameters for multiple consecutive excitation cycles, the new acoustic excitation time sequence is arranged completely on the time axis, and this time sequence is compared point by point with the circumferential cyclic rhythm time sequence corresponding to the abnormal cycle position. When the new acoustic excitation time node no longer overlaps with the circumferential cyclic rhythm time node on the time axis, a mismatch relationship is formed. This mismatch relationship is maintained in subsequent excitation cycles, so that the acoustic excitation frequency rhythm is stably in a state of misalignment with the circumferential cyclic rhythm corresponding to the abnormal cycle position. Through the above steps, the acoustic excitation frequency rhythm is adjusted around the adjustment starting position, the excitation interval is shifted in a progressive manner, and the excitation time interval parameters are synchronously adjusted according to the changes in the acoustic energy residence time in the circumferential propagation record, so that the adjusted acoustic excitation frequency rhythm forms a mismatch relationship with the circumferential cyclic rhythm corresponding to the abnormal cycle position.

[0039] This invention constructs a dual-mode broadband acoustic wave joint analysis mechanism for transmission and reflection, establishes circumferential propagation records under the same time reference, and performs time-expansion processing. This enables the separation and identification of multiple circumferential cyclic propagation behaviors formed inside the annular cavity in the time dimension, thereby distinguishing the cyclic propagation components contained in the closed high-intensity echo from the response of the real entity interface. By extracting the repetitive circumferential rhythm and circumferential cyclic features, the invention achieves precise positioning of abnormal cyclic locations, ensuring that the energy retention behavior caused by annular voids is no longer masked by simple intensity features, thus improving the accuracy of underwater pile foundation void identification and the reliability of imaging interpretation.

[0040] After determining the location of the abnormal cycle, this invention identifies energy distribution imbalance sections by tracing the synchronization relationship between the attenuation trend of the broadband transmitted signal and the enhancement trend of the broadband reflected signal. It then progressively shifts and reconstructs the acoustic excitation frequency rhythm around the initial adjustment position, creating a mismatch between the acoustic excitation rhythm and the circumferential cycle rhythm. This alters the original cyclic superposition conditions and reduces the impact of circumferential propagation on the imaging results. This method achieves active control while maintaining the broadband acoustic wave coverage, helping to improve the tomographic imaging results' ability to reflect the true stress state around the pile and enhancing the stability of underwater pile foundation structure safety assessment.

[0041] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for detecting voids in underwater pile foundations using transmission-reflection dual-mode broadband acoustic tomography, characterized in that, Includes the following steps: During the underwater pile foundation void detection process, broadband transmission signal continuous propagation data and broadband reflection signal continuous propagation data are collected, and the time change information of sound energy during the circumferential propagation of sound energy in the pile foundation is recorded simultaneously to form a circumferential propagation record. Based on the circumferential propagation record, time expansion processing is performed to extend the closed high-intensity echo formed in the circumferential propagation record along the time axis in segments, extract the continuous retention segment of sound energy, and generate the retention intensity record. Based on the retention intensity records, the propagation paths of the continuous propagation data of broadband transmitted signals and the continuous propagation data of broadband reflected signals are split, the recurring detour rhythms are screened, the circumferential loop features are extracted, and the abnormal loop locations are determined. The steps for breaking down the propagation path and determining the location of abnormal loops based on the retention intensity records are as follows: Based on the start and end times of the continuous lodging segment in the lodging intensity record, corresponding locations are made in the continuous propagation data of broadband transmitted signals and broadband reflected signals, and the corresponding time windows are extracted to form a propagation segment centered on the continuous lodging segment, thereby realizing the propagation path splitting. Arrange the propagation segments sequentially according to their internal time structure, align the propagation segments with the same continuous stagnation segment number within multiple excitation cycles, compare the time intervals of peak occurrences, and filter out recurring detour rhythms. Based on the recurring detour rhythm, the corresponding continuous lingering section is mapped to the time position in the circumferential propagation record. The synchronous time arrangement of the detour rhythm in the continuous propagation data of broadband transmitted signal and broadband reflected signal is recorded, and the circumferential loop feature is extracted. By continuously sorting the persistent lingering sections by their numbers, the persistent lingering sections that exhibit the same detour rhythm in multiple excitation cycles are identified as abnormal loop positions. By tracing back the changes in the continuous propagation data of the broadband transmission signal around the abnormal cycle location, comparing the synchronization relationship between the attenuation trend of the broadband transmission signal and the enhancement trend of the broadband reflection signal, the energy distribution imbalance section is determined, and the adjustment starting position is formed. The sound wave excitation frequency rhythm is adjusted around the starting position, the excitation interval is offset in a progressive manner, and the excitation time interval parameter is adjusted synchronously according to the change of sound energy residence time in the circumferential propagation record, so that the adjusted sound wave excitation frequency rhythm forms a non-matching relationship with the circumferential cycle rhythm corresponding to the abnormal cycle position. The acoustic excitation time sequence formed by offsetting the excitation interval in a progressive manner is compared and arranged with the circumferential cyclic rhythm time sequence corresponding to the abnormal cyclic position, maintaining the non-overlapping state of the two on the time axis and forming a non-matching relationship.

2. The underwater pile foundation void detection method using transmission-reflection dual-mode broadband acoustic tomography according to claim 1, characterized in that, The steps for acquiring continuous propagation data of broadband transmitted signals and broadband reflected signals and forming a circumferential propagation record are as follows: The system deploys sound wave transmitting positions and multiple receiving positions, transmits broadband sound wave excitation signals, controls the start time, duration and excitation interval of the excitation signals to form a fixed rhythm, and synchronously collects continuous propagation data of broadband transmitted signals and broadband reflected signals in each excitation cycle. Around each excitation cycle, the continuous propagation data of broadband transmission signal and broadband reflection signal are time-calibrated, the start time of acoustic excitation is set as a unified time zero point, and the time node of acoustic energy entering the circumferential path of the pile foundation and the energy change process along the circumferential path of the pile foundation are recorded. Based on the time calibration results, the continuous propagation data of broadband transmission signals and broadband reflection signals formed by multiple excitation cycles are arranged in chronological order to identify the time nodes when sound energy enters, the time intervals of residence, and the time nodes when it exits, thus forming a circumferential propagation record. Based on the circumferential propagation record, the acoustic energy residence segments with the same time interval in multiple excitation cycles are arranged accordingly, the repetitive propagation rhythm is extracted, and the circumferential cyclic propagation phenomenon is determined based on the repetitive propagation rhythm.

3. The underwater pile foundation void detection method using transmission-reflection dual-mode broadband acoustic tomography according to claim 2, characterized in that, The steps for performing time-expansion processing based on circumferential propagation records and generating retention intensity records are as follows: Traverse the excitation cycle in the circumferential propagation record to locate the echo entry time node, echo energy concentration time node and echo exit time node of the closed high-intensity echo, and extract the continuous propagation data of broadband transmitted signal and broadband reflected signal within the corresponding time interval. The time axis is segmented and extended around the time node from the echo entry point to the echo exit point, and the time interval between adjacent energy peaks is divided into propagation sub-segments, and the start time and end time of the propagation sub-segments are recorded. The acoustic energy retention segment is determined based on the start and end times of the propagation sub-segment, and the corresponding time range is marked in the continuous propagation data of broadband transmitted signal and the continuous propagation data of broadband reflected signal. Arrange the sustained acoustic energy retention sections sequentially, record the section number, start time, end time, and energy change data within the corresponding time range, and establish a retention intensity record.

4. The underwater pile foundation void detection method using transmission-reflection dual-mode broadband acoustic tomography according to claim 1, characterized in that, Around the same persistent lingering segment number, the peak occurrence time intervals of propagation segments within multiple excitation cycles are arranged. When the peak occurrence time interval remains consistent within consecutive excitation cycles and presents a synchronous time arrangement in the continuous propagation data of broadband transmitted signals and the continuous propagation data of broadband reflected signals, the corresponding persistent lingering segment is marked as an abnormal cycle position.

5. The underwater pile foundation void detection method using transmission-reflection dual-mode broadband acoustic tomography according to claim 1, characterized in that, The steps for identifying the energy distribution imbalance zone around the abnormal cycle location and determining the initial adjustment position are as follows: Based on the serial number of the persistent lingering section corresponding to the abnormal cycle position, the start time node and the end time node are extracted from the circumferential propagation record to construct a complete time window. Within this time window, the continuous propagation data of the broadband transmission signal is traced back to form the attenuation trend. Based on the same time window, the continuous propagation data of broadband reflected signals are synchronously backtracked and extracted to form an enhanced change trend, so that the attenuation change trend of broadband transmitted signals and the enhancement change trend of broadband reflected signals are arranged correspondingly under a unified time reference. Based on a unified time reference, the amplitude change direction of continuous propagation data of broadband transmitted signals and continuous propagation data of broadband reflected signals at the same time nodes is compared point by point. Time segments in which continuous attenuation and continuous enhancement occur simultaneously are extracted to determine the energy distribution imbalance segments. The starting time node of the energy distribution imbalance section in the circumferential propagation record is marked, and this starting time node is determined as the adjustment start position. Corresponding positioning is then performed in the continuous propagation data of broadband transmitted signals and the continuous propagation data of broadband reflected signals.

6. The underwater pile foundation void detection method using transmission-reflection dual-mode broadband acoustic tomography according to claim 5, characterized in that, Around the continuous stagnation section corresponding to the abnormal cycle position, the attenuation trend of the continuous propagation data of the broadband transmitted signal and the enhancement trend of the continuous propagation data of the broadband reflected signal are synchronously arranged within multiple excitation cycles. Only when the attenuation trend and enhancement trend continue to correspond at the same time position are the time section determined to be the energy distribution imbalance section.

7. The underwater pile foundation void detection method using transmission-reflection dual-mode broadband acoustic tomography according to claim 5, characterized in that, The steps for adjusting the sound wave excitation frequency and rhythm around the initial position are as follows: Around the time coordinate corresponding to the adjustment start position, determine the initial adjustment period, record the reference excitation time interval, and add a fixed time increment to the next excitation time node after the adjustment start position to form a new excitation time node; Based on the new excitation time node, the excitation interval is shifted in a progressive manner for subsequent excitation cycles, and the same time increment is accumulated in each excitation cycle to form a gradually staggered acoustic excitation time sequence. By extracting the acoustic energy residence time variation segments corresponding to the abnormal cycle positions in the circumferential propagation record, and excluding the time lengths that overlap with the acoustic energy residence time and the circumferential cycle rhythm time interval when setting the excitation time interval parameter.

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