CN111158043B - System and method for detecting hidden danger at pile bottom of bored pile - Google Patents

System and method for detecting hidden danger at pile bottom of bored pile Download PDF

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Publication number
CN111158043B
CN111158043B CN202010012705.0A CN202010012705A CN111158043B CN 111158043 B CN111158043 B CN 111158043B CN 202010012705 A CN202010012705 A CN 202010012705A CN 111158043 B CN111158043 B CN 111158043B
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pile
vibration
signal
hidden danger
spectrum
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CN111158043A (en
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朱德兵
刘润行
朱朴厚
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Central South University
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Central South University
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01VGEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/02Generating seismic energy
    • G01V1/143Generating seismic energy using mechanical driving means, e.g. motor driven shaft
    • G01V1/147Generating seismic energy using mechanical driving means, e.g. motor driven shaft using impact of dropping masses
    • EFIXED CONSTRUCTIONS
    • E02HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02DFOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D33/00Testing foundations or foundation structures
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01VGEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/22Transmitting seismic signals to recording or processing apparatus
    • G01V1/223Radioseismic systems
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01VGEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/28Processing seismic data, e.g. analysis, for interpretation, for correction
    • G01V1/30Analysis

Abstract

The invention relates to a system and a method for detecting hidden danger at the bottom of a bored pile. A pile bottom hidden danger detection system for a hole-forming pile-grouting pile comprises: the earthquake recorder and the first earthquake sensing device; the first vibration sensing device is embedded in peripheral rock-soil media of the pile hole or mud wall protection liquid of the pile hole, and is used for detecting a background vibration signal and transmitting the background vibration signal to the seismic recorder; the seismic recorder comprising: the device comprises an acquisition trigger device, a preposed conditioner, an analog-to-digital converter, a central processing unit, a display and a memory; the system obtains the background vibration signal through the first vibration sensing device, can eliminate signal interference generated by the inconsistency of the seismic sources to a certain extent, obtains the two-dimensional vibration spectrum through the technical means of abnormal elimination of continuous impact response signals, average superposition of adjacent multiple impact signals and the like, and can reliably find the hidden danger at the bottom of the pile through the abnormal characteristics of the two-dimensional vibration spectrum.

Description

System and method for detecting hidden danger at pile bottom of bored pile
Technical Field
The invention relates to the field of detection of hidden danger at the bottom of a hole-forming cast-in-place pile, in particular to a system and a method for detecting hidden danger at the bottom of a hole-forming cast-in-place pile.
Background
The hammering or impacting pore-forming cast-in-place pile has the advantages of low cost, small air pollution and relatively small noise during electrification operation, small risk during operation in karst and other complex stratums and the like, and is widely applied to design and construction of roads and bridges. According to the design standard, the pile bottom bearing layer must meet certain thickness and strength, but because of the existence of complex geological structures such as karst, even if advanced drilling exploration is carried out, the existence of local karst hidden danger at the pile bottom is still difficult to avoid, thereby bringing serious threat to the pile foundation poured subsequently and even the superstructure.
In order to solve the problem, the corresponding detection methods include a pile-bottom knock reflection seismic method (ZL201010539461.8), a geological radar detection method (ZL201210383637.4), an ultrasonic method (ZL201410276785.5), a seismic reflection wave array detection method (ZL201721486233.2) and the like. The reflection wave method and the geological radar detection method need space for manual work or convenient construction operation, and are suitable for manual hole digging piles; the construction equipment and the construction working procedure of the ultrasonic method are complex, and the detection effect is poor if the ultrasonic sensor lacks good coupling conditions during field operation; patent document zl200510037364.x discloses a method for detecting and judging the lithology of a final hole at the bottom of a pile foundation pile, which analyzes the strength and the structure of an underground rock stratum by detecting factors such as the vibration frequency of an impact shock wave emitted when a heavy hammer impacts the underground rock stratum.
Therefore, it is necessary to develop and develop a technique and equipment that can effectively detect the hidden danger at the bottom of the pile without affecting the construction operation of the pile foundation, which is very beneficial to punching the bored pile.
Disclosure of Invention
In view of the defects of the prior art, the invention aims to provide a system and a method for detecting hidden danger at the bottom of a bored pile, which can detect an effectively excited vibration signal by using hammering vibration in construction, and analyze and obtain related parameters of the hidden danger at the bottom of the pile by combining the change characteristics of the vibration signal when an excitation source approaches the hidden danger position from far to near.
In order to achieve the purpose, the invention adopts the following technical scheme:
a pile bottom hidden danger detection system for a hole-forming pile-grouting pile comprises: the earthquake recorder and the first earthquake sensing device;
the first vibration sensing device is embedded in peripheral rock-soil media of the pile hole or mud wall protection liquid of the pile hole, and is used for detecting a background vibration signal and transmitting the background vibration signal to the seismic recorder;
the seismic recorder comprising: the device comprises an acquisition trigger device, a preposed conditioner, an analog-to-digital converter, a central processing unit, a display and a memory;
the acquisition triggering device is used for acquiring a hammering time signal of the impact hammer for hammering the pile bottom and transmitting the hammering time signal to the central processing unit;
the preposed conditioner is connected with the first vibration sensing device, connected with the analog-to-digital converter and used for sending a received analog signal to the analog-to-digital converter after being preprocessed;
the analog-to-digital converter is connected with the central processing unit and is used for converting the analog signal transmitted by the preposed conditioner into a digital signal and transmitting the digital signal to the central processing unit;
the central processing unit is used for starting the preposed conditioner to receive data for the first time according to the hammering time signal, storing the digital signal received by the analog-to-digital converter in the memory, generating a two-dimensional vibration spectrum according to a calculation sequence, and sending the two-dimensional vibration spectrum and the hidden danger parameter to a display for displaying; and storing the two-dimensional vibration spectrum and the hidden danger parameters in the memory.
The pile bottom hidden danger detection system for the pore-forming pile-grouting preferably further comprises a second vibration sensing device, wherein the second vibration sensing device is embedded in peripheral rock-soil media of a pile hole or mud wall protection liquid of the pile hole or is arranged on an impact hammer and used for detecting a reference vibration signal and transmitting the reference vibration signal to the seismic recorder;
the second vibration sensing device is connected with the preposed conditioner.
Preferably, the pile bottom hidden danger detection system for the hole-forming pile-grouting pile is characterized in that the first vibration sensing device is formed by connecting two or more broadband acceleration sensors in parallel or in series;
the second vibration sensing device is composed of two or more broadband acceleration sensors or broadband acceleration hydrophones which are connected in parallel or in series.
Preferably, the system for detecting the hidden danger at the pile bottom of the hole-forming pile-grouting pile further comprises a communication device; the communication device is a wired communication device or a wireless communication device; the wireless communication device is one of a Bluetooth communication device, a WiFi communication device, a 4G communication device and an Internet of things communication device; the central processor communicates with the server through the communication device.
Preferably, the acquisition triggering device is arranged on the impact hammer or the impact hammer release device and is provided with a triggering communicator; and the trigger communicator is correspondingly selected from the communication devices.
A method for detecting hidden danger at the bottom of a bored pile by using the detection system comprises the following steps:
s1, starting from the moment that the pile hole enters the bearing stratum, detecting the background vibration signal generated when the impact hammer hammers the pile bottom according to the sequence that the impact hammer hammers the pile bottom by the first vibration sensing device and transmitting the background vibration signal to the seismic recorder, and calculating a background vibration frequency spectrum by the central processing unit according to the calculation sequence;
s2, synthesizing a two-dimensional vibration spectrum by the central processing unit according to the background vibration spectrum and the calculation sequence;
and S3, analyzing whether the hidden danger exists and hidden danger parameters by the central processing unit according to the two-dimensional vibration spectrum.
Preferably, the method for detecting the hidden danger at the bottom of the bored pile further includes, in step S1:
starting from the entry of the pile hole into the bearing stratum, the second vibration sensing device also detects the reference vibration signal generated when the impact hammer hammers the pile bottom according to the sequence of the impact hammer hammering the pile bottom and transmits the reference vibration signal to the seismic recorder, and the central processing unit calculates a reference vibration frequency spectrum according to the calculation sequence;
the step S2 further includes: and the central processor respectively calculates a normalization amplitude spectrum according to the background vibration spectrum and the reference vibration spectrum in a calculation order, and synthesizes the two-dimensional vibration spectrum according to the normalization amplitude spectrum and the calculation order.
Preferably, in the method for detecting the pile bottom hidden danger of the bored pile, the calculation formula of the normalization amplitude spectrum is formula (1) or formula (2):
wherein, FR(f) Is a normalized amplitude spectrum; fbj(f) As a background vibration spectrum; fck(f) Is a reference vibration frequency spectrum;
wherein, FR(f) Is a normalized amplitude spectrum; fbj(f) As a background vibration spectrum; fck(f) Is a reference seismic spectrum.
Preferably, the calculation sequence is a hammering sequence or a hammering footage.
Preferably, when the calculation order is that the hammering footage is performed, the background vibration signal and the reference vibration signal of all hammering times in the hammering footage are obtained, an average background vibration signal and an average reference vibration signal are obtained respectively, and the background vibration frequency spectrum and the reference vibration frequency spectrum are obtained by calculating the average background vibration signal and the average reference vibration signal respectively.
Compared with the prior art, the system and the method for detecting the pile bottom hidden danger of the bored pile provided by the invention have the advantages that the background vibration signal is obtained through the first vibration sensing device, the signal interference generated by the inconsistency of the seismic sources can be eliminated to a certain extent, the two-dimensional vibration spectrum is obtained through the technical means of abnormal rejection of continuous impact response signals, superposition averaging of adjacent multiple impact signals and the like, the pile bottom hidden danger can be found quickly, the reliability of the test vibration signal is ensured, and the data support is provided for effectively detecting the pile bottom hidden danger.
Drawings
Fig. 1 is a schematic structural diagram of a pile bottom hidden danger detection system of a bored pile according to embodiment 1 of the present invention;
FIG. 2 is a schematic structural diagram of a pile bottom hidden danger detection system of a bored pile according to embodiment 2 of the present invention;
FIG. 3 is a block diagram of the seismic recorder provided by the present invention;
FIG. 4 is a calculation wave diagram of a calculation sequence in the method for detecting the pile bottom hidden danger of the bored concrete pile provided by the present invention;
FIG. 5 is an inspection view of embodiment 2 of the present invention, wherein the abscissa is the hammer penetration;
FIG. 6 is a wave chart of embodiment 3 of the present invention without normalization;
fig. 7 is a wave diagram after normalization operation in embodiment 3 according to the present invention.
Detailed Description
In order to make the objects, technical solutions and effects of the present invention clearer and clearer, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
Referring to fig. 1 and 3, the present invention provides a system for detecting hidden troubles at the bottom of a pile for forming a hole and grouting, comprising: the earthquake recorder 1 and the first earthquake sensing device 2;
the first vibration sensing device 2 is embedded in the peripheral rock-soil medium of the pile hole or the mud wall protection liquid of the pile hole, and is used for detecting a background vibration signal and transmitting the background vibration signal to the seismic recorder 1;
the seismic recorder 1 includes: the system comprises an acquisition triggering device 11, a preposed conditioner 12, an analog-to-digital converter 13, a central processing unit 14, a display 16 and a memory 17;
the acquisition triggering device 11 is configured to acquire a hammering time signal of the impact hammer 4 hammering the pile bottom, and transmit the hammering time signal to the central processing unit 14; in general, the acquisition triggering device 11 is connected to the central processing unit 14 through a line; however, if the collecting and triggering device 11 is an independent device and is installed on the percussion hammer 4 releasing device or the percussion hammer 4, it can be connected to the cpu 14 through the communication device 15;
the preposed conditioner 12 is connected with the first vibration sensing device 2, connected with the analog-to-digital converter 13, and used for sending the received analog signal to the analog-to-digital converter 13 after being preprocessed;
the analog-to-digital converter 13 is connected to the central processing unit 14, and is configured to convert an analog signal transmitted by the preconditioner 12 into a digital signal and transmit the digital signal to the central processing unit 14;
the central processing unit 14 is configured to start the preconditioner 12 to perform primary data reception according to the hammering time signal, store the digital signal received by the analog-to-digital converter 13 in the storage 17, generate a two-dimensional vibration spectrum according to a calculation order, and send the two-dimensional vibration spectrum and the hidden danger parameter to the display 16 for display; and stores the two-dimensional vibration spectrum and the hidden danger parameter in the memory 17.
Correspondingly, the invention also provides a method for detecting the hidden danger at the bottom of the bored pile by using the detection system, which comprises the following steps:
s1, starting from the pile hole entering the bearing stratum, the first vibration sensing device 2 detects the background vibration signal generated when the impact hammer 4 hammers the pile bottom according to the sequence of the impact hammer 4 hammering the pile bottom and transmits the background vibration signal to the seismic recorder 1, and the central processing unit 14 calculates the background vibration frequency spectrum according to the calculation sequence;
s2, the central processing unit 14 synthesizes a two-dimensional vibration spectrum according to the background vibration spectrum and the calculation sequence;
and S3, analyzing whether the hidden danger exists and hidden danger parameters by the central processing unit 14 according to the two-dimensional vibration spectrum.
Specifically, the pile bottom hidden danger detection method provided by the invention only needs to use one vibration sensing device, and no matter the first vibration sensing device is embedded in a rock-soil medium or slurry wall protection liquid, the two-dimensional vibration spectrum can be synthesized according to the vibration spectrum and the calculation sequence, so that whether hidden dangers exist or not is analyzed, and the hidden danger parameters of the hidden dangers are output. It should be noted that the calculation order is a hammer order or hammer footage. The hidden danger parameters comprise the size of the hidden danger and the distance between the hidden danger and the pile bottom.
Example 2
Referring to fig. 2-4, the present invention provides a system for detecting hidden troubles at the bottom of a bored pile, including: the earthquake recorder 1, the first earthquake sensing device 2 and the second earthquake sensing device 3;
the first vibration sensing device 2 is embedded in the peripheral rock-soil medium of the pile hole or the mud wall protection liquid of the pile hole, and is used for detecting a background vibration signal and transmitting the background vibration signal to the seismic recorder 1; it should be noted that the primary purpose of the first vibration sensing device 2 is to detect a background vibration signal and normalize the reference vibration signal detected by the second vibration sensing device 3, and the embedding depth is not limited, but the acceleration sensing device needs to be installed within a certain distance range from the pile foundation hole according to the specific situation of the site, and the factors considered comprehensively include the size of the pile hole, and the like, and are generally embedded within the range of 10-20m of the pile hole; in consideration of the comprehensiveness of signal detection, the acceleration sensing device uses a broadband vibration sensor; the slurry is mainly buried in the peripheral rock-soil medium and can be buried in the slurry wall-protecting liquid according to requirements; in general, the first vibration sensing device 2 is an acceleration sensor;
the second vibration sensing device 3 is embedded in peripheral rock-soil media of a pile hole or mud wall protection liquid of the pile hole or is arranged on the impact hammer 4 and used for detecting a reference vibration signal and transmitting the reference vibration signal to the seismic recorder 1; it should be noted that the second vibration sensing device 3 is mainly buried in the slurry wall-protecting liquid, and is not typically buried in the same medium as the first vibration sensing device 2, and is used for detecting the reference vibration signal; of course, sometimes it is not necessary to obtain reference vibration signals in different media, and at this time it is buried in a position similar to the first vibration sensing device 2, for example within 10-20m from the pile hole; in general, the second vibration sensing device 3 is an acceleration sensor or an acceleration hydrophone;
the seismic recorder 1 includes: the system comprises an acquisition triggering device 11, a preposed conditioner 12, an analog-to-digital converter 13, a central processing unit 14, a communication device 15, a display 16 and a memory 17;
the acquisition triggering device 11 is configured to acquire a hammering time signal of the impact hammer 4 hammering the pile bottom, and transmit the hammering time signal to the central processing unit 14; the acquisition triggering device 11 may be manually triggered or an electrical signal triggering device, which is not limited in the present invention; when the manual triggering is used, it is required that a user checks the hammering of the hole-forming percussion hammer 4, the collecting and triggering device 11 is manually driven to send a corresponding control signal to the central processor 14 through the communication device 15, where the control signal may be sent by a key or manually sent by other means, and the central processor 14 controls the pre-conditioner 12 to receive the background vibration signal and the reference vibration signal once; when an electric signal trigger device is used at that time, the acquisition trigger device 11 acquires the moment whether the impact hammer 4 falls down or hammers the pile bottom, and then automatically sends an acquisition starting control signal to the central processing unit;
the pre-conditioner 12 is configured to receive the background vibration signal transmitted by the first vibration sensing device 2 and the reference vibration signal transmitted by the second vibration sensing device 3, convert the signals into a background analog signal and a reference analog signal after conditioning, and send the signals to the analog-to-digital converter 13; the preconditioner 12 is a device commonly used in the art, and has all or part of the corresponding functions of filtering, amplifying or analog-to-digital conversion, and the like, and the invention is not particularly limited; it should be noted that the filtering function requires that the pre-conditioner 12 has a signal amplifying circuit commonly used in the art, and the specific use is whichever, the present invention is not limited, as long as the pre-conditioning of the background vibration signal and the reference vibration signal can be realized, and most of the devices available in the market at present can be realized; the selection of other devices or circuits with the pre-conditioning function is similar to the implementation of the amplification function, and is not described herein again; certainly, the pre-conditioner 12 needs to receive the detection signals of the first vibration sensing device 2 and the second vibration sensing device 3 at the same time, and at this time, a dual circuit operation is required, that is, if the pre-conditioner 12 has a signal amplification function, two amplification circuits are provided, one of the amplification circuits is used for receiving the background vibration signal, and the other one is used for receiving the reference vibration signal; other functional circuits are similar and are not described herein;
the analog-to-digital converter 13 is configured to convert the background analog signal and the reference analog signal into a background digital signal and a reference digital signal, respectively, and transmit the background digital signal and the reference digital signal to the central processing unit 14; in this application, the analog-to-digital converter 13 is a multi-channel synchronous acquisition analog-to-digital converter 13,
the central processor 14 is configured to receive the hammer time signalStarting an earthquake recorderThe first vibration sensing device 2 and the second vibration sensing device 3 detect the background vibration signal and the reference vibration signal respectively, store the background vibration signal and the reference vibration signal in real time, calculate and receive the background digital signal and the reference digital signal frequency spectrum transmitted by the analog-to-digital converter 13, further calculate a normalization amplitude spectrum, generate a two-dimensional vibration spectrum and hidden danger parameters, and send the two-dimensional vibration spectrum and the hidden danger parameters to the display 16 for display and the storage 17 for storage respectively. In the present invention, the type of the processor is not particularly limited as long as the corresponding detection method can be completed, and a general microprocessor in the art can complete the detection; of course, there is no problem in selecting the intel i 7-series processor, or a general (Microcontroller Unit) may be selected, and other processors may be used as long as they can implement the corresponding functions.
The communication device 15 is used for sending and receiving communication information according to the instruction of the processor; in a specific implementation, the detection data and the calculation data of the system can be uploaded to a server for storage or fine analysis, the system needs to be connected with a server, a computer, a mobile phone and other remote devices through the communication device 15, and the processor transmits the detection data and the two-dimensional vibration spectrum to the server; correspondingly, the communication mode of the communication device 15 may be wired communication or wireless communication, specifically, the field operation is the standard; preferably, the communication device 15 is a wireless communication device 15; meanwhile, the remote equipment such as the server, the computer, the mobile phone and the like can also send a control instruction to the processor through the communication device 15, so that the remote shutdown and start of the earthquake recorder 1 and the modification of related parameters are realized;
the display 16 is used for displaying a two-dimensional vibration spectrum and the hidden danger parameters according to the instruction of the processor;
the memory 17 is used for storing the detection information data and the processing data.
Correspondingly, the invention also provides a method for detecting the hidden danger at the bottom of the bored pile by using the detection system, which comprises the following steps:
s1, starting from the entry of the pile hole into the bearing stratum, sequentially detecting the background vibration signal and the reference vibration signal generated when the impact hammer 4 strikes the pile bottom by the first vibration sensing device 2 and the second vibration sensing device 3, and after passing through the preconditioner 12 and the analog-to-digital converter 13, the central processor 14 respectively calculates a background vibration frequency spectrum and a reference vibration frequency spectrum according to the calculation order; specifically, the punching impact hammer 4 is a universal device for pile foundation hole forming, the invention is not limited, and meanwhile, in the implementation process of the method, additional equipment for hammering the pile bottom is not needed; meanwhile, the algorithm of the background vibration frequency spectrum and the reference vibration frequency spectrum uses a common method in the field of vibration wave detection, and the method is not limited in the invention and can be obtained by using a calculation method in the field;
s2, the central processing unit 14 respectively calculates normalization amplitude spectrums according to the calculation sequence of the background vibration frequency spectrum and the reference vibration frequency spectrum, and synthesizes two-dimensional vibration spectrums according to the calculation sequence; it should be noted that the purpose of calculating the normalized amplitude spectrum is to eliminate or reduce the background influence of the vibration of the large-stratum structure and highlight the vibration response frequency spectrum characteristics of the hidden danger of the small-scale pile bottom, so that the results of other algorithms for realizing the effect are also the normalized amplitude spectrum of the invention;
and S3, analyzing whether the hidden danger exists and hidden danger parameters by the central processing unit 14 according to the two-dimensional vibration spectrum.
Specifically, under the hammering action of the impact hole forming hammer, huge vibration is enough to enable a hole bottom geological structure (soil body and rock stratum) and a relatively fine geological structure (such as a karst cave, a boulder, a weak interlayer and the like) to generate vibration response, and the response characteristics or vibration spectrums of different geological structures and fine structures of the stratum are different. The geometric dimension of the geological structure is relatively large, the main frequency of the formed vibration response or vibration response spectrum is low, and after the impact hammer 4 enters the bearing stratum, if no tiny geological structure hidden danger exists near the pile bottom, the vibration response of the pile maintains a relatively stable frequency spectrum characteristic; the micro geological structure related to the hidden danger at the bottom of the pile is relatively small in geometric dimension, and a vibration response spectrum formed under the excitation of impact vibration has high frequency; therefore, there is a significant frequency band difference between the two in the vibration spectrum. According to the structural modal test analysis theory, when the response of a fine geological structure is analyzed, the hidden danger of the unfavorable geological structure with a large geometric dimension exists, the response frequency of the hidden danger is in a relatively low frequency position on the abnormal frequency band of the vibration response, and otherwise, the hidden danger of the unfavorable geological structure is in a relatively high frequency position. Further, if there is an abnormal structural risk at or near the pile bottom, an abnormal structural risk farther from the impact hammer 4 (for example, several tens of meters), as the hammering footage increases, the amplitude of the high-frequency abnormal response signal changes slowly or hardly, and if the abnormal structural risk is closer to the pile bottom (for example, several meters or less), the amplitude of the high-frequency abnormal response signal increases faster. The existence of the unfavorable geological structure, the approximate distance characteristic and the approximate size scale can be distinguished through the exact existence and the change characteristic of the high-frequency response abnormal signal.
The depth of the pile bottom entering the supporting layer is preferably 1-3 times of the diameter of the pile body according to the building foundation design standard GB 50007-2011. When the depth of the pile bottom entering the bearing stratum is determined, the influences of special soil, karst, seismic subsidence liquefaction and the like are considered, and the specific condition is determined according to construction conditions.
For example, if a karst cave exists in the supporting layer, the karst cave is exactly positioned at the bottom of the pile foundation and is 8 meters away from the top surface of the supporting layer, the depth of the supporting layer of the pile foundation is 5 meters according to design requirements, and no karst cave hidden danger exists within 5 meters of the bottom of the pile, then the distance from the bottom surface of the pile foundation to the top plate of the karst cave is changed from 8 meters to 3 meters when the impact hammer 4 enters the supporting layer, the change is huge, so that the signal response generated by exciting the karst cave has obvious gradual increase characteristics along with the gradual approach of the impact hammer 4 to the karst cave, the amplitude spectrum which is consistent with the natural vibration frequency of the karst cave structure is reflected on the frequency spectrum and is rapidly enhanced, and the existence of the hidden danger can be obviously judged through the characteristics. Obviously, if no karst cave exists in the bearing stratum or the karst cave is far away from the pile bottom, the vibration wave signals and the frequency spectrum received by the acceleration sensing device and the acceleration hydrophone device do not change greatly along with the hammering depth of the impact hammer 4, because the rock entering footage of 5 meters is too small relative to the thickness of the base rock of the bearing stratum and too small relative to the distance of the far karst cave, and the change is not obvious.
Preferably, in this embodiment, the first vibration sensing device 2 is formed by connecting two or more broadband acceleration sensors in parallel or in series;
the second vibration sensing device 3 is composed of two or more broadband acceleration sensors or broadband acceleration hydrophones which are connected in parallel or in series.
Specifically, the acceleration sensor and the acceleration hydrophone both adopt broadband acceleration sensors, and the preferred range of the broadband acceleration sensors is 10Hz-10 KHz.
Preferably, in this embodiment, the calculation formula of the relative amplitude spectrum is formula (1) or formula (2):
wherein, FR(f) Is a normalized amplitude spectrum; fbj(f) As a background vibration spectrum; fck(f) Is a reference vibration frequency spectrum;
wherein, FR(f) Is a normalized amplitude spectrum; fbj(f) As a background vibration spectrum; fck(f) Is a reference seismic spectrum.
Specifically, in detecting the shock signal of the impact hammer 4, if a single sensing device (the acceleration sensing device or the acceleration hydrophone is used singly) is used for shock response measurement and spectrum analysis, the energy of the shock response signal generated by the geological structure of the stratum with larger scale is too strong, the construction response signal of the hidden danger with small scale, especially high-frequency information, is submerged, and the resolution of the abnormal response signal related to the hidden danger is very low. According to the implementation of the detection method provided by the invention, the first vibration sensing device 2, preferably the embedded rock-soil medium, detects the background vibration signal, and due to the absorption and attenuation of the rock-soil medium, the low-frequency component is approximately reserved, and the high-frequency component is absorbed and attenuated; the reference vibration signal detected by the first vibration sensing device 2 embedded in the slurry dado liquid is better reserved due to the dissipation of shear waves (the shear waves are waves with the propagation direction perpendicular to the vibration direction of the medium particles and are also called transverse waves) and approximate wave guiding phenomena. Therefore, after the pile hole internal and external signals from the same hammering excitation response are obtained, the vibration spectrum of the vibration spectrum normalization pile hole liquid internal sensor measurement signal vibration spectrum of the signals in the rock soil outside the hole is utilized, namely the background vibration signal normalization reference vibration signal can highlight the high-frequency signal characteristics and inhibit the low-frequency response signal frequency band which is not related to the abnormal structure hidden danger greatly, so that the identification of the abnormal structure response information is facilitated, and the resolution is particularly facilitated to show the gradual change characteristic analysis of the high-frequency band signal along with the increase of the footage. Meanwhile, in consideration of slight difference in amplitude and frequency characteristics of the excitation source of the multi-time impact hammer 4, the vibration spectrum of the vibration spectrum normalization pile hole liquid internal sensor of the rock-soil signal beside the hole is utilized to measure the signal vibration spectrum, and the interference abnormity generated by the self-inconsistency of the vibration source is weakened to a certain extent. The source of vibration inconsistency is generally caused by the inconsistent drop height of the impact ram 4.
Preferably, in this embodiment, the calculation order is a hammer order or a hammer footage. The calculation sequence is a calculation period selected in field implementation, and can be calculated once by selecting one hammering, or can be calculated once according to the hammering footage after the depth of the pile hole is increased by a certain length. Of course, a predetermined number of hammering times may be selected and counted once.
As a preferable scheme, in this embodiment, when the calculation order is the hammering footage, the background vibration signal and the reference vibration signal of all hammering times in the hammering footage are obtained, and an average background vibration signal and an average reference vibration signal are obtained respectively, and the background vibration frequency spectrum and the reference vibration frequency spectrum are calculated from the average background vibration signal and the average reference vibration signal respectively.
Although the force and the state of each hammering of the impact hammer 4 are approximately similar, occasionally, the vibration source of each hammering is abnormal, and in order to ensure the stability of the acquisition record, the optimization can be carried out in continuous multiple excitation response signals, and abnormal excitation response caused by the vibration source is eliminated. The response signals of adjacent hammer excitations should be similar or identical, according to which principle a stable signal is selected as the active signal from more than two signals. The stabilization signal is the corresponding average vibration signal.
The average background vibration signal and the average reference vibration signal can be respectively obtained by detecting the background vibration signal and the reference vibration signal which are hammered for multiple times, so that the signal to noise ratio of the collected signals is improved, the stability of the signals is enhanced, and the average background vibration signal and the average reference vibration signal which are synchronously formed by superposition are obtained. Under the condition, the footage of the impact hammer 4 entering the bearing stratum is used as a coordinate parameter, and the signal-to-noise ratio of the effective signal can be improved in a mode of averaging multiple hammering response signals in a section of footage. The method for subsequently forming the two-dimensional vibration spectrum F (F, i) is not limited, and can be the same or different, and the analysis standard can be adaptively changed.
Preferably, in this embodiment, the seismic recorder further includes a communication device 15; the communication device 15 is one of a bluetooth communication device, a WiFi communication device, a 4G communication device and an internet of things communication device; the central processor 14 communicates with the server via the communication means 15.
As a preferable scheme, in this embodiment, the collecting and triggering device 11 is mounted on the impact hammer 4 or a release device of the impact hammer 4 or an impact rope, and has a triggering communicator; the trigger communicator is selected in correspondence with the communication device 15.
As a preferred scheme, in this embodiment, the hidden danger parameters include: the size of the hidden danger and the distance from the pile bottom. It should be noted that the size of the hidden danger and the distance from the pile bottom are both obtained by analyzing the two-dimensional vibration spectrum, and the process of analyzing the two-dimensional vibration spectrum is greatly related to the situation of field implementation, so the specific analysis result is different according to the implementation situation.
Example 3 two-dimensional spectral analysis characteristics of pile hole internal and external sensors collected respectively and normalized by division method
Please refer to fig. 5, the first vibration sensing device 2 is a broadband acceleration sensor with a bandwidth of 10Hz-10KHz, and is embedded in the rock-soil medium 10m away from the center of the pile outside the pile hole; the second vibration sensing device 3 is a broadband acceleration hydrophone with the bandwidth of 10Hz-10KHz and is embedded in the slurry wall protection liquid in the pile hole. Burying a broadband acceleration sensor with the bandwidth of 10Hz-10KHz in a geotechnical medium which is 10m away from the center of a pile and is outside a pile hole and subjected to impact hole-forming operation with the diameter of 1.5m in a karst development area, burying a broadband acceleration hydrophone with the bandwidth of 10Hz-10KHz in slurry wall-protecting liquid in the pile hole while avoiding a hanging hammer cable by 40cm and being 10m away from the slurry liquid level when a pile hammer enters a bearing layer, connecting the acceleration sensor and the acceleration hydrophone to the seismograph 1, utilizing a double-path synchronous seismograph 1 to sequentially and synchronously record the geotechnical vibration signals and the slurry vibration signals generated by hammering the pile bottom of the pile foundation impact hammer and to respectively calculate the geotechnical vibration frequency spectrums and the slurry vibration frequency spectrums of the two vibration signals, and then calculating the normalization spectrum, establishing a two-dimensional coordinate system according to the hammering sequence and the normalized amplitude spectrum to form the two-dimensional vibration spectrum; the high-frequency band on the two-dimensional vibration spectrum has a salient anomaly with 1300Hz main frequency as a center and a salient anomaly with 980Hz main frequency as a center, the frequency band widths of the two abnormal main frequencies 1/2 are respectively 80Hz and 200Hz when the main frequency amplitudes are increased, the 1300Hz main frequency amplitude is gradually increased along with the increase of a hammering sequence, the increased amplitude is obvious, the 980Hz main frequency amplitude is almost unchanged, and through two-dimensional frequency spectrum characteristic analysis, the 1300Hz main frequency abnormal reaction pile bottom possibly has a karst structure abnormal hidden danger similar to a spherical cavity and is closer to the pile bottom; additional hidden construction hazards may exist near the 980Hz main frequency anomaly characterization, but the distance from the 980Hz main frequency anomaly characterization to the pile bottom is far, so that the hidden construction hazards can be avoided.
In order to further ensure the reliability of the signals, the first vibration sensing device 2 is composed of 2 or more broadband acceleration sensors, and sensor signals outside the pile hole are synthesized in parallel or in series; the second vibration sensing device 3 is composed of 2 or more broadband acceleration hydrophones, and sensor signals in pile holes are synthesized in parallel or in series.
Further, in this embodiment, when the first vibration sensing device 2 is a plurality of acceleration sensors, the acceleration sensors are respectively embedded in a plurality of directions such as the south, the west, the north, and the south of the pile hole.
Example 4 two-dimensional spectral feature analysis of Single-pile out-of-hole sensor signals, typical Signal features
Referring to fig. 6-7, the first vibration sensing device 2 is embedded in the geotechnical medium, and the first vibration sensing device 2 is four acceleration sensors. In the magma area, boulder hazards may exist in the bearing zone. Embedding a broadband acceleration sensor with the same parameters in rock-soil media with the diameter of 2.0m, which are located at four positions of the south, the east, the west and the north outside a pile hole and are 10m away from the center of the pile hole; when the impact hammer 4 enters the bearing stratum, the earthquake recorder 1 is used, the background vibration signal generated when the pile foundation pore-forming impact hammer 4 begins to enter the bearing stratum is recorded successively and synchronously, the vibration frequency spectrum of the background vibration signal is calculated, and the first vibration sensing device is embedded in the rock-soil medium, so that a two-dimensional vibration response spectrum can be formed without normalization calculation; the high-frequency band on the two-dimensional vibration response spectrum has a prominent abnormality with 1100Hz (numerical values of horizontal and vertical axes are not marked in the drawing) main frequency as a center, the frequency band width of the abnormal main frequency 1/2 main frequency amplitude is respectively 200Hz, the 1100Hz main frequency amplitude is gradually increased along with the increase of a hammering sequence, the main frequency bandwidth is gradually increased, and through two-dimensional frequency spectrum characteristic analysis, the 1100Hz main frequency abnormal reaction pile bottom can possibly have an abnormal hidden danger of an orphan structure and is close to the pile bottom. Of course, it is also possible to use the method steps provided by the present invention, when the first vibration sensing device 2 and the second vibration sensing device 3 are installed in the same medium, the central processing unit 14 independently analyzes the vibration response signals acquired from the same medium, and obtains the two-dimensional vibration spectrum according to the calculation order, and then the analysis method is the same as that in embodiment 3, and the result is unchanged.
It should be noted that, in this embodiment, the first vibration sensing apparatus may further include four acceleration hydrophones, and the implementation process is as described above and is not described again.
It should be noted that, in all embodiments, the first and second vibration sensing devices may also be speed sensors, and the physical sensitive elements thereof may be capacitors, inductors, resistors, photoelectric gratings, piezoelectrics, electromagnetic converters, superconducting materials, etc., and their selective use does not affect the main structures of the detection method and the detection system, and the implementation processes thereof are as described above and will not be described again.
It should be understood that equivalents and modifications of the technical solution and inventive concept thereof may occur to those skilled in the art, and all such modifications and alterations should fall within the scope of the appended claims.

Claims (8)

1. A method for detecting hidden danger at the bottom of a bored pile is characterized by comprising the following steps:
s1, starting from the moment that the pile hole enters the bearing stratum, detecting a background vibration signal generated when the impact hammer hammers the pile bottom according to the sequence that the impact hammer hammers the pile bottom by the first vibration sensing device and transmitting the background vibration signal to a seismic recorder, and calculating a background vibration frequency spectrum by the central processing unit according to the calculation sequence; the second vibration sensing device also detects a reference vibration signal generated when the impact hammer hammers the pile bottom according to the sequence of the impact hammer hammering the pile bottom and transmits the reference vibration signal to the seismic recorder, and the central processing unit calculates a reference vibration frequency spectrum according to the calculation sequence;
s2, the central processing unit respectively calculates a normalization amplitude spectrum according to the background vibration spectrum and the reference vibration spectrum and according to the calculation order, and synthesizes a two-dimensional vibration spectrum according to the normalization amplitude spectrum and the calculation order,
the calculation formula of the normalization amplitude spectrum is formula (1) or formula (2):
wherein, FR(f) Is a normalized amplitude spectrum; fbj(f) As a background vibration spectrum; fck(f) Is a reference vibration frequency spectrum;
and S3, analyzing whether the hidden danger exists and hidden danger parameters by the central processing unit according to the two-dimensional vibration spectrum.
2. The method for detecting the pile bottom hidden danger of the bored pile according to claim 1, wherein the calculation order is a hammering order or a hammering footage.
3. The method for detecting the pile bottom hidden danger of the bored pile according to claim 2, wherein when the calculation order is the hammering footage, the background vibration signal and the reference vibration signal of all hammering times in the hammering footage are obtained to obtain an average background vibration signal and an average reference vibration signal respectively, and the background vibration frequency spectrum and the reference vibration frequency spectrum are calculated from the average background vibration signal and the average reference vibration signal respectively.
4. A pile bottom hidden danger detection system for a hole-forming cast-in-place pile by adopting the pile bottom hidden danger detection method of the hole-forming cast-in-place pile, which is characterized by comprising the following steps: the earthquake recorder and the first earthquake sensing device;
the first vibration sensing device is embedded in peripheral rock-soil media of the pile hole or mud wall protection liquid of the pile hole, and is used for detecting a background vibration signal and transmitting the background vibration signal to the seismic recorder;
the seismic recorder comprising: the device comprises an acquisition trigger device, a preposed conditioner, an analog-to-digital converter, a central processing unit, a display and a memory;
the acquisition triggering device is used for acquiring a hammering time signal of the impact hammer for hammering the pile bottom and transmitting the hammering time signal to the central processing unit;
the preposed conditioner is connected with the first vibration sensing device, connected with the analog-to-digital converter and used for sending a received analog signal to the analog-to-digital converter after being preprocessed;
the analog-to-digital converter is connected with the central processing unit and is used for converting the analog signal transmitted by the preposed conditioner into a digital signal and transmitting the digital signal to the central processing unit;
the central processing unit is used for starting the preposed conditioner to receive data for the first time according to the hammering time signal, storing the digital signal received by the analog-to-digital converter in the memory, generating a two-dimensional vibration spectrum according to a calculation sequence, and sending the two-dimensional vibration spectrum and the hidden danger parameter to a display for displaying; and storing the two-dimensional vibration spectrum and the hidden danger parameters in the memory.
5. The system for detecting the hidden danger at the bottom of the pile for forming and filling the pile according to claim 4, further comprising a second vibration sensing device which is embedded in the peripheral geotechnical medium of the pile hole or the slurry wall protecting liquid of the pile hole or is arranged on an impact hammer and used for detecting a reference vibration signal and transmitting the reference vibration signal to the seismic recorder;
the second vibration sensing device is connected with the preposed conditioner.
6. The pile bottom hidden danger detecting system for the hole-forming pile-grouting pile according to claim 5, wherein the first vibration sensing device is formed by connecting two or more broadband acceleration sensors in parallel or in series;
the second vibration sensing device is formed by connecting two or more broadband acceleration sensors in parallel or in series.
7. The system for detecting hidden danger at pile bottom of hole-forming pile-grouting pile according to claim 4, wherein the seismic recorder further comprises a communication device; the communication device is a wired communication device or a wireless communication device; the wireless communication device is one of a Bluetooth communication device, a WiFi communication device and a 4G communication device; the central processor communicates with the server through the communication device.
8. The system for detecting the hidden danger at the pile bottom of the hole-forming pile-grouting pile as claimed in claim 7, wherein the acquisition triggering device is arranged on the impact hammer or the impact hammer releasing device and is provided with a triggering communicator; and the trigger communicator is correspondingly selected from the communication devices.
CN202010012705.0A 2020-01-07 2020-01-07 System and method for detecting hidden danger at pile bottom of bored pile Active CN111158043B (en)

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CN1928260A (en) * 2005-09-08 2007-03-14 陈彦平 Method for foundation pile end hole rock character detection and judgment technique
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EP2662499A3 (en) * 2012-05-08 2016-03-09 Technische Universität Hamburg-Harburg Quality assurance method for creating piles and open profile for the same
CN205804434U (en) * 2016-07-19 2016-12-14 广东真正工程检测有限公司 A kind of foundation detection device
CN110515117A (en) * 2019-07-19 2019-11-29 广州市高速公路有限公司 A kind of underground karst cavity detection method to be impulsed based on pile monkey with decision-tree model

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1928260A (en) * 2005-09-08 2007-03-14 陈彦平 Method for foundation pile end hole rock character detection and judgment technique
CN103255785A (en) * 2012-02-15 2013-08-21 陈彦平 Technology for performing foundation pile quality detection and geology survey by adopting single tube longitudinal wave method
EP2662499A3 (en) * 2012-05-08 2016-03-09 Technische Universität Hamburg-Harburg Quality assurance method for creating piles and open profile for the same
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