CN114439056B - A system for detecting the bearing capacity of pile foundations using distributed piezoelectric cable impedance sensing technology and its construction and detection methods - Google Patents

Abstract

The invention discloses a system for detecting pile foundation bearing capacity by using a distributed piezoelectric cable impedance sensing technology, which is characterized in that: including multichannel impedance analyzer and distributed piezoelectric cable, distributed piezoelectric cable distributes along pile length direction and embeds in the pile body, distributed piezoelectric cable encircles pile body evenly distributed at least three, distributed piezoelectric cable and multichannel impedance analyzer electrical signal connection, distributed piezoelectric cable includes piezoelectric cable, piezoelectric cable wire and switch switching device, wherein piezoelectric cable and piezoelectric cable wire parallel distribution, a plurality of departments set up control switch switching device between piezoelectric cable wire and the piezoelectric cable, through the position that the multichannel impedance analyzer is to be detected of switch switching device control multichannel impedance analyzer, distributed piezoelectric cable wholly adopt the crust parcel constraint. The construction method and the detection method of the system are also disclosed. The system has stronger anti-skid capability and lower cost.

Description

The system and application of distributed piezoelectric cable impedance sensing technology to detect the bearing capacity of pile foundation Its construction and testing methods

technical field

The invention relates to the field of pile foundation engineering and the field of piezoelectric impedance technology, in particular to a system for detecting the bearing capacity of pile foundation by using distributed piezoelectric cable impedance sensing technology. The invention also relates to a construction method of a system for detecting the bearing capacity of a pile foundation by using a distributed piezoelectric cable impedance sensing technology. The invention also relates to a detection method of a system for detecting the bearing capacity of a pile foundation by using the distributed piezoelectric cable impedance sensing technology.

Background technique

The pile foundation project is an important part of the building foundation. During the construction process, the construction quality of the pile foundation has a great influence on the bearing capacity of the pile foundation. The stability of the pile foundation directly affects the stability and use of the superstructure during the operation and maintenance process. Therefore, it is particularly important to detect during the construction of pile foundation projects and during long-term operation and maintenance. However, the environment in the on-site construction and operation and maintenance process is complex, and the pile foundation data collection environment is harsh, which puts forward higher requirements for the detection of pile foundations. Only by accurately detecting the change process of pile foundation bearing capacity, transmitting the detection signal in time and making analysis and early warning, and timely warning of possible foundation damage in actual engineering, can we better improve the monitoring of pile foundation construction process and Research on bearing characteristics during operation and maintenance.

At present, the commonly used detection methods for detecting concrete pouring piles and PHC pipe piles are steel bar gauges, resistive strain gauges, optical fiber Bragg gratings, and distributed optical fibers. The most commonly used are fiber gratings and distributed fibers. However, distributed optical fibers have many disadvantages: (1) Distributed optical fiber demodulators are expensive, large in size, and monopolized by foreign technologies; (2) Air or dust enters the flange, causing the laser to fail to transmit and loss of optical fiber signals; ( 3) The optical fiber is relatively fragile and needs to be protected by an outer layer of steel strands.

The piezoelectric cable consists of four layers from the inside to the outside, which are alloy, PVDF copper wire and polyethylene protective layer. Piezoelectric cables have high tensile strength, and the operating temperature range of PVDF piezoelectric cables is very wide, ranging from -20 degrees Celsius to 50 degrees Celsius. The piezoelectric coefficient g ₃₃ remains basically unchanged. Nowadays, piezoelectric cables are mostly used in traffic flow detection and other aspects, but are rarely used in perimeter safety detection such as pile foundation detection. However, the impedance of the piezoelectric cable has a linear relationship with the force, so it has great application prospects in perimeter security detection.

Contents of the invention

The purpose of the present invention is to provide a system for detecting the bearing capacity of pile foundations using distributed piezoelectric cable impedance sensing technology, which has stronger anti-skid ability and lower cost. The object of the present invention also includes providing a construction method of a system that utilizes distributed piezoelectric cable impedance sensing technology to detect the bearing capacity of pile foundations. The object of the present invention also includes providing a detection method of a system for detecting the bearing capacity of a pile foundation by using the distributed piezoelectric cable impedance sensing technology.

To achieve the above object, the present invention provides the following technical solutions:

A system for detecting the bearing capacity of pile foundations using distributed piezoelectric cable impedance sensing technology, which is characterized in that it includes a multi-channel impedance analyzer and distributed piezoelectric cables, distributed along the length of the pile body and built-in In the pile body, at least three distributed piezoelectric cables are evenly distributed around the pile body, and the distributed piezoelectric cables are connected to the electrical signal of the multi-channel impedance analyzer. The distributed piezoelectric cables include piezoelectric cables, piezoelectric cable conductors and switching devices , wherein the piezoelectric cable and the piezoelectric cable conductors are distributed in parallel, and a switch exchange device is arranged between the piezoelectric cable conductor and the piezoelectric cable, and the position to be detected by the multi-channel impedance analyzer is controlled by the switch exchange device. The distributed piezoelectric cable is restrained by sheath wrapping as a whole.

Preferably, the pile body is a PHC pipe pile, and the surface of the PHC pipe pile is provided with a wiring groove along the pre-designed route to be tested on the surface of the pile body, and the distributed piezoelectric cable is placed in the wiring groove and solidified with a cementitious material For packaging, four groups of the distributed piezoelectric cables are laid out at intervals of 90° in each test section.

Preferably, the pile body is a cast-in-place pile, and the steel cage of the cast-in-place pile is fixed with a distributed piezoelectric cable by wire binding and epoxy resin on the four longitudinal reinforcements uniformly distributed along the cross-section at intervals of 90°.

The present invention also provides the construction method of the system for detecting the bearing capacity of the pile foundation by using the distributed piezoelectric cable impedance sensing technology, which is characterized in that it includes the following steps:

(1) Cable embedding: The distributed piezoelectric cables are buried in the pile body in a surrounding manner, and four groups of the distributed piezoelectric cables are laid around each detection section at an interval of 90°, and fixed points are fixed after the distributed piezoelectric cables are buried. ;

(2) Data acquisition line connection: The end of the piezoelectric cable conductor is connected with the multi-channel impedance analyzer to form a distributed piezoelectric cable impedance sensing technology to detect the pile foundation bearing capacity of the pile body for data acquisition.

Preferably, the pile body is a PHC pipe pile, and its construction steps include:

(1) Slotted wiring: pre-design the route to be tested along the surface of the pile body, and then use a cutting tool to slot along the designed route. The depth and width are subject to the distributed piezoelectric cables. Each detection section is surrounded Lay four groups of distributed piezoelectric cables at intervals of 90°, and fix them at fixed points after the distributed piezoelectric cables are embedded;

(2) Glue protection: the wiring groove is filled, pasted and surface protected with epoxy resin;

(3) Data acquisition line connection: The end of the piezoelectric cable conductor is connected with the multi-channel impedance analyzer to form a distributed piezoelectric cable impedance sensing technology to detect the bearing capacity of the PHC pipe pile foundation for data acquisition.

Preferably, the pile body is a cast-in-place pile, and its construction steps include:

(1) Embedded cables: On the cast-in-place pile reinforcement cage, one distributed piezoelectric cable is fixed on the four longitudinal reinforcements evenly distributed along the cross-sectional interval of 90° by binding wire and epoxy resin;

(2) Pouring the pile body: hoist the cast-in-place pile reinforcement cage bound with the distributed piezoelectric cable into the pile hole, and then pour concrete so that the concrete wraps the distributed piezoelectric cable;

(3) Data acquisition line connection: The end of the piezoelectric cable conductor is connected with a multi-channel impedance analyzer to form a distributed piezoelectric cable impedance sensing technology to detect the bearing capacity of the cast-in-situ pile foundation for data acquisition.

The present invention provides a detection method for the above-mentioned system that uses distributed piezoelectric cable impedance sensing technology to detect the bearing capacity of pile foundation. Under the action of pile foundation bearing capacity, the pile body generates stress and strain, so that the piezoelectric The impedance of the cable sensor changes, and the output signal of the impedance change is used to determine the axial force change of the cast-in-situ pile or PHC pipe pile, so as to calculate the side friction resistance and pile end bearing capacity of the cast-in-place pile or PHC pipe pile, including:

(1) The axial impedance Z(h) of the piezoelectric cable is obtained by testing with a multi-channel impedance analyzer. Since the change of impedance has a linear relationship with the strain, the axial strain ε(h) of the piezoelectric cable is calculated. Since The piezoelectric cable is fixed on the surface of the pile body. Under the static load, the axial deformation of the piezoelectric cable is consistent with the axial direction of the pile body, so the strain of the pile body is also the strain ε(h), and the stress σ(h) of the pile body is:

σ(h)=ε(h)·E _c , where E _c is the elastic modulus of the cast-in-place pile.

According to the pile body stress σ(Z), the pile body axial force Q(h) is:

Q(h)=σ(h)·A, where A is the cross-sectional area of the pile body.

(2) By testing the impedance change of the piezoelectric cables implanted in the pile body, the strain values of the distributed piezoelectric cables under different load deformations along the pile body can be obtained, and ε ₁ (h) and ε ₂ (h) are respectively The strain test value of the symmetrical part of the pile body along the horizontal load direction at the depth h obtained from the test, the strain on one side of the pile body is under tension and the other side is under compression, then the axial compressive strain ε _a (h) and the bending strain value ε _m (h) are respectively:

Preferably, the multi-channel impedance analyzer integrates transmitting and receiving signals, and the measured value is the impedance change of multiple piezoelectric cables with a frequency of 1 kHz and a voltage of 1 V; the multi-channel impedance analyzer, It has the function of controlling the switch to detect the switching device, and can realize the transmission of the switch command.

Compared with prior art, the beneficial effect of the present invention is:

(1) The piezoelectric cable in the present invention is cheaper than the optical fiber, and the piezoelectric cable is solid inside and is not affected by on-site dust, etc., while the distributed optical fiber is easily affected by dust, air, etc., which affects the distributed optical fiber detection accuracy;

(2) The piezoelectric cable itself has a layer of polyethylene protective layer, which is not easy to damage, while the distributed optical fiber is relatively fragile and needs the protection of the outer steel strand;

(3) Compared with the distributed optical fiber demodulator, the multi-channel impedance analyzer is cheaper. The portable multi-channel impedance analyzer is smaller in size than the fiber optic demodulator, and it is easy to carry. It can realize the large-area detection of pile foundation bearing capacity. .

Description of drawings

Fig. 1 is the schematic diagram of detecting pile foundation bearing capacity by the distributed piezoelectric cable impedance sensing technology provided by Embodiment 1 of the present invention;

Fig. 2 is the structural representation of the multi-channel impedance analyzer in Fig. 1;

Fig. 3 is a schematic structural diagram of the distributed piezoelectric cable in Fig. 1;

4 is a schematic diagram of the layout of the distributed piezoelectric cables in the PHC pipe pile provided by Embodiment 1 of the present invention;

Figure 5 is a cross-sectional view of Figure 4

6 is a schematic diagram of the arrangement of distributed piezoelectric cables in the bored pile provided by Embodiment 2 of the present invention;

FIG. 7 is a cross-sectional view of FIG. 6 .

Reference signs:

1-Pile, 2-Distributed piezoelectric cable, 3-Multi-channel impedance analyzer, 4-Piezoelectric cable conductor, 5-Piezoelectric cable, 6-Switch switching device, 7-Multi-channel impedance analyzer switch, 8 -Multi-channel impedance analyzer detection depth knob, 9-Multi-channel impedance analyzer impedance acquisition button, 10-Multi-channel impedance analyzer wiring hole, 11-Heat shrink tube; 12, Wiring groove.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Please refer to Figures 1 to 5, a system for detecting the bearing capacity of pile foundations using distributed piezoelectric cable impedance sensing technology provided in Embodiment 1 of the present invention, including a multi-channel impedance analyzer 3 and distributed piezoelectric cables 2, distributed Piezoelectric cables 2 are distributed along the length of the pile body and built into the pile body 1. At least three distributed piezoelectric cables 2 are evenly distributed around the pile body 1. In this embodiment, 4 are distributed. The distributed piezoelectric cables 2 and multiple The channel impedance analyzer 3 is connected to the electrical signal, and the distributed piezoelectric cable 2 includes a piezoelectric cable 5, a piezoelectric cable conductor 4 and a switching device 6, wherein the piezoelectric cable 5 and the piezoelectric cable conductor 4 are distributed in parallel, and the piezoelectric cable conductor 4 and the piezoelectric cable 5 are provided with switching devices 6 at multiple places, through which the position to be detected by the multi-channel impedance analyzer 3 is controlled. The distributed piezoelectric cable 2 as a whole is restrained by wrapping.

Referring to Figures 3-5, the distributed piezoelectric cable 2 is packaged with a heat-shrinkable tube 11, which can effectively protect the cable. The pile body 1 is a PHC pipe pile, and the surface of the PHC pipe pile is provided with a wiring groove 12 along the pre-designed route to be tested on the surface of the pile body. The distributed piezoelectric cable 2 is placed in the wiring groove 12 and is made of a gel material For curing and encapsulation, four groups of the distributed piezoelectric cables 2 are arranged at intervals of 90° in each test section. The above structure facilitates the impedance distributed piezoelectric cables 2 to detect the change of the axial force of the pile body in a synchronous manner.

Referring to Figures 1-4, the present invention also provides a construction method for the above-mentioned system for detecting the bearing capacity of pile foundations using distributed piezoelectric cable impedance sensing technology, including the following steps:

(1) Slotted wiring: pre-design the route to be tested along the surface of the pile body, and then use a cutting tool to slot along the designed route. The depth and width shall be subject to the distributed piezoelectric cable 2. Arrange four groups of the distributed piezoelectric cables 2 at intervals of 90°, and fix them at fixed points after the distributed piezoelectric cables 2 are embedded;

(2) Glue protection: the wiring slot 12 is filled, pasted and surface protected with epoxy resin;

(3) Data acquisition line connection: the end of the piezoelectric cable conductor 4 is connected to the multi-channel impedance analyzer 3 to form a system for detecting the bearing capacity of the PHC pipe pile foundation with distributed piezoelectric cable 2 impedance sensing technology for data acquisition.

The detection method of the system for detecting the bearing capacity of the pile foundation using the distributed piezoelectric cable impedance sensing technology includes, under the action of the bearing capacity of the pile foundation, stress and strain are generated on the pile body, so that the distributed piezoelectric cable 2 The impedance of the cast-in-situ pile changes, and the output signal of the impedance change is used to determine the axial force change of the cast-in-place pile or PHC pipe pile, so as to calculate the side friction resistance and the change of the pile end bearing capacity of the cast-in-place pile or PHC pipe pile, including:

(1) The axial impedance Z(h) of the piezoelectric cable 5 is obtained through the test of the multi-channel impedance analyzer 3. Since the change of the impedance has a linear relationship with the strain, the axial strain ε(h) of the piezoelectric cable 5 is calculated ), since the piezoelectric cable 5 is fixed on the surface of the pile body, under the static load, the axial deformation of the piezoelectric cable 5 is consistent with the axial direction of the pile body, so the strain of the pile body is also the strain ε(h), and the stress of the pile body σ (h) is:

σ(h)=ε(h)·E _c , where E _c is the modulus of elasticity of the pile body 1;

According to the pile body stress σ(Z), the pile body axial force Q(h) is:

Q(h)=σ(h)·A, where A is the cross-sectional area of the pile body.

(2) By testing the impedance change of the piezoelectric cable 5 implanted in the pile body, the strain value of the distributed piezoelectric cable under different load deformations along the pile body can be obtained. Let ε ₁ (h) and ε ₂ (h) be respectively In order to obtain the strain test value of pile body 1 at the depth h at the symmetrical position along the horizontal load direction, one side of the pile body is under tension and the other side is under compression, then the axial compressive strain ε _a (h) and the value of bending strain ε _m (h) are respectively:

The above-mentioned multi-channel impedance analyzer 3 integrates transmitting and receiving signals, and the measured value is the impedance change of multiple piezoelectric cables under a frequency of 1kHz and a voltage of 1V; the multi-channel impedance analyzer 3 has a control The switch detects the function of the switching device 6 and can realize the transmission of switch commands.

With reference to Fig. 1, Fig. 2, Fig. 3, Fig. 6, shown in Fig. 7, embodiment 2 of the present invention is basically the same as embodiment 1, and its difference is only: described pile body 1 is cast-in-place pile, and the upper edge of cast-in-situ pile reinforcement cage A distributed piezoelectric cable 2 is respectively fixed on the four longitudinal ribs evenly distributed at 90° cross-sectional intervals by wire binding and epoxy resin.

Its construction steps include:

(1) Embed cables: fix a distributed piezoelectric cable 2 on the cast-in-place pile reinforcement cage and fix a distributed piezoelectric cable 2 on the 4 longitudinal reinforcements evenly distributed along the cross-sectional interval of 90° by binding wire and epoxy resin;

(2) Pouring the pile body: hoist the cast-in-situ pile reinforcement cage bound with the distributed piezoelectric cable into the pile hole, and then pour concrete so that the concrete wraps the distributed piezoelectric cable 2;

(3) Data acquisition line connection: the end of the piezoelectric cable conductor 4 is connected to the multi-channel impedance analyzer 3 to form a system for detecting the bearing capacity of the cast-in-place pile foundation with the distributed piezoelectric cable 2 impedance sensing technology for data acquisition.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (8)

1. A system for detecting pile foundation bearing capacity by using distributed piezoelectric cable impedance sensing technology is characterized in that: including multichannel impedance analyzer and distributed piezoelectric cable, distributed piezoelectric cable distributes along pile length direction and embeds in the pile body, distributed piezoelectric cable encircles pile body evenly distributed at least three, distributed piezoelectric cable and multichannel impedance analyzer electrical signal connection, distributed piezoelectric cable includes piezoelectric cable, piezoelectric cable wire and switch exchange device, wherein piezoelectric cable and piezoelectric cable wire parallel distribution, a plurality of departments set up switch exchange device between piezoelectric cable wire and the piezoelectric cable, through switch exchange device control multichannel impedance analyzer's position that will detect, distributed piezoelectric cable wholly adopt the crust parcel constraint.

2. The system for detecting pile foundation bearing capacity by using distributed piezoelectric cable impedance sensing technology according to claim 1, wherein: the pile body is a PHC pipe pile, a wiring groove is formed in the surface of the PHC pipe pile along a route to be tested, the distributed piezoelectric cables are placed in the wiring groove and are solidified and packaged by adopting cementing materials, and four groups of distributed piezoelectric cables are distributed at intervals of 90 degrees in each test section.

3. The system for detecting pile foundation bearing capacity by using distributed piezoelectric cable impedance sensing technology according to claim 1, wherein: the pile body is a filling pile, and 4 longitudinal ribs which are uniformly distributed on the filling pile reinforcement cage along the section at intervals of 90 degrees are respectively fixed with a distributed piezoelectric cable through binding wires and epoxy resin.

4. A method of constructing a system for detecting pile foundation bearing capacity using distributed piezoelectric cable impedance sensing technology as claimed in claim 1, wherein: the method comprises the following steps:

(1) Burying a cable: the distributed piezoelectric cables are embedded into the pile body in a surrounding mode, four groups of distributed piezoelectric cables are distributed at 90-degree surrounding intervals of each detection section, and fixed points are adopted for fixation after the distributed piezoelectric cables are embedded;

(2) And (3) connecting a data acquisition line: the end heads of the piezoelectric cable wires are connected with a multichannel impedance analyzer to form a system for detecting pile foundation bearing capacity of the pile body by using the distributed piezoelectric cable impedance sensing technology for data acquisition.

5. The construction method of the system for detecting pile foundation bearing capacity by using the distributed piezoelectric cable impedance sensing technology according to claim 4, wherein the construction method comprises the following steps: the pile body is PHC pipe pile, and the construction steps comprise:

(1) Grooving wiring: a route to be tested is designed in advance along the surface of the pile body, then a cutting tool is used for grooving along the designed route, the depth and the width of the groove are based on the fact that distributed piezoelectric cables can be placed in the groove, four groups of distributed piezoelectric cables are distributed around each detection section at 90-degree intervals, and fixed points are adopted for fixation after the distributed piezoelectric cables are buried;

(2) Gluing protection: the wiring groove is filled, adhered and surface-protected by epoxy resin;

(3) And (3) connecting a data acquisition line: the end heads of the piezoelectric cable wires are connected with a multichannel impedance analyzer to form a distributed piezoelectric cable impedance sensing technology system for detecting the pile foundation bearing capacity of the PHC pipe pile for data acquisition.

6. The construction method of the system for detecting pile foundation bearing capacity by using the distributed piezoelectric cable impedance sensing technology according to claim 4, wherein the construction method comprises the following steps: the pile body is a filling pile, and the construction steps comprise:

(1) Burying a cable: 4 longitudinal ribs uniformly distributed on the cast-in-place pile reinforcement cage at intervals of 90 degrees along the section are respectively fixed with a distributed piezoelectric cable through binding wires and epoxy resin;

(2) Pouring the pile body: hoisting a bored concrete pile reinforcement cage bound with the distributed piezoelectric cable into the pile hole, and then pouring concrete to enable the concrete to wrap the distributed piezoelectric cable;

(3) And (3) connecting a data acquisition line: the end heads of the piezoelectric cable wires are connected with a multichannel impedance analyzer to form a distributed piezoelectric cable impedance sensing technology system for detecting the bearing capacity of the pile foundation of the cast-in-place pile for data acquisition.

7. A method of detecting a system for detecting pile foundation bearing capacity using distributed piezoelectric cable impedance sensing technology as claimed in claim 1, wherein: under the effect of pile foundation bearing force, pile body produces stress and strain, so that the impedance of piezoelectricity cable sensor changes, utilizes the output signal of impedance change to judge the axial force change of bored concrete pile or PHC tubular pile to calculate the change of the side friction resistance and pile tip bearing force of bored concrete pile or PHC tubular pile, include:

(1) The axial impedance Z (h) of the piezoelectric cable is obtained through the test of the multichannel impedance analyzer, the axial strain epsilon (h) of the piezoelectric cable is calculated because the change of the impedance and the strain form a linear relation, the piezoelectric cable is fixed on the surface of the pile body, the axial deformation of the piezoelectric cable is consistent with the axial direction of the pile body under static load force, the strain epsilon (h) of the pile body is also obtained, and the stress sigma (h) of the pile body is as follows:

σ(h)＝ε(h)·E _c wherein E is _c Is the elastic modulus of the pile body.

According to pile body stress sigma (Z), pile body axial force Q (h) is:

q (h) =σ (h) ·a, where a is the shaft cross-sectional area,

(2) The strain value of the distributed piezoelectric cable under different load deformations along the pile body can be obtained by testing the impedance change of the piezoelectric cable implanted into the pile body, and epsilon is set ₁ (h) And epsilon ₂ (h) Respectively testing the strain test values of the symmetrical parts of the pile body at the depth h along the horizontal load direction, and axially compressing the strain epsilon when one side of the pile body is pulled and the other side is pressed _a (h) And bending strain value epsilon _m (h) The method comprises the following steps of:

8. the method for detecting the pile foundation bearing capacity by using the distributed piezoelectric cable impedance sensing technology according to claim 7, wherein the method comprises the following steps: the multichannel impedance analyzer integrates transmitting and receiving signals, and the measured value is the impedance change of a plurality of piezoelectric cables under the conditions of 1kHz and 1V voltage; the multichannel impedance analyzer has the function of controlling the switch detection switching device, and can realize switch command emission.

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