A method and device for measuring horizontal displacement of foundation pit support piles

Abstract

The present invention provides a method and device for measuring the horizontal displacement of foundation pit support piles, comprising: marking a measuring surface every other length unit along the length direction of a metal rod; four strain gauges are attached around each measuring surface, and the four strain gauges are evenly spaced; the metal rod is buried in the foundation pit support pile, and the top of the metal rod is exposed on the upper surface of the foundation pit support pile; the horizontal displacement and rotation angle of the top of the metal rod are monitored, and the strain of each strain gauge is collected; the horizontal displacement of each measuring surface on the metal rod is obtained by calculation; thereby the horizontal displacement of the foundation pit support pile is obtained. The advantage of the present invention is that the present invention only needs to attach four strain gauges on each measuring surface of the metal rod, calculate the stress at the corresponding position according to the strain generated by the strain gauge when the metal rod is bent, and use the stress to calculate the deflection of the metal rod when it is bent, thereby reflecting the horizontal displacement generated by the inclined foundation pit support pile.

Description

[Technical field]

[0001] The invention relates to the technical field of construction engineering monitoring, and in particular to a method and a device for measuring the horizontal displacement of foundation pit support piles. [Background technology]

[0002] Foundation pit support is a measure of support, reinforcement and protection for the side walls of the foundation pit and the surrounding environment to ensure the safety of underground structure construction and the surrounding environment of the foundation pit. Common forms of foundation pit support include: 1. Pile support, pile support, pile anchor, and pile cantilever; 2. Underground continuous wall support, ground-connected wall + support; 3. Cement retaining wall, etc. Foundation pit support piles may tilt during use. The tilt degree of foundation pit support piles can be indicated by monitoring the horizontal displacement of the tilted foundation pit support piles.

[0003] Existing patent document 1: Named "A method for improving the accuracy of the azimuth and tool face angle of a fiber optic gyro inclinometer used in small wells", publication number CN103104251A, discloses the use of the attitude angle relationship between the azimuth and the tool face angle to monitor the degree of inclination. Existing patent document 2: Named "A linear fixed wireless deep hole inclinometer and deep hole inclinometer system", publication number CN103498665A, discloses the calculation of horizontal displacement by the inclination of each measuring hole. The existing monitoring methods mainly have the following problems: 1. The gyro inclinometer may slide in the casing, affecting the monitoring; 2. Each measuring hole needs to be equipped with an element for monitoring the inclination, which is expensive. [Summary of the invention]

[0004] The technical problem to be solved by the present invention is to provide a method and device for measuring the horizontal displacement of foundation pit supporting piles, which can perform the measurement stably and firmly.

[0005] The present invention is implemented as follows: A method for measuring the horizontal displacement of foundation pit support piles, comprising:

[0006] Along the length of the metal rod, mark a measuring surface every other length unit;

[0007] Four strain gauges are attached around each of the measuring surfaces, and the four strain gauges are evenly spaced;

[0008] The metal rod is buried in the foundation pit supporting pile, and the top end of the metal rod is exposed on the upper surface of the foundation pit supporting pile;

[0009] monitoring the horizontal displacement and rotation angle of the top end of the metal rod and collecting the strain of each strain gauge;

[0010] The horizontal displacement of each measuring surface on the metal rod is obtained by calculation;

[0011] Thereby, the horizontal displacement of the foundation pit supporting piles is obtained.

[0012] Furthermore, the calculation process is specifically as follows:

[0013] The strain values ​​of the four strain gauges at a distance of i length units from the top of the metal rod are ε i1 , ε i2 , ε i3 , ε i4 , where i is a positive integer;

[0014] According to formula (1) σ = Eε, the stress value corresponding to the position of the strain gauge is obtained as follows: σ i1 , σ i2 , σ i3 , σ i4 , where E is the elastic modulus of the metal rod;

[0015] According to formula (2)

[0016]

[0017] Calculate the maximum tensile stress value σ of each measuring surface i,max ;

[0018] According to formula (3)

[0019]

[0020] Where M is the bending moment, I z is the moment of inertia, y is the ordinate of the stress point, and d is the cross-sectional diameter of the bending rod; calculate the bending moment M of each measuring surface i ;

[0021] According to formula (4), EI z ω=-∫[∫M(x)dx]dx+C1x+C2, where ω is the cross-sectional deflection of the bending rod, i.e., the horizontal displacement, I z is the moment of inertia, C1 and C2 are constants;

[0022] The boundary conditions are the horizontal displacement ω0 and the rotation angle θ0 of the top of the metal rod. The horizontal displacement ω of each measuring surface on the metal rod is calculated. i .

[0023] Furthermore, along the length direction of the metal rod, a measuring surface is marked every one meter.

[0024] Furthermore, each of the strain gauges is provided with a wire, each of the wires is led upward along the rod body of the metal rod, and the other end of each of the wires is connected to a strain measuring instrument.

[0025] Furthermore, a displacement angle monitor is installed on the upper surface of the support pile, and the displacement angle monitor can monitor the horizontal displacement and angle of the top end of the metal rod.

[0026] A device for measuring horizontal displacement of foundation pit supporting piles, comprising:

[0027] A metal rod with a measuring surface marked every other unit of length along its length;

[0028] Strain gauges are attached to the measuring surfaces; four strain gauges are arranged around each measuring surface and are evenly spaced;

[0029] a strain gauge electrically connected to each of the strain gauges;

[0030] A displacement and rotation angle monitor, capable of monitoring the horizontal displacement and rotation angle of the top end of the metal rod;

[0031] The metal rod is used to be buried in the foundation pit supporting pile, and the top end of the metal rod is exposed on the upper surface of the foundation pit supporting pile.

[0032] Furthermore, a measuring surface is marked every one meter along the length direction of the metal rod.

[0033] Furthermore, each of the strain gauges is provided with a wire, each of the wires is led upward along the rod body of the metal rod, and the other end of each of the wires is connected to the strain measuring instrument.

[0034] Furthermore, it also includes a computer, which is electrically connected to the strain measuring instrument and the displacement angle monitoring instrument.

[0035] The advantages of the present invention are as follows: the present invention only needs to attach four strain gauges on each measuring surface of the metal rod, calculate the stress at the corresponding position according to the strain amount generated by the strain gauge when the metal rod is bent, and use the stress to infer the deflection of the metal rod when it is bent, thereby reflecting the horizontal displacement generated by the inclined foundation pit support pile; the strain gauge is fixed on the metal rod and will not slide; compared with the existing measurement method that requires the special arrangement of components such as gyro inclinometers that specifically monitor the inclination, the technical solution of the present invention has lower cost and more stable measurement.

Brief Description of the Drawings

[0036] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0037] Figure 1 It is an execution flow chart of the method for measuring the horizontal displacement of foundation pit supporting piles of the present invention.

[0038] Figure 2 It is a structural schematic diagram of the metal rods in the present invention buried in the foundation pit supporting piles.

[0039] Figure 3 It is a schematic diagram of measuring surfaces marked at intervals along the length direction of the metal rod in the present invention.

[0040] Figure 4 It is a schematic diagram of the arrangement of strain gauges around the measuring surface in the present invention.

[0041] Figure 5 It is a schematic diagram of the inclination of the foundation pit supporting piles and the metal rods in the present invention.

[0042] Figure 6 It is a schematic diagram of stress analysis of measuring points on the measuring surface in the present invention.

[0043] Figure 7 It is a schematic block diagram of a device for measuring horizontal displacement of foundation pit supporting piles according to the present invention.

[0044] Reference numerals: metal rod 100 ; metal rod 101 ; strain gauge 200 ; measuring surface 300 ; foundation pit support pile 400 ; strain measuring instrument 500 ; displacement angle monitor 600 ; computer 700 . [Specific implementation method]

[0045] The embodiment of the present invention solves the technical problem of unstable measurement in the prior art by providing a method and device for measuring the horizontal displacement of foundation pit support piles, and achieves the technical effect of stable measurement with low cost.

[0046] The technical solution in the embodiment of the present invention is to solve the above-mentioned problem. The overall idea is as follows: four strain gauges are attached to each measuring surface of the metal rod, and the stress at the corresponding position is calculated according to the strain generated by the strain gauge when the metal rod is bent. The deflection of the metal rod when it is bent is inferred using the stress. Since the metal rod is buried in the foundation pit support piles, the horizontal displacement caused by the inclined foundation pit support piles is reflected.

[0047] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0048] See also Figures 1 to 7 , a preferred embodiment of the method and device for measuring the horizontal displacement of foundation pit support piles of the present invention. The measuring method of the present invention comprises the following steps:

[0049] S10. Along the length direction of the metal rod 100 , mark a measuring surface 300 every other length unit; in this embodiment, mark a measuring surface 300 every one meter. The rod body of the metal rod 100 is cylindrical, and the measuring surface 300 represents the cross section of the metal rod 100 .

[0050] S20, four strain gauges 200 are attached around each measuring surface 300, and the four strain gauges 200 are evenly spaced to form four measuring points, that is, the lines connecting two adjacent strain gauges 200 to the center of the measuring surface 300 are in a vertical relationship.

[0051] S30, burying the metal rod 100 in the foundation pit supporting pile 400, with the top end 101 of the metal rod 100 exposed on the upper surface of the foundation pit supporting pile 400; in this way, if the foundation pit supporting pile 400 tilts, the metal rod 100 will tilt accordingly and bend.

[0052] Each of the strain gauges 200 is provided with a conductor, each of the conductors is led upward along the rod body of the metal rod 100, and the other end of each of the conductors is connected to the strain gauge 500. The strain gauge 500 adopts a static strain test system with model DH3816. A displacement angle monitor 600 is installed on the upper surface of the support pile, and the displacement angle monitor 600 can monitor the horizontal displacement and angle of the top 101 of the metal rod 100. The displacement angle monitor 600 can use GNSS technology, and GNSS is a global navigation satellite system, such as the Zhonghaida V98GNSS RTK system. The displacement angle monitor can also include an inclinometer and a total station; the inclinometer uses the ACE5411 portable digital inclinometer to measure the top angle of the metal rod; the total station uses the STS-772 series win total station to measure the horizontal displacement of the top of the metal rod.

[0053] S40, monitoring the horizontal displacement and rotation angle of the top end 101 of the metal rod 100, collecting the strain of each strain gauge 200; and recording these data.

[0054] S50, the horizontal displacement of each measuring surface 300 on the metal rod 100 is calculated; the corresponding positions of each measuring surface 300 of the bent metal rod 100 and the foundation pit support pile 400 are obtained, thereby obtaining the horizontal displacement of the foundation pit support pile 400. The inclination of the foundation pit support pile 400 is stably monitored; the strain gauge 200 is attached to the metal rod 100 and buried in the foundation pit support pile 400, so that the strain gauge 200 cannot slide, thereby improving the accuracy of measurement.

[0055] The calculation process is specifically as follows:

[0056] The strain values ​​of the four strain gauges at a distance of i length units from the top of the metal rod are ε i1 , ε i2 , ε i3 , ε i4 , where i is a positive integer; for example, the strains of the four strain gauges at a distance of one meter from the top of the metal rod are ε 11 , ε 12, ε 13 , ε 14 ; The strains of the four strain gauges at a distance of two meters from the top of the metal rod are ε 21 , ε 22 , ε 23 , ε 24 ; And so on. When the metal rod is bent, according to the strain of the strain gauge at the corresponding position, we can know whether the measuring point at the corresponding position of the metal rod is stretched or compressed.

[0057] The following formula is based on the "Mechanics of Materials". From the formula (1) σ = Eε, the stress value corresponding to the position of the strain gauge is obtained as: σ i1 , σ i2 , σ i3 , σ i4 , where E is the elastic modulus of the metal rod; that is, the stresses at the four measuring points on the measuring surface one meter away from the top of the metal rod are σ 11 , σ 12 , σ 13 , σ 14 ; The stresses at the four measuring points on the measuring surface two meters away from the top of the metal rod are σ 21 , σ 22 , σ 23 , σ 24 ; and so on. The stress values ​​of the four measuring points on the measuring surface of the bent metal rod are positive, indicating tensile stress, and negative, indicating compressive stress.

[0058] like Figure 6 As shown in the figure, there are four measuring points on a certain measuring surface, marked as A, B, C, and D, and the corresponding stress is σ i1 , σ i2 , σ i3 , σ i4 ; The center of the measuring surface is marked as O, the neutral axis of the measuring surface is marked as Z, the intersection of the vertical line from measuring point A to the neutral axis Z is marked as E, and the intersection of the vertical line from measuring point B to the neutral axis Z is marked as F. When the metal rod is bent, in an ideal state, the stress σ at measuring point A is i1 and the stress σ at measuring point C i3 are opposite to each other, the stress σ at point B i2 and the stress σ at the measuring point D i4 They are opposite numbers, but there are deviations in practice, so the average value is taken to determine the stress σ at the measuring point A. A With the measuring point σ D The stress is:

[0059]

[0060]

[0061] because Figure 6 In the equation, ΔAEO and ΔDFO are equal, so the length of DF is equal to the length of EO; according to the formula in Mechanics of Materials: is the calculation formula for the normal stress at any point on the cross section of a straight beam in pure bending; where M is the bending moment, I Z is the moment of inertia, and y is the ordinate of the stress point; it can be seen that the stress at the measuring point is proportional to the vertical distance from the measuring point to the neutral axis. Figure 6 In the circular cross section, the vertical distance to the neutral axis is the largest, which is equal to the radius of the circle. The point with the maximum stress is marked as G. The stress at this point is expressed as σ i,max , represents the maximum tensile stress.

[0062] Recombination Figure 6 ,but

[0063]

[0064]

[0065]

[0066]

[0067] Right now

[0068]

[0069] We get formula (2).

[0070] The maximum tensile stress value σ of each measuring surface is calculated by formula (2): i,max ;

[0071] According to formula (3)

[0072]

[0073] Where M is the bending moment, I Z is the moment of inertia, y is the ordinate of the stress point, and d is the cross-sectional diameter of the bending rod; calculate the bending moment M of each measuring surface i ,Right now

[0074]

[0075] The differential equation is approximated by the deflection curve, that is,

[0076] Formula (4) EI z ω=-∫[∫M(x)dx]dx+C1x+C2, where ω is the cross-sectional deflection of the bending rod, i.e., the horizontal displacement, I zis the moment of inertia, C1 and C2 are constants; the boundary conditions are the horizontal displacement ω0 and the rotation angle θ0 of the top of the metal rod. The discrete points of the bending moment of each depth of the measuring surface obtained above are brought into the differential equation, and the differential equation of this discrete data is solved using the existing MATLAB tool to calculate the horizontal displacement ω of each measuring surface on the metal rod. i This reflects the horizontal displacement of the foundation pit support piles.

[0077] The measuring device of the present invention comprises:

[0078] The metal rod 100 has a measuring surface 300 marked at every length unit along its length direction; in this embodiment, a measuring surface 300 is marked at every one meter. The rod body of the metal rod 100 is cylindrical, and the measuring surface 300 represents the cross section of the metal rod 100.

[0079] The strain gauge 200 is attached to the measuring surface 300; four strain gauges 200 are arranged around each measuring surface 300 and are evenly spaced to form four measuring points, that is, the lines connecting two adjacent strain gauges 200 to the center of the measuring surface 300 are in a vertical relationship.

[0080] The strain gauge 500 is electrically connected to each of the strain gauges 200; each of the strain gauges 200 is provided with a wire, each of the wires is led upward along the rod of the metal rod 100, and the other end of each of the wires is connected to the strain gauge 500. The strain gauge 500 adopts a static strain test system of model DH3816.

[0081] The displacement and rotation angle monitor 600 can monitor the horizontal displacement and rotation angle of the top 101 of the metal rod 100; the displacement and rotation angle monitor 600 can use GNSS technology, GNSS is a global navigation satellite system, such as the V98GNSS RTK system of Hi-Target. The displacement and rotation angle monitor can also include an inclinometer and a total station; the inclinometer uses the ACE5411 portable digital inclinometer to measure the top rotation angle of the metal rod; the total station uses the STS-772 series win total station to measure the horizontal displacement of the top of the metal rod.

[0082] The metal rod 100 is used to be buried in the foundation pit supporting pile 400, and the top end 101 of the metal rod 100 is exposed on the upper surface of the foundation pit supporting pile 400. The strain gauge 500 and the displacement angle monitor 600 are both installed above the foundation pit supporting pile 400.

[0083] The device further comprises a computer 700 , which is electrically connected to the strain measuring instrument 500 and the displacement angle monitoring instrument 600 .

[0084] If the foundation pit support pile 400 tilts, the built-in metal rod 100 will bend with the tilt. The four strain gauges 200 on each measuring surface 300 of the bent metal rod 100 will produce corresponding strains, and the strain measuring instrument 500 will collect the strain values ​​of each strain gauge 200, and the strain measuring instrument 500 will transmit the collected strain data to the computer 700. The displacement angle monitor 600 collects the horizontal displacement and angle of the top 101 of the metal rod 100, and the displacement angle monitor 600 transmits the collected displacement angle data to the computer 700. The computer 700 then calculates the horizontal displacement of each measuring surface 300 on the metal rod 100 at this time according to the formula mentioned above, reflecting the horizontal displacement of the foundation pit support pile 400, and finally the computer 700 displays the result on the screen.

[0085] Although the specific implementation modes of the present invention are described above, those skilled in the art should understand that the specific implementation modes described are only illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for measuring the horizontal displacement of foundation pit support piles, characterized in that: include: Along the length of the metal rod, mark a measuring surface every other length unit; Four strain gauges are attached around each of the measuring surfaces, and the four strain gauges are evenly spaced; The metal rod is buried in the foundation pit supporting pile, and the top end of the metal rod is exposed on the upper surface of the foundation pit supporting pile; Each of the strain gauges is provided with a wire, each of the wires is led upward along the rod body of the metal rod, and the other end of each of the wires is connected to a strain measuring instrument; A displacement and rotation angle monitor is installed on the upper surface of the support pile, and the displacement and rotation angle monitor can monitor the horizontal displacement and rotation angle of the top end of the metal rod; monitoring the horizontal displacement and rotation angle of the top end of the metal rod and collecting the strain of each strain gauge; The horizontal displacement of each measuring surface on the metal rod is obtained by calculation; Thereby, the horizontal displacement of the foundation pit supporting piles is obtained; The calculation process is specifically as follows: The distance from the top of the metal rod i The strain values ​​of the four strain gauges per length unit are ε i1 , ε i2 , ε i3 、 ε i4 ,in i is a positive integer; According to formula (1) , the stress value corresponding to the strain gauge position is obtained as: σ i1 , σ i2 , σ i3 , σ i4 ,in E is the elastic modulus of the metal rod; According to formula (2) ; Calculate the maximum tensile stress value of each measuring surface σ i,max ; According to formula (3) ; in M is the bending moment, I z is the moment of inertia, y is the ordinate of the stress point, d is the cross-sectional diameter of the bent rod; Calculate the bending moment of each of the measuring surfaces M i ; According to formula (4) ,in, ω is the cross-sectional deflection of the bending rod, i.e. the horizontal displacement, I z is the moment of inertia, C 1 and C 2 is a constant; The boundary condition is the horizontal displacement of the top of the metal rod ω 0 With corner θ 0 , calculate the horizontal displacement of each measuring surface on the metal rod ω i .

2. A method for measuring horizontal displacement of foundation pit support piles according to claim 1, characterized in that: Along the length direction of the metal rod, one measuring surface is marked every one meter.

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