CN110714489A - Distributed optical fiber sensing monitoring system for horizontal displacement of foundation pit and periphery - Google Patents
Distributed optical fiber sensing monitoring system for horizontal displacement of foundation pit and periphery Download PDFInfo
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- CN110714489A CN110714489A CN201911040735.6A CN201911040735A CN110714489A CN 110714489 A CN110714489 A CN 110714489A CN 201911040735 A CN201911040735 A CN 201911040735A CN 110714489 A CN110714489 A CN 110714489A
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- optical cable
- cable
- sensing optical
- strain sensing
- fiber
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D33/00—Testing foundations or foundation structures
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D2600/00—Miscellaneous
- E02D2600/10—Miscellaneous comprising sensor means
Abstract
The invention relates to a distributed optical fiber sensing and monitoring system for horizontal displacement of a foundation pit and the periphery, which comprises a reinforcement cage, an optical fiber grating strain sensing optical cable and a metal-based cable-shaped strain sensing optical cable; the fiber grating strain sensing optical cable and the metal-based cable strain sensing optical cable are arranged on the steel reinforcement cage at intervals in the cross section in the width direction, and the free ends of the fiber grating strain sensing optical cable and the metal-based cable strain sensing optical cable are respectively and electrically connected with a fiber grating demodulator.
Description
Technical Field
The invention relates to a distributed optical fiber sensing monitoring system for horizontal displacement of a foundation pit and the periphery of the foundation pit.
Background
The soil body can deform like other materials after being subjected to external force, the deformation property is complex, and the influence factors are various. In the process of excavation of the foundation pit, physical properties such as the stress state of a soil body are changed, and pressure difference occurs on two sides of the foundation pit, so that structures such as a retaining wall body and a pile can generate displacement in the horizontal direction.
The deep foundation pit horizontal displacement monitoring mainly monitors the horizontal displacement of the side of a foundation pit or a pile in the foundation pit vertical to the side. In a relatively busy place such as a city center, not only is the foundation pit large in scale, but also the surrounding buildings are particularly compact, and the required accuracy is also high. Therefore, the monitoring of the deformation of the diaphragm wall and the internal force of the structure is very important in the excavation process of the foundation pit.
The invention content is as follows:
the invention provides a monitoring system capable of monitoring whether a diaphragm wall deforms or displaces in real time, and the technical scheme for achieving the purpose is as follows:
a distributed optical fiber sensing monitoring system for horizontal displacement of a foundation pit and the periphery comprises a steel reinforcement cage, an optical fiber grating strain sensing optical cable and a metal-based cable-shaped strain sensing optical cable; the free ends of the fiber grating strain sensing optical cable and the metal-based cable strain sensing optical cable are respectively and electrically connected with a fiber grating demodulator, and the fiber grating demodulator acquires sensing parameters of the fiber grating strain sensing optical cable and the metal-based cable strain sensing optical cable; the fiber bragg grating strain sensing optical cable is used for sensing deformation of a contact part or the vicinity of the contact part of the fiber bragg grating strain sensing optical cable and the reinforcement cage, and the metal-based cable-shaped strain sensing optical cable is used for sensing integral deformation of the reinforcement cage; a dense distributed temperature sensing optical cable is also arranged on the reinforcement cage near the metal-based cable-shaped strain sensing optical cable and used for temperature compensation; the dense distributed temperature sensing optical cable is led to the ground, is electrically connected with the optical fiber demodulation equipment and is used for data measurement;
after the fiber bragg grating strain sensing optical cable, the metal-based cable-shaped strain sensing optical cable and the dense distributed temperature sensing optical cable are arranged on the reinforcement cage, the reinforcement cage is poured by using concrete, and a ground connecting wall is formed;
the fiber bragg grating strain sensing optical cable comprises optical fibers, metal reinforcing parts are closely arranged on the peripheries of the optical fibers, and sheaths are sleeved on the peripheries of the metal reinforcing parts.
The fiber bragg grating strain sensing optical cable and the reinforcement cage can be arranged together in a bundling or sticking mode.
The invention has simple structure, can monitor the change of the diaphragm wall in real time and provides guarantee for construction and safety.
Drawings
FIG. 1 is a schematic view of the present invention;
FIG. 2 is a schematic view of a metal matrix cable strain sensing cable;
FIG. 3 is a deformation diagram of the reinforcement cage under a horizontal load;
description of the figures: the device comprises a steel reinforcement cage 1, a metal-based cable-shaped strain sensing optical cable 2, an optical fiber 2-1, a metal reinforcement 2-2, a sheath 2-3, a fiber bragg grating strain sensing optical cable 3 and a dense distributed temperature sensing optical cable 4;
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
In the figure, a distributed optical fiber sensing monitoring system for foundation pit and peripheral horizontal displacement comprises a reinforcement cage 1, a metal-based cable strain sensing optical cable 2 and a fiber grating strain sensing optical cable 3 are arranged on the reinforcement cage 1 at intervals in the cross section of the width direction, the fiber grating strain sensing optical cable 3 and the metal-based cable strain sensing optical cable 2 are electrically connected with a fiber grating demodulator, and the fiber grating demodulator is also called a BOTDR device or a BOTDR demodulator.
The fiber bragg grating demodulator acquires sensing parameters of a fiber bragg grating strain sensing optical cable 3 and a metal-based cable-shaped strain sensing optical cable 2; the fiber bragg grating strain sensing optical cable 3 is used for sensing deformation of key parts of the reinforcement cage 1, the periphery of the underground diaphragm wall body is most sensitive to stress and is easy to deform, and the key parts can be the periphery of the underground diaphragm wall or the key stress sensitive parts are determined according to specific conditions of projects.
The metal-based cable-shaped strain sensing optical cable 2 is used for sensing the integral deformation of the reinforcement cage 1; a dense distributed temperature sensing optical cable 4 is arranged on the reinforcement cage 1 near the metal-based cable-shaped strain sensing optical cable 2, and the dense distributed temperature sensing optical cable 4 is used for temperature compensation, so that the influence on the sensitivity of the metal-based cable-shaped strain sensing optical cable 2 and the fiber grating strain sensing optical cable 3 due to too low temperature is avoided; the dense distributed temperature sensing optical cable 4 is led to the ground, the optical cable is connected in series on the ground, and is connected with optical fiber demodulation equipment for measuring temperature data;
the fiber bragg grating strain sensing optical cable 3, the metal-based cable-shaped strain sensing optical cable 2 and the dense distributed temperature sensing optical cable 4 are arranged, and then the cross section of the dense distributed temperature sensing optical cable is in a U-shaped structure.
After the fiber bragg grating strain sensing optical cable 3, the metal-based cable-like strain sensing optical cable 2 and the dense distributed temperature sensing optical cable 4 are arranged on the reinforcement cage, the reinforcement cage is poured by using concrete to form a ground connecting wall;
the diaphragm wall is formed by pouring a reinforcement cage and concrete, the diaphragm wall is regarded as a whole after pouring, deformation measured by optical fibers fixed on the reinforcement cage can be regarded as deformation of the whole diaphragm wall, and the horizontal displacement condition of the diaphragm wall can be calculated through measurement data.
During the concrete operation, a groove is dug around a building to be monitored, fiber grating strain sensing optical cables 3, metal-based cable-shaped strain sensing optical cables 2 and dense distributed temperature sensing optical cables 4 are distributed on the manufactured reinforcement cage 1 at intervals, and then the reinforcement cage 1 is placed in the groove dug in advance and is molded by casting to form the ground connection wall.
The reinforcement cage 1 is located close to the building so that the building will respond substantially the same when the reinforcement cage 1 is deformed, and therefore the reinforcement cage 1 is used to monitor changes in the building. And the data acquisition of the optical fiber sensor is realized by adopting an optical fiber grating demodulator, so that the deformation and the structural internal force of the diaphragm wall in the excavation process of the foundation pit are monitored.
Because the optical cable on the reinforcement cage 1 can be buried in the ground for a long time, the rigidity of the optical cable needs to be good, and the structure of the optical cable is changed in the invention; specifically, the metal-based cable-shaped strain sensing optical cable 2 comprises an optical fiber 2-1, metal reinforcements 2-2 are closely arranged on the periphery of the optical fiber 2-1, the metal reinforcements 2-2 surround the optical fiber 2-1 in the middle, and a sleeve 2-3 is sleeved on the periphery of the metal reinforcements 2-2 to wrap the metal reinforcements 2-2 and the optical fiber 2-1.
The calculation of the deformation parameters of a lower cage after deformation or displacement is described below;
when the reinforcement cage is subjected to bending deformation, the horizontal displacement of the reinforcement cage can be calculated by testing the strain values of the optical fiber sensors (the fiber bragg grating strain sensing optical cable 3, the metal-based cable-like strain sensing optical cable 2 and the dense distributed temperature sensing optical cable 4) implanted in the reinforcement cage.
Let ε1(z) and ε2And (z) respectively obtaining strain test values of symmetrical parts of the reinforcement cage at the depth z along the horizontal load direction, wherein one side of the reinforcement cage, which is stressed when the reinforcement cage is strained, is stressed. Axial compressive strain epsilona(z) and bending strain εmThe values of (z) are respectively:
wherein ε 1 and ε 2 represent the strain values at depth z at two symmetric locations in the horizontal load direction, respectively;
deformation condition of the reinforcement cage under the action of horizontal load: under the action of a horizontal load p, the displacement of the top of the reinforcement cage is changed from m to m' -n, at the moment, the length of a longitudinal arc line segment O1O2 on a neutral axis of the reinforcement cage is selected to be dz, the curvature radius of an O1O2 line segment on the neutral layer is selected to be rho (z), the rotation angle of the structure body is d theta, and the bending strain at the position from the neutral axis y (z) is:
relationship between bending strain and displacement of structure in bending direction:
when the reinforcement cage is bent, the relationship between the curvature radius and the bending moment is
Wherein EI is the bending rigidity (KN m2) of the pile body; e is the elastic modulus of the pile body material; and I is the converted section moment of inertia of the pile body.
Thus, can obtain
whether the diaphragm wall changes or not is calculated according to the bending moment, and when the bending moment exceeds a preset safety value, the diaphragm wall needs to be adjusted to attach importance.
The method can accurately sense the change of the diaphragm wall, and in the construction process, the horizontal displacement condition of the diaphragm wall is calculated by the measured data epsilon 1 and epsilon 2 and the known pile body section inertia moment I and the known pile body material elasticity modulus E data, so that the construction safety is ensured.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention shall be included in the scope of the present invention.
Claims (5)
1. The utility model provides a foundation ditch and peripheral horizontal displacement's distributed optical fiber sensing monitoring system, includes the steel reinforcement cage, its characterized in that: the fiber grating strain sensing optical cable and the metal-based cable-shaped strain sensing optical cable are also included; the free ends of the fiber grating strain sensing optical cable and the metal-based cable strain sensing optical cable are respectively and electrically connected with a fiber grating demodulator, and the fiber grating demodulator acquires sensing parameters of the fiber grating strain sensing optical cable and the metal-based cable strain sensing optical cable; the fiber bragg grating strain sensing optical cable is used for sensing deformation of a contact part or the vicinity of the contact part of the fiber bragg grating strain sensing optical cable and the reinforcement cage, and the metal-based cable-shaped strain sensing optical cable is used for sensing integral deformation of the reinforcement cage; a dense distributed temperature sensing optical cable is also arranged on the reinforcement cage near the metal-based cable-shaped strain sensing optical cable and used for temperature compensation; the dense distributed temperature sensing optical cable is led to the ground, is electrically connected with the optical fiber demodulation equipment and is used for data measurement;
after the fiber bragg grating strain sensing optical cable, the metal-based cable-shaped strain sensing optical cable and the dense distributed temperature sensing optical cable are arranged on the reinforcement cage, the reinforcement cage is poured by using concrete, and a ground connecting wall is formed;
the fiber bragg grating strain sensing optical cable comprises optical fibers, metal reinforcing parts are closely arranged on the peripheries of the optical fibers, and sheaths are sleeved on the peripheries of the metal reinforcing parts. And completing the serial connection of the optical cables on the ground.
2. The distributed optical fiber sensing monitoring system for foundation pit and peripheral horizontal displacement according to claim 1, wherein: the cross section of the fiber bragg grating strain sensing optical cable, the metal-based cable-shaped strain sensing optical cable and the densely distributed temperature sensing optical cable after being arranged is of a U-shaped structure.
3. The distributed optical fiber sensing monitoring system for foundation pit and peripheral horizontal displacement according to claim 1, wherein: the metal reinforcing piece is made of aluminum alloy.
4. The distributed optical fiber sensing monitoring system for foundation pit and peripheral horizontal displacement according to claim 1, wherein: the sheath is made of any one of PVC and EVC.
5. The distributed optical fiber sensing monitoring system for foundation pit and peripheral horizontal displacement according to claim 1, wherein: the diameter of the metal reinforcing member is larger than or equal to the diameter of the optical fiber.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112697997A (en) * | 2020-12-09 | 2021-04-23 | 南京大学 | Slope state inversion method based on distributed optical fiber strain sensing |
| CN113026829A (en) * | 2021-03-09 | 2021-06-25 | 南京大学 | Bored concrete pile integrity detection device and method based on dense distributed fiber bragg grating temperature sensing technology |
| CN113216207A (en) * | 2021-05-14 | 2021-08-06 | 中铁一局集团(广州)建设工程有限公司 | Underground diaphragm wall afterloading optical fiber monitoring device and construction method |
| CN113503163A (en) * | 2021-07-22 | 2021-10-15 | 苏州大学 | Monitoring method for construction deformation of shield-driven underground diaphragm wall |
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2019
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112697997A (en) * | 2020-12-09 | 2021-04-23 | 南京大学 | Slope state inversion method based on distributed optical fiber strain sensing |
| CN113026829A (en) * | 2021-03-09 | 2021-06-25 | 南京大学 | Bored concrete pile integrity detection device and method based on dense distributed fiber bragg grating temperature sensing technology |
| CN113026829B (en) * | 2021-03-09 | 2022-05-03 | 南京大学 | Bored concrete pile integrity detection device and method based on dense distributed fiber bragg grating temperature sensing technology |
| CN113216207A (en) * | 2021-05-14 | 2021-08-06 | 中铁一局集团(广州)建设工程有限公司 | Underground diaphragm wall afterloading optical fiber monitoring device and construction method |
| CN113216207B (en) * | 2021-05-14 | 2022-05-10 | 中铁一局集团(广州)建设工程有限公司 | Underground diaphragm wall post-installation optical fiber monitoring device and construction method |
| CN113503163A (en) * | 2021-07-22 | 2021-10-15 | 苏州大学 | Monitoring method for construction deformation of shield-driven underground diaphragm wall |
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Application publication date: 20200121 |