CN106677231A - Refined measurement method for pile body deformation of cast-in-place pile - Google Patents

Abstract

The invention discloses a method for finely measuring the deformation of cast-in-place piles, which includes axially arranging optical fibers on steel cages, coiling protection during hoisting and lowering stages, continuing to arrange steel cages after welding, protection before pouring concrete, welding and data collection , protection after collection and other steps. The invention applies the OBR optical fiber data acquisition technology to the deformation monitoring of cast-in-situ piles, and has the characteristics of good anti-interference ability, high monitoring precision, wide monitoring range, good engineering adaptability, simple and fast operation, and the like.

Description

Refined Measurement Method of Pile Body Deformation

technical field

The invention belongs to the technical field of geotechnical engineering monitoring, and relates to a method for monitoring deformation of a foundation structure, in particular to a method for finely measuring deformation of cast-in-place piles.

Background technique

With the construction of large-scale high-rise buildings and the development of underground space, engineering construction has higher and higher requirements for foundation bearing capacity. Natural foundations often cannot meet the needs of projects, and foundations need to be reinforced before construction. As a kind of rigid pile, cast-in-situ pile is widely used in engineering because of its large diameter, deep processing depth, wide application range, and convenient construction. It is of great significance to understand the force and deformation of the cast-in-situ pile under load to study the bearing characteristics of the cast-in-situ pile and to popularize the application and improvement of the cast-in-situ pile. At present, in actual engineering and scientific research tests, the monitoring of the axial force of cast-in-situ piles mainly adopts the method of laying axial force meters on the steel bars, and the monitoring of the deformation of cast-in-situ piles mainly adopts the method of laying incline measuring tubes in the pile body. method. Arranging axial force meters on steel bars belongs to point monitoring, and the data are not comprehensive enough. Moreover, when the pile length is too long, a large number of axial force meters and lead wires need to be arranged. Laying the inclinometer tube in the pile is to use the characteristics of simultaneous deformation of the inclinometer tube and the pile body, and indirectly measure the deformation of the pile body by measuring the deformation of the inclinometer tube. In actual operation, due to the elastic modulus of the inclinometer tube body material The elastic modulus of the pile body material is inconsistent, resulting in asynchronous denaturation of the two, and due to the manual error of the measuring tube measurement, the reliability of the monitoring results of the pile body deformation is not high.

Distributed optical fiber sensor based on OBR optical frequency domain reflection (Optical Backscatter Reflectometer) technology is currently the most advanced optical fiber technology in the field of optoelectronic information. This technology not only has strong anti-interference ability of general optical fiber sensing technology, but also has a high survival rate in harsh environments. In addition to its characteristics, it also has the characteristics of distributed measurement. At the same time, because OBR technology is essentially a coherent detection technology based on Rayleigh scattering, its measurement sensitivity and spatial resolution are much higher than other distributed optical fiber sensors. At present, the relatively mature distributed sensing technologies mainly include BOTDR technology, BOTDA technology and BOFDA technology, and the minimum spatial resolutions are 1m, 0.05m and 0.2m respectively. For pile foundation monitoring, the spatial resolution of BOTDR technology is too low, while both BOTDA technology and BOFDA technology require double-ended detection, that is, optical cables are required to form a loop, which is very inconvenient in actual use.

Contents of the invention

Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a refined measurement method for the deformation of cast-in-place piles.

Technical solution: In order to solve the above technical problems, the refined measurement method of cast-in-situ pile body deformation provided by the present invention mainly includes the following steps:

1) Arrange the optical fiber on the steel cage along the axial direction of the steel bar, and bind it with cable ties at the stirrup of the steel cage, and straighten the optical fiber when binding;

2) When the steel cage is hoisted and lowered, coil up the remaining optical fiber and fix it on the steel cage, and continue to arrange it when the steel cage is welded until the length of the optical fiber covers the entire steel cage;

3) Before pouring concrete, protect the optical fiber protruding from the pile with a protective sleeve to prevent damage to the optical fiber during the grouting process;

4) Splice the optical fiber protruding from the pile body with the jumper, and then connect it to the OBR reflectometer for optical path connectivity inspection and initial data collection;

5) After collecting the data, put the jumper wire and the optical fiber protruding from the pile into an iron box with a notch for protection, and put a warning sign on the side.

Preferably, in step 1), the strain collection optical fiber is arranged around the pile body, distributed in a cross shape on the pile section, and the corresponding temperature compensation optical fiber is arranged on the adjacent axial reinforcement.

As a preference, in step 1), the optical fibers are arranged in different ways according to the length of the pile. When the length of the pile is less than 35m, a U-shaped arrangement is adopted to realize the temperature self-compensation of the strain of the pile body. A total of 4 optical fibers are arranged. In particular, when the pile length is not greater than 8m, a single optical fiber can be laid in a U-shape to reduce the number of monitoring times. Similarly, according to the length of the pile, two optical fibers U-shaped layout, three optical fibers U-shaped layout, etc. can be adopted. When the length of the pile is greater than 35m, single-ended laying is adopted and a temperature compensation optical fiber is specially set near the optical fiber to be tested, and a total of 8 optical fibers are arranged.

Preferably, the temperature compensation optical fiber in step 1) needs to be covered with a hollow circular tube with a certain rigidity before laying, so as to ensure that the optical fiber in the circular tube is not stressed.

As a preference, when performing data collection in step 4), insert 8 jumper connectors into the OBR fiber optic data acquisition instrument (single interface) in sequence, use the "strain" module for the strain collection fiber, and use the "temperature" module for the temperature collection fiber.

Beneficial effects: the present invention applies the OBR optical fiber data acquisition technology to monitoring the deformation of cast-in-situ piles, and designs corresponding operation steps, which has the following beneficial effects:

1. Using optical fiber technology, compared with traditional monitoring methods, the reliability and stability of optical fiber monitoring results are higher, and the sensor layout process is simpler;

2. Using OBR technology, OBR technology has the characteristics of distributed measurement, single-ended detection, millimeter-level measurement accuracy, etc., and the OBR data acquisition instrument is small and light, with higher precision and more convenient collection than other optical fiber technologies;

3. Utilizing the characteristics of OBR optical fiber data acquisition technology, this method can not only monitor the deformation of the cast-in-situ pile, but also measure the axial force distribution of each part of the pile by using the characteristics of the full length of the optical fiber, and use the millimeter-level measurement accuracy Judging the weak surface of the cast-in-situ pile, using the sensitivity of optical fiber to temperature to measure the heat of hydration during the solidification process of the cast-in-place pile, and then making a comprehensive evaluation of the pile quality and engineering characteristics of the cast-in-place pile.

In addition to the above-mentioned technical problems solved by the present invention, the technical features constituting the technical solutions, and the advantages brought by the technical features of these technical solutions, other The technical problems, other technical features contained in the technical solution and the advantages brought by these technical features will be further described in detail with reference to the accompanying drawings.

Description of drawings

Fig. 1 is the overall structure schematic diagram of the embodiment of the present invention;

Fig. 2 is the interface of the cast-in-place pile OBR monitoring data processing system;

Figure 3a is a schematic diagram of a U-shaped arrangement of multiple optical fibers;

Figure 3b is a top view of Figure 3a;

Figure 4a is a schematic diagram of a U-shaped layout of a single optical fiber;

Figure 4b is a top view of Figure 4a;

Figure 5a is a schematic diagram of the linear arrangement of optical fibers;

Fig. 5b is a top view of Fig. 5a.

detailed description

Example:

The schematic diagram of the overall structure of this embodiment is shown in Figure 1, 1 is a jack, 2 is a backing plate, 3 is an optical fiber protruding from the pile body, and is protected with a protective sleeve, 4 is a temperature compensation optical fiber, and 5 is a target optical fiber, that is, the strain Collecting optical fiber, 6 is an I-shaped beam, used as a reaction frame to provide load reaction force, 7 is a high-strength steel bar, connected to the reaction frame and cast-in-place pile, the connection method is welding, 8 is a pile near the test pile, used to fix the reaction force shelf. 9 is an optical fiber jumper, which is connected to the optical fiber to be tested and inserted into the acquisition instrument for data acquisition, 10 is an OBR optical fiber data acquisition instrument, and 11 is an OBR monitoring data processing system for cast-in-situ piles. Figure 2 is the interface of the OBR monitoring data processing system for cast-in-situ piles, Figure 3 is a schematic diagram of the U-shaped layout of multiple optical fibers, 3a is a schematic diagram of the pile body layout, and 3b is a schematic diagram of the cross-sectional layout. Figure 4 is a schematic diagram of a U-shaped layout of a single optical fiber, 4a is a schematic diagram of a pile body layout, and 4b is a schematic diagram of a cross-sectional layout. Figure 5 is a schematic diagram of the linear layout of optical fibers, 5a is a schematic diagram of the layout of the pile body, and 5b is a schematic diagram of the cross-sectional layout.

The length of the cast-in-situ pile of the present embodiment is 30m. When in use, the refined measurement method for the deformation of the cast-in-place pile based on the OBR technology includes the following steps:

1) Select the optical fiber layout method according to the pile length, and use a single fiber U-shaped layout for a 30m long pile, and cut out the corresponding fiber length.

2) Put half of the optical fiber on the hollow tube as a temperature compensation optical fiber, and use AB glue to bond the hollow tube and the optical fiber at the bottom of the optical fiber to prevent the hollow tube from sliding along the optical fiber;

3) Arrange the optical fiber on the reinforcement cage along the axial direction of the reinforcement, and bind it with cable ties at the stirrup of the reinforcement cage. When binding, the strain collection optical fiber is stretched properly, and the temperature compensation optical fiber is placed in a natural state without applying force;

4) When the steel cage is hoisted and lowered, coil up the remaining optical fiber and fix it on the steel cage, and then continue to arrange it when the steel cage is welded until the length of the fiber covers the entire steel cage;

5) Before pouring concrete, protect the optical fiber protruding from the pile with a protective sleeve to prevent damage to the optical fiber during the grouting process;

6) Splice the optical fiber protruding from the pile body with the jumper, and then connect it to the OBR reflectometer to check the connectivity of the optical path. After the optical path is normal, apply the primary load and collect the initial data;

7) Import the data into the OBR monitoring data processing system of the cast-in-place pile, and the system automatically processes the optical fiber data;

8) After monitoring, put the jumper wire and the optical fiber protruding from the pile into an iron box with a notch for protection, and put a warning sign on the side.

9) It should be noted that OBR technology is different from other fiber optic technologies. The length of the fiber cannot be changed, so the connection between the fiber jumper and the fiber cannot be interrupted. It must be ensured that the connection between the fiber jumper and the fiber is intact throughout the test phase. If it is interrupted, then The initial value needs to be re-determined and the test performed a second time.

The invention applies the OBR technology to the measurement of the deformation of the cast-in-situ pile, utilizes the high precision of the OBR to realize the precise measurement of the deformation of the pile, and designs different laying methods according to different pile lengths to meet the engineering needs. At the same time, using the cast-in-situ pile OBR monitoring data processing system, this method can not only monitor the deformation of the cast-in-place pile, but also obtain the axial force of each part of the pile through the strain data, judge the weak surface of the pile body, and calculate the perfusion The heat of hydration during the pile solidification process can be used to make a comprehensive evaluation of the pile quality of the cast-in-situ pile.

This method mainly has the following characteristics: (1) The optical fiber technology is applied to the monitoring of the deformation of the cast-in-situ pile, which has the characteristics of non-destructive, real-time, and fast. When used, PE optical fiber is used to enhance the anti-interference ability of the optical fiber to adapt to the harsh conditions of the project line Environment; (2) OBR (Optical Backscatter Reflectometer) technology is used for data collection and processing, which can achieve -125dB sensitivity and 1.5mm resolution within a monitoring range of 70m, realizing zero dead zone and high-precision monitoring of pile deformation; (3) Different layout techniques are adopted according to different pile lengths: when the pile length is less than 35m, U-shaped layout is adopted to realize the temperature self-compensation of pile body strain; when the pile length is greater than 35m, single-end layout is adopted and waiting A temperature compensation optical fiber is specially installed near the measuring optical fiber; (4) According to the measurement characteristics of the OBR technology, the optical fiber connector and the jumper part are protected with a closed iron box; (5) In addition to being able to monitor the deformation of the cast-in-place pile, this method It can also measure the axial force distribution of each part of the pile body by using the characteristics of the fiber optic fiber length, use millimeter-level measurement accuracy to judge the weak surface of the pile body, and use the sensitivity of the fiber optic to temperature to measure the hydration of the cast-in-place pile during solidification Heat, so as to make a comprehensive evaluation of the pile quality of the cast-in-place pile.

Inspired by the above-mentioned ideal embodiment according to the present invention, through the above-mentioned description content, relevant workers can make various changes and modifications within the scope of not departing from the technical idea of the present invention. The technical scope of the present invention is not limited to the content in the specification, but must be determined according to the scope of the claims.

Claims (6)

1. A refined method for measuring deformation of cast-in-place pile piles, characterized in that it comprises the following steps: Step 1, in the reinforcement cage manufacturing stage, the optical fiber is arranged axially on the reinforcement cage; Step 2: During the hoisting and lowering stage of the reinforcement cage, coil up and protect the remaining optical fibers. After the reinforcement cage is welded, continue to arrange the remaining optical fibers; Step 3, protect the optical fiber protruding from the pile before pouring concrete; Step 4: Splice the optical fiber protruding from the pile body with the jumper, and connect the jumper to the OBR reflectometer for data collection; Step 5, after collection, protect the optical fibers and jumpers that will protrude from the pile. 2. The refined measurement method for cast-in-place pile body deformation according to claim 1, characterized in that: the optical fiber includes a strain acquisition optical fiber and a temperature compensation optical fiber, and the strain acquisition optical fiber is arranged around the pile body, and the cross section of the pile is in the shape of Cross-shaped distribution, the corresponding temperature compensation optical fiber is arranged on the adjacent axial steel bars. 3. The method for finely measuring the deformation of cast-in-place piles according to claim 1, characterized in that: in the step 1, different optical fiber layout methods are adopted according to the length of the pile, and when the pile length is less than 35m, a U-shaped method is used Layout to realize the temperature self-compensation of the pile body strain, a total of 4 optical fibers are arranged; when the pile length is not greater than 8m, a single optical fiber U-shaped layout is used to reduce the number of monitoring times; when the pile length is greater than 35m, single-ended layout is used A temperature compensation optical fiber is specially set up near the optical fiber to be tested, and a total of 8 optical fibers are arranged. 4. The refined measurement method for the deformation of cast-in-situ piles according to claim 2, characterized in that: before the temperature compensation optical fiber is laid, a hollow circular tube with a certain rigidity is placed on the outside to ensure that the optical fiber in the circular tube does not Force. 5. the refined measurement method of cast-in-situ pile pile body deformation according to claim 1, is characterized in that: as preferably, when carrying out data collection in step 4, jumper connector is inserted into OBR optical fiber data acquisition instrument successively and detects, and described The OBR fiber optic data acquisition instrument has a strain module and a temperature module, the strain module is used for the strain collection fiber, and the temperature module is used for the temperature collection fiber. 6. The refined measurement method for the deformation of cast-in-situ piles according to claim 2, characterized in that: the strain collection optical fiber is stretched properly when the strain collection optical fiber is bound, and the temperature compensation optical fiber is placed in a natural state without applying force .