CN103882893B - Pile foundation dynamic load test system and test method based on fiber grating - Google Patents

Abstract

The invention discloses a pile foundation dynamic load test system and test method based on optical fiber gratings. The test system includes a reaction force frame device, a dynamic loading device, a soil holding tank and a monitoring device. The test method is to use a set of dynamic loading system to simulate various vibration waves acting on the foundation pile, and measure the stress-strain deformation of the foundation pile through the sensing fiber grating arranged in the pile foundation. In the present invention, the reaction force frame device and the soil holding tank are poured together to ensure the stability and reliability of the reaction force transmission; the dynamic loading device can accurately control the loading waveform and load in the dynamic test process; the monitoring device has a fast response speed and can be monitored remotely. The sensing fiber grating has little effect on the pile body.

Description

Pile foundation dynamic load test system and test method based on fiber grating

technical field

The invention relates to a test device and a test method of a foundation structure, in particular to a pile foundation dynamic load test system and a test method based on an optical fiber grating.

Background technique

In the existing related projects, the pile foundation design method under the static force is mostly used in the design, and the influence of the vibration load is rarely considered. The bearing capacity can only be used as the design control standard, and the method of greatly increasing the bearing capacity as a safety reserve is designed. . In recent years, with the rapid development of my country's high-speed railway construction, the requirements for high-speed, high comfort, high safety, and high-density continuous operation of high-speed railways have become higher and higher. Require. When a high-speed train passes the bridge, due to the dynamic action, the dynamic response of the pier body is significant. At the same time, under the load of the high-speed train, the bridge pile foundation will inevitably be affected. However, there are relatively few studies on the dynamic characteristics of the bridge pile foundation under dynamic load. When the train crosses the bridge, the actual working state of the pile is not only subjected to static force (dead load) but also dynamic. In order to simulate the static and dynamic loads of dead load and traffic load on the pile top, it is particularly important to carry out static and dynamic load tests on pile foundations. Due to the insufficiency of dynamic load-related tests and theoretical research, the current understanding of the bearing and deformation characteristics of pile foundations under dynamic loads is far from enough, and the existing evaluation standards lag far behind engineering practice. To guide engineering design, it is necessary to carry out systematic experiments and theoretical studies on the characteristics of pile foundations under dynamic loads to deepen the understanding of the bearing and deformation mechanism of pile foundations under dynamic loads. Due to the relative difficulty in simulating vibration waveforms, there are few dynamic loading systems capable of accurately simulating various waveforms, and there are relatively few sensors capable of high-speed, stable, and accurate monitoring of pile foundations under vibration conditions. In order to accurately monitor the bearing and deformation of pile foundations under dynamic loads, make the design of pile foundations under dynamic loads more rational, have better safety, and have more reasonable economic indicators. The stress-strain monitoring system has important engineering practice value.

Contents of the invention

Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a fiber grating-based pile foundation dynamic load test system and test method.

Technical solution: In order to solve the above technical problems, the fiber grating-based pile foundation dynamic load test system provided by the present invention includes:

a soil holding tank having side walls and a bottom wall made of reinforced concrete;

The reaction frame includes a pair of parallel door-shaped brackets. The door-shaped brackets are connected by channel steel columns and I-beam upper beams through bolts. The middle part of the upper beams of the pair of door-shaped brackets is connected with the lower beam. The bottom of the channel steel column is embedded in the reinforced concrete side wall of the soil holding tank;

The dynamic loading device includes a backing plate, an upper hinge support, a lower hinge support and a dynamic load applying device. The backing plate and the upper hinge support are fixed to the middle of the lower beam by bolts. The dynamic load applying device includes a hydraulic jack , an oil pump, a cooling system and a control system, the upper hinge support and the lower hinge support are respectively installed at both ends of the hydraulic jack, the control system is connected to the hydraulic jack, and the oil pump is connected to the hydraulic oil circuit of the hydraulic jack , the cooling system is installed on the oil pump;

Engineering pile, the pile body is embedded in the soil of the soil holding tank, the top of the pile body is fixedly connected with the lower hinge support, and the surface of the pile body is equipped with sensing optical fibers, and the sensing optical fibers are connected to the fiber grating dynamic demodulator and data processing and save system.

When in use, the test method of the above-mentioned test system comprises the following steps:

1) Use the reaction frame, dynamic loading device and soil tank to build the test system;

2) Use sandpaper to clean the position where the sensing optical fiber is to be buried on the surface of the prefabricated engineering pile;

3) Apply the blended epoxy resin on the polished position, and let it stand after application;

4) After the epoxy resin to be applied is fully solidified, fix the straightened sensing fiber on the epoxy resin layer with quick-drying glue, and then encapsulate the fixed sensing fiber with epoxy resin, and record the sensing fiber at the same time. The position and length of the fiber grating on the sensing fiber;

5) Lay the soil layer at the bottom of the soil holding tank, and then put the engineering piles with pre-embedded fiber gratings into the soil holding tank, and then arrange the soil layers in layers in the soil holding tank to the designated position, and place the top of the engineering piles with the The hinge support connection at the bottom of the hydraulic jack;

6) Connect the power loading device and the jack, and use the power loading system to preload the engineering pile, so that the top of the pile is in close contact with the hinge support at the bottom of the hydraulic jack;

7) Connect the sensing fiber to the fiber grating dynamic demodulator, use the control system to adjust the dynamic load, and record the data of the sensing fiber at the same time.

Beneficial effects: the test system and method adopted in the present invention can reliably monitor the stress and strain of the pile foundation under the action of dynamic load. Due to the full size test, the loaded dynamic load is much smaller than the original load. In this test system, the dynamic loading device is fixed on the reaction frame through high-strength bolts. The dynamic loading device can accurately simulate any load and waveform. Among them, the reaction force frame device adopts a steel structure, and the soil holding tank adopts a reinforced concrete structure. By pouring channel steel into the reinforced concrete of the soil holding tank to form a whole, the stability of the overall structure can be increased; the lower beam is connected to two parallel The midpoint of the upper beam forms an I-shaped stable structure, which can evenly disperse the reaction force of the dynamic load to the columns of the two door-shaped brackets, greatly reducing the deviation or inclination after the dynamic load is applied in the test risk of equipment damage. The hinge supports are installed at both ends of the dynamic load hydraulic jack, which greatly improves the stability of the system and the reliability of test data, and reduces the difficulty of installation and calibration. The loading waveform and load during the dynamic test can be precisely controlled through the control system and the hydraulic jack, and various vibration wave effects can be simulated.

The traditional monitoring methods currently use electrical strain gauges to monitor the strain of the pile body, which has the disadvantages of being susceptible to moisture and electromagnetic interference, and cannot fully obtain the deformation characteristics of the pile body, and is easily damaged in the dynamic load test, resulting in missing monitoring data. It cannot fully reflect the deformation of the pile body, and it is difficult to realize the optimal design and construction of the pile. If it is necessary to comprehensively analyze the deformation characteristics of the pile body, more sensors must be arranged, and there are too many wires drawn from the sensors, which will be very troublesome in the actual operation process. Therefore, it is particularly important to adopt a convenient and effective method to monitor the stress and deformation of piles. Fiber Bragg grating FBG (FiberBraggGrating) technology has the characteristics of combining transmission and sensing media. FBGs with different grating pitches are placed on different positions of the same optical fiber, and wavelength division multiplexing technology is used to achieve stress and temperature control. Quasi-distributed measurement makes all the gratings along the optical fiber layout path become sensitive elements, thus realizing quasi-distributed measurement. Optical fiber is both a sensing medium and a transmission channel. It has many advantages such as small size, light weight, strong geometric adaptability, anti-electromagnetic interference, good electrical insulation, high sensitivity, and easy remote monitoring. It can be used in piles Body dynamic deformation monitoring.

Description of drawings

Fig. 1 is the structural representation of the embodiment of the present invention;

Fig. 2 is the structural representation of the embodiment of the present invention;

Fig. 3 is a sectional view of the engineering pile in Fig. 1 .

Detailed ways

The present invention will be described in detail below in conjunction with the examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

The fiber grating-based pile foundation dynamic load test system of this embodiment is shown in FIG. 1 and FIG. 2 , including a reaction frame, a dynamic loading device and a soil holding tank 17 . Wherein the reaction frame includes a pair of gate-shaped brackets arranged in parallel, which are formed by connecting channel steel columns 15 and I-beam upper beams 1 through high-strength bolts 14, and the lower beam 4 is connected to the middle of a pair of upper beams 1 Forming an I-shape, the bottom of the channel steel column 15 is poured into one body with the reinforced concrete side wall of the soil holding tank 17.

The dynamic loading device includes a backing plate 2, an upper hinge support 5, a lower hinge support and a dynamic load application device. The backing plate 2 and the upper hinge support 5 are fixed to the middle part of the lower beam 4 through the second high-strength bolt 3, and the dynamic load The application device includes a hydraulic jack 7 , an oil pump 8 and a cooling system 9 , and a control system 6 . The upper hinge support 5 and the lower hinge support are respectively installed at both ends of the hydraulic jack 7, the control system 6 is connected to the hydraulic jack 7, the oil pump 8 is connected to the hydraulic oil circuit of the hydraulic jack 7, and the cooling system 9 is installed on the oil pump 8 .

The pile body of the engineering pile 12 is embedded in the soil of the soil holding tank 17, and the top of the pile body is fixedly connected with the lower hinge support. A sensing fiber 13 is installed on the surface of the engineering pile 12 , and the sensing fiber 13 is connected to a fiber grating dynamic demodulator 11 and a data processing and saving system 10 .

As shown in Figure 3, the sensing optical fiber 13 on the surface of the engineering pile is packaged in epoxy resin 18, and is filled with epoxy resin 18 between the sensing optical fiber 13 and the engineering pile, and the outer side of the sensing optical fiber 13 is also wrapped with a ring Oxygen 18.

During use, the fiber grating-based pile foundation dynamic load test method of the present embodiment comprises the following steps:

1) Connect the reaction frame, power loading device, soil holding tank and monitoring device to form a test system. The reaction force frame device is composed of I-shaped steel and channel steel, welding is used between the I-shaped steel, and high-strength bolts are riveted between the I-shaped steel and the channel steel. The channel steel is connected with the soil holding tank, and the bottom of the channel steel is poured in the soil holding tank. The dynamic loading device is composed of a dynamic loading controller, a dynamic load applying device, an oil pump and a cooling device, etc. The power loading device is connected with the reaction frame through backing plates, high-strength bolts and upper hinge supports.

2) Use sandpaper to clean the position where the fiber grating is to be embedded on the surface of the prefabricated engineering pile.

3) Apply the blended epoxy resin on the polished position, the width of the application is about 5cm, and the thickness is about 2mm.

4) The applied epoxy resin generally needs to stand for 24 hours. After the applied epoxy resin is fully solidified, use quick-drying glue to fix the straightened sensing fiber on the epoxy resin layer, and then use epoxy resin to The fixed sensing fiber is packaged, and the position and length of the fiber grating on the sensing fiber are recorded at the same time, so as to be used for monitoring and analysis;

5) Lay the soil layer at the bottom of the soil holding tank, and then put the engineering piles with pre-embedded fiber gratings into the soil holding tank, and then arrange the soil layers in layers in the soil holding tank to the designated position, and place the top of the engineering piles with the The hinge support connection at the bottom of the hydraulic jack;

6) Connect the control system of the dynamic load application device to the hydraulic jack, connect the oil pump device and the cooling device at the same time, and debug the dynamic load application device. After everything is normal, first use the dynamic loading system to preload the engineering pile. Make the top of the pile in close contact with the hinge support at the bottom of the hydraulic jack, and at the same time check and adjust so that the load applied by the dynamic loading device can just be transferred to the top of the pile.

7) Connect the sensor to the fiber grating dynamic demodulator, debug various coefficients, and reconfirm whether the loading and monitoring system is normal. If not, check whether there is a problem with the connection of each component, whether the fiber grating is damaged, etc. If normal, then It is possible to experiment. The dynamic loading device is used to simulate the action of various vibration waves, and the data collected by the fiber grating is recorded at the same time.

Claims (1)

1., based on a method of testing for the pile foundation Dynamic loading test system of fiber grating, this pilot system comprises:

Soil holding groove, has the sidewall and diapire be made up of steel concrete;

Reaction frame, comprise the portal trestle of pair of parallel setting, described portal trestle is bolted by channel steel upright post and i iron top rail and forms, and is connected with lower transverse beam in the middle part of the top rail of described a pair portal trestle, and the bottom of described channel steel upright post embeds in the steel concrete sidewall of soil holding groove;

Power charger, comprise backing plate, upper hinge support, lower hinge support and dynamic load bringing device, described backing plate and upper hinge support are secured by bolts in the middle part of lower transverse beam, described dynamic load bringing device comprises hydraulic jack, oil pump, cooling system and control system, described upper hinge support and lower hinge support are installed on the two ends of hydraulic jack respectively, described control system and hydraulic jack control connection, the hydraulic circuit of described oil pump access hydraulic jack, described cooling system is installed on oil pump;

Engineering pile, its pile body embeds in the soil of soil holding groove, and pile body top is fixedly connected with lower hinge support, and pile body surface is provided with sensor fibre, described sensor fibre incoming fiber optic grating dynamic demodulation instrument and data processing and saved system;

It is characterized in that comprising the following steps:

1) use reaction frame, power charger and soil holding groove build pilot system;

2) the position sand papering prefabricated engineering pile surface will being buried underground sensor fibre is clean;

3) epoxy resin be in harmonious proportion in the clean position of polishing is smeared, and smears rear leaving standstill;

4) after epoxy resin to be applied fully solidifies, with Instant cement, stretching sensor fibre is fixed on epoxy resin layer, and then with epoxy resin, the sensor fibre fixed is encapsulated, record position and the length of fiber grating on sensor fibre simultaneously;

5) bottom soil holding groove, lay soil layer, then the engineering pile of pre-buried good fiber grating is put into soil holding groove, then in soil holding groove, the hinged-support of the top of engineering pile with hydraulic jack top/bottom part, to the position of specifying, is connected by layered arrangement soil layer;

6) connect power charger, with power charger, precompressed is carried out to engineering pile, make the hinged-support close contact of stake top and hydraulic jack top/bottom part;

7) by sensor fibre connecting fiber grating dynamic demodulation instrument, utilize control system to adjust dynamic load, record the data of sensor fibre simultaneously.