CN108982263A - The single pile developed based on soil deformation and shear band recycles t-z model parameter measuring device - Google Patents

Abstract

The invention discloses a kind of single pile circulation t-z model parameter measuring devices, including rack, experimental box, hydraulic loading system, PIV system etc. developed based on soil deformation and shear band；Experimental box is made of for holding the soil body organic glass；Hydraulic loading system is placed in above experimental box, and there are two the effects of aspect for it: (1) for applying consolidation stress to the soil body to simulate various soil mass stress state；(2) vertical cyclic load is applied to stake；PIV system is used to observe pile body in the displacement field variation and the formation and development of stake Soil Interface shear band by vertical cyclic load pile week soil particle.The measurement of pile side friction and pile body shifting when stake may be implemented by cyclic load in the present apparatus, and the related mechanics parameter of pile-soil interaction t-z model is obtained accordingly, on the other hand, it can use the formation and evolution of PIV systematic observation pile peripheral earth deformation and shear band, and then disclose pile-soil interaction under cyclic load from microcosmic point and weaken mechanism.

Description

Parameter Measurement of Cyclic t-z Model of Single Pile Based on Soil Deformation and Shear Zone Development device

technical field

The invention relates to a single pile cycle t-z model parameter measuring device based on soil deformation and shear zone development. The device can measure the relationship between load and displacement of a single pile under cyclic action, and can obtain important t-z model curves in engineering; At the same time, with the help of the PIV observation system, the deformation of the soil around the pile and the formation and development of the shear zone can be obtained, and the mechanism of the circulation weakening of the pile-soil interface can be explained microscopically.

Background technique

When a pile bears a vertical load, the vertical resistance mainly comes from the side friction resistance between the pile and the soil and the pile end resistance. For the long piles commonly used in engineering at present, the side friction resistance plays an important role. The American API standard proposes to use the t-z model to describe the relationship between pile side resistance and displacement, which is widely used in engineering design. At present, relevant scholars have designed experimental devices and experimental methods based on direct shear unit experiments to test and calibrate the t-z curve, but this method has the influence of boundary effects, so it cannot accurately reflect the actual performance of pile side friction.

In addition, the change rule and internal mechanism of the side friction resistance of piles subjected to vertical cyclic loads need to be further studied. It is generally believed that after being subjected to cyclic loading, a certain range of soil on the side of the pile will undergo local shearing and gradually form a shear band. The shear band determines the vertical bearing capacity of the pile and determines the parameter values of the t-z model. However, at present Little is known about the formation and development of pile side shear zones.

Contents of the invention

The object of the present invention is to provide a measuring device for parameters of a single pile cycle t-z model based on soil deformation and shear zone development to address the deficiencies in the prior art. The feature of the device is: on the one hand, it can realize the relationship between the side resistance of the pile body and the vertical displacement of the pile body, and on the other hand, it can monitor the displacement field of the soil around the pile body when the pile body is subjected to cyclic load.

The present invention takes the following technical solutions:

A single pile cycle t-z model parameter measurement device based on soil deformation and shear zone development, including a frame, a hydraulic loading system, an experiment box, and a PIV system; the experiment box is a plexiglass box for holding soil samples; the hydraulic loading system Placed above the test box, it is used to apply initial soil pressure to simulate the stress state of the soil, and provide vertical cyclic load to the pile to simulate the vertical cyclic load of the pile in actual use; the PIV system is used to observe the soil around the pile Changes in the displacement field.

In the above technical solution, the frame includes a base, a main reaction force column, a main reaction force beam, a secondary reaction force column, and a secondary reaction force beam, and the main reaction force column and the secondary reaction force column are vertically fixed on the base Above, the main reaction beam is erected and fixed on the main reaction column, and the secondary reaction beam is erected and fixed on the secondary reaction column. The hydraulic loading system includes a main oil cylinder and a secondary oil cylinder, which are respectively fixed on the main reaction beam and the secondary reaction beam. Below; the pile body is a half-pile after the conventional pile body is cut longitudinally along the axis. The lower part of the main oil cylinder is connected to the loading end of the pile head, an upper plate is placed on the soil sample of the test box, and the lower end of the secondary oil cylinder is connected to the upper plate. The main oil cylinder is used to apply vertical cyclic load to the pile body to simulate the load effect (vehicle load, etc.) on the pile body in actual use. The secondary oil cylinder is used to apply pressure to the soil in the box to simulate soil in different consolidation states.

The PIV system includes a computer, a laser emitter, a synchronizer, a CCD camera, and a scattered light column. The synchronizer is controlled by a computer to adjust the light source of the laser emitter. The light is evenly scattered on the soil through the scattered light column, and the CCD camera shoots the entire pile. The change of the soil particles around the pile, and the shooting information is fed back to the computer.

All the contact surfaces between the pile body and the test box are covered with vaseline.

In the past, the t-z observation device could not overcome the influence of the end resistance, which caused large errors in the experimental results. This device uses the method of suspending the pile end to eliminate the end resistance, and uses Vaseline on the contact surface between the pile body and the experimental box to reduce the pile and test box as much as possible. The effect of friction between the glass boxes.

When the load applied by the main oil cylinder is t, the corresponding displacement of the pile end is z, and the shear force between the pile and soil is τ, then:

Among them: L: pile length (m);

D: pile diameter (m).

The pile-soil shear force τ can be obtained according to the above formula, and the soil in the shear zone satisfies Hooke's law, so:

t=kz

Where: k: stiffness coefficient of shear zone soil (kN/m);

z: displacement of pile body (m).

The stiffness coefficient of the shear zone soil under cyclic loading can be obtained from this.

Adopting the device of the present invention can measure pile side displacement and resistance under cyclic load on the one hand, calibrate the t-z model parameters, obtain t-z curve, on the other hand, can observe pile side soil deformation, observe shear band From the perspective of soil deformation, the influence of cyclic loading on the stiffness coefficient of soil in the shear zone is explored, and the mechanism of pile-soil action is further revealed.

Description of drawings

Figure 1 is a simplified model of the shear band;

Fig. 2 is a schematic diagram (front view) of the experimental box structure of the present invention;

Fig. 3 is the overall structural representation (left side view) of the present invention;

Fig. 4 is a schematic diagram (sectional view) of the experimental box structure of the present invention;

Fig. 5 is a schematic diagram of a PIV device;

Fig. 6 is a schematic structural view (top view) of the experimental box of the present invention;

Fig. 7 is a schematic diagram (top view) of the pile body in the present invention;

Among them, 1. Main reaction beam, 2. Main oil cylinder, 3. Main counter column, 4. Soil sample, 5. Pile body, 6. Ball, 7. Base, 8. Upper plate, 9. LVDT, 10. LVDT fixture, 11. Axial force meter, 12. Secondary reaction beam, 13. Secondary oil cylinder, 14. Axial force meter, 15. Secondary reaction column, 16. CCD camera, 17. Camera bracket, 18. Synchronizer, 19. Laser emitter, 20. Scattered light column bracket, 21. Scattered light column.

Detailed ways

With reference to Fig. 2-7, the measuring device of the single pile circulation t-z model parameter based on soil mass deformation and shear zone development of the present invention comprises frame, hydraulic loading system, experiment box, PIV system; Frame comprises base 7, The main reaction force column 3, the main reaction force beam 1, the secondary reaction force column 15, the secondary reaction force beam 12, the main reaction force column 3 and the secondary reaction force column 15 are all vertically fixed on the base 7, and the main reaction force beam 1 Erected and fixed on the main reaction column 3, the secondary reaction beam 12 is erected and fixed on the secondary counter column 15, the experimental box is a plexiglass box for containing soil samples, fixed on the base, and an upper plate is placed above the soil samples; Pile body 5 is a half-pile after the conventional pile body is cut longitudinally along the axis. The bottom of the tank can be equipped with a ball 6 hydraulic loading system, including the main cylinder 2 and the secondary cylinder 13, which are respectively fixed and installed under the main reaction beam 1 and the secondary reaction beam 12. The main cylinder is connected to the loading end of the pile head for loading the pile body. Vertical cyclic load, the secondary oil cylinder is connected with the upper plate to apply pressure to the soil, which is used to simulate the soil in different consolidation states. The PIV system is used to observe the change of the soil displacement field around the pile, including a computer, a laser transmitter 19, a synchronizer 18, a CCD camera 16, and a scattered light column 21. The synchronizer 18 is controlled by the computer to adjust the light source of the laser transmitter 19, and the light passes through the scattered light column. 21 scatters evenly on the soil, and the CCD camera 16 photographs the changes of soil particles around the pile throughout the pile, and feeds the shooting information back to the computer.

All the contact surfaces between the pile and the test box are covered with vaseline, and balls can also be embedded in the contact between the bottom of the test box and the pile to minimize the impact of frictional resistance on the experiment.

In addition, the observation device may also include software and a data acquisition system, such as a computer, a data acquisition instrument, etc. The data acquisition instrument is connected to various sensors for data acquisition, and the computer analyzes and processes the data and issues instructions according to user settings.

Take the sand sample as an example to briefly describe the test process that adopts the device of the present invention below:

When working, disassemble the servo loading system, apply vaseline on the flat side of the pile, put the pile into the glass box, align the central axis of the pile with the engraved line on the glass box, and pass the lower end of the pile through the hole at the bottom of the experiment box. Artificially fix the pile, add sand to the glass box, at this time the pile has been fixed by sand, and place the upper board on the sand. Install the servo loading system and apply the consolidation load until the soil deformation is stable.

② Turn on the PIV system to realize real-time monitoring of the displacement field of soil particles around the pile when the pile is subjected to cyclic loading.

③Using the servo motor to control the main oil cylinder to apply vertical cyclic load to the pile, the displacement of the pile body can be obtained by using the LVDT, and the lateral frictional resistance of the pile can be read by the oil cylinder to obtain the t-z curve.

After the test, carefully clean the test box and prepare for the next set of tests.

Claims (4)

1. a kind of single pile developed based on soil deformation and shear band recycles t-z model parameter measuring device, which is characterized in that packet Including rack, hydraulic loading system, experimental box, PIV system；Experimental box is organic glass case for containing soil sample；Hydraulic loaded system System is placed in above experimental box, for applying initial soil pressure to simulate the stress state of the soil body, and provides vertical circulation lotus to stake It carries to simulate the vertical cyclic load that the stake in actual use is subject to；PIV system is used to observe the variation of soil around pile displacement field.

2. a kind of single pile circulation t-z model parameter developed based on soil deformation and shear band according to claim 1 is surveyed Measure device, which is characterized in that the rack include pedestal (7), main counter-force column (3), main reaction beam (1), secondary counter-force column (15), Secondary reaction beam (12), main counter-force column (3) and time counter-force column (15) are fixed on vertically on pedestal (7), and main reaction beam (1) sets up solid Due on main counter-force column (3), secondary reaction beam (12) erection is fixed on time anti-column (15), and hydraulic loading system includes master cylinder (2), secondary oil cylinder (13) is fixedly installed in respectively below main reaction beam (1) and time reaction beam (12)；The pile body (5) is normal It is longitudinal to half after cuing open along axis to advise pile body, pile body section is close to experiment chamber interior wall and is squeezed into soil sample, and pile body lower end passes through Experimental box bottom and pedestal are simultaneously hanging, are connected below master cylinder with pile crown loading end, are placed with upper plate on experimental box soil sample (4) (8), secondary oil cylinder lower end is connected with upper plate.

3. a kind of single pile circulation t-z model parameter developed based on soil deformation and shear band according to claim 1 is surveyed Measure device, which is characterized in that the PIV system includes computer, laser emitter (19), synchronizer (18), CCD camera (16), light beam (21) are scattered, laser emitter (19) light source is adjusted by computer control synchronizer (18), light passes through scattering Light beam (21) scattering is uniformly beaten on the soil body, and CCD camera (16) shoots the variation of the soil around pile particle of entire pile body, and will shooting Information feeds back to computer.

4. a kind of single pile circulation t-z model parameter developed based on soil deformation and shear band according to claim 1 Measuring device, which is characterized in that all contact surfaces of the pile body and experimental box are wiped with vaseline.