CN115559361A

CN115559361A - Indoor pile foundation model test device and method for multiple horizontal cyclic loading working conditions

Info

Publication number: CN115559361A
Application number: CN202211190546.9A
Authority: CN
Inventors: 章定文; 曾彪; 杨泳; 王安辉
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2022-09-28
Filing date: 2022-09-28
Publication date: 2023-01-03

Abstract

The invention discloses an indoor pile foundation model test device for multiple horizontal cyclic loading working conditions. The loading system is connected with the model pile in the model box through a pile sleeve which can be inserted and locked; the insertion rod is arranged at the port of the force sensor, and the force sensor is detachably designed; a vacuum consolidation system which is vacuumized from the bottom is arranged in the model box to simulate a real soil environment; the drawable and guide rail design of the model box can quickly adjust the position of the loading system, and a plurality of groups of tests can be carried out by one-time sample preparation; by adopting the PLC control system and the electronic data acquisition system, the test parameters are accurate and controllable, the test operation is simple and convenient, and the pile foundation indoor model tests under various loading amplitudes and various loading paths such as one-way step-by-step loading, one-way horizontal cyclic loading, two-way symmetrical horizontal cyclic loading, two-way asymmetrical horizontal cyclic loading and the like can be performed at 0-5kN.

Description

Indoor pile foundation model test device and method for multiple horizontal cyclic loading working conditions

Technical Field

The invention relates to the technical field of indoor pile foundation model test equipment, in particular to an indoor pile foundation model test device for multiple horizontal cyclic loading working conditions.

Background

Pile foundations of high-rise buildings, cross-sea bridges, ports and wharfs and under ocean wind power bear vertical loads and also bear large horizontal loads, and the pile foundations mainly come from wind power, earthquake loads, impact force caused by vehicles and brakes, wave loads, ship impact and the like. These horizontal loads are more of a variety of regular and irregular horizontal cyclic loads than the instantaneous loads in some extreme cases. Because the field loading test is time-consuming and labor-consuming, and the field test operation is difficult for some marine pile foundations, many scholars at home and abroad adopt an indoor model test method to explore the load response of the pile foundations under the action of horizontal cyclic load.

The existing research preferentially pays attention to whether the result of the indoor model test can reflect the actual working condition, but ignores the influence of the model test device on the test accuracy, and has slight deficiency on the research on the aspect of the optimization design of the model test device. The existing indoor pile foundation model test devices are mainly divided into two types, one type is a large device adopting a vibration exciter or a servo hydraulic loading system, the size of the device is often larger, the actual loaded response of the pile foundation can be well reflected, the cost is high, the operation is complex, and the switching is difficult, time and labor are wasted for simulating tests under different working conditions. The other type is based on the moment principle, and realizes cyclic loading through the synergistic effect of a balancing weight, a motor, a pulley and a rope, and the device is small, exquisite, light and rich in creativity. However, when the test conditions require a large horizontal cyclic load, such devices often result in an inaccurate applied load due to inertia and friction between the rope and the pulley. Therefore, it is of great significance to develop an indoor pile foundation model test device which is suitable for various horizontal cyclic loading working conditions and has economical and practical functions.

The patent number is, CN 112160353A, the name is "pile soil interaction indoor test device and installation method under the effect of combined cyclic load" discloses an indoor test device, including counter-force system and mold box and a plurality of parameter acquisition original paper, this test device can show the response of pile and soil body and the effect law each other under horizontal circulation and vertical load combined action, can carry out the pile soil interaction test of different pile foundation forms under different combined loads. However, the device cannot solidify the soil body in the model box, so that the soil body and the in-situ soil keep the same stress state, and therefore the test reliability is poor. In addition, the device realizes cyclic loading through two loading electric cylinders, and the cooperation of two loading electric cylinders is difficult to realize, so that the precision of applied load is difficult to accurately control.

CN 106088169A, entitled "multiple degree of freedom cyclic loading device for offshore wind turbine foundation indoor experimental study" patent technology, utilizes a movable pulley and a fixed pulley to form a pulley system, and combines a cyclic stepping motor, a spring base and the like to realize cyclic loading in any period and any form by controlling the moving distance and the moving speed of the cyclic stepping motor. The technology cannot be applied to the working condition of large horizontal load, and test parameters such as loading period and loading amplitude cannot be accurately controlled. The research paper 'the development of a cyclic loading device suitable for an indoor model test and the experimental research' is basically similar to the technical scheme of the patent and has similar problems.

The patent number is, CN111851605B, the name is "a pile foundation model loading device for vertical/horizontal circulation loading" patent technology, rotates vertical rigidity pivot through control speed regulating motor to drive the counter weight and be horizontal circular motion, realize vertical circulation loading and horizontal circulation loading under the different cyclic amplitude, still have the test parameter precision not high, the less scheduling problem of experimental loading amplitude.

Disclosure of Invention

Aiming at the technical problems, the driving electric cylinder is matched with a PLC control system, the loading amplitude is expanded to 0 to 5kN, and the method is applicable to indoor model tests of various pile foundations; meanwhile, the loading system can realize various horizontal cyclic loading working conditions. In addition, due to the design of the drawable model box and the guide rail on the drawable model box, the force sensor can be detachably designed, a plurality of groups of tests can be carried out by one-time sample preparation, the test variables can be effectively controlled, the indoor pile foundation model test is simple and convenient to operate, and the test result is accurate.

In order to achieve the technical purpose, the invention adopts the following technical scheme:

an indoor pile foundation model test device for multiple horizontal cyclic loading conditions, comprising:

the model box comprises a plurality of sections of box body units, the box body units are connected through a sealing guide rail to realize a pull-out box body structure, and a sand cushion layer, a soil body and a sealing cover are sequentially filled in the box body from bottom to top; the model piles are inserted into the soil body of the model box;

the guide rail comprises two vertical guide rails fixedly connected with the box walls on two sides of the model box, two longitudinal guide rails connected to the tops of the vertical guide rails and two horizontal guide rails connected between the two longitudinal guide rails, wherein the vertical guide rails can realize vertical height adjustment, the two longitudinal guide rails are arranged along the length direction of the model box, the horizontal guide rails can realize longitudinal position adjustment on the longitudinal guide rails, and driving electric cylinders are mounted on the horizontal guide rails and can realize horizontal position adjustment on the horizontal guide rails; a driving shaft of the driving electric cylinder is connected with the pile top of the model pile through a force sensor and a pile sleeve;

the vacuum pipe is vertically arranged, the upper end of the vacuum pipe is inserted into the upper part of the soil body, the lower end of the vacuum pipe is communicated with a bottom pipe which is embedded in the sand cushion layer and is horizontally arranged, one end of the bottom pipe is closed, and the other end of the bottom pipe is connected with a vacuum pump arranged outside the mold box;

the drain hole is arranged on the box wall on one side of the bottom of the model box;

the displacement sensor is arranged on a transmission shaft connected with the driving shaft of the driving electric cylinder and used for monitoring the horizontal displacement at the pile top;

the laser displacement meter is arranged in the model box and close to the soil body and is used for monitoring the corner of the model pile on the surface of the soil body;

the controller is in signal connection with the driving electric cylinder;

and the signal acquisition module is connected with the force sensor, the displacement sensor and the laser displacement meter.

Furthermore, a box body panel positioned on the leftmost side of the whole model box is made of transparent materials and is used for observing the internal condition of the model box; the box body panel positioned at the rightmost side of the whole model box can be turned along the bottom of the box body, so that soil bodies can be loaded and unloaded conveniently.

Furthermore, the range of the driving electric cylinder is 0 to 5kN.

Furthermore, the pile sleeve comprises an insertion rod and a circular groove with a hole, the insertion rod is fixed at the port of the force sensor, and the upper section and the lower section of the insertion rod are respectively provided with a spring button; the round groove with the hole is fixed on the model pile, and after the inserting rod is inserted into the round groove with the hole, the spring button is locked, so that the inserting rod and the round groove with the hole are locked.

Furthermore, the driving electric cylinder is provided with more than or equal to 2 sets of force sensors, and the force sensors are detachably connected with the transmission shaft.

Further, the controller is a PLC.

Furthermore, the width of the model box is set to be more than or equal to 2 x 10D, and D is the pile diameter of the model pile.

Furthermore, the bottom of the model box is provided with a lockable pulley for quickly adjusting the position of the model box.

The invention further discloses a test method of the indoor pile foundation model test device for multiple horizontal cyclic loading working conditions, soil bodies are respectively placed in the mould box models according to the test scheme, the vacuum pipes are distributed in the mould boxes, and the vacuum pumps are connected;

starting a vacuum pump, discharging pore water in the soil body to a drain hole through a sand cushion layer by a drain plate under the action of vacuum negative pressure of the soil body in the mold box, and performing vacuum consolidation;

and adjusting the driving electric cylinder to the position of the model pile in the model box through the guide rail, and connecting the force sensor at the end part of the driving electric cylinder with the model pile.

The controller is opened, the driving shaft connects the driving force generated by the driving electric cylinder to the pile sleeve through the force sensor, and therefore horizontal acting forces with different loading amplitudes and different loading paths are applied to the model pile;

the controller is used for realizing stress control and displacement control and comprises unidirectional step-by-step loading, unidirectional horizontal cyclic loading, bidirectional symmetrical horizontal cyclic loading and bidirectional asymmetrical horizontal cyclic loading; meanwhile, basic parameters of the test are set through loading software, wherein the basic parameters comprise loading frequency, stress amplitude, displacement amplitude, loading period, loading time and cycle number;

the signal acquisition module is used for synchronously acquiring data of the force sensor, the displacement sensor and the laser displacement meter in real time, and also can acquire data of a strain gauge additionally arranged on the pile body, and the data in the acquisition system is exported into an EXCLE file, so that later-stage editing is facilitated;

when the number of test groups is large, the multiple sections of box body units are pulled to the length required by the test, multiple model piles are inserted into the model box at intervals along the length of the soil body of the box body, the electric driving cylinders are adjusted to different positions through the guide rails, the model piles at different positions in the soil body are loaded, the vacuum consolidation system works once, multiple groups of working condition tests can be carried out, and the test period is saved.

The invention has the following beneficial effects:

first, traditional mould case type generally sets up to fixed box, when carrying out the multiunit experiment, often need repeat concreties and the stake of inserting to the soil body, wastes time and energy. The design that the drawable model box is matched with the guide rail is adopted, the movement of the loading system at any spatial position in the model box can be realized, model piles at different positions in the soil body are loaded, and the soil body vacuum consolidation system works once according to the test requirement, so that a plurality of groups of working condition tests can be carried out, and the test period is saved.

Secondly, a single driving electric cylinder is adopted and is connected with the model pile in an inserting and locking mode, tension and compression bidirectional loading can be achieved in a single direction, and the loading amplitude is accurate and controllable; meanwhile, the loading amplitude range is expanded to 0 to 5kN, so that the method is applicable to indoor model tests of various pile foundations; and the PLC control system is matched to realize the pile foundation indoor model test under various loading amplitudes and various loading paths.

Thirdly, the sand cushion layer at the bottom of the model box is matched with the vacuum pipe to be inserted from the bottom of the soil body, which is different from the traditional indoor vacuum consolidation technology, and the vacuum pipe is inserted from the upper soil body.

Fourthly, due to the detachable design of the force sensor, sensors with different measuring ranges are flexibly adopted for model piles with different rigidity, and the test result can be more accurate.

And the right side of the model box is in a reversible design, so that the test soil body is convenient to load and unload.

Drawings

FIG. 1 is a schematic view of an indoor mold apparatus according to the present invention;

FIG. 2 is a top view of the mold box of the present invention;

FIG. 3 is a side view of a mold box of the present invention;

FIG. 4 is a schematic view of a pile cover structure;

FIG. 5 is a schematic view of various cyclic loading conditions of the present invention;

the reference numbers in the figures illustrate: 1-a model box; 2-model pile; 3-a drainage plate; 4-a guide rail; 5-vacuum holes; 6-a drain hole; 7-a pulley; 8-vacuum tube; 9-sealing cover; 10-a sand cushion layer; 11-a vacuum pump; 12-driving an electric cylinder; 13-a drive shaft; 14-a displacement sensor; 15-a force sensor; 16-pile sleeves; 17-a laser displacement meter; 18-a PLC control system; 19-a data acquisition system; 20-a guide rail; 21-positioning knob; 22-toughened glass; 23-right side steel plate; 24-box sealing guide rails; 25-an insertion rod; 26-circular groove with hole; 27 a spring button; 28-circular hole.

Detailed Description

The invention will be elucidated on the basis of an embodiment shown in the drawing. The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is not limited by the following description of the embodiments.

The invention will be described in further detail below with reference to the following figures and specific embodiments.

The embodiment is as follows:

refer to fig. 1-4.

During normal service, the offshore wind power foundation bears horizontal cyclic load effects such as wind, waves and water flow for a long time, so that the pile foundation is induced to generate large accumulated deformation, and when the deformation is too large, a fan can be inclined, and the service life and safety of an upper structure are damaged. In order to explore the load response of the offshore wind power foundation under the action of various cyclic loads, the method is used for indoor pile foundation model test loading under various horizontal cyclic loading working conditions to develop model test research.

The test designs 3 groups of working conditions, namely single-pile unidirectional step-by-step loading, single-pile bidirectional symmetric cyclic loading and single-pile bidirectional asymmetric cyclic loading. The length of the model pile 2 is 1m, the pile diameter is 0.05m, and the depth of the soil is 0.6m. The number of the test groups is comprehensively considered, the pile length, the pile diameter and the soil body effective stress area of the foundation edge of the model pile 2 are comprehensively considered, the size of a first section of box body of the model box is 1m multiplied by 1m (length multiplied by width multiplied by height), the size of a second section of box body and a third section of box body of the model box is 0.5m multiplied by 1m, the wall thickness is 5 mm, the model box is drawn, the second section of box body and the third section of box body are gradually unfolded along the box body sealing guide rail 24, and the total size of the model box after the model box is unfolded is 2m multiplied by 1 m. The design ensures that the distance between the model pile 2 and the side wall of the model box 1 exceeds 10D, the influence of boundary effect can be not considered, the test can be completed by one-time sample preparation, the test period is saved, and the working efficiency is improved. The front and the back of the model box 1 are formed by welding steel plates, and the left side surface adopts toughened glass 22 for observing the internal condition of the model box 1; the right side steel plate 23 can be turned over along the bottom edge of the right side to form an 'inclined bridge' shape, so that soil is convenient to load and unload; six guide rails 20 are arranged on the model box and comprise two vertical guide rails fixedly connected with box walls on two sides of the model box, two longitudinal guide rails connected to the tops of the vertical guide rails and two horizontal guide rails connected between the two longitudinal guide rails, wherein the vertical guide rails can realize vertical height adjustment, the two longitudinal guide rails are arranged along the length direction of the model box, the horizontal guide rails can realize longitudinal position adjustment on the longitudinal guide rails, and driving electric cylinders are arranged on the horizontal guide rails and can realize horizontal position adjustment on the horizontal guide rails; a driving shaft of the driving electric cylinder is connected with the pile top of the model pile through a force sensor and a pile sleeve;

each guide rail 20 is provided with a positioning knob 21, so that the loading system can be moved and fixed at any position on the model box;

four lockable pulleys 7 are provided at the bottom of the mold box for quick adjustment of the position of the mold box 1. According to the test scheme, soil and a model box are respectively placed in a model box, vacuum pipes are distributed, and a vacuum pump is connected.

In order to drain and solidify the soft clay in the model box 1, a set of vacuum solidification system is arranged in the model box; two rows of small holes are formed in the positions, 5cm away from the bottom surface, of the front side surface and the rear side surface of the bottom of the model box 1, one row is a vacuum hole 5, and the other row is a drain hole 6; the side wall sets up drain bar 3 around model case 1, sets up the sand bedding course 10 of 10cm thickness at the bottom and plays the anti-filter effect, passes through sand bedding course 10 with the vacuum tube 8 of L type through vacuum hole 5, inserts the upper portion soil body (soft clay), and vacuum pump 11 is connected to the vacuum tube 8 other end of L type. A sealing cover 9 is arranged on the top of the mold box 1 to ensure a vacuum environment. After the vacuum pump 11 is started, under the action of vacuum negative pressure, pore water in soil is discharged from the sand cushion layer 10 to the water discharge hole 6 through the water discharge plate 3, and vacuum consolidation occurs.

In order to circularly load the model pile, a pile head is provided with a set of loading system, and the loading system consists of a driving electric cylinder 12, a transmission shaft 13, a force sensor 15, a displacement sensor 14 and a pile sleeve 16; the driving electric cylinder 12 is a main source of driving force, and the transmission shaft 13 connects the driving force generated by the driving electric cylinder with the pile sleeve 16 through the force sensor 15, so that horizontal acting forces with different loading amplitudes and different loading paths are applied to the pile. The test comprises static force step-by-step loading, bidirectional symmetrical cyclic loading and bidirectional asymmetrical cyclic loading; static force step-by-step loading is used for determining the maximum horizontal bearing capacity of the model pile, so that a force sensor with a wide range of 0 to 5kN is required to be adopted; the loading amplitude of the bidirectional cyclic loading is generally 0.1 to 0.5 times of the maximum horizontal bearing capacity, so that the bidirectional cyclic loading can be switched to a small-range force sensor of 0 to 2kN. The pile cover 16 is designed to be inserted and locked and is arranged on the model pile 2, when the insertion rod 25 on the force sensor 15 is inserted into the circular groove 26 with the hole on the pile cover, the spring button 27 is pressed down to the circular hole 28 and rebounds, and automatic locking is realized. The transmission shaft 13 is also provided with a displacement sensor 15 for monitoring the horizontal displacement at the pile top. And two laser displacement meters 17 are additionally arranged at the mud surface and used for monitoring the rotation angle of the model pile at the mud surface.

The PLC control system 18 is used for setting loading parameters and loading curves, is programmed through a program language and consists of a PLC controller, a signal converter and loading software, and the loading system acts together. The PLC control system can realize stress control and displacement control, and can also set a loading path, including unidirectional step-by-step loading, unidirectional horizontal cyclic loading, bidirectional symmetrical horizontal cyclic loading and bidirectional asymmetrical horizontal cyclic loading; meanwhile, basic parameters of the test, such as loading frequency, stress amplitude, displacement amplitude, loading period, loading time, cycle number and the like, can be set through loading software.

The data acquisition system 19 can synchronously acquire the related data of the force sensor and the displacement sensor on the loading equipment in real time by using a multi-channel data acquisition unit, and can also acquire the data of a strain gauge additionally arranged on the pile body. The data in the acquisition system can be exported into an EXCLE file, so that later-stage editing is facilitated.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

It is to be understood that the present invention is not limited to the embodiment methods, structures, and precise structures shown in the drawings, which have been described above, and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is limited only by the appended claims.

Claims

1. The utility model provides an indoor pile foundation model test device for multiple horizontal circulation loading operating mode which characterized in that includes:

the vacuum pipe is vertically arranged, the upper end of the vacuum pipe is inserted into the upper part of the soil body, the lower end of the vacuum pipe is communicated with a bottom pipe which is embedded in the sand cushion layer and is horizontally arranged, one end of the bottom pipe is closed, and the other end of the bottom pipe is connected with a vacuum pump arranged outside the model box;

the controller is in signal connection with the driving electric cylinder;

2. An indoor pile foundation model test device for multiple horizontal cyclic loading working conditions according to claim 1, wherein a box body panel at the leftmost side of the whole model box is made of transparent materials and used for observing the internal conditions of the model box; the box body panel positioned at the rightmost side of the whole model box can be turned along the bottom of the box body, so that the soil body is convenient to load and unload.

3. The indoor pile foundation model test device for multiple horizontal cyclic loading working conditions according to claim 1, wherein the measuring range of the driving electric cylinder is 0-5 kN.

4. An indoor pile foundation model test device for multiple horizontal cyclic loading conditions according to claim 1, wherein the pile sleeve comprises an insertion rod and a circular groove with a hole, the insertion rod is fixed at the port of the force sensor, and the upper section and the lower section of the insertion rod are respectively provided with a spring button; the round groove with the hole is fixed on the model pile, and after the insertion rod is inserted into the round groove with the hole, the spring button is locked, so that the insertion rod and the round groove with the hole are locked.

5. The indoor pile foundation model test device for multiple horizontal cyclic loading working conditions according to claim 1, wherein more than or equal to 2 sets of force sensors are matched with the driving electric cylinder, and the force sensors are detachably connected with the transmission shaft.

6. An indoor pile foundation model test device for multiple horizontal cyclic loading conditions according to claim 1, wherein the controller is a PLC.

7. An indoor pile foundation model test device for multiple horizontal cyclic loading conditions according to claim 1, wherein the width of the model box is set to be more than or equal to 2 x 10D, and D is the pile diameter of the model pile.

8. An indoor pile foundation model test device for multiple horizontal cyclic loading conditions according to claim 1, wherein lockable pulleys are arranged at the bottom of the model box for quickly adjusting the position of the model box.

9. A test method of the indoor pile foundation model test device for multiple horizontal cyclic loading working conditions based on any one of claims 1 to 8 is characterized in that,

respectively putting soil bodies into the mold boxes according to the test scheme, and arranging vacuum tubes in the mold boxes and connecting the vacuum tubes with a vacuum pump;

adjusting the driving electric cylinder to the position of the model pile in the model box through the guide rail, and connecting a force sensor at the end part of the driving electric cylinder with the model pile;

the controller is opened, and the driving shaft connects the driving force sent by the driving electric cylinder to the pile sleeve through the force sensor, so that horizontal acting forces with different loading amplitudes and different loading paths are applied to the model pile;

the signal acquisition module is used for synchronously acquiring data of the force sensor, the displacement sensor and the laser displacement meter in real time, and also acquiring data of a strain gauge additionally arranged on the pile body, and the data in the acquisition system is exported to be an EXCLE file, so that later-stage editing is facilitated;

when the number of the test groups is large, the multi-section box body units are pulled to the length required by the test, a plurality of model piles are inserted into the model box at intervals along the length of the soil body of the box body, the electric cylinder is driven to adjust the guide rails to different positions, the model piles at different positions in the soil body are loaded, the vacuum consolidation system works once, a plurality of groups of working condition tests can be carried out, and the test period is saved.