WO2021244185A1

WO2021244185A1 - Testing apparatus and testing method for simulating influence of cavity existing on pile end on bearing performance of pile foundation

Info

Publication number: WO2021244185A1
Application number: PCT/CN2021/089804
Authority: WO
Inventors: 周佳锦; 龚晓南
Original assignee: 浙江大学
Priority date: 2020-06-01
Filing date: 2021-04-26
Publication date: 2021-12-09
Also published as: CN111622277A; JP7236781B2; JP2022542132A; CN111622277B

Abstract

Disclosed in the present invention are a testing apparatus and testing method for simulating an influence of a cavity existing near a pile end on bearing performance of a pile foundation. The testing apparatus comprises a semicircular model box, an organic glass plate, a water injection system, a loading motor, and an industrial camera. According to the present invention, the water injection system is used to inject water into a sandy soil layer in the model box to simulate the case where an underground pipeline is broken and water overflows and the resulting case where a cavity appears in a soil layer; a control point and a mark point are provided in a sandy soil layer area, and the process of cavity formation and the displacement of sandy soil particles in the sandy soil layer during the loading process of a model pile are analyzed by means of the particle image velocimetry method and according to a photo taken by the industrial camera. The present invention has a reasonable structure and a simple operation, can be used for studying the influence of the cavity existing near the pile end on the bearing performance of the pile foundation, and the influence rule of different cavity positions and different cavity sizes on the bearing performance of the pile foundation, and provides an effective means for studying the influence of the cavity existing near the pile end on the bearing performance of the pile foundation.

Description

Test device and test method for simulating the influence of pile end with cavity on bearing performance of pile foundation

Technical field

The invention relates to a test device for studying the influence of the existence of an underground cavity on the bearing performance of a pile foundation in the field of geotechnical engineering.

Background technique

In recent years, accidents such as road collapses, tilting or collapse of buildings caused by underground cavities have occurred frequently, causing huge social and economic losses. Researchers and engineering technicians in the field of geotechnical engineering at home and abroad have begun to study the formation mechanism of voids and the development process. Underground cavities are mainly caused by the rupture of underground water pipelines, which causes internal erosion of nearby soil, and the volume of the cavities will slowly develop over time. When the buried depth of the cavity is relatively shallow, the volume of the cavity will develop to a certain extent, which will cause the collapse of the upper soil layer. Many road collapse accidents in many cities at home and abroad are caused by the development of this type of cavity. Domestic and foreign scholars have analyzed and studied the causes of road collapse in cities, and conducted some research on the formation mechanism of underground cavities and the development process of cavities. At the same time, they also proposed some geophysical exploration techniques for detecting shallow cavities.

The current research on underground cavities mainly focuses on the shallow underground cavities and the influence of the existence of underground cavities on the stability of road subgrade. There is no research on the bearing performance of the building foundation when the underground cavities are deep. When there is a cavity near the pile end of a building's pile foundation, it will affect the bearing performance of the pile foundation. When the distance between the cavity and the pile end is relatively close or the cavity volume is large, the ultimate bearing capacity of the pile foundation will be greatly reduced. , And may cause the building to collapse, causing serious loss of life and property.

The existence of voids near the pile foundation of a building will bring great safety hazards to the building, but there is no relevant research in this area. When the underground cavity is far away from the pile foundation or the volume of the cavity is small, the existence of the cavity has little effect on the pile foundation; when the cavity is close to the pile foundation or the cavity volume is large, it will affect the bearing performance of the pile foundation. Need to deal with underground cavities. Through the study of the influence on the bearing performance of the pile foundation when there is a cavity near the pile end, and the law of the influence on the bearing performance of the pile foundation when the cavity position and the size of the cavity are different, the size of the cavity that needs to be treated and the size of the cavity are summarized. The critical value of the distance between the cavity and the pile foundation provides a scientific basis for related engineering problems in actual engineering, and it is always of great significance.

Summary of the invention

The purpose of the present invention is mainly to study the influence on the bearing performance of the pile foundation when there is a cavity near the pile end, which can be used to simulate the influence on the bearing performance of the pile foundation when the cavity position is different and the cavity size is different.

The technical solutions adopted by the present invention to solve its technical problems are:

A test device for simulating the influence of a cavity near the end of the pile on the bearing performance of the pile foundation, including a semicircular model box, a plexiglass plate, a water injection system, a loading motor, and an industrial camera;

The semicircular model box is composed of a model box base and a semicircular model box frame welded on the base; the model box base is composed of a bottom plate and a support, and the bottom plate is directly welded to the support; Water injection holes are arranged at certain intervals; the plexiglass plate is fixed on the frame of the semicircular model box as an observation surface; the bottom of the semicircular model box is filled with a sand layer of a certain thickness; the sand layer A clay layer is filled on it; marking points need to be arranged during the filling process of the sand layer to observe the displacement of the sand layer during the test; the sand layer area inside the plexiglass plate is equipped with a control for image analysis The inside of the plexiglass plate is also covered with a thin plexiglass plate so that the control point will not move during the test; an earth pressure sensor is also embedded in the sand layer to test the soil pressure at the end of the pile during the test; After the clay layer is filled, the model piles are placed in the model box. The model piles can be prefabricated piles or on-site cast-in-place piles. The cross-section of the model piles is semicircular; the water injection system consists of an air compressor, It is composed of a water storage tank and a water injection pipe. One end of the water injection pipe is connected to the water storage tank, and the other end enters the sand layer through the water injection hole on the bottom plate; the loading motor is fixed above the semicircular model box; for the industrial camera During the test, photographs of the sand layer in the semi-circular model box were taken at regular intervals to record the displacement of the sand layer during the test.

In the above technical solution, further, the ratio of the diameter of the semicircular model box frame to the diameter of the model pile is not less than 10;

The distance between the end of the model pile and the bottom plate is not less than 20 times the diameter of the model pile.

Further, the pile end of the model pile needs to enter the sand layer 1-3, and the depth of the pile end into the sand layer needs to be greater than 2 times the diameter of the model pile.

Further, the earth pressure sensor is arranged at different depths and different distances below the end of the model pile to measure the vertical earth pressure.

Further, the model pile may be a prefabricated pile or an on-site cast-in-place pile. If it is a prefabricated pile, after the soil is filled, the model pile is pressed into the soil by a loading motor; if it is an on-site cast-in-place pile, the soil After the filling of the body is completed, drill holes and pour model piles in the drilled space.

Further, there are water injection holes on the bottom plate of the model box at regular intervals, and in each test, one of the water injection holes is opened and the other water injection holes are closed.

Further, the water injection system uses an air compressor to inject water into the water injection hole, simulating the process of overflowing from a broken underground pipeline.

Further, after the sand layer in the model box is affected by the water flow at the water injection hole, internal erosion will occur, and a cavity will be generated near the water injection hole. The size of the cavity is adjusted according to the water injection pressure and the water injection time. Stop water injection when the test requirements are met.

Further, the semicircular model box frame is provided with two pillars, the loading motor is fixed above the semicircular model box through the two pillars, and the beam of the loading motor can be vertically moved along the pillars through pulleys. Move, thereby driving the loading motor to move up and down.

Further, according to the control points and the marked points, the photos taken by the industrial camera can be analyzed through the computer program to obtain the sand displacement changes in the sand layer during the test.

The present invention also provides a test method for simulating the impact on the bearing performance of the pile foundation when there is a cavity at the end of the pile. The method is implemented based on the above device and includes the following steps:

Paste the control points for image analysis in the sandy soil layer on the inner side of the plexiglass plate, and then cover the inner side of the plexiglass plate with a thin plexiglass plate so that the control points will not move during the test; in the semicircular model First fill the sand layer in the box. Mark points are arranged during the sand layer filling process to observe the displacement change of the sand layer during the test; at the same time, during the sand layer filling process, different depths below the pile end of the model Several soil pressure sensors are buried at different distances; after the sand layer is filled, a clay layer is filled on it; after the clay layer is filled, the model piles are placed in the semi-circular model box, and the model piles are prefabricated piles or on-site pouring Pile: After the model pile is set up, open a certain water injection hole on the bottom plate, and inject water from the water injection hole into the sand layer through the water injection system, so that a cavity appears near the water injection hole. The size of the cavity can be adjusted according to the water injection pressure and water injection time. Control (the development process of the cavity can be directly observed through the plexiglass plate). During the water injection process, the sandy soil area is photographed by an industrial camera; after the cavity size reaches the design requirements, the water injection hole is closed, and the model pile is loaded by the loading motor. During the process, the industrial camera took pictures of the sandy soil layer area.

Compared with the prior art, the beneficial effects of the present invention are:

1. In the present invention, a water injection system is used to inject water through a water injection hole set at the bottom of the model box, which can simulate the overflow of broken underground pipelines and the resulting voids in the soil layer.

2. In the present invention, by setting control points and marking points in the sand layer area, according to the photos taken by the industrial camera, the formation process of the hollow hole in the bottom water injection sand layer can be analyzed by the particle image velocity method, and the sand during the loading process of the model pile The displacement changes of sand particles in the soil layer.

3. In the present invention, the position relationship between the underground cavity and the pile foundation and the size of the underground cavity can be adjusted, and the law of influence on the bearing performance of the pile foundation can be studied when the relative position of the cavity and the pile foundation are different and the size of the cavity is different.

Description of the drawings

Figure 1 is a schematic front view of the test device;

Figure 2 is a top view of the test device;

Figure 3 is a schematic diagram of the bottom water injection process;

Figure 4 is a schematic diagram of the test device when the cavity is small;

Figure 5 is a schematic diagram of the test device when the cavity is large;

In the picture: semicircular model box 1, model box base 1-1, bottom plate 1-1-1, support 1-1-2, water injection hole 1-1-3, semi-circular model box frame 1-2, Sand layer 1-3, clay layer 1-4, model pile 1-5, marking point 1-6, earth pressure sensor 1-7, cavity 1-8, plexiglass plate 2, control point 2-1, second Plexiglass plate 2-2, water injection system 3, air compressor 3-1, pressure gauge 3-1-1, pressure regulating switch 3-1-2, water storage tank 3-2, water injection pipe 3-3, water injection valve 3-3-1, load motor 4, pillar 4-1, beam 4-2, pulley 4-3, industrial camera 5.

detailed description

The present invention will be further described below in conjunction with the drawings and embodiments.

As shown in Figures 1-5, it is a test device that can simulate the impact on the bearing performance of the pile foundation when there is a cavity near the pile end. At the same time, it can test the bearing performance of the pile foundation when the relative position of the cavity and the pile foundation are different, and the size of the cavity is different. Research on the law of influence. The test device includes five parts: semicircular model box 1, plexiglass plate 2, water injection system 3, loading motor 4 and industrial camera 5. The semicircular model box 1 is composed of a model box base 1-1 and a semicircular model box frame 1-2 welded on the model box base 1-1; the model box base 1-1 is composed of a bottom plate 1-1 -1 and the support 1-1-2, the bottom plate 1-1-1 is directly welded to the support 1-1-2; the thickness of the bottom plate 1-1-1 is 50mm, and the bottom plate 1-1-1 There are water injection holes 1-1-3 at regular intervals, and the distance between adjacent water injection holes is generally 20-50cm; the semicircular model box frame 1-2 is a semicircular arc made of 10mm thick steel plate, The diameter is 2m; the plexiglass plate 2 is fixed on the semicircular model box frame 1-2 as an observation surface, and the thickness of the plexiglass plate 2 is 10mm; the interior of the semicircular model box 1 is first filled in the bottom The thickness of the sand layer 1-3; during the filling process of the sand layer 1-3, marking points 1-6 need to be arranged to observe the displacement of the sand layer during the test. The horizontal and vertical spacing of the marking points is generally between Between 20-50mm, it is necessary to bury several soil pressure sensors 1-7 at different depths and distances below the pile ends of model piles 1-5; 4; After the clay layer 1-4 is filled, the model piles 1-5 are placed in the model box. The model piles can be prefabricated piles or on-site cast-in-place piles, and the diameter of the model piles needs to be less than 200mm; the plexiglass board 2Fixed on the semicircular model box frame 1-2 as the observation surface, the inside of the plexiglass plate 2 is filled with sandy soil layer 1-3, and the control points 2-1 for image analysis are pasted, and the control points are horizontal and vertical. The spacing is generally 100-200mm, and then a thin second plexiglass plate 2-2 is covered on the inside of the plexiglass plate 2, so that the control point 2-1 will not move during the test; the water injection system 3 is compressed by air The machine 3-1, the water storage tank 3-2 and the water injection pipe 3-3. One end of the water injection pipe 3-3 is connected to the water storage tank 3-2, and the other end enters through the water injection hole 1-1-3 on the bottom plate Sand layer 1-3; the semicircular model box frame 1-2 is welded with two pillars 4-1, the loading motor 4 is fixed on the top of the model box through the two pillars 4-1, and the loading motor The beam 4-2 can be moved in the vertical direction along the pillar 4-1 through the pulley 4-3, thereby driving the loading motor 4 to move up and down; the industrial camera 5 photographs the sand and soil in the model box at regular intervals during the test The photos of layers 1-3 record the displacement changes of the sand layer during the test.

The test method of the present invention for simulating the influence on the bearing performance of the pile foundation when there is a cavity at the end of the pile is as follows:

First, paste the control points 2-1 for image analysis in the sandy soil layer 1-3 area inside the plexiglass plate 2, and then cover a thin plexiglass plate 2-2 on the inside of the plexiglass plate 2 to make the control points 2-1 will not move during the test; first fill the sand layer 1-3 in the semicircular model box 1, and arrange the marking points 1-6 during the sand layer filling process to observe the sand layer during the test. Displacement changes; at the same time, several soil pressure sensors 1-7 should be buried at different depths and distances below the pile ends of the model piles 1-5 during the filling process of the sand layer; after the sand layer is filled, a clay layer should be filled on it 1-4; After the clay layer is filled, the model piles 1-5 are placed in the soil layer. The model piles can be prefabricated piles or on-site cast-in-place piles. When the model piles are prefabricated piles, load the motor after the soil is filled. Press the model pile 4 to press the prefabricated pile into the soil. When the model pile is an on-site cast-in-place pile, drill the hole after the soil is filled and pour the model pile in the drilled space; after the model pile is set, it will be A certain water injection hole 1-1-3 on the bottom plate 1-1-1 of the model box is opened, and the water is injected from the water injection hole 1-1-3 into the sand layer 1-3 through the water injection system 3, so that a water injection hole appears near the water injection hole 1-1-3. Cavities 1-8, the size of the cavity can be controlled according to the water injection pressure and water injection time. The development process can be directly observed through the plexiglass plate), during the water injection process, the sand layer 1-3 areas are photographed by the industrial camera 5; after the hole size meets the design requirements, the water injection hole 1-1-3 is closed, and the motor 4 is loaded Load the model piles 1-5, and during the loading process, the industrial camera 5 photographs the sandy soil layer 1-3 areas. The load and displacement applied by the loading motor 4 can be automatically read and stored. During the test, the soil pressure change law of the soil at the end of the pile is automatically measured by a static strain tester, and the displacement change law of the sand particles in the sand layer during the test. The photos taken by industrial cameras can be analyzed by computer software.

Claims

A test device for simulating the influence of the pile end with a cavity on the bearing performance of the pile foundation, which is characterized in that it includes a semicircular model box (1), a plexiglass plate (2), a water injection system (3), and a loading motor (4) , And industrial cameras (5);

The semicircular model box (1) is composed of a model box base (1-1) and a semicircular model box frame (1-2) welded on the model box base (1-1); the model box base (1-1) Consists of a bottom plate (1-1-1) and a support (1-1-2), the bottom plate (1-1-1) is directly welded to the support (1-1-2); The bottom plate (1-1-1) is provided with a water injection hole (1-1-3); the organic glass plate (2) is fixed on the semicircular model box frame (1-2) as an observation surface; The bottom of the circular model box (1) is filled with a sand layer (1-3), and a clay layer (1-4) is filled on the sand layer; marking points (1) are arranged in the sand layer (1-3) -6), used to observe the displacement changes of the sand layer during the test; the inner sand layer (1-3) of the organic glass plate (2) is equipped with control points (2-1) for image analysis; sand The soil pressure sensor (1-7) is also buried in the layer to test the soil pressure at the end of the pile during the test; the center of the semicircular model box (1) is provided with model piles (1-5), so The section of the model pile (1-5) is semicircular; the water injection system (3) is composed of an air compressor (3-1), a water storage tank (3-2) and a water injection pipe (3-3). One end of the water injection pipe (3-3) is connected to the water storage tank (3-2), and the other end enters the sand layer (1-3) through the water injection hole (1-1-3) on the bottom plate (1-1-1) ); The loading motor (4) is fixed above the semicircular model box (1); the industrial camera (5) is used to photograph the sand layer (1-) in the semicircular model box (1) during the test 3) photos to record the displacement changes of the sand layer (1-3) during the test.
The test device for simulating the impact on the bearing performance of the pile foundation when there is a cavity at the end of the pile according to claim 1, wherein the diameter of the semicircular model box frame (1-2) is the same as that of the model pile (1-5). ) The diameter ratio is not less than 10; the distance between the pile end of the model pile (1-5) and the bottom plate (1-1-1) is not less than 20 times the diameter of the model pile.
The test device for simulating the impact on the bearing performance of the pile foundation when the pile end has a cavity according to claim 1, wherein the pile end of the model pile (1-5) needs to enter the sand layer (1-3) , And the depth of the pile tip into the sand layer must be greater than 2 times the diameter of the model pile.
The test device for simulating the impact on the bearing performance of the pile foundation when there is a cavity at the pile end according to claim 1, wherein the soil pressure sensor (1-7) is set below the pile end of the model pile (1-5) It is used to measure vertical earth pressure at different depths and different horizontal distances.
The test device for simulating the impact on the bearing performance of the pile foundation when the pile end has a cavity according to claim 1, characterized in that the water injection hole (1-1-3) on the bottom plate (1-1-1) of the model box ) In each test, only one of them is opened, and the other water injection holes are closed.
The test device for simulating the impact on the bearing performance of the pile foundation when there is a cavity in the pile end according to claim 1, wherein the water injection system (3) injects water into the water injection hole (3) through an air compressor (3-1). In 1-1-3), the process of rupturing and overflowing of underground pipelines is simulated.
The test device for simulating the impact on the bearing performance of the pile foundation when there is a cavity in the pile end according to claim 1, wherein the sand layer (1-3) is affected by the water flow at the water injection hole (1-1-3). After the action of, internal erosion will occur, and a cavity (1-8) will be created near the water injection hole (1-1-3).
The test device for simulating the influence on the bearing performance of the pile foundation when there is a cavity at the pile end according to claim 1, wherein the semicircular model box frame (1-2) is provided with two pillars (4- 1), the loading motor (4) is fixed above the semicircular model box (1) through a pillar (4-1), and the loading motor (4) can move freely in the vertical direction along the pillar.
The test device for simulating the impact on the bearing performance of the pile foundation when the pile end has a cavity according to claim 1, characterized in that, according to the control point (2-1) and the marking point (1-6), the computer program is used to process the The photograph of the sand layer (1-3) taken by the industrial camera (5) can obtain the displacement change of the sand layer (1-3) during the test.
A test method for simulating the impact on the bearing performance of the pile foundation when the pile end has a cavity, characterized in that the method is implemented based on the device according to any one of claims 1-9, and comprises the following steps:

Paste the control points (2-1) for image analysis in the area of the sand layer (1-3) on the inner side of the plexiglass plate (2), and then cover the inner side of the plexiglass plate (2) with a second layer of plexiglass Plate (2-2), so that the control point (2-1) will not move during the test; first fill the sand layer (1-3) in the semi-circular model box (1), the sand layer filling process Marking points (1-6) are arranged in the middle to observe the displacement changes of the sand layer during the test; at the same time, during the filling process of the sand layer (1-3), at different depths below the pile end of the model pile (1-5) Several soil pressure sensors (1-7) are buried at different distances; after the sand layer (1-3) is filled, a clay layer (1-4) is filled on it; after the clay layer (1-4) is filled Place the model piles (1-5) in the semi-circular model box (1). The model piles (1-5) are precast piles or on-site cast-in-place piles; place a certain water injection hole on the bottom plate (1-1-1) (1-1-3) Open, and inject water from the water injection hole (1-1-3) into the sand layer (1-3) through the water injection system (3), making it near the water injection hole (1-1-3) A cavity (1-8) appears. During the water injection process, an industrial camera (5) is used to take pictures of the sandy soil layer (1-3) area; the water injection hole (1-1- 3) Turn off, load the model piles (1-5) through the loading motor (4), and during the loading process, the industrial camera (5) photographs the sandy soil layer (1-3) area.