CN113790982A - Pile-unsaturated soil interface friction visualization test device and method - Google Patents

Pile-unsaturated soil interface friction visualization test device and method Download PDF

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CN113790982A
CN113790982A CN202110872868.0A CN202110872868A CN113790982A CN 113790982 A CN113790982 A CN 113790982A CN 202110872868 A CN202110872868 A CN 202110872868A CN 113790982 A CN113790982 A CN 113790982A
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pile
soil sample
soil
sensor
sample
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CN113790982B (en
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邓波
杨明辉
徐瑶
彭炳龙
樊军伟
彭成
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University of South China
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/24Investigating strength properties of solid materials by application of mechanical stress by applying steady shearing forces
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00Sampling; Preparing specimens for investigation
    • G01N1/28Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N13/00Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00Investigating strength properties of solid materials by application of mechanical stress
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Abstract

The invention discloses a pile-unsaturated soil interface friction visual test device and a method, which comprises a frame, an axial pressure loading device, an axial pressure control device, a sealed pressure chamber, a soil sample, a hollow transparent pile, a sample preparation split cylinder, a confining pressure control device, a tensiometer, a moisture sensor, a DIC camera, an image data acquisition device, a dry-wet circulation device, a torsion control device and a computer. The testing device and the method have reasonable structure and simple operation, can prepare homogeneous pile soil samples, can perform a pile soil interface friction test considering the cyclic desorption effect under different stress conditions to obtain pile-unsaturated soil interface mechanical parameters which are more consistent with actual working conditions, and obtain the shear failure form of the pile soil interface by using a digital image correlation technique (DIC).

Description

Pile-unsaturated soil interface friction visualization test device and method
Technical Field
The invention relates to the technical field of interface shearing of soil and a structure, in particular to a test device and a method for interface shearing visualization of unsaturated soil and a structure.
Background
In the field of geotechnical engineering, foundation soil in a natural state is repeatedly subjected to the effects of atmospheric precipitation and evaporation, rising and falling of underground water level and other phenomena, so that the engineering characteristics of a pile-soil interface are in periodic dynamic change for a long time, and further the pile-unsaturated soil interface in the foundation shows a mechanical response law different from the interaction of common saturated soil or dry soil and a pile. However, relatively few studies have been made on the unsaturated properties of pile-soil interfaces; particularly, under the cyclic dehumidification, the interfacial friction force characteristic between the pile and the unsaturated soil cannot be determined, so that the integral bearing capacity calculation of the pile foundation is directly influenced, and the unsaturated soil theory cannot be systematically popularized and applied in geotechnical engineering to a certain extent. In addition, in essence, the continuous change of the microscopic structure in the shearing deformation process of the pile-soil interface is the root cause of different engineering characteristics in the macroscopic view, and the opacity of the pile and the soil body causes that the morphological change of each part of the soil sample cannot be directly observed during shearing. Therefore, under the condition of simulating the change of the climatic environment, the development of the visual research on the mechanical property mechanism and the shearing failure mode of the pile-unsaturated soil contact interface has important engineering significance, and particularly aims at the problem of large deformation of the pile-soil interface of the twisted pile foundation.
Chinese patent document CN201410077507.7 discloses a pile-soil contact surface friction force testing device and method considering the influence of temperature. However, the technical scheme can only apply confining pressure to the soil body, namely the pressure applied to the soil body around the pile along the pile body is equal to the pressure applied to the soil body around the pile in the direction perpendicular to the pile body, and the condition that the stress of the soil body around the pile in the two directions is unequal in the actual engineering cannot be considered; chinese patent document CN201210078542.1 discloses a device and a method for testing pile-soil contact surface friction based on a conventional geotechnical triaxial apparatus, the technical scheme can apply axial pressure and confining pressure to the soil body, and can measure static and dynamic deformation characteristics of the pile-soil contact surface. However, this solution does not allow for the visual observation of the displacement characteristics of the contact surface; on the basis of the two technical schemes, chinese patent document CN201610263630.7 discloses a visual test device for the damage form of the pile-soil contact surface of the special-shaped pile and a use method thereof, which realize visual observation of the shear damage characteristic of the pile-soil contact surface of the special-shaped pile with full scale under different temperatures, pile types and loading modes. However, the three technical solutions cannot prepare a homogeneous pile soil sample, and cannot measure the change of the water content of the soil body and the matrix suction force in the shearing process, and cannot consider the influence of the cyclic desorption on the shearing characteristic of the pile soil interface. Therefore, it is necessary to develop an indoor shearing device and a testing method which can accurately simulate the pile-unsaturated soil interface shearing failure mode under the cyclic desorption and stress coupling, monitor the suction force of soil matrix and the change of water content in real time, and reflect the displacement of the pile-unsaturated soil shearing surface soil particles really by adopting DIC technology.
Disclosure of Invention
In order to solve the problems, the invention provides a pile-unsaturated soil interface friction visualization test device and method, which solve the problems in the prior art.
In order to achieve the technical effects, the technical scheme of the invention is as follows:
a pile unsaturated soil interface friction visual test device comprises a frame, wherein a torsion device is arranged on the frame and connected with a hollow transparent pile, a sealing pressure chamber is arranged on the periphery of the hollow transparent pile, a soil sample is filled between the sealing pressure chamber and the hollow transparent pile, and the hollow transparent pile and the soil sample form a pile-soil contact interface; the sealing pressure chamber is communicated with a confining pressure control device; an axial pressure loading device is arranged right above the soil sample; the soil sample is communicated with a dry-wet circulating device; the matched soil sample is provided with a tensiometer and a moisture sensor; a camera device aiming at a pile-soil contact interface is arranged in the hollow transparent pile; the torsion device, the confining pressure control device, the axial pressure loading device, the tensiometer and the moisture sensor are all in communication connection with an image data acquisition device.
The frame comprises a workbench, the upper surface of the workbench is provided with an upright post, a cross beam is fixed on the upright post, and the bottom of the workbench is provided with a support; the cross beam is connected with the upright post to form a reaction frame, and the reaction frame is connected with a shaft pressure loading device; the workbench is provided with a threaded hole a for connecting the stand column, a threaded hole b for connecting the sealing pressure chamber, a groove a for embedding the O-shaped sealing ring, a clamping groove, a round hole for embedding the hollow transparent pile, a connecting hole for connecting the dry-wet circulating device and a ventilation pipeline.
The shaft pressure loading device comprises a cylinder, the cylinder is connected with a dowel bar, a shaft pressure sensor is mounted on the dowel bar, and the dowel bar is connected with a telescopic rod; but take shape on the telescopic link and have slot b, slot b middle part is taken shape and is had screw hole c, and telescopic link passes through screw hole c and links to each other with the dowel steel, places O type sealing washer in the slot b.
In a further improvement, the sealing pressure chamber is communicated with the confining pressure control device through a vent pipeline; the sealed pressure chamber comprises a rubber film wrapped on the outer side of the soil sample, and an outer cover cylinder is arranged outside the rubber film; the top of the outer cover cylinder is provided with a piston sleeve, a sealing ring is arranged in the piston sleeve, and the sealing ring is connected with the dowel bar in a sealing way; a top cover positioned above the soil sample is arranged at the upper part between the rubber film and the hollow transparent pile; the top cover is provided with a loading hole, a threaded hole d and a groove c and is communicated with a steam pipeline, the loading hole is in contact connection with the telescopic rod, and an O-shaped sealing ring is arranged in the groove c; the top of the hollow transparent pile is provided with an inner cover cylinder positioned in the outer cover cylinder;
a base is installed at the bottom of the soil sample, an annular groove is formed in the top of the base, the annular groove is communicated with a ventilation pipeline and is used for placing permeable stones, and filter paper is placed between the permeable stones and the soil sample; the bottom of the base is provided with a convex block, and the convex block is connected with a clamping groove on the frame; the rubber film is attached to the outer side wall of the soil sample, and two ends of the rubber film are fastened on the top cover and the base by using rubber bands;
an opening penetrating through a tensiometer is formed on the rubber film, and the tensiometer is fixed on the rubber film through an L-shaped grommet a; sealant is filled between the L-shaped grommet a and the tensiometer; the end part of the tensiometer is connected with a ceramic head which is contacted with the soil sample; a moisture sensor is also formed on the rubber film;
the moisture sensor is fixed on the rubber film through an L-shaped grommet b; sealant is filled between the L-shaped grommet b and the moisture sensor; and the TDR probe on the moisture sensor is contacted with the soil sample.
In a further improvement, the camera device comprises a DIC camera which is fixed on a bracket, and the bracket is fixed in the inner cover cylinder; the top of the inner cover cylinder is also fixed with a floodlight.
In a further improvement, the dry-wet circulating device comprises a hot air generator and a steam generator, and the hot air generator is communicated with a ventilation pipeline through a peristaltic pump; the steam generator is communicated with a steam pipeline through a peristaltic pump; a steam line; the ventilation pipeline is communicated with the bottom of the soil sample through a permeable stone, and the steam pipeline is communicated with the top of the soil sample through a closable perforated plate.
In a further improvement, the torsion device comprises a torsion shaft connected with the bottom of the hollow transparent pile, and an angular displacement sensor and a torque sensor are mounted on the torsion shaft; the torsion shaft is connected with a rotary disc, the rotary disc is connected with a magnet, a coil is installed on the periphery of the magnet, and the coil is fixed to the frame through a supporting rod.
In a further improvement, the confining pressure control device comprises an air pump communicated with the sealed pressure chamber and a barometer used for detecting the air pressure in the sealed pressure chamber.
A test method adopting the pile-unsaturated soil interface friction visualization test device is characterized by comprising the following steps:
s1, drying the soil sample, mixing the dried soil sample with distilled water to prepare a soil sample with a preset water content, and storing the soil sample in an environment with controlled humidity and temperature for 24 hours to ensure the water-vapor balance of the whole soil sample;
s2, manufacturing an annular calibration box according to the size of the soil sample, filling the soil sample into the calibration box, controlling the soil sample to be compacted at different times t, and calculating the density rho of the corresponding soil sample by adopting a cutting ring method after each compactiontAnd obtaining a relation curve of the density t and the compaction time t of the soil sample under different water contents:
ρt=a1×ln(t)+a2 (1)
wherein a is1And a2Is a calibration coefficient;
s3, manufacturing hollow transparent piles with different surface roughness according to the actual engineering, and connecting the hollow transparent piles with the torsion shaft;
s4, sequentially placing permeable stones and filter paper on a base, connecting a sample preparation split cylinder with a workbench, sleeving a rubber membrane on the inner side of the sample preparation split cylinder, fixing the rubber membrane by using a rubber band, sequentially adding the mass of a soil sample into the rubber membrane according to trisections according to a preset dry density, and making an annular soil sample when the required height of a corresponding layer is reached;
s5, sequentially placing an openable and closable perforated plate and a top cover at the upper end of the annular soil sample, removing the sample preparation split cylinder, fastening two ends of a rubber film on the top cover and a base, adjusting a telescopic rod to be just contacted with the top cover, and respectively installing a tensiometer and a moisture sensor at the perforated part of the rubber film;
s6, coating vaseline among the top cover, the base and the pile body for sealing, connecting the outer cover cylinder and the inner cover cylinder with the workbench and the top cover respectively, installing a DIC camera on the bracket, adjusting the lens to be opposite to the pile soil contact surface, and connecting the axial pressure sensor, the laser displacement sensor, the moisture sensor, the tensiometer, the torque sensor, the angular displacement sensor and the DIC camera with an image data acquisition device respectively;
when S7, cyclic dehumidification and K0 consolidation are carried out, two schemes are adopted according to actual design working conditions: 1) firstly, carrying out K0 consolidation on a soil sample, starting a dry-wet circulating device after the consolidation is finished, and respectively carrying out cyclic dehumidification on the soil sample for a plurality of times; 2) firstly, starting a dry-wet circulating device, circularly dehumidifying a soil sample for a plurality of times, and then carrying out K0 consolidation;
and (3) cyclic dehumidification process: opening a steam valve, preheating a steam generator for 2min, then opening a peristaltic pump, enabling water steam to enter from the top of a soil sample, recording the changes of the water content and the substrate suction force respectively displayed by a water sensor and a tensiometer, closing the peristaltic pump and the steam generator when the water content and the substrate suction force reach the required simulated water content, standing for 5-10 min, only opening a drying valve after the water content and the substrate suction force are stable, preheating a hot air generator for 2min, then opening the peristaltic pump, enabling hot air to enter from the bottom of the soil sample, controlling the circulating moisture desorption degree by controlling the change of the water content, closing the peristaltic pump and the hot air generator when the required water content is reached, standing for 5-10 min, completing one circulating moisture desorption, and setting different circulating moisture desorption times according to the test requirements;
k0 consolidation process: closing the closable porous plate, starting the axial pressure loading device and the confining pressure control device, firstly applying confining pressure, monitoring vertical deformation of the top cover by using a laser displacement sensor, and feeding back a deformation value to a computer, so as to adjust the axial pressure applied by the axial loading device, realize the K0 consolidation condition, and loading until the deformation of the soil sample in 24 hours is not more than 0.01mm, and then completing the consolidation;
s8, when a pile-soil contact interface is sheared, keeping the confining pressure and the axial pressure of a soil sample unchanged, starting a torsion device and a torsion control device, setting a torsion rate to apply torque to the hollow transparent pile, and transmitting the readings of an axial pressure sensor, a laser displacement sensor, a moisture sensor, a tensiometer, a torque sensor and an angular displacement sensor and time sequence images shot by a DIC camera to a computer for storage through an image data acquisition device;
and S9, analyzing the test data, and analyzing the time sequence image by combining with a DIC program to obtain the displacement change of the pile-soil contact interface shear zone, the relation between the water content and the shear strength and the cyclic desorption times and the relation between the water content and the matrix suction force along with the change of the shear displacement in the shearing process.
The invention has the following remarkable effects:
1) the computer is matched with the adjusting shaft pressure loading device and the confining pressure control device, so that K0 consolidation of the soil sample is effectively realized.
2) Through the connection of the sealed pressure chamber and the dry-wet circulating device, the soil sample is effectively subjected to cyclic dehumidification.
3) Through the connection of the tensiometer, the moisture sensor and the image data acquisition device, the suction force and the moisture content of the soil sample matrix in the interface shearing process are effectively monitored.
4) The DIC technology can be used for relatively truly reflecting the shearing failure mode of the pile-unsaturated soil interface in a microscopic mode.
5) The testing device provided by the invention is simple in structure, convenient to operate and easy to realize.
6) And accurately controlling the energy uniform transfer at different depths of the soil sample by using a density-time calibration curve so as to prepare a homogeneous sample.
Drawings
FIG. 1 is a schematic structural diagram of a pile-unsaturated soil interface visualization test device under cyclic desorption moisture and stress coupling;
FIG. 2 is a schematic view of the structure of the working platform of FIG. 1;
FIG. 3 is a schematic view of the telescopic rod of FIG. 1;
FIG. 4 is an enlarged view of a portion A of FIG. 1;
FIG. 5 is a schematic view of the structure of the outer cylinder cover in FIG. 1;
FIG. 6 is a schematic view of the inner barrel cover of FIG. 1;
FIG. 7 is a schematic view of the structure of the top cover of FIG. 1;
FIG. 8a is a first schematic view of the base structure in FIG. 1;
FIG. 8b is a second schematic view of the base structure shown in FIG. 1;
FIG. 9 is an enlarged view of part B of FIG. 1;
FIG. 10 is an enlarged view of portion C of FIG. 1;
FIG. 11a is a schematic top view of the closable perforated plate of FIG. 1;
FIG. 11b is a schematic side view of the closable multi-hole plate of FIG. 1;
FIG. 12 is a detail view of the twisting device of FIG. 1;
FIG. 13a is a schematic side view of a sample preparation split cylinder;
FIG. 13b is a schematic top view of the sample preparation split cartridge;
FIG. 14 is a graph of soil sample density versus compaction time.
In the figure: 1-1, a cross beam; 1-2, upright columns; 1-3, a workbench; 1-3-1, a threaded hole a; 1-3-2, a threaded hole b; 1-3-3, groove a; 1-3-4 card slots; 1-3-5, connecting hole; 1-3-6, round hole; 1-4, a bracket; 2-1, a cylinder; 2-2, a dowel bar; 2-3, an axial pressure sensor; 2-4, a telescopic rod; 2-4-1, groove b; 2-4-2, a threaded hole c; 2-5, a laser displacement sensor; 3. a shaft pressure control device; 4-1, an outer cover cylinder; 4-1-1, piston sleeve; 4-1-2, sealing ring; 4-2, inner cover cylinder; 4-3, a top cover; 4-3-1, loading holes; 4-3-2, a threaded hole d; 4-3-3, groove c; 4-4, a base; 4-4-1, an annular groove; 4-4-2, bumps; 4-5, a rubber membrane; soil sample 5, soil sample; 6. hollow transparent piles; 7. a confining pressure control device; 8. a vent line; 9. a tensiometer; 9-1, ceramic heads; 9-2, L-shaped grommet a; 10. a moisture sensor; 10-1, TDR probe; 10-2, L-shaped grommet b; 11. a DIC camera; 12. a bracket; 13. a floodlight; 14. an image data acquisition device; 15. a dry-wet circulation device; 16-1, a steam pipeline; 16-2, the porous plate can be closed; 16-3, a ventilation pipeline; 16-4, permeable stone; 17-1, torsion axis; 17-2, a strut; 17-3, a coil; 17-4, an angular displacement sensor; 17-5, a torque sensor; 17-6, a turntable; 17-7, a magnet; 18. a torsion control device; 19. a computer; 20-1, preparing a sample split cylinder; 20-2 and a lantern ring.
Detailed Description
In order that those skilled in the art may better understand the present invention and enable its practice, the present invention is further described below in conjunction with the accompanying drawings.
Example 1:
referring to fig. 1, 11a, 11b and 13a, 13b, the present embodiment provides a pile-unsaturated soil interface friction visualization test apparatus under cyclic desorption moisture and stress coupling, including a frame, an axial pressure loading device, an axial pressure control device, a sealed pressure chamber, a soil sample, a hollow transparent pile, a sample preparation split cylinder, a confining pressure control device, a tensiometer, a moisture sensor, a DIC camera, an image data acquisition device, a dry-wet cycle device, a torsion control device and a computer; the frame is sequentially provided with an axial loading device, a sealing pressure chamber and a twisting device from top to bottom; the axial pressure loading device and the confining pressure control device are respectively connected with the sealing pressure chamber; the hollow transparent pile is coaxially arranged at the lower end of the inner cover cylinder, and the lower end of the hollow transparent pile is connected with the torsion device; an annular soil sample is filled between the hollow transparent pile and the rubber membrane, filter paper and permeable stones are arranged at the lower end of the soil sample and placed on the base, and a closable porous plate and a top cover are arranged at the upper end of the soil sample; the closable porous plate is formed by combining an upper plate and a lower plate, and the pore passage of the upper plate can be opened and closed by rotating; sealing materials are filled among the top cover, the base and the hollow transparent piles; the dry-wet circulating device is connected with the upper end and the lower end of the soil sample; the tensiometer and the moisture sensor are symmetrically arranged on the rubber film; the DIC camera is positioned at the lower end of the inner sleeve, and the lens is opposite to a pile-soil contact interface; the axial pressure sensor, the laser displacement sensor, the moisture sensor, the tensiometer, the torque sensor, the angular displacement sensor and the DIC camera are respectively connected with the image data acquisition device, and the data and the image are transmitted to the computer for recording, reading and processing through the image data acquisition device.
The hollow transparent pile is made of transparent organic glass, the hollow transparent pile is in the shape of a hollow cylinder, the diameter of the hollow cylinder is 100-300 mm, the height of the hollow cylinder is 500-800 mm, the wall thickness of the periphery of the hollow cylinder is 10-20 mm, and the wall thickness of the bottom surface of the hollow cylinder is 20-40 mm.
The sealing material adopts vaseline.
Referring to fig. 1 to 2, the frame includes a cross beam, a post, a table, and a bracket; the cross beam is connected with the upright post to form a reaction frame, and the reaction frame provides support for the axial compression loading device; the workbench is provided with a threaded hole a, a threaded hole b, a groove a, a ventilation pipeline, a clamping groove, a connecting hole and a round hole; the upright post is connected with the threaded hole a; the groove a is provided with an O-shaped sealing ring; a hollow transparent pile is embedded in the round hole; the lower end of the workbench is connected with the bracket.
Referring to fig. 1 and 3 to 4, the axial pressure loading device at least includes a cylinder, a dowel bar, an axial pressure sensor, a telescopic rod and a laser displacement sensor; the cylinder is fixed on the cross beam and is connected with the axial pressure control device; the upper end of the dowel bar is connected with the cylinder, the middle part of the dowel bar is fixedly provided with the shaft pressure sensor, and the lower end of the dowel bar is connected with the threaded hole c of the telescopic rod through a bolt; the telescopic rod is provided with a groove b, and an O-shaped sealing ring is placed in the groove b; the laser displacement sensor is fixed on the cross beam, and the probe is aligned to the top cover.
Referring to fig. 1, 5-8 a and 8b, the sealed pressure chamber is connected with the confining pressure control device through a vent pipeline in the dowel; the sealed pressure chamber at least comprises an outer cover cylinder, an inner cover cylinder, a top cover, a base and a rubber film; the top of the outer cover cylinder is provided with a piston sleeve, a sealing ring is arranged in the piston sleeve, and the sealing ring is connected with the dowel bar in a sealing manner; the lower end of the outer cover cylinder is connected with the threaded hole b through a bolt; the top cover is provided with a loading hole, a threaded hole d, a groove c and a steam pipeline, the loading hole is in contact connection with the telescopic rod, and an O-shaped sealing ring is placed in the groove c; the lower end of the inner sleeve is connected with the threaded hole d through a bolt; an annular groove is formed in the top of the base, and a ventilation pipeline is arranged in the annular groove and used for placing permeable stones; the bottom of the base is provided with a convex block, and the convex block is connected with the clamping groove; the rubber film is attached to the outer side wall of the soil sample, and two ends of the rubber film are fastened on the top cover and the base through rubber bands.
The sample preparation split cylinder described with reference to fig. 13a and 13b is fixed with a collar, the outer wing of which is connected to the work table by a bolt.
Referring to fig. 9, the joint of the tensiometer and the rubber film is provided with an opening, and the tensiometer is fixedly connected with the rubber film through an L-shaped grommet a; sealant is filled between the L-shaped cable a and the tensiometer; the ceramic head is in contact with a soil sample.
Referring to fig. 10, the moisture sensor is provided with an opening at the joint with the rubber membrane and is fixedly connected by passing through an L-shaped grommet b; sealant is filled between the L-shaped cable b and the moisture sensor; the TDR probe is contacted with the soil sample.
Referring to fig. 1, the DIC camera is fixed on a bracket fixed in an inner housing; the floodlight is fixed on the top of the inner cover tube and provides a light source for the DIC camera.
Referring to fig. 1, the dry-wet cycle device includes at least a hot-air generator, a steam generator and a peristaltic pump; hot air produced by the hot air generator is pressurized by a peristaltic pump and then enters the soil sample from the ventilation pipeline; the steam generated by the steam generator enters the soil sample from a steam pipeline after being pressurized by a peristaltic pump; the peristaltic pump drives hot air and steam to rapidly complete water-vapor exchange in the soil sample.
Referring to fig. 1 and 12, the torsion control device is connected to the torsion device; the torsion device at least comprises a torsion shaft, a support rod, a coil, an angular displacement sensor, a torque sensor, a turntable and a magnet; the upper end of the torsion shaft is connected with the bottom of the hollow transparent pile, the middle part of the torsion shaft is sequentially fixed with an angular displacement sensor and a torque sensor from top to bottom, and the lower end of the torsion shaft is connected with the rotary table; the support rod is fixed at the bottom of the workbench, and the lower part of the support rod is connected with a coil; the coils are distributed on the periphery of the turntable; the magnets are arranged in the coils in a one-to-one correspondence manner.
Example 2:
referring to the device described in example 1, in this example, firstly, a soil sample is subjected to K0 consolidation, after the consolidation is completed, cyclic desorption and moisture absorption are respectively performed for a plurality of times, and finally, a pile-unsaturated soil interface shear test is performed to discuss the change of the displacement of an interface shear band and the quantitative relationship between the water content, the shear strength and the cyclic desorption and moisture absorption times in the shearing process, so as to reveal the mechanical properties and the load transfer mechanism of the pile-soil interface.
The test method comprises the following steps:
s1, drying the soil sample, mixing the dried soil sample with distilled water to prepare a soil sample with a certain water content, and storing the soil sample in an environment with controlled humidity and temperature for 24 hours to ensure the water-vapor balance of the whole soil sample;
s2, manufacturing an annular calibration box according to the size of the pile soil sample, filling the calibration box with the soil sample, controlling the soil sample to be compacted at different time t, and calculating the density t of the corresponding soil sample by adopting a cutting ring method after each compaction, thereby obtaining the relation curve of the density t of the soil sample under different water contents and the compaction time t:
ρt=a1×ln(t)+a2 (1)
wherein a is1And a2Is a calibration coefficient;
in particular, typical ρ at different water contentstThe-t curve is shown in fig. 14;
s2, manufacturing hollow transparent piles with different surface roughness according to the actual engineering, and connecting the pile body with the torsion shaft;
s3, sequentially placing permeable stones and filter paper on a base, connecting a sample preparation split cylinder with a workbench, sleeving a rubber membrane on the inner side of the sample preparation split cylinder, fixing the rubber membrane by using a rubber band, sequentially adding the mass of a soil sample into the rubber membrane according to trisections according to a preset dry density, and making an annular soil sample when the required height of a corresponding layer is reached;
s4, sequentially placing an openable and closable perforated plate and a top cover at the upper end of the annular soil sample, fastening two ends of a rubber film on the top cover and a base, removing the sample preparation split cylinder, adjusting a telescopic rod to be just contacted with the top cover, and respectively installing a tensiometer and a moisture sensor at the perforated part of the rubber film;
s5, coating vaseline among the top cover, the base and the pile body for sealing, connecting the outer cover cylinder and the inner cover cylinder with the workbench and the top cover respectively, installing a DIC camera on the bracket, adjusting the lens to be opposite to the pile soil contact surface, and connecting the axial pressure sensor, the laser displacement sensor, the moisture sensor, the tensiometer, the torque sensor, the angular displacement sensor and the DIC camera with an image data acquisition device respectively;
s6, firstly, performing a cyclic dehumidification process, namely opening a steam valve, preheating a steam generator for 2min, then opening a peristaltic pump to enable water steam to enter from the top of the soil sample, recording the changes of the water content and the substrate suction force respectively displayed by a water sensor and a tensiometer, closing the peristaltic pump and the steam generator when the water content reaches the required simulated water content, standing for 5-10 min, only opening a drying valve after the values of the water content and the substrate suction force are stable, preheating a hot air generator for 2min, then opening the peristaltic pump to enable hot air to enter from the bottom of the soil sample, controlling the cyclic dehumidification degree by controlling the change of the water content, closing the peristaltic pump and the hot air generator when the required water content is reached, standing for 5-10 min, and completing one cyclic dehumidification, and setting 1, 3, 5 and 10 cyclic dehumidification according to the test requirements; then, performing a K0 consolidation process, namely closing the closable porous plate, starting the axial pressure loading device and the confining pressure control device, firstly applying confining pressure, monitoring the vertical deformation of the top cover by using a laser displacement sensor, feeding back a deformation value to a computer, adjusting the axial pressure applied by the axial loading device to realize a K0 consolidation condition, and loading until the deformation of the soil sample within 24 hours is not more than 0.01mm, and then completing the consolidation;
s7, when a pile-soil contact interface is sheared, keeping the confining pressure and the axial pressure of a soil sample unchanged, starting a torsion device and a torsion control device, setting a torsion rate to apply torque to the hollow transparent pile, and transmitting the readings of an axial pressure sensor, a laser displacement sensor, a moisture sensor, a tensiometer, a torque sensor and an angular displacement sensor and time sequence images shot by a DIC camera to a computer for storage through an image data acquisition device;
and S8, analyzing the test data, and analyzing the time sequence image by combining with the compiled DIC program to obtain the displacement change of the pile-soil contact interface shear zone, the relation between the water content-shear strength-cyclic desorption times and the relation between the water content-matrix suction force and the change of the shear displacement in the shearing process.
Example 3:
referring to the device of example 1, in this example, a soil sample is subjected to cyclic dehumidification for several times, then is subjected to K0 consolidation, and after the consolidation is completed, a pile-soil interface shear test is performed to discuss the displacement change of an interface shear zone and the quantitative relation between the water content-shear strength-cyclic dehumidification times in the shearing process, so as to reveal the pile-unsaturated soil interface mechanical characteristics and the load transfer mechanism.
The test method is the same as that of example 2 except for the step S6, and the step S6 is changed to:
s6, firstly carrying out a K0 consolidation process, namely closing the closable perforated plate, starting the axial pressure loading device and the confining pressure control device, firstly applying confining pressure, monitoring vertical deformation of the top cover by using a laser displacement sensor, feeding back a deformation value to a computer, adjusting the axial pressure applied by the axial loading device to realize a K0 consolidation condition, and loading until the deformation of the soil sample in 24 hours is not more than 0.01mm, and then completing consolidation; and then, carrying out a cyclic desorption and moisture absorption process, namely opening a steam valve, preheating a steam generator for 2min, then opening a peristaltic pump to enable water steam to enter from the top of the soil sample, recording the changes of the water content and the substrate suction force respectively displayed by a water sensor and a tensiometer, closing the peristaltic pump and a steam generator when the water content reaches the required simulated water content, standing for 5-10 min, only opening a drying valve after the water content and the substrate suction force are stable, preheating a hot air generator for 2min, then opening the peristaltic pump to enable hot air to enter from the bottom of the soil sample, controlling the cyclic desorption and moisture absorption degree by controlling the change of the water content, closing the peristaltic pump and the hot air generator when the required water content is reached, standing for 5-10 min, and completing one cyclic desorption and moisture absorption, wherein 1, 3, 5 and 10 cyclic desorption and moisture absorption are set according to the test requirements.
Example 4:
referring to the device described in example 1, this example studies the soil-water characteristic curve of unsaturated soil under cyclic desorption and stress coupling on the basis of examples 2 and 3, specifically extracts the change data of soil sample matrix suction and water content in the K0 consolidation process and the change data of soil sample matrix suction and water content with shear displacement in the shearing process, and draws the soil-water characteristic curve of unsaturated soil according to the change data.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (9)

1. The pile-unsaturated soil interface friction visual test device is characterized by comprising a frame, wherein a torsion device is arranged on the frame and connected with a hollow transparent pile (6), a sealed pressure chamber is arranged on the periphery of the hollow transparent pile (6), a soil sample (5) is filled between the sealed pressure chamber and the hollow transparent pile (6), and the hollow transparent pile (6) and the soil sample (5) form a pile-soil contact interface; the sealing pressure chamber is communicated with a confining pressure control device; an axial pressure loading device is arranged right above the soil sample (5); the soil sample (5) is communicated with a dry-wet circulating device; the matched soil sample (5) is provided with a tensiometer (9) and a moisture sensor (10); a camera device aiming at a pile-soil contact interface is arranged in the hollow transparent pile (6); the torsion device, the confining pressure control device, the axial pressure loading device, the tension meter (9) and the moisture sensor (10) are all connected with an image data acquisition device (14) in a communication mode.
2. The pile-unsaturated soil interface friction visualization test device according to claim 1, wherein the frame comprises a workbench (1-3), an upright (1-2) is installed on the upper surface of the workbench (1-3), a cross beam (1-1) is fixed on the upright (1-2), and a support (1-4) is installed at the bottom of the workbench (1-3); the cross beam (1-1) and the upright column (1-2) are connected to form a reaction frame, and the reaction frame is connected with a shaft pressure loading device; the working table (1-3) is provided with a threaded hole a (1-3-1) used for connecting an upright post (1-2), a threaded hole b (1-3-2) used for connecting a sealing pressure chamber, a groove a (1-3-3) used for embedding an O-shaped sealing ring, a clamping groove (1-3-4), a round hole (1-3-6) used for embedding a hollow transparent pile (6), a connecting hole (1-3-5) used for connecting a dry-wet circulating device and a ventilation pipeline (16-3).
3. The pile-unsaturated soil interface friction visualization test device according to claim 1, wherein the axial pressure loading device comprises a cylinder (2-1), the cylinder (2-1) is connected with a dowel bar (2-2), an axial pressure sensor (2-3) is mounted on the dowel bar (2-2), and the dowel bar (2-2) is connected with a telescopic rod (2-4); a groove b (2-4-1) is formed in the telescopic rod (2-4), a threaded hole c (2-4-2) is formed in the middle of the groove b (2-4-1), the telescopic rod (2-4) is connected with the dowel bar (2-2) through the threaded hole c (2-4-2), and an O-shaped sealing ring is placed in the groove b (2-4-1).
4. The pile-unsaturated soil interface friction visual testing device of claim 3, wherein the sealed pressure chamber is communicated with a confining pressure control device through a vent pipeline; the sealed pressure chamber comprises a rubber film (4-5) wrapped on the outer side of the soil sample (5), and an outer cover cylinder (4-1) is arranged outside the rubber film (4-5); the top of the outer cover cylinder (4-1) is provided with a piston sleeve (4-1-1), a sealing ring (4-1-2) is arranged in the piston sleeve (4-1-1), and the sealing ring (4-1-2) is connected with a dowel bar (2-2) in a sealing way; a top cover (4-3) positioned above the soil sample (5) is arranged at the upper part between the rubber film (4-5) and the hollow transparent pile (6); the top cover (4-3) is provided with a loading hole (4-3-1), a threaded hole d (4-3-2) and a groove c (4-3-3) and is communicated with a steam pipeline (16-1), the loading hole (4-3-1) is in contact connection with the telescopic rod (2-4), and an O-shaped sealing ring is placed in the groove c (4-3-3); the top of the hollow transparent pile (6) is provided with an inner cover cylinder (4-2) positioned in the outer cover cylinder (4-1);
a base (4-4) is installed at the bottom of the soil sample (5), an annular groove (4-4-1) is formed in the top of the base (4-4), the annular groove (4-4-1) is communicated with a ventilation pipeline (16-3) and is used for placing a permeable stone (16-4), and filter paper is placed between the permeable stone (16-4) and the soil sample (5); the bottom of the base (4-4) is provided with a bump (4-4-2), and the bump (4-4-2) is connected with a clamping groove (1-3-4) on the frame; the rubber film (4-5) is attached to the outer side wall of the soil sample, and two ends of the rubber film (4-5) are fastened on the top cover (4-3) and the base (4-4) by using rubber bands;
an opening which passes through a tension meter (9) is formed on the rubber film (4-5), and the tension meter (9) is fixed on the rubber film (4-5) through an L-shaped grommet a (9-2); sealant is filled between the L-shaped grommet a (9-2) and the tensiometer (9); the end part of the tensiometer (9) is connected with a ceramic head (9-1) which is contacted with the soil sample (5); a moisture sensor (10) is also formed on the rubber film (4-5);
the moisture sensor (10) is fixed on the rubber film (4-5) through an L-shaped grommet b (10-2); sealant is filled between the L-shaped grommet b (10-2) and the moisture sensor (10); and a TDR probe (10-1) on the moisture sensor (10) is contacted with the soil sample (5).
5. The pile-unsaturated soil interface friction visual testing device according to claim 4, characterized in that the camera device comprises a DIC camera (11), the DIC camera (11) is fixed on a bracket (12), and the bracket (12) is fixed in the inner cover cylinder (4-2); the top of the inner cover cylinder (4-2) is also fixed with a floodlight (13).
6. The pile-unsaturated soil interface friction visualization test device according to claim 1, wherein the dry-wet cycle device comprises a hot air generator and a steam generator, the hot air generator is communicated with a ventilation pipeline (16-3) through a peristaltic pump; the steam generator is communicated with a steam pipeline (16-1) through a peristaltic pump; a steam line (16-1); the ventilation pipeline (16-3) is communicated with the bottom of the soil sample (5) through a permeable stone (16-4), and the steam pipeline (16-1) is communicated with the top of the soil sample (5) through a closable porous plate (16-2).
7. The pile-unsaturated soil interface friction visualization test device according to claim 1, wherein the torsion device comprises a torsion shaft (17-1) connected with the bottom of the hollow transparent pile (6), and an angular displacement sensor (17-4) and a torque sensor (17-5) are mounted on the torsion shaft (17-1); the torsion shaft (17-1) is connected with a rotary table (17-6), the rotary table (17-6) is connected with a magnet (17-7), a coil (17-3) is arranged on the periphery of the magnet (17-7), and the coil (17-3) is fixed on the frame through a support rod (17-2).
8. The pile-unsaturated soil interface friction visualization test device according to claim 1, wherein the confining pressure control device comprises an air pump communicated with the sealed pressure chamber and an air pressure gauge for detecting air pressure in the sealed pressure chamber.
9. A test method adopting the pile-unsaturated soil interface friction visualization test device of any one of claims 1-8, which is characterized by comprising the following steps:
s1, drying the soil sample, mixing the dried soil sample with distilled water to prepare a soil sample with a preset water content, and storing the soil sample in an environment with controlled humidity and temperature for 24 hours to ensure the water-vapor balance of the whole soil sample;
s2, manufacturing an annular calibration box according to the size of the soil sample, filling the soil sample into the calibration box, controlling the soil sample to be compacted at different times t, and calculating the density rho of the corresponding soil sample by adopting a cutting ring method after each compactiontAnd obtaining a relation curve of the density t and the compaction time t of the soil sample under different water contents:
ρt=a1×ln(t)+a2 (1)
wherein a is1And a2Is a calibration coefficient;
s3, manufacturing hollow transparent piles with different surface roughness according to the actual engineering, and connecting the hollow transparent piles with the torsion shaft;
s4, sequentially placing permeable stones and filter paper on a base, connecting a sample preparation split cylinder with a workbench, sleeving a rubber membrane on the inner side of the sample preparation split cylinder, fixing the rubber membrane by using a rubber band, sequentially adding the mass of a soil sample into the rubber membrane according to trisections according to a preset dry density, and making an annular soil sample when the required height of a corresponding layer is reached;
s5, sequentially placing an openable and closable perforated plate and a top cover at the upper end of the annular soil sample, removing the sample preparation split cylinder, fastening two ends of a rubber film on the top cover and a base, adjusting a telescopic rod to be just contacted with the top cover, and respectively installing a tensiometer and a moisture sensor at the perforated part of the rubber film;
s6, coating vaseline among the top cover, the base and the pile body for sealing, connecting the outer cover cylinder and the inner cover cylinder with the workbench and the top cover respectively, installing a DIC camera on the bracket, adjusting the lens to be opposite to the pile soil contact surface, and connecting the axial pressure sensor, the laser displacement sensor, the moisture sensor, the tensiometer, the torque sensor, the angular displacement sensor and the DIC camera with an image data acquisition device respectively;
when S7, cyclic dehumidification and K0 consolidation are carried out, two schemes are adopted according to actual design working conditions: 1) firstly, carrying out K0 consolidation on a soil sample, starting a dry-wet circulating device after the consolidation is finished, and respectively carrying out cyclic dehumidification on the soil sample for a plurality of times; 2) firstly, starting a dry-wet circulating device, circularly dehumidifying a soil sample for a plurality of times, and then carrying out K0 consolidation;
and (3) cyclic dehumidification process: opening a steam valve, preheating a steam generator for 2min, then opening a peristaltic pump, enabling water steam to enter from the top of a soil sample, recording the changes of the water content and the substrate suction force respectively displayed by a water sensor and a tensiometer, closing the peristaltic pump and the steam generator when the water content and the substrate suction force reach the required simulated water content, standing for 5-10 min, only opening a drying valve after the water content and the substrate suction force are stable, preheating a hot air generator for 2min, then opening the peristaltic pump, enabling hot air to enter from the bottom of the soil sample, controlling the circulating moisture desorption degree by controlling the change of the water content, closing the peristaltic pump and the hot air generator when the required water content is reached, standing for 5-10 min, completing one circulating moisture desorption, and setting different circulating moisture desorption times according to the test requirements;
k0 consolidation process: closing the closable porous plate, starting the axial pressure loading device and the confining pressure control device, firstly applying confining pressure, monitoring vertical deformation of the top cover by using a laser displacement sensor, and feeding back a deformation value to a computer, so as to adjust the axial pressure applied by the axial loading device, realize the K0 consolidation condition, and loading until the deformation of the soil sample in 24 hours is not more than 0.01mm, and then completing the consolidation;
s8, when a pile-soil contact interface is sheared, keeping the confining pressure and the axial pressure of a soil sample unchanged, starting a torsion device and a torsion control device, setting a torsion rate to apply torque to the hollow transparent pile, and transmitting the readings of an axial pressure sensor, a laser displacement sensor, a moisture sensor, a tensiometer, a torque sensor and an angular displacement sensor and time sequence images shot by a DIC camera to a computer for storage through an image data acquisition device;
and S9, analyzing the test data, and analyzing the time sequence image by combining with a DIC program to obtain the displacement change of the pile-soil contact interface shear zone, the relation between the water content and the shear strength and the cyclic desorption times and the relation between the water content and the matrix suction force along with the change of the shear displacement in the shearing process.
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CN115046892A (en) * 2022-06-30 2022-09-13 重庆大学 Testing device for soil-rock mixture seepage model test under dry-wet cycle condition
CN115876579A (en) * 2022-08-25 2023-03-31 中国科学院西北生态环境资源研究院 Creep test method for pile-frozen soil shear sample
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