RU2467305C1 - Instrument of triaxial compression with measurement of contact stresses - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: invention relates to the field of construction and is designed to define mechanical properties of construction and road materials, including reinforced soils, under complicated stressed-deformed condition. The device comprises a frame, a body with a base, a cover and side walls, a working chamber with an elastic shell and pressure chambers arranged in it and joined with loading and metering accessories. One of side walls of the body is arranged as rigid and movable with inbuilt force sensors, besides, displacement of the wall is monitored with a step motor, and the material sample is lifted using a movable platform with a hydraulic drive.

EFFECT: expansion of instrument functionality and increased accuracy of research by measurement of contact stresses and local deformations.

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Description

Technical field

The technical solution relates to the field of construction and is intended to determine the mechanical properties of building and road materials, including reinforced soils, in a complex stress-strain state.

State of the art

An analogue of the claimed technical solution is the "Triaxial compression device" (patent for the invention (United States Patent) Triaxial compression test apparatus, No. 3728895, April 24, 1973, M. C. G01N 3/08) [1].

Summary of the analogue.

A high-speed device for triaxial testing, having a hollow rectangular frame with a central rectangular working chamber for accommodating the test sample and rectangular cavities on each side of the frame, in which a movable stamp is placed, having an internal movable wall made in the form of a flexible diaphragm, which under the action of fluid pressure through the fitting compresses the test sample along the respective axis of the cavities, and sensors generating signals representing pressure and movement of the Enki.

The main application of the device is the testing of soil and rock samples, and other natural and artificial materials, to determine their mechanical properties.

The disadvantage of the analogue is the inability to conduct soil tests with the measurement of contact stresses on the faces of the sample due to the lack of sensors for measuring them on a flexible diaphragm.

The next analogue of the proposed technical solution is “A device for studying the properties of soils under triaxial compression” (USSR author's certificate for the invention No. 700838, application No. 2629174 / 29-33 of 09/06/1975, applicant of the Moscow Order of the Red Banner of Labor Engineering Institute named after V.V. Kuybysheva, authors Z. G. Ter-Martirosyan, D. M. Akhpatelov, Yu.S. Grigoryev, V. A. Tishchenko, M. Cl. ² G01N 33/24, G01N 3/10, published on November 30 .1979, bull. 44) [2], comprising a housing with a base, a cover and side walls, placed in it with a working chamber with elastic a casing and pressure chambers associated with load and measuring devices, characterized in that, in order to increase the accuracy of measurements and reduce the complexity of the work, the casing is equipped with elastic grooves having internal grooves and a quadrangular support frame with screws missing at the corners of the support frame, each the pressure chamber is formed by the groove of the elastic gasket and the wall of the working chamber, and the screws are supported on the side walls of the housing, which, in turn, are pivotally connected to the base.

The disadvantages of this analogue are the complexity of preparing the device for testing and placing a soil sample in the working chamber, the inability to directly measure the axial deformations of the soil sample, the inability to measure contact stresses due to the presence of an elastic shell.

The closest analogue (prototype) of the claimed technical solution is the “Triaxial compression device” (RF patent for the invention No. 2418283, application No. 2010018180 dated 04.03.2010, the applicant “NPP Geotek” LLC, authors G. Boldyrev, E. Boldyreva ., Idrisov I.Kh., Elatontsev A.I., IPC G01N 3/08, published 05/10/2011, bull. 13) [3], including a frame, a casing with a base, a cover and side walls placed in it by a working chamber with an elastic shell and pressure chambers associated with load and measuring devices, four double-acting pneumatic cylinders vertically mounted on the frame, the lower rods of the pneumatic cylinders are attached to the vertically movable platform, the horizontally movable platform is located on the vertically movable platform, the base and soil sample in a removable form, the upper rods of the pneumatic cylinders are attached to the traverse, and the traverse to the cover, each pressure chamber has three linear displacement sensor, the side walls of the housing being one-piece, and the base and cover removable.

The disadvantage of the prototype is the inability to measure contact stresses and strains on the side walls due to the presence of elastic shells.

Explanation of the disadvantages of the prototype.

1. In the prototype, to create a complex stress state, elastic shells are used through which pressure is transferred to a sample of material. The presence of a flexible boundary in the form of elastic shells does not allow one to study the nature of the distribution of contact stresses, since their measurements require the presence of a rigid boundary. Moreover, the nature of the distribution of contact stresses depends not only on the level of the stress state, but also on the magnitude of the displacement of the rigid boundary for cases of active and passive pressures. The movement of the border in the prototype is not provided.

2. The device allows you to measure the total deformation of the sample in the direction of its three mutually perpendicular axes, but does not allow to measure local deformations on the faces of the sample material.

The essence of the technical solution

A known device for triaxial testing of soils, including a frame, a housing with a base, a cover and side walls, housed in it with a working chamber with an elastic shell and pressure chambers associated with load and measuring devices, characterized in that, in order to reduce the complexity and increase productivity tests, the device is equipped with four double-acting pneumatic cylinders mounted vertically on the frame, the lower rods of the pneumatic cylinders are connected to a vertically movable platform, vertically A horizontal platform, a base and a soil sample in a removable form are located on the movable platform, the upper rods of the pneumatic cylinders are attached to the traverse, and the traverse to the cover, each pressure chamber has three linear displacement sensors, the side walls of the housing being one-piece, and the base and cover removable.

The purpose of this technical solution is to expand the functionality of the device and increase the accuracy of research by measuring contact stresses and local deformations.

This goal is achieved by the fact that one of the side walls of the pressure chamber is made rigid with a built-in movable rigid stamp. The hard stamp has force sensors and is connected to the servo drive, which allows you to set the movement of the stamp both in the direction inside the material sample and in the opposite direction. To ensure tightness around the perimeter of the hard stamp introduced a sealing ring.

A digital camera is used to measure local deformations, and one of the walls of the working chamber is made transparent.

Management of the device is performed using a measuring system with direct and feedback.

List of figures, drawings and other materials

Figure 1 shows a drawing of a General view of a triaxial compression device with a measurement of contact stresses.

Figure 2 shows an axonometric image of a triaxial compression device.

Figure 3 shows a top view of a triaxial compression device.

Figure 4 shows the structural diagram of the control device triaxial compression.

An example of the implementation of a technical solution

In figure 1, 2, 3, 4, a triaxial compression device with contact stress measurement comprises a frame 1, on which is fixed a housing consisting of a base 2, four side walls 3, 4, 5, 6 and a cover 7, interconnected on threaded studs 8 and fixed by nuts 9. Base 2, three side walls 3, 5, 6 have a pressure chamber 10 with an elastic shell 11, fittings 12. The cover 7 has a transparent window 13. Two fittings 14, 15 are inserted in two diagonally located corners of the housing to one of which a back pressure pipeline 16 is connected, and to the other, dates pore pressure chamber 17.

One of the side walls, for example 4, has a round hard stamp 18 with a group of force sensors 19 for measuring contact stresses. The stamp 18 is moved in the guide cylinder 20 by a rod 21 connected to the servo drive 22. The servo drive 22 is fixed by three posts 23 to the base plate 24. The base plate 24 is mounted by the posts 23 to one side of the housing. The stamp 18 has two o-rings 25.

For the manufacture of a sample of cohesive soil 26, a removable mold 27 is used.

To measure local deformations, the digital camera 28 is mounted on a traverse 29 and connected to a computer 47.

Four hydraulic superchargers 31, 32, 33, 34 with servos and two receivers 35, 36 are fixed on frame 1.

Pore pressure sensor 17, pressure sensors 37, 38, 39, 40 of hydraulic superchargers 31, 32, 33, 34, pressure sensors 41, 42 of receivers 35, 36, a group of force sensors 19 through a cable line 43, signal amplification unit 44, analog the digital converter 45 and the RS-485 46 interface are connected to the computer 47 and together form a data acquisition system.

The servos of the hydraulic superchargers 31, 32, 33, 34, the servo of the hard stamp 22 through the cable line 48, the digital-to-analog converter 49, the RS-485 interface 46 are connected to the computer 47 and together form a control measuring system.

Digital camera 28 via USB is connected to computer 47.

The loading system includes a movable platform 50 with hydraulic drive and a table 51.

A triaxial compression device with contact stress measurement operates as follows.

1. Preparation of the device for work for testing cohesive soils

1.1. The movable platform 48 is moved inward as far as it will go into the frame, and then, using hydraulics, the table is lifted all the way to the base of the housing 2.

1.2. Unscrewing the nuts 9 on the housing from the side of the base 2, lower the table 49 together with the base.

1.3. Move the movable platform 50 with the base 2 to the place of manufacture of a sample of cohesive soil 26.

1.4. On the base 2, a detachable mold 27 is installed and a sample of cohesive soil 26 is made with a given density and humidity. If necessary, reinforcing elements in the form of a geogrid or other materials are introduced into the specimen in the prescribed ratio during the manufacturing process. Before making a soil sample, the inner walls of the mold are coated with grease to reduce adhesion. To maintain a flat lower face of the manufactured soil sample, liquid is supplied into the pressure chamber 10 of the base 2 until it is completely filled.

1.5. Disassemble the split mold 27.

1.6. The movable platform 50 is moved back all the way into the frame 1.

1.7. Using hydraulics of the moving platform, the base 2 is lifted with a soil sample 26 to the stop of the base 2 in the housing. Fix the base with 2 nuts 9.

1.8. Through the fittings 14, 15, the method of back pressure performs water saturation of the soil sample.

1.9. Pore pressure sensor 17, pressure sensors 37, 38, 39, 40, pressure sensors 41, 42, a group of force sensors 19, servos of hydraulic superchargers 31, 32, 33, 34, a hard stamp servo 22 through an analog-to-digital converter 45, a digital-to-analog converter 49, the RS-485 interface is connected to a computer 47.

2. Preparation for testing loose soils

2.1. Unscrew the nuts 9 and remove the cover 7.

2.2. Bulk soil with a given density and humidity is placed in the chamber of the device. If necessary, during the manufacturing process, reinforcing elements in the form of a geogrid or other materials are introduced into the sample in a predetermined ratio.

2.3. Install the lid 7 back and fix it with nuts 9.

2.5. Pore pressure sensor 17, pressure sensors 37, 38, 39, 40, pressure sensors 41, 42, a group of force sensors 19, servos of hydraulic superchargers 31, 32, 33, 34, a hard stamp servo 22 through an analog-to-digital converter 45, a digital-to-analog converter 49, the RS-485 interface is connected to a computer 47.

3. Test procedure

3.1. According to the test program, the computer sends a signal to the hydraulic supercharger 31 and through the nozzle 14, the required back pressure is created in the soil sample, which is measured by the pore pressure sensor 17. Using the computer 47 and the bracket 29, the camera 28 is installed at the required distance from the transparent window 13.

3.2. According to the test program, the computer 47 sends signals with a given frequency to the servos of the hydraulic superchargers 31, 32, 33, 34, which through the fittings 12 supply fluid pressure to the elastic shells 11 and compress the soil sample. In the process of power loading by a group of force sensors 19, contact stresses are fixed with a fixed rigid stamp 18.

3.3. In the test process according to claim 3.2, using a digital camera 28, photographs are taken at each loading stage through a transparent window 13 and local deformations on the upper face of the soil sample are measured in a known manner [4].

This technique for non-contact measurement of deformation in physical models is a system that combines digital photography, photogrammetry and digital image processing (PIV - particle image velocimetry - measurement of velocity from particle images), which allows you to determine the deformation field at the boundary of models under the action of an external load .

3.4. During the tests according to paragraphs 3.2, 3.3, using a servo drive 22, the hard stamp 18 is displaced by a predetermined amount towards the sample face (passive state) or vice versa (active state) and contact stresses on the surface of the hard stamp are measured by force sensors 19.

3.5. Tests in the cycle according to paragraphs 3.2-3.4 are carried out until the destruction of the soil sample.

Industrial applicability

This triaxial compression device with contact stress measurement is industrially feasible and has advanced functional characteristics.

The use of this technical solution allows the study of the mechanical properties of soil samples under various boundary conditions and force loading, which increases the accuracy of the studies.

Literature

1. US patent for invention No. 3728895 from 04.24.1973. Posted by Garrett D.Shaw.

2. USSR author's certificate for the invention No. 700838 of 06/09/1975. Authors: Z.G. Ter-Martirosyan, D.M. Akhpatelov, Yu.S. Grigoriev, V.A. Tishchenko.

3. RF patent for the invention No. 2418283 of 03/04/2010. Authors: Boldyrev G.G., Boldyreva E.G., Idrisov I.Kh., Elatontsev A.I. (prototype).

4. White D.J., Take W.A., Bolton M.D., Munachen S.E. A deformation measurement system for geotechnical testing based on digital imaging, close-range photogrammetry, and PIV image analysis. 15th International Conference on Soil Mechanics and Geotechnical Engineering, 2001, pp. 539-542. (Translation. Deformation measuring system for geotechnical testing, based on digital image processing, local photogrammetry and PIV analysis. 15th International Conference on Soil Mechanics and Geotechnical Engineering, 2001, pp. 539-542).

Claims (3)

1. A triaxial compression device with contact stress measurement, including a frame, a housing with a base, a cover and side walls, housed in it with a working chamber with an elastic shell and pressure chambers associated with load and measuring devices, characterized in that, in order to expand the functionality , one of the side walls of the body is rigid and movable with built-in force sensors, and the wall is controlled by a stepper motor, and the lifting of the material sample is performed using mobile platform with hydraulic drive. 2. The triaxial compression device with contact stress measurement according to claim 1, characterized in that it further comprises a digital camera for measuring local deformations, and one of the walls (cover) of the working chamber is made transparent. 3. The triaxial compression device with contact stress measurement according to claim 1, characterized in that the operation of the device is controlled using a measuring system with direct and feedback.

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