RU2418283C1 - Instrument of triaxial compression - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: instrument comprises a frame, a body with a base, a cover and side walls, a working chamber arranged in it with elastic shell and pressure chambers joined to loading and measurement accessories. The instrument is equipped with four pneumatic cylinders of double action, which are fixed vertically on the frame. The lower stems of pneumatic cylinders are connected to vertically moved platform. A horizontally moved platform is arranged on the vertically moved platform. The base and the sample of soil in a detachable form. Upper stems of pneumatic cylinders are connected to a cross beam, and the cross beam - to the cover. Each pressure chamber has three linear displacement transducers. Side walls of the body are non-detachable, and the cover and the base are detachable.

EFFECT: reduced labour intensiveness and higher efficiency of material samples testing in conditions of triaxial compression.

6 dwg

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 soils, in difficult stress-strain conditions.

State of the art

An analogue of this technical solution is the "Device for testing samples under triaxial compression" (copyright certificate No. 520533 dated 11/15/1973, author Kogan EA, IPC G01N 3/10, published 05.07.76), containing the housing located in it elastic membranes that form a closed volume for the placement of the test sample, and pressure sources that transfer the load to the membranes, characterized in that, in order to ensure uniform load across the entire surface of the faces of the sample, it is equipped with paired coaxial load plates having each at the end along the perimeter there is a protrusion on which an elastic membrane is fixed, and hydraulic jacks, the pistons of which are coaxial with the loading plates, the cavities are hydraulically connected with the cavities formed by the loading plates and membranes, and the working areas of the loading plates and the pistons of the jacks aligned with them are equal to each other and equal to the areas the faces of the test sample adjacent to the respective load plates.

The disadvantage of the analogue is the low productivity of testing soil samples, since considerable time is required for disassembling the device and installing a sample of material in it. In addition, in this device it is impossible to conduct tests with the measurement of pore pressure inside the test sample due to leaks in the housing. The presence of hard protrusions in the load plates during their mutually perpendicular movement leads to their closure in the corners of the sample and thereby limit its deformation, which excludes the applicability of this device for large deformations.

The next analogue of the proposed technical solution is “A device for studying the properties of soils under conditions of triaxial compression” (copyright certificate No. 1280082 of 02/20/1985, author Zaitsev VA, IPC G01N 3/10, published 12/30/1986), including a frame with load devices, a body made of separate blocks in the form of truncated tetrahedral pyramids, forming an isolated cubic space with elastic shell elements facing each other with small bases, and measuring devices, characterized in that for the purpose To increase the accuracy of measurements, each block is made in the form of a base plate, movably mounted middle and corner elements on it and a fixed central element, as well as overlapping plates located on the small base of the block and fixed on the central and middle elements, elements of the elastic shell are made prestressed with an internal cavity in size of the small base of the block filled with liquid, while the middle elements of each block are movably connected to the central and Glov elements and fixedly - middle elements of the neighboring blocks.

The disadvantage of the analogue is the low productivity of testing soil samples, since considerable time is required for disassembling the device, installing a soil sample in it and moving the housing blocks to contact with the faces of the test sample. In addition, in this device it is impossible to conduct tests with the measurement of pore pressure inside the test sample due to leaks in the cubic space for the sample of the studied soil.

The closest analogue (prototype) of the claimed technical solution is “A device for studying the properties of soils under conditions of triaxial compression” (USSR copyright certificate for invention No. 700838, applicant of the Moscow Order of the Red Banner of Labor VV Kuibyshev Institute of Civil Engineering, authors З .G. Ter-Martirosyan, D.M.Akhpatelov, Yu.S. Grigoryev, V.A. Tishchenko, IPC G01N 33/24, G01N 3/10, published 01/30/1979), including a housing with a base, a cover and side the walls placed in it by a working chamber with an elastic shell and chambers pressure, 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 pressure chamber formed by the groove of the elastic strip 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 disadvantage of the prototype is the complexity of preparing the device for testing and placing a soil sample in the working chamber, the inability to directly measure the axial deformation of the soil sample.

Explanation of the disadvantages of the prototype.

1. In the prototype, to place the soil sample in the device, four power screws must be unscrewed, the cover removed, the four side walls with pressure chambers with elastic shells fixed on them, and only after that put the soil sample on the base. With large sizes of the soil sample, for example, when studying the mechanical properties of gravelly, crushed stone and coarse-grained soils, clay soils with inclusions, the size of the material sample is taken at least 300 × 300 × 300 mm. The weight of such soil samples is at least G = V × γ = 0.3 × 0.3 × 0.3 × 22.0 = 0.594 kN. Putting this soil sample manually weighing 54 kg or more on the base of the prototype device is a time-consuming operation. In addition, when testing sandy, gravelly and coarse-grained soils, it is impossible, due to their flowability, to maintain the shape and structure of the sample when it is moved from the preparation site to the base of the device. At the same time, it is impossible to prepare a sample of cohesive or loose soil with a given density, humidity and correct geometric dimensions directly in the working chamber of the device due to the deformation of the elastic shells during the formation of the soil sample.

2. After placing the soil sample on the base, it is necessary to assemble the device in the reverse sequence - lift the four side walls with pressure chambers attached to them with elastic shells, put and fasten the cover, tighten the four power screws. Together, these operations increase the time required to prepare the device for testing and thereby reduce its productivity.

3. The device does not provide a measurement of the strain of the sample in the direction of its three mutually perpendicular axes in a direct way without measuring the volume of fluid supplied to the pressure chambers.

The essence of the technical solution

A known device for triaxial testing of soils, including 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, a quadrangular support frame.

The purpose of this technical solution is to reduce the complexity of the preparation of the device for testing, increase test performance and measure axial strain of the sample.

The goal is achieved in that the device has two platforms. The first platform moves vertically with four double-acting pneumatic cylinders mounted on the frame. The second platform has the ability to move horizontally and then vertically on the first platform.

On the second platform, a base with a form is installed. The pressure chamber at the base is filled with liquid.

A sample of the material is made in a mold with desired physical properties. Next, the sample in the mold on the base moves horizontally on the second platform to the first platform.

The first and second platforms, the base and the sample of material in the form move vertically up to the stop of the base in one-piece side walls. After that, the base is fastened with nuts to the side walls.

The form is pulled vertically upward from the working chamber of the device using pneumatic cylinders.

A cover is installed and fixed, pressure chambers are filled with liquid, load and measuring devices are connected and material is tested.

Axial deformation is measured along each of the three coordinate axes using displacement sensors that are integrated in the pressure chambers.

List of drawings

Figure 1 shows the design of a quadrangular frame.

Figure 2 shows the design of a triaxial compression device with a soil sample in the mold on the platform before its vertical movement.

Figure 3 shows the design of the device of triaxial compression after vertical movement of a sample of material in the working chamber of the device with the lid up.

Figure 4 shows the design of the triaxial compression device at the time of pulling out the form from the device.

Figure 5 shows a perspective view of a triaxial compression device with a soil sample in the mold on the platform after its manufacture.

Figure 6 shows a perspective view of a triaxial compression device after moving a soil sample into the device body with the top cover raised.

An example of the implementation of a technical solution

In Fig. 1, Fig. 2, Fig. 3, Fig. 4, the triaxial compression device comprises a frame 1 on which a housing is fixed, consisting of a quadrangular frame 2 with threaded rods 3, a base 4, four side walls 5 and a cover 6 connected between each other on threaded rods 3 and fixed by nuts 7. The base, four side walls and the cover have a pressure chamber 8 with an elastic shell 9, fittings 10 and linear displacement sensors 11. Two channels 12 are made in one of the corners of the quadrangular frame at different heights; which are introduced measuring and discharge tube 13, respectively having 14 nozzles.

Four double-acting pneumatic cylinders 15 are mounted vertically on the frame 1, and the lower rods 16 of the pneumatic cylinders 15 are fixed to a vertically movable platform 17, on which the platform 18. The platform 17 has two stops 19. The upper rods 20 of the pneumatic cylinders 15 are attached to the rectangular crossarm 21, and the traverse is connected rigidly by four studs 22 to the cover 6. The cover has four grips 23.

For the manufacture of a soil sample 24, a removable mold 25 with eyelets 26 is used.

The triaxial compression device operates as follows.

1. The platform 18 is moved to the stops 19 on the platform 17, and then, turning on the pneumatic cylinders 15, lift them all the way to the base of the housing 4.

2. Unscrewing the nuts 7 on the housing from the side of the base 4 and turning on the pneumatic cylinders 15, lower the platforms 18, 17 to the base of the frame 1.

3. Move the platform 18 horizontally with the base 4 to the place of manufacture of the soil sample 24.

4. A detachable mold 25 is mounted on the base 4 and a soil sample is made at a predetermined density and humidity. Before the manufacture of the 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 of the base 4 until it is completely filled.

5. The platform 18 is moved back horizontally to the stops 19 on the platform 17.

6. Unscrew the nuts 7 from the side of the cover 6.

7. Turning on the pneumatic cylinders 15, lift the cover 6, platforms 17, 18, base 4 and mold 25 with a sample of soil 24 until the base 4 rests in the housing. Fix the base 4 with nuts 7 on the studs 3.

8. Turning on the pneumatic cylinders 15, lower the lid 6 until the grippers 23 enter the eyes 26 of the mold 25.

9. Turning on the pneumatic cylinders 15, lift the cover 6 and pull out the mold 25 from the device body.

10. Release the grippers 23 and take off the mold 25.

11. Turning on the pneumatic cylinders 15, lower the cover 6 all the way into the housing and fasten with nuts 7 to the studs 3.

12. Through the channels 12, a drill is introduced into the soil sample, and cylindrical holes are made with a diameter equal to the diameter of the measuring and injection 13 tubes and length to the center of the sample.

13. Through the channels 12, the measuring and discharge tubes 13 are inserted into the holes made, which are fixed by a thread and a seal on the frame 2. The fittings 14 are connected to the tubes 13.

14. To the fittings 10, 14 and displacement sensors 11 are connected load and measuring devices.

15. According to the test program, using fittings 10, fluid pressure is applied to the elastic shells 9 and, using displacement sensors 11, the deformation of the soil sample is measured in three mutually perpendicular directions. Pore pressure inside the sample is measured by a pressure sensor that connects to the measuring tube. The back pressure inside the sample is created by a hydraulic supercharger through the discharge tube and is monitored by a pressure transducer.

Industrial applicability

The use of this technical solution allows to reduce the complexity and increase the productivity of testing samples of materials under conditions of triaxial compression.

Claims (1)

A triaxial compression device, including a frame, a housing with a base, a cover and side walls, a working chamber with an elastic shell and pressure chambers connected with load and measuring devices, which is characterized in that, in order to reduce the complexity and increase the test productivity, the device equipped with four double-acting pneumatic cylinders mounted vertically on the frame, lower rods of pneumatic cylinders attached to a vertically movable platform, on a vertically movable platform the yoke is horizontally movable platform, a base and a sample of soil in the form of a removable, upper rods of pneumatic cylinders are attached to the cross member and traverse the cover, each pressure chamber has three linear encoder, wherein the housing side walls are integral, and the base and cover are detachable.

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