RU2423682C1 - Instrument for compression tests of soils - Google Patents

Abstract

FIELD: construction. ^ SUBSTANCE: instrument comprises a body with a porous bottom, a ring with soil, a loading accessory of a piston and measurement accessories for measurement of pore and side pressure. The instrument is made of four hydraulically and electrically interconnected parts: a press, an odometer, a unit of signals amplification and conversion from sensors into a digital form with a computer and an interface and a backpressure unit. ^ EFFECT: increased accuracy of soil pore and side pressure measurement, expansion of investigation range and increased efficiency of tests. ^ 7 cl, 5 dwg

Description

Technical field

The invention relates to the field of construction and is intended to determine the mechanical properties of soils in laboratory conditions.

State of the art

An analogue of the invention is a COMPRESSION-FILTER DEVICE (certificate for utility model RU 54597 U1, application 2005138873 dated 12.13.2005, patent holder and author Solomin S.F., IPC E02D 1/02, published July 10, 2006).

1. A compression-filtration device containing a base, a working ring, a separator liner, a stamp with a section for applying a load and connected with measuring devices, characterized in that the inner surface of the working ring is equipped with a spring loaded and axially movable sleeve.

2. The compression-filtration device according to claim 1, characterized in that the height of the sleeve is commensurate with the thickness of the test soil sample.

3. The compression-filtration device according to claim 1, characterized in that the inner diameter of the sleeve corresponds to the diameter of the peripheral annular groove of the separator insert, and the lower inner end of the sleeve interacts with the side surface of the peripheral annular groove of the separator insert.

4. The compression-filtration device according to claim 1, characterized in that the upper inner end of the sleeve interacts with the lateral annular surface of the stamp.

5. The compression-filtration device according to claim 1, characterized in that the compressive force of the spring, spring-loaded movable sleeve, is greater than the total weight of the sleeve with a soil sample.

6. The compression-filtration device according to claim 1 or 4, characterized in that between the sleeve and the spring is placed a flat support washer.

7. The compression-filtration device according to claim 1, characterized in that the connection of the base and the working ring is made by means of a union nut and a sealing ring between the contacting ends of the base and ring.

The disadvantage of the analogue is the inability to conduct soil tests with the measurement of pore and side pressures.

The next analogue of the invention is the DEVICE FOR COMPRESSION TESTS OF SOILS (patent for invention RU 2045756 C1, application 93014282/33 of 03.23.1993, patentee and author Vorobyov EA, IPC G01N 3/08, E02D 1/00, published 10.10. 1995), including the base, working rings of different diameters for soil samples, mounted one below the other in increasing diameter from top to bottom, upper and lower perforated dies, means for creating vertical unloading and strain gauges, characterized in that it is made in the form of tr x detachable sections mounted coaxially under each other, each of which is formed by the upper and lower dies and the working ring placed between them and the pressure ring connected to the dies, while the upper dies are made in the form of tanks for pouring water with flat perforated bottoms and inclined solid ring walls with horizontal through holes are formed on the outer surface of the lower dies of the upper and middle sections with lateral walls having shoulders for installing strain gauges; These surface facing the perforated bottoms of the upper die the lower sections - corresponding protrusions annular grooves, the inner wall of the clamping rings has a tapered surface for self-centering of the working ring.

The disadvantage of the analogue is the inability to conduct soil tests with the measurement of both pore and side pressures.

The closest analogue (prototype) of the present invention is a DEVICE FOR MEASURING LATER PRESSURE IN SOIL (USSR author's certificate for the invention No. 939638, application 2868832 / 29-33 dated 10.01.80, applicant of the Leningrad Order of the Red Banner of Labor, Institute of Civil Engineering, authors A. V. Golli and L.K. Tikhomirova, M. cl. ³ E02D 1/00, published on 06/30/82), including a body with a porous bottom, a tensor ring with strain gauges, load and measuring devices, characterized in that in order to increase the accuracy and expansion range And in studies, it is equipped with a manometer with flexible needles, and the body with a rigid ring connected to the tensor ring with a sealed elastic material, the rigid ring and the tensor ring made with lateral coaxial holes in which the flexible needles are passed, and the tensor ring is mounted above the porous bottom with a gap of 0.005 -1 mm.

The disadvantage of the prototype is the low accuracy of the measurement of pore pressure, the influence of the design of the pore pressure sensor and the load device on the deformation of the soil sample, the inability to conduct tests with water saturation of the soil sample with reverse pressure, and the complexity of preparing the device for testing.

The explanation of the disadvantages of the prototype

1. In the prototype, a pore pressure needle is inserted inside the soil sample, which prevents the movement of soil particles, increases the stiffness of the soil, introduces heterogeneity into the sample, thereby reducing the accuracy of the axial strain measurement. It is also known that when a needle is pressed into a sample, it is easily clogged with soil, which can completely exclude the possibility of measuring pore pressure. From the prototype it is not clear how to remove air from the needle cavity and the manometer chamber and fill this volume with water, otherwise the presence of air bubbles will not allow to accurately measure pore pressure.

2. In the prototype, the rod of the loading device passes through a soil sample. There is a need to create a through hole in the soil sample, which cannot be done in sandy and sandy loamy soils. Secondly, friction forces arise between the rod of the loading device and the soil, which affects the measured deformation of soil compression.

3. In the prototype, when measuring pore pressure, soil samples are preliminarily completely saturated with water, for example, by the back pressure method. The design of the device does not allow you to perform this operation due to leaks in the guide glass.

Explanations According to GOST 12248-96, compression compression tests are performed with a soil sample with a diameter of 71 mm and a height of 25 mm, which is located in a steel ring, which makes it impossible to expand in the radial direction. The tests are carried out under conditions of one-dimensional deformation. The load on the soil sample is applied through the stamp in steps with stabilization of compression deformations at each loading stage. The test duration for clay soils is up to 2-3 days. Only axial deformation and axial force are measured. To determine the compressibility index of the soil (compression modulus of deformation), K. Tertzagi's theoretical solutions are used. This solution was obtained by filtering pore water in two directions: to the upper and lower boundaries of the soil sample.

The theoretical solution obtained by Wissa, A.E.Z., Christian, J.T., Davis, E.N. and Heiberg, S., “Consolidation at Constant Rate of Strain”, Journal of the Soil Mechanics and Foundations Division, ASCE, Vol 97, No. SM10, 1971, pp. 1393-1413, for the case of one-sided filtration when compressing the soil sample, not with a step load (kN), but with a load with a given strain rate (mm / min). In this case, the test duration is reduced to several hours. This type of loading, one-way filtration and measurement of pore and lateral pressure are implemented in the present invention.

The essence of the technical solution

A known device for compression testing of soils, including a body with a porous bottom, a ring with soil, a loading device from a piston and measuring devices for measuring pore and side pressure.

The purpose of the invention is to improve the accuracy of measurement of pore and lateral pressure of the soil, expanding the range of studies and increasing the performance of the tests.

This goal is achieved in that the device is made of four hydraulically and electrically interconnected parts: a press, an odometer, an amplification unit and converting signals from sensors into a digital form with a computer and interface and a back pressure unit.

The odometer has a chamber filled with liquid and a sensor for measuring side pressure;

A soil sample is placed in a rubber sheath.

A pore pressure sensor is installed in the central part on the lower impermeable boundary of the soil sample.

A soil sample is located on a movable perforated platform.

Water saturation of the soil sample is performed by back pressure.

Compression tests are performed automatically, with a given rate of axial deformation, under the control of a computer.

List of drawings and other materials

Figure 1 shows the design of the odometer.

Figure 2 shows the design of the odometer after moving the soil sample to the working position.

Figure 3 - odometer installed in the press.

Figure 4 shows the control and measurement of pore and lateral pressure.

Figure 5 shows an axonometric image of the odometer (in section).

An example of the implementation of a technical solution

In Fig.1 and Fig.2, the odometer contains a base 1 with three non-through cylindrical holes 2. Three movable rods 4 are inserted into the holes 2 on the springs 3, on which the perforated platform 5 rests.

The odometer has a pore pressure sensor 6 in the center of the base and a ceramic filter 7. The odometer is equipped with channels 8 for creating back pressure and a fitting 9 for connecting to the back pressure unit.

The working chamber is made of a steel or transparent shell 10, in the side surface of which a fitting 11 is mounted for connection with a back pressure unit, as well as a side pressure sensor 12 that transmits the pressure value to the automatic control unit, and a trigger valve 13.

The cylindrical rubber shell 14 is mounted on the protrusions 15 of the shell 10.

The odometer cover 16 includes a ceramic filter 17, a hollow piston 18, a steel ring 19 with a soil sample embedded in it 20. A pipe 21 passes through the hollow piston 18.

Sealing of the hollow piston 18 is provided by the lateral o-rings 22 through which it passes. The sealing of the odometer cover is provided by the support ring 23. The cover 16 is attached to the base 1 with three screws 24. Tightening the screws ensures that the shell 14 is fixed in its working position and is sealed.

Figure 3 shows the connection in a single unit of the odometer and press. The press has a base 25 with a stepper motor 26 inside the base 25. The press is equipped with axial displacement sensors 27 and force 28, and is also equipped with an adjusting screw 29. The press is designed to impact the odometer 30 with vertical force from the bottom up, that is, the press plate 31 presses on the odometer 30 upwards.

Figure 4 shows a diagram of automatic control and measurement of pore and lateral pressure, which consists of three blocks:

"A" - a compression unit containing an odometer built into the press;

“B” - block for creating back pressure;

"C" - automatic control unit.

All three blocks are combined into a single automatic control system and form a compression device.

Block "B" creating a back pressure consists of a tank 32, equipped with fittings 33, 50 and a pressure sensor 34, has connecting piping 43, 44, 45 and valves 46, 47, 48, 49.

The automatic control unit “C” includes a computer 35 connected by an interface 36 to an automatic conversion apparatus 37 (EPA).

Automatic control unit “C” is connected by cables 38 (force), 39 (displacement), 40 (lateral pressure), 41 (pore pressure), 42 (stepper motor drive) with compression unit “A” and cable 51 with unit “B” creating back pressure. Automatic converting equipment 37 amplifies and converts signals into digital form from sensors: pore pressure 6, lateral pressure 12 (Fig. 1, 2), back pressure 34 (Fig. 4), force 28 and displacement 27 (Fig. 3).

Compression unit “A” is connected by cables 38, 39, 40, 41, 42 with automatic control unit “C”, pipelines 43, 44, 45 with back pressure unit “B”.

Compression device operates as follows.

Stage 1. Preparation of the odometer for testing.

1.1 Having unscrewed the fixing screws 24, remove the odometer cover 16 and install a ring 19 with a soil sample 20 into the support ring 23 of the cover. Then, put the cover 16 back and tightly fix it with screws 24 to the base of the odometer.

1.2 Set the odometer base 1 (Fig.3) on the plate 31 of the press 25, then set the axial displacement transducer 27 in the working position and eliminate the gap between the force transducer 28 and the hollow piston 18 (Fig.1, 2) with the adjusting screw 29 (Fig.3 )

Stage 2. Connecting the odometer 1 to the back pressure unit "B" and the automatic control unit "C" (figure 4)

2.1 Pipelines 43, 44, 45 (FIG. 4) of the back pressure unit “B” are connected to the odometer fittings 9, 11, 21 (FIGS. 1, 2), respectively.

2.2 Sensor cables: forces 38, displacement 39, lateral pressure 40, pore pressure 41 are connected to the automatic control unit "C".

Stage 3. Connecting the odometer 1 and press 25 to the computer 35 of the automatic control unit "C"

3.1 Connect the cable 42 (figure 4) of the drive of the stepper motor 26 (figure 3) to the block "C".

3.2 Connect the automatic converting equipment 37 through the interface 36 (figure 4) to the computer 35.

Stage 4. Implementation of the automatic test method and test sequence

4.1 Close the valve 47 of the block "B" back pressure (figure 4). A vacuum ejector is connected to the nozzle 50, the valve 49 is opened, and a pressure of 15 ... 30 kPa is created in the odometer chamber 1, sufficient to expand the rubber shell 14.

4.2 At the command of a computer, a signal is transmitted to the automatic converting apparatus 37 (Fig. 4) to the stepper motor 26 of the press 25 (Fig. 3) and an axial force is generated, which is transmitted through the hollow piston 18 and the ceramic filter 17 to the soil sample 20 in the odometer (Fig. 4) .12). The frictional forces between the steel ring 19 and the lateral surface of the soil sample 20 are overcome. A vertical movement of the soil sample 20 is created together with the perforated platform 5. The movement of the sample 20 (Figs. 1, 2) is measured by a displacement sensor 27 (Fig. 3).

In automatic mode, the computer controls the amount of movement of the hollow piston 18, and when the amount of displacement reaches the height of the soil sample 20 (FIGS. 1, 2), the computer automatically turns off the stepper motor 26 (FIG. 3). A sample of soil 20 occupied a working position inside the rubber shell 14 (figure 2).

4.3 Close the valve 49 and disconnect the vacuum ejector from the nozzle 50 (figure 4).

4.4 Open the drain valve 13 (Figs. 1, 2), then the valve 47 (Fig. 4) and fill the odometer working chamber with degassed water from the reservoir 32. After removing the air from the working chamber, the drain cock 13 and the valve 47 are closed.

4.5 Automation of water saturation of the soil sample. The backpressure taps 46, 48 are opened and through the fitting 33 (FIG. 4) in the tank 32, a predetermined backpressure value is created by the air compressor. The back pressure value is controlled by a pressure sensor 34. The pressure sensor 6 (Fig. 1) automatically measures the pore pressure in the soil sample according to the developed program. The difference between the back and pore pressure should not be more than 10 ... 15 kPa. Then, in steps of 15 ... 30 kPa, the back pressure is increased until the soil sample is completely saturated with water S _r = 92 ... 95%. Water saturation is completed if the measured pore pressure is equal to the back pressure.

4.6 After automated water saturation of the soil sample, the cranes 46, 48 are closed and, using the developed program, a compression test is carried out with a constant rate of axial deformation (mm / min) to a given effective stress. During the tests, the total and effective vertical and lateral stresses, pore pressure and axial deformation are measured.

Industrial applicability

The use of the invention improves the accuracy of measurement of pore and lateral pressure, the introduction of an automatic control system for the loading process and the collection of information from sensors increases the productivity of the tests. In addition, the use of one-way filtration and continuous loading allows reducing the test time by up to 8 times, which can be seen from the attached test results (Appendix 1). Thus, the invention also improves operational characteristics and creates a significant technical and economic effect.

Literature

1. GOST 12248-96. Soils. Laboratory methods for characterizing strength and deformability. - Publishing House of Standards, 01/01/1997.

4. Certificate for utility model RU 54597 U1, IPC E02D 1/02, published July 10, 2006.

2. Golly A.V., Tikhomirova L.K. Device for measuring lateral pressure in soils. USSR copyright certificate No. 939638, M. Kl. E02D 1/00, BI No. 24, 06/30/1982.

3. Vorobyov EA The device for compression testing of soils. Patent for invention RU No. 2045756, M. Cl. G01N 3/08, E02D 1/00, 10/10/1995.

Claims (7)

1. A device for compression testing of soils, including a body with a porous bottom, a ring with soil, a loading device made of a piston and measuring devices for measuring pore and side pressure, characterized in that, in order to improve the accuracy of measurement and operational characteristics, it is made of four hydraulically and electrically interconnected parts: press, odometer, amplification unit and conversion of signals from sensors into digital form with a computer and interface and back pressure unit. 2. The device for compression testing of soils according to claim 1, characterized in that the odometer has a chamber filled with liquid, and a sensor for measuring lateral pressure. 3. The device for compression testing of soils according to claim 1, characterized in that the soil sample is placed in a rubber shell. 4. The device for compression testing of soils according to claim 1, characterized in that the pore pressure sensor is installed in the Central part on the lower impermeable boundary of the soil sample. 5. The device for compression testing of soils according to claim 1, characterized in that the soil sample is on a movable perforated platform. 6. The device for compression testing of soils according to claim 1, characterized in that the water saturation of the soil sample is performed by back pressure. 7. The device for compression testing of soils according to claim 1, characterized in that the compression tests are performed automatically with a given axial strain rate under computer control.

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