Installation for determining rate of dissolution of karst rocks

Abstract

FIELD: testing equipment.SUBSTANCE: invention concerns an installation for determining the rate of dissolution of karst rocks, consisting of a working chamber connected to a primary and receiving tank by means of a pipeline. At the bottom of the working chamber there is a perforated support table for placing the test sample. The holes at the top of the working chamber have plugs. The bottom of the working chamber is connected to the primary container by means of a pipeline in which the first feed valve is installed, located below the working chamber, while the first outlet valve, connected to the top of the working chamber, is used to release air from the installation. The top of the working chamber is connected to the primary tank by a pipeline in which a second feed valve is installed, located above the first outlet valve. The bottom of the working chamber is connected to the pump by means of a pipeline in which a second outlet valve is installed, located below the first feed valve and used to drain the solvent from the working chamber. Thermometers are installed at the bottom of the primary container and at the top of the working chamber.EFFECT: expansion of the functional capabilities of the experimental setup, an increase in the accuracy of experiments and a reduction in the time required for their preparation.6 cl, 2 dwg, 1 tbl

Description

[0001] The invention relates to the field of construction and mining, namely to equipment for determining the rate of dissolution of karst rocks (soils), assessed during design, survey and scientific research work.

[0002] When constructing buildings and structures in karst areas, the design of engineering protection measures or the rejection of them is justified, in particular, by the size of karst deformations, in the assessment of which the rate of dissolution of karst rocks is used [SP 22.13330.2016 (with amendments No. 1-5), clause 6.12.15]. It is determined based on the results of experimental tests in the field or laboratory conditions [SP 22.13330.2016 (with amendments No. 1-5), note to Table 6.15a]. In mining, the rate of rock dissolution is estimated in a similar way and is used in the design of mine workings and underground storage facilities, and in the extraction of minerals [Permyakov R.S., Romanov V.S., Beldy M.P. Salt extraction technology. M.: Nedra, 1981. 271 .s].

[0003] An experimental setup for dissolving rock salt (salt rocks) is known from the prior art [Starostin R.A., Koshelev A.E. Modern methods for determining the rate of dissolution of rocks. Automation of the technique for determining the dissolution rate coefficient of rock salt for laboratory tests / / Mining information and analytical bulletin.-2018.-№4. - P. 54-62. DOI: 10.25018 / 0236-1493-2018-4-0-54-62], consisting of a rectangular container filled with a solvent of a given chemical composition and temperature, as well as a sieve for collecting particles separating from the sample during the experiment. The cylindrical test sample, without any discontinuities, is placed on a stand suspended from a vertical stand via a dynamometer (allowing one to monitor the change in the sample mass over time), and then lowered for a specified time into a container with a prepared solvent.

[0004] The main drawbacks of the setup under consideration are that, firstly, it does not allow solvent flow through discontinuities in the test samples. Secondly, during experiments, the setup does not provide for solvent movement, supply of new (initial) solvent, or removal of spent solvent. Taken together, these shortcomings limit the setup's use to a very limited range of engineering problems.

[0005] Also known from the prior art is an experimental setup for studying the dissolution rate of karst rocks. It is described in the Recommendations for Laboratory Physical Modeling of Karst Processes (PNIIIS. Moscow, 1984). This setup includes working cylinders containing wax-coated samples of dissolved rocks, to which a solvent (usually tap water at room temperature) is supplied from pressure tanks. After passing through the working cylinders, the solvent, the flow rate of which is regulated by appropriate clamps, is diverted into receiving vessels. This setup is used to test cylindrical sulfate rock samples with an artificial rectangular hole along their longitudinal axis.

[0006] This setup has the following major drawbacks. First, the solvent flow rate is regulated by clamps. Experience has shown that clamps cannot ensure a constant solvent flow rate throughout the experiment. Second, to prevent solvent contact with the side surface of the sample, the gap between the side surface of the sample and the inner surface of the working cylinder is filled with paraffin. However, this solution is not only labor-intensive but also reduces the accuracy of rock dissolution rate determination. Regarding the latter issue, when the paraffin is heated to its melting point to allow removal of the test sample from the working cylinder, the paraffin does not completely drain from the sample, which distorts its mass after the experiment.

[0007] The closest technical solution to the proposed invention is the installation for determining the dissolution rate of karst rocks, disclosed in the works [Utkin M.M., Utkin M.V. Practical experience of determining the dissolution rate of karst rocks in laboratory conditions at one of the stages of the M-12 Moscow - Nizhny Novgorod - Kazan high-speed highway / / Privolzhsky Scientific Journal. - 2022. - No. 2. - P. 90-99; Utkin M.M., Utkin M.V. Quantitative assessment of the dissolution rate of gypsum rocks in the zone of a large karst cavity and beyond it / / Scientific notes of the Crimean Federal University named after V.I. Vernadsky. Geography. Geology. - 2023. - Vol. 9 (75). - No. 4. - P. 76-85].The installation consists of working cylinders, support and upper centering plates with a hole, between which there are cylindrical rock samples with a hole prepared for dissolution, clamping devices, pressure and receiving tanks, feed and discharge valves, discharge pumps, and connecting lines.

[0008] In the setup under consideration, both of the above-mentioned shortcomings of the setup given in the 1984 PNIIIS Recommendations were eliminated. The first shortcoming, concerning the variability of the solvent flow rate, was eliminated by adding outlet pumps after the lower adjustable clamps (outlet taps), and the second - by different protection of the sample surfaces from contact with the solvent, namely, the end surfaces were protected with the help of support and upper centering plates with an opening and clamping devices, and the side surface - by wrapping it with film or putting an elastic impermeable shell on it.

[0009] As the experience of conducting experimental tests has shown, the installation designed by M.M. and M.V. Utkin has three main drawbacks (they are also fully inherent in the previous installation).

[0010] Often, the formation of holes of various cross-sections in test samples and (or) the cylindrical samples themselves, which are cut from different rocks, turns out to be impractical or even impossible.

[0011] In the setup under consideration, the solvent is supplied from top to bottom, which creates air locks in the setup, which have a very negative effect on the constancy of the solvent consumption throughout the entire experiment.

[0012] The unit uses a solvent at room temperature. However, for salts, solvent temperature significantly affects their dissolution rate. Therefore, the unit can be used to dissolve carbonate and the vast majority of sulfate rocks, but not saline or all sulfate rocks.

[0013] The technical result of the proposed invention is the expansion of the functional capabilities of the experimental setup, increasing the accuracy of experiments and reducing the time for their preparation.

[0014] The technical result is achieved by a setup for determining the dissolution rate of karst rocks consisting of a working chamber, on the bottom of which a perforated support table is installed, on which, in turn, the test sample is placed. The openings in the top of the working chamber, which are necessary for mounting the clamping device, are closed with plugs. The bottom of the working chamber is connected to the primary container via a pipeline, in which the first feed valve is installed, located below the working chamber and used during the experimental preparation stage to fill the working chamber with solvent from the bottom up. The first outlet valve, connected to the top of the working chamber, is used to vent air from the setup.The top of the working chamber is connected to the primary tank via a pipeline containing a second inlet valve, located above the first outlet valve and used during the experiment to initiate or stop the flow of solvent from top to bottom in the working chamber. The bottom of the working chamber is connected to the pump via a pipeline containing a second outlet valve, located below the first inlet valve and used to drain solvent from the working chamber. The flow rate of the solvent, which can have any chemical composition, is regulated by the pump, after which it is discharged down the pipeline into the receiving tank. The solvent temperature at the bottom of the primary tank and at the top of the working chamber is monitored by thermometers.

[0015] The working chamber is sealed, with removable end panels. It can be made of transparent material or have a special observation window. A mesh for collecting insoluble residue can be located at the bottom of the working chamber. Additionally, a thermometer can be installed at the bottom of the working chamber to measure the temperature loss of the solvent as it passes through the test sample.

[0016] The pump can be connected to the first outlet valve connected to the top of the working chamber via a pipeline in order to shorten the experiment time.

[0017] Fig. 1 shows the basic diagram of the experimental setup, where:

[0018] 1 - working chamber;

[0019] 2 - perforated support table;

[0020] 3 - test sample;

[0021] 4 - plugs;

[0022] 5 - first feed tap;

[0023] 6 - first outlet valve;

[0024] 7 - second supply tap;

[0025] 8 - primary capacity;

[0026] 9 - second outlet valve;

[0027] 10 - pump;

[0028] 11 - receiving container;

[0029] 12 - thermometers.

[0030] The setup operates as follows. A dried karst rock sample prepared for testing is first weighed, then its dimensions are measured. The test sample is then placed in the working chamber 1 of the setup.

[0031] To ensure solvent flow around the surfaces of test sample 3, it is placed on perforated support table 2, previously installed on the bottom of working chamber 1. The chamber is then closed. Plugs 4 are installed in the openings at the top of working chamber 1 intended for the clamping device.

[0032] During the experimental preparation phase, a solvent of the required chemical composition and temperature is prepared in primary vessel 8. The temperature is monitored by thermometer 12. By opening first outlet valve 6 and then first feed valve 5, the working chamber 1 is filled from the bottom up with solvent from primary vessel 8, causing air to escape from the setup. Both valves are then closed.

[0033] During the experiment, the second feed valve 7 and the second outlet valve 9 are opened. Then, the pump 10 sets the required flow rate of the solvent moving from top to bottom, and its temperature in the working chamber 1 is monitored by the thermometer 12. The spent solvent is discharged into the receiving tank 11. During the experiment, the chemical composition of the solvent is monitored before and after it passes through the working chamber 1.

[0034] After the completion of the experiment, counted from the moment of switching off the pump 10 and the subsequent prompt emptying of the working chamber 1, the test sample 3 is removed from the working chamber 1, after which the mass of the dried sample and its dimensions are measured, the volume of the solvent that has passed through the working chamber 1 is determined. Then, through the change in the mass and (or) dimensions of the sample, or through the change in mineralization and the actual volume of the spent solvent, knowing the duration of the experiment, the dissolution rate of the karst rock is calculated.

[0035] The setup allows testing to be carried out by ensuring the passage of the solvent through a discontinuity in the test sample.

[0036] Fig. 2 shows the application of the installation using a clamping device.

[0037] To do this, the side surfaces of test specimen 3 are first isolated from contact with the solvent. It is then secured in working chamber 1 at the bottom by a supporting centering plate with opening 13, and at the top by an upper centering plate with opening 14. Working chamber 1 is then sealed at the top and bottom. To prevent solvent contact with the end surfaces of test specimen 3, it is pressed with clamping device 15.

[0038] Expansion of the installation’s functionality is achieved through the use of a perforated support table and thermometers.

[0039] The use of a perforated support table makes it possible to: First, test soft rock specimens. When cutting cylindrical specimens from soft rock and / or forming holes in them, the specimens may break. This can be avoided, for example, by testing solid specimens (requiring no preparation) or cutting solid quadrangular prismatic specimens, in particular, cubes without holes. Second, test specimens using several schemes. The first scheme ensures the passage of all solvent through the discontinuity in the specimen. However, for example, in cases of low karst (karst-suffosion) hazard and / or the absence of karst cavities, the inventor often uses a second scheme, which involves flowing the solvent around the surfaces of a solid specimen. This scheme is impossible to implement in the setups disclosed in the 1984 PNIIIS Recommendations and the invention prototype.

[0040] The use of thermometers makes it possible to control the temperature of the solvent, which allows, having prepared a solvent of a given temperature, to test samples of not only poorly soluble and the vast majority of moderately soluble rocks, but also the rest of the moderately soluble and especially all the readily soluble rocks, as well as to test samples of insoluble and poorly soluble rocks containing moderately and readily soluble particles in their composition.

[0041] The accuracy of experiments is improved by adding an air removal system to the setup, consisting of a first inlet valve, a first outlet valve, and a connecting line. This air removal ensures a constant solvent flow throughout the experiment.

[0042] The reduction in the time required to prepare experiments is achieved by using a perforated support table, since, for example, it is much faster to make a test sample in the shape of a cube than in the shape of a cylinder with a through hole along its longitudinal axis.

[0043] Thus, the proposed installation has expanded functionality, allows for more accurate and time-consuming experimental tests on the dissolution of karst rocks.

[0044] An example of the practical application of the proposed invention. A construction site requires a quantitative assessment of the dissolution rate of karst rocks, represented by gypsum.

[0045] During the field stage of engineering and geological surveys, the following was done: a core of gypsum rocks was taken from a drilled well, and experimental filtration work was carried out in the interval of occurrence of groundwater associated with sulfates (fissure-karst waters) (filtration coefficient k ф =15.68 m / day), the temperature of groundwater was determined (8.1°C) and the volume required for the experiments was collected.

[0046] The laboratory stage consisted of the following. Three gypsum test samples were prepared from the collected core. The samples were cubic in shape, with a distance of approximately 2.5 cm between opposite faces. The collected fissure-karst water was used as a solvent, filling the primary vessels of the setup. During the experimental preparation stage, the solvent temperature was brought to ambient temperature and monitored in the primary vessels and working chambers using thermometers.

[0047] Rock samples were tested in the experimental setup's working chambers for 21 days. The mass and dimensions of the dried samples were measured before and after the experiments. During the experiments, the chemical composition of the solvent was determined before and after its passage through the working chambers. Furthermore, the volume of solvent passing through each working chamber was determined at the end of the experiments. Specifically, based on the decrease in mass and dimensions of the samples, as well as the duration of the experiments, the dissolution rate of karst rocks was calculated. The main initial data and experimental results are presented in the table.

[0048]

[0049]

[0050] Thus, based on the results of the experimental tests, the dissolution rate of karst rocks was determined. For gypsum, it ranges from 0.17 to 0.65 cm / year or from 0.97 to 1.02 cm / year, depending on the calculation method. Subsequently, in accordance with SP 22.13330.2016 (with amendments Nos. 1-5), the dissolution rate of gypsum was taken into account when predicting the extent of karst deformations and the subsequent development of a set of anti-karst measures.

Claims

1. An apparatus for determining the rate of dissolution of karst rocks, consisting of a working chamber connected to a primary and receiving container by means of a pipeline, characterized in that a perforated support table for placing a test sample is installed at the bottom of the working chamber, the openings in the top of the working chamber have plugs, the bottom of the working chamber is connected to the primary container by means of a pipeline in which the first feed valve is installed, located below the working chamber, wherein the first outlet valve, connected to the top of the working chamber, is used to release air from the apparatus, the top of the working chamber is connected to the primary container by a pipeline in which a second feed valve is installed, located above the first outlet valve, the bottom of the working chamber is connected to a pump by means of a pipeline in which a second outlet valve is installed, located below the first feed valve and used to drain the solvent from the working chamber,and thermometers are installed at the bottom of the primary container and at the top of the working chamber.

2. The installation according to paragraph 1, characterized in that the working chamber is made of a transparent material.

3. The installation according to paragraph 1, characterized in that the working chamber has a window for observation.

4. The installation according to paragraph 1, characterized in that a mesh for collecting insoluble residue is provided at the bottom of the working chamber.

5. The installation according to paragraph 1, characterized in that a thermometer is additionally installed at the bottom of the working chamber.

6. The installation according to paragraph 1, characterized in that the pump is connected by means of a pipeline to the first discharge valve connected to the top of the working chamber.

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