An annular test device and method for radial permeability coefficient of loess under different pressures

Abstract

The present invention discloses an annular test device and method for measuring the radial permeability of loess under different pressures. The device comprises a base, an annular pressure cap, an inner water head output meter, and an outer water head output meter. The base comprises a water inlet space, an annular lofting groove, and a water outlet space, from the outer cavity to the inner cavity. The top of the water inlet space is connected to the output end of the outer water head output meter, and the top of the water outlet space is connected to the inner water head output meter. The inner and outer circular walls of the annular lofting groove near the bottom are respectively provided with water outlet holes and water inlet holes. A bending element signal receiver is provided at the bottom of the annular lofting groove. An annular pressure block of the same size as the annular lofting groove is provided at the bottom of the annular pressure cap, and a bending element signal transmitter is provided at the bottom of the annular pressure block. The device can simulate the radial permeability and changes of loess under different load pressures in actual engineering.

Description

Technical Field

[0001] The invention belongs to the field of civil engineering tests and relates to an annular test device and method for radial permeability coefficient of loess under different pressures. Background Art

[0002] The permeability of loess is an important component of its engineering properties and can be characterized by its permeability coefficient. It is generally believed that the permeability coefficient of soil varies with pressure and density: the greater the pressure or density, the smaller the permeability coefficient. Furthermore, the permeability coefficient exhibits anisotropic characteristics. Compared to traditional sand, loess has a unique horizontal stratigraphic structure, and its unique water sensitivity makes the anisotropy of its permeability coefficient particularly pronounced. Furthermore, the radial permeability coefficient of loess can change after long-term engineering disturbances. For example, in vertical shaft foundation disturbance areas or composite foundation sites, the radial permeability coefficient of loess inevitably adjusts due to changes in soil properties. However, traditional permeability coefficient testing instruments and methods can only measure the vertical permeability coefficient of soil. Existing testing methods do not consider the effect of pressure on the permeability coefficient during the test process, and ignore factors such as the soil stress state and seepage pathways. This often results in significant deviations from the actual permeability coefficient. Therefore, determining the variation pattern of the radial permeability coefficient of loess has become a crucial issue that cannot be circumvented to ensure the safe implementation of urban underground engineering projects in loess areas. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide an annular test device and method for the radial permeability coefficient of loess under different pressures, which can simulate the radial permeability coefficient and changes of loess under different load pressures in actual engineering.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] An annular test device for radial permeability of loess under different pressures, comprising a base, an annular pressure cap, an inner water head output instrument and an outer water head output instrument;

[0006] The base is cylindrical with a cavity. From the outer cavity to the inner cavity, there are water inlet space, annular lofting groove and water outlet space in sequence. The top of the water inlet space is connected to the output end of the outer water head output meter, and the top of the water outlet space is connected to the inner water head output meter via a water outlet channel. The inner water head output meter is higher than the water outlet space. Multiple water outlet holes and water inlet holes are respectively provided on the inner and outer circular walls of the annular lofting groove near the bottom. The water outlet holes and water inlet holes are respectively connected to the water outlet space and the water inlet space. The inner and outer circular walls of the annular lofting groove near the bottom are respectively provided with inner and outer annular water permeable filter paper. A bending element signal receiver is provided at the bottom of the annular lofting groove.

[0007] An annular pressure block with the same size as the annular lofting groove is provided at the bottom of the annular pressure cap, and a bending element signal transmitter is provided at the position corresponding to the lower bending element at the bottom of the annular pressure block.

[0008] Preferably, the annular pressure cap is sealed to the annular lofting groove.

[0009] Furthermore, the outer ring of the annular pressure block of the annular pressure cap is provided with a sealing outer rubber ring, and the inner ring of the annular lofting groove is provided with a sealing inner rubber ring.

[0010] Preferably, a solidification instrument base is provided at the bottom of the base, a dial indicator stand is provided on the solidification instrument base, the dial indicator stand is a linear sliding device, a dial indicator is provided on the dial indicator stand, and the measuring end of the dial indicator faces the annular lofting groove.

[0011] Preferably, the inner annular water-permeable filter paper and the outer annular water-permeable filter paper are both higher than or equal to the height of the water outlet and the water inlet.

[0012] Preferably, there are multiple water outlet holes and water inlet holes, which are evenly distributed on the inner and outer circular walls near the bottom of the annular lofting groove.

[0013] Preferably, an outlet pipe channel is provided on the annular pressure cap, and the water outlet channel passes through the outlet pipe channel.

[0014] A ring test method for measuring radial permeability of loess under different pressures based on the device includes the following steps:

[0015] S1, placing the annular soil sample into the annular lofting groove, and placing the annular pressure cap on the annular soil sample;

[0016] S2, applying an overburden load to the annular pressure cap until the annular soil sample reaches the maximum compression under the current load;

[0017] S3, measuring the wave velocity corresponding to the initial moisture content of the annular soil sample under the current overburden pressure by means of the bending element signal transmitter and the bending element signal receiver, thereby obtaining the initial saturation of the annular soil sample;

[0018] S4, the external head output instrument sets a head pressure, the water flows to the water inlet space, then enters the annular soil sample through the water inlet hole and the external annular permeable filter paper, and then enters the water outlet space through the internal annular permeable filter paper and the water outlet hole in sequence, and then overflows through the water outlet channel. When the overflow water flow no longer changes with time and the water outlet is stable, it indicates that the seepage in the annular soil sample has reached a steady-state flow;

[0019] S5, measuring the wave velocity of the annular soil sample in the current state by the bending element signal transmitter and the bending element signal receiver, thereby obtaining the saturation of the annular soil sample in the current state;

[0020] S6, when the water in the outlet channel enters the inner water head output instrument, the water head size of the inner water head output instrument is set, and the stable seepage flow of the annular soil sample is recorded by the inner water head output instrument, and then the permeability coefficient of the annular soil sample in the current state is calculated;

[0021] S7, repeat S2-S6, change the overlying load, and obtain the radial permeability coefficient and its variation relationship of the annular soil sample under different overlying loads.

[0022] Preferably, the permeability coefficient calculation formula is:

[0023]

[0024] Where K h is the radial permeability coefficient of the ring sample, q is the seepage rate of the ring sample per minute, measured by the inner head output instrument, h is the height of the ring sample, r1 is the outer diameter of the ring sample, r0 is the outer diameter of the ring sample, γ w is the density of water, p1 is the water pressure of the outer ring of the sample, that is, the head pressure of the outer head output instrument, and p0 is the water pressure of the inner ring of the sample, that is, the head pressure of the inner head output instrument.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention provides a water inlet space, an annular lofting groove and a water outlet space. The water inlet space is connected to an outer water head output meter, and the water outlet space is connected to an inner water head output meter. The annular lofting groove is used to place an annular soil sample. The outer water head output meter gives a water head pressure. The water flows to the water inlet space, then enters the annular soil sample through the water inlet hole and the outer annular permeable filter paper, and then enters the water outlet space through the inner annular permeable filter paper and the water outlet hole in sequence. After that, the water flows out through the water outlet channel, and the inner water head output meter records the seepage flow of the annular soil sample, thereby obtaining the permeability coefficient of the annular soil sample, adjusting the size of the overlying load, and thus being able to simulate the radial permeability coefficient and changes of loess under different load pressures in actual engineering.

[0027] Furthermore, the annular pressure cap is sealed to the annular lofting groove, thereby ensuring that water cannot pass through. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a cross-sectional view of the overall structure of the present invention;

[0029] Figure 2 is a three-dimensional schematic diagram of the test device of the present invention;

[0030] Figure 3 It is a three-dimensional schematic diagram of the base of the present invention.

[0031] Among them: 1- dial indicator; 2- dial indicator stand; 3- pipe outlet channel; 4- annular pressure cap; 5- sealed outer rubber ring; 6- sealed outer annular groove; 7- water outlet channel; 81- bending element signal transmitter, 82- bending element signal receiver; 9- sealed inner annular groove; 10- sealed inner rubber ring; 11- water outlet space; 12- water inlet channel; 13- consolidation instrument base; 14- water inlet space; 15- outer annular permeable filter paper; 16- inner annular permeable filter paper; 17- water outlet hole; 18- annular setting out groove; 19- water inlet hole; 20- inner water head output meter; 21- outer water head output meter DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] It should be noted that the words "front", "rear", "left", "right", "up" and "down" used in the following description refer to directions in the accompanying drawings, and the words "inside" and "outside" refer to directions toward or away from the geometric center of a specific component, respectively.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0035] like Figure 1 As shown, the annular test device for radial permeability coefficient of loess under different pressures according to the present invention is characterized in that it includes a base, an annular pressure cap 4, an inner water head output meter 20 and an outer water head output meter 21.

[0036] The base is cylindrical with a cavity. From the outer cavity to the inner cavity, there are water inlet space 14, annular lofting groove 18 and water outlet space 11. The water inlet space 14 and the annular lofting groove 18 are circular ring structures, and the water outlet space 11 is a hollow cylinder.

[0037] A plurality of water outlet holes 17 and water inlet holes 19 are respectively provided on the inner and outer circular walls near the bottom of the annular lofting groove 18. The water outlet holes 17 and the water inlet holes 19 are respectively connected to the water outlet space 11 and the water inlet space 17. There are multiple water outlet holes 17 and water inlet holes 19, which are evenly distributed on the inner and outer circular walls near the bottom of the annular lofting groove and have the same height to ensure that the water inlet and outlet heights are the same.

[0038] An inner annular water-permeable filter paper 16 and an outer annular water-permeable filter paper 15 are respectively disposed on the inner and outer circular walls near the bottom of the annular lofting groove 18. The inner and outer annular water-permeable filter papers 16 and 15 serve as water-permeable and air-permeable experimental materials. The inner and outer annular water-permeable filter papers 16 and 15 are both higher than or equal to the height of the water outlet 17 and water inlet 19.

[0039] A bending element signal receiver 82 is provided at the bottom of the annular lofting groove.

[0040] The top of the water inlet space 14 is connected to the output end of the external water head output meter 21 through a pipe and a valve. The external water head output meter 21 can output the equivalent water head pressure and record the output flow.

[0041] The top of the water outlet space 11 is connected to the inner water head output meter 20 through the water outlet channel 7. A valve is provided on the water outlet channel 7. The inner water head output meter 20 is higher than the water outlet space 11. The inner water head output meter 20 can output the equivalent water head pressure and record the input flow.

[0042] An annular pressure block with the same size as the annular lofting groove 18 is provided at the bottom of the annular pressure cap 4, and an outlet pipe channel 3 is provided on the annular pressure cap 4. The diameter of the outlet pipe channel 3 is larger than the diameter of the water outlet channel 7, and is used to pass through the water outlet channel 7. The water outlet channel 7 passes through the outlet pipe channel 3. A bending element signal transmitter 81 is provided at the bottom of the annular pressure block at a position corresponding to the lower bending element 82.

[0043] The annular pressure cap 4 is sealed and connected to the annular lofting groove 18. The outer ring of the annular pressure block of the annular pressure cap 4 is provided with a sealing outer rubber ring 5 and a sealing outer annular groove 6. The sealing outer rubber ring 5 is snapped on the outside of the annular pressure cap 4 through the sealing outer annular groove 6. The outer diameter of the sealing outer rubber ring 5 is the same as the inner outer diameter of the annular lofting groove 18; the inner ring of the annular lofting groove 18 is provided with a sealing inner rubber ring 10 and a sealing inner annular groove 9. The sealing inner rubber ring 10 is snapped through the sealing inner annular groove 9. The outer diameter of the sealing inner rubber ring 9 is the same as the inner diameter of the annular lofting groove 18, ensuring that the top of the annular lofting groove 18 is sealed and water cannot pass through.

[0044] A consolidation instrument base 13 is provided at the bottom of the base. A dial indicator frame 2 is provided on the consolidation instrument base 13. The dial indicator frame 2 is a linear sliding device. A dial indicator 1 is provided on the dial indicator frame 2. The measuring end of the dial indicator 1 faces the annular lofting groove 18.

[0045] The bending element signal transmitter 81 and the bending element signal receiver 82 form a bending element kit, which can simultaneously test compression wave P wave and shear wave S wave, and the input frequency and waveform can be defined by oneself. Among them, the compression wave P wave can well detect the saturation of the sample. The higher the saturation, the faster the wave speed.

[0046] The specific process of the method for measuring the radial permeability coefficient of loess under different pressures using the above device is as follows:

[0047] Step 1: Place the inner annular water-permeable filter paper 16 and the outer annular water-permeable filter paper 15 in the annular lofting groove 18.

[0048] Step 2: Place the loess to be tested in the annular lofting groove 18. If the soil sample to be tested is remolded soil, compact it in the annular lofting groove 18 according to the designed dry density. If the soil sample to be tested is undisturbed soil, cut the soil sample into a suitable shape and place it in the annular lofting groove 18. The height of the annular soil sample is 4 cm.

[0049] Step three: carefully align the outlet pipe channel 3 of the annular pressure cap 4 with the water outlet channel 7 , and place the annular pressure cap 4 on the annular soil sample of the annular lofting groove 18 .

[0050] Step 4: Place the permeation device on the consolidation instrument base 13 , install the dial indicator 1 on the dial indicator stand 2 according to the compression test process specification, adjust the range of the dial indicator 1 , and make the dial indicator 1 contact the annular pressure cap 4 .

[0051] Step five: apply a load to the annular pressure cap 4 through a one-dimensional consolidation instrument, and record the compression of the annular soil sample at a predetermined time, that is, the reading of the dial indicator 1. When the reading of the dial indicator 1 does not change significantly for a long time, it is considered that the annular soil sample has reached the maximum compression under the current load, that is, when it reaches stability, the consolidation is completed, and then a permeability test is carried out under this pressure.

[0052] Step six, the wave velocity of this state is measured by the bending element signal transmitter 81 and the bending element signal receiver 82. At this time, it is the wave velocity corresponding to the initial water content under the current overburden pressure, and the initial saturation of the annular soil sample is obtained.

[0053] Step seven, give the water inlet channel 12 a head pressure (provided by the outer head output meter 21, such as 30kPa), the water flows through the water inlet channel 12 in turn, reaches the water inlet space 14, and then enters the annular soil sample through the water inlet hole 21 and the outer annular water-permeable filter paper 15. Due to the presence of the sealing inner rubber ring 10 and the sealing outer rubber ring 5, the water flow will not overflow from the top of the annular lofting groove 18, but enter the water outlet space 11 through the water outlet hole 17 of the inner annular water-permeable filter paper 16, and then the water flow overflows through the water outlet channel 7; when the water overflowing from the water outlet channel 7 no longer changes with time and the water outlet is stable, it indicates that the seepage in the annular soil sample has reached a steady-state flow.

[0054] Step nine: measure the wave velocity in the current state through the bending element signal transmitter 81 and the bending element signal receiver 82, and calculate the saturation of the annular soil sample in the current overburden pressure state according to the wave velocity result.

[0055] Step 10. When the water in the outlet channel 7 enters the inner water head output meter 20, set the water head size of the inner water head output meter 20 (needs to be smaller than the output pressure value of the outer water head output meter 21, such as 20kPa), and record the stable seepage flow of the annular soil sample through the inner water head output meter 20 or the outer water head output meter 21 (the flow of the inner water head output meter 20 or the outer water head output meter 21 is the same), and then calculate the permeability coefficient of the annular soil sample in the current state, and the preliminary measurement is completed.

[0056] The formula for calculating the permeability coefficient is:

[0057]

[0058] In the formula

[0059] K h Radial permeability coefficient of annular specimen (m / s).

[0060] q is the seepage rate of the ring sample per minute, which can be measured by the outer head output meter or the inner head output meter (mL / min).

[0061] h is the height of the ring specimen (mm).

[0062] r1: outer diameter of the ring specimen (mm).

[0063] r0: outer diameter of the ring specimen (mm).

[0064] γ w Water density (N / m 3 ).

[0065] p1: Water pressure outside the specimen, i.e., water pressure of the outer head output instrument (kPa).

[0066] p0 is the water pressure inside the sample, i.e. the water head pressure of the internal water head output instrument (kPa).

[0067] Change the water head pressure of the outer water head output instrument 21, but keep the water head of the inner water head output instrument 20 smaller than that of the outer water head output instrument 21. Repeat the test at least three times. When the permeability coefficient measured under different water heads is within the allowable difference range, it proves that the permeability coefficient measurement is correct.

[0068] Step 11: Change the overlying load and repeat steps 8, 9 and 10 to obtain the radial permeability coefficient and its variation relationship of the annular soil sample under different overlying loads.

[0069] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0070] It should be understood that the above description is for illustrative purposes only and is not intended to be limiting. Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the present teachings should not be determined with reference to the above description, but rather with reference to the preceding claims and the full scope of equivalents to which such claims are entitled. For the purpose of completeness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein from the preceding claims is not a disclaimer of such subject matter, nor should it be considered that the applicants did not consider such subject matter to be part of the disclosed inventive subject matter.

Claims

1. A ring-shaped test device for radial permeability of loess under different pressures, characterized in that: It includes a base, an annular pressure cap (4), an inner water head output meter (20) and an outer water head output meter (21); The base is cylindrical with a cavity, and from the outer cavity to the inner cavity, there are a water inlet space (14), an annular lofting groove (18) and a water outlet space (11). The top of the water inlet space (14) is connected to the output end of the outer head output meter (21), and the top of the water outlet space (11) is connected to the inner head output meter (20) through the water outlet channel (7). The inner head output meter (20) is higher than the water outlet space (11); the annular lofting groove (18) is adjacent to the outer head output meter (21). A plurality of water outlet holes (17) and water inlet holes (19) are respectively provided on the inner and outer circular walls near the bottom, the water outlet holes (17) and the water inlet holes (19) are respectively communicated with the water outlet space (11) and the water inlet space (14), an inner annular water-permeable filter paper (16) and an outer annular water-permeable filter paper (15) are respectively provided on the inner and outer circular walls near the bottom of the annular lofting groove (18), and a bending element signal receiver (82) is provided at the bottom of the annular lofting groove (18); An annular pressure block having the same size as the annular lofting groove (18) is provided at the bottom of the annular pressure cap (4), and a bending element signal transmitter (81) is provided at a position corresponding to the bending element signal receiver (82) at the bottom of the annular pressure block.

2. The annular test device for radial permeability of loess under different pressures according to claim 1, characterized in that: The annular pressure cap (4) is sealed and connected to the annular lofting groove (18).

3. The annular test device for radial permeability of loess under different pressures according to claim 2, characterized in that: The outer ring of the annular pressure block of the annular pressure cap (4) is provided with a sealing outer rubber ring (5), and the inner ring of the annular lofting groove (18) is provided with a sealing inner rubber ring (10).

4. The annular test device for radial permeability of loess under different pressures according to claim 1, characterized in that: A consolidation instrument base (13) is provided at the bottom of the base, a dial indicator frame (2) is provided on the consolidation instrument base (13), the dial indicator frame (2) is a linear sliding device, a dial indicator (1) is provided on the dial indicator frame (2), and a measuring end of the dial indicator (1) faces the annular lofting groove (18).

5. The annular test device for radial permeability of loess under different pressures according to claim 1, characterized in that: The inner annular water-permeable filter paper (16) and the outer annular water-permeable filter paper (15) are both higher than or equal to the height of the water outlet hole (17) and the water inlet hole (19).

6. The annular test device for radial permeability of loess under different pressures according to claim 1, characterized in that: There are a plurality of water outlet holes (17) and water inlet holes (19), which are evenly distributed on the inner and outer circular walls near the bottom of the annular lofting groove (18).

7. The annular test device for radial permeability of loess under different pressures according to claim 1, characterized in that: An outlet pipe channel (3) is provided on the annular pressure cap (4), and a water outlet channel (7) passes through the outlet pipe channel (3).

8. A method for measuring radial permeability of loess under different pressures using a ring test apparatus according to any one of claims 1 to 7, characterized in that: The following processes are included: S1, placing the annular soil sample into the annular setting out groove (18), and placing the annular pressure cap (4) on the annular soil sample; S2, applying an overburden load to the annular pressure cap (4) until the annular soil sample reaches a maximum compression under the current load; S3, measuring the wave velocity corresponding to the initial moisture content of the annular soil sample under the current overburden pressure by means of the bending element signal transmitter (81) and the bending element signal receiver (82), thereby obtaining the initial saturation of the annular soil sample; S4, the outer head output instrument (21) gives a head pressure, the water flows to the water inlet space (14), then enters the annular soil sample through the water inlet hole (19) and the outer annular permeable filter paper (15), and then enters the water outlet space (11) through the inner annular permeable filter paper (16) and the water outlet hole (17) in sequence, and then overflows through the water outlet channel (7). When the overflow water flow no longer changes with time and the water outlet is stable, it indicates that the seepage in the annular soil sample has reached a steady-state flow; S5, measuring the wave velocity of the annular soil sample in the current state through the bending element signal transmitter (81) and the bending element signal receiver (82), thereby obtaining the saturation of the annular soil sample in the current state; S6, when the water in the outlet channel (7) enters the inner water head output instrument (20), the water head size of the inner water head output instrument (20) is set, and the stable seepage flow of the annular soil sample is recorded through the inner water head output instrument (20), and the permeability coefficient of the annular soil sample in the current state is calculated; S7, repeat S2-S6, change the overlying load, and obtain the radial permeability coefficient and its variation relationship of the annular soil sample under different overlying loads.

9. The ring test method for measuring radial permeability of loess under different pressures according to claim 8, characterized in that: The formula for calculating the permeability coefficient is: Where, K h is the radial permeability coefficient of the annular sample, q is the seepage rate per minute of the annular sample, measured by the inner head output instrument (20), h is the height of the ring specimen, r 1 is the outer diameter of the ring specimen, r 0 is the outer diameter of the ring specimen, γ w is the weight of water, p 1 is the water pressure outside the sample, that is, the water head pressure of the outer head output instrument (21), p 0 is the water pressure inside the sample, i.e. the water head pressure of the internal water head output instrument (20).

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