CN113916744A - Method and system for testing permeability coefficient of foam soil under total stress - Google Patents
Method and system for testing permeability coefficient of foam soil under total stress Download PDFInfo
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- CN113916744A CN113916744A CN202111179542.6A CN202111179542A CN113916744A CN 113916744 A CN113916744 A CN 113916744A CN 202111179542 A CN202111179542 A CN 202111179542A CN 113916744 A CN113916744 A CN 113916744A
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- 239000006260 foam Substances 0.000 title claims abstract description 89
- 239000002689 soil Substances 0.000 title claims abstract description 80
- 230000035699 permeability Effects 0.000 title claims abstract description 54
- 238000012360 testing method Methods 0.000 title claims abstract description 38
- 238000000034 method Methods 0.000 title claims abstract description 30
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 212
- 239000011148 porous material Substances 0.000 claims abstract description 42
- 238000012545 processing Methods 0.000 claims abstract description 5
- 239000002245 particle Substances 0.000 claims description 13
- 230000008569 process Effects 0.000 claims description 13
- 238000002347 injection Methods 0.000 claims description 12
- 239000007924 injection Substances 0.000 claims description 12
- 238000006073 displacement reaction Methods 0.000 claims description 8
- 230000008595 infiltration Effects 0.000 claims description 7
- 238000001764 infiltration Methods 0.000 claims description 7
- 230000009467 reduction Effects 0.000 claims description 6
- 108010074864 Factor XI Proteins 0.000 claims description 3
- 230000001133 acceleration Effects 0.000 claims description 3
- 230000005484 gravity Effects 0.000 claims description 3
- 230000001502 supplementing effect Effects 0.000 claims 2
- 239000012466 permeate Substances 0.000 claims 1
- 238000005259 measurement Methods 0.000 abstract description 7
- 230000035515 penetration Effects 0.000 description 7
- 239000013589 supplement Substances 0.000 description 6
- 238000010276 construction Methods 0.000 description 4
- 239000000243 solution Substances 0.000 description 4
- 210000001503 joint Anatomy 0.000 description 3
- 239000004576 sand Substances 0.000 description 3
- 230000008859 change Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000003607 modifier Substances 0.000 description 2
- 230000003020 moisturizing effect Effects 0.000 description 2
- 241001391944 Commicarpus scandens Species 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000008187 granular material Substances 0.000 description 1
- 230000037361 pathway Effects 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 230000005641 tunneling Effects 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/082—Investigating permeability by forcing a fluid through a sample
- G01N15/0826—Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/088—Investigating volume, surface area, size or distribution of pores; Porosimetry
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- Immunology (AREA)
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- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
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Abstract
The invention discloses a method and a system for testing the permeability coefficient of foam soil under total stress, for this reason, the method for testing the permeability coefficient of foam soil under total stress provided by the embodiment of the invention comprises the steps of filling a foam soil sample in a loading cavity of a permeameter; n +1 pore water pressure gauges are uniformly distributed on the loading cavity along the height direction of the loading cavity; wherein, a pore water pressure gauge is arranged at the top and the bottom of the loading cavity; connecting the pore water pressure gauge with a data acquisition instrument; applying a constant pressure water head and vertical total stress on a foam soil sample in the permeameter, opening an automatic drain valve on a drain pipe, measuring the water pressure in a loading cavity by using a pore water pressure gauge, and acquiring data by using a data acquisition instrument; and processing the data acquired by the data acquisition instrument, and calculating to obtain the permeability coefficient. The testing method can realize the measurement of the permeability coefficient of the foam soil under the conditions of total stress and high water pressure, and the measured permeability coefficient is more in line with the actual situation on site.
Description
Technical Field
The invention belongs to the technical field of geotechnical test measurement, and particularly relates to a method and a system for testing the permeability coefficient of foam soil under total stress.
Background
The earth pressure balance shield is widely applied to urban underground tunnel construction due to high efficiency and safety, and water-rich sandy strata can be inevitably encountered along with the continuous increase of the construction quantity of the earth pressure balance shield tunnels. When the earth pressure balance shield passes through a water-rich sandy stratum, gushing accidents are easy to happen, the construction period is prolonged if the gushing accidents are light, economic losses are caused, and casualties and the like are caused if the gushing accidents are heavy. The modifier is usually added to the face of a tunnel to improve the impermeability of the muck, the modifier which is most used in the sandy stratum at present is foam which is filled between pores of soil particles to block seepage channels of the soil particles, but the foam is a metastable system, the impermeability of the foam soil is gradually reduced along with the increase of time as the foam soil is broken or taken away by water flow, and particularly under the condition of high water pressure, the foam is more easy to break and migrate, so that the measurement of the permeability coefficient along with the change of time has important engineering significance for guiding shield construction.
Some scholars have proposed permeability coefficient measuring devices or methods. For example, the Chinese invention patent (application number: 201911182461.4, patent name: a soil body permeability test device and method under variable stress condition) provides a soil body permeability test device under variable stress condition, the real stress state of a sample can be simulated in the test process, the stress state of one surface or a plurality of surfaces of the sample can be changed according to requirements, and the permeability coefficient change rule of a soil body in the stress increasing and decreasing process can be accurately obtained. The Chinese invention patent (application number: 201810683637.3, patent name: a method and a device for testing the permeability coefficient of foam improved sandy residue soil under high water pressure) provides a permeability coefficient testing device, and the permeability coefficient of the foam improved sandy residue soil under high water pressure can be measured by providing a high position water head. The Chinese utility model (application number: 201510108411.7, patent name: constant and variable head composite penetration testing device) relates to a device which is provided with an exhaust valve on a sample barrel and a water injection device respectively, realizes the adjustment of water pressure by adjusting the air pressure and the exhaust valve in the water injection device and is compatible with constant head and variable head penetration tests. None of the above patents considers the influence of the total stress on the permeability of the foam soil, and cannot truly reflect the permeability of the foam soil in the soil warehouse.
Disclosure of Invention
The invention provides a method and a system for testing the permeability coefficient of foam soil under total stress aiming at the problem that the influence of the total stress and the high water pressure cannot be fully considered in the existing foam soil permeability coefficient test.
Therefore, the method for testing the permeability coefficient of the foam soil under the total stress provided by the embodiment of the invention comprises the following steps:
filling a foam soil sample in a loading cavity of the permeameter;
n +1 pore water pressure gauges are uniformly distributed on the loading cavity along the height direction of the loading cavity; wherein, a pore water pressure gauge is arranged at the top and the bottom of the loading cavity;
connecting the pore water pressure gauge with a data acquisition instrument;
applying a constant pressure water head and vertical total stress on a foam soil sample in the permeameter, opening an automatic drain valve on a drain pipe, measuring the water pressure in a loading cavity by using a pore water pressure gauge, and acquiring data by using a data acquisition instrument;
and processing the data acquired by the data acquisition instrument, and calculating to obtain the permeability coefficient.
Specifically, the specific calculation process of the permeability coefficient is as follows:
the first step is as follows: and (3) calculating the permeability coefficient of the soil sample between two adjacent pore water pressure gauges, wherein the calculation formula is as follows:
in the formula: xi is a reduction factor, nxIs the porosity of the foam under total vertical stress, v is the kinematic viscosity of water, g is gravity plusSpeed, nfiIs the water pressure piPorosity of lower foam, d10,fiIs the water pressure piEffective particle size of lower foam, water pressure piThe average value of the readings of two adjacent pore water pressure meters is obtained;
the second step is that: calculating the integral equivalent permeability coefficient by the following calculation formula:
in the formula: l is the height of the soil foam sample, hiIs a seepage path of the soil sample between two adjacent pore water pressure meters;
the solving process of the reduction factor xi is as follows:
in the formula: d10,sIs the effective grain size of soil particles in the foam soil sample.
In particular, the water pressure piPorosity n of lower foamfiCalculated by the following formula:
in the formula: e.g. of the typefiIs the water pressure piThe porosity of the lower foam, FER is the expansion ratio of the foam, and p is the atmospheric pressure.
In particular, the water pressure piEffective particle diameter d10,fiCalculated by the following formula:
in the formula: d10,fIs the effective particle size of the foam at atmospheric pressure p.
The system for testing the permeability coefficient of the foam soil under the total stress provided by the embodiment of the invention comprises a permeameter and a data acquisition instrument, wherein the permeameter comprises:
permeating the cylinder;
the bottom plate is fixedly arranged at the bottom of the permeation cylinder;
the piston is arranged inside the permeation cylinder in a sliding mode;
the constant-pressure water head is communicated with the water inlet hole on the piston through a water inlet pipe;
the drain pipe is communicated with the drain hole on the bottom plate;
the axial loading system is used for applying vertical total stress to the foam soil sample;
a loading cavity for containing a foam soil sample is formed among the permeation cylinder, the piston and the bottom plate, a plurality of pore water pressure meters are arranged on the loading cavity along the height direction of the loading cavity, a displacement sensor is arranged on the piston, and the displacement sensor and the pore water pressure meters are connected with the data acquisition instrument;
the pore water pressure gauge is used for measuring the water pressure in the loading cavity, the pore water pressure gauge at the bottommost end is arranged at the bottom plate, and the pore water pressure gauge at the topmost end is arranged on the piston.
Specifically, the axial loading system includes air pump, first gas-supply pipe and first servo pneumatic valve, the fixed roof that is equipped with in top of infiltration barrel, the infiltration barrel the piston with be formed with the atmospheric pressure chamber between the roof, the both ends of first gas-supply pipe respectively with air pump and atmospheric pressure chamber intercommunication, first servo pneumatic valve sets up on the first gas-supply pipe.
Specifically, the constant pressure flood peak is provided by high-pressure water injection system, high-pressure water injection system includes the constant pressure water tank, the constant pressure water tank is a sealed box, and the bottom with the inlet tube intercommunication, the top through the second gas-supply pipe with the air pump intercommunication, be equipped with the servo atmospheric pressure valve of second on the second gas-supply pipe.
Specifically, high pressure water injection system still includes storage water tank and intelligent water injector, intelligent water injector pass through the moisturizing pipe connect in the constant voltage water tank with between the storage water tank, the moisturizing pipe inserts the tip of constant voltage water tank one end is equipped with the water level inductor, the water level inductor with intelligent water injector electric connection.
Specifically, be equipped with the flowmeter on the drain pipe, the flowmeter with the data acquisition instrument is connected, all be equipped with the stagnant water valve on inlet tube and the drain pipe.
Specifically, permeable plates are respectively arranged between the foam soil sample and the piston and between the foam soil sample and the bottom plate
Specifically, the drain pipe is communicated with the pressure chamber, an automatic drain valve is arranged at the bottom of the pressure chamber, the air pump is communicated with the pressure chamber through a third air pipe, and a third servo air pressure valve is arranged on the third air pipe.
Compared with the prior art, at least one embodiment of the invention has the following beneficial effects: the invention can realize the measurement of the permeability coefficient of the foam soil under the total stress and the high water pressure, the measured permeability coefficient is more in line with the actual situation on site, and the test system has the advantages of automatic control of the water pressure, simple and convenient operation and high test precision.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a test system provided in an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of a permeameter according to an embodiment of the present invention;
wherein: 1. a permeameter; 101. permeating the cylinder; 102. a base plate; 103. a piston; 104. a drain pipe; 105. a top plate; 2. a data acquisition instrument; 3. an axial loading system; 301. an air pump; 302. a first gas delivery pipe; 303. a first servo pneumatic valve; 4. a foam soil sample; 5. a pore water pressure gauge; 6. a display; 7. a displacement sensor; 8. a pneumatic chamber; 9. a high pressure water injection system; 901. a constant pressure water tank; 902. a second gas delivery pipe; 903. a second servo pneumatic valve; 904. a water storage tank; 905. an intelligent water injector; 906. a water replenishing pipe; 907. a water level sensor; 10. a water stop valve; 11. a pressure chamber; 12. a third gas delivery pipe; 13. a third servo pneumatic valve; 14. an automatic drain valve; 15. an automatic switching valve; 16. a flow meter.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the invention.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
Referring to fig. 1 and 2, a system for testing permeability coefficient of foam soil under total stress comprises a permeameter 1, a data acquisition instrument 2 and an axial loading system 3, wherein the permeameter 1 comprises a permeable cylinder 101, a bottom plate 102, a piston 103, a constant pressure water head and a water discharge pipe 104, the bottom plate 102 is fixedly arranged at the bottom of the permeable cylinder 101, the piston 103 is slidably arranged in the permeable cylinder 101, a loading cavity for containing a foam soil sample 4 is formed among the permeable cylinder 101, the piston 103 and the bottom plate 102, the axial loading system 3 acts on the piston 103 for applying vertical total stress to the foam soil sample 4, the constant pressure water head is communicated with a water inlet hole on the piston 103 through a water inlet pipe, the water discharge pipe 104 is communicated with the bottom plate 102, a plurality of pore water pressure gauges 5 are arranged on the loading cavity along the height direction of the loading cavity, the pore water pressure gauges 5 are used for measuring water pressure in the loading cavity, the pore water pressure gauge 5 at the bottom end is arranged at the bottom plate 102, the topmost pore water pressure gauge 5 is arranged on the piston 103, is linked with the piston 103, is externally connected with the display 6 of the data acquisition instrument 2, is also provided with a displacement sensor 7 on the piston 103, can realize the measurement of the moving distance of the piston 103 through the displacement sensor 7, and the displacement sensor 7 and the pore water pressure gauge 5 are connected with the data acquisition instrument 2.
The process of testing the permeability coefficient of the foam soil under the total stress by using the testing system with the structure comprises the following steps:
filling a foam soil sample in a loading cavity of the permeameter;
installing an n +1 pore water pressure gauge on a pore body on the loading cavity, wherein n is a positive integer and is more than or equal to 2;
connecting the pore water pressure gauge with a data acquisition instrument;
applying a constant pressure water head and vertical total stress on a foam soil sample in the permeameter, opening an automatic drain valve on a drain pipe, measuring the water pressure in a loading cavity by using a pore water pressure gauge, and acquiring data by using a data acquisition instrument;
and processing the data acquired by the data acquisition instrument, and calculating to obtain the permeability coefficient.
Specifically, the specific calculation process of the permeability coefficient is as follows:
the first step is as follows: and (3) calculating the permeability coefficient of the soil sample between two adjacent pore water pressure gauges, wherein the calculation formula is as follows:
the second step is that: calculating the integral equivalent permeability coefficient by the following calculation formula:
wherein the water pressure piPorosity n of lower foamfiCalculated by the following formula:
water pressure piEffective particle diameter d10,fiCalculated by the following formula:
the solving process of the reduction factor xi is as follows:
in the formula: xi is a reduction factor, nxIs the porosity of the foam under the application of total vertical stress, v is the kinematic viscosity of water, g is the acceleration of gravity, n is the acceleration of gravityfiIs the water pressure piPorosity of lower foam, d10,fiIs the water pressure piEffective granule of lower foamDiameter, water pressure piIs the average value of the readings of two adjacent pore water pressure meters, l is the height of the foam soil sample, hiIs a seepage path of the soil sample between two adjacent pore water pressure gauges efiIs the water pressure piThe porosity of the lower foam, FER is the expansion ratio of the foam, d10,fIs the effective particle size of the foam at atmospheric pressure p, d10,sIs the effective grain size of soil particles in the foam soil sample.
The invention can realize the measurement of the permeability coefficient of the foam soil under the total stress and the high water pressure, provides a specific permeability coefficient solving formula, has a measuring result more conforming to the actual working condition in front of the tunnel face of the shield tunneling machine, and has the advantages of simpler operation process, higher measuring precision and the like.
Referring to fig. 1, in some embodiments, the axial loading system 3 includes an air pump 301, a first air pipe 302 and a first servo air pressure valve 303, the top of the permeation cylinder 101 is fixedly provided with a top plate 105, an air pressure cavity 8 is formed between the permeation cylinder 101, the piston 103 and the top plate 105, two ends of the first air pipe 302 are respectively communicated with the air pump 301 and the air pressure cavity 8, the first servo air pressure valve 303 is arranged on the first air pipe 302, and high-pressure air output by the air pump 301 enters the air pressure cavity 8 through the first servo air pressure valve 303 at a set constant air pressure, so as to push the piston 103 to apply an axial load to the foam soil sample 4.
Referring to fig. 1, in other embodiments, the constant pressure water head is provided by a high pressure water injection system 9, the high pressure water injection system 9 includes a constant pressure water tank 901, the constant pressure water tank 901 is a closed box, the bottom of the constant pressure water tank 901 is communicated with the water inlet pipe, the top of the constant pressure water tank is communicated with the air pump 301 through a second air pipe 902, a second servo air pressure valve 903 is disposed on the second air pipe 902, high pressure air output by the air pump 301 enters the constant pressure water tank 901 through the second servo air pressure valve 903 at a set constant air pressure, and water in the water tank is forced to enter the loading cavity through the water inlet pipe at a constant pressure, so that the provision of the constant pressure water head is achieved. The control of water pressure is realized by adopting a servo air pressure control technology in the embodiment, and the device has the advantages of automatic water pressure control, simplicity and convenience in operation and high test precision.
Referring to fig. 1, specifically, high pressure water injection system 9 further includes a water storage tank 904 and an intelligent water injector 905, the intelligent water injector 905 is connected between the constant pressure water tank 901 and the water storage tank 904 through a water supplement pipe 906, the water supplement pipe 906 is inserted into the bottom of the constant pressure water tank 901, and is connected with a water level sensor 907, the water level sensor 907 is electrically connected with the intelligent water injector 905, when the water level sensor 907 senses 1/5 that the water level is lower than the height of the constant pressure water tank 901, the intelligent water injector 905 starts to realize automatic water supplement, when the water supplement reaches the set time, if the water supplement reaches 4/5 of the height of the constant pressure water tank 901, the intelligent water injector 905 stops water supplement. In addition, a water tap can be arranged above the water storage tank 904, and the water storage tank 904 can be replenished through the water tap.
Referring to fig. 1 and 2, it can be understood that, in the practical design, the penetration cylinder 101 is a transparent hollow cylinder, the height of the penetration cylinder is greater than 2.5 times of the diameter, the top plate 105 and the bottom plate 102 of the penetration cylinder are respectively connected with the hollow cylinder through flanges, an air inlet, a piston 103 hole and an air release valve are arranged above the top plate 105, a first air pipe 302 is in butt joint with the air inlet, a hollow piston 103 rod of the piston 103 penetrates through the piston 103 hole in a sealing manner to be in butt joint with an inlet pipe, a water outlet is arranged below the bottom plate 102 and is in butt joint with a drain pipe 104, water stop valves 10 are arranged on the inlet pipe and the drain pipe 104, the piston 103 slides up and down along the penetration cylinder 101, the diameter of the piston 103 is consistent with the inner diameter of the penetration cylinder 101, the effective stroke of the piston 103 is smaller than the length of the hollow piston 103 rod, and high-pressure water flows into the loading cavity through the hollow piston 103 rod.
Referring to fig. 1, in some embodiments, the drain pipe 104 is communicated with the pressure chamber 11, the automatic drain valves 14 are disposed at the bottom of the pressure chamber 11, the air pump 301 is communicated with the pressure chamber 11 through the third air pipe 12, the third air pipe 12 is provided with the third servo pneumatic valve 13, the water flowing out of the permeation cylinder 101 flows into the automatic drain valves 14 in the pressure chamber 11, the automatic drain starting height is 4/5 at the height of the pressure chamber 11, and the automatic drain stopping height is 1/5 at the height of the pressure chamber 11. The embodiment can provide high pressure water heads for the upper side and the lower side of the foam soil simultaneously, and the hydraulic gradient of the foam soil is more accordant with the actual situation on site, so that the measured permeability coefficient is more accordant with the actual engineering.
Referring to fig. 1, specifically, the number of the pressure chambers 11 is two, and the water flowing out of the permeation cylinder 101 flows into two pressure chambers 11 alternatively through the automatic switching valve 15. Specifically, the air pressure in the air pressure chamber 8 is greater than the air pressure in the constant pressure water tank 901, the air pressure in the constant pressure water tank 901 is greater than the air pressure in the lower pressure chamber 11, and the volume of the water storage tank 904 is greater than 2 times the volume of the constant pressure water tank 901. The water drainage pipe 104 is provided with a flowmeter 16, the flowmeter 16 is connected with the data acquisition instrument 2, and water permeable plates are arranged between the foam soil sample 4 and the piston 103 and between the foam soil sample 4 and the bottom plate 102. Of course, the exchange of the permeation pathway can be achieved by adjusting the air pressure in the constant pressure water tank 901 and the pressure containing chamber 11.
The working process of the test system with the structure is as follows:
s1: assembling the test system according to the connection relation of the test system, closing water stop valves on the water inlet pipe and the water discharge pipe, and opening a water tap to inject water into the water storage tank;
s2: measurement of maximum porosity n of dry sandmaxAdding water and foam into dry sand, stirring to form foam soil, measuring the porosity n of the foam soil, wherein the porosity n of the foam soil is greater than the maximum porosity n of the dry sandmax；
S3: putting a permeable plate on a bottom plate of a permeameter, pouring the stirred foam soil into a permeation cylinder and flattening, putting a permeable plate on the flattened foam soil, wherein the filling height is more than 2 times of the diameter of the permeameter;
s4: the piston is aligned and placed into the infiltration cylinder, a bolt between the top plate and the infiltration cylinder is quickly screwed, the piston is further pre-pressed to be in contact with the upper permeable plate, the water inlet pipe at the bottom end of the constant-pressure water tank is connected to the top end of the piston rod, and the first gas pipe is connected to the top plate of the infiltration instrument;
s5: closing the air escape valve, sequentially setting and opening pressure values of the first servo air pressure valve, the second servo air pressure valve and the third servo air pressure valve, and opening the air pump;
s6: simultaneously opening water stop valves on the water inlet pipe and the water discharge pipe, and acquiring data by using a data acquisition instrument;
s7: and processing the data acquired by the data acquisition instrument, and calculating to obtain the permeability coefficient.
The invention can provide high pressure water head and apply high stress to the foam soil at the same time, thereby measuring the permeability coefficient of the foam soil under the condition of total stress, and the measured permeability coefficient is more in line with the engineering practice.
Any embodiment disclosed herein above is meant to disclose, unless otherwise indicated, all numerical ranges disclosed as being preferred, and any person skilled in the art would understand that: the preferred ranges are merely those values which are obvious or representative of the technical effect which can be achieved. Since the numerical values are too numerous to be exhaustive, some of the numerical values are disclosed in the present invention to illustrate the technical solutions of the present invention, and the above-mentioned numerical values should not be construed as limiting the scope of the present invention.
Meanwhile, if the invention as described above discloses or relates to parts or structural members fixedly connected to each other, the fixedly connected parts can be understood as follows, unless otherwise stated: a detachable fixed connection (for example using bolts or screws) is also understood as: non-detachable fixed connections (e.g. riveting, welding), but of course, fixed connections to each other may also be replaced by one-piece structures (e.g. manufactured integrally using a casting process) (unless it is obviously impossible to use an integral forming process).
In addition, terms used in any technical solutions disclosed in the present invention to indicate positional relationships or shapes include approximate, similar or approximate states or shapes unless otherwise stated. Any part provided by the invention can be assembled by a plurality of independent components or can be manufactured by an integral forming process.
The above examples are merely illustrative for clearly illustrating the present invention and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. Nor is it intended to be exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the scope of the invention.
Claims (10)
1. A method for testing the permeability coefficient of foam soil under total stress is characterized by comprising the following steps:
filling a foam soil sample (4) in a loading cavity of the permeameter (1);
n +1 pore water pressure meters (5) are uniformly distributed on the loading cavity along the height direction of the loading cavity, wherein one pore water pressure meter (5) is uniformly distributed at the top and the bottom of the loading cavity;
connecting the pore water pressure gauge (5) with the data acquisition instrument (2);
applying a constant pressure water head and vertical total stress to a foam soil sample (4) in a permeameter (1), opening an automatic drain valve (14) on a drain pipe (104), measuring the water pressure in a loading cavity by using a pore water pressure gauge (5), and acquiring data by using a data acquisition instrument (2);
and processing the data acquired by the data acquisition instrument (2), and calculating to obtain the permeability coefficient.
2. The method for testing the permeability coefficient of foam soil under total stress according to claim 1, wherein the method comprises the following steps: the specific calculation process of the permeability coefficient is as follows:
the first step is as follows: and (3) calculating the permeability coefficient of the soil sample between two adjacent pore water pressure gauges, wherein the calculation formula is as follows:
in the formula: xi is a reduction factor, nxIs the porosity of the foam under total vertical stress, v is the kinematic viscosity of water, g is the acceleration of gravity, n is the rate of gravityfiIs the water pressure piPorosity of lower foam, d10,fiIs the water pressure piEffective particle size of lower foam, water pressure piThe average value of the readings of two adjacent pore water pressure meters is obtained;
the second step is that: calculating the integral equivalent permeability coefficient by the following calculation formula:
in the formula: l is the height of the soil foam sample, hiIs a seepage path of the soil sample between two adjacent pore water pressure meters;
the solving process of the reduction factor xi is as follows:
in the formula: d10,sIs the effective grain size of soil particles in the foam soil sample.
3. The method for testing the permeability coefficient of foam soil under total stress according to claim 2, wherein the method comprises the following steps: water pressure piPorosity n of lower foamfiCalculated by the following formula:
in the formula: e.g. of the typefiIs the water pressure piThe porosity of the lower foam, FER is the expansion ratio of the foam, and p is the atmospheric pressure.
4. The method for testing the permeability coefficient of foam soil under total stress according to claim 2, wherein the method comprises the following steps: water pressure piEffective particle diameter d10,fiCalculated by the following formula:
in the formula: d10,fIs the effective particle size of the foam at atmospheric pressure p.
5. A system for testing the permeability coefficient of foam soil under total stress comprises a permeameter (1) and a data acquisition instrument (2), and is characterized in that the permeameter (1) comprises:
a permeate cylinder (101);
the bottom plate (102) is fixedly arranged at the bottom of the permeation cylinder body (101);
the piston (103) is arranged inside the permeation cylinder (101) in a sliding mode, and a loading cavity for containing a foam soil sample (4) is formed among the permeation cylinder (101), the piston (103) and the bottom plate (102);
the constant-pressure water head is communicated with a water inlet hole in the piston (103) through a water inlet pipe;
a drain pipe (104) which is communicated with the drain hole on the bottom plate (102);
the device also comprises an axial loading system (3) acting on the piston (103), wherein the axial loading system (3) is used for applying vertical total stress to the foam soil sample (4);
a plurality of pore water pressure meters (5) are arranged on the loading cavity along the height direction of the loading cavity, a displacement sensor (7) is arranged on the piston (103), and the displacement sensor (7) and the pore water pressure meters (5) are connected with the data acquisition instrument (2);
the pore water pressure gauge (5) is used for measuring the water pressure in the loading cavity, the pore water pressure gauge (5) at the bottommost end is arranged at the bottom plate (102), and the pore water pressure gauge (5) at the topmost end is arranged on the piston (103).
6. The system for testing permeability coefficient of foam soil under total stress according to claim 5, wherein: axial loading system (3) include air pump (301), first air-supply pipe (302) and first servo atmospheric pressure valve (303), the fixed roof (105) that is equipped with in top of infiltration barrel (101), infiltration barrel (101) piston (103) with be formed with atmospheric pressure chamber (8) between roof (105), the both ends of first air-supply pipe (302) respectively with air pump (301) and atmospheric pressure chamber (8) intercommunication, first servo atmospheric pressure valve (303) set up on first air-supply pipe (302).
7. The system for testing permeability coefficient of foam soil under total stress according to claim 6, wherein: the constant-pressure water head is provided by a high-pressure water injection system (9), the high-pressure water injection system (9) comprises a constant-pressure water tank (901), the constant-pressure water tank (901) is a closed box body, the bottom of the constant-pressure water tank is communicated with the water inlet pipe, the top of the constant-pressure water tank is communicated with the air pump (301) through a second air pipe (902), and a second servo air pressure valve (903) is arranged on the second air pipe (902).
8. The system for testing permeability coefficient of foam soil under total stress according to claim 7, wherein: the high-pressure water injection system (9) further comprises a water storage tank (904) and an intelligent water injector (905), wherein the intelligent water injector (905) is connected between the constant-pressure water tank (901) and the water storage tank (904) through a water supplementing pipe (906), a water level sensor (907) is arranged at the end part of one end, inserted into the constant-pressure water tank (901), of the water supplementing pipe (906), and the water level sensor (907) is electrically connected with the intelligent water injector (905).
9. The system for testing the permeability coefficient of foam soil under total stress according to any one of claims 5 to 8, wherein: the water discharge pipe (104) is provided with a flowmeter, the flowmeter is connected with the data acquisition instrument (2), and the water inlet pipe and the water discharge pipe (104) are both provided with a water stop valve (10).
10. The system for testing permeability coefficient of foam soil under total stress according to claim 7, wherein: the drain pipe (104) is communicated with the pressure chamber (11), an automatic drain valve (14) is arranged at the bottom of the pressure chamber (11), the air pump (301) is communicated with the pressure chamber (11) through a third air conveying pipe (12), and a third servo air pressure valve (13) is arranged on the third air conveying pipe (12).
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