Device for reinforcing microorganisms in expansive soil and measuring expansive force and frost heaving force of expansive soil

Abstract

The utility model provides an expansive soil microorganism reinforcement and expansive force and frost heaving force measurement device, and belongs to the technical field of expansive soil mechanics, the expansive soil microorganism reinforcement and expansive force and frost heaving force measurement device comprises a base (1), a temperature control ring (2), a sleeve (3) and a top cover (4), the bottom of the temperature control ring (2) is connected to the base (1), and a soil sample to be tested is placed in the temperature control ring (2); a water inlet (5) is formed in the bottom of the base (1) and penetrates through the top of the base (1); the top cover (4) covers the top of the temperature control ring (2), and a plurality of through holes matched with the sleeves (3) are formed in the top cover (4); a plurality of through holes are formed in the side wall of the sleeve (3), and the bottom of the sleeve (3) is sealed; the sleeve (3) is made of a nylon plastic material; the device can be used for uniformly filling microorganisms into expansive soil and providing accurate measurement data.

Description

Technical Field

[0001] The utility model belongs to the technical field of expansive soil mechanics, and in particular relates to a device for measuring microbial reinforcement of expansive soil and its expansion force and frost heave force. Background Art

[0002] Expansive soil engineering is gradually advancing towards seasonally frozen areas. Affected by the extremely high and low temperature complex geological environment, the expansive soil slopes repeatedly experience dry-wet-freeze-thaw coupling cycles every year. Expansive soil has cracks, expansion and contraction, strength attenuation, and over-consolidation. Due to its poor properties and difficulty in improvement, it is called a typical "problem soil" in the engineering community. Under the influence of the dry-wet-freeze-thaw coupling cycle, the stress field, moisture field, and temperature field in the expansive soil are constantly changing. When the soil temperature is below 0°C, part of the water in the soil freezes into ice, causing the soil volume to expand. This is the frost heave of the soil; and when the temperature rises, the ice in the soil gradually melts, causing the soil structure to be destroyed and the strength to be sharply attenuated, causing the soil to sink under its own weight, and eventually causing serious damage to the expansive soil channel. Therefore, it is extremely important to reinforce the expansive soil in seasonally frozen areas.

[0003] Microbial reinforcement technology (MICP technology) is a new type of rock and soil reinforcement technology developed in recent years. It has the advantages of being eco-friendly, highly environmentally adaptable, and easy to control the reaction process. Its reinforcement principle is to use microorganisms to induce the generation of a large amount of calcium carbonate precipitates with cementing properties in a short period of time, thereby enhancing the bonding strength between soil particles and filling the pores between particles, thereby effectively improving the physical and mechanical properties of the soil.

[0004] The Chinese invention patent with the publication number CN113049628B discloses a combined tester for the wet swelling and frost heaving force of expansive soil. The tester's sample cavity system includes a steel sealing cover plate, a cylindrical steel sample cavity and a steel base that are connected in a matching manner; the water injection system includes a water inlet interface, a water seepage port, a water outlet interface and a vacuum device, the water inlet interface and the water seepage port are interconnected, the water outlet interface is arranged on the steel sealing cover plate, and the outer end of the water outlet interface is connected to the vacuum device; the array-type thin film pressure digital display sensor in the stress monitoring system is arranged close to the inner wall of the cylindrical steel sample cavity and connected to the data acquisition module. The structure of the tester is reasonably set up, and the relationship between the expansion force of the expansive soil acting on the rigid constraint structure during the soaking and swelling of the expansive soil and the soaking time can be tested under completely rigid constraint conditions throughout the process, as well as the relationship between the frost heaving force of the expansive soil in the freeze-thaw process under different saturation conditions and the freezing time and freezing temperature, providing an important basis for the construction of expansive soil engineering in seasonally frozen areas.

[0005] Although the above device can test the swelling and frost heaving force of expansive soil, it cannot meet the test requirements of simultaneously measuring the swelling force and frost heaving force of microbial reinforced expansive soil under dry-wet-freeze-thaw coupling. The main problems are:

[0006] (1) Traditional microbial reinforcement technology is mostly used for coarse-grained soils such as sand. Expansive soil is a clay soil that expands dramatically after being soaked in water and shrinks significantly after losing water. It is easy to cause blockage during microbial grouting and it is difficult to inject the reaction liquid into the soil. Therefore, the reinforced samples often show uneven reinforcement and no obvious improvement in various soil indicators. The above-mentioned device only injects water from the bottom to the top of the soil sample through the water inlet interface at the bottom, which is bound to cause blockage during the microbial grouting process.

[0007] (2) The above-mentioned device freezes and melts the soil samples through the temperature control system at the bottom of the steel base. Except for the soil samples close to the temperature control system, which undergo freeze-thaw changes in a timely manner following the temperature changes, the freeze-thaw process of the other soil samples is relatively delayed. In other words, the force measured by the sensor for the soil samples far away from the temperature control system is not the normal frost heave force, but the corresponding strain force generated by the expansion, compression or contraction and collapse of the soil samples below it. In this way, it is impossible to ensure that the measured frost heave force is accurate. Summary of the invention

[0008] The purpose of the utility model is to solve the problems mentioned in the background technology and to provide a device for measuring the microbial reinforcement of expansive soil and its expansion force and frost heave force, which can uniformly inject microorganisms into the expansive soil and provide accurate measurement data.

[0009] In order to achieve the above technical purpose, the technical solution adopted by the utility model is:

[0010] A device for microbial reinforcement of expansive soil and measurement of its expansion force and frost heave force, comprising a base, a temperature control ring, a sleeve and a top cover, wherein the bottom of the temperature control ring is connected to the base, and a soil sample to be tested is placed in the temperature control ring; a water inlet is provided at the bottom of the base, and the water inlet passes through the top of the base; the top cover is arranged on the top of the temperature control ring, and a plurality of through holes matching the sleeve are provided on the top cover; a plurality of through holes are provided on the side wall of the sleeve, and the bottom of the sleeve is sealed; the sleeve is made of nylon plastic.

[0011] Preferably, the outer wall of the temperature control ring is provided with a liquid inlet and a liquid outlet; the interior of the temperature control ring is a liquid pipeline stacked in a spiral ring, and the two ends of the liquid pipeline are respectively connected to the liquid inlet and the liquid outlet.

[0012] Preferably, the bottom of the sleeve is conical.

[0013] Preferably, the liquid inlet of the temperature control ring is connected to a liquid nitrogen freezer.

[0014] Preferably, a grouting pipe is detachably connected to the top of the sleeve, the grouting pipe is connected to a peristaltic pump, and the peristaltic pump is connected to a liquid storage tank.

[0015] Preferably, a temperature and humidity sensor is provided on the top of the base.

[0016] Preferably, the temperature and humidity sensor is provided with a plurality of temperature and humidity measuring optical fibers, which are arranged on the top of the base and the inner wall of the temperature control ring, and a temperature insulation coating is provided between the temperature and humidity measuring optical fibers and the inner wall of the temperature control ring.

[0017] Preferably, the water inlet is connected to a water supply device outside the base.

[0018] Preferably, the device also includes a measuring device matching the sleeve, the measuring device includes a pressure sensor, a force gauge and a needle-type test line, the two ends of the needle-type test line are respectively connected to the pressure sensor and the force gauge, and the pressure sensor can extend into the interior of the sleeve.

[0019] Preferably, the through holes on the top cover are distributed in a plurality of rings, and the through holes on each ring are distributed equidistantly.

[0020] The beneficial effects of the utility model are:

[0021] 1. By setting multiple through holes on the top cover, the sleeve is inserted into the soil sample through the through holes of the top cover, and the side wall of the sleeve is provided with multiple through holes, the microbial slurry used for expansive soil reinforcement can be added to the soil sample in layers through the through holes of the sleeve. Because it is layered filling, it can avoid gradual filling from a certain direction. As the filling progresses, the expansive soil expands after infiltration and blocks the subsequent filling, avoiding the problem of difficult or uneven filling of the microbial slurry. Only when the expansive soil is evenly filled can the subsequent measurement results be accurate and meaningful.

[0022] 2. This application proposes a temperature control ring that fits and fixes around the soil sample to freeze or heat the surrounding area of ​​the soil sample at the same time. The annular structure of the temperature control ring takes into account the plane stress condition of the soil sample. In actual engineering, the inferior damage of the soil sample often occurs in the X and Y planes (that is, the horizontal direction). This is an improvement and innovation made for the traditional upper and lower temperature control structures that only consider the stress in the Z direction (vertical direction) of the soil sample (because the traditional temperature control structure is set at the top or top of the soil sample, the force changes measured by the soil sample far away from the temperature control structure are actually caused by the change in its vertical force, rather than the change in the force caused by its own frost heave force change in the horizontal direction), and the measured frost heave force is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 :Structural diagram of this device Figure 1 ;

[0024] Figure 2 :Structural diagram of this device Figure 2 ;

[0025] Figure 3: Schematic diagram of the stainless steel top cover structure;

[0026] Figure 4 a: front view of the sleeve;

[0027] Figure 4 b: side view of the sleeve;

[0028] Figure 5 a: Schematic diagram of microbial grouting;

[0029] Figure 5 b: Schematic diagram of the sleeve and measuring device structure when the soil sample is not expanded;

[0030] Figure 5 c: Schematic diagram of the sleeve and measuring decoration structure when the soil sample expands;

[0031] Figure 6 : Top view of the temperature control ring.

[0032] Label names in the figure:

[0033] 1. Base, 2. Temperature control ring, 3. Sleeve, 4. Top cover, 5. Water inlet, 6. Water supply equipment, 7. Liquid nitrogen freezer, 8. Grouting pipe, 9. Peristaltic pump, 10. Liquid storage tank, 11. Temperature and humidity sensor, 12. Needle test line, 13. Pressure sensor, 14. Dynamometer, 15. Water tank, 16. Water pipe, 17. Water inlet valve, 18. Drain valve. DETAILED DESCRIPTION

[0034] The embodiments of the present invention are described in further detail below in conjunction with the accompanying drawings.

[0035] It should be noted that the terms such as "upper", "lower", "left", "right", "front", "back", etc. used in the utility model are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present utility model without substantially changing the technical content.

[0036] like Figure 1-6 As shown, the present application provides a device for microbial reinforcement of expansive soil and its expansion force and frost heave force measurement, including a base 1, a temperature control ring 2, a sleeve 3 and a top cover 4, the bottom of the temperature control ring 2 is connected to the base 1, the soil sample to be tested is placed in the temperature control ring 2, and the top cover 4 is arranged on the top of the temperature control ring 2. The temperature control ring 2 can be connected to the base 1 through a clamp, and the top cover 4 is also connected to the temperature control ring 2 through a clamp. Of course, it can also be connected in other ways, as long as a sealed connection can be ensured, such as through threaded connections.

[0037] The base 1 is made of phenolic resin, has good thermal insulation performance, and can maintain its structural stability in extremely high or low temperature environments.

[0038] The outer wall of the temperature control ring 2 is provided with a liquid inlet and a liquid outlet; the interior of the temperature control ring 2 is a liquid pipeline spirally stacked into a ring, and the two ends of the liquid pipeline are respectively connected to the liquid inlet and the liquid outlet, and the liquid inlet of the temperature control ring 2 is detachably connected to the liquid nitrogen refrigerator 7, and liquid nitrogen is injected into the temperature control ring 2 through the liquid nitrogen refrigerator 7 to cool the soil sample; when the soil sample needs to be heated to melt it later, the liquid nitrogen refrigerator 7 can be removed, and hot water can be added to the temperature control ring 2 to promote the melting of the soil sample; or hot water can be not added to allow the soil sample to melt naturally at room temperature, depending on the actual situation.

[0039] The temperature control ring 2 fully seals the soil sample on all sides to achieve in-situ freezing of the soil, solving the problem of difficulty in re-sampling after the frozen soil undergoes volume change. The traditional cold bath tray is placed on the upper or lower part of the soil sample. The stress monitored by the soil sample in the cold bath tray is actually the stress caused by the deformation (expansion or contraction) of the soil in the Z direction (vertical direction). It is impossible to accurately obtain the comprehensive stress after the expansion force of this part of the soil sample in the X and Y directions (horizontal directions) and the force in the Z direction, that is, the frost heave force measured by the traditional cold bath tray setting method is not accurate for soil samples far away from the cold bath tray, which will affect the actual effect judgment of the microbial reinforcement effect.

[0040] The liquid nitrogen freezer 7 adopts a machine of model YDD-760-445P, whose surface is made of stainless steel, durable and corrosion-resistant, and the device assists in supplying cold source to the soil. The temperature of liquid nitrogen stored in the liquid nitrogen freezer 7 can be adjusted through the built-in display screen, and its lowest can be adjusted to -200°C, which fully meets the extreme low temperature conditions (-40°C) in the seasonal freezing zone. At the same time, this liquid nitrogen freezer 7 can monitor the internal liquid nitrogen surplus in real time through the display screen to avoid insufficient liquid nitrogen supply during the test.

[0041] The top cover 4 is made of stainless steel, which is mainly rust-proof and corrosion-resistant, and effectively prevents the top cover 4 from being wetted by water, causing the inner wall to undergo an oxidation reaction, that is, being corroded by water to produce oxides, thereby interfering with the urease reaction between microorganisms and soil, and affecting the formation of mineral products with gelling properties in the reinforced soil. Furthermore, the stainless steel top cover is covered on the upper surface of the soil sample, and its rigid material can seal the soil sample, prevent leakage of water and liquid nitrogen, and effectively isolate interference from the external environment.

[0042] The top cover 4 is provided with a plurality of through holes matching the sleeve 3. The through holes on the top cover 4 are distributed in a plurality of rings, and the through holes on each ring are distributed equidistantly (for details, please refer to Figure 6), of course, the through holes on the top cover 4 may also be distributed in a different manner, but it is preferably arranged in this manner. The conduction of the soil's own stress often diffuses from the center of the soil sample to the surrounding areas. Therefore, the holes in the stainless steel top cover are arranged in a circle from the inside to the outside in accordance with this conduction feature, and can evenly and accurately detect the stress distribution inside the soil and the law of force changes; the mineralization products generated inside the microbial reinforced soil, its growth rate, volume, and mineralization range are affected by many factors such as the environment and temperature. The multi-porous structural arrangement of the top cover 4 makes the soil force measuring points more and more uniform, which can effectively solve the problem of inaccurate force measurement values ​​due to different reinforcement degrees of the reinforced soil.

[0043] When the swelling force test of the expansive soil is subsequently carried out, the soil sample needs to be supplied with water from bottom to top. The through hole on the top of the top cover 4 can also facilitate the naked eye observation of whether the height of the water level inside the soil sample meets the test specification requirements (i.e., pure water is injected into the soil sample, so that the water enters the soil body from bottom to top, and the water surface is kept about 5 mm higher than the soil sample).

[0044] The sleeve 3 is inserted into the soil sample through the through hole on the top cover 4 for subsequent microbial slurry injection and expansion force and frost heave force measurement. The sleeve 3 is always inserted in the soil sample and does not move during the filling and measurement process to avoid disturbing the soil sample and affecting the measurement results.

[0045] The side wall of the sleeve 3 is provided with a plurality of through holes, and the bottom of the sleeve 3 is sealed. In this way, the microbial slurry is injected into the sleeve 3, and the microbial slurry is then injected into the soil sample through the through holes on the side wall of the sleeve 3 (the grouting process can be referred to Figure 5 a); the bottom of the sleeve 3 is conical, which facilitates its insertion into the soil sample; the through hole on the side wall of the sleeve 3 can refer to Figure 4 a and Figure 4 b, that is, a row of through holes evenly arranged from top to bottom are provided on the left and right side walls of the sleeve 3. Of course, the through holes do not have to be arranged in this way, as long as enough through holes are provided, uniform grouting into the soil sample can be achieved.

[0046] The sleeve 3 is made of nylon plastic material, which has strong wear resistance and plasticity, and has a certain degree of scalability. In this way, during the expansion or contraction of the soil sample, the sleeve 3 will shrink or restore its original state (the state before being squeezed and shrunk) at any time due to the change of the squeezing force of the surrounding soil sample. The above process can be referred to Figure 5 b and Figure 5c; in this way, a measuring device can be inserted into the sleeve 3 to measure the expansion force or frost heave force; the device also includes a measuring device matched with the sleeve 3, the measuring device includes a pressure sensor 13, a force gauge 14 and a needle-type test line 12, the two ends of the needle-type test line 12 are respectively connected to the pressure sensor 13 and the force gauge 14, the pressure sensor 13 can be extended into the sleeve 3, the expansion force and frost heave force are tested by the pressure sensor 13, the needle-type test line 12 is equivalent to the data line and the power supply line, and the force gauge 14 displays the test results; during the test, the expansion force and frost heave force of soil samples at different depths can be tested by adjusting the depth of the pressure sensor 13 in the sleeve 3.

[0047] The needle-type test line 12 adopts the model 9465-10 needle-type test line, which is easy to insert into the above-mentioned slender sleeve to reduce the impact on the inside of the soil sample; a pressure sensor 13 is provided on the outside of the needle-type probe at the front end of the needle-type test line 12. When the expansive soil expands when encountering water, shrinks when losing water, and changes its volume due to "freezing, heaving, thawing and sinking", the internal soil particles are squeezed, and the squeezing sleeve 3 shrinks it, thereby applying plane stress to the pressure sensor 13, transmitting the signal to the terminal dynamometer 14 to measure the self-stress of the soil.

[0048] The needle probe at the front end of the needle test line 12 and the pressure sensor 13 can also be wrapped with a plastic insulation layer to protect the sensor from the influence of moisture and temperature, ensuring that the sensor accurately transmits dynamic signals; a rubber ring is sleeved between the contact surface of the needle test line 12 and the top cover 4, which can further ensure the airtightness of the soil sample device.

[0049] The pressure sensor 13 adopts the model AE-S, with a measurement range of -0.1-6000 (kPa) and an accuracy level of 0.5. When the soil sample is not filled with water and frozen, the pressure sensor 13 is in contact with the inner wall of the sleeve but the two will not be squeezed, so as to ensure that the pressure sensor 13 is not disturbed by the contact and squeezing of the sleeve 3 at the beginning of the test, so that the force measurement value is accurate; the pressure sensor 13 can be used between -40℃ and 120℃, and can withstand the ultra-low temperature liquid nitrogen transportation of the liquid nitrogen freezer; further, the surface of the pressure sensor 13 has waterproof and dustproof properties, which can avoid the interference caused by water infiltration of the soil.

[0050] The dynamometer adopts the model SGLF, with a measuring range of up to 500KN and a measuring accuracy of 3%. The needle-type test line 12 is connected to the dynamometer 14, and the front-end pressure sensor 13 transmits a signal to the terminal dynamometer 14 through the transmission line after being squeezed by the soil body, so as to display the frost heave force and expansion force of the expansive soil.

[0051] The top of the sleeve 3 is detachably connected to a grouting pipe 8, which is connected to a peristaltic pump 9, which is connected to a liquid storage tank 10. The liquid storage tank 10 stores microbial slurry to be filled. The microbial slurry in the liquid storage tank 10 is extracted by the peristaltic pump 9 and then output to the sleeve 3 through the grouting pipe 8 to add the microbial slurry to the soil sample. When the grouting is completed, the grouting pipe 8 can be drawn out, and when the set time comes, the corresponding test can be carried out after the microorganisms complete the reinforcement of the soil sample. A sealing ring can be provided between the grouting pipe 8 and the top of the sleeve 3 to prevent the microbial slurry from overflowing during the filling process.

[0052] The peristaltic pump 9 adopts model BF600-1C and has multiple channels to realize simultaneous grouting. The microbial reaction liquid passes through the peristaltic pump and the grouting pipe to realize grouting reinforcement of the soil; the peristaltic pump can adjust the grouting rate and the pressure of the slurry release according to actual needs to ensure that the microbial reaction liquid can evenly penetrate into the soil sample.

[0053] A water inlet 5 is provided at the bottom of the base 1, and the water inlet 5 runs through the top of the base 1. The water inlet 5 is connected to a water supply device 6 outside the base 1. The water supply device 6 injects water into the soil sample through the water inlet 5 to achieve infiltration of the soil sample so as to measure its expansion force.

[0054] The water supply device 6 includes a water tank 15 and a water pipe 16. The water pipe 16 is arranged at the bottom of the water tank 15. The lower side of the water pipe 16 is connected to the water inlet 5. The lower side of the water pipe 16 is also provided with a fork for drainage (see Figure 1 and Figure 2 ), the water tank 15 is placed on the bracket, the height of the water tank 15 is the height of the top cover 4, and the height of the bifurcation is not higher than (preferably lower than) the height of the bottom of the water inlet 5; the water pipe 16 is provided with an inlet valve 17 above the bifurcation, and a drain valve 18 below the bifurcation. When it is necessary to inject water into the soil sample, the inlet valve 17 is opened and the drain valve 18 is closed; after the water injection is completed, the inlet valve 17 is also closed, and when it is necessary to drain water, only the drain valve 18 is opened.

[0055] A temperature and humidity sensor 11 is provided on the top of the base 1, and the temperature and humidity sensor 11 is provided with a plurality of temperature and humidity measuring optical fibers. The temperature and humidity measuring optical fibers are arranged on the top of the base 1 and on the inner wall of the temperature control ring 2. The temperature and humidity measuring optical fibers arranged on the top of the base 1 should be away from the water inlet 5 to avoid causing excessive errors in the humidity measurement of the soil sample; a temperature insulation coating is provided between the temperature and humidity measuring optical fiber and the inner wall of the temperature control ring 2. The temperature insulation coating is provided between the two to prevent the liquid nitrogen or hot water in the temperature control ring 2 from affecting the measurement results of the temperature and humidity measuring optical fiber.

[0056] The temperature and humidity sensor 11 adopts a sensor of model YGC-TS, which is an all-in-one soil sensor that can simultaneously measure the volumetric moisture content and temperature of the soil. It has the advantages of being waterproof, corrosion-resistant, and highly accurate, and is suitable for measuring special soils such as frozen soil. The temperature and humidity sensor 11 is used to monitor the temperature / humidity inside the soil sample when the expansive soil undergoes dry, wet, frozen, and thaw stages, and to measure the temperature / humidity changes inside the soil body at each stage to determine whether it meets the actual working conditions on site. In conjunction with the pressure sensor 13 and the dynamometer 14, the relationship data and fitting curve of the frost heave force of the expansive soil changing with temperature can be obtained.

[0057] The temperature and humidity measuring optical fiber model is YP-T-30-01, with a temperature measurement range of -60 to 150°C (long-term temperature resistance of 150°C, short-term temperature resistance of 200°C), and a humidity measurement range of 15 to 95RH%, which can accurately measure changes in the temperature field and moisture field inside the soil.

[0058] The present application provides a method for using a device for microbial reinforcement of expansive soil and its expansion force and frost heave force measurement, comprising the following steps:

[0059] S1. First, prepare soil samples by layered compaction method according to geotechnical test standards; place the soil samples in a temperature control ring inlaid with temperature and humidity optical fiber; then, place the soil samples with temperature control rings fixed around them on the base and fix them with clamps on both sides of the base.

[0060] S2. First place the stainless steel top cover on top of the soil sample, and fix it with the clamps on both sides and the temperature control ring around the soil sample; align the sleeve with the hole on the surface of the stainless steel top cover, and insert it into the soil through the hole; connect one end of the liquid inlet pipe to the liquid nitrogen freezer, and the other end to the liquid inlet of the temperature control ring; connect the water inlet on the base and the water tank through a water pipe.

[0061] S3. Perform microbial grouting on the expansive soil sample. Connect one end of the grouting tube to the peristaltic pump and place the other end in the sleeve. Turn on the peristaltic pump and perform microbial grouting at a certain grouting speed. After each grouting, let it stand for 6 to 12 hours to complete a round of grouting. Repeat the above steps for multiple rounds of grouting until the target number of grouting times is reached. Turn off the peristaltic pump, take out the grouting tube in the sleeve, and keep the sleeve inserted into the soil and keep it still.

[0062] S4. Dry-wet-freeze-thaw coupled cycle of microbial reinforced soil samples:

[0063] First, the soil sample goes through a "wet stage" and its expansion force is measured at the same time. The water inlet valve is opened to supply water to the soil sample to soak the expansive soil sample to reach a "wet" state. The height of the water level is observed through the hole in the stainless steel top cover. When the water level is submerged about 5 mm below the soil sample, the water inlet valve is closed. Next, the needle-type probe at the front end of the needle-type test line is inserted into the rubber ring. The needle-type probe is connected to a pressure sensor and then aligned with the hole in the stainless steel top cover and inserted into the internal sleeve. The end of the needle-type test line is connected to the force gauge and the force gauge is turned on.

[0064] Expansive soil expands when it meets water, and the soil particles are squeezed inside, applying plane stress to the pressure sensor outside the needle probe. The initial expansion force reading of the soil sample is recorded, and the expansion force reading is measured every 1 to 2 hours. If the reading change of the soil sample during the interval is less than 1%, it means that the soil sample is no longer expanding. At this time, the pressure sensor measures the maximum expansion force under the humidity. The moisture inside the soil sample is monitored in real time by using temperature and humidity optical fiber and temperature and humidity sensors, and the moisture changes of the expansive soil sample during the test are recorded throughout the process.

[0065] If the soil sample has not reached a completely saturated state, the above steps can be repeated until the soil sample reaches a completely saturated state, the needle-type test wire is removed, and the expansion force test is stopped.

[0066] S5. The soil sample goes through the "drying stage". (The water inlet valve is in the closed state) Open the drain valve on the drain pipe to drain the water inside the soil sample, simulating the natural drying state of the expansive soil sample. According to the actual working conditions of frozen soil in seasonally frozen areas, refer to the average saturation of expansive soil at different depths on site, and set the change of soil sample drying amplitude to be achieved by drying to the specified saturation (such as 70% drying amplitude corresponds to 30% soil sample saturation). During the soil sample drying stage, the temperature and humidity sensor monitors the saturation change inside the sample, and the drying process stops when the target saturation is reached.

[0067] S6. The soil sample undergoes a “freezing stage” and its frost heave force is measured:

[0068] Manually open the liquid nitrogen freezer, adjust the temperature of the liquid nitrogen according to the actual working conditions in the seasonal freezing zone, and let the liquid nitrogen flow through the temperature control ring to make the soil sample feel ultra-low temperature around it to freeze the soil sample. The freezing time is 12 to 15 hours. During this period, record the frost heave force reading of the soil sample at the beginning of freezing, and measure and record the reading every 1-2 hours. When the soil sample reading changes by less than 1%, its maximum frost heave force can be obtained. The internal temperature of the soil sample is monitored by temperature and humidity optical fiber and temperature and humidity sensor, and the temperature change of the expansive soil sample during the test is recorded throughout the test, so as to obtain the relationship data of frost heave force with temperature. When the internal temperature of the soil sample reaches the target value, the liquid nitrogen freezer is turned off to stop the freezing process.

[0069] S7. Thawing of soil samples: Place the soil samples at room temperature for natural thawing (or add hot water of appropriate temperature (set according to actual conditions) into the temperature control ring). The thawing time is 12 to 24 hours. Changes in soil sample stress can also be continuously detected during the thawing process. After completing all the above operations, dismantle the entire device and the test is completed.

[0070] The above are only preferred implementations of the utility model. The protection scope of the utility model is not limited to the above embodiments. All technical solutions under the idea of ​​the utility model belong to the protection scope of the utility model. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the utility model.

Claims

1. A device for microbial reinforcement of expansive soil and measuring its expansion force and frost heave force, characterized in that: The invention comprises a base (1), a temperature control ring (2), a sleeve (3) and a top cover (4); the bottom of the temperature control ring (2) is connected to the base (1), and the soil sample to be tested is placed in the temperature control ring (2); the bottom of the base (1) is provided with a water inlet (5), and the water inlet (5) passes through the top of the base (1); the top cover (4) is arranged on the top of the temperature control ring (2), and the top cover (4) is provided with a plurality of through holes matching the sleeve (3); the side wall of the sleeve (3) is provided with a plurality of through holes, and the bottom of the sleeve (3) is sealed; the sleeve (3) is made of nylon plastic.

2. A device for measuring the microbial reinforcement of expansive soil and its expansion force and frost heave force according to claim 1, characterized in that: The outer wall of the temperature control ring (2) is provided with a liquid inlet and a liquid outlet; the interior of the temperature control ring (2) is a liquid pipeline stacked in a spiral shape into a ring, and the two ends of the liquid pipeline are respectively connected to the liquid inlet and the liquid outlet.

3. A device for microbial reinforcement of expansive soil and its expansion force and frost heave force measurement according to claim 1, characterized in that: The bottom of the sleeve (3) is conical.

4. A device for microbial reinforcement of expansive soil and its expansion force and frost heave force measurement according to claim 2, characterized in that: The liquid inlet of the temperature control ring (2) is detachably connected to the liquid nitrogen freezer (7).

5. The device for microbial reinforcement of expansive soil and its expansion force and frost heave force measurement according to claim 1, characterized in that: The top of the sleeve (3) is detachably connected to a grouting pipe (8), the grouting pipe (8) is in communication with a peristaltic pump (9), and the peristaltic pump (9) is connected to a liquid storage tank (10).

6. A device for microbial reinforcement of expansive soil and measuring its expansion force and frost heave force according to claim 1, characterized in that: A temperature and humidity sensor (11) is provided on the top of the base (1).

7. A device for microbial reinforcement of expansive soil and measuring its expansion force and frost heave force according to claim 6, characterized in that: The temperature and humidity sensor (11) is provided with a plurality of temperature and humidity measuring optical fibers, the temperature and humidity measuring optical fibers being arranged on the top of the base (1) and on the inner wall of the temperature control ring (2), and a temperature insulation coating being provided between the temperature and humidity measuring optical fibers and the inner wall of the temperature control ring (2).

8. The device for microbial reinforcement of expansive soil and its expansion force and frost heave force measurement according to claim 1, characterized in that: The water inlet (5) is in communication with a water supply device (6) outside the base (1).

9. The device for microbial reinforcement of expansive soil and its expansion force and frost heave force measurement according to claim 1, characterized in that: The device also includes a measuring device matched with the sleeve (3), the measuring device including a pressure sensor (13), a force gauge (14) and a needle-type test line (12), the two ends of the needle-type test line (12) being respectively connected to the pressure sensor (13) and the force gauge (14), and the pressure sensor (13) being able to extend into the interior of the sleeve (3).

10. The device for microbial reinforcement of expansive soil and measurement of its expansion force and frost heave force according to claim 1, characterized in that: The through holes on the top cover (4) are distributed in a plurality of rings, and the through holes on each ring are distributed equidistantly.

Images