CN112746607A - Equipment and method for reinforcing foundation by inducing calcium carbonate precipitation through electroosmosis and microorganisms - Google Patents
Equipment and method for reinforcing foundation by inducing calcium carbonate precipitation through electroosmosis and microorganisms Download PDFInfo
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- CN112746607A CN112746607A CN202110042721.9A CN202110042721A CN112746607A CN 112746607 A CN112746607 A CN 112746607A CN 202110042721 A CN202110042721 A CN 202110042721A CN 112746607 A CN112746607 A CN 112746607A
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
- E02D3/12—Consolidating by placing solidifying or pore-filling substances in the soil
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
- E02D3/11—Improving or preserving soil or rock, e.g. preserving permafrost soil by thermal, electrical or electro-chemical means
Abstract
The invention provides equipment and a method for reinforcing a foundation by inducing calcium carbonate precipitation through electroosmosis and microorganism combination. The device and the method realize the drainage consolidation of the soil body through an electroosmosis system and drive the microorganisms to move in the soil body; the supply of the microorganism liquid and the cementing liquid is ensured through a grouting system; the design of the monitoring and control system realizes the real-time control of the system pH and the soil body temperature in the combined reinforcement process, and inhibits the reduction of the microbial activity. The device and the method provided by the invention can be used for researching the action mechanism of the electroosmosis drainage combined MICP for reinforcing the foundation, optimizing the reinforcing method and evaluating the reinforcing effect, provide a new technical choice for reinforcing the soft soil, and have very important significance for the relevant research and the field application of the propulsion electroosmosis combined microorganism for reinforcing the foundation.
Description
Technical Field
The invention relates to the field of soft soil foundation reinforcement, in particular to a device and a method for reinforcing a foundation by electroosmosis and microorganism induction calcium carbonate precipitation.
Background
With the increase of population and the continuous promotion of urbanization in China, the demand of human living and other purposes on land is continuously increased. At present, a large amount of engineering construction land has the problem of insufficient bearing capacity, and must be reinforced before construction so as to meet engineering requirements.
The existing foundation treatment methods, such as a dynamic compaction method, a compaction pile method and the like, have high construction cost and large disturbance to the surrounding soil body, and have the problem of difficult approach in large-area and high-depth field application because large machines are required in the foundation reinforcement process. The vacuum preloading method is an effective soft soil foundation reinforcing method, but the drainage plate can be gradually blocked along with the proceeding of consolidation drainage, so that the reinforcing effect is limited. Cement grouting is commonly used to reinforce sandy soils. When it is used for reinforcing soft soil foundation, high grouting pressure is often required due to high viscosity of cement paste, and there is a problem in that the grout is difficult to spread and migrate. Although the chemical grouting has good groutability, the grouting materials such as epoxy resin, polyurethane, acrylamide and the like contain undesirable components which cause serious pollution to the environment and even threaten human health.
The electroosmosis method is an effective soft soil foundation reinforcing method. The electric field is applied to the two ends of the soil body to enable the cations to drag water molecules to move towards the cathode, so that electroosmotic seepage is formed and the water molecules are discharged from the soil body, and effective foundation reinforcement is realized. However, the conventional electroosmosis method easily causes uneven foundation reinforcement. Because the pore water mainly flows from the anode to the cathode, the water content of the soil body near the anode is lower, and the water content of the soil body near the cathode is higher, so that the strength of the soil body near the anode is larger than that of the soil body near the cathode.
Microorganism induced calcium carbonate precipitation (MICP) is a new green and efficient soil body reinforcement technology which is emerging in recent years. The method utilizes the activity of microorganisms to decompose organic matters to generate carbonate and an alkaline environment, can generate calcium carbonate in the environment with calcium ions, fills the pores of the soil body and forms cementation among the soil particles, thereby improving the strength of the soil body. Generally, microorganisms have negative charges, and cells move from the cathode to the anode in a directional manner under the action of an electric field. Therefore, the combination of the MICP technology and the electroosmotic reinforcement technology is expected to effectively improve the strength of the soil body near the cathode.
The invention provides a device and a method for reinforcing a foundation by combining electroosmosis with MICP by designing an electroosmosis system, a grouting system and a monitoring and control system. The key points are the combination of an electroosmosis reinforcement method and a MICP method and the real-time monitoring and control of the temperature and the pH value of the soil body. The device can realize the combined action of electroosmosis and MICP, and can control the pH value of the system and the temperature of the soil body in real time in the whole experiment process, so that microorganisms can maintain higher activity in the whole reinforcing process. The method for reinforcing the foundation by combining the electroosmosis with the MICP is a new technical scheme in the field of foundation reinforcement, provides a new choice for improving the soft soil foundation, and provides a research foundation for the development of the technology for reinforcing the soft soil foundation by combining the electroosmosis with the MICP.
Disclosure of Invention
The invention provides equipment and a method for reinforcing a foundation by inducing calcium carbonate precipitation through electroosmosis and microorganisms, aiming at the problem of non-uniformity of the existing electroosmosis reinforced soil body. The device can realize the combined action research of electroosmosis and MICP. The experimental method provided by the invention has a very strong guiding significance for exploring the action mechanism of the combined reinforcement technology.
The technical scheme of the invention is as follows:
an electroosmosis combined microorganism induced calcium carbonate precipitation device for reinforcing a foundation comprises an electroosmosis system, a grouting system and a monitoring and control system; the electroosmosis system is mainly used for discharging pore water of the soil body and driving biological-chemical ions to move in the soil body; the grouting system is used for providing microorganism liquid, cementing liquid and pH buffer liquid; the monitoring and control system is mainly used for controlling the pH value of the system and the temperature of the soil body, analyzing the evolution of the biochemical-mechanical properties of the soil body in the reinforcing process and after the reinforcement is finished, and exploring the action mechanism of reinforcing the soft soil foundation by combining electroosmosis with MICP;
the electroosmosis system comprises a sample cavity 1, an anode cavity 3, a cathode cavity 2, a partition plate 4 with a drainage hole, an anode plate 5, a cathode plate 6, a power supply 10, a lead 11 and an overflow port; the sample cavity 1, the cathode cavity 2 and the anode cavity 3 are all made of organic glass plates; the sample cavity 1 is a cuboid and is used for containing soft soil to be reinforced; the cathode cavity 2 and the anode cavity 3 are respectively positioned at two sides of the sample cavity 1 and are separated by a partition plate 4 with a drainage hole; the cathode cavity 2 contains an injection liquid mainly comprising a bacterial liquid, and the anode cavity 3 contains a cementing liquid to be injected and is also used for buffering and collecting pore water discharged from a soil body under the action of an electric field; through holes with the diameter of 5mm are uniformly distributed on the partition plate 4 with the drainage holes and are used as liquid circulation channels; the anode plate 5 and the cathode plate 6 are respectively arranged in the anode cavity 3 and the cathode cavity 2 and are respectively tightly attached to the inner end surfaces of the anode cavity and the cathode cavity, and the inner end surfaces are end surfaces far away from the sample cavity; the two electrode plates are respectively connected with a power supply 10 through leads 11; the power supply 10 applies an electric field to two ends of the soil body through the electrode plates to drive cations in the soil body to drive pore water to move to the cathode plate 6; in addition, the voltage and the current provided by the power supply 10 are both adjustable, and the power supply can be used for research on reinforcing soft soil foundation by combining electroosmosis drainage and MICP under different voltage and current conditions; an overflow port is arranged at the position, close to the top, of the outer side of the cathode cavity 2, along with the increase of pore water discharged from a soil body and the continuous injection of microbial liquid in the cathode cavity 2, the amount of liquid in the cathode cavity 2 is increased, and when the liquid level exceeds the overflow port, redundant liquid flows out of the overflow port and flows into the measuring cylinder 24 through the rubber hose 23; the overflow port is arranged to prevent the liquid in the liquid outlet cavity from overflowing the sample cavity 1; similarly, the outer side of the anode cavity 3 is also provided with an overflow port to prevent the cementing liquid injected into the anode cavity 3 from overflowing the sample cavity 1 due to excessive cementing liquid;
the monitoring and control system comprises a pH sensor 18, a pH acquisition module 19, a voltage acquisition module 13, a current acquisition module 14, a temperature acquisition module 17, a current and voltage measurement hole 12, a temperature measurement hole 15, a pagoda joint, a temperature measurement lead 16, a low-resistance measuring needle and a PC terminal 20; one side wall of the sample cavity 1 is provided with two rows of through holes which are respectively a current and voltage measuring hole 12 and a temperature measuring hole 15, and a hollow pagoda joint is screwed in the through holes; one end of a temperature measuring lead 16 is inserted into the soil body through a temperature measuring hole 15, and the other end is connected with a temperature acquisition module 17; the temperature acquisition module 17 is connected with the PC terminal 20 through a signal converter and transmits acquired temperature data to the PC terminal 20; one end of the low-resistance measuring probe is inserted into the soil body through a current and voltage measuring hole 12, and the other end of the low-resistance measuring probe is connected with a voltage acquisition module 13 and a current acquisition module 14 through leads 11 respectively and is used for acquiring the change conditions of voltage and current in the experimental process in real time; the voltage acquisition module 13 and the current acquisition module 14 are connected with the PC terminal 20 through signal converters, and transmit current and voltage data to the PC terminal 20; one end of a pH sensor 18 is arranged in the cathode cavity 2, and the other end of the pH sensor is connected with a pH acquisition module 19 to acquire the pH change condition of the solution in the cathode cavity 2 in real time; the pH acquisition module 19 is connected with the PC terminal 20 through a signal converter and transmits pH data acquired by the pH sensor 18 in the test process to the PC terminal 20; the monitoring and control system can monitor and collect the voltage, current, temperature and pH of the effluent liquid in the experimental process in real time. The monitoring and control system is cooperated with the grouting system to realize real-time control of system pH and soil body temperature, and provide more appropriate environmental conditions for the electroosmosis combined with MICP to reinforce soft soil foundation.
The grouting system comprises a peristaltic pump 25, a chemical liquid reservoir 28, a microorganism liquid reservoir 30, a buffer liquid reservoir 31, a cold and hot water reservoir 29, a rubber hose 23, a water stop valve 27, a temperature control tank 7, a temperature control tank filling opening 8 and a temperature control tank water outlet 9; the microbial liquid reservoir 30 stores cultured bacterial liquid to provide thalli or urease for MICP, so that the urea decomposition is continuously carried out in the experimental process; connecting a microorganism liquid reservoir (30) with the cathode cavity (2) through a rubber hose (23), wherein the rubber hose (23) passes through a pump head of the peristaltic pump (25); the peristaltic pump 25 pumps the fluid by alternately squeezing and releasing the elastic delivery rubber hose 23; the peristaltic pump 25 can control the grouting rate, can make the microbiological liquid supplement to the positive pole cavity 3 continuously according to the grouting rate presumed; a buffer liquid reservoir 31 for storing the pH buffer liquid is connected with the peristaltic pump 25, and the pH buffer liquid is continuously injected into the cathode cavity 2 through the peristaltic pump 25, so that the pH of the cathode cavity 2 and soil body near the cathode is kept between 9 and 10; the cementing liquid reservoir is used for storing cementing liquid, is connected with the peristaltic pump 25 through a rubber hose 23 and is further connected with the anode cavity 3, so that calcium ions are continuously provided for the soil body, and the substrate supply of the MICP reaction is ensured; the cold and hot water reservoir 29 is connected with the peristaltic pump 25 through the rubber hose 23; the other side of the peristaltic pump 25 is connected with the temperature control tank 7 through a rubber hose 23 to provide circulating cold water or hot water for the temperature control tank 7; two peristaltic pumps 25 are arranged, wherein one peristaltic pump 25 is used for providing the anode cavity 3 with microorganism liquid and pH buffer solution, and the other peristaltic pump 25 is used for providing the cathode cavity 2 and the temperature control tank 7 with cementing liquid and cold and hot water; the peristaltic pump 25 is connected with the PC terminal 20 through a signal converter; after receiving the real-time pH data transmitted by the pH acquisition module 19, the PC terminal 20 analyzes the real-time pH data; under the action of an electric field, water electrolysis can occur at the cathode to generate hydroxide ions, so that the pH value of the cathode solution is increased; when the pH value of the solution in the cathode cavity 2 exceeds a set pH limit value, a water stop valve 27 of a pH buffer solution is closed, the pH buffer solution is injected into the anode cavity 3, and the pH value of the solution in the cathode cavity 2 is reduced to keep the pH value in a range suitable for the growth of microorganisms; the PC terminal 20 processes the temperature data transmitted by the temperature acquisition module 17, when the soil body temperature exceeds 30 ℃, the water stop valve 27 connected with the cold and hot water liquid reservoir 29 is closed, cold water is injected into the temperature control tank 7, when the temperature in the soil body is reduced to 30 ℃, the water stop valve 27 on the cold and hot water liquid reservoir 29 is opened, and water in the temperature control tank 7 is discharged, so that the soil body temperature is always kept in a range suitable for the growth of microorganisms; the peristaltic pump 25 adopts a multi-channel pump head to realize simultaneous and time-sharing grouting of different solutions.
A method for reinforcing a foundation by calcium carbonate precipitation induced by electroosmosis combined with microorganisms comprises the following steps:
firstly, soft soil to be reinforced is placed in a sample cavity 1, so that the uniformity of a soil sample is ensured; standing for a certain time to naturally solidify and drain the soil body; monitoring the solution in the anode cavity 3 and the cathode cavity 2, and stopping consolidation when the volume of the solution is not changed any more; closing the water stop valve 27, opening the peristaltic pump 25, and respectively injecting microbial liquid and cementing liquid into the cathode cavity 2 and the anode cavity 3; the microorganism is Pasteurella multocida, and the concentration of the bacterial liquid is determined by Optical Density (OD) at 600nm600To measure; the cementing liquid consists of 1M of urea and calcium nitrate; when the liquid levels of the solutions in the anode cavity 3 and the cathode cavity 2 reach the overflow port, the power supply 10 is turned on, an electric field is applied to two ends of the soil body, and drainage consolidation is started; under the action of the electric field, microorganisms in the cathode cavity 2 and calcium ions in the anode cavity 3 respectively move to the anode and the cathode under the action of the electric field; after the experiment begins, the pH acquisition module 19, the temperature acquisition module 17, the voltage acquisition module 13 and the current acquisition module 14 are communicated to collect data of pH, temperature, voltage and current of the soil body and the solutions in the anode cavity 3 and the cathode cavity 2 in the experiment process in real time; setting the pH threshold value of the cathode cavity 2 to be 10, closing a water stop valve 27 of a pH buffer solution when the pH value of the solution in the cathode cavity 2 exceeds 10, and injecting the pH buffer solution into the cathode cavity 2 through a peristaltic pump 25 to keep the pH value of the soil body in the cathode cavity 2 and the soil body near the cathode between 9 and 10; setting the soil temperature threshold value to be 30 ℃, closing the cold and hot water stop valve 27 when the soil temperature exceeds 30 ℃, and injecting cold water into the temperature control tank 7 through the peristaltic pump 25 until the soil temperature is kept at 30 ℃; opening the water stop valve 27, stopping water injection, and discharging water in the temperature control tank 7; after the test is finished, the power supply 10 is turned off, and the temperature measuring lead and the low-resistance measuring pin are taken out; then measuring the shearing strength at different positions of the reinforced soil by using a cross plate shearing instrument; sampling and drying after the determination is finished to determine the water content of the soil body;
the method for calculating the water content of the soil body comprises the following steps
Wherein w is the water content, mwAfter the strength measurement, the weight of the sample taken at the strength measurement position is measured; m isdAfter the strength is measured, the weight of the sample taken at the strength measuring position after drying;
in addition, crushing the dried soil sample, mixing the soil sample and water according to the mass ratio of 1:5, and fully mixing for 2 hours in an automatic mixer to prepare uniform slurry; centrifuging the slurry in a centrifuge at 8000r/min to obtain supernatant; taking the centrifuged supernatant, and measuring the pH value and the conductivity of the supernatant by using a pH meter and a conductivity meter; another certain amount of supernatant is taken, and the calcium ion content is measured by an ion chromatograph; and then analyzing the action mechanism of the electroosmosis combined MICP for reinforcing the soil body, and evaluating the improvement effect of the electroosmosis combined MICP reinforcing method on the soft soil foundation.
The invention has the beneficial effects that: the electroosmosis combined microorganism reinforcing device and the method provided by the invention combine the action mechanism of electroosmosis drainage and MICP, and realize the synergistic action of drainage consolidation and MICP. Compared with the traditional electroosmosis equipment, the device provided by the invention can inject microorganism liquid and cementing liquid into the soil body while performing electroosmosis drainage reinforcement, so that MICP is generated in the soil body, calcium carbonate is generated, pores of the soil body are filled, and the strength of the soil body is improved. The specially designed pH and temperature monitoring and control system can acquire and control the pH and soil temperature of the system in real time, and solves the problem that the higher pH and the higher soil temperature of the cathode inhibit the activity of microbial urease in the electroosmosis process. The method provided by the invention can be used for researching the action mechanism of reinforcing the soft soil foundation by the electroosmosis combined with the MICP, evaluating the improvement effect of the electroosmosis combined with the MICP reinforcing method on the soft soil foundation and providing a foundation and a reference for popularizing the application of reinforcing the soft soil foundation by the electroosmosis combined with the MICP method in practical engineering.
Drawings
FIG. 1 is a front view of an electroosmotic system of the apparatus of the invention;
FIG. 2 is a top view of the apparatus of the present invention;
FIG. 3 is a side view of a sample cartridge spacer in the apparatus of the present invention;
FIG. 4 is a front view of a grouting system of the apparatus of the present invention;
FIG. 5 is a front view of the temperature control system of the apparatus of the present invention.
In the figure: 1, a sample box; 2 a cathode cavity; 3 an anode cavity; 4, a clapboard with a drainage hole; 5, an anode plate; 6, a cathode plate; 7, a temperature control groove; 8, controlling the water injection port of the tank by the temperature; 9, controlling the water outlet of the tank by temperature; 10, a power supply; 11 a conductive line; 12 current voltage measurement holes; 13 a voltage acquisition module; 14, a current acquisition module; 15 temperature measuring holes; 16, measuring the temperature of a conducting wire; 17 a temperature acquisition module; 18 a pH sensor; a 19pH acquisition module; 20PC terminals; 21 an overflow port of the anode cavity; 22 cathode chamber overflow port; 23 rubber hose; 24 measuring cylinder; 25 peristaltic pumps; 26 rubber hose matched with peristaltic pump; 27 a water stop valve; 28 a chemical liquid reservoir; 29 cold and hot water reservoirs; 30 a microbial reservoir; 31 buffer reservoir.
Detailed Description
In order to make the technical solutions of the present invention better understood, those skilled in the art will make the present invention more detailed with reference to the accompanying drawings and the detailed description.
The invention discloses equipment and a method suitable for electroosmosis combined with MICP to reinforce a foundation. The equipment comprises an electroosmosis system, a grouting system and a monitoring and control system.
As shown in fig. 1 to 5, the electroosmosis system includes a sample chamber 1, a cathode chamber 2, an anode chamber 3, a partition plate 4 with a drain hole, an anode plate 5, a cathode plate 6, a power supply 10, a lead wire 11, an anode chamber overflow port 21, a cathode chamber overflow port 22, a rubber hose 23, and a measuring cylinder 24. Sample chamber 1 is made by the organic glass board, and the shape is the cuboid, and the size is 254mm x 50mm x 100mm for hold the soft soil of treating the reinforcement. The two sides of the sample cavity 1 are respectively a cathode cavity 2 and an anode cavity 3 which are both made of organic glass plates, and the size is 50mm multiplied by 100 mm. Wherein the cathode cavity 2 holds the microorganism liquid to be injected into the soil body. Besides the cementing liquid to be injected into the soil body, the anode cavity 3 is also used for buffering and collecting pore water discharged from the soil body under the action of an electric field. The sample cavity 1 and the cathode cavity 2, a partition plate 4 made of organic glass plate is respectively used between the sample cavity 1 and the anode cavity 3, and through holes 34 with the diameter of 5mm are uniformly distributed on the partition plate 4 with the drainage hole and are used as water flow channels. The anode plate 5 and the cathode plate 6 are both made of titanium alloy materials, have the same size as the partition plate, and are respectively arranged on one sides, far away from the sample box 1, in the anode cavity 3 and the cathode cavity 2. The two electrode plates are respectively connected with a power supply through leads 11. The voltage and current provided by the power supply 10 are both adjustable, the maximum voltage is 24V, and the maximum current is 3A. And overflow ports with the diameter of 7mm are respectively arranged at the middle positions 3cm away from the top outside the cathode cavity 2 and the anode cavity 3 and are respectively a cathode cavity overflow port 22 and an anode cavity overflow port 21. A pagoda joint with the large diameter end and the outer diameter of 6.9mm is screwed into the overflow port, and the small diameter end of the pagoda joint is connected with a rubber hose 23 and used for discharging redundant solution in the two chambers. The drained solution is collected with a measuring cylinder 24.
The monitoring system comprises a current and voltage measuring hole 12, a voltage collecting module 13, a current collecting module 14, a temperature measuring hole 15, a temperature measuring lead 16, a temperature collecting module 17, a pH sensor 18, a pH collecting module 19 and a PC terminal 20. 5 temperature measuring holes 15 with the diameter of 10mm and the distance of 50mm are uniformly arranged on a lateral panel of the sample chamber 1, wherein the distance between the temperature measuring holes 15 and the bottom plate is 20mm, and a pagoda joint is screwed into each temperature measuring hole 15 and is used as a channel of a temperature measuring lead for measuring temperature. One end of the temperature measuring lead 16 is inserted into the soil body through the temperature measuring hole 15, and the other end is connected with the temperature acquisition module 17 and used for acquiring the soil body temperature in the test process in real time. The temperature acquisition module 17 is connected with the PC terminal 20 through a signal converter, and transmits the acquired temperature data to the PC terminal 20. Similarly, 5 current and voltage measuring holes 12 with the diameter of 6mm are arranged on the lateral panel of the sample cavity 1 at a distance of 45mm from the bottom plate, and pagoda joints are screwed into the current and voltage measuring holes 12 to be used as voltage and current measuring channels. The low-resistance measuring needle is inserted into the soil body through the current and voltage measuring hole, and the other end of the low-resistance measuring needle is connected with the current acquisition module 14 and the voltage acquisition module 13 and used for acquiring current and voltage changes and the distribution condition of voltage along the soil body in the experimental process in real time. The current collection module 14 and the voltage collection module 13 are connected with the PC terminal 20 through a signal converter, and transmit collected current and voltage data to the PC terminal 20. One end of the pH sensor 18 is arranged in the cathode cavity 2, and the other end is connected with the pH acquisition module 19 to acquire the pH change condition of the solution in the anode cavity 2 in real time. The pH acquisition module 19 is connected with the PC terminal 20 through a signal converter, and transmits pH data acquired by the pH sensor 18 in the test process to the PC terminal 20. The monitoring system of the experimental equipment can monitor and collect data of voltage, current, temperature and effluent liquid pH in the experimental process in real time, and is used for analyzing the action mechanism of the electroosmosis combined with the MICP for reinforcing the soft soil foundation.
The grouting system comprises a peristaltic pump 25, a rubber hose 26 matched with the peristaltic pump, a water stop valve 27, a chemical liquid reservoir 28, a cold and hot water reservoir 29, a microorganism reservoir 30, a buffer liquid reservoir 31, a temperature control tank 7, a water injection port 8 of the temperature control tank, a water outlet 9 of the temperature control tank and the like. The microbial reservoir 30 is made of glass, and has an open upper portion for storing a microbial liquid. One end of a rubber hose 26 matched with the peristaltic pump is placed in the microorganism liquid storage device 30, and a pipe orifice is positioned at the bottom of the microorganism liquid storage device 30. A rubber hose 26 matched with the peristaltic pump passes through the pump head of the peristaltic pump 25, the other end of the rubber hose is placed in the cathode cavity 2, and the pipe orifice is positioned at the upper part of the cathode cavity 2. A water stop valve 27 is arranged between the rubber hose 26 and the liquid reservoir matched with the peristaltic pump to control the opening and closing of the conveying channel. The buffer reservoir 31 is made of glass, has an open upper portion, and is used for containing a pH buffer; the pH buffer consisted of a 1M sodium bicarbonate solution. One end of a rubber hose 26 matched with the peristaltic pump is placed in the buffer liquid storage device 31, and the nozzle is positioned at the bottom of the buffer liquid storage device 31. A rubber hose 26 matched with the peristaltic pump passes through the pump head of the peristaltic pump 25, the other end of the rubber hose is placed in the cathode cavity 2, and the pipe orifice is positioned at the upper part of the cathode cavity 2. A water stop valve 27 is arranged between the rubber hose 26 and the liquid reservoir matched with the peristaltic pump to control whether the pH buffer solution is injected or not. The peristaltic pump 25 can control flow rate, pumping time, and has a function of timing pumping, etc. The pump head has 12 passages, so that simultaneous and time-sharing grouting of different solutions can be realized. During the experiment, the water stop valve is closed, the peristaltic pump 25 is started, and then the microbial fluid and the buffer fluid are injected into the cathode cavity 2 at a constant speed. The water stop valve 27 on the rubber hose 26 matched with the peristaltic pump can be opened and closed at any time, so that simultaneous and time-sharing grouting of microorganisms and buffer liquid is realized. The peristaltic pump 25 is connected to the PC terminal 20 through a signal converter. And the PC terminal 20 is used for analyzing the real-time pH data transmitted by the pH acquisition module 18. When the pH of the cathode chamber 2 exceeds the set pH limit, the stop valve 27 for delivering pH buffer is closed, and pH buffer is injected into the anode chamber 3 to lower the pH of the cathode chamber 2 to maintain it within a range suitable for microbial growth.
The cementing liquid reservoir is used for storing cementing liquid. One end of a rubber hose 26 matched with the peristaltic pump is connected with the cementing liquid reservoir, and the other end of the rubber hose is connected with the anode cavity 3 through the pump head of the peristaltic pump 25 to provide cementing liquid for the anode. The temperature control groove 7 is positioned on the side wall of the sample box, and the side wall is not provided with a voltage and current and a temperature measuring hole. The temperature control channel 7 is bonded to the sample chamber 1 by means of plexiglass glue. The middle positions of the two ends of the temperature control groove 7, which are 3cm away from the top, are respectively provided with a through hole, and the through holes are screwed into pagoda joints and respectively used as a water injection port 8 and a water outlet 9 of the temperature control groove. One end of a rubber hose 26 matched with the peristaltic pump is connected with a cold and hot water reservoir 29, and the other end of the rubber hose is connected with a water filling port 8 of the temperature control groove after passing through the peristaltic pump 25. The peristaltic pump 25 is connected to the PC terminal 20 through a signal converter. The PC terminal 20 analyzes the temperature data transmitted by the temperature acquisition module 17, and when the soil temperature exceeds 30 ℃, the water stop valve 27 connected with the cold and hot water reservoir 29 is closed, and cold water is injected into the temperature control tank 7. During filling, the water stop valve 27 on the outlet opening is opened. When the temperature in the soil body is reduced to 30 ℃, a water stop valve on the cold and hot water reservoir 29 is opened, and the discharged water is collected by a measuring cylinder 33. The temperature control tank 7 can keep the soil body temperature in a range suitable for the growth of microorganisms all the time.
The test method of the present invention comprises: soft soil with certain water content is placed in the sample cavity 1 in three layers, and the uniformity of a soil sample is ensured. Standing for a certain time to enable the soil body to naturally drain and solidify. The solution in the anode chamber 3 and the cathode chamber 2 is monitored and consolidation is stopped when the volume of the solution no longer changes. And (3) opening the peristaltic pump 25, and respectively injecting the microbial fluid and the cementing fluid into the cathode cavity 2 and the anode cavity 3 at the injection flow rate of 2 ml/min. The concentration of the microbial liquid was measured by the optical density at 600nm, namely OD600To measure. OD of microbial liquid used in experiment600It was 2, and the urease activity was 5U/ml. The adopted cementing liquid consists of urea and calcium nitrate. The solution concentration was 1M. When the liquid level of the solution in the anode cavity 3 and the solution in the cathode cavity 2 reach the overflow port 21 of the anode cavity and the overflow port 22 of the cathode cavity, the power supply 10 is turned on, an electric field is applied to the two ends of the soil body, and drainage consolidation is started. Under the action of the electric field, the microorganisms in the cathode chamber 2 and the calcium ions in the anode chamber 3 will move towards the anode and the cathode respectively under the action of the electric field. After the experiment is started, the pH acquisition module 19, the temperature acquisition module 17, the voltage acquisition module 13 and the current acquisition module 14 are communicated, and the pH and the temperature of the soil body and the solution in the anode cavity 3 and the cathode cavity 2 in the experiment process are collected in real timeDegree, voltage and current data. Setting the pH threshold value of the cathode cavity 2 to be 10, closing a water stop valve 27 of a pH buffer solution when the pH value in the cathode cavity 2 exceeds 10, and continuously injecting the pH buffer solution into the cathode cavity 2 through a peristaltic pump 25 to keep the pH value of the soil body in the cathode cavity 2 and the vicinity of the cathode to be about 10. The soil body temperature threshold value is set to be 30 degrees, when the temperature in the soil body exceeds 30 degrees, the cold and hot water stop valve 27 is closed, and cold water is injected into the temperature control groove 7 by using the peristaltic pump 25 until the soil body temperature is kept at 30 degrees. The water stop valve is opened to stop water injection and discharge the water in the temperature control tank 7. After the test is completed, the power supply 10 is turned off, and the temperature measuring wire and the low-resistance probe are taken out. The shear strength was measured at different locations of the consolidated soil using a cross plate shear apparatus. And (5) sampling and drying after the determination is finished, and determining the water content of the soil body.
The method for calculating the water content of the soil body comprises the following steps
Wherein w is the water content, mwAfter the strength measurement, the weight of the sample taken at the strength measurement position is measured; m isdAfter the strength is measured, the weight of the sample taken at the strength measuring position after drying;
in addition, the dried soil sample is taken and crushed, and the soil sample and water are mixed according to the mass ratio of 1:5, and are fully mixed for 2 hours in an automatic mixer to prepare uniform slurry. The slurry was centrifuged in a centrifuge at 8000r/min to obtain a supernatant. Taking the centrifuged supernatant, and measuring the pH value and the conductivity value of the soil body by using a pH meter and a conductivity meter. Another certain amount of supernatant is taken, and the calcium ion content is measured by an ion chromatograph. And then analyzing the action mechanism of the electroosmosis combined MICP for reinforcing the soil body, and evaluating the improvement effect of the electroosmosis combined MICP reinforcing method on the soft soil foundation.
Claims (2)
1. The device for reinforcing the foundation by inducing calcium carbonate precipitation through electroosmosis combined with microorganisms is characterized by comprising an electroosmosis system, a grouting system and a monitoring and control system; the electroosmosis system is mainly used for discharging pore water of the soil body and driving biological-chemical ions to move in the soil body; the grouting system is used for providing a microorganism liquid, a cementing liquid and a pH buffer liquid; the monitoring and control system is mainly used for controlling the pH value of the system and the temperature of the soil body and analyzing the evolution of the bio-chemical-mechanical properties of the soil body in the reinforcing process and after the reinforcement is finished; researching the action mechanism of the electroosmosis combined with the MICP for reinforcing the soft soil foundation;
the electroosmosis system comprises a sample cavity (1), an anode cavity (3), a cathode cavity (2), a partition plate (4) with a drainage hole, an anode plate (5), a cathode plate (6), a power supply (10), a lead (11) and an overflow port; the sample cavity (1), the cathode cavity (2) and the anode cavity (3) are all made of organic glass plates; the sample cavity (1) is a cuboid and is used for containing soft soil to be reinforced; the cathode cavity (2) and the anode cavity (3) are respectively positioned at two sides of the sample cavity (1) and are separated by a partition plate (4) with a drainage hole; the cathode cavity (2) is filled with injection liquid mainly comprising bacterial liquid, and the anode cavity (3) is used for buffering and collecting pore water discharged from a soil body under the action of an electric field besides the cementing liquid to be injected; through holes with the diameter of 5mm are uniformly distributed on the partition plate (4) with the drainage holes and are used as liquid circulation channels; the anode plate (5) and the cathode plate (6) are respectively arranged in the anode cavity (3) and the cathode cavity (2); the anode cavity and the cathode cavity are respectively tightly attached to an inner end surface of the anode cavity and the cathode cavity, and the inner end surface is an end surface far away from the sample cavity; the two electrode plates are respectively connected with a power supply (10) through leads (11); the power supply (10) applies an electric field to two ends of the soil body through the electrode plates to drive positive ions in the soil body to drive pore water to move to the negative plate (6); in addition, the voltage and the current provided by the power supply (10) are adjustable, and the power supply can be used for research on reinforcing soft soil foundation by combining electroosmosis drainage and MICP under different voltage and current conditions; an overflow port is arranged at the position, close to the top, of the outer side of the cathode cavity (2), along with the increase of pore water discharged from a soil body and the continuous injection of microbial liquid into the cathode cavity (2), the amount of liquid in the cathode cavity (2) is increased, and when the liquid level exceeds the overflow port, redundant liquid flows out of the overflow port and flows into the measuring cylinder (24) through the rubber hose (23); the overflow port is arranged to prevent the liquid in the liquid outlet cavity from overflowing the sample cavity (1); similarly, an overflow port is also arranged on the outer side of the anode cavity (3) to prevent the cementing liquid injected into the anode cavity (3) from overflowing the sample cavity (1) due to excessive cementing liquid;
the monitoring and control system comprises a pH sensor (18), a pH acquisition module (19), a voltage acquisition module (13), a current acquisition module (14), a temperature acquisition module (17), a current and voltage measurement hole (12), a temperature measurement hole (15), a pagoda joint, a temperature measurement lead (16), a low-resistance probe and a PC terminal (20); one side wall of the sample cavity (1) is provided with two rows of through holes which are a current and voltage measuring hole (12) and a temperature measuring hole (15), and a hollow pagoda joint is screwed in the through holes; one end of a temperature measuring lead (16) is inserted into the soil body through a temperature measuring hole (15), and the other end is connected with a temperature acquisition module (17); the temperature acquisition module (17) is connected with the PC terminal (20) through a signal converter and transmits acquired temperature data to the PC terminal (20); one end of the low-resistance measuring probe is inserted into a soil body through a current and voltage measuring hole (12), and the other end of the low-resistance measuring probe is respectively connected with a voltage acquisition module (13) and a current acquisition module (14) through a lead (11) and is used for acquiring the change conditions of voltage and current in the experimental process in real time; the voltage acquisition module (13) and the current acquisition module (14) are connected with the PC terminal (20) through the signal converter, and transmit current and voltage data to the PC terminal (20); one end of a pH sensor (18) is arranged in the cathode cavity (2), and the other end of the pH sensor is connected with a pH acquisition module (19) to acquire the pH change condition of the solution in the cathode cavity (2) in real time; the pH acquisition module (19) is connected with the PC terminal (20) through a signal converter and transmits pH data acquired by the pH sensor (18) in the test process to the PC terminal (20); the monitoring and control system can monitor and collect voltage, current, temperature and effluent liquid pH data in the experimental process in real time; the monitoring and control system is cooperated with the grouting system to realize real-time control of the pH value and the soil body temperature of the system and provide more appropriate environmental conditions for reinforcing the soft soil foundation by the electroosmosis combined with the MICP;
the grouting system comprises a peristaltic pump (25), a chemical liquid reservoir (28), a microorganism liquid reservoir (30), a buffer liquid reservoir (31), a cold and hot water reservoir (29), a rubber hose (23), a water stop valve (27), a temperature control tank (7), a temperature control tank filling opening (8) and a temperature control tank water outlet (9); the microbial liquid reservoir (30) stores cultured bacterial liquid to provide thalli or urease for MICP and ensure the continuous urea decomposition in the experimental process; the microorganism liquid reservoir (30) is connected with the cathode cavity (2) through a rubber hose (23), wherein the rubber hose (23) passes through a pump head of the peristaltic pump (25); a peristaltic pump (25) pumps the fluid by alternately squeezing and releasing the elastic delivery rubber hose (23); the peristaltic pump (25) can control the grouting rate, so that the microbial liquid can be continuously supplemented into the anode cavity (3) according to the set grouting rate; a buffer liquid reservoir (31) for storing pH buffer liquid is connected with the peristaltic pump (25), and the pH buffer liquid is continuously injected into the cathode cavity (2) through the peristaltic pump (25) so that the pH of the cathode cavity (2) and soil body near the cathode is kept between 9 and 10; the cementing liquid reservoir is used for storing cementing liquid, is connected with the peristaltic pump (25) through a rubber hose (23) and is further connected with the anode cavity (3) to continuously provide calcium ions to the soil body so as to ensure the supply of a reaction substrate of the MICP reaction; the cold and hot water reservoir (29) is connected with the peristaltic pump (25) through a rubber hose (23); the other side of the peristaltic pump (25) is connected with the temperature control tank (7) through a rubber hose (23) to provide circulating cold water or hot water for the temperature control tank (7); two peristaltic pumps (25) are arranged in total, wherein one peristaltic pump (25) is used for providing the anode cavity (3) with microorganism liquid and pH buffer solution, and the other peristaltic pump (25) is used for providing the cathode cavity (2) and the temperature control tank (7) with cementing liquid and cold and hot water; the peristaltic pump (25) is connected with the PC terminal (20) through a signal converter; after receiving the real-time pH data transmitted by the pH acquisition module (19), the PC terminal (20) analyzes the real-time pH data; under the action of an electric field, water electrolysis can occur at the cathode to generate hydroxide ions, so that the pH value of the cathode solution is increased; when the pH value of the solution in the cathode cavity (2) exceeds a set pH limit value, a water stop valve (27) of a pH buffer solution is closed, the pH buffer solution is injected into the anode cavity (3), and the pH value of the solution in the cathode cavity (2) is reduced to keep the pH value in a range suitable for the growth of microorganisms; the PC terminal (20) processes the temperature data transmitted by the temperature acquisition module (17), when the soil body temperature exceeds 30 ℃, the water stop valve (27) connected with the cold and hot water liquid storage device (29) is closed, cold water is injected into the temperature control tank (7), when the temperature in the soil body is reduced to 30 ℃, the water stop valve (27) on the cold and hot water liquid storage device (29) is opened, and water in the temperature control tank (7) is discharged, so that the soil body temperature is always kept in a range suitable for the growth of microorganisms; the peristaltic pump (25) adopts a multi-channel pump head to realize simultaneous and time-sharing grouting of different solutions.
2. A method for reinforcing a foundation by calcium carbonate precipitation induced by electroosmosis combined with microorganisms is characterized by comprising the following steps:
firstly, soft soil to be reinforced is placed in a sample cavity (1) to ensure the uniformity of a soil sample; standing for a certain time to naturally solidify and drain the soil body; monitoring the solution in the anode cavity (3) and the solution in the cathode cavity (2), and stopping consolidation when the volume of the solution is not changed any more; closing the water stop valve (27), opening the peristaltic pump (25), and respectively injecting microbial liquid and cementing liquid into the cathode cavity (2) and the anode cavity (3); the microorganism is Pasteurella multocida, and the concentration of the bacterial liquid is determined by Optical Density (OD) at 600nm600To measure; the cementing liquid consists of 1M of urea and calcium nitrate; when the liquid levels of the solutions in the anode cavity (3) and the cathode cavity (2) reach overflow ports, a power supply (10) is turned on, an electric field is applied to two ends of a soil body, and drainage consolidation is started; under the action of the electric field, microorganisms in the cathode cavity (2) and calcium ions in the anode cavity (3) respectively move to the anode and the cathode under the action of the electric field; after the experiment begins, the pH acquisition module (19), the temperature acquisition module (17), the voltage acquisition module (13) and the current acquisition module (14) are communicated, and pH, temperature, voltage and current data of the solution in the soil body, the anode cavity (3) and the cathode cavity (2) in the experiment process are collected in real time; setting the pH threshold value of the cathode cavity (2) to be 10, closing a water stop valve (27) of a pH buffer solution when the pH value of the solution in the cathode cavity (2) exceeds 10, and injecting the pH buffer solution into the cathode cavity (2) through a peristaltic pump (25) to keep the pH value of the soil body in the cathode cavity (2) and the vicinity of the cathode between 9 and 10; setting the soil temperature threshold value to be 30 ℃, closing a cold and hot water stop valve (27) when the soil temperature exceeds 30 ℃, and injecting cold water into the temperature control tank (7) through a peristaltic pump (25) until the soil temperature is kept at 30 ℃; opening a water stop valve (27), stopping water injection, and discharging water in the temperature control tank (7); after the test is finished, the power supply (10) is turned off, and the temperature measuring lead and the low-resistance measuring pin are taken out; then measuring the shearing strength at different positions of the reinforced soil by using a cross plate shearing instrument; sampling and drying after the determination is finished to determine the water content of the soil body;
the method for calculating the water content of the soil body comprises the following steps
Wherein w is the water content, mwAfter the strength measurement, the weight of the sample taken at the strength measurement position is measured; m isdAfter the strength is measured, the weight of the sample taken at the strength measuring position after drying;
in addition, crushing the dried soil sample, mixing the soil sample and water according to the mass ratio of 1:5, and fully mixing for 2 hours in an automatic mixer to prepare uniform slurry; then centrifuging the slurry in a centrifuge at a rate of 8000 r/min; taking the centrifuged supernatant, and measuring the pH value and the conductivity of the soil body by using a pH meter and a conductivity meter; another certain supernatant is taken, and the calcium ion content in the supernatant is measured by an ion chromatograph; and then analyzing the action mechanism of the electroosmosis combined MICP for reinforcing the soil body, and evaluating the improvement effect of the electroosmosis combined MICP reinforcing method on the soft soil foundation.
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| CN113417295A (en) * | 2021-06-07 | 2021-09-21 | 海南大学 | Foundation pit microorganism soil gravity type enclosure structure and construction method thereof |
| CN113774897A (en) * | 2021-10-22 | 2021-12-10 | 西安建筑科技大学 | Method for curing sandy soil through MICP (micro-emulsified concrete) low-pH value mixed grouting |
| CN114232597A (en) * | 2021-11-23 | 2022-03-25 | 辽宁工程技术大学 | Electric field control microorganism mineralization reinforcing soil body mold device |
| CN114892638A (en) * | 2022-05-19 | 2022-08-12 | 辽宁工程技术大学 | Negative-pressure rotary grouting device based on MICP technology and application method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113417295A (en) * | 2021-06-07 | 2021-09-21 | 海南大学 | Foundation pit microorganism soil gravity type enclosure structure and construction method thereof |
| CN113417295B (en) * | 2021-06-07 | 2022-08-12 | 海南大学 | Foundation pit microorganism soil gravity type enclosure structure and construction method thereof |
| CN113774897A (en) * | 2021-10-22 | 2021-12-10 | 西安建筑科技大学 | Method for curing sandy soil through MICP (micro-emulsified concrete) low-pH value mixed grouting |
| CN114232597A (en) * | 2021-11-23 | 2022-03-25 | 辽宁工程技术大学 | Electric field control microorganism mineralization reinforcing soil body mold device |
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