A test method for microbial induced carbonate precipitation to solidify sand

Abstract

The present application relates to sand solidification technical field, disclose a kind of test method for microbial induced calcium carbonate precipitation solidification sand, the experimental device includes test mould, gas delivery module, vacuum pumping module, liquid adding module, temperature control module and monitoring module.The upper and lower ends of the test mould are respectively provided with upper sealing cover and lower sealing cover, the sand sample is contained in the test mould, and the upper sealing cover and the lower sealing cover are respectively formed with first space and second space with the upper and lower ends of the test mould.By controlling temperature, air pressure and other environmental factors during injection to inhibit the activity of microorganisms, the entrance is avoided from being blocked due to "first contact first reaction", and the injection method of the mixed solution of microorganisms is optimized by using the full contact mode, so that the mixed solution and the sand sample are more fully contacted, the injection time is shortened, and the unevenness of calcium carbonate generation is reduced.

Description

Technical Field

[0001] This invention relates to the field of sand and soil solidification technology, specifically to an experimental method for solidifying sand and soil by inducing calcium carbonate precipitation through microorganisms. Background Technology

[0002] Microbial soil solidification is a relatively new research field in environmental geotechnical engineering in recent years. Its core technology is MICP (Microbially Induced Calcite Precipitation). Through the action of microorganisms, calcium sources such as urea are decomposed in a green and environmentally friendly way, forming calcium carbonate precipitates between soil particles, thereby achieving soil solidification and improving soil stiffness and strength.

[0003] Traditional MIP (Multiphase Injection Processing) technology employs a multiphase, multiple-stage introduction method. The "first contact, first reaction" approach easily leads to clogging at the sand sample inlet and highly uneven distribution of the generated calcium carbonate, resulting in biased experimental results and affecting research conclusions. Currently, the difficulty in controlling calcium carbonate uniformity and the efficiency of technology application are the main factors limiting the widespread application of MIP technology.

[0004] CN108761044A discloses an experimental device and method for microbial-induced calcium carbonate precipitation and solidification of sand under negative pressure; CN108008110A discloses an optimization method for microbial solidification of sand based on temperature conditions. These two patents primarily control only one factor in the microbial solidification process of sand using the MIP (Microbial Induction Precipitation) technology to address the problem of calcium carbonate inhomogeneity. Their aim is to improve the experimental results, but they do not specifically consider the complexity of the combined effects of temperature, air pressure, and oxygen concentration in the gas environment on the technical effect during actual engineering applications of MIP technology in different regions. Therefore, they cannot provide a more intuitive and accurate reference for specific engineering projects.

[0005] Therefore, in this relatively new research field of environmental geotechnical engineering, it is essential to design an experimental device and method for microbial-induced calcium carbonate precipitation and solidification of sand based on the control of multiple factors such as temperature, air pressure, and oxygen concentration, in order to solve the problems of uneven calcium carbonate formation and enhance the scientific rigor of the experiment. Summary of the Invention

[0006] In order to solve the problems existing in the prior art, the present invention aims to provide a test method for microbial-induced calcium carbonate precipitation and solidification of sandy soil.

[0007] On one hand, this invention discloses an experimental apparatus for microbial-induced calcium carbonate precipitation and solidification of sandy soil, comprising: The test mold is provided with an upper sealing cover and a lower sealing cover at its upper and lower ends, respectively. The test mold contains a sand sample. The upper sealing cover and the lower sealing cover form a first space and a second space with the upper and lower ends of the test mold, respectively. A gas delivery module, used to adjust the oxygen concentration inside the test mold; A vacuum module, used to adjust the vacuum level inside the test mold; A liquid addition module is disposed above the test mold and is used to inject the microbial mixture required for the test into the test mold; Temperature control module, the temperature control module is used to adjust the temperature inside the test mold and the liquid addition module; The monitoring module is connected to the gas delivery module, the vacuum module, the liquid addition module, and the temperature control module, and is used to monitor the oxygen concentration, vacuum level, temperature inside the test mold, and the temperature inside the liquid addition module.

[0008] Preferably, the gas delivery module includes a gas pump and a gas delivery pipe with a valve. One end of the gas delivery pipe is connected to the gas pump, and the other end passes through the upper sealing cover and is connected to the first space.

[0009] Preferably, the vacuum module includes a vacuum pump and a gas pipe with a valve. One end of the gas pipe is connected to the vacuum pump, and the other end passes through the lower sealing cover and is connected to the second space.

[0010] Preferably, the liquid addition module includes multiple liquid storage containers, a mixing container with a mechanical stirring structure, and a connecting pipe with a valve. The multiple liquid storage containers are all connected to the mixing container through branch pipes, and the mixing container is connected to the first space through the connecting pipe with the valve.

[0011] Preferably, each of the branch pipes is equipped with a metering valve.

[0012] Preferably, the temperature control module includes a temperature control switch, a refrigeration / heating device, and a temperature control circuit. The temperature control circuit is connected from the refrigeration / heating device to the test mold and the liquid addition module, respectively. The temperature control switch is used to control the heating temperature of the refrigeration / heating device.

[0013] Preferably, the monitoring module includes a monitoring data output display terminal, a transmission line, and a monitoring sensing element. The monitoring sensing element is used to monitor the oxygen concentration, vacuum degree, and temperature inside the test mold, as well as the temperature inside the liquid addition module. The monitoring data output display terminal is connected to the monitoring sensing element through the transmission line, and is used to display the oxygen concentration data, vacuum degree data, and temperature data inside the test mold, as well as the temperature data inside the liquid addition module.

[0014] Preferably, the sand sample is sealed with geotextile.

[0015] Preferably, the bottom of the lower sealing cap is provided with a residual liquid recovery hole, and a liquid outlet pipe with a valve is connected to the residual liquid recovery hole.

[0016] On the other hand, the present invention also discloses a test method for microbially induced calcium carbonate precipitation and solidification of sandy soil, comprising the following steps: S1: Collect sufficient sand samples on site and collect local temperature and oxygen concentration indicators in the gas environment; by analyzing the mineral components in the sand samples, preliminarily determine the raw material ratio of the injected microbial mixture; S2: Place the sand sample into the test mold, and install the upper and lower sealing caps to seal the test mold; S3: Prepare the microbial mixture using the liquid addition module according to the test requirements, and set it aside for later use; S4: The environment of the test mold is evacuated by the vacuum module, and microbial mixture is added to the test mold by the liquid addition module under negative pressure. S5: Based on the local temperature and oxygen concentration in the gas environment, the temperature and oxygen concentration inside the test mold are regulated by the temperature control module and the gas delivery module to solidify the sand sample with microorganisms. S6: Repeat steps S3-S5 to investigate the effects of different temperatures, oxygen concentrations, vacuum levels, and raw material ratios of the microbial mixture on the solidification of the sand sample.

[0017] The experimental method for microbial-induced calcium carbonate precipitation and solidification of sandy soil described in this invention has the following advantages: (1) This experimental apparatus and method inhibits the activity of microorganisms by controlling environmental factors such as temperature and air pressure during the injection process, avoiding blockage of the inlet due to "first contact, first reaction". At the same time, it optimizes the injection method of microbial mixture by adopting a full contact method, so that the mixture and sand sample can be in more sufficient contact, shortening the injection time and reducing the non-uniformity of calcium carbonate formation; (2) This method embodies the idea of ​​unified control of the experimental environment such as temperature, oxygen concentration, and the ratio of reaction solution to microorganisms, improving the operability and scientific nature of the experimental process, reducing experimental costs, shortening the experimental cycle, and providing more support for the engineering application of MIP technology. To ensure accurate technical indicators and create economic benefits; (3) This method provides a standardized and controlled test process for indoor testing of MICP technology before its actual engineering application. By conducting indoor comparison and repeated tests under simulated engineering environmental conditions, the optimal MICP technology test parameters that match the engineering environment are obtained, thus promoting the development of MICP technology. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the experimental device for microbial-induced calcium carbonate precipitation and solidification of sand, as described in this invention.

[0019] Explanation of reference numerals in the attached figures: 1. Test mold, 11. Upper sealing cover, 12. Lower sealing cover, 121. Liquid outlet pipe, 101. First space, 102. Second space; 2. Gas delivery module; 21. Gas pump; 22. Gas delivery pipe; 3. Vacuum module, 31. Vacuum pump, 32. Gas tubing; 4. Liquid addition module; 41. Liquid storage container; 42. Mixing container; 43. Connecting pipe; 5. Temperature control module; 6. Monitoring module. Detailed Implementation Example 1

[0020] like Figure 1 As shown in the figure, this embodiment discloses an experimental device for microbial-induced calcium carbonate precipitation and solidification of sand, including an experimental mold 1, a gas delivery module 2, a vacuum module 3, a liquid addition module 4, a temperature control module 5, and a monitoring module 6. The experimental mold 1 has an upper sealing cap 11 and a lower sealing cap 12 at its upper and lower ends, respectively. The experimental mold 1 contains a sand sample. The upper and lower sealing caps 11 and 12 form a first space 101 and a second space 102 with the upper and lower ends of the experimental mold 1, respectively. The main function of the first space 101 formed by the upper sealing cap 11 is to ensure that the mixed liquid makes full and complete contact with the upper surface of the sand sample during the injection process, thereby accelerating the injection rate and making the injection more uniform. The second space 102 can determine whether the mixed liquid has been completely and sufficiently injected.

[0021] The gas delivery module 2 is used to adjust the oxygen concentration inside the test mold 1. Specifically, the gas delivery module 2 provides the function of regulating the oxygen concentration in the test mold 1 during the reaction process, and the gas temperature is monitored and regulated by the monitoring module 6 and the temperature control module 5.

[0022] The vacuum module 3 is used to adjust the vacuum level inside the test mold 1. Specifically, the vacuum module 3 provides vacuum level control for the test mold 1 during the injection of liquids such as microbial mixtures into the sand sample.

[0023] The liquid addition module 4 is located above the test mold 1 and is used to inject the microbial mixture required for the test into the test mold 1. Specifically, the liquid addition module 4 is the main container for preparing microbial mixtures such as microbial suspensions and nutrient solutions. The container has volume measurement and mechanical stirring functions, and its internal temperature is monitored and controlled by the monitoring module 6 and the temperature control module 5.

[0024] Temperature control module 5 is used to regulate the temperature inside the test mold 1 and the liquid addition module 4. Monitoring module 6 is connected to gas delivery module 2, vacuum module 3, liquid addition module 4 and temperature control module 5, and is used to monitor the oxygen concentration, vacuum degree and temperature inside the test mold 1 and the temperature inside the liquid addition module 4.

[0025] In the specific experiment, the sand sample was placed into the test mold 1, and then the test mold 1 was sealed with the upper sealing cap 11 and the lower sealing cap 12. The required microbial mixture was then prepared using the liquid addition device 4. The microbial mixture consisted of 5 g / L soybean peptone, 3 g / L meat extract peptone, 20.0 g / L CO(NH2)2, 20 g / L yeast extract, and 10 g / L (NH4)2SO4. The equipment was then evacuated to 0.06 MPa–0.08 MPa using the vacuum module 3. Under negative pressure, the microbial mixture was injected into the test mold 1 through the liquid addition module 4. After the mixture was injected, the temperature and oxygen concentration inside the test mold 1 were adjusted using the gas delivery module 2 and the temperature control module 5, according to the experimental requirements, to solidify the sand sample under the specified temperature and oxygen concentration conditions. Throughout the experiment, the solidification oxygen concentration and temperature could be changed using the gas delivery module 2 and the temperature control module 5 to conduct repeated comparative experiments. This embodiment inhibits the activity of microorganisms by controlling environmental factors such as temperature and air pressure during the injection process, avoiding blockage of the inlet due to "first contact, first reaction". At the same time, it optimizes the injection method of microbial mixture by adopting a full contact method, so that the mixture can have more sufficient contact with the sand sample, shorten the injection time, and reduce the unevenness of calcium carbonate formation.

[0026] In this embodiment, the test mold 1 is the main container for the test reaction. The container should facilitate the loading and unloading of sand samples and the injection and extraction of liquids such as microbial mixtures and gases such as oxygen. The internal temperature, vacuum degree and oxygen concentration are monitored and controlled by the monitoring module 6, temperature control module 5, vacuum module 3 and gas delivery module 2. The specifications and dimensions of the test mold 1 can be customized according to the specific test specifications.

[0027] Preferably, the gas delivery module 2 includes a gas pump 21 and a gas delivery pipe 22 with a valve. One end of the gas delivery pipe 22 is connected to the gas pump 21, and the other end passes through the upper sealing cover 11 and is connected to the first space 101. When it is necessary to adjust the oxygen concentration inside the test mold 1, oxygen can be delivered through the gas pump 21 to adjust the oxygen concentration inside the test mold 1. The monitoring module 6 can detect the oxygen concentration inside the test mold 1. After the oxygen concentration reaches the test requirements, the valve on the gas delivery pipe 22 is closed. The valve can be a solenoid valve.

[0028] Preferably, the vacuum module 3 includes a vacuum pump 31 and a gas pipe 32 with a valve. One end of the gas pipe 32 is connected to the vacuum pump 31, and the other end passes through the lower sealing cover 12 and is connected to the second space 102. When it is necessary to evacuate the test mold 1, the vacuum pump 31 evacuates the space inside the test mold 1. The vacuum level inside the test mold 1 is monitored by the monitoring module 6. After the vacuum level reaches the test requirements, the valve on the gas pipe 32 is closed. This valve can also be a solenoid valve.

[0029] Preferably, the liquid addition module 4 includes multiple liquid storage containers 41, a mixing container 42 with a mechanical stirring structure, and a connecting pipe 43 with a valve. The multiple liquid storage containers 41 are all connected to the mixing container 42 via branch pipes, and the mixing container 42 is connected to the first space 101 via the connecting pipe 43 with a valve. Each liquid storage container 41 can be filled with the various raw materials required for the microbial mixture, which are then injected into the mixing container 42. The microbial mixture is stirred by the mechanical stirring structure to achieve uniform mixing. The microbial mixture is then injected into the first space 101 through the connecting pipe 43, and then passes through a sand sample to solidify the sand sample. Furthermore, each branch pipe is equipped with a metering valve, which can control the amount of each raw material added to the liquid storage container 41, facilitating different experiments.

[0030] Preferably, the temperature control module 5 includes a temperature control switch, a refrigeration / heating device, and a temperature control circuit. The temperature control circuit extends from the refrigeration / heating device and is connected to the test mold 1 and the liquid addition module 4, respectively. The temperature control switch is used to control the heating temperature of the refrigeration / heating device. The refrigeration / heating device heats or cools the test mold 1. Specifically, the refrigeration / heating device is connected to the mixing container 42 of the liquid addition module 4 to heat the mixed solution in the mixing container 42, thereby controlling the addition temperature of the mixed solution.

[0031] Preferably, the monitoring module 6 includes a monitoring data output display terminal, a transmission line, and monitoring sensing elements. The monitoring sensing elements monitor the oxygen concentration, vacuum level, and temperature within the test mold 1, as well as the temperature within the liquid addition module 4. The monitoring data output display terminal is connected to the monitoring sensing elements via the transmission line and displays the oxygen concentration data, vacuum level data, temperature data within the test mold 1, and temperature data within the liquid addition module 4. The monitoring sensing elements include temperature sensing elements, oxygen concentration detection elements, and pressure detection elements. Multiple temperature sensing elements are present, some distributed within the test mold 1 and others distributed in the mixing container 42. The temperature sensing elements are connected to the monitoring data output display terminal via the transmission line, displaying the temperature of the test mold 1 and the microbial mixture, facilitating observation of the test data by the experimenter. The oxygen concentration detection element is located within the gas delivery module 2 to monitor the oxygen delivery rate, and the pressure detection element is connected to the vacuum module 3 to monitor the vacuum level.

[0032] Preferably, the sand sample is sealed with geotextile, which mainly serves to allow water and air to pass through. Simultaneously, it prevents sand particles from being extracted from the mold during the air extraction process, thus enhancing its stability. A residual liquid recovery hole is provided at the bottom of the lower sealing cover 12, and a liquid outlet pipe 121 with a valve is connected to the residual liquid recovery hole to facilitate the recovery of residual mixture after the reaction. Example 2

[0033] On the other hand, this embodiment also discloses a test method for microbially induced calcium carbonate precipitation and solidification of sandy soil, including the following steps.

[0034] Preparation: Collect sufficient sand samples on site and collect local temperature and oxygen concentration in the gas environment; by analyzing the mineral components in the sand samples, preliminarily determine the raw material ratio of the injected microbial mixture.

[0035] Start the test: Customize a certain number of test molds 1 of the corresponding size according to the requirements of subsequent test dimensions, and prepare sand samples. Put the sand samples into the test molds 1, and install the upper sealing cover 11 and the lower sealing cover 12 to seal the test molds 1.

[0036] According to the experimental requirements, the microbial mixture is prepared using the liquid addition module 4 for later use. Specifically, the temperature of the liquid addition module is adjusted to 4℃. Based on the raw material ratio of the injected microbial mixture initially determined in the preparation work, the mixture is prepared and mechanically stirred until homogeneous for later use.

[0037] At a temperature of 4℃, the environment of the test mold 1 is evacuated using the vacuum module 3. Under negative pressure, the microbial mixture is added to the test mold 1 via the liquid addition module 4. After injection, the temperature and oxygen concentration inside the test mold 1 are controlled by the temperature control module 5 and the gas delivery module 2 according to the local air temperature and oxygen concentration in the gas environment, allowing the microorganisms to solidify the sand sample. After sufficient reaction, the residual mixture in the test mold 1 is recovered, and all sand samples are removed.

[0038] Prepare microbial mixtures with different raw material ratios, and repeat steps S4-S5 to investigate the effects of different temperatures, oxygen concentrations, microbial mixtures, and vacuum levels on the solidification of sand samples.

[0039] Specifically, the temperature is varied in increments of 2 degrees Celsius above and below the actual engineering temperature. If the actual engineering temperature is 25°C, tests are conducted at 21°C, 23°C, 27°C, and 29°C. Test groups are designed at 1% increments within a preset oxygen concentration range. For example, if the oxygen concentration is between 19.5% and 23.5%, tests are conducted at 19.5%, 20.5%, 21.5%, 22.5%, and 23.5%.

[0040] Subsequent testing and analysis: Triaxial compressive strength tests were conducted on the sand samples, and the residual mixture was analyzed to obtain key information required for engineering construction, such as the uniaxial compressive strength of the sand samples and the test results of the residual mixture. The results were analyzed to determine if the requirements for engineering application were met. If they were met, the test results data were submitted, and the test was successfully completed. If not, the test reaction conditions were adjusted according to the actual situation, and the test was repeated, or the construction method was adjusted. The mechanical properties of the solidified sand samples were investigated through triaxial compressive strength tests and subsequently uniaxial compressive strength tests. Secondly, the analysis of the mixture involved analyzing the composition of the residual mixture to investigate the formation of calcium carbonate.

[0041] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention.

[0042] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of this invention.

Claims

1. A test method for microbial-induced calcium carbonate precipitation and solidification of sandy soil, characterized in that, Its testing apparatus includes: The test mold (1) is provided with an upper sealing cover (11) and a lower sealing cover (12) at its upper and lower ends respectively. The test mold (1) contains a sand sample. The upper sealing cover (11) and the lower sealing cover (12) form a first space (101) and a second space (102) with the upper and lower ends of the test mold (1) respectively. Gas delivery module (2), the gas delivery module (2) is used to adjust the oxygen concentration in the test mold (1), the gas delivery module (2) includes a gas pump (21) and a gas delivery pipe (22) with a valve, one end of the gas delivery pipe (22) is connected to the gas pump (21), and the other end passes through the upper sealing cover (11) and is connected to the first space (101); Vacuum module (3), the vacuum module (3) is used to adjust the vacuum level in the test mold (1). The vacuum module (3) includes a vacuum pump (31) and a gas pipe (32) with a valve. One end of the gas pipe (32) is connected to the vacuum pump (31), and the other end passes through the lower sealing cover (12) and is connected to the second space (102). Liquid addition module (4), the liquid addition module (4) is disposed above the test mold (1) and is used to inject the microbial mixture required for the test into the test mold (1). The liquid addition module (4) includes multiple liquid storage containers (41), a mixing container (42) with a mechanical stirring structure and a connecting pipe (43) with a valve. The multiple liquid storage containers (41) are all connected to the mixing container (42) through branch pipes. The mixing container (42) is connected to the first space (101) through the connecting pipe (43) with a valve. Temperature control module (5), the temperature control module (5) is used to adjust the temperature inside the test mold (1) and the liquid addition module (4); The monitoring module (6) is connected to the gas delivery module (2), the vacuum module (3), the liquid addition module (4) and the temperature control module (5), and is used to monitor the oxygen concentration, vacuum degree, temperature in the test mold (1) and the temperature in the liquid addition module (4); Its test method includes the following steps: S1: Collect sufficient sand samples on site and collect local temperature and oxygen concentration indicators in the gas environment; by analyzing the mineral components in the sand samples, preliminarily determine the raw material ratio of the injected microbial mixture; S2: The sand sample is placed into the test mold (1), and the upper sealing cover (11) and the lower sealing cover (12) are installed to seal the test mold (1); S3: Prepare the microbial mixture using the liquid addition module (4) according to the test requirements, and set it aside for later use; S4: The environment of the test mold (1) is evacuated by the vacuum module (3), and microbial mixture is added to the test mold (1) under negative pressure by the liquid addition module (4); S5: Based on the local temperature and oxygen concentration in the gas environment, the temperature and oxygen concentration in the test mold (1) are controlled by the temperature control module (5) and the gas delivery module (2) to solidify the sand sample by microorganisms. S6: Prepare microbial mixtures with different raw material ratios, and repeat steps S4-S5 to investigate the effects of different temperatures, oxygen concentrations, microbial mixtures, and vacuum levels on the solidification of the sand samples.

2. The experimental method for microbial-induced calcium carbonate precipitation and solidification of sandy soil according to claim 1, characterized in that, Each of the branch pipes is equipped with a metering valve.

3. The experimental method for microbial-induced calcium carbonate precipitation and solidification of sandy soil according to claim 1, characterized in that, The temperature control module (5) includes a temperature control switch, a refrigeration / heating device and a temperature control circuit. The temperature control circuit is connected from the refrigeration / heating device and is connected to the test mold (1) and the liquid addition module (4) respectively. The temperature control switch is used to control the heating temperature of the refrigeration / heating device.

4. The test method for microbial-induced calcium carbonate precipitation and solidification of sandy soil according to claim 3, characterized in that, The monitoring module (6) includes a monitoring data output display terminal, a transmission line, and a monitoring sensing element. The monitoring sensing element is used to monitor the oxygen concentration, vacuum degree, and temperature inside the test mold (1) and the temperature inside the liquid addition module (4). The monitoring data output display terminal is connected to the monitoring sensing element through the transmission line. The monitoring data output display terminal is used to display the oxygen concentration data, vacuum degree data, and temperature data inside the test mold (1) and the temperature data inside the liquid addition module (4).

5. The test method for microbial-induced calcium carbonate precipitation and solidification of sandy soil according to any one of claims 1-4, characterized in that, The sand sample was sealed with geotextile.

6. The test method for microbial-induced calcium carbonate precipitation and solidification of sandy soil according to any one of claims 1-4, characterized in that, The bottom of the lower sealing cover (12) is provided with a residual liquid recovery hole, and a liquid outlet pipe (121) with a valve is connected to the residual liquid recovery hole.

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