A test method for evaluating the long-term effects of grouting on water quality in water-rich sand layers

Abstract

The present invention discloses a test method for evaluating the long-term effect of grouting on the water quality of water-rich sand layers, comprising the following steps: S1, construction of a model test system, S2, pretreatment of experimental materials and filling of grouting models, S3, slurry selection and closed grouting, S4, grouting body penetration, S5, water quality analysis of the filtered water, S6, water chemical analysis and evaluation. The method of the present invention has the replaceability of grouting materials and the adjustability of the seepage flow rate, and can realize feedback adjustment of the seepage flow rate and long-term real-time dynamic monitoring and recording through devices such as flow meters; the permeability of the grouting body can also be measured simultaneously during the process of grouting body penetration; by analyzing the water quality information of the grouting body leachate, the pollution effect of grouting on the groundwater environment and the interaction between the slurry and the geological body can be explored; the method of the present invention also provides a subsequent water chemical analysis template of the grouting body leachate, thereby constituting an indoor system evaluation of grouting pollution.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrogeology and environmental geotechnical engineering, and particularly relates to a test method for evaluating the long-term impact of grouting on the water quality of a water-rich sand layer. Background Art

[0002] Grouting, as an engineering technology widely used in the field of mine management, plays an indispensable role in shaft reinforcement, tunnel stabilization, and leakage prevention. However, while this technology brings the advantage of improved stability to mining projects, it also poses a potential pollution risk to the regional groundwater environment. From the perspective of the mechanism of action, the large amount of slurry used in the grouting operation will change the pH, total dissolved solids content and ion concentration of the regional groundwater, thereby affecting the groundwater quality. In view of this potential hazard, it is necessary to carry out sustainable long-term model test research on the impact of specific grouting materials on groundwater quality, in order to explore the characteristics and laws of grouting pollution, and evaluate its pollution level and degradation cycle.

[0003] Currently, most existing research on the impact of grouting on the groundwater environment is conducted based on mine grouting sites. Specifically, water samples are collected from underground drainage holes and excavation water points, and the collected water samples are sent for testing, and then related water quality chemical analysis is carried out to explore the intrinsic relationship between grouting activities and groundwater environmental changes. This method has a certain degree of randomness and is greatly restricted by the actual site conditions and engineering plans. It cannot rule out the excessive interference of local abnormal geochemical characteristics of the rock and soil on water quality. The sampling cost and cycle are long, time-consuming and labor-intensive, not flexible, and poorly targeted. Existing indoor research mainly relies on water-rock interaction tests under static conditions. This method cannot provide dynamic groundwater dynamics and cannot achieve groundwater infiltration.

[0004] Therefore, it is urgent to expand the existing research methods and construct a new post-grouting infiltration model system of geological bodies based on a variety of grouting materials, which can simulate the groundwater flow rate within a specific range and has the characteristics of recyclability and sustainability. In this way, a research and evaluation method system for grouting pollution of groundwater environment is formed, so as to more accurately evaluate the potential impact of grouting activities on the groundwater environment and its mechanism of action, and provide a scientific basis and decision-making support for the coordinated development between underground engineering construction and environmental protection. Summary of the Invention

[0005] Technical problem to be solved: In response to the above technical problems, the present invention provides a test method for evaluating the long-term impact of grouting on the water quality of water-rich sand layers, based on a grouting pollution impact evaluation method for a long-term dynamic filtration system of a geological body (water-rich sand layer) after grouting, in which different types of grouting materials can be replaced and the groundwater flow rate can be adjusted within a certain range.

[0006] Technical solution: The present invention provides a test method for evaluating the long-term effect of grouting on the water quality of water-rich sand layers, comprising the following steps:

[0007] S1. Construction of model test system: The model test system includes a groundwater supply unit, a grouting and infiltration unit, a seepage flow rate monitoring and calibration unit, and a grouting body leachate pretreatment and storage unit, which are connected in sequence;

[0008] S2. Experimental material pretreatment and grouting model filling:

[0009] S2-1. Experimental Material Pretreatment: Based on the specific working conditions to be studied, in-situ sand samples were selected from the study area. Systematic testing was conducted on the key properties of the sand, and the obtained data served as preliminary basic data for subsequent experiments. The sand was screened using a vibrating screen to remove particles larger than 5 mm in size. The sand was repeatedly washed with deionized water to filter out biohumus and various metabolic substances.

[0010] S2-2. Evenly fill the pre-treated sand into the grouting mold according to the designed height and smooth its surface to ensure uniform distribution of the sand. Pre-press the filled sand with the help of a reaction loading device. After pre-pressing, introduce groundwater to fully saturate the mold bucket.

[0011] S3. Slurry selection and closed grouting: Select the type of slurry according to the research plan requirements and perform closed grouting on the sand in the model;

[0012] S4. Grouting body penetration: After the slurry is fully solidified, select an appropriate seepage velocity to use the groundwater in the study area to penetrate the grouting body model;

[0013] S5. Conduct water quality analysis on the filtered water: Conduct comprehensive and special water quality analysis on the water filtered from the grouting body;

[0014] S6. Hydrochemical analysis and evaluation: Based on the water quality test data obtained, analyze the degree of pollution caused by grouting on the water quality of the sandy geological layer and its dynamic change effect over time.

[0015] Preferably, the groundwater supply unit in the model test system includes a constant water head tank, the water inlet of the constant water head tank is connected to the water outlet of the water supply tank, and the water supply port of the constant water head tank is connected to the grouting and infiltration unit; the grouting and infiltration unit includes a grouting unit and a infiltration unit, and the same grouting bucket is used for the grouting unit and the infiltration unit in turn. When the grouting bucket is used for the grouting unit, the grouting bucket includes a bucket side wall, an upper flange cover plate and a lower flange cover plate, and a grouting limit cover plate is provided on the lower surface of the upper flange cover plate, and one end of the grouting pipe passes through the upper flange cover plate and the grouting limit cover plate in sequence, and a drainage pipe interface is provided on the lower flange cover plate, and the drainage pipe interface is externally connected to a drainage pipe; when the grouting bucket is used for the infiltration unit, the A joint is provided on the upper end surface of the grouting barrel, which is connected to the water supply port of the constant head tank through a pipe. An infiltration buffer bin is provided on the upper part of the grouting barrel, and the bottom of the infiltration buffer bin is an infiltration limiting mesh plate. A water outlet bin is provided below the grouting barrel, and the water outlet of the water outlet bin is connected to the pretreatment and storage unit of the grouting body leachate; the pretreatment and storage unit of the grouting body leachate includes a buffer sedimentation bag, a filter separator and a liquid storage tank connected in sequence, and the liquid inlet of the buffer sedimentation bag is connected to the water outlet of the water outlet bin through a pipe; the infiltration flow rate monitoring and calibration unit includes a flow meter, which is arranged on a pipe connecting the liquid inlet of the buffer sedimentation bag and the water outlet of the water outlet bin, and the flow meter is provided with a digital display system.

[0016] Furthermore, the groundwater supply unit also includes a recycling circulating water tank, the water inlet of the recycling circulating water tank is connected to the drain outlet of the constant water head tank; the pipe connecting the water inlet of the constant water head tank and the water outlet of the water supply tank and the pipe connecting the water inlet of the recycling circulating water tank and the drain outlet of the constant water head tank are both provided with water stop valves, and a filter is provided in the pipe between the water stop valve and the water supply tank.

[0017] Furthermore, the constant water head tank includes a water supply chamber and a drainage chamber, the water supply chamber and the drainage chamber are connected by a partition, a plurality of ball valves are provided on the partition, the ball valve is located in the drainage chamber, a drainage valve is provided in the drainage port at the lower part of the side wall of the drainage chamber, a movable cover is provided at the top of the water supply chamber, a water inlet joint is provided on the water inlet of the movable cover, and a water supply valve is provided in the water supply port at the lower part of the side wall of the water supply chamber.

[0018] Furthermore, a throttle valve is provided on the pipe connecting the water supply valve of the constant water head tank and the joint.

[0019] Furthermore, a support is provided at the bottom of the constant water head tank, a pressure gauge interface is opened on the side wall of the water outlet bin, and a pressure gauge is provided at the pressure gauge interface; a sand blocking net is provided in the water outlet of the water outlet bin.

[0020] Furthermore, a water stop clamp and a constant flow valve are provided in sequence on the pipeline between the water outlet of the water outlet bin and the flow meter.

[0021] Preferably, the types of slurry in step S3 include inorganic cement-based slurry, organic chemical slurry and composite slurry, the inorganic cement-based slurry includes ordinary Portland cement, slag cement, pozzolana cement, fly ash cement and composite Portland cement; the organic chemical slurry includes phosphoric acid curing agent urea-formaldehyde resin, oxalic acid curing agent urea-formaldehyde resin, acrylate, epoxy resin and polyurethane; the composite slurry includes cement-water glass slurry, epoxy resin-cement composite slurry and polyurethane-cement composite slurry.

[0022] Preferably, the indicators of water quality analysis in step S5 include general measurement indicators and organic indicators, and the general measurement indicators include K + , Ca 2+ 、Na + Mg 2+ 、CI - 、 OH - 、 F - 、 Br - and As well as pH, total dissolved solids TDS, electrical conductivity EC, total hardness TH and oxidation-reduction potential ORP; the organic indicators include total organic carbon TOC, chemical oxygen demand COD, free formaldehyde, methylene bisacrylamide, bisphenol A and free isocyanate.

[0023] Preferably, the specific process of step S6 is:

[0024] S6-1. Draw a Piper diagram based on the measured leachate ion concentration to determine the hydrochemical type of the leachate. This will analyze the pattern of changes in the hydrochemical type of groundwater caused by the grouting fluid and identify the negative effects of grouting pollutants on the overall hydrochemical characteristics of regional groundwater at a macro level.

[0025] S6-2. Develop time-dependent evolution curves of water quality indicators and ion concentrations to analyze the impact patterns and changing trends of the grouting fluid on groundwater quality indicators. By fitting indicators that change significantly during monitoring, accurately determine the time required for the grouting contamination effect to change from significant to negligible. This allows for the identification of the underlying mechanisms of grouting contaminants affecting regional groundwater quality at a microscopic level, and the assessment of the impact period of grouting on groundwater ion balance.

[0026] S6-3. Draw a Schoeller diagram to analyze the degree of disturbance to groundwater quality caused by the grouting project. By analyzing the fluctuation range of water quality indicators, determine the degree of normalization and degradation of groundwater quality in the area after grouting.

[0027] S6-4. Draw a correlation heat map to analyze the internal connections and interactions between various pollution factors in the grouting pollution process, and analyze the sources and mechanisms of grouting pollutants from the perspective of indicator correlation;

[0028] S6-5. Draw a PCA principal component map to analyze the dominant role of the grouting fluid in the groundwater pollution process and reveal the main mechanism of action in the slurry pollution process from the perspective of multivariate statistical dimensionality reduction.

[0029] Beneficial effects: 1) Replaceability of grouting materials: After completing the percolation test of one slurry, the device can be disassembled and replaced with another slurry to be studied, thereby realizing continuous, flexible, and highly customized experimental research; 2) Adjustability of seepage flow rate: The required percolation flow rate can be adjusted by changing the water head height and valve opening; 3) Feedback adjustment of the permeation flow rate and long-term real-time dynamic monitoring and recording can be achieved through devices such as flow meters; 4) The permeability of the grouting body can also be measured simultaneously during the percolation of the grouting body; 5) By analyzing the water quality information of the grouting body leachate, the pollution effect of grouting on the groundwater environment and the interaction between the slurry and the geological body can be explored; 6) The method of the present invention also provides a subsequent water chemical analysis sample of the grouting body leachate, thereby constituting an indoor system evaluation of grouting pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the overall structure of the model test system of the present invention;

[0031] Figure 2 It is a structural schematic diagram of the constant head tank of the present invention;

[0032] Figure 3 This is a schematic structural diagram of the grouting bucket of the present invention when used as a grouting unit;

[0033] Serial numbers in the figure: 1. Upper flange cover, 2. Grouting limit cover, 3. Grouting body, 4. Sand body, 5. Drain pipe interface, 6. Lower flange cover, 7. Bucket side wall, 8. Grouting pipe, 9. Joint, 10. Infiltration buffer chamber, 11. Upper screw, 12. Infiltration limit mesh, 13. Grouting bucket, 14. Lower screw, 15. Bracket, 16. Pressure gauge, 17. Water outlet chamber, 18. Sand blocking net, 19. Water stop clamp, 20. Constant flow valve, 21. Photoelectric micro Flow meter, 22. Digital display system, 23. Buffer sedimentation capsule, 24. Filter separator, 25. Liquid storage tank, 26. Recovery circulating water tank, 27. Water supply tank, 28. Filter, 29. Water stop valve, 30. Constant head tank, 31. Throttle valve, 32. Water supply chamber, 33. Tank wall, 34. Partition, 35. Water supply valve, 36. Support, 37. Drain valve, 38. Drain chamber, 39. Water level valve, 40. Water inlet joint, 41. Movable cover, 42. Drain pipe. DETAILED DESCRIPTION

[0034] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments:

[0035] Example 1

[0036] like Figure 1 As shown: the model test system includes a groundwater supply unit I, a grouting and infiltration unit II, a seepage flow rate monitoring and calibration unit III and a grouting body leachate pretreatment and storage unit IV which are connected in sequence. The groundwater supply unit I includes a constant water head tank 30, the water inlet of the constant water head tank 30 is connected to the water outlet of the water supply tank 27, and the water supply port of the constant water head tank 30 is connected to the grouting and infiltration unit; it also includes a recycling water tank 26, the water inlet of the recycling water tank 26 is connected to the drain port of the constant water head tank 30, and a water stop valve 29 is provided on the pipe connecting the water inlet of the constant water head tank 30 and the water outlet of the water supply tank 27 and the pipe connecting the water inlet of the recycling water tank 26 and the drain port of the constant water head tank 30, and a filter screen 28 is provided in the pipe between the water stop valve 29 and the water supply tank 27. Figure 2 As shown: the constant water head tank 30 is composed of a tank wall 33 and a tank bottom, including a water supply chamber 32 and a drainage chamber 38. The water supply chamber 32 and the drainage chamber 38 are connected by a partition 34. The partition 34 is provided with several ball valves 39. The ball valve 39 is located in the drainage chamber 38, wherein the water supply chamber 32 can maintain the pressure head (water level) constant by switching the ball valve 39 at the corresponding water level position on the partition 34; a drainage valve 37 is provided in the drainage port at the lower part of the side wall of the drainage chamber 38, the top of the water supply chamber 32 is provided with a movable cover plate 41, the water inlet of the movable cover plate 41 is provided with a water inlet joint 40, the water supply port at the lower part of the side wall of the water supply chamber 32 is provided with a water supply valve 35, the water supply valve 35 of the constant water head tank 30 is connected to the joint 9 and a throttle valve 31 is provided on the pipe, and a support 36 is provided at the bottom of the constant water head tank 30. The groundwater supply unit I provides a stable and adjustable seepage pressure head so that the groundwater can continuously penetrate the grouting body in the barrel.

[0037] The above-mentioned grouting and infiltration unit II includes a grouting unit and an infiltration unit. The same grouting bucket 13 is used for the grouting unit and the infiltration unit successively. When the grouting bucket 13 is used for the grouting unit, as shown in FIG. Figure 3As shown: the grouting bucket 13 includes a bucket side wall 7, an upper flange cover plate 1 and a lower flange cover plate 6. The upper flange cover plate 1 is connected to the bucket side wall 7 by an upper screw 11, and a grouting limit cover plate 2 is provided on the lower surface of the upper flange cover plate 1. The grouting limit cover plate 2 can limit the vertical expansion displacement of the sand body 4 during grouting. One end of the grouting pipe 8 passes through the upper flange cover 1 and the grouting limit cover 2 in sequence. The lower flange cover 6 is connected to the barrel side wall 7 by a lower screw 14, and a drain pipe interface 5 is opened on the lower flange cover 6. The drain pipe interface 5 is externally connected to the drain pipe 42. During grouting, due to the extrusion and displacement effect of the injected slurry, excess water will be discharged from the drain pipe 42; when the grouting barrel 13 is used for the infiltration unit, the upper end face of the grouting barrel 13 is provided with a joint 9, and the joint 9 is connected to the water supply port of the constant head tank 30 through a pipeline. An infiltration buffer bin 10 is provided above the inside of the grouting barrel 13, and the bottom of the infiltration buffer bin 10 is an infiltration limit mesh plate 12. The infiltration limit mesh plate 12 can keep the top interface of the sand and soil flat at all times during the infiltration process. A water outlet chamber 17 is located below the grouting bucket 13. The outlet of the water outlet chamber 17 is connected to the seepage flow rate monitoring and calibration unit III. A pressure gauge interface is provided on the sidewall of the water outlet chamber 17, and a pressure gauge 16 is installed at the pressure gauge interface. A sand blocking net 18 is installed within the outlet of the water outlet chamber 17. This unit enables long-term, constant-flow (flow rate) dynamic infiltration of groundwater into the grouting geological body (sand and soil).

[0038] The aforementioned seepage flow rate monitoring and calibration unit III includes a flow meter 21, which is installed on the pipe connecting the liquid inlet of the buffer sedimentation bladder 23 and the outlet of the water outlet tank 17. This flow meter 21 is equipped with a digital display system 22 based on the digital circuit of an Arduino development board. This unit uses the flow meter 21 to measure the water flow rate per unit time in the outlet pipeline, converting it into the corresponding instantaneous groundwater seepage flow rate within the grouting bucket 13. The flow rate within the bucket is further controlled by adjusting the placement height of the constant head tank 30, fine-tuning the water level within the head tank, and the opening of the downstream constant flow valve 20 in the pipeline to achieve the desired value. Furthermore, during the subsequent long-term infiltration process, the flow meter 21 can be connected to the digital display system 22 via the Arduino development board to monitor the outlet flow rate in real time and record the instantaneous and cumulative flow rates.

[0039] The grouting body leachate pretreatment and storage unit IV comprises a buffer settling bladder 23, a filter separator 24, and a liquid storage tank 25, all connected in sequence. The liquid inlet of the buffer settling bladder 23 is connected to the outlet of the water outlet tank 17 via a pipe. A water stop clamp 19 and a constant flow valve 20 are installed in the pipe between the outlet of the water outlet tank 17 and the flowmeter 21. The leachate flowing out of the barrel first flows through the buffer settling bladder 23, where relatively large impurities are removed by sedimentation. The leachate then enters the filter separator 24, where it is filtered through a 45μm water filter to remove fine impurity particles. Finally, the treated leachate flows into the liquid storage tank 25 for storage. This process provides a preliminary purification effect, ensuring the high purity of the leachate entering the liquid storage tank 25, laying a good foundation for liquid quality for subsequent related processing or analytical applications.

[0040] The working method of the above-mentioned model test system comprises the following steps:

[0041] S1, pre-grouting: the sand and soil in the intended study area is loaded into the grouting bucket 13, filled and leveled to a preset height, pre-pressed by the reaction loading device to achieve the density required by the study conditions, and then saturated with water to make the sand and soil reach a saturated state. The drainage pipe interface 5 of the grouting bucket 13 is opened, and the slurry is injected to extrusion and displacement effect. The excess water will be discharged from the drainage pipe 42; the grouting limit cover 2 in the grouting bucket 13 is fixed, the grouting material to be studied is prepared into a slurry, and closed grouting is performed into the sand and soil through the grouting pipe 8. After the grouting is completed, the water outlet port of the drainage pipe 42 is connected to the water stop clamp 19 and the constant flow valve 20;

[0042] S2. Determine the groundwater dynamic conditions in the proposed study area, and calculate the hydraulic gradient J by using Darcy's law V = K·J, and then calculate the hydraulic gradient J by h L = J·L preliminary estimate of the required groundwater infiltration head, that is, the pressure head h at the top interface of the sand and soil in the bucket L After estimating the parameters, adjust the height of the constant head tank 30 and inject groundwater of the corresponding water level height into the constant head tank 30 from the water supply tank 27 to provide a constant infiltration pressure head h L ; Where V is the average groundwater velocity in the study area, K is the permeability coefficient of the sand in the bucket after grouting, and L is the length of the permeability path, that is, the filling height of the sand in the bucket;

[0043] S3. Before starting infiltration, keep the top interface of the sand and soil in the grouting bucket 13 flat, and install the infiltration limit mesh plate 12, the upper flange cover plate 1 and the corresponding pipes and joints 9. Reserve the upper space generated by the deformation of the sand and soil in the grouting bucket 13 during pre-compression as a seepage buffer chamber 10 to make the infiltration flow lines uniformly distributed in the same direction and avoid radial seepage at the water inlet;

[0044] S4. Connect the seepage flow rate monitoring and calibration unit, open the connector 9 on the top of the grouting bucket 13 and the throttle valve 31 on the upper part of the water supply pipeline, calibrate the digital flow meter 22 to adjust the water head height in the constant head tank 30 and the opening of the constant flow valve 20 on the lower part of the pipeline to make the flow rate in the grouting bucket 13 consistent with the preset flow rate; after the flow rate calibration, calibrate the knob position of the constant flow valve 20, and the subsequent emergency throttling operation is achieved through the water stop clamp 19;

[0045] S5. Connect the pretreatment and storage unit of the grouting body leachate and start long-term infiltration of the grouting body. During this period, the leachate is initially purified by the buffer sedimentation capsule 23 and the filter separator 24. Then, according to the different requirements of the specific test plan, water samples are taken from the liquid storage tank 25 at regular intervals and in fixed quantities, or the liquid storage tank is replaced.

[0046] S6. Use relevant instruments to conduct various tests such as full water quality analysis and special analysis on the water samples as needed to obtain the required property data for subsequent research, evaluation and application.

[0047] The grouting material of the system of the present invention is replaceable: after completing the filtration test of one slurry, the grouting barrel 13 can be disassembled and replaced with another slurry to be studied, thereby realizing continuous, flexible, and highly customized experimental research; the seepage flow rate is adjustable: the required filtration flow rate can be adjusted by changing the head height of the constant head tank 30 and the opening of the constant flow valve 20; the feedback adjustment of the seepage flow rate and long-term real-time dynamic monitoring and recording can be achieved through devices such as the flow meter 21.

[0048] Example 2

[0049] The test method for evaluating the long-term effect of grouting on the water quality of a water-rich sand layer using the model test system described in Example 1 includes the following steps:

[0050] S1. Construction of model test system:

[0051] In order to carry out indoor grouting pollution assessment experiments, the present invention constructs a test platform composed of multiple components working together. The model experimental system covers multiple key units, among which the groundwater supply unit is the starting link, responsible for providing a stable water flow that meets the simulation requirements; the grouting body infiltration unit connected thereto is used to simulate the infiltration process of the grouting body in the actual geological environment; the infiltration flow rate monitoring and calibration unit accurately measures and calibrates the infiltration velocity in real time to ensure the accuracy of the experimental data; and the grouting body leachate pretreatment and storage unit performs preliminary treatment on the leachate and properly stores it to provide reliable samples for subsequent in-depth analysis. With the help of a constant head device, the entire system gets rid of its dependence on an electrical power source, thereby ensuring that long-term and stable infiltration simulation of the grouting body can be implemented. The model test system is as described in Example 1.

[0052] S2. Experimental material pretreatment and grouting model filling:

[0053] Before conducting the grouting experiment, it is necessary to select in-situ sand and soil samples in the study area based on the specific working conditions to be studied, and conduct systematic tests on key properties such as the chemical composition and mineral composition of the sand and soil. The data obtained will serve as preliminary basic data for subsequent experiments. In order to effectively avoid the size effect that may occur during grouting and subsequent seepage, a vibrating screening machine is used to select the sand and soil to remove particles with a particle size greater than 5mm. At the same time, the sand and soil are repeatedly washed with deionized water to filter out the biological humus and various metabolic substances contained therein, thereby maximally eliminating the interference factors on the experimental results caused by local abnormal geochemical characteristics;

[0054] After completing the above pretreatment, the sand is evenly filled into the grouting model according to the established design height, and its surface is smoothed to ensure the uniformity of the sand distribution. To simulate the in-situ pressure state of the sand, the loaded sand is pre-loaded with a reaction loading device to simulate the density of the actual stratum. After pre-loading, groundwater is introduced to fully saturate the model bucket, thereby simulating the water-rich environment in the actual stratum.

[0055] According to the requirements of the experimental plan, a blank control group model barrel was set up as the experimental control benchmark. Except for the grouting variables, the other conditions were consistent with those of the experimental group. At the same time, according to the same operating procedures, a number of test barrels were set up simultaneously to carry out multiple parallel experiments.

[0056] S3. Grout selection and closed grouting: Select the type of grout according to the research plan requirements and perform closed grouting on the sand in the model. Applicable grouts include but are not limited to: inorganic cement-based grouts: ordinary Portland cement, slag cement, pozzolana cement, fly ash cement, composite Portland cement; organic chemical grouts: phosphoric acid curing agent urea-formaldehyde resin, oxalic acid curing agent urea-formaldehyde resin, acrylate, epoxy resin, polyurethane; composite grouts: cement-water glass grout, epoxy resin-cement composite grout, polyurethane-cement composite grout;

[0057] During grout injection, a reciprocating piston grouting pump, constant pressure air pump, or screw pump can be selected as the grouting power equipment, depending on the specific situation, to ensure stable and accurate injection of the grout into the sandy medium. During this process, the dynamic changes in grouting pressure are collected and recorded in real time through the coordinated use of pressure transmitters and paperless recorders.

[0058] S4. Grouting Infiltration: After the slurry has fully solidified, select an appropriate seepage velocity to infiltrate the grouting model. Groundwater from the study area is used for infiltration. For the water velocity parameters involved in the infiltration process, values ​​matching the average groundwater velocity in the study area are generally selected as the basic simulation conditions to reflect the prevailing groundwater seepage conditions in the area. However, considering the specific research objectives and diverse needs of different experimental schemes, custom flow velocity settings can be made within a reasonable range.

[0059] S5. Analyze the water quality of the filtered water: During the test, collect the water filtered from the grouting body and conduct comprehensive water quality analysis and special analysis. Water quality testing and analysis indicators include but are not limited to: General measurement indicators: K + , Ca 2+ 、Na + Mg 2+ 、CI - 、 OH - 、 F - 、 Br - 、 pH, total dissolved solids (TDS), electrical conductivity (EC), total hardness (TH), and redox potential (ORP). Organic indicators include total organic carbon (TOC), chemical oxygen demand (COD), free formaldehyde, methylene bisacrylamide (MBA), bisphenol A (BPA), and free isocyanate (TDI). Leachate is collected and analyzed at intervals starting with frequent and then sparse.

[0060] S6. Hydrochemical analysis and evaluation: Based on the acquired water quality test data, analyze the degree of pollution caused by grouting on the water quality of the sandy soil stratum and its dynamic change effect over time. The hydrochemical analysis methods of the grouting leachate mainly include the following:

[0061] 1) Based on the measured leachate ion concentration, plot the Piper diagram and other diagrams to determine the hydrochemical type of the leachate. This allows analysis of the pattern of changes in the groundwater hydrochemical type caused by the grouting fluid. This allows for the identification of the negative effects of grouting contaminants on the overall hydrochemical characteristics of the regional groundwater at a macro level.

[0062] 2) Plot the time-varying curves of water quality indicators and ion concentrations to analyze the impact patterns and changing trends of the grouting fluid on groundwater quality indicators. By fitting the indicators that change significantly during monitoring, the time required for the grouting contamination effect to change from significant to negligible can be accurately determined. This allows the inherent mechanism of grouting contaminants affecting regional groundwater quality to be identified at a microscopic level, and the impact period of grouting on groundwater ion balance can be assessed.

[0063] 3) Draw a Schoeller diagram to analyze the degree of disturbance to groundwater quality caused by the grouting project. By analyzing the fluctuation range of water quality indicators, the degree of normalization and degradation of groundwater quality in the area after grouting can be determined;

[0064] 4) Draw a correlation heat map to analyze the internal connections and interactions between various pollution factors in the grouting pollution process, thereby analyzing the formation sources and mechanisms of grouting pollutants from the perspective of indicator correlation;

[0065] 5) Draw the PCA principal component map to analyze the dominant role of the grouting fluid in the groundwater pollution process, and then reveal the main mechanism of the slurry pollution process from the perspective of multivariate statistical dimensionality reduction.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A test method for evaluating the long-term effect of grouting on the water quality of water-rich sand layers, characterized in that: The following steps are involved: S1. Construction of model test system: The model test system includes a groundwater supply unit, a grouting and infiltration unit, a seepage flow rate monitoring and calibration unit, and a grouting body leachate pretreatment and storage unit, which are connected in sequence; S2. Experimental material pretreatment and grouting model filling: S2-1. Experimental Material Pretreatment: Based on the specific working conditions to be studied, in-situ sand samples were selected from the study area. Systematic testing was conducted on the key properties of the sand, and the obtained data served as preliminary basic data for subsequent experiments. The sand was screened using a vibrating screen to remove particles larger than 5 mm in size. The sand was repeatedly washed with deionized water to filter out biohumus and various metabolic substances. S2-2. Evenly fill the pre-treated sand into the grouting mold according to the designed height and smooth its surface to ensure uniform distribution of the sand. Pre-press the filled sand with the help of a reaction loading device. After pre-pressing, introduce groundwater to fully saturate the mold bucket. S3. Slurry selection and closed grouting: Select the type of slurry according to the research plan requirements and perform closed grouting on the sand in the model; S4. Grouting body penetration: After the slurry is fully solidified, select an appropriate seepage velocity to use the groundwater in the study area to penetrate the grouting body model; S5. Conduct water quality analysis on the filtered water: Conduct comprehensive and special water quality analysis on the water filtered from the grouting body; S6. Hydrochemical analysis and evaluation: Based on the acquired water quality test data, analyze the degree of pollution caused by grouting on the water quality of the sandy geological layer and its dynamic change effect over time; The groundwater supply unit in the model test system includes a constant water head tank (30), the water inlet of the constant water head tank (30) is connected to the water outlet of the water supply tank (27), and the water supply port of the constant water head tank (30) is connected to the grouting and penetration unit; the grouting and penetration unit includes a grouting unit and a penetration unit, and the same grouting bucket (13) is used for the grouting unit and the penetration unit in sequence. When the grouting bucket (13) is used for the grouting unit, the grouting bucket (13) includes a bucket side The wall (7), the upper flange cover plate (1) and the lower flange cover plate (6), the lower surface of the upper flange cover plate (1) is provided with a grouting limit cover plate (2), one end of the grouting pipe (8) passes through the upper flange cover plate (1) and the grouting limit cover plate (2) in sequence, the lower flange cover plate (6) is provided with a drainage pipe interface (5), and the drainage pipe interface (5) is externally connected to a drainage pipe (42); when the grouting bucket (13) is used for the infiltration unit, the upper end of the grouting bucket (13) A joint (9) is provided on the surface, and the joint (9) is connected to the water supply port of the constant head tank (30) through a pipeline. An infiltration buffer bin (10) is provided above the inside of the grouting barrel (13), and the bottom of the infiltration buffer bin (10) is an infiltration limit mesh plate (12). A water outlet bin (17) is provided below the grouting barrel (13), and the water outlet of the water outlet bin (17) is connected to the pretreatment and storage unit of the grouting body leachate; the pretreatment and storage unit of the grouting body leachate The device comprises a buffer sedimentation capsule (23), a filter separator (24) and a liquid storage tank (25) connected in sequence, wherein the liquid inlet of the buffer sedimentation capsule (23) is connected to the water outlet of the water outlet bin (17) via a pipe; the permeation flow rate monitoring and calibration unit comprises a flow meter (21), the flow meter (21) is arranged on a pipe connecting the liquid inlet of the buffer sedimentation capsule (23) and the water outlet of the water outlet bin (17), and the flow meter (21) is provided with a digital display system (22).

2. A test method for evaluating the long-term effect of grouting on the water quality of a water-rich sand layer according to claim 1, characterized in that: The groundwater supply unit further comprises a recycling water tank (26), the water inlet of the recycling water tank (26) being connected to the outlet of the constant water head tank (30); a stop valve (29) is provided on the pipe connecting the water inlet of the constant water head tank (30) and the water outlet of the water supply tank (27), and on the pipe connecting the water inlet of the recycling water tank (26) and the outlet of the constant water head tank (30), and a filter screen (28) is provided in the pipe between the stop valve (29) and the water supply tank (27).

3. A test method for evaluating the long-term effect of grouting on the water quality of a water-rich sand layer according to claim 1, characterized in that: The constant water head tank (30) comprises a water supply chamber (32) and a drainage chamber (38), wherein the water supply chamber (32) and the drainage chamber (38) are connected via a partition (34), wherein a plurality of ball valves (39) are provided on the partition (34), wherein the ball valves (39) are located in the drainage chamber (38), wherein a drainage valve (37) is provided in a drainage port at a lower portion of a side wall of the drainage chamber (38), wherein a movable cover plate (41) is provided at the top end of the water supply chamber (32), wherein a water inlet joint (40) is provided at a water inlet of the movable cover plate (41), and wherein a water supply valve (35) is provided in a water supply port at a lower portion of a side wall of the water supply chamber (32).

4. A test method for evaluating the long-term effect of grouting on the water quality of a water-rich sand layer according to claim 3, characterized in that: A throttle valve (31) is provided on the pipeline connecting the water supply valve (35) of the constant water head tank (30) and the joint (9).

5. The test method for evaluating the long-term effect of grouting on the water quality of water-rich sand layers according to claim 1, characterized in that: A support (36) is provided at the bottom of the constant water head tank (30), a pressure gauge interface is provided on the side wall of the water outlet bin (17), and a pressure gauge (16) is provided at the pressure gauge interface; a sand blocking net (18) is provided in the water outlet of the water outlet bin (17).

6. A test method for evaluating the long-term effect of grouting on water quality in water-rich sand layers according to claim 1, characterized in that: A water stop clamp (19) and a constant flow valve (20) are sequentially provided on the pipeline between the water outlet of the water outlet bin (17) and the flow meter (21).

7. A test method for evaluating the long-term effect of grouting on water quality of water-rich sand layers according to claim 1, characterized in that: The types of slurries in step S3 include inorganic cement-based slurries, organic chemical slurries and composite slurries. The inorganic cement-based slurries include ordinary Portland cement, slag cement, pozzolana cement, fly ash cement and composite Portland cement; the organic chemical slurries include phosphoric acid curing agent urea-formaldehyde resin, oxalic acid curing agent urea-formaldehyde resin, acrylate, epoxy resin and polyurethane; the composite slurries include cement-water glass slurry, epoxy resin-cement composite slurry and polyurethane-cement composite slurry.

8. The test method for evaluating the long-term effect of grouting on water quality of water-rich sand layers according to claim 1, characterized in that: The water quality analysis indicators in step S5 include general measurement indicators and organic indicators. The general measurement indicators include K + , Ca 2+ 、Na + Mg 2+ 、CI - 、SO4 2- 、CO3 2- 、HCO3 - OH - PO4 3- 、F - 、NO2 - Br - and NO3 - As well as pH, total dissolved solids TDS, electrical conductivity EC, total hardness TH and oxidation-reduction potential ORP; the organic indicators include total organic carbon TOC, chemical oxygen demand COD, free formaldehyde, methylene bisacrylamide, bisphenol A and free isocyanate.

9. A test method for evaluating the long-term effect of grouting on water quality of water-rich sand layers according to claim 1, characterized in that: The specific process of step S6 is: S6-1. Draw a Piper diagram based on the measured leachate ion concentration to determine the hydrochemical type of the leachate. This will analyze the pattern of changes in the hydrochemical type of groundwater caused by the grouting fluid and identify the negative effects of grouting pollutants on the overall hydrochemical characteristics of regional groundwater at a macro level. S6-2. Develop time-dependent evolution curves of water quality indicators and ion concentrations to analyze the impact patterns and changing trends of the grouting fluid on groundwater quality indicators. By fitting indicators that change significantly during monitoring, accurately determine the time required for the grouting contamination effect to change from significant to negligible. This allows for the identification of the underlying mechanisms of grouting contaminants affecting regional groundwater quality at a microscopic level, and the assessment of the impact period of grouting on groundwater ion balance. S6-3. Draw a Schoeller diagram to analyze the degree of disturbance to groundwater quality caused by the grouting project. By analyzing the fluctuation range of water quality indicators, determine the degree of normalization and degradation of groundwater quality in the area after grouting. S6-4. Draw a correlation heat map to analyze the internal connections and interactions between various pollution factors in the grouting pollution process, and analyze the sources and mechanisms of grouting pollutants from the perspective of indicator correlation; S6-5. Draw a PCA principal component map to analyze the dominant role of the grouting fluid in the groundwater pollution process and reveal the main mechanism of action in the slurry pollution process from the perspective of multivariate statistical dimensionality reduction.

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