Test method for evaluating long-term influence of grouting on water quality of water-rich sand layer

Abstract

The invention discloses a test method for evaluating the long-term influence of grouting on the water quality of a water-rich sand layer. The test method comprises the following steps: S1, building a model test system; S2, pretreating an experimental material and filling a grouting model; S3, selecting slurry and performing closed grouting; the method has replaceability of the grouting material and adjustability of the seepage flow velocity, and feedback adjustment of the seepage flow velocity and long-term real-time dynamic monitoring recording can be achieved through devices such as a flow meter; in the grouting percolation process, the permeability of the grouting body can be measured at the same time; the pollution effect of grouting on the groundwater environment and the interaction between slurry and a geologic body can be explored by analyzing the water quality information of the grouting percolate; the invention further provides a subsequent water chemical analysis sample plate of the grouting leachate, so that indoor systematic evaluation on grouting pollution is formed.

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 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] At present, most of the existing studies on the impact of grouting on the groundwater environment are carried out based on the mine grouting site. Specifically, water samples are collected from underground drainage holes and excavation water points, and the collected water samples are sent for inspection, and then the relevant 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, is too restricted by the actual site conditions and engineering plans, and cannot rule out the excessive interference of local abnormal geochemical characteristics of rock and soil on water quality. The sampling cost and cycle are long, time-consuming and labor-intensive, not flexible enough, and poorly targeted. The 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. Therefore, a new post-grouting infiltration model system of geological bodies is constructed 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 of 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 a water-rich sand layer, comprising the following steps:

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

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

[0009] S2-1. Pretreatment of experimental materials: According to the specific working conditions to be studied, select in-situ sand samples in the study area, and carry out systematic tests on the key properties of the sand, and use the obtained data as the preliminary basic data for subsequent experiments; use a vibrating screening machine to select the sand and remove particles with a particle size greater than 5mm; use deionized water to repeatedly wash the sand and filter out biological humus and various metabolic substances;

[0010] S2-2, evenly fill the pre-treated sand into the grouting model according to the designed height, and level its surface to ensure the uniformity of sand distribution; pre-press the filled sand with the help of a reaction loading device, and introduce groundwater after pre-pressing to fully saturate the model 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 trough, the water inlet of the constant water head trough is connected to the water outlet of the water supply tank, and the water supply port of the constant water head trough 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 is used for the grouting unit and the penetration unit successively. 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, a grouting limit cover plate is provided on the lower surface of the upper flange cover plate, one end of the grouting pipe passes through the upper flange cover plate and the grouting limit cover plate in sequence, and a drain pipe interface is opened on the lower flange cover plate, and the drain pipe interface is externally connected to a drain pipe; when the grouting bucket is used for the penetration unit, the A joint is provided on the upper end surface of the grouting barrel, and the joint is connected to the water supply port of the constant head tank through a pipeline. 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 comprises a buffer sedimentation capsule, a filter separator and a liquid storage tank connected in sequence, and the liquid inlet of the buffer sedimentation capsule is connected to the water outlet of the water outlet bin through a pipeline; the infiltration flow rate monitoring and calibration unit comprises a flow meter, and the flow meter is arranged on the pipeline connecting the liquid inlet of the buffer sedimentation capsule 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; water stop valves are provided on the pipe connecting the water inlet of the constant water head tank and the water outlet of the water supply tank, and on the pipe connecting the water inlet of the recycling circulating water tank and the drain outlet of the constant water head tank, 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 pipeline 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 water quality analysis indicators 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, analyze the change pattern of the grouting fluid on the hydrochemical type of groundwater, and identify the negative effects of grouting pollutants on the overall hydrochemical characteristics of regional groundwater from a macro perspective;

[0025] S6-2. Draw the time evolution curves of water quality indicators and ion concentrations to analyze the influence and change trend of the grouting fluid on groundwater quality indicators. By fitting the indicators that have changed significantly during monitoring, accurately determine the time required for the grouting pollution effect to change from significant to negligible, identify the internal mechanism of grouting pollutants on regional groundwater quality changes at the microscopic level, and evaluate the impact period of grouting on groundwater ion balance;

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

[0027] S6-4. Draw a correlation heat map to analyze the internal connection and interaction between various pollution factors in the grouting pollution process, and analyze the formation source and mechanism of grouting pollutants from the perspective of indicator correlation;

[0028] S6-5. Draw the PCA principal component map to analyze the dominant role of the grouting liquid 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, so as to realize continuous circulation, flexible and highly customized experimental research; 2) Adjustability of infiltration flow rate: The required percolation flow rate can be adjusted by changing the head height and the valve opening; 3) Feedback adjustment of the infiltration flow rate and long-term real-time dynamic monitoring and recording can be realized 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 a constant head tank of the present invention;

[0032] Figure 3 It is a schematic diagram of the structure when the grouting bucket of the present invention is 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, drainage pipe interface, 6, lower flange cover, 7, barrel side wall, 8, grouting pipe, 9, joint, 10, infiltration buffer bin, 11, upper screw, 12, infiltration limit mesh plate, 13, grouting barrel, 14, lower screw, 15, bracket, 16, pressure gauge, 17, water outlet bin, 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 is described in detail below in conjunction with 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 infiltration unit II, a seepage flow rate monitoring and calibration unit III and a grouting body permeate 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 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 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 stop valve 29 and the water supply tank 27. As shown 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, wherein the water supply chamber 32 is connected to the drainage chamber 38 through a partition 34, and a plurality of ball valves 39 are provided on the partition 34, and 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 valves 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, a movable cover plate 41 is provided at the top end of the water supply chamber 32, and a water inlet joint 40 is provided on the water inlet of the movable cover plate 41, a water supply valve 35 is provided in the water supply port at the lower part of the side wall of the water supply chamber 32, 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, 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 penetration unit II includes a grouting unit and a penetration unit. The same grouting bucket 13 is used for the grouting unit and the penetration 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, and 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 the 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, and 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, and an infiltration buffer bin 10 is provided on the upper part of the grouting barrel 13, and the bottom of the infiltration buffer bin 10 is an infiltration limit mesh plate 12, and 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 bin 17 is provided below the grouting barrel 13, and the water outlet of the water outlet bin 17 is connected to the seepage velocity monitoring and calibration unit III; 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. Through this unit, groundwater can achieve long-term constant flow (flow rate) dynamic infiltration of the geological body (sand body) after grouting.

[0038] The above-mentioned infiltration flow rate monitoring and calibration unit III includes a flow meter 21, which is arranged on a pipe connecting the liquid inlet of the buffer sedimentation capsule 23 and the water outlet of the water outlet tank 17, and the flow meter 21 is provided with a digital display system 22 based on the digital circuit of the Arduino development board. The unit measures the water flow rate per unit time in the outlet pipeline through the flow meter 21, and converts it to obtain the corresponding instantaneous infiltration flow rate of groundwater in the grouting bucket 13, and then further regulates the flow rate in the bucket by adjusting the placement height of the constant head tank 30, fine-tuning the water level in the head tank and the opening of the lower constant flow valve 20 of the pipeline to reach the expected value. In addition, in the subsequent long-term infiltration process, the flow meter 21 can be connected to the digital display system 22 through the Arduino development board to monitor the outlet flow rate in real time and record the instantaneous and cumulative flow rates.

[0039] The pretreatment and storage unit IV of the grouting body leachate includes a buffer sedimentation capsule 23, a filter separator 24 and a liquid storage tank 25 connected in sequence. The liquid inlet of the buffer sedimentation capsule 23 is connected to the water outlet of the water outlet bin 17 through a pipeline; the pipeline between the water outlet of the water outlet bin 17 and the flow meter 21 is provided with a water stop clamp 19 and a constant flow valve 20 in sequence. The leachate flowing out of the barrel first flows through the buffer sedimentation capsule 23. During this process, the impurities with relatively large particle size in the leachate are removed due to precipitation; then, the leachate enters the filter separator 24 and is filtered through the 45μm water filter head therein, thereby filtering out fine impurity particles; finally, the leachate after the above treatment flows into the liquid storage tank 25 for storage. This process plays a preliminary purification role, ensuring that the leachate flowing into the liquid storage tank 25 has a high degree of purity, and laying a good foundation for the quality of the liquid for subsequent related treatment or analysis applications.

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

[0041] S1, pre-grouting: put the sand and soil in the proposed study area into the grouting bucket 13, fill it flat to a preset height, pre-press it through the reaction force loading device to make it reach the density required by the study conditions, then saturate it with water to make the sand and soil reach a saturated state, open the drainage pipe interface 5 of the grouting bucket 13, inject the slurry to squeeze and displace it, and the excess water will be discharged from the drainage pipe 42; fix the grouting limit cover plate 2 in the grouting bucket 13, prepare the grouting material to be studied into slurry, and perform closed grouting 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 use Darcy's law V = K·J to calculate the hydraulic slope J, and then use h L = J·L Preliminary estimate of the required groundwater infiltration head, that is, the pressure head at the top interface of the sand and soil in the bucket h 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 proposed study area, K is the permeability coefficient of the sand and soil in the barrel after grouting, and L is the length of the permeability path, i.e., the filling height of the sand and soil in the barrel;

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

[0044] S4, connect the seepage flow rate monitoring and calibration unit, open the joint 9 on the upper part of the grouting bucket 13 and the throttle valve 31 on the upper part of the water delivery pipeline, calibrate the digital flow meter 22 to feedback and adjust the water head height in the constant head tank 30 and the opening of the constant flow valve 20 at the lower position of the pipeline, so that the flow rate in the grouting bucket 13 is 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 realized 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 preliminarily purified by the buffer sedimentation capsule 23 and the filter separator 24; then, according to the different requirements of the specific test scheme, water samples are taken from the liquid storage tank 25 at regular and quantitative intervals 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 collected 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 the filtration test of one slurry is completed, the grouting barrel 13 can be disassembled and replaced with another slurry to be studied, so as to realize continuous circulation, flexible and highly customized experimental research; the seepage flow rate is adjustable: the head height of the constant head tank 30 and the opening of the constant flow valve 20 can be changed to adjust to the required seepage flow rate; the feedback adjustment of the seepage flow rate and long-term real-time dynamic monitoring and recording can be realized 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 the 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 with 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 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 rate in real time to ensure the accuracy of the experimental data; and the grouting body permeate pretreatment and storage unit performs preliminary treatment on the permeate 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 percolation simulation can be implemented on the grouting body. 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 samples in the study area according to the specific working conditions to be studied, and conduct systematic tests on the key properties of the sand, such as the chemical composition and mineral composition, and use the obtained data as the 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 remove particles with a particle size greater than 5 mm. At the same time, the sand is repeatedly washed with deionized water to filter out the biological humus and various metabolic substances contained therein, so as to minimize 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 leveled to ensure the uniformity of the sand distribution. In order to simulate the in-situ pressure state of the sand on site, the loaded sand is pre-pressed with the help of a reaction loading device to simulate the density of the actual stratum. After pre-pressing, groundwater is introduced to fully saturate the model barrel, 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 the experimental group. At the same time, according to the same operating process, a number of test barrels were set up synchronously to carry out multiple parallel experiments.

[0056] 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. Applicable slurries include but are not limited to - inorganic cement-based slurries: ordinary Portland cement, slag cement, pozzolana cement, fly ash cement, composite Portland cement; organic chemical slurries: phosphoric acid curing agent urea-formaldehyde resin, oxalic acid curing agent urea-formaldehyde resin, acrylate, epoxy resin, polyurethane; composite slurries: cement-water glass slurry, epoxy resin-cement composite slurry, polyurethane-cement composite slurry;

[0057] When injecting slurry, a reciprocating piston grouting pump, a constant pressure air pump or a screw pump can be selected as the grouting power equipment according to the specific situation to ensure that the slurry can be stably and accurately injected into the sand medium. During this period, the dynamic changes of the grouting pressure are collected and recorded in real time by using pressure transmitters and paperless recorders and other equipment in coordination.

[0058] S4. Grouting body penetration: After the slurry is fully solidified, select an appropriate seepage velocity to penetrate the grouting body model. The groundwater in the study area is used for penetration. For the setting of water flow velocity parameters involved in the penetration process, in general, a value matching the average groundwater flow velocity in the study area is selected as the basic simulation condition to reflect the general state of groundwater seepage in the area. However, considering the specific research purposes and diversified needs of different test schemes, the flow velocity can also be customized within a reasonable range.

[0059] S5. Water quality analysis of the filtered water: During the test, the water filtered out of the grouting body is collected and subjected to full water quality analysis, special analysis and other tests. 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, conductivity EC, total hardness TH, redox potential ORP. Organic indicators: total organic carbon TOC, chemical oxygen demand COD, free formaldehyde, methylene bisacrylamide (MBA), bisphenol A (BPA), free isocyanate (TDI). The collected leachate is analyzed for water quality according to the principle of setting the time interval from dense to sparse.

[0060] 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 soil geological layer and its dynamic change effect over time. The hydrochemical analysis methods of the grouting body leachate involved mainly include the following contents:

[0061] 1) Draw Piper diagrams and other diagrams based on the measured leachate ion concentration to determine the hydrochemical type of the leachate, so as to analyze the change pattern of the grouting fluid on the hydrochemical type of groundwater, thereby identifying the negative effects of grouting pollutants on the overall hydrochemical characteristics of regional groundwater from a macro perspective;

[0062] 2) Draw the time evolution curve of water quality indicators and ion concentration to analyze the influence and change trend of the grouting fluid on groundwater quality indicators. By fitting the indicators that have changed significantly during monitoring, the time required for the grouting pollution effect to change from significant to negligible can be accurately determined. In this way, the internal mechanism of grouting pollutants on regional groundwater quality changes can be identified at the microscopic level, and the impact period of grouting on groundwater ion balance can be evaluated;

[0063] 3) Draw Schoeller diagrams to analyze the degree of disturbance of groundwater quality caused by grouting. 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 connection and interaction between various pollution factors in the grouting pollution process, so as to analyze the formation source and mechanism 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 liquid 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 protection scope 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 infiltration unit, a permeation flow rate monitoring and calibration unit, and a grouting body leachate pretreatment and storage unit connected in sequence; S2. Experimental material pretreatment and grouting model filling: S2-1. Pretreatment of experimental materials: According to the specific working conditions to be studied, select in-situ sand samples in the study area, and carry out systematic tests on the key properties of the sand, and use the obtained data as the preliminary basic data for subsequent experiments; use a vibrating screening machine to select the sand and remove particles with a particle size greater than 5mm; use deionized water to repeatedly wash the sand and filter out biological humus and various metabolic substances; S2-2, evenly fill the pre-treated sand into the grouting model according to the designed height, and level its surface to ensure the uniformity of sand distribution; pre-press the filled sand with the help of a reaction loading device, and introduce groundwater after pre-pressing to fully saturate the model 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 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.

2. 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 groundwater supply unit in the model test system comprises 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 comprises a grouting unit and a penetration unit, and the same grouting bucket (13) is used for the grouting unit and the penetration unit successively. When the grouting bucket (13) is used for the grouting unit, the grouting bucket (13) comprises a bucket side The invention relates to a wall (7), an upper flange cover plate (1) and a lower flange cover plate (6), wherein a grouting limit cover plate (2) is provided on the lower surface of the upper flange cover plate (1), one end of a grouting pipe (8) passes through the upper flange cover plate (1) and the grouting limit cover plate (2) in sequence, and a drainage pipe interface (5) is provided on the lower flange cover plate (6), and the drainage pipe interface (5) is externally connected to a drainage pipe (42); when a grouting bucket (13) is used for a permeation 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. A permeation buffer bin (10) is provided above the inside of the grouting barrel (13), and the bottom of the permeation buffer bin (10) is a permeation 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 permeate; the pretreatment and storage unit of the grouting body permeate The invention comprises a buffer sedimentation capsule (23), a filter separator (24) and a liquid storage tank (25) which are 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) through a pipeline; the permeation flow rate monitoring and calibration unit comprises a flow meter (21), wherein the flow meter (21) is arranged on a pipeline 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).

3. A test method for evaluating the long-term effect of grouting on water quality of water-rich sand layers according to claim 2, 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 drain outlet of the constant water head tank (30); 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 on the pipe connecting the water inlet of the recycling water tank (26) and the drain outlet 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).

4. A test method for evaluating the long-term effect of grouting on water quality of water-rich sand layers according to claim 2, characterized in that: The constant water head tank (30) comprises a water supply chamber (32) and a drainage chamber (38). The water supply chamber (32) and the drainage chamber (38) are connected via a partition (34). The partition (34) is provided with a plurality of ball valves (39). The ball valves (39) are located in the drainage chamber (38). A drainage valve (37) is provided in a drainage port at the lower part of the side wall of the drainage chamber (38). A movable cover plate (41) is provided at the top end of the water supply chamber (32). A water inlet joint (40) is provided at the water inlet of the movable cover plate (41). A water supply valve (35) is provided in the water supply port at the lower part of the side wall of the water supply chamber (32).

5. A test method for evaluating the long-term effect of grouting on water quality of water-rich sand layers according to claim 4, 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).

6. A test method for evaluating the long-term effect of grouting on water quality of water-rich sand layers according to claim 2, 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).

7. A test method for evaluating the long-term effect of grouting on water quality of water-rich sand layers according to claim 2, characterized in that: A water stop clamp (19) and a constant flow valve (20) are sequentially arranged on the pipeline between the water outlet of the water outlet bin (17) and the flow meter (21).

8. 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 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.

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 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 - , 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.

10. 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, analyze the change pattern of the grouting fluid on the hydrochemical type of groundwater, and identify the negative effects of grouting pollutants on the overall hydrochemical characteristics of regional groundwater from a macro perspective; S6-2. Draw the time evolution curves of water quality indicators and ion concentrations to analyze the influence and change trend of the grouting fluid on groundwater quality indicators. By fitting the indicators that have changed significantly during monitoring, accurately determine the time required for the grouting pollution effect to change from significant to negligible, identify the internal mechanism of grouting pollutants on regional groundwater quality changes at the microscopic level, and evaluate the impact period of grouting on groundwater ion balance; S6-3. Draw Schoeller diagrams to analyze the degree of disturbance of groundwater quality caused by grouting works, and determine the degree of normalization and degradation of groundwater quality in the area after grouting by analyzing the fluctuation range of water quality indicators; S6-4. Draw a correlation heat map to analyze the internal connection and interaction between various pollution factors in the grouting pollution process, and analyze the formation source and mechanism of grouting pollutants from the perspective of indicator correlation; S6-5. Draw the PCA principal component map to analyze the dominant role of the grouting liquid 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.

Images