High-risk pollution source management and control method for irregular refuse landfill

Abstract

The invention provides an irregular refuse landfill high-risk pollution source management and control method which comprises the following steps: determining a high-risk pollution source, and delimiting an anti-seepage project area; grouting holes are formed in the anti-seepage engineering area, grouting pipes are arranged in the grouting holes, the grouting pipes penetrate through the landfill layer and enter the anti-seepage target layer, a stop-grouting plug is arranged on each grouting pipe, a grouting section is arranged between each stop-grouting plug and the bottom end of the corresponding grouting pipe, and a grout outlet hole is formed in each grouting section; grouting is conducted in the grouting pipe in a static pressure grouting mode, a waterproof top plate is formed at the lower end of the landfill layer, grouting needs to be conducted 3-4 times before final setting of the grout, and the concentration and the grouting pressure of the initial grout are both smaller than those of the re-grouting grout; and interval grouting is conducted on the grouting pipes. The static pressure grouting technology is adopted to construct and restore the weak area of the waterproof roof of the confined aquifer at the bottom of the high-risk pollution source, grout can be effectively restrained from overflowing upwards, the grout enters an anti-seepage target layer as much as possible, the grout is saved, and the grouting anti-seepage effect is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental engineering, and in particular to a method for controlling high-risk pollution sources in informal garbage landfills. Background Art

[0002] High-risk pollution source control refers to the use of remediation technology, engineering control and institutional control measures to block the exposure pathways of landfill waste pollutants, stop the spread of pollution, and prevent the impact on surrounding human health and ecological receptors. Due to the flow and connectivity of groundwater, as well as the degree of dependence of people's daily production and life on water sources, landfill waste has a greater impact on groundwater pollution. Therefore, preventing high-risk pollution sources from migrating downward to aquifers is the key to the management of informal landfills.

[0003] At present, barrier technology is widely used in the risk control of polluted sites, including vertical barrier technology and horizontal isolation layer technology. The latter mainly adopts the form of horizontal paving on the surface to block the migration and transportation of polluted media to the surrounding environment, including concrete horizontal barrier, clay horizontal barrier, flexible horizontal barrier and other technologies.

[0004] Static pressure grouting technology: Static pressure grouting technology uses the principles of hydraulic pressure, air pressure and electrochemistry to inject a strongly solidified slurry into the formation through a grouting pipe. The slurry takes up its place by squeezing out moisture and air in soil particles or rock cracks through filling, penetration, compaction and splitting. After solidification, the slurry binds the originally loose soil particles or cracks into a whole, thereby changing the physical and mechanical properties of the rock and soil.

[0005] The advantages of static pressure grouting technology for repairing the waterproof roof of the pressurized aquifer are: the slurry has a large diffusion range, the grouting effect on gravel and sandy pebble formations is good, the grouting consolidation body has good bonding degree, the grouting slurry completely enters the formation, and the slurry utilization rate is high.

[0006] The disadvantages of static pressure grouting technology for repairing the waterproof roof of a confined aquifer are: the grouting slurry is poorly controllable, and it is easy to cause slurry leakage and slurry runaway. The slurry is easy to flow out of the anti-seepage area, and the anti-seepage affected area is difficult to effectively control. Summary of the invention

[0007] The present invention proposes a method for controlling high-risk pollution sources in informal landfills, which mainly targets the weak areas of the waterproof top plate of the pressurized aquifer at the bottom of the high-risk pollution source, and uses static pressure grouting technology to reconstruct and restore it. It can also effectively inhibit the slurry from overflowing upward, so that as much slurry as possible can enter the anti-seepage target layer, thereby saving slurry and improving the grouting anti-seepage effect.

[0008] The technical solution of the present invention is implemented as follows: a method for controlling high-risk pollution sources in informal landfills, comprising the following steps:

[0009] (1) Identify high-risk pollution sources and delineate anti-seepage engineering areas;

[0010] (2) Grouting holes are arranged in the anti-seepage engineering area. Grouting pipes are arranged in the grouting holes. The grouting pipes pass through the landfill garbage layer and enter the anti-seepage target layer. A grouting plug is arranged on the grouting pipe. The grouting section is between the grouting plug and the bottom end of the grouting pipe. The grouting section is provided with a grouting hole;

[0011] (3) Grouting is carried out into the grouting pipe by static pressure grouting to form a water-proof roof at the lower end of the landfill garbage layer. Grouting is carried out 3-4 times before the slurry is finally set, with an interval of no more than 1 hour. The initial slurry is used for the first grouting, and the subsequent 2-3 times of re-injection are made with re-injection slurry. The concentration and grouting pressure of the initial slurry are both lower than those of the re-injection slurry. At the beginning of static pressure grouting, a relatively thin slurry and a relatively low grouting pressure are used, and then the slurry concentration and the grouting pressure are gradually increased until the designed process parameters are reached;

[0012] The arranged grouting holes are divided into alternately arranged sequence I grouting holes and sequence II grouting holes. To prevent the occurrence of grouting through holes, the grouting pipes are grouted at intervals according to the sequence I grouting holes and the sequence II grouting holes.

[0013] Furthermore, in step (2), the anti-seepage target layer includes a sand and gravel layer, the lower end of the grouting pipe enters the sand and gravel layer 3-3.5m, the grouting section is 2.5-3m long, a grouting hole is arranged every 20cm along the vertical direction of the grouting section, and a total of 4 rows of grouting holes are arranged along the circumferential direction of the grouting section.

[0014] Furthermore, inside the anti-seepage engineering area: the gravel layer is directly connected to the landfill garbage layer, or there is a high-risk pollution source between the two, the lower end of the grouting pipe enters the gravel layer by 3.5m, and the grouting section is 2.5m long; around the anti-seepage engineering area: there is only a silt layer between the gravel layer and the landfill garbage layer, the lower end of the grouting pipe enters the gravel layer by 3m, and the grouting section is 3m long.

[0015] Furthermore, in step (2), both the initial slurry and the re-injection slurry include cement, bentonite, an accelerator and a binder, wherein the amount of bentonite is 30% to 40% of the mass of cement, the amount of the accelerator is 2% to 4% of the mass of cement, the amount of the binder is 2% to 5% of the mass of cement, the water-cement ratio of the initial slurry is 1.6-1.8:1, the initial grouting pressure is 0.5-2MPa, the water-cement ratio of the re-injection grouting is 0.5-1.5:1, and the re-grouting pressure is 2.1-4MPa.

[0016] Furthermore, the cement is 42.5 ordinary Portland cement; the clay content in the bentonite is not less than 25%, the plasticity index is greater than 14, the sand content is not more than 5%, and the organic matter content is not more than 3%; the accelerator uses water glass, and the binder is silica sol to increase the permeability of the slurry.

[0017] Furthermore, in step (2), a crawler hydraulic drill is used to drill the grouting hole while lowering the casing. The depth of the grouting hole is determined according to the formation conditions revealed by drilling during construction. The deviation between the actual position of the grouting hole and the designed position shall not exceed 10 cm. Then, the grouting pipe is installed. The grouting plug is made of sponge material. The diameter of the grouting plug is larger than the inner diameter of the grouting hole. The hole is sealed with cement slurry. Finally, the casing is pulled out. After the cement slurry solidifies, the grouting of step (3) is carried out.

[0018] Furthermore, in step (1), three methods, namely, drilling, ground geophysical exploration and sample testing, are used to identify the morphological characteristics of the landfill layer, determine the pollution source and delineate the anti-seepage engineering area; among them, the ground geophysical exploration method uses a combination of four methods, namely, geological radar, high-density electrical method, seismic frequency resonance exploration and high-precision magnetic method, to determine the characteristics of the landfill and identify high-risk pollution sources.

[0019] Furthermore, in step (3), the grouting pump is connected to the upper end of the grouting pipe through a soft grouting pipe. The gaps at both ends of the soft grouting pipe are fixed and sealed for single-liquid grouting.

[0020] Furthermore, when the injection rate of the grouting section is no more than 1 L / min under the maximum design pressure, the grouting can be terminated after continuing to grout for 30 minutes.

[0021] Furthermore, in step (2), multiple groups of production tests are carried out before large-scale grouting construction. Four grouting holes can be tested as one group, and a quality inspection hole is arranged at the center. The spacing of the grouting holes in the same group remains consistent, while the spacing of the grouting holes in different groups gradually decreases from large to small. The spacing of the grouting holes is determined based on the test results and is controlled at 2 to 4 m. The spacing of the grouting holes can also be determined based on relevant cases in existing public literature and pilot and production test data.

[0022] Beneficial effects of the present invention:

[0023] The confined aquifer is very thick and is a water-bearing stratum with pressure-bearing properties. The anti-seepage target layer is relatively thin, generally 2.5-3.5m, and is located 2.5-3.5m below the top of the confined aquifer.

[0024] (1) The method of the present invention solves the shortcomings of the existing static pressure grouting method, can be used for deep horizontal grouting anti-seepage, can effectively inhibit the slurry from overflowing upward, and allows as much slurry as possible to enter the anti-seepage target layer, saving slurry and improving the grouting anti-seepage effect; through this method, a continuous and stable waterproof layer is formed, the "skylight" of the aquifer is closed, and the continuous and stable waterproof top plate of the pressure aquifer is restored, thereby preventing the diffusion of pollutants and achieving the purpose of preventing groundwater pollution.

[0025] (2) The method of the present invention does not pollute the environment during the construction process and has significant ecological benefits. Compared with other measures to eliminate the environmental risks of landfill waste (excavation and transportation, high-pressure jet grouting for anti-seepage, etc.), the present invention significantly reduces construction costs.

[0026] (3) The method of the present invention has a small borehole diameter during construction, and directly forms an impermeable layer at the bottom of the landfill, without the need to excavate the ground, causing little damage and disturbance to the existing ground, and causing little ground settlement during construction. It is economical, reliable, and durable. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 Plan layout of grouting holes, quality inspection holes and monitoring wells;

[0029] Figure 2 It is a cross-sectional view of the grouting hole and the grouting pipe;

[0030] Figure 3 The cross-section of the grouting holes in different grouting formations: (a) containing a silt layer, (b) containing a high-risk pollution source, (c) containing a high-risk pollution source and a silt layer, and (d) the landfill garbage layer and the sand and gravel layer are in contact;

[0031] Figure 4 Schematic diagram of the structure of the grouting pipe.

[0032] Grouting hole 1, grouting pipe 2, grouting plug 3, grouting section 4, grouting hole 5, sand and gravel layer 6, landfill garbage layer 7, high-risk pollution source 8, silt layer 9, grouting pump 10, soft grouting pipe 11, anti-seepage target layer 12. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] 1. Project Overview

[0035] Taking the pilot project of anti-seepage transformation of a landfill in a certain area of ​​Anyang City as an example, the application of high-risk pollution source control mode in actual engineering is introduced.

[0036] Through preliminary environmental investigations, it was determined that the carbide slag in the landfill was a high-risk pollution source. The project mainly carried out anti-seepage engineering in the area where the carbide slag overlapped with the "skylight" of the pressurized aquifer, closed the "skylight" of the aquifer, and restored the continuous waterproof roof.

[0037] In order to identify the scope of different types of landfill waste, a total of 32 landfill exploration holes were drilled, including control exploration holes and supplementary exploration holes. The control exploration holes are mainly used to identify the overall landfill scope of the No. 7 landfill, and a total of 5 holes were arranged; the supplementary exploration holes are mainly used to identify the landfill scope of industrial solid waste such as steel slag, fly ash, carbide slag, and chemical waste slag in the No. 7 landfill, and a total of 27 holes were arranged.

[0038] Through sampling and testing, it was found that the hexavalent chromium and cadmium in the carbide slag samples exceeded the standard, and the iron, manganese, lead, pH value and some organic matter indicators were obviously abnormal, indicating that carbide slag is a high-risk pollution source.

[0039] Based on the three-dimensional high-density electrical method, the basic morphological characteristics of the landfill were determined. The average depth of the garbage ranged from 0 to 25 meters, showing the characteristics of deep in the north and shallow in the south. The volume of the landfill calculated based on the three-dimensional results was 1006505m 3 . Based on the high-precision magnetic method, the key distribution areas of ferromagnetic materials are determined: the northeastern part of the survey area, the northern part of the survey area, the southwestern part of the survey area, and the western part of the survey area.

[0040] Comprehensive interpretation was conducted by combining four geophysical exploration techniques to delineate the area of ​​pebbles that are in direct contact between the underground aquifer and the upper landfill garbage. A three-dimensional distribution diagram of carbide slag was drawn. The basic characteristics of carbide slag are: the landfill depth is large, it has been soaked by groundwater, and the lower part is in direct contact with the "skylight" area of ​​the aquifer, which poses the greatest risk. Finally, it was decided to carry out the next step of work in the skylight area where the carbide slag is located.

[0041] 2. Implementation of the high-risk pollution source control methods of informal landfills in this project

[0042] The layout of the anti-seepage engineering area and the grouting holes 1, such as Figure 1 As shown, the arranged grouting holes 1 are divided into alternately arranged sequence I grouting holes and sequence II grouting holes. To prevent the occurrence of grouting through holes, the grouting pipes 2 are grouted at intervals according to the sequence I grouting holes and the sequence II grouting holes.

[0043] like Figure 2-4 As shown in the figure, the diffusion radius is calculated using the spherical diffusion formula. Based on the inferred diffusion radius, combined with relevant cases in the Technical Specification for Grouting of Cover Layers of Water Conservancy and Hydropower Projects (DL / T5267-2012) and pilot and production test data, the row spacing is determined to be 2.0m, and the hole spacing is determined to be 2.0m. Figure 2 shown.

[0044] The borehole diameter is 135mm, and the inner diameter of the grouting pipe is 20mm. The hole depth is determined according to the ground conditions revealed by drilling during construction. The grouting pipe 2 passes through the landfill garbage layer 7 and enters the anti-seepage target layer 12. A stop plug 3 is fixed on the grouting pipe 2. The stop plug 3 is made of sponge material. The diameter of the stop plug 3 is slightly larger than the inner diameter of the grouting hole 1. Cement slurry is used to seal the grouting hole 1 on the upper side of the stop plug 3. The cement slurry has the same formula as the grouting slurry. Between the stop plug 3 and the bottom end of the grouting pipe 2 is the grouting section 4, and the grouting section 4 is provided with a slurry outlet hole 5.

[0045] The anti-seepage target layer 12 includes a gravel layer 6. Inside the anti-seepage project area: the gravel layer 6 is directly connected to the landfill layer 7, or there is a high-risk pollution source 8 between the two. The lower end of the grouting pipe 2 enters the gravel layer 3.5m, and the grouting section is 2.5m long. Figure 3 (b)- Figure 3 (d) As shown; the perimeter of the anti-seepage project area: the grouting hole is 3m deep into the sand and gravel layer below the silt layer 9, and the grouting section is 3m long. Figure 3 As shown in (a), it is ensured that grouting is performed in the sand and gravel layer 6 to form a continuous and effective anti-seepage layer.

[0046] The grouting pump 10 is connected to the upper end of the grouting pipe 2 through the soft grouting pipe 11. The gaps at both ends of the soft grouting pipe 11 are fixed and sealed for single-liquid grouting. The grouting slurry adopts cement-bentonite mixed slurry. Before the slurry is finally set, grouting is required 3-4 times, with a time interval of no more than 1 hour. The static pressure grouting pressure is 4MPa, and the initial grouting pressure is 1.5MPa. The initial slurry is used for the first grouting, and the subsequent 2-3 times of re-injection use re-injection grouting. The initial grouting ratio of each hole is water: cement: bentonite = 700Kg: 400Kg: 120Kg, and the re-injection grouting ratio is water: cement: bentonite = 700Kg: 500Kg: 280Kg, using PC42.5 composite silicate cement and calcium-based bentonite. When the grouting section is under the maximum design pressure and the injection rate is not more than 1L / min, continue to grout for 30min, and the grouting can be ended. When the geological conditions are complex, the groundwater flow rate is high, the injection volume is large, and the grouting pressure is low, the continuous grouting time should be appropriately extended. During the grouting process, if the grouting pressure or injection rate suddenly changes greatly, the cause should be immediately identified and appropriate measures should be taken to deal with it. If grouting or leakage is found during the grouting process, low pressure, thick slurry, flow limitation, and quantity limitation should be used according to the specific situation.

[0047] The grouting construction process is as follows: measurement - drilling rig in place - drilling - casing installation - drilling hole - installing grouting pipe / stop plug - sealing hole - pulling out casing - grouting. The structure of the grouting pipe is as follows: Figure 4 shown.

[0048] 3. Effect verification

[0049] (1) 12 quality inspection holes were set up. Through water injection test, the permeability coefficient of the anti-seepage target layer after grouting was 1.04×10 -6 ~3.81×10 -5 cm / s, compared with the original formation permeability coefficient before grouting (1.98×10 -2 ~1.26×10 -3 cm / s); reaching the permeability level of silty clay, it can be regarded as an aquiclude, which can effectively prevent pollution factors from migrating downward into the underlying aquifer.

[0050] (2) Core testing showed that cement slurry was clearly visible to the naked eye in all 12 quality inspection holes of this work. The color was grayish white, the distribution depth was 25.0 to 31.4 m, and the distribution thickness was 1.0 to 4.4 m.

[0051] (3) Based on a comprehensive analysis of the quality inspection results, it is believed that the anti-seepage project has formed a continuous and stable impermeable layer, which can close the "skylight" of the aquifer and restore the continuous and stable impermeable roof of the confined water layer, thereby achieving the purpose of preventing groundwater pollution and reducing the impact of the landfill on the groundwater environment.

[0052] 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, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for controlling high-risk pollution sources in informal landfills, characterized in that: The following steps are involved: (1) Identify high-risk pollution sources and delineate anti-seepage engineering areas; (2) Grouting holes are arranged in the anti-seepage engineering area. Grouting pipes are arranged in the grouting holes. The grouting pipes pass through the landfill garbage layer and enter the anti-seepage target layer. A grouting plug is arranged on the grouting pipe. The grouting section is between the grouting plug and the bottom end of the grouting pipe. The grouting section is provided with a grouting hole; (3) Grouting is performed into the grouting pipe by static pressure grouting to form a continuous waterproof roof at the lower end of the landfill garbage layer. Grouting is performed 3-4 times before the slurry is finally set, with the time interval not exceeding 1 hour. The initial slurry is used for the first grouting, and the subsequent 2-3 times are injected with the secondary slurry. The concentration and grouting pressure of the initial slurry are both lower than those of the secondary slurry. The arranged grouting holes are divided into alternately arranged sequence I grouting holes and sequence II grouting holes, and the grouting pipes are grouted at intervals according to the sequence I grouting holes and the sequence II grouting holes.

2. A method for controlling high-risk pollution sources in informal landfills according to claim 1, characterized in that: In step (2), the anti-seepage target layer includes a gravel layer, the lower end of the grouting pipe enters the gravel layer 3-3.5m, the grouting section is 2.5-3m long, a grouting hole is set every 20cm along the vertical direction of the grouting section, and a total of 4 rows of grouting holes are set along the circumferential direction of the grouting section.

3. A method for controlling high-risk pollution sources in informal landfills according to claim 2, characterized in that: Inside the anti-seepage project area: the gravel layer is directly connected to the landfill layer, or there is a high-risk pollution source between the two. The lower end of the grouting pipe enters the gravel layer by 3.5m, and the grouting section is 2.5m long. Around the anti-seepage project area: there is only a silt layer between the gravel layer and the landfill layer. The lower end of the grouting pipe enters the gravel layer by 3m, and the grouting section is 3m long.

4. A method for controlling high-risk pollution sources in informal landfills according to claim 1, characterized in that: In step (2), the initial slurry and the re-injection slurry both include cement, bentonite, an accelerator and a binder, wherein the amount of bentonite is 30% to 40% of the mass of cement, the amount of the accelerator is 2% to 4% of the mass of cement, the amount of the binder is 2% to 5% of the mass of cement, the water-cement ratio of the initial slurry is 1.6-1.8:1, the initial grouting pressure is 0.5-2MPa, the water-cement ratio of the re-injection slurry is 0.5-1.5:1, and the re-grouting pressure is 2.1-4MPa.

5. A method for controlling high-risk pollution sources in informal landfills according to claim 4, characterized in that: The cement is 42.5 ordinary Portland cement; the clay content in the bentonite is not less than 25%, the plasticity index is greater than 14, the sand content is not more than 5%, and the organic matter content is not more than 3%; the accelerator is water glass, and the binder is silica sol.

6. A method for controlling high-risk pollution sources in informal landfills according to claim 2, characterized in that: In step (2), a crawler hydraulic drill is used to drill the grouting hole while lowering the casing. The depth of the grouting hole is determined according to the stratum conditions revealed during drilling during construction. The deviation between the actual position of the grouting hole and the designed position shall not exceed 10 cm. Then, the grouting pipe is installed. The grouting plug is made of sponge material. The diameter of the grouting plug is larger than the inner diameter of the grouting hole. The hole is sealed with cement slurry. Finally, the casing is pulled out. After the cement slurry solidifies, the grouting of step (3) is carried out.

7. A method for controlling high-risk pollution sources in informal landfills according to claim 1, characterized in that: In step (1), three methods, namely drilling, ground geophysical exploration and sample testing, are used to identify the morphological characteristics of the landfill layer, determine the pollution source and delineate the anti-seepage project area; among them, the ground geophysical exploration method uses a combination of four methods, namely geological radar, high-density electrical method, seismic frequency resonance exploration and high-precision magnetic method, to determine the characteristics of the landfill and identify high-risk pollution sources.

8. The method for controlling high-risk pollution sources in informal landfills according to claim 1 is characterized in that: In step (3), the grouting pump is connected to the upper end of the grouting pipe through the soft grouting pipe.

9. The method for controlling high-risk pollution sources in informal landfills according to claim 1 is characterized in that: When the injection rate of the grouting section is no more than 1L / min under the maximum design pressure, continue grouting for 30 minutes and then the grouting can be terminated.

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