CN110541436A - Double-layer HDPE (high-density polyethylene) film vertical antifouling barrier structure containing leakage detection layer and method - Google Patents
Double-layer HDPE (high-density polyethylene) film vertical antifouling barrier structure containing leakage detection layer and method Download PDFInfo
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Abstract
The invention discloses a double-layer HDPE film vertical antifouling barrier structure containing a leakage detection layer and a method. The method comprises the steps that a vertical antifouling separation wall body penetrates into a water barrier layer from the ground surface through a site aquifer to separate a polluted aquifer from an uncontaminated aquifer, the wall body comprises HDPE geomembranes, high-permeability materials and a leakage monitoring well, a groove is formed in the wall body, the groove extends into the water barrier layer, the HDPE geomembranes are arranged on the inner wall surfaces of the groove to form double-layer HDPE geomembranes, and the lower portion of the double-layer HDPE geomembrane is embedded into the water barrier layer vertically; and a leakage monitoring well is arranged in the center of the groove, and a high-permeability material is arranged in the groove around the leakage monitoring well. The vertical antifouling barrier structure has the advantages of multiple antifouling functions, low permeability, high reliability and the like, has the advantages of full-depth section leakage detection, timely monitoring feedback and the like, is mature in construction technology, and can effectively avoid barrier structure failure caused by HDPE geomembrane hole breaking.
Description
Technical Field
The invention relates to a method for preventing and controlling pollution risks of soil and underground water and soil, in particular to a vertical antifouling barrier structure with a double-layer HDPE film and a method thereof.
Background
The rapid development of the economy of China causes serious soil and underground water and soil pollution. The centralized disposal sites for wastes such as municipal solid wastes (especially tens of thousands of unqualified simple municipal solid waste landfill sites or storage yards) generally have the problem of underground pollution, and the contents of heavy metals and organic pollutants in the sites left after a large number of industrial enterprises are moved are obviously out of limits. The vertical antifouling separation wall is a main technical means for effectively controlling the pollution of the pollution source to the surrounding underground environment.
The HDPE geomembrane is fully called as a high-density polyethylene geomembrane, is widely used for vertical antifouling and barrier in recent years at home and abroad, and has good impermeability and strong heavy metal and organic matter resistance and control capability.
The problem of connection defect between geomembrane width exists in the antifouling separation structure of current individual layer HDPE geomembrane vertical. If the form of inter-web lap joint is adopted, leakage is easy to form at the lap joint part because the lateral stress of the vertical barrier structure is small (particularly shallow). Therefore, most of the single-layer HDPE geomembrane vertical antifouling barrier structures adopt a lock catch connection mode, but are influenced by the construction technology level, the lock catch connection position is easy to have defects in the construction process to cause leakage, for example, the lock catch of the membrane width in the membrane discharging process is bent or foreign matters are mixed to cause that a newly inserted membrane width cannot be inserted to a preset depth, or the lock catch between the membrane widths is disengaged, or the lock catch water stopping strip between the membrane widths is not placed in place to cause that a local water stopping strip is lost.
The integrity of the HDPE geomembrane and the sealing performance between membrane webs are key factors for ensuring the effectiveness of the vertical antifouling barrier structure of the geomembrane. The integrity of the membrane and the tightness between membrane webs are detected by an electrical method in the construction period, the method is originally mainly applied to a horizontal liner containing a geomembrane, the sensitivity of the method is reduced when the thickness of a soil layer on the geomembrane is more than 1m, and the method is not suitable when the thickness of the soil layer is more than 3 m. The effect of electric detection in the vertical barrier wall is not as good as that of detection of a horizontal liner, the detection of the defect of the shallow geomembrane with the depth of less than 10m is relatively reliable, and the detection of the defect of the geomembrane with the depth of more than 10m is relatively poor. The existing single-layer soil barrier wall or geomembrane vertical antifouling long-term service performance monitoring mainly adopts a monitoring well system, namely a monitoring well is arranged at the downstream of the barrier wall at a certain distance to monitor the quality of underground water. If a leak is detected downstream, this indicates that the barrier wall has failed. The system can not feed back the service condition of the barrier wall in time, and can not prevent the pollutant diffusion behavior in time. On the other hand, the influence range of the monitoring wells is limited and is influenced by the dilution of underground water, and the leakage condition of the area between the two monitoring wells cannot be monitored in time.
disclosure of Invention
the invention aims to provide a double-layer HDPE film vertical antifouling barrier structure containing a leakage detection layer and a method thereof.
the invention is realized by the following technical scheme:
A vertical antifouling barrier structure of a double-layer HDPE film containing a leakage detection layer comprises:
The perpendicular antifouling separation structure of double-deck HDPE membrane sets up in the soil body, and the soil body is including polluting aquifer, uncontaminated aquifer and water barrier, its characterized in that: the double-layer HDPE geomembrane vertical antifouling barrier structure comprises a double-layer HDPE geomembrane vertical barrier wall body arranged between a polluted aquifer and an uncontaminated aquifer, wherein the double-layer HDPE geomembrane vertical barrier wall body comprises an HDPE geomembrane, a high-permeability material and a leakage monitoring well, a groove is formed between the polluted aquifer and the uncontaminated aquifer, the groove extends into the aquifer, the HDPE geomembranes are arranged on the inner wall surfaces of the grooves to form the double-layer HDPE geomembrane, and the lower part of the double-layer HDPE geomembrane vertical barrier wall body is embedded into the aquifer below the site aquifer; a leakage monitoring well is arranged in the center of the groove, high-permeability materials are arranged in the grooves on the two sides and the bottom of the leakage monitoring well, and the periphery of the high-permeability materials is surrounded and coated by an HDPE geomembrane; the upper end of the leakage monitoring well extends out of the ground and is sealed by a monitoring well protective cover, and guide walls are arranged on two sides of the groove at the top; the double-layer HDPE geomembrane is surrounded by a back cover low-permeability material outside the part embedded into the water-resisting layer at the bottom of the vertical partition wall body.
The HDPE geomembrane is a high-density polyethylene film, and the main components of the HDPE geomembrane are 97.5 percent of high-density polyethylene, about 2.5 percent of carbon black, a small amount of anti-aging agent, antioxidant, ultraviolet absorbent, stabilizer and the like.
The field aquifer refers to soil layers with large permeability coefficients such as silt or sandy soil.
The ground surfaces of the grooves on the two sides are provided with anchoring ditches, the HDPE geomembrane extends out of the ground and then extends through the anchoring ditches to be arranged, and concrete is filled on the surface of the HDPE geomembrane of each anchoring ditch, so that the tops of the HDPE geomembranes are anchored and fixed by the anchoring ditches.
And a leakage detection layer is formed by the high-permeability material and the leakage monitoring well and is arranged in the double-layer HDPE geomembrane.
The vertical barrier wall body of double-deck HDPE geomembrane be provided with wall side low permeability backfill near the one side of uncontaminated aquifer, wall side low permeability backfill arranges in the vertical soil body space between wall and the HDPE geomembrane, wall side low permeability backfill bottom extends to the interface between uncontaminated aquifer and the water barrier, forms the compound vertical antifouling barrier structure of double-deck HDPE geomembrane that contains the seepage detection layer.
In a specific implementation, the wall side low permeability backfill and the side of the back cover low permeability material of the double-layer HDPE geomembrane are aligned.
The thickness of the wall body of the double-layer HDPE geomembrane vertical barrier wall is 0.3 m-0.9 m.
The thickness of the HDPE geomembrane of the double-layer HDPE geomembrane vertical barrier wall body is 2.0 mm-3.0 mm.
The embedded depth of the double-layer HDPE geomembrane in the vertical barrier wall body embedded into the waterproof layer is not less than 1.5m, and the depth of the double-layer HDPE geomembrane in the vertical barrier wall body is not more than 20 m.
The permeability coefficient of the low-permeability backfill material and the low-permeability material at the back cover is not more than 1 x 10 < -7 > cm/s.
The low-permeability backfill material and the bottom sealing low-permeability material are soil-bentonite, cement-bentonite or soil-cement-bentonite.
Specifically, the soil-bentonite material is a mixture of soil/bentonite/water, wherein bentonite slurry accounts for 30-40% of the total mass of the mixture, and the bentonite slurry accounts for 5-10% of the mass of the bentonite slurry. The mother soil accounts for 60-70% of the total mass of the mixture.
specifically, the cement-bentonite material is a mixture of cement/bentonite/water, a mixture of ground granulated blast furnace slag/cement/bentonite/water or a mixture of fly ash/cement/bentonite/water, wherein the mass of the cement accounts for 15-30% of the total mass of the mixture; the mass of the bentonite accounts for 5-10% of that of the bentonite slurry, and the mass of the bentonite slurry prepared from the bentonite and water accounts for 70-85% of the total mass of the mixture.
Specifically, the soil-cement-bentonite material is a mixture of soil/cement/bentonite/water, wherein the mass of the parent soil accounts for 50-65% of the total mass of the mixture; the mass of the cement accounts for 5-10% of the total mass of the mixture; the mass of the bentonite accounts for 5-10% of that of the bentonite slurry, and the mass of the bentonite slurry accounts for 30-40% of the total mass of the mixture.
the high-permeability material is medium coarse sand, a sand-water mixture, a geonet or a geogrid with good grading. Specifically, if the wall thickness is designed to be small, geogrids or geonets can be preferentially adopted for filling; if the wall thickness is designed to be large, sand or a sand-water mixture can be preferably used for backfilling.
The leakage monitoring well is a perforated pipe. In particular to a perforated pipe with non-woven fabric wrapping on the outer side, and the distance between the perforated pipes is 10 m-20 m.
The water-resisting layer is a natural water-resisting layer with the permeability coefficient less than 1 x 10 < -7 > cm/s.
Secondly, a construction method of the vertical antifouling barrier structure of the double-layer HDPE geomembrane comprises the following steps:
1) Leveling a field, and determining the horizontal central axis and the width of a wall body of a double-layer HDPE vertical antifouling separation wall between a polluted aquifer and an uncontaminated aquifer on the ground of the field; the horizontal central axis is the central line of the double-layer HDPE geomembrane which is vertical to the barrier wall body and is positioned on the ground;
2) according to the horizontal central axis of the vertical barrier wall body of the double-layer HDPE geomembrane and the width of the wall body, firstly constructing guide walls in foundations on two sides of the ground surface part of the vertical barrier wall body of the double-layer HDPE geomembrane, and performing grooving operation after the guide walls reach 70% of design strength;
3) Preparing bentonite slurry which takes water and bentonite as main raw materials;
4) A groove is formed between the polluted aquifer and the uncontaminated aquifer according to the horizontal central axis of the wall body, guide walls are fixedly arranged in soil bodies on two sides of the upper end of the groove, which are positioned on the ground, and the lower end of the groove extends into the water-resisting layer;
5) Before arranging the HDPE geomembrane, filling a low-permeability material with the depth of not less than 1.5m in a groove where the water-resisting layer is positioned by using a conduit method, and filling a bentonite material in the groove above the water-resisting layer, wherein the bentonite material is soil-bentonite, cement-bentonite or soil-cement-bentonite;
6) Cutting the HDPE geomembrane and welding the lock catches on the membrane, such as welding positions 14 of the HDPE geomembrane and the lock catches, interlocking the cut HDPE geomembranes by using joints and injecting a water stop strip to seal to form a continuous structure, bending the HDPE geomembrane into a concave shape, fixing the HDPE geomembrane on a steel frame matched with the surface of the inner wall of the groove, inserting the HDPE geomembrane into the slurry until the required depth is reached, and then taking out the steel frame; in specific implementation, a plurality of HDPE geomembranes are required to be sequentially arranged along the horizontal length in the groove for assembly construction, and the steel frame of the former membrane is taken out after the latter membrane is inserted.
7) After the HDPE geomembrane is inserted into the slurry and the bentonite material at the bottom to a preset depth, anchoring the top of the HDPE geomembrane extending out of the ground surface, or welding the HDPE geomembrane with another HDPE geomembrane covered on the ground;
8) vertical leakage monitoring wells are placed between the HDPE geomembranes on the inner walls of the two sides of the groove, high-permeability materials are filled between the leakage monitoring wells and the HDPE geomembranes, and the upper ends of the high-permeability materials are flush with the ground. And finally, a monitoring well protective cover can be arranged at the top end of the groove to seal and protect the leakage monitoring well.
For the double-layer HDPE geomembrane composite antifouling barrier structure, after the step 3), low-permeability backfill materials are filled between the HDPE geomembrane and the inner wall, close to the uncontaminated aquifer, of the groove.
Anchoring the top of the HDPE geomembrane extending out of the ground surface, specifically: and (3) arranging anchoring ditches on the ground surfaces at two sides of the groove, extending the HDPE geomembrane out of the ground and extending the HDPE geomembrane to extend through the anchoring ditches for arrangement, and filling concrete on the surface of the HDPE geomembrane in the anchoring ditches to ensure that the top of the HDPE geomembrane is anchored and fixed by adopting the anchoring ditches.
the bentonite slurry is injected into the groove to play a role of protecting the wall in the groove digging stage; for the double-layer HDPE geomembrane composite antifouling barrier structure, the original bentonite slurry is replaced when the low-permeability backfill material is backfilled.
The invention has the following beneficial effects:
(1) According to the technical scheme, the double-layer low-permeability HDPE geomembrane is used as the main separator of the vertical separation wall, and compared with the existing single-layer HDPE geomembrane vertical antifouling separation structure, the possibility of integral failure of the separation structure caused by defects among membrane webs is reduced, and the reliability of the separation structure is improved. In addition, compared with a single-layer structure, the double-layer HDPE geomembrane structure has stronger capability of preventing and controlling the leakage of pollutants, solves the problems of difficulty in controlling the seepage of underground water of centralized pollution sources such as polluted sites and the like and preventing and controlling the leakage of the pollutants, and is particularly suitable for working conditions with serious pollution or high requirements on prevention and control of the pollution.
(2) according to the technical scheme, the leakage detection layer consisting of the high-permeability material and the leakage monitoring well is arranged between the two layers of HDPE geomembranes, so that the leakage condition of the first layer of HDPE geomembrane can be fed back in time, and the leakage can be repaired in time if the leakage is detected in the construction period.
(3) According to the technical scheme, the leakage detection layer consisting of the high-permeability material and the leakage monitoring well is arranged between the two layers of HDPE geomembranes, so that the long-term service performance of the barrier structure after construction can be monitored. Compared with the existing leakage monitoring means, the method has the advantages that the monitoring area covers the full section of the barrier wall, the leakage condition is fed back in time, the secondary barrier is used for preventing leakage, and the pollution prevention and control are carried out in time, and solves the problems that the service performance information of the existing barrier wall is difficult to feed back, and the pollutant leakage prevention and control are not timely; and a monitoring well is not required to be arranged outside the barrier structure, so that the integral land area of the vertical antifouling barrier structure and the monitoring system is reduced, and the land utilization rate of a landfill site is improved.
(4) The technical scheme of the invention combines some ideas of clay and bentonite impervious walls, and the wall has small rigidity and strong adaptability to the deformation of the side surface of the foundation; the double-layer HDPE geomembrane composite barrier structure with two layers of low-permeability backfill is adopted for the working condition with higher antifouling requirement, so that the HDPE film is protected from being punctured by sharp particles, and extra safety guarantee is provided for the barrier wall.
Drawings
FIG. 1 is a schematic diagram of the present invention applied to a landfill site.
FIG. 2 is a schematic cross-sectional view of a vertical antifouling barrier wall structure of a double-layer HDPE film of the present invention.
FIG. 3 is a schematic cross-sectional view of the double-layer HDPE film composite vertical antifouling barrier wall structure of the present invention.
FIG. 4 is a schematic cross-sectional view of a vertical antifouling barrier wall structure with a double-layer HDPE film according to the present invention.
In the figure: 1. the double-layer HDPE geomembrane vertical antifouling barrier structure; 2. a contaminated aquifer; 3. an uncontaminated aqueous layer; 4. a water barrier layer; 5. HDPE geomembranes; 6. a high permeability material; 7. a leakage monitoring well; 8. anchoring the ditch; 9. a guide wall; 10. a protective cover of the monitoring well; 11. wall side low permeability backfill; 12. a back cover low permeability material; 13. locking; 14. and welding the HDPE geomembrane and the lock catch.
Detailed Description
the invention is described in further detail below with reference to the following detailed description and accompanying drawings:
As shown in fig. 1 and 2, the embodiment of the invention comprises a double-layer HDPE geomembrane vertical antifouling barrier structure 1 arranged between a polluted aquifer 2 and an uncontaminated aquifer 3, wherein the wall body consists of a concave HDPE membrane 5, a bottom-sealing low-permeability material 12 at the bottom of the membrane, a high-permeability material 6 between the two membranes, and a leakage monitoring well 7 arranged in the high-permeability material 6, the double-layer HDPE geomembrane 5 is embedded in a water-resisting layer 4 below the double-layer HDPE geomembrane to form a stable upstream water level surface and a downstream water level surface in the aquifer, and guide walls 9 arranged at two sides of the ground surface part of the double-layer HDPE geomembrane vertical barrier structure.
The specifically implemented site soil body comprises a polluted aquifer 2, an uncontaminated aquifer 3 and a water barrier 4, the double-layer HDPE film vertical antifouling barrier structure comprises a double-layer HDPE geomembrane vertical barrier wall body arranged between the polluted aquifer 2 and the uncontaminated aquifer 3, the double-layer HDPE geomembrane vertical barrier wall body comprises an HDPE geomembrane 5, a high-permeability material 6 and a leakage monitoring well 7, a groove is formed between the polluted aquifer 2 and the uncontaminated aquifer 3, the groove extends into the water barrier 4, HDPE geomembranes are uniformly arranged on the inner wall surface and the bottom surface of the groove to form a double-layer HDPE geomembrane, and the lower part of the double-layer HDPE geomembrane vertical barrier wall body is embedded into the water barrier 4 below the site aquifer; a leakage monitoring well 7 is arranged in the center of the groove, high-permeability materials 6 are arranged in the grooves on the two sides and the bottom of the leakage monitoring well 7, the leakage monitoring well 7 is surrounded by the high-permeability materials 6, the periphery of the high-permeability materials 6 is surrounded and coated by HDPE geomembranes 5, the high-permeability materials 6 are positioned between the leakage monitoring well 7 and the HDPE geomembranes 5, and a gap is formed between the bottom surface of the leakage monitoring well 7 and the HDPE geomembranes 5; the upper end of the leakage monitoring well 7 extends out of the ground and is sealed through a monitoring well protective cover 10, the monitoring well protective cover 10 is installed at the upper end opening of the groove and is connected to the side face of the top of the HDPE geomembrane 5, guide walls 9 are arranged on two sides of the top of the groove, and the guide walls 9 are arranged on two sides of the vertical barrier wall body of the double-layer HDPE geomembrane and are tightly attached to the HDPE geomembrane 5; the part of the double-layer HDPE geomembrane embedded into the water-resisting layer 4 at the bottom of the vertical partition wall body is externally coated with the low-permeability material 12, namely, the part of the double-layer HDPE geomembrane embedded into the water-resisting layer 4 at the bottom of the vertical partition wall body is externally filled and surrounded by the low-permeability material 12, and the low-permeability material 12 is positioned in the water-resisting layer 4.
The double-layer HDPE geomembrane vertical barrier wall body runs through the water barrier layer from the earth surface through the site water-bearing layers, and the site water-bearing layers on the two sides are a polluted area and an uncontaminated area. If the engineering seepage-proofing requirement is higher, a layer of low-permeability backfill can be additionally arranged on one side, close to the uncontaminated aquifer, of the double-layer HDPE geomembrane to form a double-layer HDPE film composite antifouling barrier structure with a seepage detection layer. Namely, the double-layer HDPE geomembrane composite vertical barrier structure is considered, the structure of the structure is shown in figure 3, and a layer of low-permeability backfill 11 is added on one side or two sides of the double-layer HDPE geomembrane close to the uncontaminated aquifer on the basis of the structure.
The double-layer HDPE geomembrane vertical antifouling barrier structure 1 is arranged in a site aquifer, has the thickness of 0.3-0.9 m, and is embedded into the waterproof layer 4 to the depth of not less than 1.5 m. The double-layer HDPE geomembrane wall body 2 is a main part for realizing the function of preventing and controlling underground pollution, and the permeability coefficient of the complete HDPE geomembrane is generally less than 1 multiplied by 10 < -12 > cm/s. The bottom of the double-layer HDPE film is sealed by adopting a low-permeability material such as soil-bentonite and the like to prevent the bottom of pollutants from flowing and leaking, the two films are connected by adopting two rows of lock catches 13, the top of the double-layer film is anchored by adopting an anchoring ditch 8, and if the upper part of the field is covered with the HDPE geomembrane, the connection form of welding with the overlying HDPE geomembrane can be adopted. According to engineering requirements, one side or two sides of the double-layer HDPE geomembrane can be further provided with a layer of low-permeability backfill material 11, such as bentonite, cement bentonite or soil-cement-bentonite.
the middle leakage monitoring well 7 is mainly used for monitoring the leakage condition of upstream pollutants after the upstream pollutants pass through the first HDPE film, and whether the underground water in the monitoring well detects the pollutants or not is used for judging the effectiveness of the upstream geomembrane. The main material of the monitoring well is a non-woven fabric wrapped HDPE perforated pipe or a galvanized perforated pipe, the distance between the bottom of the pipe and the bottom of the double-layer HDPE film is 0.5-1 m when the bottom of the pipe reaches the horizontal line of the water-resisting layer 4, and the top of the pipe exceeds the ground surface by 0.5-1.5 m. And arranging leakage monitoring holes in the leakage detection layer at intervals of a certain depth, wherein the monitoring hole position at the bottommost part is lower than the horizontal line of the waterproof layer 4, the monitoring hole position at the highest part is lower than the ground surface by 0.5-1 m, and the leakage condition of pollutants in the full-depth range of the antifouling barrier wall is monitored.
The high-permeability material 6 is mainly used as a carrier of the middle leakage monitoring well 7, the main material is medium coarse sand or sand/water mixture with good gradation, the wall body is small in thickness or can be filled with geogrids or geonets when a composite vertical antifouling barrier structure is adopted, the materials are good in water permeability, if pollutants leak, the pollutants can quickly enter the leakage monitoring well 7 through the high-permeability material 6, and leakage can be found in time.
The HDPE geomembrane at the top is anchored by the anchoring ditches 8. The ground surface that the slot is located both sides is seted up anchor ditch 8, and HDPE geomembrane 5 extends behind the ground and extends past anchor ditch 8 and arrange, fills the concrete on 5 surfaces of HDPE geomembrane of anchor ditch 8 for 5 tops of HDPE geomembrane adopt anchor ditch 8 anchor fixed. Namely, after the anchoring ditch is dug, the HDPE geomembrane and the protective layer geotextile are laid and are immediately pressed by concrete or soil blocks. If the site has the overlying HDPE geomembrane, the HDPE geomembrane on one side of the double-layer HDPE geomembrane vertical barrier structure, which is close to the upstream pollution site, can be welded with the overlying HDPE geomembrane to form a whole, and the other side still adopts an anchoring form.
The main function of the guide wall 9 is to prevent foundation soil on two sides of the shallow groove from collapsing into the groove when the groove of the vertical antifouling barrier wall is excavated, and to guide the groove in the process of excavating the groove. The guide wall 9 is of a cast-in-place concrete structure, the strength grade of concrete is not lower than C20, the thickness is not smaller than 200mm, a bidirectional reinforcement is adopted, the top surface is higher than the ground by 100mm and higher than the underground water level by more than 0.5m, and the clear distance of the guide wall is widened by 30 mm-50 mm compared with the design thickness of the vertical antifouling partition wall.
The concrete construction steps of the invention are as follows:
(1) According to the plane layout drawing of the double-layer HDPE vertical antifouling separation wall, the field is leveled, the roadbed is filled on the construction machinery route if necessary, the stability of the foundation is improved, and the horizontal central axis of the double-layer HDPE vertical antifouling separation wall is drawn on the ground.
(2) Determining the width of the wall body with the separation structure, firstly constructing guide walls of the double-layer HDPE geomembrane vertical separation wall body in the foundations on two sides of the earth surface part according to the horizontal central axis of the drawn double-layer HDPE vertical antifouling separation wall, wherein vertical excavation is adopted in the construction of the guide walls, and single-side vertical mold one-step pouring molding is adopted. After the guide wall concrete is poured and the inner formwork is removed, in order to prevent the guide wall from deforming, two pairs of upper and lower struts with the horizontal interval of 1m are arranged in the guide wall groove, and earth is filled back into the guide wall groove so as to prevent the guide wall from displacing, and when the guide wall concrete is naturally cured to over 70% of the design strength, the grooving operation can be carried out.
(3) The bentonite slurry is prepared by preferably adopting sodium bentonite with better quality or calcium bentonite subjected to sodium treatment, and the bentonite slurry needs to be hydrated for not less than 24 hours after being mixed. The density of the bentonite slurry is not less than 1.05g/cm3, and the apparent viscosity is not less than 36 s.
(4) And (5) excavating the groove of the vertical antifouling isolation wall, and adopting a hydraulic grab machine, an excavator and other mechanical operations. The distance error between the excavated groove route and the design axis is not more than 0.6m, the groove route is ensured to be basically vertical, and the error between the excavated depth and the design depth is not more than 15 cm. And after the trench is excavated, bottom cleaning is carried out by adopting an excavating machine or other suitable modes, and loose soil and stone materials at the bottom of the trench are removed.
when the trench is excavated, hydrated bentonite slurry is injected into the trench and is kept higher than the water level of underground water by more than 60cm, so that the foundation soil on two sides of the trench is prevented from collapsing grooves or having larger lateral deformation towards the direction of the trench.
And adopting a hydraulic grab machine to excavate the grooves of the vertical antifouling partition wall, reserving an unearthed area which is smaller than the width of the hydraulic grab in the advancing direction of excavation, excavating one groove behind the reserved area, excavating the reserved area, and further finishing the excavation of the two grooves.
(5) Preparing proper low-permeability backfill slurry, such as soil-bentonite and the like, and paving a layer of low-permeability material with the thickness not less than 1.5m at the bottom of the trench by using a conduit method.
(6) And cutting the HDPE geomembrane according to the designed depth and width of the vertical separation wall body, and respectively welding E-shaped lock catches 13 at the positions, 1m away from the bottom to the top, of two sides of the HDPE geomembrane. And welding by a heat seal welding machine in a double-track wedge welding mode.
(7) The double-layer HDPE geomembrane adopts a steel frame lower membrane technology, the HDPE geomembrane cut in the step (6) is bent into a concave shape and fixed on the steel frame, the splicing length and width of the frame can be reasonably adjusted according to the installation depth and the width of the membrane, as shown in figure 4, a water stop strip is inserted into a lock catch 13 of the geomembrane which is firstly placed, the water stop strip is placed along with the geomembrane, after the first geomembrane reaches the specified depth, the steps are repeated by using a second steel frame, the second geomembrane is placed, the water stop strip is not inserted into the lock catch 13 at one side close to the first geomembrane, the lock catch is aligned with two rows of lock catches 13 of the first geomembrane in the groove, and the water stop strip is still inserted into the lock catch 13. After the second geomembrane is placed at the specified depth, the first geomembrane may be removed from the steel frame, and the steel frame withdrawn from the trench and reused. And repeating the installation process until all the geomembranes are installed. Longitudinal cross-sectional views of the barrier structure between the two layers of film are shown in figure 4. If the double-layer HDPE film composite barrier structure is adopted, the low-permeability backfill material 11 is backfilled at the wall side after the HDPE film is installed.
(8) And after the installation is finished, an anchoring ditch is excavated on the outer side of the guide wall, the HDPE geomembrane and the protective layer geotextile are laid, and the HDPE geomembrane and the protective layer geotextile are immediately pressed by concrete or soil blocks. If the site has the overlying HDPE geomembrane, the HDPE geomembrane on one side of the top of the vertical barrier structure of the double-layer HDPE geomembrane close to the upstream polluted site and the overlying HDPE geomembrane can be welded 14 to form a whole, and the other side still adopts an anchoring mode.
(9) After the construction of the double-layer HDPE geomembrane is completed, the manufactured HDPE perforated pipe or galvanized perforated pipe wrapped by the non-woven fabric is placed between the two layers of membranes to serve as a monitoring well, the monitoring well is fixed and filled with a high-permeability material after being placed into a specified depth, then the low-permeability material at the top is leveled with the ground elevation, and the monitoring well is covered.
the implementation shows that the middle leakage detection layer provided by the invention can be used for quality detection of the antifouling separation wall in the construction period and long-term monitoring of pollutant leakage and migration of the antifouling separation wall after construction, construction is performed by adopting a trench digging and wall protecting method, the whole structure has the advantages of multiple antifouling properties, low permeability, high reliability and the like, leakage detection and monitoring of a full-depth section can be realized, timely feedback can be realized, and hole breaking of the HDPE geomembrane can be effectively avoided.
The antifouling separation wall is suitable for underground water seepage control and pollutant diffusion prevention and control of a centralized pollution source, and is particularly suitable for working conditions with serious pollution or high pollution prevention and control requirements.
Claims (10)
1. The utility model provides a contain double-deck HDPE membrane vertical antifouling separation structure on seepage detection layer, double-deck HDPE membrane vertical antifouling separation structure sets up in the soil body, and the soil body is including polluting aquifer (2), uncontaminated aquifer (3) and water barrier (4), its characterized in that: the double-layer HDPE geomembrane vertical antifouling barrier structure comprises a double-layer HDPE geomembrane vertical barrier wall body arranged between a polluted water-bearing layer (2) and an uncontaminated water-bearing layer (3), wherein the double-layer HDPE geomembrane vertical barrier wall body comprises an HDPE geomembrane (5), a high-permeability material (6) and a leakage monitoring well (7), a groove is formed between the polluted water-bearing layer (2) and the uncontaminated water-bearing layer (3), the groove extends into a water-resisting layer (4), the HDPE geomembranes are arranged on the inner wall surfaces of the groove to form the double-layer HDPE geomembrane, and the lower part of the double-layer HDPE geomembrane vertical barrier wall body is embedded into the water-resisting layer (4); a leakage monitoring well (7) is arranged in the center of the groove, high-permeability materials (6) are arranged in the grooves at the two sides and the bottom of the leakage monitoring well (7), and the periphery of each high-permeability material (6) is surrounded and coated by an HDPE geomembrane (5); the upper end of the leakage monitoring well (7) extends out of the ground and is sealed by a monitoring well protective cover (10), and guide walls (9) are arranged on two sides of the top of the groove; the double-layer HDPE geomembrane vertically seals the low-permeability material (12) at the bottom of the part embedded into the water-resisting layer (4) at the bottom.
2. The vertical antifouling barrier structure of claim 1, wherein the double-layer HDPE film containing a leakage detection layer is characterized in that: the ground surface that the slot is located both sides set up anchor ditch (8), HDPE geomembrane (5) extend behind the ground and extend past anchor ditch (8) and arrange, pack the concrete on HDPE geomembrane (5) surface at anchor ditch (8) for HDPE geomembrane (5) top adopts anchor ditch (8) anchor fixed.
3. The vertical antifouling barrier structure of claim 1, wherein the double-layer HDPE film containing a leakage detection layer is characterized in that: a leakage detection layer is formed by a high-permeability material (6) and a leakage monitoring well (7), and is arranged in the double-layer HDPE geomembrane.
4. The vertical antifouling barrier structure of claim 1, wherein the double-layer HDPE film containing a leakage detection layer is characterized in that: the vertical barrier wall body of double-deck HDPE geomembrane be provided with wall side low permeability backfill (11) near one side of uncontaminated aquifer (3), wall side low permeability backfill (11) arrange in leading the vertical soil body space between wall (9) and HDPE geomembrane (5), wall side low permeability backfill (11) bottom extends to below the interface between uncontaminated aquifer (3) and water barrier (4), forms the compound perpendicular antifouling separation structure of double-deck HDPE geomembrane that contains the seepage detection layer.
5. The vertical antifouling barrier structure of claim 1, wherein the double-layer HDPE film containing a leakage detection layer is characterized in that: the thickness of the wall body of the double-layer HDPE geomembrane vertical barrier wall is 0.3 m-0.9 m.
6. The vertical antifouling barrier structure of claim 1, wherein the double-layer HDPE film containing a leakage detection layer is characterized in that: the low-permeability backfill (11) is soil-bentonite, cement-bentonite or soil-cement-bentonite; the bottom sealing low-permeability material (12) is soil-bentonite, cement-bentonite or high molecular polymer.
7. the vertical antifouling barrier structure of claim 1, wherein the double-layer HDPE film containing a leakage detection layer is characterized in that: the high-permeability material (6) is medium coarse sand, a sand-water mixture, a geonet or a geogrid.
8. a construction method of a double-layer HDPE geomembrane vertical antifouling barrier structure applied to the barrier structure of any one of claims 1 to 7 is characterized in that the construction method comprises the following steps:
1) Leveling a field, and determining the horizontal central axis and the width of a wall body of a double-layer HDPE vertical antifouling separation wall between a polluted aquifer (2) and an uncontaminated aquifer (3) on the ground of the field; the horizontal central axis is the central line of the double-layer HDPE geomembrane which is vertical to the barrier wall body and is positioned on the ground;
2) According to the horizontal central axis of the vertical barrier wall body of the double-layer HDPE geomembrane and the width of the wall body, firstly constructing guide walls in foundations on two sides of the ground surface part of the vertical barrier wall body of the double-layer HDPE geomembrane, and performing grooving operation after the guide walls reach 70% of design strength;
3) Preparing bentonite slurry which takes water and bentonite as main raw materials;
4) A groove is formed between the polluted water-bearing layer (2) and the uncontaminated water-bearing layer (3) according to the horizontal central axis of the wall body, guide walls (9) are fixedly arranged in soil bodies on two sides of the upper end of the groove, which are positioned on the ground, and the lower end of the groove extends into the water-resisting layer (4);
5) filling a low-permeability material (12) with the depth not less than 1.5m in the groove where the water-resisting layer (4) is positioned by using a conduit method, and filling a bentonite material in the groove above the water-resisting layer (4);
6) Cutting the HDPE geomembrane (5), welding the lock catches (13) on the geomembrane, interlocking the cut HDPE geomembranes (5) with joints and injecting a water stop strip for sealing to form a continuous structure, bending the HDPE geomembrane (5) into a concave shape, fixing the HDPE geomembrane on a steel frame, inserting the HDPE geomembrane into slurry until the required depth is reached, and then taking out the steel frame;
7) after the HDPE geomembrane (5) is inserted into the slurry and the bentonite material at the bottom to a preset depth, anchoring the top of the HDPE geomembrane (5) extending out of the ground surface, or welding the HDPE geomembrane with another HDPE geomembrane covered on the ground;
8) Vertical leakage monitoring wells (7) are arranged between HDPE geomembranes (5) on the inner walls of the two sides of the groove, high-permeability materials (6) are filled between the leakage monitoring wells (7) and the HDPE geomembranes (5), and the upper ends of the high-permeability materials (6) are level to the ground.
9. The construction method of the double-layer HDPE geomembrane vertical antifouling barrier structure according to claim 8, is characterized in that: for the double-layer HDPE geomembrane composite antifouling barrier structure, after the step 3), low-permeability backfill (11) is filled between the HDPE geomembrane (5) and the inner wall of the groove close to the uncontaminated aquifer (3).
10. The construction method of the double-layer HDPE geomembrane vertical antifouling barrier structure according to claim 8, is characterized in that: anchoring the top of the HDPE geomembrane (5) extending out of the ground surface, specifically: and (3) arranging anchoring ditches (8) on the ground surfaces at two sides of the groove, extending the HDPE geomembrane (5) out of the ground and extending the HDPE geomembrane to extend through the anchoring ditches (8) for arrangement, and filling concrete on the surface of the HDPE geomembrane (5) in the anchoring ditches (8) so that the top of the HDPE geomembrane (5) is anchored and fixed by adopting the anchoring ditches (8).
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