Vertical blocking construction method for underground water composite anti-seepage wall of polluted site

Abstract

The invention relates to a vertical blocking construction method for an underground water composite diaphragm wall in a polluted site, which mainly comprises the following steps: excavating a guide wall groove, and building a guide wall in the guide wall groove; the guide wall groove is divided into a plurality of groove sections, a rotary drilling rig is used for forming a plurality of guide holes in the groove sections, a grooving machine is used for grooving the area between every two guide holes at intervals in a segmented mode, and a cut-off wall groove body is formed; mixing 8-10 parts by weight of cement, 6-8 parts by weight of sodium bentonite, 1-2 parts by weight of fly ash and 30-45 parts by weight of water to prepare slurry, and pouring the slurry into the diaphragm wall groove body until the height of the slurry reaches the elevation of the guide wall; a plurality of HDPE films are arranged in the length direction of the cut-off wall groove body; forming the diaphragm wall after the slurry is condensed; according to the construction method, the novel slurry is adopted, and the flowing property of the slurry is good before initial setting, so that the slurry can still be directly poured after pouring, the slurry can be directly poured after grooving, and the steps of slurry wall protection and slurry replacement are omitted.

Description

Technical Field

[0001] The invention relates to a vertical barrier construction method for a composite anti-seepage wall for groundwater in a polluted site, belonging to the technical field of anti-seepage wall construction. Background Art

[0002] With the construction of a number of solid waste landfills, tailings ponds and general solid waste slag sites in the process of industrial development, soil and groundwater pollution problems have been caused in the originally unpolluted land. Based on this background and the urgent need to solve the problem of groundwater pollution, our unit, based on the actual project, has summarized and invented a vertical barrier technology that uses HDPE geomembrane combined with cement fly ash composite anti-seepage wall to effectively prevent groundwater pollution from spreading outside the site.

[0003] In the prior art of anti-seepage wall construction, the trenching and membrane laying process is difficult to implement after the slurry is poured, because the slurry used to cast the wall has a high viscosity and poor fluidity before initial setting. Therefore, it is necessary to first use mud to protect the trench section, then lay the membrane, and finally pour the wall material to replace the mud. For example, patent CN201710941627.0 discloses a construction method for a composite underground anti-seepage isolation wall structure, which includes the following steps: a. digging a trench at the location where the anti-seepage isolation wall is to be set, injecting wall protection mud into the trench, laying the functional layer membrane material along the trench line, and splicing two adjacent membrane materials, and hanging a weight block at the bottom of the membrane material; b. slowly sinking the membrane material into the wall protection mud, and maintaining the flatness and verticality of the membrane during the sinking process; c. sinking the membrane material to the design elevation; d. injecting wall material into the trench to discharge the wall protection mud. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a vertical barrier construction method of a composite anti-seepage wall which eliminates the mud wall protection step.

[0005] To achieve the above-mentioned object, the present invention proposes a technical solution: a method for vertically isolating groundwater composite anti-seepage walls in contaminated sites, comprising excavating a guide wall trench around the contaminated site according to the designed width of the anti-seepage wall, and constructing a guide wall in the guide wall trench; The guide wall trench is divided into several sections, several pilot holes are opened in the sections using a rotary drilling rig, and the area between the pilot holes is slotted into sections using a slotting machine to form an anti-seepage wall slot body, the depth of which extends to the impermeable stratum; Prepare a slurry by mixing 8-10 parts of cement, 6-8 parts of sodium bentonite, 1-2 parts of fly ash, and 30-45 parts of water by weight. Pour the slurry into the anti-seepage wall trench until the slurry height reaches 30-50 cm below the guide wall elevation. Several HDPE membranes are installed along the length of the anti-seepage wall trough. When installing the HDPE membranes, transversely arranged steel bars and counterweights are installed at one end of the HDPE membranes. At least one end of the HDPE membrane is lowered to the bottom of the anti-seepage wall trough under the action of the gravity of the counterweights, and the sides of two adjacent HDPE membranes overlap each other. Slurry is added until the slurry height reaches the guide wall elevation. After the slurry solidifies, the anti-seepage wall is formed.

[0006] A preferred embodiment of the above technical solution is that the weight ratio of the materials in the slurry is cement: sodium bentonite: fly ash: water = 9:7:1:40.

[0007] The above technical solution is further designed as follows: when setting the HDPE membrane, several perforations are set at one end of the HDPE membrane, and a transversely set steel bar is tied through the perforations on both sides of the thickness direction of the HDPE membrane end, a counterweight block is tied through the perforations at both ends of the width direction of the HDPE membrane end, and a wire is tied in the middle of the width direction of the HDPE membrane end. The drill rod of the rotary drilling rig is used to support the wire, control the drill rod to descend, and push the HDPE membrane down to the bottom of the anti-seepage wall trough to ensure the verticality of the HDPE membrane, and then retract the drill rod.

[0008] The thickness of the HDPE film is 2-3 mm, and the overlapping width of two adjacent HDPE films is 10-20 cm.

[0009] The several sections of the guide wall groove are numbered. When dividing the grooves into sections, the odd-numbered sections are constructed first, and then the even-numbered sections are constructed. The construction length of the even-numbered sections covers the adjacent odd-numbered sections by 20 cm at both ends.

[0010] After the HDPE membrane is installed, the anti-seepage wall is subjected to water-enclosing and curing for 12-15 days.

[0011] The beneficial effects of the present invention are: The present invention designs a slurry with a new mix ratio, which has good fluidity before initial setting, so that the membrane can be directly laid after pouring. Therefore, the method of the invention can directly pour the slurry after trenching, eliminating the steps of mud wall protection and mud replacement. The slurry also meets the anti-seepage requirements after solidification and formation, thereby saving construction time and costs, reducing pollution to the surrounding environment, facilitating construction, and saving energy and protecting the environment.

[0012] Although the slurry of the present invention can be directly applied as a membrane, it is still thicker than mud. Therefore, it is difficult to ensure the verticality of the HDPE membrane by relying solely on the gravity of the counterweight when applying the membrane. Therefore, the present invention provides an iron wire on the HDPE membrane. When digging holes in accordance with this method, the drill bit of the rotary drilling rig is removed, and the drill rod is used to push the iron wire to guide the lowering of the HDPE membrane, thereby ensuring the verticality of the HDPE membrane.

[0013] The method of the present invention effectively solves the problem of groundwater pollution spreading outside the site, and can be applied to soil remediation, groundwater control, and landfill and solid waste landfill closure projects in industrial contaminated sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a flow chart of the present invention; Figure 2 Schematic diagram of the cross section of the composite anti-seepage wall; Figure 3 This is a schematic diagram of the groove section division of the guide wall groove; Figure 4 Schematic diagram of opening guide holes for the slot section; Figure 5 This is a schematic diagram of trenching construction; Figure 6 Schematic diagram of anti-seepage membrane construction. DETAILED DESCRIPTION

[0015] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Example 1

[0016] The method for vertically isolating groundwater composite anti-seepage walls in a contaminated site according to this embodiment includes the following steps: Step 1: Excavate a guide wall trench around the contaminated site according to the designed width of the anti-seepage wall, and build a guide wall in the guide wall trench.

[0017] Step 2: Divide the guide wall trench into several sections, use a rotary drilling rig to open several guide holes in the sections, and use a slotting machine to segment the area between the two guide holes into slots to form an anti-seepage wall slot body. The depth of the anti-seepage wall slot body extends to the impermeable stratum.

[0018] Step 3: Mix 8 parts of cement, 6 parts of sodium bentonite, 1 part of fly ash and 30 parts of water by weight to prepare a slurry, and pour the slurry into the anti-seepage wall groove until the slurry height reaches below the guide wall elevation.

[0019] Step 4: Set up several HDPE membranes along the length direction of the anti-seepage wall trough. When setting up the HDPE membranes, set transverse steel bars and counterweights at one end of the HDPE membranes. At least under the action of the counterweight, lower this end of the HDPE membrane to the bottom of the anti-seepage wall trough. The sides of two adjacent HDPE membranes overlap each other, and add slurry until the slurry height reaches the guide wall elevation.

[0020] Step 5: Carry out water-enclosing maintenance on the anti-seepage wall, and the anti-seepage wall is formed after the slurry solidifies. Example 2

[0021] like Figure 1As shown, the vertical barrier construction method of the composite anti-seepage wall for groundwater in the contaminated site of this embodiment has the following construction process: construction preparation → measurement and layout → construction of guide wall → drilling holes to form trenches → trench inspection → slurry pouring → HDPE membrane construction → water enclosure maintenance → inspection and acceptance.

[0022] Specifically, construction preparation; Prepare the water, electricity, etc. required for construction, clean the construction site, establish a construction background, including storage barrels, mixing barrels, slurry storage tanks, mixers and water tanks, etc., and set up fences, warning lights and signs; select rotary drilling rigs and grab bucket trenching machines as construction machinery and equipment.

[0023] Measuring and setting out; Carry out line marking and other work on the construction site according to the design drawings and construction requirements.

[0024] Build guide walls; After pre-compression of foundation soil according to the design size of the anti-seepage wall and the position of the marking line, the guide wall trench is excavated by excavator. For concrete pavement, it needs to be broken before excavating the trench; the trench excavation width is 1100-1200mm (the net width of the guide wall is 700-800mm, the wall thickness is 200mm), and the excavation depth is 1200-1300mm.

[0025] like Figure 2 As shown, guide walls 1 are cast on both sides of the guide wall groove.

[0026] The lead hole is opened to form a groove; Divide the guide wall groove into several continuous groove sections and number them, such as Figure 3 As shown, in this embodiment, the length of the odd-numbered slot sections is about 6m, and the length of the even-numbered slot sections is about 5.6m. Figure 4 As shown, drilling points are marked at 0m, 1.5m, 3m, 4.5m, and 6m in the technical trench section and 0m, 1.4m, 2.8m, 4.2m, and 5.6m in the even-numbered sections. A rotary drilling rig is used to guide the holes, and the drilling depth is to the impermeable soil layer. For different soil types, appropriate drilling rigs can be selected for drilling. Rotary drilling guide holes can ensure better leverage during the trenching process, increase excavation efficiency and excavation depth, such as Figure 5 As shown, during the trenching process, a grab bucket trenching machine is used to perform trenching construction. The grab bucket 6 is opened and both ends are respectively inserted into the two lead holes 5. In this embodiment, the span of the grab bucket is 3m, and there is a lead hole between the spans. According to the divided trench sections, the odd-numbered trench sections are excavated first, and then the even-numbered trench sections are excavated. Since the slurry setting time designed in this embodiment is 2-3d, the trenching needs to be constructed at intervals to avoid collapse due to insufficient wall strength. Figure 3As shown, the trench sections 1, 3, 5, 2, and 4 are constructed in sequence to form an anti-seepage wall trench body. Since the length of the technical trench section is greater than that of the even-numbered trench sections, when excavating the even-numbered trench sections, the construction length of the even-numbered trench sections can cover part of the adjacent odd-numbered trench sections. Taking trench section 2 as an example, the construction length covers part of trench section 1 and trench section 3, that is, each end of the even-numbered trench section over-excavates the adjacent odd-numbered trench section by 20 cm. In this way, the over-excavated anti-seepage membrane of the odd-numbered trench section is exposed, which facilitates the overlapping of the anti-seepage membrane and prevents the existence of construction joints at the overlapping joints of the anti-seepage wall.

[0027] test tank; After trenching is completed, use a measuring rope to measure the trench depth to ensure that the excavation reaches the impermeable soil layer, and measure 2-3 measuring points in each trench section.

[0028] Slurry pouring; The slurry was prepared on-site with a weight ratio of cement: sodium bentonite: fly ash: water = 9:7:1:40. Tests have shown that after the slurry solidifies and forms, the permeability coefficient of the barrier wall material test block is less than 1×10 -7 cm / s; Under the action of pollutants, the permeability coefficient of the barrier wall material is less than 1×10 -6 cm / s; the overall composite anti-seepage wall requires a permeability coefficient of less than 1×10 -7 cm / s, and the water permeability is less than 5Lu; and the fluidity of the slurry before initial setting can meet the requirements of the lower membrane construction, without the need for mud wall protection after troughing, eliminating the mud replacement step, and at the same time, the strength, permeability coefficient and other parameters after solidification and molding meet the requirements; compared with concrete materials, it reduces the amount of cement, sand and gravel, saves energy and carbon, has a low wall elastic modulus, better integrity with the foundation soil, is not prone to stress concentration and damage, and has better crack resistance, acid resistance and corrosion resistance.

[0029] Pour the above slurry into the anti-seepage wall trench after the trench is formed to prevent the slurry from overflowing when the membrane is lowered. The slurry is poured to 30cm~50cm below the guide wall elevation. The guide wall elevation is the height of the guide wall top.

[0030] HDPE membrane construction; In this embodiment, the anti-seepage membrane is a 2-3 mm thick HDPE geomembrane with a width of 6 m to match the trench width; like Figure 6As shown, when setting the HDPE film 4, a plurality of perforations are set at one end of the HDPE film 4, and a transversely arranged steel bar 41 is respectively tied through the perforations on both sides of the thickness direction of the HDPE film 4 to ensure that the end of the HDPE film is always in a flat and unfolded state, and a counterweight block 42 is respectively tied through the perforations at both ends of the width direction of the HDPE film 4, and a wire 43 is tied in the middle of the width direction of the HDPE film 4. The wire 43 is in a loose state, so that a loop is formed between the wire 43 and the steel bar 41, and the rotary drilling rig is adjusted to the position of lowering the HDPE film, the drill bit is removed, and the drill rod of the rotary drilling rig is inserted between the wire 43 and the steel bar 41. The drill bit is connected to the drill ring at the bottom of the drill rod, and the ring can be placed on the small end without sliding up along the drill rod as the drill rod descends. Therefore, the drill rod is controlled to descend, and the drill rod can press against the ring and push the HDPE membrane 4 down to the bottom of the anti-seepage wall groove. Since the fluidity of the slurry in this embodiment is poorer than that of the mud in the prior art, it is not easy to ensure the verticality of the HDPE membrane by relying solely on the gravity of the counterweight block to lower the HDPE membrane. This process is combined with the rotary drilling rig to effectively control the lowering speed and position of the HDPE membrane, which can further ensure the verticality of the HDPE membrane 4. Then the drill rod is retracted, so that the HDPE membrane 4 remains in the anti-seepage wall groove. Figure 2 As shown, the other end of the HDPE membrane 4 is fixed to the fixing point 2 at the top of the guide wall, so that the HDPE membrane 4 is fixed in the slurry 3 poured into the anti-seepage wall trench, completing the HDPE membrane construction. Adjacent HDPE membranes are constructed using a natural overlap method, with the overlap width of the two HDPE membranes being 10-20 cm, corresponding to the excavated trench section.

[0031] After the HDPE membrane is constructed, additional slurry is poured to the top elevation of the guide wall.

[0032] The anti-seepage wall of this embodiment leverages the durability, low impermeability coefficient, and strong corrosion resistance of HDPE membrane, resulting in a flexible wall structure with enhanced anti-seepage performance. Compared to compaction grouting and other existing geomembrane vertical barrier construction methods, this method offers improved impermeability, ease of construction, and minimal site pollution.

[0033] water conservation; Afterwards, water enclosure maintenance should be carried out in time to always maintain the water level in the trough section. The maintenance time is 12-15 days.

[0034] Inspection and acceptance will be carried out after maintenance is completed. Example 3

[0035] This embodiment is basically the same as the second embodiment, except that the weight ratio of the slurry components is as follows: 10 parts of cement, 8 parts of sodium bentonite, 2 parts of fly ash and 45 parts of water are mixed to prepare the slurry.

[0036] Application Cases This case project is a groundwater anti-seepage treatment project for a phosphogypsum storage site in a certain place. The construction was carried out according to the method of Example 2. After completion, the wall was tested for integrity and permeability. The results are as follows: (1) The core drilling test of the anti-seepage wall showed that the wall materials sampled were mixed evenly and had good integrity. No quality defects such as honeycombs and holes were found. The depth of the anti-seepage wall met the design requirements. (2) According to the on-site in-hole water injection test, the permeability coefficient of the anti-seepage wall cementitious material was 3.21×10 -7 cm / s~8.31×10 -7 cm / s, less than 1×10 -6 cm / s, and the wall compressive strength is higher than 1MPa, meeting the design requirements.

[0037] The technical solutions of the present invention are not limited to the above embodiments, and any technical solutions obtained by equivalent replacement methods fall within the scope of protection required by the present invention.

Claims

1. A method for vertically isolating groundwater composite anti-seepage walls in contaminated sites, characterized by: Excavate a guide wall trench around the contaminated site according to the designed width of the cut-off wall, and build a guide wall in the guide wall trench; The guide wall trench is divided into several sections, several pilot holes are opened in the sections using a rotary drilling rig, and the area between the pilot holes is slotted into sections using a slotting machine to form an anti-seepage wall slot body, the depth of which extends to the impermeable stratum; Prepare a slurry by mixing 8-10 parts of cement, 6-8 parts of sodium bentonite, 1-2 parts of fly ash, and 30-45 parts of water by weight. Pour the slurry into the anti-seepage wall trench until the slurry height reaches 30-50 cm below the guide wall elevation. Several HDPE membranes are installed along the length of the anti-seepage wall trough. When installing the HDPE membranes, transversely arranged steel bars and counterweights are installed at one end of the HDPE membranes. At least one end of the HDPE membrane is lowered to the bottom of the anti-seepage wall trough under the action of the gravity of the counterweights, and the sides of two adjacent HDPE membranes overlap each other. Slurry is added until the slurry height reaches the guide wall elevation. After the slurry solidifies, the anti-seepage wall is formed.

2. The vertical barrier construction method for groundwater composite anti-seepage wall in contaminated sites according to claim 1 is characterized by: The weight ratio of the materials in the slurry is cement: sodium bentonite: fly ash: water = 9:7:1:

40.

3. The vertical barrier construction method for groundwater composite anti-seepage wall in contaminated sites according to claim 1 is characterized by: When setting up the HDPE membrane, set several perforations at one end of the HDPE membrane, and tie a transversely set steel bar through the perforations on both sides of the thickness direction of the HDPE membrane, tie a counterweight block through the perforations at both ends of the width direction of the HDPE membrane, and tie a wire in the middle of the width direction of the HDPE membrane. Use the drill rod of the rotary drilling rig to support the wire, control the drill rod to descend, and push the HDPE membrane down to the bottom of the anti-seepage wall trough to ensure the verticality of the HDPE membrane.

4. The vertical barrier construction method for groundwater composite anti-seepage wall in contaminated sites according to claim 3 is characterized by: The thickness of the HDPE film is 2-3 mm, and the overlapping width of two adjacent HDPE films is 10-20 cm.

5. The vertical barrier construction method for groundwater composite anti-seepage wall in contaminated sites according to any one of claims 1 to 4, characterized in that: The several sections of the guide wall groove are numbered. When dividing the grooves into sections, the odd-numbered sections are constructed first, and then the even-numbered sections are constructed. The construction length of the even-numbered sections covers the adjacent odd-numbered sections by 20 cm at both ends.

6. The vertical barrier construction method for groundwater composite anti-seepage wall in contaminated sites according to claim 5, characterized in that: After the HDPE membrane is installed, the anti-seepage wall is subjected to water-enclosing and curing for 12-15 days.

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