CN112964610B - Hypergravity model test method for simulating migration of pollutants in vertical separation wall - Google Patents
Hypergravity model test method for simulating migration of pollutants in vertical separation wall Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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Abstract
The invention discloses a supergravity model test device for simulating the migration of pollutants in a soil-bentonite vertical separation wall, which comprises a model box system, a percolate collecting system and a consolidation material supplementing and monitoring system. The invention also discloses a test method of the supergravity model test device for simulating the migration of pollutants in the soil-bentonite vertical barrier wall. The invention can realize that the soil-bentonite vertical barrier wall hypergravity model has excellent water tightness with the wall of the model box under the environment of 100g high g value and the stress state consistent with the actual engineering. The invention can simulate the migration condition of pollutants in the soil-bentonite vertical barrier wall under various water head differences, thereby obtaining the barrier breakdown behavior of the pollutants and a long-acting resistance control mechanism.
Description
Technical Field
The invention belongs to the field of geotechnical engineering tests, and particularly relates to a supergravity model test device and method for simulating the migration of pollutants in a soil-bentonite vertical barrier wall.
Background
The vertical separating wall of bentonite-soil is an antifouling separating wall for separating and sealing pollutant in polluted site, and its wall material mainly consists of backfill base soil, dry bentonite and bentonite slurry, in which the mixing amount of wall bentonite is mainly related to the kind of backfill base soil and bentonite, and is between 5% and 15%, and the actual concrete mixing amount of engineering is that the wall permeability coefficient is less than 10-9And m/s is determined. The construction steps of the soil-bentonite vertical barrier wall mainly comprise: excavating a groove, uniformly mixing backfill materials, backfilling and the like. The wall thickness is the main design parameter of the soil-bentonite vertical separation wall. The size of the slotting machine is considered in engineering practice, and is generally 0.6m-1.5 m. When the water head difference between two sides of the vertical separation wall is large, the thickness of the wall body is increased properly. The bentonite vertical separation wall is inserted into the weak permeable layer (the permeability coefficient is less than 10)-10m/s natural soil layer) can be divided into embedded type and suspended typeOther than for deeper and shallower buried contaminants. The depth of construction of vertical earth-bentonite barriers has reached 60m in the united states.
Because of the characteristics of simple and convenient construction, low cost, strong site adaptability and strong seepage-proofing capability, the soil-bentonite vertical barrier wall is gradually applied to landfill seepage-proofing engineering and underground water pollution control engineering in the 80 th century in the United states, so far, the utilization rate of the soil-bentonite vertical barrier wall in the vertical barrier project exceeds 80 percent, but the research on the long-term service performance of the percolate barrier material of the pollution-proofing and control site is very limited. At present, cement (plastic concrete or cement soil) grouting curtains are still mostly adopted for vertical barriers in China, the permeability coefficient is high, the integrity is poor, the antifouling and blocking effects are not ideal enough, and the development and application of the soil-bentonite vertical barrier wall technology just start.
The migration speed of pollutants in the soil-bentonite vertical barrier wall is slow, and the designed breakdown time is more than 30 years. Ordinary normal gravity tests cannot perform simulations for such a long time. The centrifuge has the time-lapse and scale-reduction effects, and the prototype size L is under the condition that the acceleration is ngpCorresponding to the model size Lm＝LpN, prototype time tpCorresponding model time tm＝tp/n2The 1d test time corresponds to prototype 27.4a, for example, at 100g acceleration under gravity. Therefore, the centrifuge has great advantages in simulating the migration of pollutants in the soil-bentonite vertical barrier wall.
However, the clay bentonite vertical barrier wall pollutant migration test is carried out in a centrifugal machine at home and abroad for the following reasons: (1) the molding process of the bentonite vertical barrier wall is similar to that of actual engineering, and the stress on the bentonite vertical barrier wall is ensured to be consistent with the original position; (2) the joint of the bentonite vertical barrier wall and the side wall is easy to leak, so that the test fails; (3) due to the scale reduction effect of the centrifugal machine, the general method is difficult to prepare the bentonite vertical barrier wall which is extremely thin, uniform in upper and lower thickness and high in verticality; (4) the bentonite vertical barrier wall is extremely large in sedimentation when solidified in a centrifugal machine and needs to be supplemented in time.
Disclosure of Invention
Aiming at the situation and overcoming the defects of the prior art, the invention provides a supergravity model test device and a supergravity model test method for simulating the migration of pollutants in a soil-bentonite vertical barrier wall.
In order to achieve the purpose, the invention provides the following technical scheme:
a hypergravity model test device for simulating the migration of pollutants in a soil-bentonite vertical separation wall comprises a model box system, a percolate collecting system and a consolidation material supplementing and monitoring system;
the mold box system comprises a mold box comprising an upstream region, a fill region and a downstream region separated in sequence by a partition, the upstream region configured to be capable of storing a first solution, the fill region configured to be capable of being used to provide a soil-bentonite vertical barrier wall; the downstream region is configured to be capable of storing a second solution; the partition is a porous baffle plate, and can allow a solution to pass through the baffle plate, so that the communication between an upstream area and a soil filling area is realized, and the communication between the soil filling area and a downstream area is realized;
the side surface of the upstream area is provided with a water inlet and a first water drainage hole, and the side surface of the downstream area is provided with an overflow hole and a second water drainage hole for constant head maintenance and water head difference control;
the percolate collection system comprises a collection barrel and a pore pressure meter, wherein the collection barrel is configured to be capable of collecting percolate of a model box, and the pore pressure meter is used for detecting the water level; communicating the collecting barrel with the overflow hole of the model box by using a connecting pipe;
the consolidation material supplementing and monitoring system comprises a flow guide device, an LVDT displacement sensor, a soil pressure meter and a pore pressure meter; the flow guide device is connected to the top of the model box, is used for supplementing the filler in the centrifugal consolidation process of the soil-bentonite vertical barrier wall, and can prevent the filler from leaking laterally; the soil pressure gauge and the pore pressure gauge are arranged on two sides of the soil-bentonite vertical separation wall and are respectively used for monitoring horizontal soil pressure and ultra-static pore pressure and determining ultra-static pore pressure dissipation time.
Further, a screen and filter paper are attached to one side of the porous baffle, which is in contact with the water-containing sand layer; the side of the porous baffle, which is in contact with the weakly permeable layer, is attached with a screen and filter paper.
Further, two pairs of clamping grooves are formed in the soil filling area and can be used for installing the wall-making formwork.
Furthermore, the soil filling area comprises a weakly permeable layer and a water-containing sand layer, wherein the weakly permeable layer and the water-containing sand layer are arranged in the soil filling area from bottom to top in sequence; the barrier wall is erected in the middle of the hydrous sand layer.
Further, guiding device includes the guiding gutter, and the guiding gutter top is equipped with the entry, and the guiding gutter below is provided with the export, and the guiding gutter exit is connected with the baffle.
A test method of a hypergravity model test device for simulating the migration of pollutants in a soil-bentonite vertical separation wall is disclosed, wherein the test device is the test device, and comprises the following steps:
step 1: installing the clamping groove on the side wall of the model box, inserting the porous baffle plate, partitioning the model box into an upstream area, a soil filling area and a downstream area, and installing a support frame in the upstream area and the downstream area;
step 2: paving dry bentonite between the porous baffles, and preparing a weakly permeable layer;
and step 3: inserting a wall-forming template into two clamping grooves in the middle of a model box to form a wall-forming area, inserting a barrier strip at the connecting position of the wall-forming area and the wall of the model box for the airtightness of the soil-bentonite vertical barrier wall and the side wall of the model box, and pouring dry bentonite to form a 2cm bentonite strip;
and 4, step 4: filling standard sand between the wall-making template and the porous baffle plate as a water-containing sand layer, and embedding a soil pressure gauge, a pore pressure gauge and a conductivity sensor;
and 5: firstly, the barrier strip is pulled out, then the wall-making template is pulled out, and the barrier wall filler can fill the space occupied by the original template and sink in the template pulling-out process, so that the filler needs to be supplemented in time; aligning the flow guide device to a wall making area, inserting the guide plate into the clamping groove, fixing the flow guide device on the model box by using bolts, adding a barrier wall filler into the flow guide groove, and erecting an LVDT displacement sensor at the top of the flow guide groove;
step 6: adding deionized water into an upstream area and a downstream area, transferring the whole device into a centrifuge, starting the centrifuge, carrying out centrifugal consolidation on the model, and monitoring the consolidation completion condition by an LVDT displacement sensor, a soil pressure meter and a pore pressure meter;
and 7: after consolidation is finished, adding deionized water into an upstream water tank to form a water head difference of 3cm between the upstream and the downstream, maintaining a constant water head at the upstream, monitoring the leakage amount for 1 hour by using a percolate collecting system, and judging whether the tightness is met;
when the supergravity model of the soil-bentonite vertical barrier wall passes through the tightness detection, the upstream deionized water is changed into a pollutant solution, a pollutant migration centrifugal test is carried out, and whether the soil-bentonite vertical barrier wall is broken down or not is monitored by using a conductivity sensor; the contaminant solution is an ionizable substance in water; after the change to the contaminant solution, the test was centrifuged under the same conditions as the previous centrifugation at an acceleration of 100 g.
And 8: and after the test is finished, taking out the soil-bentonite vertical separation wall, sampling at a set position, and measuring the concentration, the permeability coefficient, the density and the water content.
Further, in the step 2, the soil sample preparation and filling process of the weak permeable layer is as follows:
(1) slowly adding bentonite into deionized water, standing and hydrating for 24 hours to obtain bentonite slurry; the mass ratio of the two is as follows: bentonite 5: 95;
(2) mixing Fujian standard sand and dry bentonite for 30 minutes to prepare 8 parts of dry soil sample; the mass ratio of the sand to the sand is as follows: dry bentonite 80: 18.95;
(3) mixing and stirring each part of dry soil sample and bentonite slurry for 30 minutes to obtain a weakly permeable layer filler; and drying the soil sample according to the mass ratio of the two: bentonite mud 100: 21.05;
(4) paving a layer of dry bentonite with the thickness of 10mm at the bottom of the soil filling area, and spraying a spray can on the surface;
(5) and pouring the filler of the weakly permeable layer into the soil filling area, compacting the filler by using a self-made compaction hammer, spraying the surface by using a spraying pot, and repeating the steps until the filler of the weakly permeable layer reaches the bottom of the groove of the wall making formwork.
Further, the preparation steps of the soil-bentonite vertical barrier wall filler in the step 3 are as follows:
(1) slowly adding dry bentonite into deionized water, standing and hydrating for 24 hours to obtain bentonite slurry; mass ratio, deionized water: bentonite is 95: 5;
(2) mixing Fujian standard sand and dry bentonite for 30 minutes to prepare a dry soil sample; mass ratio, dry bentonite: the Fujian standard sand is 3:95,
(3) and mixing and stirring the dried soil sample and the bentonite slurry for 30 minutes, then carrying out slump test, and when the slump of the soil sample is less than 125mm, continuing adding deionized water for stirring until the slump is more than 125mm, thus obtaining the soil-bentonite barrier wall filler.
Furthermore, in step 4, a conductivity sensor, a soil pressure gauge and a pore pressure gauge are arranged on one side of the soil-bentonite barrier wall close to the downstream area, and the soil pressure gauge and the pore pressure gauge are arranged at the same height.
Further, in step 6, the g value of the centrifuge rises by 10g every ten minutes in the model centrifugation and consolidation stage until 100g, and whether the consolidation is completed is determined with the pore pressure change rate being basically stable.
The invention has the beneficial effects that:
(1) the test device can be used for simulating the migration process of pollutants in the soil-bentonite vertical barrier wall under different working conditions and researching the long-term service performance of the soil-bentonite vertical barrier wall.
(2) The inventive process for manufacturing the soil-bentonite vertical barrier wall can finish the whole model preparation in a very short time (about 2 hours), so that the soil-bentonite vertical barrier wall can be hung into a centrifuge to finish consolidation before the soil-bentonite loses fluidity.
(3) The invention can truly simulate the construction process of the actual engineering soil-bentonite vertical separation wall, and realizes the consistency of the stress of the soil-bentonite vertical separation wall model under the super-gravity environment and the actual engineering by combining the clamping groove and the wall making template and matching the dry bentonite edge sealing and the diversion groove.
(4) The invention can keep the good water tightness between the vertical soil-bentonite barrier wall and the side wall of the model box under the high g value of 100 g.
(5) The invention is matched with a consolidation material supplementing and monitoring system, and solves the material supplementing problem that the vertical bentonite barrier wall in the centrifuge generates huge settlement due to consolidation.
Drawings
FIG. 1 is an isometric view of a hypergravity model test apparatus when no soil sample is loaded.
FIG. 2 is an axonometric view of the hypergravity model test apparatus after molding is completed.
FIG. 3 is a cross-sectional view of the hypergravity model test apparatus after molding is completed.
FIG. 4 is a plan view of the hypergravity model test apparatus.
FIG. 5 is a top view of the hypergravity model test apparatus.
FIG. 6 is a cross-sectional view taken along line 1-1 of FIG. 5, wherein the blue bead is a pore pressure gauge; the yellow triangular edge is a conductivity sensor; the red regular pentagon is an earth pressure gauge.
Fig. 7 is a schematic structural view of the flow guide device.
Fig. 8 is a sampling view of a soil-bentonite vertical barrier wall.
FIG. 9 is a comparison graph of horizontal soil pressure and various theoretical models after the consolidation of the soil-bentonite vertical barrier wall is finished.
FIG. 10 is a comparison graph of the leakage of a vertical soil-bentonite barrier wall and theoretical analysis.
Fig. 11 is a bentonite vertical barrier wall after the test is finished.
The reference numbers in the figures are: 1-a model box; 2-a collection barrel; 3-a first support frame; 31-a second support; 4-a flow guide device; 5-a first drain hole; 51-a second drain hole; 6-overflow holes; 7-pvc transparent hard tube; 8-water inlet holes; 9-LVDT displacement sensors; 10-an upstream region; 11-soil-bentonite vertical barrier walls; 12-a water-containing sand layer; 13-a water-weakly permeable layer; 14-a porous baffle; 15-a downstream region; 16-a card slot; 17-ribbed plates; 18-a diversion trench; 19-bolt holes; 20-a guide plate; 21-a soil sample permeability coefficient sampling hole; 22-soil sample density and water content sampling holes; 23-soil sample concentration sampling hole, 24-fixing plate.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments provided in the present application without any inventive step are within the scope of protection of the present application.
Reference in the specification to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the specification. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Those of ordinary skill in the art will explicitly and implicitly appreciate that the embodiments described herein may be combined with other embodiments without conflict.
Unless defined otherwise, technical or scientific terms referred to herein shall have the ordinary meaning as understood by those of ordinary skill in the art to which this application belongs. Reference to "a," "an," "the," and similar words throughout this application are not to be construed as limiting in number, and may refer to the singular or the plural. The present application is directed to the use of the terms "including," "comprising," "having," and any variations thereof, which are intended to cover non-exclusive inclusions; reference to "connected," "coupled," and the like in this application is not intended to be limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. Reference herein to "a plurality" means greater than or equal to two. "and/or" describes an association relationship of associated objects, meaning that three relationships may exist, for example, "A and/or B" may mean: a exists alone, A and B exist simultaneously, and B exists alone. Reference herein to the terms "first," "second," "third," and the like, are merely to distinguish similar objects and do not denote a particular ordering for the objects.
The materials for the respective members in the test apparatus of the present invention may be those listed in example 1 below, or may be other materials, and the present invention is not limited to the materials for the respective members in the test apparatus.
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Example 1
As shown in figures 1-6, the invention provides a hypergravity model test device for simulating the migration of pollutants in a soil-bentonite vertical barrier wall, which comprises a model box system, a percolate collecting system and a consolidation material supplementing and monitoring system.
The model box system comprises a model box 1, wherein the model box 1 comprises an upstream area 10, a soil filling area and a downstream area 15, the upstream area 10, the soil filling area and the downstream area 15 are sequentially separated by partitions, the upstream area 10 is configured to store a first solution, and the soil filling area is configured to be capable of placing a soil-bentonite vertical partition wall for carrying out experiments. The downstream region 15 is configured to be capable of storing a second solution. The first solution may be an initial contaminant solution, or a solution of other substances capable of ionization in water, or may be deionized water. The second solution may be a solution of a substance capable of ionization in water, such as a sodium chloride solution, or the first solution may also be deionized water.
In this embodiment, the material of the mold box 1 is high-strength steel, and the material of the mold box may be other materials, and the material of the mold box is not limited in the present invention. The inner wall of the model box 1 needs to be sprayed with antirust paint, so that the influence of iron ions on the test is avoided.
In some preferred modes, as shown in fig. 1, the side wall of the model box 1 is provided with a clamping groove 16, the clamping groove is configured to be capable of installing a fixed partition, and the clamping groove 16 is connected with the model box 1 and can be fixedly connected or detachably connected. In some preferred modes, the clamping grooves 16 are arranged in pairs, in this embodiment, four pairs of clamping grooves 16 are arranged inside the model box 1; one of the pockets 16 of each pair is disposed in a first side wall of the mold box 1, and the other pocket 16 is disposed in an opposite side wall of the mold box.
In some preferred forms, the partition is a porous barrier 14 capable of allowing the first solution to pass through the porous barrier to allow communication between the upstream zone 10 and the landfill zone, and between the landfill zone and the downstream zone 15. In this embodiment, the porous baffle 14 is made of pvc, and is inserted into the slot 16 during the experiment without being pulled out. In other embodiments, the porous barrier 14 may be made of other materials, and the material of the porous barrier is not limited in the present invention.
In this embodiment, the porous baffle 14 has a thickness of 8mm, a hole diameter of 10mm, and a hole pitch of 40mm, and a 10-mesh screen and filter paper are attached to the side in contact with the water-containing sand layer 12 and the weakly water permeable layer 13.
In some preferred modes, as shown in fig. 1 to 6, the upstream region 10 is provided with an upstream water inlet 8 and a first drain hole 5 on the side, and the downstream region 15 is provided with an overflow hole and a second drain hole 51 on the side; for constant head maintenance and head differential control. In some preferred forms, the upstream inlet opening 8 is located above the first drain opening 5 and the overflow opening is located above the second drain opening 51. In this embodiment, the overflow hole 6, the water inlet hole 8, the first drain hole 5, and the second drain hole 51 use high-pressure thickened pneumatic ball valve switches.
In some preferred forms, as shown in fig. 1-3, the upstream region 10 is internally provided with a first support frame 3 configured to support the multi-orifice baffle 14 in a hypergravity environment without a change in volume of the upstream region 10. In some embodiments, one end of the first support frame 3 is fixedly connected with the side wall of the model box 1, and the other end is connected with the porous baffle 14; or the first support frame 3 is only contacted with the side wall of the model box 1 and the porous baffle 14 and is not connected; in some preferred modes, gaskets are arranged at the contact positions of the first support frame 3, the side wall of the model box 1 and the porous baffle 14, so that the contact between the first support frame and the side wall of the model box 1 is tighter, the support frame cannot be displaced, and the support frame can be better supported. 1-3, the downstream region 15 is provided with a second support shelf 31 configured to support the perforated barrier 14 in a hypergravity environment without changing the volume of the downstream region 15. The second supporting frame 31 may be disposed in the same manner as the first supporting frame 3 (as described above), and will not be described herein again. The first support frame 3 and the second support frame 31 are made of high-strength steel and are used for supporting the porous baffle 14.
In some preferred forms, as shown in fig. 1, two pairs of slots 16 are provided in the fill area and are configured to be used for mounting wall forms, where the slots 16 may be provided in the same manner as the slots 16 described above. In this embodiment, the clamping groove 16 is made of aluminum alloy and is fixed on the sidewall of the mold box 1 by using high-strength structural adhesive. The wall-making template is made of acrylic materials and is used for preparing the supergravity model of the soil-bentonite vertical separation wall.
In some preferred modes, the soil-filled area comprises a weak permeable layer 13 and a water-containing sand layer 12, as shown in fig. 3, the weak permeable layer 13 and the water-containing sand layer 12 are arranged inside the soil-filled area from bottom to top; the vertical bentonite-clay barrier wall stands upright in the middle of the hydrous sand layer 12 (the middle refers to a non-edge position and not only to the middle of the hydrous sand layer).
As shown in fig. 6, the vertical soil-bentonite barrier walls are inserted deep into the weakly permeable layer, and this is done to prevent the solution from passing through the bottom of the barrier walls to form defects. The depth of the inserted weak permeable layer is referenced to the actual engineering, the actual engineering is generally inserted by 2-4m, in the embodiment, in order to ensure that the bottom of the separation wall does not leak, the depth is larger than the actual engineering.
The weakly permeable layer 13 is composed of Fujian standard sand and Ohio bentonite, the dry weight ratio is 4:1, and the water content is 20%. The soil-bentonite vertical barrier wall 11 is composed of Fujian standard sand and Ohio bentonite, the dry weight ratio is 19:1, and the water content is 38%. The water-containing sand layer 12 is pure Fujian standard sand, and the water content is 10%.
In some preferred modes, the percolate collection system comprises a collection tank 2 and a pore pressure gauge, the collection tank 2 being configured to be able to collect the percolate from the model box 1, the pore pressure gauge being used to detect the water level; in some preferred modes, the collecting barrel 2 is communicated with the model box 1, and the pore pressure meter is arranged at the bottom of the collecting barrel 2; in some preferred forms, a pvc transparent rigid pipe 7 is used to connect the collection tank 2 to the overflow aperture of the mold box 1.
In this embodiment, the collecting barrel 2 is made of materialIs acrylic. The pore pressure meter is arranged at the bottom of the collecting barrel 2, can detect the water seepage level h, and obtains the seepage Q ═ pi r according to the conversion of the inner diameter r of the collecting barrel 22h。
In this embodiment, the height of the collecting vessel 2 is 15cm, the inner diameter is 4cm, the outer diameter is 6cm, the monitoring accuracy of the flow of the filtrate under 100g can reach pi x 4 by matching with a pore pressure meter with the measuring range of 0.1Mpa and the accuracy of 0.2 percent2X 1000X 0.2%/100 ═ 1.0053ml, during the test, three collecting tanks 2 were connected in series using pvc pipes, so that the percolate collection rate could reach π X421508ml, the measuring range and the precision of the collecting system can meet the requirements of slow seepage speed and long test time of the experiment.
The consolidation material supplementing and monitoring system comprises a flow guide device 4, an LVDT displacement sensor 9, a soil pressure meter and a pore pressure meter. In some preferred modes, the flow guide device 4 is connected to the top of the model box 1 and is used for filling supplement in the centrifugal consolidation process of the soil-bentonite vertical barrier wall and can prevent the filling from leaking laterally.
In this embodiment, the diversion device 4 is made of acrylic and is fixed to the top of the mold box 1 by bolts. The flow guide device 4 can realize the function of supplementing the soil bentonite filler to the soil-bentonite vertical separation wall in the centrifugal machine and preventing the filler from leaking laterally.
In some preferred modes, as shown in fig. 7, the guiding device 4 comprises a guiding groove 18, an inlet is arranged above the guiding groove, an outlet is arranged below the guiding groove, and the filling material can enter the guiding groove 18 from the inlet and flow out of the guiding groove 18 from the outlet. In some preferred forms, the guiding device 4 includes a fixing plate 24, the fixing plate 24 is fixedly connected to the guiding groove 18, and the fixing plate 24 is located on both sides of the guiding groove 18 and configured to fix the guiding groove 18 to other devices or components. In some preferred forms, the fixing plate 24 is provided with screw holes or bolt holes for connecting and fixing the deflector 4 to other components.
In some preferred modes, as shown in fig. 7, ribbed plates 17 are arranged on two sides of the diversion trench 18, so that the strength of the diversion trench 18 can be enhanced, and the structure of the diversion trench is more stable. In some preferred modes, the ribbed plates 17 are connected with the side surfaces of the diversion trench 18 and also connected with the fixing plates 24.
In some preferred embodiments, as shown in fig. 7, a guide plate 20 is connected to the outlet of the guiding groove 18, the guide plate 20 can guide the discharging direction of the filler, and the guide plate 20 can be inserted into the clamping groove 16 to connect the guiding groove 18 with the mold box 1.
In this embodiment, the guiding gutter 18 is a transparent acrylic guiding gutter 18, and the transparent material enables the state and the flow direction of the filler to be observed, which is convenient for operation. In this embodiment, as shown in the figure, the thickness of the acrylic plate is 2cm, and the height of the diversion trench 18 is 20 cm. The bottom of the diversion trench 18 is provided with a guide plate 20 with the height of 3cm, which can be inserted into the clamping groove 16 to separate the water-containing sand layer 12, thereby ensuring that the bentonite filler perfectly flows into a gap generated by the settlement of the soil-bentonite vertical separation wall.
In some preferred embodiments, as shown in fig. 6, the LVDT displacement sensor 9 is disposed on top of the flow guide 4 for monitoring the amount of consolidation settlement, in this embodiment, the LVDT displacement sensor 9 is fixed on top of the flow guide 1817 using a clamp for monitoring the amount of consolidation settlement.
In some preferred modes, the soil pressure gauge and the pore pressure gauge can be arranged on two sides of the vertical bentonite-bentonite barrier wall, in this embodiment, as shown in fig. 6, the soil pressure gauge and the pore pressure gauge are arranged on the right side of the vertical bentonite-barrier wall, and of course, the soil pressure gauge and the pore pressure gauge can be arranged on the left side and the right side of the vertical bentonite-barrier wall or on the left side of the vertical bentonite-barrier wall.
The soil pressure gauge and the pore pressure gauge are respectively used for monitoring horizontal soil pressure and hyperstatic pore pressure and determining hyperstatic pore pressure dissipation time, and when the readings of the soil pressure gauge and the pore pressure gauge are not reduced, the end of consolidation can be judged.
A test method of a supergravity model test device for simulating the migration of pollutants in a soil-bentonite vertical barrier wall comprises the following steps:
step 1: installing a clamping groove 16 on the side wall of a model box 11, inserting a porous baffle plate 14, partitioning the model box 1 into an upstream area 10, a soil filling area and a downstream area 15, and arranging steel support frames (comprising a first support frame and a second support frame) between the porous baffle plate 14 and the box wall;
step 2: paving dry bentonite with the thickness of 1cm between the porous baffles 14, and preparing a soil layer with extremely low permeability coefficient as the weakly permeable layer 13 by using a layering compaction method;
and step 3: and (3) inserting the wall-making template into two clamping grooves 16 in the middle of the model box 1 to form a wall forming area, inserting a barrier strip at the connecting position of the wall forming area and the wall of the model box 1 for the airtightness of the soil-bentonite vertical barrier wall and the side wall of the model box 1, and pouring dry bentonite to form a 2cm bentonite strip. Directly pouring the slurry (namely the soil-bentonite barrier wall filler) into the bottom of the wall forming area through the diversion bag, and gradually lifting the diversion bag along with the pouring of the slurry to achieve the purpose of removing bubbles;
in this embodiment, two barrier strips are vertically placed on both sides of the wall forming area, and dry bentonite is added after the barrier strips are vertically placed with the wall forming template.
And 4, step 4: filling Fujian standard sand as a water-containing sand layer 12 between a wall-making template and a porous baffle plate 14 by a layered compaction method, and burying a soil pressure meter, a pore pressure meter and a conductivity sensor at a set position, as shown in figure 6;
and 5: the barrier wall filler can fill the space occupied by the original template and sink in the process of pulling out the wall making template, and the filler needs to be supplemented in time. Aligning the flow guide device 4 to a wall making area, inserting the bottom guide plate 20 into the clamping groove, fixing the flow guide device 4 on the model box 1 by using bolts, adding a barrier wall filler into the flow guide groove 18, and erecting an LVDT displacement sensor 9 at the top of the flow guide groove 18;
step 6: deionized water is added into the upstream area 10 and the downstream area 15, the whole device is transferred into a centrifuge, the centrifuge is started to carry out centrifugal consolidation on the model, and the completion condition of the consolidation is monitored by an LVDT displacement sensor 9, a soil pressure gauge and a pore pressure gauge. In this embodiment, the levels of the deionized water added to the upstream zone 10 and the downstream zone 15 are as high; the height of which coincides with the height of the lowest overflow aperture of the downstream area 15.
And 7: after consolidation is finished, deionized water is added in the upstream area, a water head difference of 3cm is formed between the upstream area 10 and the downstream area 15, the upstream water inlet hole 8 is connected with a Ma bottle to maintain a constant water head, a percolate collecting system is used for monitoring the leakage amount for 1 hour, and whether the airtightness is met is judged. The simulation showed that the leak-free flow was 7ml per hour and if a leak of less than 7ml was monitored for 1 hour, the seal was satisfied.
When the supergravity model of the soil-bentonite vertical barrier wall passes through tightness detection, converting upstream deionized water into a pollutant solution (pollutants can be substances which can be ionized in water, such as salt, heavy metal, acid and the like), carrying out a pollutant migration centrifugal test, and monitoring whether the soil-bentonite vertical barrier wall is broken down by using a conductivity sensor; in this embodiment, the height of the contaminant solution in the upstream area and the height of the deionized water in the downstream area have a certain height difference, and the height difference between the contaminant solution in the upstream area and the deionized water in the downstream area is 3 cm.
After the change to the contaminant solution, the centrifugation test conditions were the same as the previous centrifugation conditions, and the centrifugation acceleration was 100 g.
And 8: after the test is completed, the soil-bentonite vertical barrier wall is taken out, and as shown in fig. 8, the concentration 22, the permeability coefficient 20, the density and the water content 21 are sampled at the set position of the soil-bentonite vertical barrier wall. In fig. 8, the values are in mm, the vertical direction represents the height of the barrier wall, and the horizontal direction represents the length of the barrier wall.
During the actual test, in step 1, the wall thickness of the mold box 1 is 20mm, and the internal dimension of the box is as follows: 770mm long, 400mm wide and 510mm high.
The overflow hole is used for controlling the liquid level of the downstream water tank. In this embodiment, as shown in fig. 6, the number of the overflow holes 6 is 3, the distances from the top surface of the model box 1 to the overflow holes are 3, 6 and 9cm, and the distance from the water inlet 8 to the top surface of the model box 1 to the overflow holes is 9cm, so that various water head difference working conditions can be realized. The aluminum alloy clamping grooves 16 are four pairs, and the two pairs are 510mm long and are used for installing the porous baffles 14 of the upstream and downstream water tanks; two pairs of 400mm long wall templates are used for installing wall making templates, four pairs of clamping grooves are fixed at the appointed positions of the side walls of the model box by using high-strength structural adhesive and are stabilized for 72 hours by using a clamp. The steel support frames 3 are two, one steel support size 510mm x 35mm x 30mm is placed in the upstream water tank 10, and one steel support size 510mm x 35mm x 8mm is placed in the downstream water tank 15, so that the porous baffle plate 14 can be supported in a high-gravity environment, and the volume of the water tank is not changed.
In practical tests, the soil sample preparation and filling steps of the weakly permeable layer 13 in the step 2 are as follows:
(1) slowly adding bentonite into deionized water, standing and hydrating for 24 hours to obtain bentonite slurry; the mass ratio of the two is as follows: bentonite 5: 95;
(2) mixing Fujian standard sand and dry bentonite for 30 minutes to prepare 8 parts of dry soil sample; the mass ratio of the sand to the sand is as follows: dry bentonite 80: 18.95;
(3) mixing and stirring each part of dry soil sample and bentonite slurry for 30 minutes to obtain a weakly permeable layer filler; and drying the soil sample according to the mass ratio of the two: bentonite mud 100: 21.05;
(4) paving a layer of dry bentonite with the thickness of 10mm at the bottom of the soil filling area, and spraying a spray can on the surface;
(5) pouring a part of the filler (one part) of the weakly permeable layer into the soil filling area, compacting the filler by using a self-made compaction hammer, spraying the surface by using a spraying pot, and repeating the steps until the soil filling reaches the bottom of the clamping groove 16 of the wall making template. And filling the weak permeable layer with filler (eight parts in total) for eight times.
In the actual test, the preparation steps of the filler for the soil-bentonite vertical barrier wall 11 in the step 3 are as follows:
(1) slowly adding dry bentonite into deionized water, standing and hydrating for 24 hours to obtain bentonite slurry; mass ratio, deionized water: dry bentonite 95: 5;
(2) mixing Fujian standard sand and dry bentonite for 30 minutes; preparing a dry soil sample; mass ratio, dry bentonite: the Fujian standard sand is 3: 95;
(3) and mixing and stirring the dried soil sample and the bentonite slurry for 30 minutes, then carrying out slump test, and when the slump of the soil sample is less than 125mm, continuing adding deionized water for stirring until the slump is more than 125mm, thus obtaining the soil-bentonite barrier wall filler. And (2) drying the soil sample according to the mass ratio: bentonite mud 98: 40.
The arrangement positions of the sensors in step 4 during the actual test are shown in fig. 6. And a conductivity sensor, a soil pressure gauge and a pore pressure gauge are arranged on one side of the soil-bentonite barrier wall close to the downstream area, and the soil pressure gauge and the pore pressure gauge are arranged at the same height. The conductivity sensor is also provided in the upstream region, and the pore pressure gauge is provided in the upstream region and the downstream region.
In the actual test, the height of the filler of the soil-bentonite vertical barrier wall filler in the diversion trench 18 in the step 5 is calculated by a layering summation method, and the height is 10 cm.
In step 6 of the actual test, the g value of the centrifugal machine in the centrifugal consolidation stage of the model rises by 10g every ten minutes until 100g, whether the consolidation is finished is determined according to the basically stable pore pressure change rate, the test is consolidated for 7 hours,
the distribution of the horizontal soil pressure of the soil-bentonite vertical barrier wall after consolidation is shown in fig. 9, the variation trend of the tested soil pressure along the depth is consistent with the prediction of the Li et al (2017) model, and the fact that the stress of the soil-bentonite vertical barrier wall model obtained by the molding method is consistent with the actual engineering is proved.
In the tightness detection stage, the leakage amount of the bentonite vertical barrier wall is shown in fig. 8, and the leakage amount is slightly smaller than a theoretical value, which proves that good water tightness is kept between the bentonite vertical barrier wall and the side wall of the model box.
In the embodiment, in the pollutant migration stage, the solution in the upstream water tank is changed into a NaCl solution with a concentration of 1mol/L, and the model is continuously operated for 36 hours under 100g, so as to simulate the service time of 41 years.
In the actual test, after the centrifugal test in the step 7 is completed, the water-containing sand layers 12 on the two sides of the soil-bentonite vertical partition wall are dug, as shown in fig. 9, the vertical thickness of the soil-bentonite vertical partition wall body is uniform, the verticality is high, the surface is smooth, and the soil sample at the joint with the clamping groove 16 is compact and uniform.
It should be understood by those skilled in the art that various features of the above-described embodiments can be combined in any combination, and for the sake of brevity, all possible combinations of features in the above-described embodiments are not described in detail, but rather, all combinations of features which are not inconsistent with each other should be construed as being within the scope of the present disclosure.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application.
Claims (7)
1. The hypergravity model test method for simulating the migration of pollutants in the vertical separation wall is characterized by comprising the following steps of:
step 1: installing the clamping groove on the side wall of the model box, inserting the porous baffle plate, partitioning the model box into an upstream area, a soil filling area and a downstream area, and installing a support frame in the upstream area and the downstream area;
step 2: paving dry bentonite between the porous baffles, and preparing a weakly permeable layer;
(1) slowly adding bentonite into deionized water, standing and hydrating for 24 hours to obtain bentonite slurry; the mass ratio of the two is as follows: bentonite 5: 95;
(2) mixing standard sand and dry bentonite for 30 minutes to prepare 8 parts of such dry soil sample; the mass ratio of the sand to the sand is as follows: dry bentonite 80: 18.95;
(3) mixing and stirring each part of dry soil sample and bentonite slurry for 30 minutes to obtain a weakly permeable layer filler; and drying the soil sample according to the mass ratio of the two: bentonite mud 100: 21.05;
(4) paving a layer of dry bentonite with the thickness of 10mm at the bottom of the soil filling area, and spraying a spray can on the surface;
(5) pouring the filler of the weakly permeable layer into the soil filling area, compacting the filler by using a self-made compaction hammer, spraying the surface of the filler by using a spraying pot, and repeating the steps until the filler of the weakly permeable layer reaches the bottom of the plate groove of the wall making formwork;
and step 3: inserting the wall-making template into two clamping grooves in the middle of the model box to form a wall-forming area, inserting a barrier strip at the connecting position of the wall-forming area and the wall of the model box for the airtightness of the soil-bentonite barrier wall and the side wall of the model box, and pouring dry bentonite to form a 2cm bentonite strip;
(1) slowly adding dry bentonite into deionized water, standing and hydrating for 24 hours to obtain bentonite slurry; mass ratio, deionized water: bentonite is 95: 5;
(2) mixing Fujian standard sand and dry bentonite for 30 minutes to prepare a dry soil sample; mass ratio, dry bentonite: the Fujian standard sand is 3: 95;
(3) mixing and stirring the dried soil sample and the bentonite slurry for 30 minutes, wherein the dried soil sample comprises the following components in percentage by mass: bentonite slurry 98: 40; performing slump test, and when the slump of the soil sample is less than 125mm, continuing adding deionized water for stirring until the slump is more than 125mm to obtain the soil-bentonite barrier wall filler;
and 4, step 4: filling standard sand between the wall-making template and the porous baffle plate as a water-containing sand layer, and embedding a soil pressure gauge, a pore pressure gauge and a conductivity sensor;
and 5: firstly, the barrier strip is pulled out, then the wall-making template is pulled out, and the barrier wall filler can fill the space occupied by the original template and sink in the template pulling-out process, so that the filler needs to be supplemented in time; aligning the flow guide device to a wall making area, inserting the guide plate into the clamping groove, fixing the flow guide device on the model box by using bolts, adding a barrier wall filler into the flow guide groove, and erecting an LVDT displacement sensor at the top of the flow guide groove;
step 6: adding deionized water into an upstream area and a downstream area, transferring the whole device into a centrifuge, starting the centrifuge, carrying out centrifugal consolidation on the model, and monitoring the consolidation completion condition by an LVDT displacement sensor, a soil pressure meter and a pore pressure meter;
and 7: after consolidation is finished, adding deionized water in an upstream area to form a water head difference of 3cm between the upstream area and the downstream area, keeping a constant water head at the upstream area, monitoring the leakage amount for 1 hour by using a percolate collecting system, and judging whether the tightness is met;
when the supergravity model of the soil-bentonite vertical barrier wall passes through the tightness detection, the upstream deionized water is changed into a pollutant solution, a pollutant migration centrifugal test is carried out, and whether the soil-bentonite vertical barrier wall is broken down or not is monitored by using a conductivity sensor; the contaminant solution is an ionizable substance in water; in the centrifugal test, the centrifugal acceleration is 100 g;
and 8: after the test is finished, taking out the soil-bentonite vertical separation wall, sampling at a set position, and measuring the concentration, the permeability coefficient, the density and the water content;
the test device applied to the test method comprises a model box system, a percolate collecting system and a consolidation material supplementing and monitoring system;
the mold box system comprises a mold box comprising an upstream region, a fill region and a downstream region separated in sequence by a partition, the upstream region configured to be capable of storing a first solution, the fill region configured to be capable of being used to provide a soil-bentonite vertical barrier wall; the downstream region is configured to be capable of storing a second solution; the partition is a porous baffle plate, and can allow a solution to pass through the baffle plate, so that the communication between an upstream area and a soil filling area is realized, and the communication between the soil filling area and a downstream area is realized;
the side surface of the upstream area is provided with a water inlet and a first water drainage hole, and the side surface of the downstream area is provided with an overflow hole and a second water drainage hole for constant head maintenance and water head difference control;
the percolate collection system comprises a collection barrel and a pore pressure meter, wherein the collection barrel is configured to be capable of collecting percolate of a model box, and the pore pressure meter is used for detecting the water level; communicating the collecting barrel with the overflow hole of the model box by using a connecting pipe;
the consolidation material supplementing and monitoring system comprises a flow guide device, an LVDT displacement sensor, a soil pressure meter and a pore pressure meter; the flow guide device is connected to the top of the model box, is used for supplementing the filler in the centrifugal consolidation process of the soil-bentonite vertical barrier wall, and can prevent the filler from leaking laterally; the soil pressure gauge and the pore pressure gauge are arranged on two sides of the soil-bentonite vertical separation wall and are respectively used for monitoring horizontal soil pressure and ultra-static pore pressure and determining ultra-static pore pressure dissipation time.
2. The hypergravity model test method for simulating contaminant transport in a vertical barrier wall according to claim 1, wherein a screen and filter paper are attached to the side of the porous baffle contacting the water-containing sand layer; the side of the porous baffle, which is in contact with the weakly permeable layer, is attached with a screen and filter paper.
3. The method of claim 1, wherein two pairs of slots are provided in the fill area and are configured to receive wall forms.
4. The hypergravity model test method for simulating the migration of pollutants in a vertical barrier wall according to claim 1, characterized in that the soil filling area comprises a weakly permeable layer and a hydrous sand layer, and the weakly permeable layer and the hydrous sand layer are arranged in the soil filling area from bottom to top; the barrier wall is erected in the middle of the hydrous sand layer.
5. The hypergravity model test method of simulating contaminant migration in a vertical baffle wall as claimed in claim 1, wherein the diversion device comprises a diversion trench, an inlet is arranged above the diversion trench, an outlet is arranged below the diversion trench, and a guide plate is connected to the outlet of the diversion trench.
6. The hypergravity model test method for simulating contaminant migration in a vertical baffle wall as claimed in claim 1, wherein in step 4, a conductivity sensor, a soil pressure gauge and a pore pressure gauge are arranged on one side of the soil-bentonite baffle wall near the downstream region, and the soil pressure gauge and the pore pressure gauge are arranged at the same height.
7. The method of claim 1, wherein in step 6, the g value of the centrifuge increases by 10g every ten minutes until 100g in the centrifugal consolidation stage of the model, and the consolidation is determined to be completed with a substantially constant rate of change of pore pressure.
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