NL2028968A

NL2028968A - Anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas and construction method thereof

Info

Publication number: NL2028968A
Application number: NL2028968A
Authority: NL
Inventors: Peng Tao; Luo Lin; Dai Deqiu; Feng Wei; Bao Haimei
Original assignee: Inst Geochemistry Cas
Priority date: 2020-12-16
Filing date: 2021-08-13
Publication date: 2021-10-22
Also published as: NL2028968B1; CN112593579A

Abstract

The disclosure provides an anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas and a construction method thereof. The anti-seepage soft 5 pit for purifying sewage using mud-mixed clay in karst mountain areas includes a soil pit and a clay layer laid on the bottom of the soil pit, a mud-mixed clay layer thereon provided on the clay layer, and a water puriﬁcation layer provided on the mud-mixed clay layer. The construction method of the anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas of the present disclosure includes the 10 following steps: A. laying clay on the soil pit l, and injecting water thereto, stirring and compacting to obtain a clay layer 2; B. laying a mud-mixed clay on the clay layer 2 to obtain a mud-mixed clay layer 3; C. sprinkling a water purification material evenly on the bottom of mud-mixed clay layer 3 to obtain a water purification layer 4; and D. sowing grass seeds on a side slope of mud-mixed clay layer 2. The anti-seepage soft pit 15 according to the present disclosure has good anti-seepage effect, and thus could play a role of sewage treatment and slope care.

Description

ANTI-SEEPAGE SOFT PIT FOR PURIFYING SEWAGE USING MUD-MIXED CLAY IN KARST MOUNTAIN AREAS AND CONSTRUCTION METHOD THEREOF TECHNICAL FIELD

[01] The present disclosure relates to the technical field of anti-seepage structures, and in particular to an anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas and a construction method thereof.

BACKGROUND ART

[02] In karst areas, due to the serious development of underground lava fissures, untreated rural domestic sewage will seep into groundwater or seepage into surface rivers through the fissures, causing river or groundwater pollution, and worsening the drinking water quality of local residents and even downstream residents. In order to prevent such things from happening, many anti-seepage structures have been built in karst areas.

[03] Traditional anti-seepage and plugging technologies, such as concrete anti-seepage walls and splitting curtain grouting, have small construction depths and poor stratum adaptability, some of which require large or heavy equipment, which is expensive and difficult to access the leakage location. These technologies are often unable to accurately tind the source of leakage, and have a poor plugging effect. In addition, most of these technologies have adverse effects on the environment.

[04] Therefore, it has become one of the research hotspots in the field of domestic sewage treatment in karst areas to look for an effective, economical and environmentally friendly anti-seepage method.

SUMMARY

[05] An object of the present disclosure is to provide an anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas and a construction method thereof. The anti-seepage soft pit according to the present disclosure has good anti-seepage effect, and thus could play a role of sewage treatment and slope care.

[06] The present disclosure provides the following technical solutions:

[07] An anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas, comprising a soil pit, a clay layer laid on the bottom of the soil pit, a mud-mixed clay layer provided on the clay layer, and a water purification layer provided on the mud-mixed clay layer.

[08] In some embodiments, in the above anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas, a side slope of the mud-mixed clay layer is provided with grass seeds.

[09] In some embodiments, in the above anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas, the clay layer has a thickness of 500- 1000 mm, the mud-mixed clay layer has a thickness of 500-1000 mm, and the water purification layer has a thickness of 3-20 mm.

[10] In some embodiments, in the above anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas, the water purification layer is made of a water purification material which consists of particles prepared by mixing aluminum sulfate and a stone powder with a mass ratio of (25-35): (50-60), wherein the particles have a particle size of 2-3 mm.

[11] In some embodiments, in the above anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas, the water purification layer is made of a water purification material which consists of particles prepared by mixing aluminum sulfate and a stone powder with a mass ratio of 6 : 11, wherein the particles have a particle size of 2-3 mm.

[12] In some embodiments, in the above anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas, the mud-mixed clay layer is made of a material which is a mixture of clay and bottom mud with a mass ratio of (5-15): (85-95).

[13] In some embodiments, in the above anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas, the material for making the mud-mixed clay layer 4 contains 70-80% of powder and 10-20% of fine sand, and has a particle size not larger than 0.04 mm.

[14] In some embodiments, in the above anti-seepage soft pit for purifying sewage using mud-doped clay in karst mountain area, the material for making the mud-mixed clay layer 4 contains 75% of powder and 15% of fine sand, and has a particle size not larger than 0.04 mm.

[15] The present disclosure also provides a construction method of the anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas, comprising the following steps:

[16] A. laying a clay on a soil pit, injecting water, stirring, compacting and leveling to obtain a clay layer;

[17] B. laying a mud-mixed clay on the clay layer to obtain a mud-mixed clay layer;

[18] C. sprinkling a water purification material evenly on the bottom of the mud-mixed clay layer to obtain a water purification layer; and

[19] D. sowing grass seeds on a side slope of the mud-mixed clay layer.

[20] Compared with the prior art, the present disclosure has the following beneficial effects: [ZI] In the present disclosure, sufficient mixing of bottom mud and clay could be utilized to reduce the saturated hydraulic conductivity of the soil, thus achieving the anti- seepage effect. The rich microbial resources in the farmland bottom mud could generate a large number of extracellular secretions under the stimulation of nutrients, finally achieving the plugging effect; meanwhile, the extracelluar secretions combine with aluminum sulfate and the stone powder to form a passivation zone, and the passivation zone not only adsorbs nutritive salts in the water body, but also forms a passivation layer on the surface of the sediment, which significantly reduces the release of endogenous nutritive salts, and the sediment-water interface in the passivation zone is oxygen-rich, which reduces the release of endogenous nutritive salts. As the water quality of the passivation zone gradually improves, deposited plants that gradually recovered could also slow down the wind and waves, fix the bottom mud, greatly enhance the water body self-purification, reduce the accumulation of ammonia nitrogen and phosphorus in the water body, so that the nutritive salts content of the water in the passivation zone is significantly lower than that in control zone, and a passivation layer is formed on the surface of the sediment, and the passivation layer prevents the supply of nutrients to the overlying water body by surface adsorption, ion exchange, physical barrier and the like, so as to achieve the purpose of controlling eutrophication of the water body, and eventually form a soft pit for purifying water. Moreover, the anti-seepage effect of the anti-seepage soft pit according to the present disclosure could reach the level of extremely micro-permeation.

BRIEF DESCRIPTION OF THE DRAWINGS

[22] Figure is a schematic diagram of the structure according to the present disclosure;

[23] in the Figure, 1 represents a soil pit, 2 represents a clay layer, 3 represents a mud- mixed clay layer, 4 represents a water purification layer, 5 represents grasses, 6 represents domestic sewage.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[24] The present disclosure will be further described accompanying with the Figure and examples, but is not limited to this.

[25] Example.

[26] An anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas, the structure of which is shown in FIG. 1, comprising a soil pit 1, a clay layer 2 laid on the bottom of the soil pit 1, a mud-mixed clay layer 3 provided on the clay layer 2, and a water purification layer 4 provided on the mud-mixed clay layer 3. The soil pit 1 refers to a natural soil pit in Karst mountain areas.

[27] Aside slope of the mud-mixed clay layer 3 is provided with grass seeds. The grass seeds will grow into grasses, which would integrate with the surrounding environment, preventing rain from washing so as to achieve the effect of slope care.

[28] The clay layer 2 has a thickness of 500-1000 mm; the mud-mixed clay layer 3 has a thickness of 500-1000 mm; the water purification layer 4 has a thickness of 3-20 mm. These thicknesses are determined after their saturated hydraulic conductivities are determined by taking soil using a ring knife, and a thickness of 500 mm is the minimum anti-seepage thickness for the clay layer 2 and the mud-mixed clay layer 3.

[29] The water purification layer 4 is made of a water purification material, which consists of spherical particles prepared by mixing aluminum sulfate and stone powder with a mass ratio of (25-35) : (50-60), and the spherical particles have a particle size of 2-3 mm. According to experiments, a mass ratio of aluminum sulfate to stone powder is preferably 6:11, which has a better removal effect on NHN and TP.

[30] The mud-mixed clay layer 3 is made of a mixture of clay and bottom mud with a mass ratio of (5-15): (85-95). The bottom mud refers to the bottom mud of farmland. Preferably, the material with a good anti-seepage effect has a mass ratio of the clay to the bottom mud of 1:9; that is, in the mud-mixed clay, the clay accounts for 10%, and the farmland bottom mud accounts for 90%. This stipulation is in accordance with the international soil-making particle classification standard: the clay has a particle size of

0.0001-0.002 mm. After analysis and determination of the mud-mixed clay with good anti-seepage effect, the results regarding particle size show that the clay with a particle size of less than 0.0027 mm accounts for 10%.

[31] The mud-mixed clay layer 3 is made of a material which contains 70-80% of powder and 10-20% of fine sand, and has a particle size not larger than 0.04 mm. 5 According to the international soil-making particle classification standard, gravel has a particle size of 3-2 mm; coarse sand has a particle size of 0.2-2 mm; fine sand has a particle size of 0.02-0.2 mm; powder has a particle size of 0.002-0.02 mm; clay has a particle size of 0.0001-0.002 mm. According to the actual measurement, the mud-mixed clay with a good anti-seepage effect contains 75% of powder and 15% of fine sand, and has a minimum particle size of 0.003 mm, a maximum particle size of 0.04 mm, a maximum water holding capacity of 67.98%, a capillary water holding capacity of

64.61%, a soil bulk density of 0.91 g-cm™, a non-capillary porosity of 3.08%, a capillary void of 58.92%, a total porosity of 62.00%, and a soil saturated hydraulic conductivity of 3.64 10% cm/s.

[32] Aconstruction method of the anti-seepage soft pit for purifying sewage using mud- doped clay in karst mountain areas was conducted as follows:

[33] A. Clay was laid on a soil pit 1, water was injected thereto, and stirred, the resulting mixture was compacted in layers, and leveled by a man-machine, obtaining a clay layer

2. In this step, clay was mixed with an appropriate amount of water, forming mud masses, which were deformed under the action of external force but did not crack, and when the external force was dissipated, the mud masses could retain their original shape. The clay combined with non-plastic raw materials to form good plastic clay masses with a certain drying strength. Water was injected in an amount that could reach the saturated state of the clay.

[B4] B. A mud-mixed clay was laid on the clay layer 2, obtaining a mud-mixed clay layer 3.

[35] C. A water purification material was sprinkled evenly on the bottom of the mud- mixed clay layer 3, obtaining a water purification layer 4; and

[36] D. Grass seeds were sowed on a side slope of the mud-mixed clay layer 2.

[37] In the present disclosure, the bottom of the soil pit 1 is compacted through the clay layer 2, and farmland bottom mud is incorporated into clay and they are fully mixed. The rich microbial resources in the farmland bottom mud are used to generate a large number of extracellular secretions under the stimulation of nutrients, thereby reducing the saturated hydraulic conductivity of the soil, and finally achieving the effect of plugging and anti-seepage. A certain proportion of aluminum sulfate and stone powder are added into the mud-mixed clay layer 3 to form a water purification layer 4, which absorbs nutritive salts in the water body and forms a passivation layer on the surface of the sediment, and the sediment-water interface in the passivation zone is oxygen-rich, which reduces the release of endogenous nutritive salts, and provides a good living environment for the growth of grass seeds, rooting around for slope protection.

[38] Example

[39] A number of experiments were carried out in the study of the present disclosure, and some experimental records and analysis are as follows:

[40] The relative properties of mud-mixed clay were tested. The saturated hydraulic conductivity of the soil is the amount of water that passes through a unit area in a unit time under a unit water potential gradient when the soil is saturated with water. It is a function of the soil texture, bulk density, and pore distribution characteristics. Saturated hydraulic conductivity has strong spatial variability due to the influence of spatial variables such as soil texture, bulk density, pore distribution, and organic matter content, wherein the pore distribution characteristics have the greatest impact on the saturated hydraulic conductivity of the soil. Saturated hydraulic conductivity of the soil is one of the important physical properties of soil, an important soil parameter for calculating the water flux in the soil profile, designing irrigation and drainage system engineering, and also an important parameter of the hydrological model. Its accuracy seriously affects the accuracy of the model.

[41] After obtaining the anti-seepage soft pit for purifying sewage using mud-mixed clay in karst mountain areas, the saturated hydraulic conductivity of the mud-mixed clay was tested by a KSAT soil saturated hydraulic conductivity meter.

[42] The mechanism of the measurement is as follows: at ambient temperature, flow rate and drive hydraulic gradient were tested by using degassed water to act vertically on the cross-section of a fully saturated mud-mixed clay sample. The mud-mixed clay and hydraulic conductivity (KS) are calculated by dividing the volumetric water flow by the soil cross-sectional area, time, the length of the mud-mixed clay sample and the head gradient along the water flow.

[43] The result is as follows:

[44] Ks (soil) = 3.64 = 10% m/s

[45] which reaches the micro-permeable grade in the permeability classification of rock and soil in the appendix of "Specifications for Geological Investigation of Water Conservancy and Hydropower Engineering”, as shown in Table 1 below, indicating that the mud-mixed clay provided by the present disclosure has a good anti-seepage effect and has reached the highest extremely micro-permeable grade. The corresponding anti- seepage soft pit also has a good anti-seepage effect.

[46] Table 1 ll ah Permeable rate q (Lu) (cm/s) q2100

[47] In addition, the correlation parameters of the mud-mixed clay were also tested. The records are as follows:

[48] Soil porosity measurement:

[49] The soil porosity indicator was determined by a ring knife method: the cover of a ring knife filled with the mud-mixed clay was removed, a filter paper was put on the perforated side and the ring knife was put in a flat-bottomed container; then water was poured thereto in an amount that the water level was slightly below the edge of the ring knife to make the ring knife fully absorb water for above 12 hours, and the resulting ring knife was weighed immediately; the ring knife after being weighted was placed in a tray which is filled with dry quartz sand for 2 hours, during which the perforated side with the filter paper 1s towards the tray, and weighed immediately.

[50] Original results: after soaking 12 hours, the total weight of the ring knife and wet soil is 585.6 g;

[51] after being placed on dry sand for 2 hours, the total weight of the ring knife and wet soil is 577.9 g;

[52] after being placed on dry sand for 12 hours, the total weight of the ring knife and wet soil is 571.8 g;

[53] The total weight of ring knife and dry soil is 430.5 g;

[54] the total weight of the dry soil in the ring knife is 227.9 g; the total weight of the ting kovife and wet soil after soaking for 12 hours - the total weight Maximum ater holding _ Ofthemsglmand deed gag 679806 capacity (35) the weight of the dry soil in the ring knife

[53] the total weight of the ring knife and wet soil after being placed on dry sand for 2 hours-the Capittary water holding _ total weight of the ring knife and dry sail 100% = 64 619%

[56] capacity (25) the weight of the dry soil in the ring knife

[57] Bulk density of the mud-mixed clay:

[58] The mud-mixed clay taken by the ring knife was dried to determine the bulk density of the soil in the fissures, which was conducted as follows: the ring knife filled with the mud-mixed clay was placed in a thermostat at 105 °C and dried to a constant weight.

[59] Bulk density of the mud-mixed clay (g-cm™) = the weight of dry soil in the ring knife / the volume of the ring knife = 0.91 g-cm™

[60] Non-capillary porosity (%) = (maximum water holding capacity-capillary water holding capacity) = bulk density of the mud-mixed clay = 3.08% capillary void (%) = capillary water holding capacity x bulk density of the mud-mixed clay = 58.93%

[61] Total porosity (%) = non-capillary void + capillary void = 62.00%

[62] This shows that the mud-mixed clay has a good anti-seepage effect, and the corresponding mud-mixed clay layer also has a good anti-seepage effect.

Claims

29. Conclusions

1. Soft anti-leakage pit for the purification of waste water using mud-mixed clay in karst mountain areas, where the pit consists of an earth pit (1), a layer of clay (2) laid on the bottom of the earth pit (1), a mud mixed clay layer (3) provided on the clay layer (2) and a water purification layer (4) provided on the mud mixed clay layer (3).

The soft anti-leakage pit for purifying wastewater using mud-mixed clay in karst mountain areas according to claim 1, wherein a side slope of the mud-mixed clay layer (3) is provided with grass seeds.

The soft anti-leakage pit for purifying waste water using mud-mixed clay in karst mountain areas according to claim 1, wherein the clay layer (2) has a thickness of 500 - 1000 mm, the mud-mixed clay layer (3) has a thickness of 500 - 1000 mm and the water purification layer (4) has a thickness of 3 - 20 mm.

The soft anti-leakage pit for purifying wastewater using mud-mixed clay in karst mountain areas according to claim 1, wherein the water purification layer (4) is made of a water purification material consisting of particles prepared by mixing aluminum sulfate and rock powder with a mass ratio of (25 — 35):(50 — 60), and the particles have a particle size of 2 — 3 mm.

The soft anti-leakage pit for purifying wastewater using mud-mixed clay in karst mountain areas according to claim 1, wherein the mud-mixed clay layer (3) is made of a material comprising a mixture of clay and bottom mud having a mass ratio of (5 — 15): (85 — 95).

The soft anti-leakage pit for purifying mud-mixed clay wastewater in karst mountain areas according to claim 5, wherein the material for making the mud-mixed clay layer (3) is 70-80% powder and 10-20% sand and has a particle size not greater than 0.04 mm.

- 10 -

The construction method for the soft anti-leakage pit for purifying waste water using mud-mixed clay in karst mountain areas according to any one of claims 1 to 6, wherein the method comprises the following steps: A. laying a clay on the earth pit (1), and injecting water therein, stirring, compacting and leveling to obtain a clay layer (2); B. laying a mud-mixed clay on the clay layer (2) to obtain a mud-mixed clay layer (3); C evenly sprinkling a water purification material on the bottom of the mud-mixed clay layer (3) to obtain a water purification layer (4); and D. sowing grass seeds on a side slope of the mud-mixed clay layer (2).