Microbial solidification horizontal ditch based on surface soil and manufacturing method

Abstract

The invention provides a surface soil-based microorganism solidification horizontal ditch and a manufacturing method thereof. A trapezoidal section groove is dug along a contour line on a loess slope surface, surface soil, short fibers, microorganism solidification bacterial liquid and cementing liquid are stirred and mixed, the mixture is backfilled to the bottom and the side wall of a ditch body of the groove in a layered mode and compacted layer by layer, then long fibers are embedded, and the surface soil-based microorganism solidification horizontal ditch is manufactured. A reinforced structure is formed, an original soil covering layer is reserved on the top of the groove, microorganism solidification bacterium liquid is sprayed on the surface of a groove body of the groove, a gravel layer is laid at the bottom of the groove to serve as a water guide inverted filter layer, grass seeds and a water-retaining agent are mixed into the covering layer on the top of the groove, and therefore the microorganism solidification horizontal groove with surface soil is prepared. The anti-erosion performance, the structural stability and the ecological compatibility of the horizontal ditch are improved, and the method is suitable for hills, mountains and other areas prone to water and soil loss.

Description

Technical Field

[0001] The invention belongs to the technical field of soil and water conservation and ecological restoration, and relates to a microbial solidification horizontal ditch based on topsoil and a manufacturing method thereof. Background Art

[0002] As a trench project excavated along contour lines, horizontal ditches play a key role in ecological governance and soil and water conservation. Their main function is to intercept surface runoff, allowing water to penetrate into the soil more fully, thereby effectively reducing soil erosion. However, under existing technical conditions, the construction of horizontal ditches faces many challenges.

[0003] At present, the choice of materials for constructing horizontal ditches is relatively limited. On the one hand, the method of directly excavating and shaping the local soil is relatively simple to construct, but the traditional soil ditch is very prone to ditch wall collapse when facing the scouring of surface runoff, and the structural stability is difficult to guarantee, which greatly shortens the service life of the horizontal ditch and increases the subsequent maintenance cost. On the other hand, although the use of cement, stone and other materials for reinforcement can significantly improve the strength of the ditch, such materials are expensive and consume huge energy during construction, which is not in line with the concept of sustainable development. More importantly, the lack of ecological compatibility of cement or stone masonry ditches will hinder the natural recovery of surrounding vegetation and cause a certain degree of damage to the ecological environment.

[0004] In addition, during the excavation of the horizontal trench, the topsoil, the fertile surface soil, is often overlooked. Topsoil is rich in nutrients and microorganisms required for plant growth and is a valuable natural resource. However, in actual projects, topsoil is often abandoned or buried due to excavation, which not only causes a huge waste of resources, but also destroys the ecological balance of the soil.

[0005] In summary, the existing horizontal ditch construction technology has the following main problems: the traditional soil ditch structure has poor stability and is easily collapsed by runoff erosion; the cement or stone ditch material cost is high, the construction energy consumption is large and lacks ecological compatibility; the topsoil resources are wasted in large quantities during the excavation process and are not effectively utilized. These problems restrict the further application and development of horizontal ditches in ecological governance and urgently need to be solved through technological innovation. Summary of the invention

[0006] In response to the problems existing in the prior art, the present invention provides a topsoil-based microbial solidification horizontal ditch and a production method, which aims to improve the erosion resistance, structural stability and ecological compatibility of the horizontal ditch, and is suitable for areas prone to soil erosion such as hills and mountains.

[0007] The present invention is achieved through the following technical solutions: A method for making a horizontal ditch based on microbial solidification of topsoil, comprising: On the loess slope, a trapezoidal cross-section trench is excavated along the contour line. The topsoil, short fibers, microbial solidification bacterial liquid, and cementing liquid are stirred and mixed. The mixture is backfilled layer by layer to the bottom and side walls of the trench, and compacted layer by layer. Then long fibers are embedded to form a reinforced structure. A native soil covering layer is reserved at the top of the trench. Microbial solidification bacterial liquid is sprayed on the surface of the trench body. A gravel layer is laid at the bottom of the trench as a water-conducting and anti-filtration layer, and grass seeds and water retention agents are mixed into the covering layer at the top of the trench, thus preparing a microbial solidified horizontal trench for topsoil; The cementing liquid is obtained by mixing calcium nitrate solution and urea solution; the microbial solidification bacterial liquid is selected from Bacillus subtilis or Bacillus alkalophilus for cultivation.

[0008] Preferably, the upper opening width of the trapezoidal cross-section trench is 80 - 120 cm, the bottom width is 40 - 60 cm, the depth is 50 - 70 cm, and the trench length is excavated in sections according to the terrain. Among them, the size of each section is 10 - 20 m, and the slope of the loess slope is 5 - 25 degrees; Preferably, the mass ratio of the topsoil, short fibers, microbial solidification bacterial liquid, and cementing liquid is 50:3:4:6, and the embedding amount of the embedded long fibers is 10 - 15 per square meter.

[0009] Preferably, the topsoil includes a coarse grain group and a fine grain group; among them, the particle size of the coarse grain group > 2 mm, the fine grain group ≤ 2 mm, and the addition ratio of the coarse grain group in the topsoil ≥ 60%.

[0010] Preferably, the Bacillus subtilis or Bacillus alkalophilus is cultured in a constant temperature shaker at 30 °C for 36 hours to obtain the microbial solidification bacterial liquid. The culture condition is pH ≥ 8.5, and the activity concentration of the microbial solidification bacterial liquid ≥ 10^8 CFU / mL.

[0011] Preferably, the cementing liquid is obtained by mixing a 1.0 mol / L calcium nitrate solution and a 1.0 mol / L urea solution in a volume ratio of 1:1.2.

[0012] Preferably, the long fibers are a short fiber group with a size of 10 - 25 cm and the short fibers have a size of 1 - 3 cm. Both the long fiber group and the short fibers are made of straw or hemp fiber.

[0013] Preferably, the mass ratio of the native soil, grass seeds, and water retention agent is 100:1:2.

[0014] Preferably, the thickness of the gravel layer is 10 cm, and the particle size of the gravel is 5 - 15 mm.

[0015] A microbial solidified horizontal trench based on topsoil, obtained based on the above-mentioned manufacturing method of a microbial solidified horizontal trench based on topsoil.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention provides a microbial solidified level ditch based on topsoil and a manufacturing method. On the loess slope, a trapezoidal cross-section groove is excavated along the contour line. By introducing microbial solidifying bacterial solutions such as Bacillus subtilis or Bacillus alkalophilus, organic substances such as extracellular polysaccharides and proteins will be produced during the growth and reproduction of the microorganisms. These substances can be tightly combined with soil particles to form stable soil aggregates, thereby significantly improving the cohesion and internal friction angle of the soil and enhancing the stability of the soil. Long fibers are embedded in the mixture to form a reinforced structure, which can effectively resist the erosion and deformation of the soil under hydraulic action, further enhancing the stability of the soil structure and the anti-erosion ability. A gravel layer is laid at the bottom of the groove as a water-conducting and anti-filter layer, which can effectively improve the permeability of the soil, promote the infiltration of rainwater and the recharge of groundwater, and at the same time prevent the loss of soil particles. Grass seeds and water-retaining agents are mixed into the covering layer at the top of the groove. The water-retaining agent can absorb and store a large amount of water and slowly release it during the dry season, providing a continuous water supply for plant growth, helping to improve the soil moisture conditions, and promoting the restoration and growth of vegetation. Through microbial solidification, reinforced structure and soil improvement measures, the physical, chemical and biological properties of the soil are improved, providing a good soil environment for the growth of vegetation. Grass seeds are mixed into the covering layer at the top of the groove. As the grass seeds germinate and grow, vegetation coverage is gradually formed, which helps to prevent soil erosion, enhance the stability of the ecosystem and biodiversity, effectively enhance the anti-erosion ability, structural stability and ecological compatibility of the level ditch, and is applicable to areas prone to soil erosion such as hills and mountains.

[0017] Furthermore, the present invention recycles topsoil as the main material, reduces resource waste, lowers the engineering cost, and realizes the efficient utilization of resources.

[0018] Furthermore, the microbial solidification technology of the present invention has no chemical pollution. The cementing liquid is obtained by mixing calcium nitrate solution and urea solution; the microbial solidifying bacterial solution is cultured by selecting Bacillus subtilis or Bacillus alkalophilus, and natural fibers are degradable, providing favorable conditions for vegetation restoration, and realizing ecological compatibility. Furthermore, the calcium nitrate cementitious body formed by biological mineralization and the fiber reinforcement act synergistically to enhance the compressive strength (≥800 kPa) and anti-scouring ability (soil loss rate ≤5%) of the ditch body, and the structural stability of the present invention is enhanced: Furthermore, the construction of the present invention is convenient, without the need for large-scale machinery, is applicable to areas with complex terrain, and conforms to the concept of low-carbon construction. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of a microbial solidified topsoil level ditch; Figure 2 It is a schematic diagram of the device for scouring experiment; Figure 3 It is the grouping table for the test experiment design in the embodiment; Figure 4 It is the diagram of two key steps for the experiment of MICP (Microbially Induced Calcium Precipitation) solidified soil; Figure 5 It is the variation of the runoff of non-MICP scoured soil samples and MICP solidified scoured soil samples with the scouring time under the scouring conditions of different slopes (5°, 15°, 25°); Figure 6 It shows, in the form of a bar chart, the comparison of the final sediment yields of different scoured soil samples under the scouring condition of 5°; Figure 7 It is the mean sediment yield line (190.29 g) and the mean plus standard deviation line (310.03 g) under the condition of 15°, comparing the relationship between the sediment yields of different soil samples and the overall average level and fluctuation range; Figure 8 It is the comparison of the final sediment yields of different scoured soil samples under the scouring condition of 25°; Figure 9 It is the variation of the sediment yield (W) of non-MICP scoured soil samples and MICP solidified scoured soil samples with the scouring time under the scouring conditions of different slopes (5°, 15°, 25°); Figure 10 It is the variation of the anti-scouring coefficient AS of non-MICP scoured soil samples and MICP solidified scoured soil samples with the scouring time under the scouring conditions of different slopes (5°, 15°, 25°). Detailed implementation manners

[0020] The present invention will be further described in detail below with specific embodiments, which are explanations of the present invention rather than limitations.

[0021] The technical solution of the present invention is as follows: (1) Material preparation Topsoil: Collect the topsoil stripped from the engineering area, remove impurities (particle size ≤ 10 mm) by screening, and divide it into a coarse grain group (> 2 mm, with a proportion ≥ 60%) and a fine grain group (≤ 2 mm).

[0022] Microbial solidifying bacterial liquid: Select conventional Bacillus subtilis ( Bacillus subtilis , normal temperature area) and Bacillus alcalophilus ( Bacillus alcalophilus , alpine and cold area), culture them in a constant temperature shaker at 30 °C for 36 hours (pH ≥ 8.5), and the active concentration of the bacterial liquid ≥ 10^8 CFU / mL.

[0023] Cementing liquid: It is prepared by mixing 1.0 mol / L calcium nitrate (Ca(NO3)2) and 1.0 mol / L urea in a volume ratio of 1:1.2, and it should be prepared immediately before use.

[0024] Natural fibers: Straw or hemp fibers are used, cut into long fiber groups (10 - 25 cm) and short fiber groups (1 - 3 cm) to enhance the cohesion within the material.

[0025] (2) Horizontal ditch excavation and shaping: Excavate a trapezoidal cross-section trench along the contour line, with the upper width of 80 - 120 cm, the bottom width of 40 - 60 cm, and the depth of 50 - 70 cm. The length of the ditch is segmented according to the terrain (each segment is 10 - 20 m). The ditch walls and bottom are trimmed flat and wetted with a small amount of water sprayed.

[0026] (3) Mix according to the mass ratio of topsoil: short fibers: bacterial solution: cementing liquid = 50:3:4:6 and stir for 5 minutes until homogeneous. Backfill the mixture layer by layer to the bottom and side walls of the ditch, with each layer thickness ≤ 15 cm, compacted layer by layer, and embed long fibers (10 - 15 fibers per square meter) to form a reinforced structure. Reserve a 10 cm thick original soil covering layer on the top of the ditch for subsequent vegetation planting.

[0027] (4) Use an atomizing sprayer to evenly spray the bacterial solution (300 - 500 mL / m 2 ) on the surface of the ditch, spray the cementing liquid after an interval of 24 h, and cycle 3 - 5 times. Cover with non-woven fabric for moisture preservation after spraying, and avoid strong rainfall scouring within 48 h.

[0028] (5) Mix grass seeds and water retention agents into the covering layer on the top of the ditch (mass ratio: original soil: grass seeds: water retention agent = 100:1:2). Lay a 10 cm thick gravel layer (particle size 5 - 15 mm) at the bottom of the ditch as a water guiding and filtering layer to prevent siltation, thus successfully preparing the microbial solidified topsoil horizontal ditch, as Figure 1 shown.

[0029] To enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0030] Example 1: On the loess slope, a trapezoidal cross-section trench is excavated along the contour line. The topsoil, short fibers, microbial solidification bacterial liquid, and cementing liquid are stirred and mixed. The mixture is backfilled layer by layer to the bottom and side walls of the trench, and compacted layer by layer. Then long fibers are embedded to form a reinforced structure. The original soil covering layer is reserved at the top of the trench. The microbial solidification bacterial liquid is sprayed on the surface of the trench body. A gravel layer is laid at the bottom of the trench as a water-conducting and anti-filtration layer, and grass seeds and water retention agents are mixed into the covering layer at the top of the trench, thereby preparing the microbial solidification horizontal trench of the topsoil; The cementing liquid is obtained by mixing a 1.0 mol / L calcium nitrate solution and a 1.0 mol / L urea solution in a volume ratio of 1:1.2.

[0031] The mass ratio of the topsoil, short fibers, microbial solidification bacterial liquid, and cementing liquid is 50:3:4:6, and the embedding amount of the embedded long fibers is 10 per square meter.

[0032] The Bacillus subtilis is cultured in a constant temperature shaker at 30°C for 36 hours to obtain the microbial solidification bacterial liquid. The culture conditions are a pH of 8.5, and the active concentration of the microbial solidification bacterial liquid ≥ 10^8 CFU / mL.

[0033] An atomizing sprayer is used to evenly spray 300 mL / m² of the bacterial liquid on the surface of the trench body. After an interval of 24 h, the cementing liquid is sprayed, and the cycle is repeated 5 times. After spraying, a non-woven fabric is covered for moisture retention, and strong rainfall scouring is avoided within 48 h.

[0034] Both the long fiber group and the short fibers are made of straw; the mass ratio of the original soil, grass seeds, and water retention agent is 100:1:2.

[0035] The thickness of the gravel layer is 10 cm, and the particle size of the gravel is 5 - 15 mm.

[0036] The upper width of the trapezoidal cross-section trench is 80 cm, the bottom width is 40 cm, the depth is 50 cm, and the trench length is excavated in sections according to the terrain. Among them, the size of each section is 10 m, The topsoil includes a coarse grain group and a fine grain group; among them, the particle size of the coarse grain group > 2 mm, and the fine grain group ≤ 2 mm. The addition ratio of the coarse grain group in the topsoil is 60%.

[0037] Example 2 On the loess slope, a trapezoidal cross-section trench is excavated along the contour line. The topsoil, short fibers, microbial solidification bacterial liquid, and cementing liquid are stirred and mixed. The mixture is backfilled layer by layer to the bottom and side walls of the trench, and compacted layer by layer. Then long fibers are embedded to form a reinforced structure. The original soil covering layer is reserved at the top of the trench. The microbial solidification bacterial liquid is sprayed on the surface of the trench body. A gravel layer is laid at the bottom of the trench as a water-conducting and anti-filtration layer, and grass seeds and water retention agents are mixed into the covering layer at the top of the trench, thereby preparing the microbial solidification horizontal trench of the topsoil; The cementing liquid is obtained by mixing a calcium nitrate solution with a concentration of 1.0 mol / L and a urea solution with a concentration of 1.0 mol / L in a volume ratio of 1:1.2.

[0038] The mass ratio of the topsoil, short fibers, microbial solidifying bacterial liquid, and cementing liquid is 50:3:4:6, and the embedding amount of the embedded long fibers is 15 per square meter.

[0039] The Bacillus alcalophilus is cultured in a constant temperature shaker at 30 °C for 36 hours to obtain the microbial solidifying bacterial liquid. The culture conditions are a pH of 9.0, and the active concentration of the microbial solidifying bacterial liquid ≥ 10^8 CFU / mL. The surface of the ditch body is evenly sprayed with 500 mL / m² of the bacterial liquid using an atomizing sprayer. After an interval of 24 h, the cementing liquid is sprayed, and the cycle is repeated 3 times. After spraying, non-woven fabric is covered for moisture retention, and strong rainfall scouring is avoided within 48 h.

[0040] Both the long fiber group and the short fibers are made of straw; the mass ratio of the original soil, grass seeds, and water-retaining agent is 100:1:2.

[0041] The thickness of the gravel layer is 10 cm, and the particle size of the gravel is 5 - 15 mm.

[0042] The upper width of the trapezoidal cross-section groove is 120 cm, the bottom width is 60 cm, the depth is 70 cm, and the groove length is excavated in sections according to the terrain. Among them, the size of each section is 20 m. The topsoil includes a coarse grain group and a fine grain group; among them, the particle size of the coarse grain group > 2 mm, and the fine grain group ≤ 2 mm. The addition ratio of the coarse grain group in the topsoil is 70%.

[0043] Example 3 On the loess slope, a trapezoidal cross-section groove is excavated along the contour line. The topsoil, short fibers, microbial solidifying bacterial liquid, and cementing liquid are stirred and mixed. The mixture is backfilled layer by layer to the bottom and side walls of the groove body of the groove, and compacted layer by layer. Then, long fibers are embedded to form a reinforced structure. A layer of original soil covering layer is reserved at the top of the groove of the groove. The microbial solidifying bacterial liquid is sprayed on the surface of the groove body of the groove. A gravel layer is laid at the bottom of the groove as a water-conducting and anti-filtration layer, and grass seeds and a water-retaining agent are mixed into the covering layer at the top of the groove, thereby preparing the microbial solidified horizontal groove of the topsoil. The cementing liquid is obtained by mixing a calcium nitrate solution with a concentration of 1.0 mol / L and a urea solution with a concentration of 1.0 mol / L in a volume ratio of 1:1.2.

[0044] The mass ratio of the topsoil, short fibers, microbial solidifying bacterial liquid, and cementing liquid is 50:3:4:6, and the embedding amount of the embedded long fibers is 15 per square meter.

[0045] The Bacillus subtilis is cultured in a constant temperature shaker at 30 °C for 36 hours to obtain a microbial solidified bacterial liquid. The culture conditions are a pH of 9.0, and the active concentration of the microbial solidified bacterial liquid is ≥10^8 CFU / mL.

[0046] Use an atomizing sprayer to evenly spray 400 mL / m² of the bacterial liquid on the surface of the trench body. After an interval of 24 h, spray the cementing liquid, and repeat the cycle 4 times. After spraying, cover it with non-woven fabric to keep it moist, and avoid strong rainfall scouring within 48 h.

[0047] Both the long fiber group and the short fibers use hemp fibers; the mass ratio of the original soil, grass seeds, and water retaining agent is 100:1:2.

[0048] The thickness of the gravel layer is 10 cm, and the particle size of the gravel is 5 - 15 mm.

[0049] The upper width of the trapezoidal cross-section trench is 100 cm, the bottom width is 50 cm, the depth is 60 cm, and the trench length is excavated in sections according to the terrain. Among them, the size of each section is 15 m. The topsoil includes a coarse particle group and a fine particle group; among them, the particle size of the coarse particle group is >2 mm, and the fine particle group is ≤2 mm. The addition ratio of the coarse particle group in the topsoil is 65%.

[0050] I. Loess solidification and erosion test By simulating the scouring environment of the horizontal trench under different slope conditions, comparing the anti-scouring differences between the undisturbed loess and the microbial solidified topsoil, and clarifying the enhancement mechanism of the MICP technology on the anti-erosion ability of the horizontal trench. The study on the anti-scouring performance of the microbial (Bacillus subtilis) solidified loess topsoil (5 cm) will adopt the method of flushing the undisturbed soil trough with a fixed flow rate of 4 L / min, and use the soil anti-scouring coefficient AS (Anti-Souribility), the amount of water required to wash away 1 g of dry soil (L / g), as the evaluation index. The soil anti-scouring performance is positively correlated with the soil anti-scouring coefficient AS. Therefore, the larger the AS, the stronger the soil anti-scouring performance; vice versa.

[0051] AS = f t / W In the formula, f is the flushing flow rate, L / min; t is the flushing time, min; W is the mass of the dried sediment, g. AS is directly proportional to the flushing flow rate and the flushing time, and inversely proportional to the sediment mass.

[0052] As Figure 2 shown, it is a schematic diagram of the device for the scouring experiment, mainly composed of the following parts: a water bucket, a sampler groove, and a flow collecting bucket. This device simulates the soil scouring process under different conditions by controlling the water flow and slope to study the anti-scouring performance and sediment yield of the soil. (1) Slope and soil sample setting Select slope gradients: 5°, 15°, 25°, simulate the typical topographic conditions of the Loess Plateau, and cover the common application scenarios of contour trenches. On the basis of the selected slopes, set up two categories of groups, the control group and the experimental group, for comparative analysis. The control group is the undisturbed loess soil samples ① - ⑨ (untreated, simulating the surface soil of natural contour trenches); the experimental group is the MICP-solidified soil samples (1) - (9) (sprayed with bacterial solution + cementing solution, simulating the surface soil of microbial-solidified contour trenches). In addition, there are 9 replicated samples in each group to ensure data reliability. Prepared by the preparation method described in Example 1, As Figure 3 shown, it is a grouped table of an experimental design for studying the erosion characteristics of soil samples in the non-MICP (microbially induced calcium nitrate precipitation) control group and the MICP-treated experimental group under different slope conditions. The table is divided into two main parts: the non-MICP control group and the MICP-treated experimental group. Each sample number corresponds to specific experimental conditions. By comparing the performances of the non-MICP control group and the MICP-treated experimental group at different slopes, the improvement effect of MICP treatment on the soil anti-erosion performance can be evaluated; (2) Soil sample preparation A: For the control group soil samples to be subjected to the erosion test, maintain infiltration for 12 h in the way of infiltrating from the bottom upwards, and then let it stand for 4 h to remove the gravitational water, and complete the erosion test within 24 h in principle.

[0053] B: Preparation of experimental group soil samples (3) Discharge calibration According to the method of Lei Junshan, Yang Qinke et al. to determine the erosion test discharge, taking the erosive rainfall in the Loess Plateau region, the rainfall intensity range of 0.5 mm / min - 2.5 mm / min and the runoff coefficient of 0.8 as the basic calculation parameters, combined with the unit width area of 0.2 m of the erosion flume used in this test 2 , the discharge range that can be adopted in this test is obtained as 0.8 L / min - 4 L / min; according to the maximum runoff of the standard plot of the Ansai Soil and Water Conservation Experimental Station of the Chinese Academy of Sciences, when conducting the erosion test on undisturbed soil, with the erosion flume of the same specification (2 m ×0.1 m) and the sampler (10 cm ×10 cm ×5 cm), the erosion discharge is determined to be 4 L / min. Therefore, the erosion discharge in this test is determined to be 4 L / min.

[0054] Use a 10 L container (unit scale ml) for discharge calibration. Manually adjust the valve to adjust the discharge size. The container receives water at the water outlet of the water bucket and times. Observe whether it can reach a capacity of 4 L in 1 min. Stop timing when it meets the requirements. Repeat the observation 3 times, and the errors are 1 ml, 0.5 ml, and 1 ml respectively. Take the average value, and the initial value of the basic actual calibration discharge in the test is 4.08 L / min.

[0055] (4) Microbially Induced Calcite Precipitation (MICP) Treated Loess Soil Samples A: Cementing solution preparation: A 1.0 mol / L calcium nitrate solution and a 1.0 mol / L urea solution are mixed at a volume ratio of 1:1.2 (economical and efficient concentration, optimized from previous research). B: Atomized spraying and curing - To protect the surface of the soil sample from damage, an atomizable handheld 50 ml small-capacity sprayer is used for spraying and curing. The spraying pressure is adjusted to the minimum, and it is best when the liquid is sprayed into a mist. The single spraying amount is 5 L / m², and the total amount is 200 ml / sample, sprayed in 4 times. After standing for 2 h, cover it for curing. As Figure 4 These are two key steps for the MICP (Microbially Induced Calcium Precipitation) soil curing experiment: water spraying operation and MICP treated soil samples; (5) Runoff Scouring Fixing the soil trough - The undisturbed soil sampler is placed in the groove of the scouring trough and tightened at the bottom with a screw tray. After the surface of the undisturbed soil is level with the scouring trough surface, water is released for scouring. As Figure 5 This shows the variation of the runoff of non-MICP scoured soil samples and MICP treated scoured soil samples with scouring time under different slope (5°, 15°, 25°) scouring conditions. In the figure, the horizontal axis represents the scouring time (min), and the vertical axis represents the runoff (L / min). Each subfigure corresponds to the experimental results under one slope condition, and the curves with different colors and symbols represent different types of soil samples; Scouring record - Under certain slope scouring conditions (5°, 15°, 25°), after the collection bucket is prepared, timing scouring is carried out. Each soil sample is scoured for 20 min in total. Sediment collection is completed every 30 s. During the scouring process, the flow velocity is measured every 1 min. The stopwatch is timed based on obvious erosion, forming a corresponding table of erosion depth. Record the time when each soil sample forms an erosion depth of 2 cm.

[0056] Drying and weighing - Use a precipitant to precipitate the sediment. After precipitation, remove the supernatant, transfer the remaining sediment to a stainless-steel numbered sample box for drying at 105° for 8 - 10 h, and then weigh all the sample boxes and record the weight of the dried sediment.

[0057] Scouring Test Results During the runoff scouring and erosion test, the erosion condition of all scoured soil samples is that under the premise of forming rill erosion, sheet erosion or large pieces of soil being washed away occur only when the slope is increased. As the slope increases, the soil erosion condition shows a more obvious change trend. In this case, the overall soil erosion condition of the MICP treated scoured soil samples is relatively ideal.

[0058] (2)Scouring duration for 2 cm erosion depth Start recording when obvious erosion occurs during the scouring test. When the erosion depth reaches 2 cm, record the scouring time t (min) of the corresponding scoured soil sample, as shown in Table 1-1. It can be seen from the data record that the time for the 15° (6) specimen to reach an erosion depth of 2 cm is the longest, which is 20 min; the time for the 15° ④ specimen, ⑥ and the 25° ⑦ specimen to form an erosion depth of 2 cm is the shortest, which is 0.5 min. It can be preliminarily seen from Table 1-1 that the shortest time for erosion depth is for non-MICP scoured soil samples, and the longest time for erosion depth is for MICP-solidified scoured soil samples.

[0059] Table 1-1 Corresponding time table for 2 cm erosion depth of scoured soil samples

[0060] Factor analysis of runoff (f) (1)Dynamic change of runoff under certain slope conditions The scouring test is a test of scouring the original soil trough with a fixed flow rate of 4 L / min. It can be seen from the figure that under certain slope conditions (5°, 15°, 25°), the runoff during the scouring process of the control group and test group soil samples changes within 2.8 - 4.2 L / min.

[0061] As Figure 6 shown, under the condition of a 5° slope, the runoff of the non-MICP scoured soil sample shows a gradually increasing trend from time 2 min to 20 min, with a sudden value of the minimum runoff of 2.86 L / min. Taking a runoff of 4 L / min as the analysis basis, the change range is 28.4%, and the time point of occurrence is the initial scouring time of 2 min. The reason for the analysis is the unstable flow rate factor in the initial stage of scouring. The change range of the runoff of the non-MICP scoured soil sample is significantly higher than that of the MICP-solidified scoured soil sample. Taking a fixed scouring flow rate of 4 L / min as the analysis basis, the change trend of the average difference in the scouring runoff of the soil samples is: control group ② > test group (1) > control group ① > test group (3), indicating that the change in the runoff of the soil sample in test group (3) is the smallest; the change difference between test group (1) and control group ① in the middle range is similar, indicating that the scouring runoff of the soil samples in test group (1) and control group ① is similar. From this, it can be analyzed that the influence of microbial solidification of the original loess on the runoff is not significant as a whole, but there are certain differences for each soil sample. The runoff of the soil sample in test group (3) is more stable when scouring the soil.

[0062] As Figure 7The average sediment yield line (190.29 g) and the average plus standard deviation line (310.03 g) under the condition of 15° are presented to more intuitively compare the sediment yield of different soil samples with the overall average level and the fluctuation range. Generally speaking, the final sediment yield of the MICP-solidified scoured soil samples is significantly lower than that of the non-MICP scoured soil samples, indicating that the MICP solidification treatment has an obvious effect on reducing the sediment yield of soil samples; The change trend of the average difference in the scouring runoff of the 15° soil samples is gentler than that of the 5° samples. The change range of the runoff of all soil samples does not exceed 20%. Initially, the runoff of the control group soil samples was still unstable, but the change range decreased by 28% compared with that of the 5° samples. Taking a fixed flow rate of 4 L / min as the basis for data analysis, the runoff scouring of the non-MICP scoured soil sample - sample (6) is the most stable, and the runoff scouring volume of the MICP-solidified scoured soil sample - sample ⑤ is the most unstable; while in the middle range, the significant difference of the MICP-solidified scoured soil samples is less than that of the non-MICP scoured soil samples, fully indicating that the significant difference in the runoff of all soil samples in the 15° test group during scouring is small, and the runoff changes little and is relatively stable.

[0063] The change trend of the average difference in the scouring runoff of the 25° soil samples is more concentrated than that of the 5° and 15° samples. The runoff of all soil samples changes slowly and evenly. The reason is that as the slope increases, the influence of the soil itself on the runoff gradually weakens, which is more obvious under the 25° slope condition. There was no initial unstable runoff phenomenon in the non-MICP scoured soil samples. Taking a fixed flow rate of 4 L / min as the basis for data analysis, the runoff scouring of the non-MICP scoured soil sample - sample ⑨ is the most stable, and the runoff scouring volume of the MICP-solidified scoured soil sample - sample (8) is the most unstable, and this law shows an opposite trend to that of the 5° and 15° samples; but in the middle range, the significant difference of the test group soil samples is less than that of the control group soil samples, which is the same as the previous trend of the 5° and 15° samples; in addition, the change values of the scouring runoff of the soil samples under the 25° condition are all small and stable, so it can be basically determined that the runoff of the MICP-solidified soil samples in the experimental group and the non-MICP scoured soil samples in the control group did not change significantly due to soil differences.

[0064] (2) Comparative analysis of runoff at different slopes Using SPSS 23.0 statistical software, an independent-samples T-test was conducted on the mean values of the data between different groups at the same slope. The data is expressed as mean standard deviation. It can be seen that there are significant differences in the runoff under the 5° slope condition in the control group, while there are basically no significant differences under the 15° and 25° conditions, and the situation in the experimental group is similar. Taking PTaking 0.05 as the basis for difference analysis, from the difference values of the P test group (0.11, 0.03, 0.02) / control group (0.24, 0.02, 0.02), it can be seen that the runoff f does not have significant differences. However, from the numerical analysis, the degree of difference in the runoff f of the non-MICP scoured soil samples in the control group is slightly higher than that of the MICP scoured soil samples in the test group. The general level of the runoff change rate is 25° < 15° < 5°, indicating that the increase in slope will slightly weaken the influence of soil samples on the scoured runoff.

[0065] Table 1-2 T-test of the mean data of the scoured runoff of 5° / 15° / 25° soil samples

[0066] Factor analysis of sediment yield (W) (1) Dynamic change analysis of sediment yield of soil samples under different slopes Scouring condition of 5°: Range of sediment yield: 0 - 120 g, the sediment yield of non-MICP scoured soil samples is greater than that of MICP solidified soil samples. Change trend: The erosion rate of non-MICP scoured soil sample ① and MICP solidified soil samples (1) and (3) slows down at about 8 minutes, and the erosion rate of non-MICP scoured soil sample ② continues to increase. 8 minutes is the key point for the stable erosion rate of MICP solidified soil samples, manifested as the depth remaining unchanged after the formation of rills. Mean comparison: The mean is 35.45 g, the sediment yield of non-MICP scoured soil sample ② is the largest (75.519 g), and the MICP solidified soil sample (3) is the smallest (10.956 g). The sediment yields of MICP solidified soil samples (1) and (3) are both lower than the mean, while those of non-MICP scoured soil samples ① and ② are higher than the mean, and ② exceeds the standard deviation. The order of the dynamic change of sediment yield is: non-MICP ② > non-MICP ① > MICP (1) > MICP (3), and the sediment yield of MICP solidified soil samples changes slowly and is relatively ideal.

[0067] Such as Figure 7 is the mean sediment yield line (190.29 g) and the mean plus standard deviation line (310.03 g) under the condition of 15°, in order to more intuitively compare the relationship between the sediment yields of different soil samples and the overall average level and fluctuation range. Generally speaking, the final sediment yield of MICP solidified scoured soil samples is significantly lower than that of non-MICP scoured soil samples, indicating that MICP solidification treatment has an obvious effect on reducing the sediment yield of soil samples; 15° Scouring condition: Range of sediment yield: 0 - 350 g. The sediment yield of non - MICP scoured soil samples is greater than that of MICP solidified soil samples. Variation trend: After 4 minutes of scouring, the sediment production rates of MICP solidified soil samples (4) and (5) decrease, and (6) remains almost unchanged; after 6 minutes, the sediment production rates of non - MICP scoured soil samples ④, ⑤, and ⑥ decrease. The key point for the stable erosion rate is from 4 to 6 minutes. After the non - MICP scoured soil samples form rills, they experience rapid sheet erosion, while the rill depth of MICP solidified soil samples remains for a longer time. Mean comparison: The mean value is 151.581 g. The sediment yield of non - MICP scoured soil sample ⑥ is the largest (268.127 g), and that of MICP solidified soil sample (6) is the smallest (15.831 g), with a reduction rate of 94.10%. The sediment yields of MICP solidified soil samples are all lower than the mean value, while those of non - MICP scoured soil samples are higher than the mean value, and ⑥ exceeds the standard deviation. The dynamic change order of sediment yield is: non - MICP ⑥ > non - MICP ④ > non - MICP ⑤ > MICP (5) > MICP (4) > MICP (6). The sediment production rate of MICP solidified soil samples is slow and the sediment yield is relatively ideal.

[0068] As Figure 8 Figure shows the comparison of the final sediment yields of different scoured soil samples under the 25° scouring condition. Generally speaking, the final sediment yield of MICP solidified scoured soil samples is significantly lower than that of non - MICP scoured soil samples, indicating that MICP solidification treatment has an obvious effect on reducing the sediment yield of soil samples; 25° Scouring condition: Range of sediment yield: 0 - 500 g. The sediment yield of non - MICP scoured soil samples is greater than that of MICP solidified soil samples. Variation trend: After 6 minutes of scouring, the sediment production rates of MICP solidified soil samples (7) and (8) decrease, and (8) remains almost unchanged; after 10 minutes, the sediment production rates of MICP solidified soil sample (8) and non - MICP scoured soil samples ⑦, ⑧, and ⑨ decrease. The key time period for the stable erosion rate is from 4 to 10 minutes. Within 4 minutes, after the MICP solidified soil samples form rills, they experience rapid sheet erosion, and the rill depth remains for a longer time. Mean comparison: The mean value is 242.121 g. The sediment yield of non - MICP scoured soil sample ⑧ is the largest (376.839 g), and that of MICP solidified soil sample (7) is the smallest (69.606 g), with a reduction rate of 81.53%. The sediment yields of MICP solidified soil samples are all lower than the mean value, while those of non - MICP scoured soil samples are higher than the mean value, and ⑧ exceeds the standard deviation. The dynamic change order of sediment yield is: non - MICP ⑧ > non - MICP ⑦ > non - MICP ⑨ > MICP (8) > MICP (9) > MICP (7). The sediment yield change of MICP solidified soil sample (7) is slow and relatively ideal.

[0069] (2) Comparative analysis of sediment yield (W) under different slopes As Figure 9Under the scouring conditions of different slopes (5°, 15°, 25°), the variation of the sediment yield (W) of non-MICP scoured soil samples and MICP-solidified scoured soil samples with the scouring time is shown. Each subfigure corresponds to the experimental results under one slope condition, and the curves of different colors and symbols represent different types of soil samples. Generally speaking, with the increase of the slope, the sediment yield of all soil samples increases, but the sediment yield of MICP-solidified soil samples is always lower than that of non-MICP scoured soil samples, indicating that the MICP solidification treatment effectively improves the anti-scouring performance of the soil samples; Using SPSS 23 statistical software, an independent samples T-test was conducted on the mean values of data between different groups at the same slope, and the data are presented as mean standard deviation. As can be seen from Tables 1-3, taking P = 0.05 as the basis for differential analysis, the sediment yield W gradually increases with the increase of the slope, and there are significant differences in the sediment yield. The significant differences in the sediment yield of the MICP test group (7.28, 22.68, 70.99) are lower than those of the non-MICP control group (37.54, 54.29, 107.37). Therefore, the sediment yield value of the MICP test group is smaller and more stable. It shows that the MICP-solidified soil samples have a significant weakening effect on the sediment yield. Generally analyzed, the increase of the slope is the main factor for the increase of the sediment yield rate of all scoured soil samples.

[0070] Table 1-3 T-test of the scouring mean data of soil samples with different slopes

[0071] Analysis of anti-scouring performance characterized by the anti-scouring coefficient (AS) The anti-scouring coefficient AS is positively correlated with the anti-scouring performance of the soil, that is, the larger the AS, the higher the anti-scouring performance of the soil. The anti-scouring coefficient AS can be used to directly describe the magnitude of the anti-scouring ability of the soil. Similarly, based on 10 groups of scouring times (t) - 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 min, a dynamic analysis of the change of the anti-scouring coefficient AS is carried out.

[0072] As Figure 10 Under the scouring conditions of different slopes (5°, 15°, 25°), the variation of the anti-scouring coefficient AS of non-MICP scoured soil samples and MICP-solidified scoured soil samples with the scouring time is shown. Each subfigure corresponds to the experimental results under one slope condition, and the curves of different colors and symbols represent different types of soil samples. Generally speaking, with the increase of the slope, the anti-scouring coefficients of all soil samples decrease, but the AS value of the MICP-solidified soil samples is always higher than that of the non-MICP scoured soil samples, indicating that the MICP solidification treatment effectively improves the anti-scouring performance of the soil samples.

[0073] (1) Dynamic change analysis of the anti-scouring coefficient (AS) at a certain slope It can be seen that under certain slope conditions (5°, 15°, 25°), the AS erosion resistance coefficients of non-MICP scoured soil samples and MICP-solidified scoured soil samples vary within 0 - 8 L / g, 0 - 4 L / g, and 0 - 1 L / g respectively during the scouring process. Under the three slope conditions, the AS of the MICP-solidified scoured soil samples, that is, the erosion resistance performance, is significantly greater than that of the non-MICP-treated scoured soil samples.

[0074] The calculation formula for the strengthening degree of the AS erosion resistance coefficient of the MICP-solidified scoured soil samples compared to the non-MICP scoured soil samples: ) Scouring condition of 5°: Change in erosion resistance coefficient: From 0 to 6 min, the AS erosion resistance coefficients of both the MICP-solidified and non-MICP scoured soil samples first increase and then decrease; after 8 min, the AS of the MICP-solidified soil sample increases slowly, while the AS of the non-MICP soil sample remains unchanged or decreases. Mean value analysis: The comprehensive mean value is 2.48 L / g. The control groups ①② and the experimental group (1) are lower than the mean value, being 1.78 L / g, 1.26 L / g, and 2.37 L / g respectively; the experimental group (3) is higher than the mean value, reaching 4.51 L / g. The order of erosion resistance performance is: MICP (3) > MICP (1) > non-MICP ① > non-MICP ②. The MICP-solidified soil sample (3) has the best erosion resistance performance, and the strengthening coefficient E(AS) is 1.26.

[0075] Scouring condition of 15°: Change in erosion resistance coefficient: Only the MICP-solidified soil sample (6) shows an obvious change, reaching the maximum value at 14 - 16 min and then dropping to 3 L / g. The changes in the other soil samples are not obvious, but the AS of the MICP-solidified soil samples is greater than that of the non-MICP soil samples. Mean value analysis: The comprehensive mean value is 0.72 L / g, which is 1.76 L / g less than the 5° condition. The order of erosion resistance performance is: MICP (6) > MICP (4) > MICP (5) > non-MICP ⑤ > non-MICP ④ > non-MICP ⑥. The MICP-solidified soil sample (6) is the best, with an AS of 2.70 L / g. The strengthening coefficient E(AS) is 6.67, which is greater than the 5° condition, indicating that there are soil samples with better solidification effects.

[0076] Scouring condition at 25°: Variation of scouring resistance coefficient: The AS of the MICP-solidified soil sample (7) continuously increased and reached the maximum value of about 1.2 g / L at 20 min; the AS of the MICP-solidified soil sample (9) decreased first and then stabilized, but was still greater than that of the non-MICP soil sample; the AS of the MICP-solidified soil sample (8) decreased first and then increased. Generally speaking, as shown in Table 1-4, the AS of the MICP-solidified soil sample was greater than that of the non-MICP soil sample. Mean analysis: The comprehensive mean value was 0.25 L / g, which was 2.23 L / g less than that at 5° and 0.47 L / g less than that at 15°. The order of scouring resistance performance was: MICP (7) > MICP (9) > MICP (8) > non-MICP⑦ > non-MICP⑨ > non-MICP⑧. The MICP-solidified soil samples (7) and (9) were above the mean value, and (8) was below the mean value but better than the control group. The strengthening coefficient E(AS) was 1.92, which was between 5° and 15°.

[0077] Table 1-4 T-test of the mean AS data of soil samples scoured under three different slope conditions

[0078] By comparing the data, it is shown that the compressive strength of the solidified gully body is increased by 3 times, and the permeability coefficient is reduced to 1×10^ -6 cm / s.

[0079] The test data show that the microbial solidification treatment significantly improves the scouring resistance coefficient (AS) of loess, with the maximum increase of 647%; the sediment yield of the solidified soil sample is reduced by more than 70%, verifying the advantages of the present invention in terms of erosion resistance and structural stability; the solidification effect is the best at a slope of 15°, providing a basis for the optimized application of the horizontal gully project in hilly areas.

[0080] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0081] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention; any ordinary technician in the industry can smoothly implement the present invention according to the drawings shown in the specification and the above description; however, any equivalent changes such as slight modifications, decorations and evolutions made by those skilled in the art within the scope of the technical solution of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes such as modifications and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for manufacturing a microbial-solidified level ditch based on topsoil, characterized in that, including, On the loess slope surface, a trapezoidal cross-section trench is excavated along the contour line. The topsoil, short fibers, microbial solidification bacterial liquid and cementing liquid are stirred and mixed. The mixture is backfilled layer by layer to the bottom and side walls of the trench, and compacted layer by layer. Then long fibers are embedded to form a reinforced structure. A layer of original soil covering layer is reserved at the top of the trench. Microbial solidification bacterial liquid is sprayed on the surface of the trench body. A gravel layer is laid at the bottom of the trench as a water-conducting and anti-filtering layer, and grass seeds and water retention agents are mixed into the covering layer at the top of the trench, so as to prepare a microbial solidified horizontal trench of topsoil; The cementing liquid is obtained by mixing calcium nitrate solution and urea solution; The microbial solidification bacterial liquid is selected from Bacillus subtilis or Bacillus alkalophilus for cultivation.

2. The method for fabricating a microbial solidified level ditch based on topsoil according to claim 1, wherein The upper width of the trapezoidal cross-section trench is 80 - 120 cm, the bottom width is 40 - 60 cm, the depth is 50 - 70 cm, and the trench length is excavated in sections according to the terrain. Among them, the size of each section is 10 - 20 m, and the slope of the loess slope surface is 5 - 25 degrees.

3. A method for manufacturing a microbial solidified level ditch based on topsoil according to claim 1, characterized in that, The mass ratio of the topsoil, short fibers, microbial solidification bacterial liquid and cementing liquid is 50:3:4:6, and the embedding amount of the embedded long fibers is 10 - 15 per square meter.

4. A method for manufacturing a microbial solidified level ditch based on topsoil according to claim 1, characterized in that, The topsoil includes a coarse grain group and a fine grain group; among them, the particle size of the coarse grain group is > 2 mm, the fine grain group is ≤ 2 mm, and the addition amount ratio of the coarse grain group in the topsoil is ≥ 60%.

5. The manufacturing method of a microbial solidified level ditch based on topsoil according to claim 1, characterized in that, The Bacillus subtilis or Bacillus alkalophilus is cultured in a constant temperature shaker at 30 °C for 36 hours to obtain the microbial solidification bacterial liquid. The culture condition is pH ≥ 8.5, and the activity concentration of the microbial solidification bacterial liquid is ≥ 10^8 CFU / mL.

6. The method for manufacturing a microbial solidified level ditch based on topsoil according to claim 1, characterized in that The cementing liquid is obtained by mixing a 1.0 mol / L calcium nitrate solution and a 1.0 mol / L urea solution according to a volume ratio of 1:1.

2.

7. A method for fabricating a microbial-solidified horizontal furrow based on topsoil according to claim 1, characterized in that, The long fibers have a size of 10 - 25 cm and the short fibers have a size of 1 - 3 cm. Both the long fiber group and the short fibers are made of straw or hemp fiber.

8. A method for manufacturing a microbial solidified level ditch based on topsoil according to claim 1, characterized in that, The mass ratio of the original soil, grass seeds and water retention agent is 100:1:

2.

9. A method for fabricating a microbial solidified level ditch based on topsoil according to claim 1, characterized in that The thickness of the gravel layer is 10 cm, and the particle size of the gravel is 5 - 15 mm.

10. A microbial solidified horizontal trench based on topsoil, obtained by the method for making a microbial solidified horizontal trench based on topsoil according to any one of claims 1 - 9.

Images