Fixing method and fixing structure for surface soil in loess subsidence area

Abstract

The invention discloses a loess subsidence area surface soil fixing method and structure, and relates to the technical field of environmental management. The loess subsidence area surface soil fixing method comprises the following steps: preparing a bacterial liquid and a cementing liquid; the bacterial liquid is bacillus pasteurii bacterial liquid, and the cementing liquid comprises urea and calcium chloride; seed pretreatment; mixing haloxylon ammodendron seeds and agropyron cristatum seeds with the bacterial liquid for seed dressing treatment; sowing and curing; sowing the pretreated haloxylon ammodendron seeds and wheatgrass seeds in the surface soil of the loess subsidence area, and alternately spraying the bacterial liquid and the cementing liquid for multiple times; final-period management: watering maintenance is carried out. According to the loess subsidence area surface soil fixing method and fixing structure, the loess surface layer impact resistance can be improved, and the short-term soil fixing effect and the long-term soil fixing effect are combined.

Description

Technical Field

[0001] This disclosure relates to the field of environmental remediation technology, and more specifically, to a method and structure for fixing topsoil in loess subsidence areas. Background Technology

[0002] Loess, due to its loose and porous structure and well-developed vertical joints, is highly susceptible to collapse and erosion under hydrological and geological processes. The Loess Plateau region of my country is a typical area of ​​this problem. This region experiences concentrated rainfall and frequent short-duration heavy rainfall events, which cause strong splash erosion and runoff scouring of the exposed or poorly vegetated loess surface, resulting in severe water, soil, and nutrient loss.

[0003] Currently, methods for controlling soil erosion mainly include engineering and biological measures. Engineering measures (such as slope protection and silt-trapping dams) are effective quickly but costly and may damage the native ecosystem. Biological measures (such as planting trees and grass) are a long-term and eco-friendly strategy, but the growth cycle from sowing to the formation of effective soil-fixing capacity of plant roots takes several weeks to months. During this "ecological window," if there is a short period of heavy rainfall, seedlings and topsoil are easily washed away, leading to the failure of the restoration project.

[0004] Microbially induced calcium carbonate precipitation (MICP) is an emerging eco-friendly soil and rock improvement technology that generates calcium carbonate crystals through the metabolic processes of microorganisms, cementing soil particles and thereby improving soil strength and erosion resistance. However, existing MIP technologies face challenges in practice, including difficulty in controlling mineralization uniformity and significant susceptibility to environmental disturbances in long-term stability. Summary of the Invention

[0005] This disclosure provides a method and structure for fixing surface soil in loess subsidence areas, which can improve the erosion resistance of the loess surface and achieve a combination of short-term and long-term soil stabilization effects.

[0006] According to one aspect of this disclosure, a method for stabilizing surface soil in loess subsidence areas is provided, comprising the following steps: Prepare bacterial solution and cementing solution; the bacterial solution is Bacillus pasteurellis bacterial solution, and the cementing solution includes urea and calcium chloride. Seed pretreatment: Haloxylon ammodendron seeds and Cercis chinensis seeds are mixed with bacterial solution for seed treatment; Sowing and solidification: Pretreated Haloxylon ammodendron seeds and Crinum asiaticum seeds were sown in the topsoil of the loess subsidence area, and bacterial solution and cementing solution were sprayed alternately multiple times. Post-maintenance: Watering and maintenance.

[0007] In one exemplary embodiment of this disclosure, seeding and curing include: Pretreated Haloxylon ammodendron seeds and Clytemnum meyraceum seeds were sown on a seed blanket. Seed blankets were laid on the surface soil in the loess subsidence area; Spray the seed mat with bacterial solution and cementing solution alternately multiple times.

[0008] In one exemplary embodiment of this disclosure, pretreated Haloxylon ammodendron seeds and Caulis Lysimachia nummularia seeds are sown on a seed mat, comprising: The seed blanket is divided into multiple array-distributed sowing units; Haloxylon ammodendron seeds and ice grass seeds are sown separately in sowing units; the seed species in the same sowing unit are the same, and the seed species in at least some adjacent sowing units are different.

[0009] In one exemplary embodiment of this disclosure, the OD600 value of the Bacillus pasteurellium culture is 0.6-1.0.

[0010] In one exemplary embodiment of this disclosure, the molar ratio of urea to calcium ions in the cementing solution is 1:1, and the concentration of calcium chloride is 0.8-1.2 mol / L.

[0011] In one exemplary embodiment of this disclosure, in the seed pretreatment step, the mass-volume ratio of bacterial solution to total seed volume is 120 mL bacterial solution: 1 kg seed.

[0012] In one exemplary embodiment of this disclosure, in the sowing and solidification step, after sowing the seeds in the topsoil of the loess subsidence area, bacterial solution and cementing solution are sprayed alternately multiple times, including: First, spray a layer of bacterial solution. After the bacterial solution has seeped into the soil, spray a layer of cementing solution. The amount of bacterial solution and cementing solution sprayed each time is 1.5-2.5 L / m².

[0013] In one exemplary embodiment of this disclosure, before repeatedly and alternately spraying the seed blanket with bacterial solution and binder, the sowing and solidification process further includes the following steps: The guide structure is installed; the guide structure has a guide channel, and multiple guide structures are inserted into the surface soil of the loess subsidence area. The guide channel is set in a vertical direction, and the side wall of the guide channel has multiple pores. The guide channel is filled with at least part of humic acid, root-promoting bacteria and organic matter.

[0014] In one exemplary embodiment of this disclosure, the installation of the guide structure is carried out simultaneously with the laying of the seed blanket in the surface soil of the loess subsidence area; the guide structure passes vertically through the seed blanket, and the maximum installation depth of the guide structure is greater than the maximum installation depth of the seed blanket.

[0015] According to another aspect of this disclosure, a structure for stabilizing surface soil in loess subsidence areas is provided, comprising: Loess matrix; Seed blankets are laid in a loess substrate and contain seeds of Haloxylon ammodendron and Agropyron cristatum. The guiding structure has a guiding channel inside, which passes vertically through the seed mat and is laid in the loess substrate. The sidewalls of the guiding channel have multiple pores. The guiding channel is filled with at least a portion of humic acid, root-promoting bacteria and organic matter. Calcium carbonate cementing layer is distributed within the loess matrix.

[0016] The method for fixing topsoil in loess subsidence areas disclosed herein involves seed mixing, which allows *Bacillus pasteurellii* to adhere to the seed surface and enter the soil environment along with the seed. During sowing and solidification, bacterial solution and cementing solution are sprayed alternately. Utilizing microbial-induced calcium carbonate precipitation technology, the urease produced by *Bacillus pasteurellii* catalyzes the hydrolysis of urea, generating carbonate ions. These carbonate ions combine with calcium ions in the cementing solution to form calcium carbonate crystals. These precipitates effectively cement the soil particles before the roots of *Haloxylon ammodendron* and *Agropyron cristatum* develop and form a network, thus creating an erosion-resistant layer that effectively resists rainfall during the "ecological window period" before plant root development. The process of microbial-induced calcium carbonate precipitation provides crucial protection for the germination of *Haloxylon ammodendron* and *Agropyron cristatum* seeds and the initial root growth. Furthermore, the microbial calcium carbonate crystals can subsequently intertwine with the well-developed fibrous roots of *Haloxylon ammodendron* and *Agropyron cristatum*, forming a three-dimensional "root-bacterium-calcium carbonate" complex, thereby enhancing soil stability and shear strength. Furthermore, the ammonium ions generated during the microbial-induced calcium carbonate precipitation reaction can serve as a nitrogen source, providing nutrients for the growth of Haloxylon ammodendron and Leymus chinensis. Microbial activity can also improve the rhizosphere microenvironment, promoting root development in both plants, thus forming a virtuous cycle of "soil stabilization through microorganisms and microbial nourishment through grass." Haloxylon ammodendron possesses a well-developed root system, enabling it to survive in extremely water-scarce conditions. Leymus chinensis is extremely drought- and cold-resistant, with a well-developed root system and strong adaptability. The combination of Haloxylon ammodendron and Leymus chinensis can play a positive role in soil structure and increasing the groundwater level. The method for stabilizing topsoil in loess subsidence areas disclosed in this paper has less ecological disturbance compared to purely engineering measures such as slope protection and sand-binding dams; and is more environmentally friendly than chemical soil stabilization agents.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0019] Figure 1 This is a schematic diagram of an exemplary embodiment of the surface soil fixation structure in the loess subsidence area disclosed herein.

[0020] Figure 2 This is a schematic diagram of a guide structure in an exemplary embodiment of the method and structure for fixing surface soil in loess subsidence areas disclosed herein.

[0021] Explanation of reference numerals in the attached figures: 1. Seed mat; 2. Guiding structure; 3. Calcium carbonate precipitation; 4. Plant seeds; 5. Loess substrate. Detailed Implementation

[0022] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore detailed descriptions of them will be omitted. Furthermore, the drawings are merely illustrative of this disclosure and are not necessarily drawn to scale.

[0023] Unless otherwise specified or stated, the technical or scientific terms used in this disclosure shall have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure pertains. The terms “a,” “an,” “the,” “the,” and “at least one” are used to indicate the presence of one or more elements / components / etc.; the terms “comprising” and “having” are used to indicate an open-ended inclusion and to mean that additional elements / components / etc. may exist in addition to the listed elements / components / etc.

[0024] This disclosure provides a method for stabilizing surface soil in loess subsidence areas. It includes the following steps S100-S400.

[0025] Step S100: Prepare bacterial solution and cementing solution; the bacterial solution is Bacillus pasteurellii bacterial solution, and the cementing solution includes urea and calcium chloride.

[0026] Step S200: Seed pretreatment; mix Haloxylon ammodendron seeds and Cercis chinensis seeds with bacterial solution for seed treatment.

[0027] Step S300: Sowing and solidification; Sow the pretreated Haloxylon ammodendron seeds and Clytemnum opus seeds in the topsoil of the loess subsidence area, and spray the bacterial solution and cementing solution alternately multiple times.

[0028] Step S400: Post-treatment management: Watering and maintenance.

[0029] The method for fixing topsoil in loess subsidence areas disclosed herein involves seed mixing, which allows *Bacillus pasteurellii* to adhere to the seed surface and enter the soil environment along with the seed. During sowing and solidification, bacterial solution and cementing solution are sprayed alternately. Utilizing microbial-induced calcium carbonate precipitation technology, the urease produced by *Bacillus pasteurellii* catalyzes the hydrolysis of urea, generating carbonate ions. These carbonate ions combine with calcium ions in the cementing solution to form calcium carbonate crystals. These precipitates effectively cement the soil particles before the roots of *Haloxylon ammodendron* and *Agropyron cristatum* develop and form a network, thus creating an erosion-resistant layer that effectively resists rainfall during the "ecological window period" before plant root development. The process of microbial-induced calcium carbonate precipitation provides crucial protection for the germination of *Haloxylon ammodendron* and *Agropyron cristatum* seeds and the initial root growth. Furthermore, the microbial calcium carbonate crystals can subsequently intertwine with the well-developed fibrous roots of *Haloxylon ammodendron* and *Agropyron cristatum*, forming a three-dimensional "root-bacterium-calcium carbonate" complex, thereby enhancing soil stability and shear strength. Furthermore, the ammonium ions generated during the microbial-induced calcium carbonate precipitation reaction can serve as a nitrogen source, providing nutrients for the growth of Haloxylon ammodendron and Leymus chinensis. Microbial activity can also improve the rhizosphere microenvironment, promoting root development in both plants, thus forming a virtuous cycle of "soil stabilization through microorganisms and microbial nourishment through grass." Haloxylon ammodendron possesses a well-developed root system, enabling it to survive in extremely water-scarce conditions. Leymus chinensis is extremely drought- and cold-resistant, with a well-developed root system and strong adaptability. The combination of Haloxylon ammodendron and Leymus chinensis can play a positive role in soil structure and increasing the groundwater level. The method for stabilizing topsoil in loess subsidence areas disclosed in this paper has less ecological disturbance compared to purely engineering measures such as slope protection and sand-binding dams; and is more environmentally friendly than chemical soil stabilization agents.

[0030] For example, before sowing and solidification in step S300, the target area can be pre-treated. The pre-treatment step may include leveling the land in the loess subsidence area, such as removing large stones and weeds, and filling obvious pits and cracks. Pre-treatment creates a stable and flat working surface for the subsequent uniform laying of the seed blanket 1 and spraying of the bacterial solution and binder, ensuring uniform treatment results.

[0031] In one exemplary embodiment of this disclosure, step S300, the sowing and curing step, may include the following steps: Step S310: Sowing the pretreated Haloxylon ammodendron seeds and Caulis thunbergii seeds on the seed mat 1.

[0032] Step S320: Lay a seed blanket 1 on the surface soil of the loess subsidence area.

[0033] Step S330: Spray the seed mat 1 with bacterial solution and cementing solution alternately multiple times.

[0034] For example, seed blanket 1 is a flexible substrate that can be used for ecological restoration. Its material may include natural fibers, such as straw or coconut fiber, or biodegradable nonwoven fabric. For example, the thickness of seed blanket 1 can be 10 mm to 25 mm, thereby providing a good moisture-retaining and heat-insulating environment for seed germination and effectively preventing seeds from sliding on the slope or being blown away by the wind. During installation, key areas prone to erosion, such as the windward side of the slope top and the runoff collection area at the slope foot, can be locally thickened as needed to provide stronger protection.

[0035] refer to Figure 1 As shown, plant seeds 4 are laid within the seed mat 1. In this exemplary embodiment, Haloxylon ammodendron seeds and Caulis thunbergii seeds can be sown into the seed mat 1 first to form a composite mat, and then the seed mat 1 can be laid onto the surface soil of the loess subsidence area. This helps to improve the uniformity of seed distribution and provides physical protection from the carrier material at the initial stage of sowing. Sowing through the seed mat 1 helps to effectively fix the Haloxylon ammodendron seeds and Caulis thunbergii seeds in the preset position, preventing the seeds from moving or being lost during the initial stage of liquid spraying or rainfall, ensuring the uniform distribution of plants in the surface soil, and improving the efficiency and success rate of sowing.

[0036] In one exemplary embodiment of this disclosure, pretreated Haloxylon ammodendron seeds and Caulis Lysimachia christinae seeds are sown on a seed mat 1, comprising: The seed mat 1 is divided into multiple array-distributed sowing units; Haloxylon ammodendron seeds and ice grass seeds are sown separately in sowing units; the seed species in the same sowing unit are the same, and the seed species in at least some adjacent sowing units are different.

[0037] Alternating sowing of Haloxylon ammodendron and Leymus chinensis seeds can create a pattern of alternating distribution of Haloxylon ammodendron and Leymus chinensis on the slope surface. Utilizing the differences in root morphology and depth between Haloxylon ammodendron and Leymus chinensis can facilitate the formation of an interwoven, multi-layered root network in the soil, thereby more effectively anchoring the soil, enhancing the integrity and stability of the fixed structure, and contributing to the optimization of plant community stability and ecological function.

[0038] In one exemplary embodiment of this disclosure, the concentration of Bacillus pasteurellium inoculum (characterized by OD600 value) is 0.6-1.0, thereby ensuring that there are sufficient quantities of microorganisms with suitable activity during spraying, thus guaranteeing the urea hydrolysis efficiency and the amount of calcium carbonate generated, and ultimately achieving the ideal soil cementation strength.

[0039] In one exemplary embodiment of this disclosure, the molar ratio of urea to calcium ions in the cementing solution is 1:1, and the concentration of calcium chloride is 0.8-1.2 mol / L. This is beneficial for improving the efficiency of microbial-induced calcium carbonate precipitation reaction, helping to generate an appropriate amount of calcium carbonate crystals with good cementing properties, and avoiding pore blockage or resource waste due to excessively high concentration, or insufficient cementation due to excessively low concentration.

[0040] In one exemplary embodiment of this disclosure, in step S200, the mass-volume ratio of bacterial solution to total seed volume is 120 mL bacterial solution: 1 kg seed. This ensures that the seed surface is fully and evenly covered by the bacterial solution while avoiding seed adhesion or excessive bacterial solution cost, thus improving the economic efficiency of the solution.

[0041] In one exemplary embodiment of this disclosure, in step S300, after the seeds are sown in the topsoil of the loess subsidence area, bacterial solution and cementing solution are sprayed alternately multiple times, including: First, spray a layer of bacterial solution. After the bacterial solution has seeped into the soil, spray a layer of cementing solution. The amount of bacterial solution and cementing solution sprayed each time is 1.5-2.5 L / m².

[0042] In this exemplary embodiment, alternating layered spraying facilitates the step-by-step and thorough penetration of the bacterial solution and cementing solution into the soil, promoting a more uniform distribution and precipitation of calcium carbonate among soil particles. This results in a more robust cementing layer and avoids excessive spraying at once, which could lead to liquid runoff or failure to penetrate the soil, forming only a hard crust on the surface. (Reference) Figure 1 As shown, calcium carbonate precipitate 3 is produced by the microbial-induced calcium carbonate precipitation process.

[0043] In one exemplary embodiment of this disclosure, before repeatedly and alternately spraying the seed blanket 1 with bacterial solution and binder, the sowing and solidification process further includes the following steps: A guide structure 2 is installed; the guide structure 2 has a guide channel, and multiple guide structures 2 are inserted into the surface soil of the loess subsidence area. The guide channel is set in a vertical direction, and the side wall of the guide channel has multiple pores. The guide channel is filled with at least one or more combinations of humic acid, root-promoting bacteria and organic matter.

[0044] The guiding structure 2 has a guiding channel, for example, referring to Figure 2 As shown, the guide structure 2 can mimic the three-dimensional interconnected porous network characteristics of natural loofah sponge. A single guide structure 2 can have multiple guide channels, and the sidewalls of the guide channels are provided with multiple artificial pores. This biomimetic structure can ensure that the pores are interconnected, providing ample channels for plant roots to extend in the soil by passing through the inner walls of the channels and the guide structure 2.

[0045] Exemplarily, the guiding structure 2 can be made of high-density polyethylene (HDPE). HDPE possesses excellent toughness, chemical stability, and corrosion resistance, ensuring that the guiding structure 2 maintains its structural integrity in the soil environment for a long period, fulfilling its function of guiding the root system without losing its function due to rapid degradation or causing environmental pollution. The high-density polyethylene described in this disclosure can refer to a density of 0.94 to 0.96 g / cm³. 3 Polyethylene.

[0046] The guiding channel can guide the downward growth of the roots of Haloxylon ammodendron and Leymus chinensis. The filling material in the guiding channel can provide nutrients for the initial growth of the roots and improve the rhizosphere microenvironment, thereby accelerating the deep rooting and soil maturation process and enhancing the plant's deep anchoring ability in the later stage.

[0047] In one exemplary embodiment of this disclosure, the steps of embedding the guide structure 2 and laying the seed mat 1 can be performed simultaneously. The guide channel passes vertically through the seed mat 1, and the maximum embedment depth of the guide structure 2 is greater than the maximum embedment depth of the seed mat 1, as shown in the reference. Figure 1 As shown. The maximum burial depth of the guide structure 2 and the seed mat 1 described in this disclosure can guide the burial depth of the bottom end of the guide structure 2 and the bottom surface of the seed mat 1. This exemplary embodiment facilitates a tight connection between the guide structure 2 and the seed mat 1, ensuring that plant seeds can contact the guide structure 2 immediately after germination. A deeper burial of the guide structure 2 helps guide the roots to extend into deeper soil layers, thereby constructing a more stable soil-stabilizing system.

[0048] In one embodiment of this disclosure, the method was tested on a slope (approximately 25°) in a loess subsidence area.

[0049] First, Bacillus pasteurellii was cultured until the OD600 value was 0.8, and a cementing solution with a concentration of 1.0 mol / L and a molar ratio of urea to calcium ions of 1:1 was prepared.

[0050] Take 1 kg of Haloxylon ammodendron and Lysimachia christinae seeds, mix them with 120 mL of bacterial solution, and ensure that the bacterial solution evenly covers the seeds.

[0051] Subsequently, the slope was leveled, and the treated Haloxylon ammodendron and Caulis Armillariae were sown in seed mat 1. Seed mat 1 was then laid on the leveled slope. Simultaneously, guide structures 2 were vertically inserted at intervals into the subsidence area. Using a sprayer, a layer of bacterial solution was first evenly sprayed at a rate of approximately 2 L / m². After it had completely penetrated the soil, a layer of binding agent was then evenly sprayed at a rate of approximately 2 L / m². This constitutes one cycle. A total of four cycles were performed.

[0052] Water twice a week to keep the soil moist.

[0053] After the above treatment, in the simulated rainfall experiment, under the experimental conditions of 120 mm / h rainfall for 1 hour, the sand yield of the treated slope was reduced by more than 95% compared with the untreated control group. Furthermore, the *Haloxylon ammodendron* and *Agropyron cristatum* seedlings emerged uniformly and grew well. Sampling analysis showed that a continuous calcium carbonate cementation layer was formed in the 0-2 cm soil layer, and the roots of *Haloxylon ammodendron* and *Agropyron cristatum* were tightly bound to the soil particles.

[0054] Comparative Example 1

[0055] In contrast, on slopes under the same conditions, only Haloxylon ammodendron and Clytemnum moss were sown without microbial-induced soil stabilization treatment. Under the same simulated rainfall conditions, significant gully erosion occurred on the slopes, with substantial loss of seeds and topsoil.

[0056] Comparative Example 2

[0057] Another comparison involved a slope with identical conditions that underwent only four microbial-induced stabilization treatments without planting Haloxylon ammodendron or Leymus chinensis. Initially, the erosion resistance was good, but after multiple wet-dry cycles, surface cracks appeared, indicating a lack of long-term anchoring and ecological function provided by plant roots.

[0058] The above experimental examples and comparative examples show that this disclosure achieves a balance between short-term rapid protection and long-term ecological stability through the synergistic effect of microbial-induced calcium carbonate precipitation technology and Haloxylon ammodendron and Leymus chinensis, with significantly better results than single technical measures.

[0059] Based on the above method, the present invention also provides a structure for fixing the surface soil in loess subsidence areas, with reference to... Figure 1 As shown. Includes: Loess matrix 5; Seed blanket 1 is laid in loess substrate 5 and contains Haloxylon ammodendron seeds and Agropyron cristatum seeds. The guide structure 2 has a guide channel inside. The guide structure 2 passes vertically through the seed blanket 1 and is laid in the loess substrate 5. The sidewall of the guide channel has multiple pores. The guide channel is filled with at least a portion of humic acid, root-promoting bacteria and organic matter. A calcium carbonate cementing layer is distributed within the loess matrix 5.

[0060] The soil stabilization structure for topsoil in loess subsidence areas disclosed in this disclosure achieves a physical soil stabilization mechanism through the design of a seed blanket 1 and guiding channels, a biological soil stabilization mechanism through Haloxylon ammodendron and Crinum asiaticum seeds, and a chemical soil stabilization mechanism through microbial-induced calcium carbonate cementation. The seed blanket 1 and the initially formed calcium carbonate cement layer maintain the stability of the topsoil and resist initial erosion; the guiding channels guide and promote the downward development of plant roots, forming deep anchorage. Ultimately, the well-developed root systems of Haloxylon ammodendron and Crinum asiaticum intertwine with the calcium carbonate crystals in the soil, forming a robust three-dimensional "root-microbe-calcium carbonate" complex, achieving good soil stabilization effects in both the short and long term.

[0061] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the appended claims.

Claims

1. A method for fixing surface soil in a loess subsidence area, characterized in that, Includes the following steps: Prepare bacterial solution and cementing solution; the bacterial solution is Bacillus pasteurellis bacterial solution, and the cementing solution includes urea and calcium chloride; Seed pretreatment; The seeds of Haloxylon ammodendron and Crinum asiaticum were mixed with the bacterial solution for seed treatment. Sowing and solidification; The pretreated Haloxylon ammodendron seeds and the Crinum asiaticum seeds were sown in the topsoil of the loess subsidence area, and the bacterial solution and the cementing solution were sprayed alternately multiple times. Post-maintenance: Watering and maintenance.

2. The method for fixing surface soil in loess subsidence areas according to claim 1, characterized in that, Seeding and solidification include: The pretreated Haloxylon ammodendron seeds and Crinum asiaticum seeds were sown on a seed blanket. The seed blanket was laid on the surface soil in the loess subsidence area; The bacterial solution and the cementing solution are sprayed alternately onto the seed mat multiple times.

3. The method for fixing surface soil in loess subsidence areas according to claim 2, characterized in that, The pretreated Haloxylon ammodendron seeds and Caulis Lysimachia nummularia seeds are sown on the seed mat, including: The seed blanket is divided into multiple array-distributed sowing units; The seeds of Haloxylon ammodendron and the seeds of Caulis Lysimachia are sown in the sowing unit respectively; the seeds in the same sowing unit are of the same type, and the seeds in at least some adjacent sowing units are of different types.

4. The method for fixing surface soil in loess subsidence areas according to claim 1, characterized in that, The OD600 value of the *Bacillus pasteurellii* bacterial culture was 0.6-1.

0.

5. The method for fixing surface soil in loess subsidence areas according to claim 1, characterized in that, The molar ratio of urea to calcium ions in the cementing solution is 1:1, and the concentration of calcium chloride is 0.8-1.2 mol / L.

6. The method for fixing surface soil in loess subsidence areas according to claim 1, characterized in that, In the seed pretreatment step, the mass-volume ratio of the bacterial solution to the total amount of seeds is 120 mL bacterial solution : 1 kg seeds.

7. The method for fixing surface soil in loess subsidence areas according to claim 1, characterized in that, In the sowing and solidification step, after sowing the seeds in the topsoil of the loess subsidence area, the bacterial solution and the cementing solution are sprayed alternately multiple times, including: First, spray a layer of the bacterial solution. After the bacterial solution has penetrated into the soil, spray another layer of the cementing solution. The amount of the bacterial solution and the cementing solution sprayed each time is 1.5-2.5 L / m².

8. The method for fixing surface soil in loess subsidence areas according to claim 2, characterized in that, Before repeatedly and alternately spraying the bacterial solution and the binding solution onto the seed mat, the sowing and solidification process also includes the following steps: A guide structure is installed; the guide structure has a guide channel, and multiple guide structures are inserted into the surface soil of the loess subsidence area. The guide channel is arranged in a vertical direction, and the side wall of the guide channel has multiple pores. The guide channel is filled with at least a portion of humic acid, root-promoting bacteria and organic matter.

9. The method for fixing surface soil in loess subsidence areas according to claim 8, characterized in that, The installation of the guide structure is carried out simultaneously with the laying of the seed blanket in the surface soil of the loess subsidence area; the guide structure passes vertically through the seed blanket, and the maximum burial depth of the guide structure is greater than the maximum burial depth of the seed blanket.

10. A structure for fixing surface soil in loess subsidence areas, characterized in that, include: Loess matrix; A seed blanket is laid within the loess substrate, and the seed blanket contains Haloxylon ammodendron seeds and Clytemnum meyraceum seeds. The guide structure has a guide channel inside, the guide structure passes vertically through the seed blanket and is laid in the loess substrate, the sidewall of the guide channel has multiple pores; the guide channel is filled with at least a portion of humic acid, root-promoting bacteria and organic matter; A calcium carbonate cementing layer is distributed within the loess matrix.

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