Method for muck recycling and backfilling for soft rock tunnel

Abstract

The application discloses a kind of for soft rock tunnel's muck recycling backfill method, it is related to soft rock tunnel construction technical field, wherein, the muck recycling backfill method for soft rock tunnel includes the grading of muck based on the soft rock structure surface feature of soft rock tunnel, obtains classified muck;Pretreatment classified muck, obtain target muck;Modification target muck, obtain backfill muck;Utilize backfill muck to carry out layered backfill to soft rock tunnel, complete the muck recycling backfill construction of soft rock tunnel.The application carries out multistage classification to the muck of soft rock tunnel by the soft rock structure surface feature of soft rock tunnel, provides basis for subsequent modification processing, and utilizes backfill muck to carry out layered backfill to soft rock tunnel, so that muck multidimensional classification, improve modification processing pertinence, effectively utilize structure surface feature and improve resource utilization efficiency.Realize the classification and utilization of muck resources, reduce environmental burden and reduce the construction cost of soft rock tunnel.

Description

Technical Field

[0001] This invention relates to the field of soft rock tunnel construction technology, and in particular to a method for recycling and backfilling slag in soft rock tunnels. Background Technology

[0002] The excavation of soft rock tunnels generates a large amount of waste soil, and the disposal and utilization of this waste soil has become an important technical issue in engineering construction.

[0003] Currently, the utilization rate of excavated soil from soft rock tunnels is low, and a large amount of excavated soil from soft rock tunnels is simply transported off-site for disposal, which not only increases transportation costs but also causes a serious environmental burden. Summary of the Invention

[0004] The main objective of this invention is to propose a method for backfilling and recycling excavated soil in soft rock tunnels. This method aims to utilize the excavated soil generated during the excavation of soft rock tunnels to backfill them, thereby reducing the environmental burden and lowering construction costs.

[0005] To achieve the above objectives, the present invention proposes a method for backfilling and recycling excavated soil in soft rock tunnels, comprising:

[0006] The slag is graded based on the soft rock structural surface characteristics of the soft rock tunnel to obtain graded slag.

[0007] Pre-treat the graded slag to obtain the target slag;

[0008] The target slag soil is modified to obtain backfill slag soil;

[0009] The soft rock tunnel is backfilled in layers using the backfill soil, thus completing the soil recycling and backfilling construction of the soft rock tunnel.

[0010] In one embodiment, the step of classifying the slag based on the soft rock structural surface characteristics of the soft rock tunnel to obtain graded slag includes:

[0011] The waste soil is classified according to its geometric dimensions to obtain primary classification waste soil;

[0012] The primary waste soil is classified according to its integrity to obtain secondary waste soil.

[0013] The secondary-level waste soil is classified according to its lithology to obtain the graded waste soil.

[0014] In one embodiment, the step of classifying the construction waste according to its geometric dimensions to obtain primary-grade construction waste includes:

[0015] The slag with a single unit size of A is considered as large slag, where 300mm ≤ A;

[0016] The slag with a single size of B is considered as medium-sized blocky slag, where 50mm ≤ B < 300mm.

[0017] The slag with a single unit size of C is considered as fine-grained slag, where C < 50 mm;

[0018] The slag is classified into large block slag, medium block slag, and fine granular slag to obtain the primary classified slag.

[0019] In one embodiment, the primary-grade waste soil is classified according to its integrity to obtain secondary-grade waste soil:

[0020] The slag with the broken surface completely along the natural structural surface is regarded as slag with the complete structural surface.

[0021] The slag soil with a fractured surface partly along the natural structural surface and partially penetrating the rock matrix is ​​referred to as semi-intact structural surface slag soil.

[0022] The slag formed entirely from the crushing of the rock matrix is ​​used as the crushed matrix slag.

[0023] The primary-level waste soil is classified into the complete structural surface waste soil, the semi-complete structural surface waste soil, and the broken matrix waste soil to obtain the secondary-level waste soil.

[0024] In one embodiment, the step of classifying the secondary-graded waste soil according to its lithology to obtain the graded waste soil includes:

[0025] Based on the lithology of the slag, the secondary slag is classified into argillaceous soft rock slag, sandy soft rock slag, and calcareous soft rock slag, thus obtaining the graded slag.

[0026] In one embodiment, the step of pre-treating the graded waste soil to obtain the target waste soil includes:

[0027] The graded slag is washed and impurities are removed to obtain slag to be processed;

[0028] The pretreated slag is crushed and shaped to obtain crushed slag;

[0029] Adjust the moisture content of the crushed slag to obtain the target slag.

[0030] In one embodiment, the step of adjusting the moisture content of the crushed slag to obtain the target slag includes:

[0031] When the graded slag is argillaceous soft rock slag, the moisture content of the crushed slag is adjusted to D, 12% ≤ D ≤ 18%;

[0032] When the graded slag is sandy soft rock slag, the moisture content of the crushed slag is adjusted to E, 8% ≤ E ≤ 15%;

[0033] When the graded slag is calcareous soft rock slag, the moisture content of the crushed slag is adjusted to F, where 10% ≤ F ≤ 16%.

[0034] In one embodiment, the step of modifying the target slag to obtain backfill slag includes:

[0035] The argillaceous soft rock slag was modified using lime and cement.

[0036] The sandy soft rock slag soil was modified using cement and fly ash.

[0037] The calcareous soft rock slag soil was modified using cement.

[0038] The target slag soil is modified to obtain the backfill slag soil.

[0039] In one embodiment, the steps of using the backfill soil to backfill the soft rock tunnel in layers, thereby completing the backfilling construction of the soft rock tunnel, include:

[0040] According to the preset backfill thickness for each layer, the soft rock tunnel is backfilled in layers using the backfill soil, thus completing the soil recycling and backfilling construction of the soft rock tunnel; wherein, the backfill thickness is G, 300mm≤F≤500mm.

[0041] In one embodiment, prior to the step of modifying the target slag to obtain backfill slag, the slag recycling and backfilling method for soft rock tunnels further includes:

[0042] The target excavated soil is used to construct the main structural surface at the backfill location of the soft rock tunnel;

[0043] The target slag is used to construct a secondary structural surface on the main structural surface.

[0044] The technical solution of this invention classifies the excavated soil from soft rock tunnels into multiple levels based on the structural characteristics of the soft rock surface, providing a foundation for subsequent modification treatment. It also utilizes backfill soil to perform layered backfilling of the soft rock tunnel, enabling multi-dimensional classification of the excavated soil, improving the targeted nature of modification treatment, effectively utilizing structural surface characteristics, and increasing resource utilization efficiency. This achieves the classification and utilization of excavated soil resources, solving problems such as poor backfill stability and significant material waste caused by traditional methods. It also reduces the environmental burden and lowers the construction cost of soft rock tunnels. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0046] Figure 1 This is a schematic flowchart of an embodiment of the method for recycling and backfilling slag in soft rock tunnels provided by the present invention.

[0047] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0050] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0051] In existing technologies, the treatment of excavated soil generated during soft rock tunnel construction faces technical bottlenecks such as insufficient systematic classification, poor targeted modification, and low resource utilization. Traditional methods typically employ simple particle size classification, failing to fully consider the unique structural features of soft rock, such as bedding planes and joints, leading to inaccurate assessments of the engineering properties of the excavated soil. In a certain tunnel project, the argillaceous soft rock excavated soil generated during excavation, due to ineffective classification and treatment, experienced uneven settlement after backfilling. Simultaneously, a large amount of sandy soft rock excavated soil was forced to be transported off-site due to a lack of reasonable utilization plans, resulting in resource waste and increased costs.

[0052] To address this technical problem, this invention proposes a method for recycling and backfilling slag in soft rock tunnels.

[0053] Please see Figure 1 In one embodiment of the present invention, the method for backfilling and recycling excavated soil for soft rock tunnels includes:

[0054] Step S10: Based on the soft rock structural surface characteristics of the soft rock tunnel, the slag is graded to obtain graded slag.

[0055] Step S20: Pre-process the graded slag to obtain the target slag;

[0056] Step S30: Modify the target slag soil to obtain backfill slag soil;

[0057] Step S40: Use the backfill soil to backfill the soft rock tunnel in layers, and complete the soil recycling and backfilling construction of the soft rock tunnel.

[0058] It should be noted that soft rock structural features refer to the naturally occurring structural characteristics such as bedding and joints within the rock. These can be identified through ground-penetrating radar scanning and core sampling analysis to determine the fragmentation pattern during the formation of the waste soil. Waste soil grading refers to multi-level classification based on structural integrity, lithology, and geometric dimensions. This can be achieved using vibrating screening combined with image recognition technology to ensure targeted treatment for different types of waste soil. Pretreatment includes physical state adjustment and impurity removal, which can be achieved through high-pressure water jet cleaning combined with jaw crusher shaping, creating suitable conditions for subsequent modification. Modification treatment refers to improving the properties of the waste soil by adding cementing materials, specifically by mixing cement, lime, and other materials in specific proportions to enhance the mechanical stability of the backfill. Layered backfilling refers to construction in layers according to a predetermined thickness, which can be achieved by using a paver and a roller for layered compaction to ensure uniform density of the backfill.

[0059] More specifically, a classification and collection device is installed at the tunnel excavation face. Using 3D laser scanning, the structural features of the excavated soil are identified, and the soil is classified into three categories based on its crushing mode: intact structural surfaces, semi-intact structural surfaces, and broken matrix. Subsequently, multi-stage screening is used to grade the soil by size, and final classification is achieved through rapid lithological testing. Different categories of excavated soil enter separate pretreatment lines. For argillaceous soft rock, high-pressure washing removes surface clay particles, while for calcareous soft rock, a cone crusher adjusts the particle shape. In the modification stage, a lime-cement composite modifier is used for argillaceous soft rock, and a fly ash-cement mixture is used for sandy soft rock, achieving uniform mixing through a twin-shaft mixer. During backfilling, an intelligent paving system controls the layer thickness, combined with a vibratory roller for directional compaction, forming a backfill body with a biomimetic structural network.

[0060] The technical solution provided by this invention classifies the excavated soil from soft rock tunnels into multiple levels based on the structural features of the soft rock surface, providing a foundation for subsequent modification treatment. It then utilizes backfill soil to perform layered backfilling of the soft rock tunnel, enabling multi-dimensional classification of the excavated soil, improving the targeted nature of modification treatment, effectively utilizing structural features, and increasing resource utilization efficiency. This achieves the classification and utilization of excavated soil resources, solving problems such as poor backfill stability and significant material waste caused by traditional methods. It also reduces the environmental burden and lowers the construction cost of soft rock tunnels.

[0061] In an embodiment of the present invention, the step of classifying the slag based on the soft rock structural surface characteristics of the soft rock tunnel to obtain graded slag includes:

[0062] Step S11: Classify the slag according to its geometric dimensions to obtain primary classified slag.

[0063] Step S12: Classify the primary waste soil according to its integrity to obtain secondary waste soil;

[0064] Step S13: Classify the secondary-graded slag according to the lithology of the slag to obtain the graded slag.

[0065] It should be noted that geometric classification refers to grading by measuring the maximum outer contour size of the construction waste particles, which can be achieved using laser scanning or mechanical screening equipment, and is used to initially distinguish construction waste with different particle size ranges. Integrity classification refers to classifying based on the degree of conformity between the fractured surface and the natural structural surface, which can be achieved using visual inspection combined with 3D imaging technology, and is used to assess the structural characteristics of construction waste particles. Lithological classification refers to differentiation through mineral composition analysis and rock mechanics testing, which can be achieved using X-ray diffraction or petrographic microscopy, and is used to identify the material properties of the construction waste.

[0066] More specifically, a multi-level classification system is set up at the tunnel excavation face. First, a vibrating screen separates the excavated soil into three categories based on geometric size: large blocks, medium blocks, and fine particles. Then, quality inspectors check the integrity of the screened soil, using a structural surface recognition algorithm to determine the degree of conformity between broken and natural structural surfaces, classifying the soil into three categories: intact structural surfaces, semi-intact structural surfaces, and broken matrix. Finally, lithological testing equipment analyzes the material composition of the classified soil, completing the final classification into argillaceous, sandy, and calcareous soft rock. The entire classification process adopts an assembly line operation mode, with different categories of excavated soil being diverted to designated storage areas via conveyor belts. This achieves the identification of the physical properties and material attributes of the excavated soil. Classification based on structural surface integrity allows for the selection of soil particles with natural structural advantages; classification based on lithological characteristics allows for the matching of corresponding modification processes to different types of excavated soil, thereby improving resource utilization and engineering reliability.

[0067] In an embodiment of the present invention, the step of classifying the slag according to its geometric dimensions to obtain primary classified slag includes:

[0068] Step S111: The slag with a single unit size of A is regarded as large slag, 300mm≤A;

[0069] Step S112: The slag with a single unit size of B is regarded as medium-sized block slag, 50mm≤B<300mm;

[0070] Step S113: The slag with a single unit size of C is regarded as fine granular slag, where C < 50 mm;

[0071] Step S114: The slag is classified into large block slag, medium block slag, and fine granular slag to obtain the primary classified slag.

[0072] It should be noted that the individual size refers to the side length of the largest circumscribed cube of the slag particle in three-dimensional space, which can be specifically calibrated using a laser 3D scanner or calipers. The geometric size classification standard is set according to the fracture characteristics of soft rock structural surfaces. Large slag blocks are usually peeled off as a whole along the main structural surface, medium-sized slag blocks include part of the structural surface and fresh cross-sections, and fine-grained slag blocks are mainly produced by matrix crushing.

[0073] More specifically, automated sorting equipment is installed at the tunnel excavation face, transporting the excavated soil to a vibrating screening device via conveyor belt. The first-stage screen uses a 300mm aperture plate to separate large lumps of excavated soil, while the second-stage screen uses a 50mm aperture plate to separate medium-sized lumps. The undersize material is collected as fine-grained excavated soil. Manual inspection is conducted simultaneously during the sorting process, and any adhered lumps are mechanically crushed for pre-treatment. The sorted excavated soil is stored in designated areas. Large lumps are directly used for structural surface reconstruction, medium-sized lumps are processed into a crushing and shaping process, and fine-grained soil is used to fill voids.

[0074] This solution establishes a size classification standard corresponding to the structural surface crushing mode, ensuring that large-sized waste soil retains its complete structural surface characteristics, medium-sized waste soil maintains a mixed crushing morphology, and fine-grained waste soil maintains its matrix crushing characteristics. This provides an accurate raw material classification basis for subsequent differentiated washing, crushing, and modification treatments. It effectively solves the problem of the disconnect between waste soil classification and structural surface characteristics, enabling waste soil of different geometric sizes to be matched with corresponding pretreatment processes. Size control of large-sized waste soil avoids structural surface damage caused by over-crushing; size limitation of medium-sized waste soil ensures crushing and shaping efficiency; and precise classification of fine-grained waste soil improves filling density, thereby comprehensively improving the engineering applicability of waste soil resource utilization.

[0075] In an embodiment of the present invention, the primary-level waste soil is classified according to its integrity to obtain secondary-level waste soil:

[0076] Step S121: The slag with the broken surface completely along the natural structural surface is regarded as slag with a complete structural surface.

[0077] Step S122: The slag soil with the broken surface part along the natural structural surface and partially through the rock matrix is ​​regarded as semi-intact structural surface slag soil.

[0078] Step S123: The slag formed entirely from the crushed rock matrix is ​​used as the crushed matrix slag.

[0079] Step S124: The primary-level waste soil is classified into the complete structural surface waste soil, the semi-complete structural surface waste soil, and the broken matrix waste soil to obtain the secondary-level waste soil.

[0080] It should be noted that "intact structural surface soil" refers to soil whose fractured surface completely follows the natural structural surface. This can be achieved through mechanical screening or manual sorting. It has a high degree of surface smoothness and retains the original characteristics of the natural structural surface, forming a stable contact surface in backfill applications. "Semi-intact structural surface soil" refers to soil whose fractured surface partially extends along the natural structural surface and partially penetrates the rock matrix. This can be distinguished through image recognition technology or manual observation. Its surface contains both smooth structural surface areas and rough cross-sectional areas, serving as a transitional connector in backfill. "Fractured matrix soil" refers to soil formed entirely from the fractured rock matrix. This can be identified through particle size screening combined with surface feature analysis. Its particles have irregular shapes and rough surfaces, and it is mainly used as a filling material in backfill.

[0081] More specifically, after completing the primary classification based on geometric dimensions, a secondary classification of the waste soil is performed through structural integrity analysis. For large-block waste soil, by observing the degree of conformity between the extension direction of its fractured surface and the natural structural surface, waste soil with intact structural surfaces is screened out. This type of waste soil can be directly used to construct the main load-bearing structure of the backfill. Medium-block waste soil, after fractured surface analysis, is distinguished as waste soil with semi-intact structural surfaces, whose partially retained structural surface features can enhance the interlayer bonding force of the backfill. Fragmented matrix waste soil identified in fine-grained waste soil, because it has completely lost its structural surface features, needs to be modified to improve its engineering performance. This classification method provides an accurate basis for subsequent differentiated treatment by establishing a structural integrity evaluation standard.

[0082] This solution introduces a structural integrity classification dimension, enabling precise identification of slag with natural structural features. This allows for full utilization of their structural advantages during backfilling. Furthermore, it employs appropriate treatment processes for slag with different integrity levels, significantly improving resource utilization. This effectively addresses the lack of consideration for structural features in existing slag classification technologies, achieving precise classification based on structural integrity. By distinguishing between intact, semi-intact, and broken matrix slag, a classification basis is provided for subsequent modification and structural reconstruction. This ensures that slag with different integrity levels is utilized effectively in the backfill, preserving the mechanical advantages of natural structural surfaces while improving the resource utilization rate of broken slag.

[0083] In an embodiment of the present invention, the step of classifying the secondary-graded slag according to the lithology of the slag to obtain the graded slag includes:

[0084] Step S131: Based on the lithology of the slag, the secondary slag is classified into argillaceous soft rock slag, sandy soft rock slag, and calcareous soft rock slag, thereby obtaining the graded slag.

[0085] It should be noted that argillaceous soft rock slag refers to slag containing clay minerals and having a high plasticity index. This can be identified through X-ray diffraction analysis of mineral composition. Its high plasticity requires controlling the moisture content to prevent excessive deformation during construction. Sandy soft rock slag refers to slag with a quartz content exceeding 60% and a sandy structure. This can be identified through sieving combined with petrographic analysis. Its interparticle friction characteristics require the use of cementing materials to enhance structural stability. Calcareous soft rock slag refers to slag with a calcium carbonate content exceeding 40% and a cemented structure. This can be detected through hydrochloric acid foaming tests combined with chemical titration. Its natural cementing ability requires the use of activators to enhance its strength.

[0086] More specifically, after completing the secondary classification based on geometric dimensions and structural integrity, mineral composition analysis was performed on the slag samples using lithological testing equipment. Slag samples containing more than 15% clay minerals such as montmorillonite were classified as argillaceous soft rock slag; slag samples with a predominantly quartz content and a particle size distribution conforming to sand standards were classified as sandy soft rock slag; and slag samples with significant carbonate mineral content and a cemented structure were classified as calcareous soft rock slag. The classified slag samples were then placed in dedicated storage areas to establish the foundation for subsequent differentiated moisture content adjustment and modification treatments.

[0087] This solution establishes a three-tiered lithological classification system, providing independent treatment pathways for silty, sandy, and calcareous waste soils, effectively avoiding performance fluctuations caused by the mixing of different lithological materials. It addresses the lack of targeted modification treatment for waste soils in existing technologies, enabling silty soft rock waste soils to undergo plasticity control, sandy soft rock waste soils to achieve enhanced structural stability, and calcareous soft rock waste soils to have their cementing capacity activated, significantly improving the backfill applicability and resource utilization rate of each type of waste soil.

[0088] In an embodiment of the present invention, the step of pre-treating the graded slag to obtain the target slag includes:

[0089] Step S21: The graded slag is washed and impurities are removed to obtain slag to be treated;

[0090] Step S22: The pretreated slag is crushed and shaped to obtain crushed slag;

[0091] Step S23: Adjust the moisture content of the crushed slag to obtain the target slag.

[0092] It should be noted that cleaning and impurity removal refers to removing contaminants from the surface of the construction waste using physical or chemical methods. Specifically, high-pressure water washing combined with surfactant treatment can effectively separate mud and oil adhering to the surface of the construction waste particles. Crushing and shaping refers to improving the size distribution of construction waste particles through mechanical crushing. Specifically, jaw crushers can be used for graded crushing, turning large pieces of construction waste into regular medium-sized particles. Moisture content adjustment refers to adjusting the moisture content of the particles according to the lithology of the construction waste. This can be achieved through natural drying or atomized humidification devices to bring construction waste of different lithologies to the optimal moisture content.

[0093] More specifically, the washing and impurity removal stage employs a circulating water system to perform multi-stage washing of the sorted slag, achieving all-round cleaning through spray heads set at different angles. During the crushing and shaping process, crushing parameters are selected based on the initial size of the slag. Large slag pieces undergo primary crushing and are then transferred to a secondary crusher for further refinement, while a screening device controls the discharge particle size. The moisture content adjustment stage uses an online monitoring system to detect the moisture content of the crushed slag in real time. When argillaceous soft rock slag is detected, an automatic water replenishment device is activated; for sandy soft rock slag, a vibrating dewatering screen is used to ensure that all types of slag reach the preset moisture content range.

[0094] This solution employs a combination of graded cleaning and selective crushing processes, preserving the original structural features of the slag and achieving precise particle size control. Coupled with an intelligent moisture content adjustment system, it provides physically stable raw materials for subsequent modification treatment. This solves the problem of insufficient slag pretreatment leading to poor modification effects in existing technologies, enabling differentiated treatment of different types of soft rock slag, improving the uniformity and stability of backfill materials, and reducing water consumption and the risk of secondary pollution. It also lays a material foundation for subsequent structural reconstruction and layered backfilling.

[0095] In an embodiment of the present invention, the step of adjusting the moisture content of the crushed slag to obtain the target slag includes:

[0096] Step S231: When the graded slag is the argillaceous soft rock slag, adjust the moisture content of the crushed slag to D, 12% ≤ D ≤ 18%.

[0097] Step S232: When the graded slag is sandy soft rock slag, adjust the moisture content of the crushed slag to E, 8% ≤ E ≤ 15%;

[0098] Step S233: When the graded slag is calcareous soft rock slag, adjust the moisture content of the crushed slag to F, where 10% ≤ F ≤ 16%.

[0099] It should be noted that argillaceous soft rock slag refers to the crushed product of soft rock containing a high proportion of clay minerals. It has a high plasticity index and is prone to water absorption and swelling. This can be identified by X-ray diffraction analysis showing a clay mineral content exceeding 30%. Sandy soft rock slag refers to the crushed product mainly composed of quartz, feldspar, and other sand particles. It has high interparticle friction. This can be identified by sieve analysis showing a particle size of 0.075–2 mm exceeding 60%. Calcareous soft rock slag refers to the crushed product containing carbonate cement. It easily dissolves in water. This can be verified by a hydrochloric acid foaming test showing a carbonate content exceeding 15%. The moisture content adjustment range is determined based on the water-holding characteristics of different lithological slag types. A higher moisture content is used for argillaceous soft rock to prevent drying and cracking, a lower moisture content for sandy soft rock to prevent particle loosening, and an intermediate moisture content for calcareous soft rock to balance the water required for cementation reactions.

[0100] Specifically, differentiated moisture content control is implemented for the sorted slag and soil during the pretreatment stage. For argillaceous soft rock slag and soil, due to its high clay mineral content, a moisture content of 12%–18% maintains interparticle bonding while preventing excessive expansion. For sandy soft rock slag and soil, due to strong interparticle mechanical interlocking, a moisture content of 8%–15% provides adequate lubrication without damaging the skeletal structure. For calcareous soft rock slag and soil, a moisture content of 10%–16% satisfies the requirements for cement hydration while preventing excessive dilution of the cementing material. The moisture content of the crushed slag and soil is monitored in real-time using an online moisture content detection device, and dynamically adjusted using spray humidification or ventilation drying equipment to ensure that all types of slag and soil reach the target moisture content range.

[0101] Compared to existing technologies, traditional waste soil treatment typically uses a uniform moisture content standard, failing to consider the differences in physical properties of waste soils with different lithologies. For example, treating argillaceous soft rock with conventional moisture content easily leads to clumping or cracking, while treating sandy soft rock with conventional methods easily results in segregation. This solution establishes a lithology-moisture content correspondence, ensuring that all types of waste soil are in their optimal moisture content state during subsequent modification treatment, significantly improving the effectiveness of cementing materials. It effectively solves the technical problem of insufficient targeted modification treatment for soft rock waste soil. Optimal moisture content ranges are set for argillaceous, sandy, and calcareous soft rock waste soils, avoiding uneven dispersion of modifiers due to insufficient moisture in argillaceous waste soil, preventing structural loosening due to excessive moisture in sandy waste soil, and ensuring sufficient cementation reaction in calcareous waste soil. This differentiated control method allows all types of waste soil to achieve optimal performance during subsequent modification treatment, significantly improving the efficiency of waste soil resource utilization.

[0102] In an embodiment of the present invention, the step of modifying the target slag soil to obtain backfill slag soil includes:

[0103] Step S31: Modify the argillaceous soft rock slag using lime and cement;

[0104] Step S32: Modify the sandy soft rock slag soil using cement and fly ash;

[0105] Step S33: Modify the calcareous soft rock slag using cement;

[0106] Step S34: Complete the modification treatment of the target slag soil to obtain the backfill slag soil.

[0107] It should be noted that the modification of argillaceous soft rock slag soil with lime and cement refers to neutralizing the expansibility of argillaceous soft rock through alkaline substances. Specifically, lime and cement can be mixed in a certain mass ratio and then added to the slag soil, reducing the activity of clay particles through calcium ion exchange. The modification of sandy soft rock slag soil with cement and fly ash refers to utilizing the micro-aggregate effect of fly ash to fill the gaps between sandy particles. Specifically, fly ash and cement can be mixed in a certain proportion and then coated on the surface of sandy particles to form a composite cemented structure. The modification of calcareous soft rock slag soil with cement refers to the reaction between cement hydration products and calcareous components. Specifically, cement can be added alone to stimulate the self-cementing ability of calcareous soft rock, forming a stable ettringite crystal network.

[0108] More specifically, argillaceous soft rock slag, containing highly reactive clay minerals, can have its water absorption and swelling characteristics effectively suppressed through the combined action of lime and cement. Sandy soft rock slag, with its weak interparticle bonding, can have its interparticle strength enhanced through the synergistic bonding of fly ash and cement. Calcareous soft rock slag, containing carbonate components, can have its potential cementing properties activated through the alkaline environment generated by cement hydration. During the modification process, differentiated cementing systems are employed for different rock types of slag, enabling each type of slag to form a stable structure matching its mineral composition.

[0109] This solution utilizes differentiated material proportions to create an anti-expansion modified layer for argillaceous soft rock, a composite cemented skeleton for sandy soft rock, and activate the self-cementing capacity of calcareous soft rock, significantly improving the targeted nature of the modification treatment. It addresses the lack of targeted modification in existing technologies for slag soil, reducing the plasticity index of argillaceous soft rock slag soil, controlling the permeability coefficient of sandy soft rock slag soil, and increasing the cementing strength of calcareous soft rock slag soil, thus achieving optimal engineering performance transformation for slag soils of different lithologies.

[0110] In an embodiment of the present invention, the steps of using the backfill soil to backfill the soft rock tunnel in layers, thereby completing the backfilling construction of the soft rock tunnel, include:

[0111] Step S41: According to the preset backfill thickness of each layer, the soft rock tunnel is backfilled in layers using the backfill soil to complete the soil recycling and backfilling construction of the soft rock tunnel; wherein, the backfill thickness is G, 300mm≤F≤500mm.

[0112] It should be noted that layered backfilling refers to a construction method in which backfill soil is laid in layers of predetermined thickness and compacted to form a continuous structure. This can be achieved using a vibratory roller in conjunction with a layered paving device. The uniformity of compaction is ensured by controlling the thickness of each layer. The predetermined backfill thickness refers to the range of single-pass backfill heights determined in advance based on the properties of the soil and the performance of the compaction equipment. The optimal thickness parameters can be determined through on-site testing. This thickness range ensures the effective depth of the compaction machinery while avoiding insufficient internal density due to excessive thickness.

[0113] More specifically, during the backfilling construction of soft rock tunnels, the thickness parameters of each backfill layer are first determined based on the type of excavated soil and the performance of the compaction equipment. For modified backfill soil, a layered paving device is used to evenly spread it in a thickness range of 300mm to 500mm. After each layer is paved, a vibratory roller is used for multiple passes of compaction. During the compaction process, the surface settlement is monitored in real time, and compaction is stopped when the settlement difference between two consecutive passes is less than a set threshold. After a single layer of backfill is completed, a nuclear density meter is used to test the density. Only after the density meets the standard can the next layer be constructed. Layered control can effectively avoid the problems of loose bottom layer and uneven density caused by excessive backfill thickness at one time, while ensuring that an effective interlocking structure is formed between each layer.

[0114] This method establishes a correlation mechanism between thickness parameters and material properties, dynamically adjusting the number of compaction passes and vibration frequency during construction. This ensures both construction efficiency and uniform compaction across the entire cross-section. It effectively solves the technical challenge of uneven compaction in backfill of soft rock tunnels. Through the coordinated control of layer thickness and compaction parameters, the backfill forms a stable layered structure, significantly reducing the risk of later settlement due to compaction differences, while also improving the engineering reliability of waste soil resource utilization.

[0115] In an embodiment of the present invention, prior to the step of modifying the target slag to obtain backfill slag, the slag recycling and backfilling method for soft rock tunnels further includes:

[0116] Step S101: Use the target slag to construct the main structural surface at the backfill location of the soft rock tunnel;

[0117] Step S102: Use the target slag to construct a secondary structural surface on the main structural surface.

[0118] It should be noted that the primary structural plane refers to the load-bearing skeleton layer formed by directionally arranged slag particles with complete structural features. This can be achieved through a combination of mechanical vibration and manual adjustment, ensuring the particle orientation aligns with the force direction to create a continuous force transmission path. The secondary structural plane refers to the support network layer formed by filling the gaps between the primary structural planes with medium-sized slag particles. This can be achieved through layered filling and localized compaction, enhancing structural stability by establishing multi-angle intersecting contact relationships.

[0119] More specifically, in the bottom area of ​​the tunnel backfill section, large blocks of excavated soil with intact structural surfaces are first selected and oriented so that their bedding planes or joint planes form an angle of 15–30 degrees with the horizontal direction, forming the main load-bearing layer. Then, medium-sized blocks of excavated soil are used to fill the gaps between the main structural surfaces in layers. Local vibration compaction is performed every 20–30 cm of filling, ensuring that the filling soil forms a contact angle of 45–60 degrees with the main structural surfaces, creating an interlocking support network. During this process, by controlling the filling sequence and compaction intensity, it is ensured that the secondary structural surfaces can effectively transfer loads without disrupting the directional arrangement characteristics of the main structural surfaces.

[0120] This method establishes a synergistic mechanism between primary and secondary structural planes, enabling the backfill to form structural features similar to natural rock masses. This significantly improves the overall stability and load-bearing efficiency of the backfill while reducing the amount of cementing material used.

[0121] Through the above technical solution, this application effectively solves the problem of lack of structural surface utilization in the existing technology of slag and soil reconstruction. By simulating the structural characteristics of natural rock mass to construct a multi-level force transmission system, the backfill slag and soil has good self-stabilizing ability in the incomplete cementation state, reducing the risk of collapse caused by structural loosening during construction, and improving the in-situ utilization rate of slag and soil resources.

[0122] Based on the above embodiments, a specific implementation method is shown here for ease of understanding:

[0123] First main step: Graded collection and pretreatment of construction waste:

[0124] A multi-dimensional hierarchical data collection method based on the structural features of soft rock:

[0125] During soft rock tunnel excavation, the first step is to establish a graded soil collection system based on the structural characteristics of soft rock. Due to its unique geological structure, soft rock fractures along different structural planes during excavation. These structural planes include bedding planes, joint planes, and fissure planes. Bedding planes are the most common structural planes in sedimentary rocks, exhibiting parallel layered structures within the rock. These planes make the rock prone to peeling and fracturing along the bedding planes under stress. Joint planes are natural fissures in the rock, typically exhibiting a regular geometric distribution. When excavation disturbance is transmitted to the joint planes, it causes rock blocks to separate along the joint planes. Fissure planes are finer fracture structures, often densely distributed within the soft rock mass, and easily expand and connect under excavation vibration.

[0126] Based on these structural features, a three-dimensional classification and collection standard was established. First, the excavated waste was classified according to the geometric size of the particles, into three basic categories: large-block waste, medium-block waste, and fine-grained waste. Large-block waste refers to rock blocks with a single particle size exceeding 300 mm. This type of waste typically retains the basic structural characteristics of the original rock, with its fractured surfaces mainly formed along major bedding planes or large joint surfaces. Medium-block waste has a single particle size between 50 mm and 300 mm. The fractured surfaces of this type of waste include both structural planes and some fresh sections penetrating the rock matrix. Fine-grained waste has a particle size less than 50 mm and is mainly composed of rock matrix fragmentation and weathering products.

[0127] Based on the geometric size classification, a secondary classification is further performed according to the integrity of the structural surface. Structural surface integrity reflects the smoothness and bonding strength characteristics of the soil particle surface. Intact structural surface soil refers to soil where the fractured surface is formed entirely along the natural structural surface, with a relatively smooth surface. This type of soil has good shape regularity and strong bearing capacity. Semi-intact structural surface soil refers to soil formed partly along the structural surface and partly through the matrix, with both smooth structural surface sections and rough, fresh cross-section sections on the surface. Crushed matrix soil refers to soil mainly formed by the crushing of rock matrix, with a rough, irregular surface and irregular particle shape.

[0128] Simultaneously, a three-tiered classification standard based on lithological characteristics should be established. The lithological differences in soft rock directly affect the physicochemical properties and backfill applicability of the slag. Muddy soft rock slag has high plasticity and strong water absorption and swelling characteristics, requiring special control of moisture content and compaction techniques in backfill applications. Sandy soft rock slag has good permeability and low plasticity, making it suitable as a drainage layer or transition layer material. Calcareous soft rock slag has a certain cementing capacity and can form strong overall strength under appropriate conditions.

[0129] This multi-dimensional, graded collection method allows for real-time classification of excavated soil at the excavation site, providing a basis for subsequent differentiated treatment. During the graded collection process, multiple temporary storage areas need to be set up near the tunnel excavation face, each corresponding to a specific type of excavated soil. This ensures that different types of excavated soil do not mix, maintaining the accuracy of classification and the targeted nature of subsequent treatment.

[0130] Slag and waste pretreatment process flow:

[0131] After the graded collection is completed, various types of waste soil need to undergo corresponding pretreatment. The purpose of pretreatment is to remove harmful components, adjust the physical state, and create conditions for subsequent modification treatment. The pretreatment process includes key steps such as washing and impurity removal, crushing and shaping, and moisture content adjustment.

[0132] The cleaning and impurity removal process primarily targets harmful substances such as mud and oil adhering to the surface of the excavated soil. During soft rock excavation, lubricants and coolants are typically used, and these substances can adhere to the soil surface, affecting subsequent treatment. The cleaning process employs high-pressure water rinsing; by controlling the water pressure and rinsing time, surface contaminants are effectively removed. For excavated soil heavily contaminated with oil, an appropriate amount of surfactant is added to enhance the cleaning effect. The wastewater after cleaning requires sedimentation treatment; the supernatant can be recycled, and the sediment can be used as a supplementary material for fine-grained excavated soil.

[0133] The crushing and shaping stage primarily targets large lumps of excavated soil and medium-sized lumps with irregular shapes. Mechanical crushing methods are used to break excessively large lumps into suitable sizes, improving particle shape and increasing bulk density and load-bearing capacity. The crushing process requires careful control of the crushing intensity to avoid over-crushing and excessive fine particle content. For excavated soil crushed along structural surfaces, its natural flatness should be preserved as much as possible, with only excessively large portions undergoing moderate crushing.

[0134] Moisture content adjustment is a crucial step in pretreatment. The moisture content of soft rock slag directly affects its engineering properties and subsequent treatment effectiveness. Excessive moisture content leads to increased cohesion and decreased bearing capacity, while insufficient moisture content negatively impacts compaction and the hydration reaction of cementing materials. Methods such as natural drying, mechanical dehydration, or wetting with water are used to adjust the moisture content of various types of slag to their optimal range. The optimal moisture content for argillaceous soft rock slag is typically between 12% and 18%, for sandy soft rock slag between 8% and 15%, and for calcareous soft rock slag between 10% and 16%.

[0135] The second main step: modification and mix optimization of waste soil.

[0136] Slag modification treatment method based on structural plane reconstruction:

[0137] Pre-treated slag soil needs to be modified to improve its engineering properties and meet the technical requirements for backfilling. Traditional slag soil modification methods mainly rely on adding cementing materials or modifiers. The modification method based on structural surface reconstruction proposed in this invention reorganizes the arrangement and contact relationships of slag soil particles, making full use of the original structural surface characteristics of soft rock to achieve a significant improvement in slag soil performance.

[0138] The core concept of structural plane reconstruction is to simulate the distribution patterns and mechanical mechanisms of structural planes in natural rock masses. In natural soft rock masses, structural planes of different directions and scales form a complex network system. This network system is both a weak link in the rock mass and an important component of its overall stability. By artificially reconstructing this network of structural planes, backfill soil can acquire mechanical properties similar to those of natural rock masses.

[0139] Structural plane reconstruction first requires establishing a particle orientation system. Based on the stress characteristics and stability requirements of the backfill area, the dominant orientation of the main structural planes is determined. For tunnel bottom backfill, the main structural planes should be inclined at a small angle to the horizontal to bear the upper load and transfer it to a stable foundation. For tunnel sidewall backfill, the main structural planes should be inclined at a small angle to the vertical to resist lateral earth pressure. Through a combination of mechanical vibration and manual adjustment, the soil particles with complete structural planes are aligned in the predetermined direction to form a continuous load-bearing structural plane.

[0140] A secondary structural surface network is established based on the primary structural surfaces. The secondary structural surfaces are mainly composed of medium-sized blocky excavated soil and some fine-grained excavated soil, and their function is to connect the primary structural surfaces, forming a stable skeletal system. The orientation of the secondary structural surfaces should be at a certain angle to the primary structural surfaces, typically 30–60 degrees, to create a mutually supporting and stable structure. The construction of the secondary structural surfaces requires control over particle size distribution and density to ensure effective load transfer without adversely affecting the primary structural surfaces.

[0141] During structural reconstruction, it is also necessary to establish effective contact between particles. Due to their surface characteristics and shape, soft rock slag particles often exhibit significant gaps and loose contact in their natural deposition state. A combination of controlled compaction and vibratory compaction increases the effective contact area between particles and improves the efficiency of contact stress transfer. Controlled compaction refers to using different compaction parameters based on the characteristics of different types of slag to avoid over-compaction that could lead to particle breakage or structural damage. Vibratory compaction involves using low-frequency, high-amplitude vibrations to rearrange particles, eliminate gaps, and increase bulk density.

[0142] To further enhance the continuity and stability of the structural surfaces, an appropriate amount of cementing material needs to be added during the reconstruction process. The selection of cementing material should consider its compatibility with soft rock and slag soil and its environmental friendliness. Cement is the most commonly used cementing material, but its strong alkalinity may have adverse effects on certain types of soft rock. Lime has a good improving effect and is particularly suitable for cohesive soft rock and slag soil. Industrial wastes such as fly ash not only have a certain cementing capacity but can also improve the gradation composition of the slag soil. The dosage of cementing material should be determined according to the type of slag soil and backfilling requirements, generally controlled between 3% and 8% of the total weight of the slag soil.

[0143] Mixture optimization design method:

[0144] Based on the structural reconstruction, mix design optimization is required to achieve the best backfill effect. Mix optimization must consider not only the proportions of different types of waste soil, but also the type and dosage of cementing materials, as well as the use of various additives.

[0145] Mix design optimization first requires establishing a target performance index system. Based on the functional requirements of the backfill area, target values ​​for key parameters such as strength, deformation, and durability indices are determined. Strength indices include compressive strength and shear strength, reflecting the backfill's ability to withstand loads. Deformation indices include compression modulus and Poisson's ratio, reflecting the deformation characteristics of the backfill under load. Durability indices include freeze-thaw resistance and impermeability, reflecting the long-term stability of the backfill.

[0146] Based on the target performance indicators, a multivariate mix design optimization model was established. This model uses the proportions of different types of construction waste as design variables, the target performance indicators as constraints, and economic and environmental benefits as optimization objectives. The range of values ​​and combinations of each design variable were determined using orthogonal experimental design. For the three basic types of construction waste, the proportion of large-lump construction waste is typically controlled between 40% and 60%, the proportion of medium-lump construction waste between 25% and 40%, and the proportion of fine-grained construction waste between 10% and 25%. This mix design ensures both the structural stability of the backfill and good compaction and integrity.

[0147] After determining the basic mix proportions, a detailed design of the cementitious material mix proportions is required. Different types of cementitious materials have significantly different mechanisms of action and effects, necessitating a reasonable combination based on the characteristics and performance requirements of the backfill soil. For argillaceous soft rock backfill soil, a composite cementitious material of lime and cement is recommended, with the lime content controlled at 2%–4% and the cement content at 3%–5%. For sandy soft rock backfill soil, a composite cementitious material of cement and fly ash is recommended, with the cement content controlled at 4%–6% and the fly ash content at 8%–12%. For calcareous soft rock backfill soil, cement can be used alone, with the content controlled at 3%–6%. This detailed mix proportion design ensures the stability and durability of the backfill under different environmental conditions.

[0148] The third main step: layered backfilling and density control

[0149] Dynamic compaction control method based on layered backfilling:

[0150] After completing the modification and mix optimization of the excavated soil, the next stage is layered backfilling and compaction control. The core of this stage lies in ensuring the overall stability and bearing capacity of the backfill through layered backfilling technology combined with dynamic compaction control methods. The purpose of layered backfilling is to control the thickness and compaction of each layer through progressive construction, avoiding settlement and cracking problems caused by excessive backfill thickness at one time.

[0151] The implementation steps for layered backfilling first require determining the thickness of each layer based on the design requirements of the backfill location. Generally, the thickness of each backfill layer should be controlled between 30 and 50 centimeters, with the specific thickness adjusted according to the properties of the soil and the stress conditions of the backfill location. After each layer of backfilling is completed, a compaction test must be conducted to ensure that the design requirements are met before proceeding to the next layer.

[0152] The application of dynamic compaction control methods is crucial during backfilling. This method dynamically adjusts construction parameters by monitoring the compaction and moisture content of the backfill in real time to ensure the quality of each backfill layer. In practice, advanced compaction testing instruments are used to acquire real-time compaction data of the backfill and compare it with design standards. If the compaction is found to be insufficient, the construction process must be adjusted immediately, such as increasing the number of compaction passes or adjusting the moisture content, to ensure the overall quality of the backfill.

[0153] During layered backfilling, it is also necessary to control the moisture content of the backfill material. Excessive moisture content increases the fluidity of the backfill soil, affecting compaction; while insufficient moisture content may lead to poor contact between particles, affecting load-bearing capacity. Therefore, before each layer of backfilling, the moisture content of the backfill soil must be tested, and appropriate watering or drying treatment should be carried out based on the test results to ensure that the moisture content is within the optimal range.

[0154] Adaptability to the construction environment:

[0155] Under soft rock geological conditions, the complexity of the construction environment necessitates highly adaptable construction methods. The physical properties and structural characteristics of soft rock present numerous challenges to the backfilling process, such as variations in the fluidity and bearing capacity of the excavated soil. Therefore, when implementing the "soft rock tunnel excavated soil recycling and backfilling method," flexible adjustments must be made based on the actual construction environment.

[0156] During construction, the backfill material must be monitored regularly to observe its settlement and deformation characteristics. If any abnormalities are found, remedial measures should be taken promptly, such as adding supports or adjusting the backfill material, to ensure construction safety and project quality. Furthermore, the construction team must possess extensive on-site experience and be able to flexibly handle various unforeseen problems based on actual conditions to ensure the smooth progress of construction.

[0157] The above description is merely an exemplary embodiment of the present invention and does not limit the scope of protection of the present invention. Any equivalent structural transformations made based on the technical concept of the present invention and the contents of the specification and drawings of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of protection of the present invention.

Claims

1. A method for muck recycling backfilling for soft rock tunnel, characterized in that, include: Based on the geometric dimensions of the slag, the slag is classified into primary categories: those with a single size A ≥ 300 mm are large block slag, those with a size 50 mm ≤ B < 300 mm are medium block slag, and those with a size C < 50 mm are fine granular slag. Based on the integrity of the slag, the primary slag is divided into secondary slag, where the broken surface is completely along the natural structural surface, the broken surface is partially along the natural structural surface and partially penetrates the rock matrix, and the broken matrix is ​​formed entirely by the broken rock matrix. Based on the lithology of the slag, the secondary classification slag is divided into argillaceous soft rock slag, sandy soft rock slag, and calcareous soft rock slag, thus obtaining graded slag. Pre-treat the graded slag to obtain the target slag; The target excavated soil is used to construct the main structural surface at the backfill location of the soft rock tunnel, and secondary structural surfaces are constructed on the main structural surface. The main structural surface refers to a load-bearing skeleton layer formed by directionally arranged excavated soil particles with complete structural surface characteristics. This can be achieved through a combination of mechanical vibration and manual adjustment, controlling the particle arrangement direction to align with the force direction to form a continuous force transmission path. The secondary structural surface refers to a support network layer formed by filling the gaps between the main structural surface with medium-sized excavated soil blocks. This can be achieved through layered filling and local compaction, enhancing structural stability by establishing multi-angle intersecting contact relationships. The target slag soil after modification treatment to construct the main structural surface and secondary structural surface is used to obtain backfill slag soil; The soft rock tunnel is backfilled in layers using the backfill soil, thus completing the soil recycling and backfilling construction of the soft rock tunnel.

2. The muck recycling and backfilling method for a soft rock tunnel according to claim 1, characterized by, The steps for pre-treating the graded waste soil to obtain the target waste soil include: The graded slag is washed and impurities are removed to obtain slag to be processed; The pretreated slag is crushed and shaped to obtain crushed slag; Adjust the moisture content of the crushed slag to obtain the target slag.

3. The muck recycling and backfilling method for a soft rock tunnel according to claim 2, characterized by, The steps of adjusting the moisture content of the crushed slag to obtain the target slag include: When the graded slag is argillaceous soft rock slag, the moisture content of the crushed slag is adjusted to D, where 12% ≤ D ≤ 18%. When the graded slag is sandy soft rock slag, the moisture content of the crushed slag is adjusted to E, where 8% ≤ E ≤ 15%; When the graded slag is calcareous soft rock slag, the moisture content of the crushed slag is adjusted to F, where 10%≤F≤16%.

4. The muck recycling and backfilling method for a soft rock tunnel according to claim 3, characterized by, The steps for modifying the target waste soil to obtain backfill waste soil include: The argillaceous soft rock slag was modified using lime and cement. The sandy soft rock slag soil was modified using cement and fly ash. The calcareous soft rock slag soil was modified using cement. The target slag soil is modified to obtain the backfill slag soil.

5. The muck recycling backfill method for a soft rock tunnel according to any one of claims 1 to 4, characterized in that, The steps for backfilling the soft rock tunnel in layers using the backfill soil, and completing the soil recycling and backfilling construction of the soft rock tunnel, include: According to the preset backfill thickness for each layer, the soft rock tunnel is backfilled in layers using the backfill soil, thus completing the soil recycling and backfilling construction of the soft rock tunnel; wherein, the backfill thickness is G, 300mm≤G≤500mm.

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