Construction method for reducing loss of shotcrete in super-long underground excavation tunnel

Abstract

This invention provides a construction method for reducing shotcrete loss in ultra-long, underground tunnels, relating to the field of tunnel construction technology in water conservancy engineering. The technical solution provided by this invention systematically reduces shotcrete loss in ultra-long, underground tunnels through a four-dimensional collaborative technology involving optimized drilling and blasting control, upgraded shotcreting equipment, improved concrete mix design, and precise control of process parameters. In this invention, nano-elasticity resistive agents are combined with a layered shotcreting process, significantly reducing the rebound rate compared to traditional methods. Furthermore, the shotcreting parameters are adjusted in real-time based on the rock surface condition, adapting to complex geological conditions. Based on the technical solution provided by this invention, the cost of concrete materials per kilometer of tunnel can be greatly reduced, and the overall construction period can be significantly shortened.

Description

Technical Field

[0001] This invention relates to the field of water conservancy engineering tunnel construction technology, and in particular to a construction method for reducing the loss of shotcrete in ultra-long underground tunnels. Background Technology

[0002] Tunneling is a core component of underground engineering projects such as water conservancy projects and transportation tunnels. Its core support technology (shotcrete process) directly affects project safety, cost, and schedule. In traditional processes, the high rebound rate and large over-excavation of shotcrete have long plagued the industry, especially in soft surrounding rock formations.

[0003] In conventional dry or wet spraying processes, concrete spraying onto the rock surface is prone to rebound due to insufficient kinetic energy or poor adhesion. This rebound is particularly pronounced in tunnel construction in Class III-V surrounding rock, leading to increased concrete wastage and material costs. Furthermore, during drill-and-blast construction, over-excavation depths are generally significant due to geological conditions and deviations in blasting parameters. Over-excavated areas require additional shotcrete filling, further exacerbating material waste. Simultaneously, over-excavation causes stress redistribution in the surrounding rock, potentially inducing localized collapses and threatening construction safety. Traditional construction methods rely on experience to control spraying distance, angle, and layer thickness, lacking scientific quantitative standards. Differences in operator skill can easily result in uneven spraying, creating a "wavy" initial support surface, requiring secondary spraying correction and reducing construction efficiency. In recent years, the industry has attempted to address these issues through material improvements and equipment upgrades, but these methods have all encountered bottlenecks.

[0004] Therefore, based on the goal of promoting green construction and reducing the loss rate of building materials, it is urgent to develop a new construction method to address the problem of shotcrete loss in ultra-long underground tunnels. Summary of the Invention

[0005] This invention provides a construction method for reducing the loss of shotcrete in ultra-long underground tunnels. Through a four-dimensional collaborative technology of optimized drilling and blasting control, upgraded shotcrete equipment, improved concrete mix design, and precise control of process parameters, the loss of shotcrete in ultra-long underground tunnels is systematically reduced.

[0006] The first aspect of this invention provides a construction method for reducing the loss of shotcrete in ultra-long cut-and-cover tunnels, the method comprising:

[0007] Based on preset drilling and blasting parameters, the blasting effect is dynamically controlled through three-dimensional modeling and simulation. The rock mass fracture range under different charge amounts is simulated to determine the target drilling and blasting parameters. The preset drilling and blasting parameters include: contour line blasting hole offset, hole spacing, single hole charge amount, and plugging length. The contour line blasting hole offset is used to offset the contour line blasting hole towards the tunnel center to form a reserved buffer layer.

[0008] Based on the target concrete performance indicators, the material mix proportions of the concrete are determined. The concrete materials include: base materials and nano-elasticity inhibitors.

[0009] Complete the drilling and blasting according to the target drilling and blasting parameters;

[0010] Based on engineering requirements, the construction parameters of the hydraulic wet spraying machine are determined, and the concrete spraying construction is completed based on the construction parameters and the layered spraying process.

[0011] Over-excavation is detected, and rebound material is recycled.

[0012] Optionally, the method further includes: determining the contour line burst hole offset using the following steps:

[0013] For Class III to V surrounding rock, calculate the offset of the blast hole outline according to the offset calculation formula:

[0014] Where is the offset, Q is the charge amount per hole, L is the hole depth, k is the surrounding rock coefficient (0.8 for Class III, 1.0 for Class IV, and 1.2 for Class V), and S is the safety margin.

[0015] Optionally, concrete performance indicators include: slump, initial setting time, and 28-day compressive strength; base materials include: cement, sand, crushed stone, water-reducing agent, accelerator, and water; and based on the target concrete performance indicators, the concrete mix proportions are determined, including:

[0016] The nano-elasticity resist agent and cement were dry-mixed at a ratio of 1:25 to obtain a mixed material.

[0017] The mixed material and other basic materials are mixed and stirred according to the candidate preset ratio of the basic materials to obtain candidate concrete;

[0018] Based on the slump, initial setting time, and 28-day compressive strength of the candidate concrete, the material mix proportions of the concrete that meet the target concrete performance indicators are determined.

[0019] Based on project requirements, the construction parameters for the hydraulic wet spraying integrated machine were determined, including:

[0020] Determine the amount of concrete to be sprayed based on project requirements;

[0021] The model, robotic arm length, and joint degrees of freedom of the hydraulic wet spraying machine are determined based on the amount of concrete sprayed.

[0022] Optionally, the layered spraying process includes:

[0023] The initial spraying layer is completed within 2 hours after the blasting. The thickness of the initial spraying layer is 3-5 cm, and the wind pressure is 0.3 MPa. It is used to seal the rock surface cracks.

[0024] The re-coating layer is completed by spraying in 2 to 3 times to the designed thickness, with a single layer thickness of 5 to 8 cm and an interval of 20 to 30 minutes between layers.

[0025] The finishing layer is completed using a spiral superposition spraying method, with the nozzle advancing spirally at a speed of 0.3m / s to ensure that the surface flatness is ≤3cm / m.

[0026] Optionally, the concrete spraying construction is completed based on the construction parameters and the layered spraying process, including:

[0027] During the spraying process, the spraying distance is determined based on the condition of the rock surface;

[0028] Determine the spraying angle within the preset deviation, and fill the uneven rock surface in a sequence of first filling the concave and then filling the convex;

[0029] Adjust the air pressure in real time according to the spray distance.

[0030] Optionally, the air pressure can be adjusted in real time based on the injection distance and the following formula:

[0031] ;

[0032] Where P is the wind pressure (MPa) and D is the jet distance (m).

[0033] Optionally, the method further includes

[0034] The spray distance is detected using a laser rangefinder;

[0035] The spray angle is detected based on a sensor;

[0036] Upload the detection data to the cloud console.

[0037] Optionally, the over-excavation amount can be detected, including:

[0038] Using a Trimble SX10 3D scanner, the cross-section is scanned after each blasting cycle to generate an over-excavation cloud map;

[0039] The over-excavation volume is calculated using PointCab software, and the over-excavated areas are marked to guide the spraying operation.

[0040] Optionally, the rebound material can be recycled, including:

[0041] A waterproof tarpaulin is laid under the sprayed surface, with an overlap of ≥30cm at the joints. The rebound material is screened to remove particles larger than 10mm, and then mixed into the fresh concrete at a ratio of 10%~15%.

[0042] The amount of concrete used in each truck is tracked by RFID tags, and the actual rebound rate is calculated by combining the amount collected by the canvas.

[0043] The technical solution provided by this invention systematically reduces the amount of shotcrete loss in ultra-long underground tunnels through a four-dimensional collaborative technology that optimizes drilling and blasting control, upgrades shotcrete equipment, improves concrete mix design, and precisely controls process parameters.

[0044] In this embodiment of the invention, the combination of nano-elasticity resist agent and layered spraying process significantly reduces the rebound rate compared to traditional processes.

[0045] In this embodiment of the invention, the injection parameters are adjusted in real time based on the rock surface condition, which can adapt to complex geological conditions.

[0046] Based on the technical solution provided by the embodiments of the present invention, the cost of concrete materials per kilometer of tunnel can be greatly reduced, and the overall construction period can be significantly shortened. Attached Figure Description

[0047] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention 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 these drawings without creative effort.

[0048] Figure 1 This is a flowchart of the construction method for reducing the loss of shotcrete in ultra-long underground tunnels provided in this embodiment of the invention;

[0049] Figure 2 This diagram illustrates a structural schematic of a peripheral hole optimization design according to an exemplary embodiment of the present invention.

[0050] Figure 3 A flow chart of the layered spraying process for a construction method to reduce the loss of shotcrete in ultra-long underground tunnels, provided in an embodiment of the present invention. Detailed Implementation

[0051] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] Currently, among the solutions for optimizing construction methods through material improvement technology, steel fiber reinforced concrete can improve tensile strength and reduce rebound rate, but steel fibers are prone to clumping and clogging the nozzle, and the cost increases; silicon-based nanomaterials can reduce rebound rate, but in actual engineering, the nanoparticles have poor dispersibility and require high precision in dosage control, making large-scale application difficult; although adding excessive amounts of accelerators can shorten the setting time, it will reduce the later strength of concrete and increase the risk of cracking.

[0053] Among the solutions that optimize construction methods through materials, equipment, and processes, automated shotcrete robotic arms can precisely control the spray trajectory, but the equipment procurement cost is high, resulting in insufficient project economics; smooth blasting technology controls over-excavation by densifying the surrounding holes and reducing the amount of explosives, but it is prone to "under-excavation-supplementary blasting" cycles in jointed strata, extending the construction period; although BIM simulation-guided construction can preview the blasting effect, the model accuracy depends on geological survey data and is not adaptable to hidden faults and fissure water.

[0054] Based on this, this invention proposes a construction method to reduce the loss of shotcrete in ultra-long underground tunnels by systematically optimizing drilling and blasting parameters, improving shotcrete technology and material ratio.

[0055] Specifically, such as Figure 1 The diagram illustrates a flowchart of the construction method for reducing shotcrete loss in ultra-long cut-and-cover tunnels provided by an embodiment of the present invention. The method includes the following steps:

[0056] S101, based on preset drilling and blasting parameters, the blasting effect is dynamically controlled through three-dimensional modeling and pre-simulation to simulate the rock mass fracture range under different charge amounts and determine the target drilling and blasting parameters. The preset drilling and blasting parameters include: contour line blasting hole offset, hole spacing, single hole charge amount and plugging length; the contour line blasting hole offset is used to offset the contour line blasting hole towards the tunnel center to form a reserved buffer layer.

[0057] In this embodiment of the invention, based on the design of the contour line blasting hole offset, for Class III to V surrounding rock, according to the offset calculation formula, the peripheral holes (i.e., contour line blasting holes) are offset towards the center of the tunnel to form a "reserved buffer layer".

[0058] This "reserved buffer layer" can reduce the impact of blasting vibrations: During tunnel blasting, the energy generated by the explosion propagates to the surrounding area in the form of vibration waves, disturbing the surrounding rock. The reserved buffer layer weakens the intensity of the blasting vibration waves, reducing their disturbance to the surrounding rock. For example, in hard rock tunnel blasting, without a buffer layer, blasting vibrations may cause microcracks to form and propagate within the surrounding rock. However, with a reserved buffer layer, when the vibration waves propagate to the buffer layer, some of the energy is absorbed and dissipated, reducing the energy transmitted to the surrounding rock. This effectively controls the generation and propagation of microcracks in the surrounding rock, maintaining its integrity and stability.

[0059] This "reserved buffer layer" also prevents over-excavation and collapse of the surrounding rock: If the surrounding holes are drilled and blasted according to the design outline, over-excavation is prone to occur in actual operation due to the uncontrollability of blasting. Over-excavation increases the free surface of the surrounding rock, redistributes stress, increases the risk of instability of the surrounding rock, and may even lead to local collapse. With a reserved buffer layer, even if there is a certain deviation in blasting, excessive over-excavation can be avoided, ensuring the stability of the surrounding rock. For example, in tunnels with weak surrounding rock, over-excavation can easily lead to problems such as rockfall and collapse. The buffer layer can play a certain protective role and buy time and conditions for subsequent support work.

[0060] In subsequent shotcrete operations, the reserved buffer layer provides more reasonable space for shotcrete construction, allowing the shotcrete to cover the surrounding rock surface more evenly and ensuring that the thickness of the shotcrete meets design requirements. Without a buffer layer, the unevenness of the surrounding rock surface caused by blasting may lead to localized areas of excessively thick or thin shotcrete. Areas that are too thin will not meet the support strength requirements, while areas that are too thick will result in material waste. For example, during the initial shotcrete operation, a buffer layer allows the shotcrete to better fill the unevenness of the surrounding rock surface, forming a support layer of uniform thickness. The buffer layer provides a better adhesion base for the shotcrete during spraying, reducing the impact of uneven surrounding rock surfaces and loose rock fragments on the bonding effect. During shotcreting, the concrete can tightly bond with the buffer layer and the surrounding rock, forming a unified support structure and improving the reliability of the support. For example, the continuous and effective bond between the shotcrete and the surrounding rock can better transfer stress and jointly resist external loads.

[0061] The reserved buffer layer reduces the adverse effects of blasting on the surrounding rock, decreasing the probability of safety accidents such as rockfalls and collapses, and providing a safer working environment for subsequent construction personnel and equipment. For example, before shotcrete support is applied after tunnel excavation, the surrounding rock is in a relatively unstable state, and the buffer layer can ensure the safety of construction personnel to a certain extent during this stage. In the long run, the reserved buffer layer reduces additional work such as over-excavation and backfilling, avoids secondary treatment costs due to rock instability, ensures the construction quality of shotcrete, reduces reinforcement costs due to insufficient support later, and effectively controls the overall cost of the project.

[0062] Specifically, in this embodiment of the invention, the following steps can be used to determine the offset of the contour line burst hole:

[0063] For Class III to V surrounding rock, the blasting offset of the outline is calculated according to the offset calculation formula:

[0064] ;

[0065] in, Q is the offset, L is the charge per hole, k is the surrounding rock coefficient (0.8 for Class III, 1.0 for Class IV, and 1.2 for Class V), and S is the safety margin.

[0066] In this embodiment of the invention, by investigating prior over-excavation data, it was found that the over-excavation depth was between 14.7cm and 43.8cm, with an average over-excavation depth of 33.8cm. Based on the geological conditions and the investigation data, it was ultimately decided to shift the peripheral blasting holes (i.e., outline blasting holes) towards the center of the tunnel to form a "reserved buffer layer".

[0067] In this embodiment of the invention, considering the representative geological conditions of the study area and the situation of ultra-long underground tunnels, the offset calculation formula is finally determined by combining theoretical technology.

[0068] Specifically, the engineering overview of the research area involved in the embodiments of the present invention is as follows:

[0069] The Gaotian Tunnel, part of the Guangdong Water Resources Allocation Project in the Beibu Gulf, is constructed using the drill-and-blast method. It is 6.51 km long with a longitudinal slope of 0.38‰, and consists of two work areas and three working faces. The tunnel has a circular cross-section with an inner diameter of 7.1 m and a reinforced concrete lining. This section primarily utilizes the drill-and-blast method, supplemented by open-cut construction. The open-cut section has a circular cross-section with an inner diameter of 7.1 m and employs a reinforced concrete box culvert structure. This open-cut section serves as the entrance and exit for muck removal and material transportation during the construction period. The Gaotian Tunnel's drill-and-blast section, excavating in Class III surrounding rock, has a circular cross-section with an excavation dimension of φ8.1 m, a total length of 3330 m, and accounts for 51.15% of the total length. The excavation cross-section of Class IV and V surrounding rock is horseshoe-shaped, with an excavation size of φ8.5m. Class IV surrounding rock is 1742.175mm, accounting for 26.76%, and Class V surrounding rock is 1336.5mm, accounting for 20.53%.

[0070] The Takada Tunnel primarily utilizes the drill-and-blast method, supplemented by open-cut excavation. Its cut-and-cover construction requires a large amount of shotcrete initial support, and the strata are soft. Traditional shotcrete construction suffers from high rebound rates and high wastage rates, posing risks in terms of construction costs, schedule, and quality. Reducing shotcrete wastage during construction is crucial for the project's cost, schedule, and quality.

[0071] The 6.51km section (GH38+260~GH44+770) of the Gaotian Tunnel in the B3 section of the Guangdong Water Resources Allocation Project in the Beibu Gulf is a key and challenging section for the project, and its construction quality directly affects the project cost. Current estimates, based on collected data, indicate that due to complex geological conditions and limited construction space, the average over-excavation during drilling and blasting reached 30cm, and the average loss of shotcrete was 33.77%, impacting both project quality and cost control.

[0072] In this embodiment of the invention, it is also necessary to determine hole pattern parameters such as hole spacing, single hole charge amount and plugging length. The hole spacing is determined according to the surrounding rock grade, the charge type is φ25mm emulsion blasting material roll, the charge amount is based on empirical values, the hole plugging length is greater than or equal to 20cm, and clay blasting mud is mechanically compacted.

[0073] In this embodiment of the invention, after determining the preset drilling and blasting parameters, the blasting effect can be dynamically controlled through three-dimensional modeling and simulation. A tunnel geological-blasting model is established using Rhino+BlastCAD software to simulate the rock mass fracture range under different charge amounts, ultimately selecting a scheme with an over-excavation amount of less than 15cm.

[0074] In this embodiment of the invention, the blasting effect is dynamically controlled based on three-dimensional modeling and simulation, and the most suitable drilling and blasting parameters are finally selected for use in actual engineering drilling and blasting.

[0075] Figure 2 This diagram illustrates a schematic representation of the peripheral hole optimization design according to an exemplary embodiment of the present invention. The offset calculation formula yields the following values: Class V surrounding rock: K=1.2, Δ=1.2×0.25 / 3 +3=3.1cm, rounded to 3cm. Further, the hole network parameters, including hole spacing, charge quantity, and plugging length, are determined based on the surrounding rock grade: Peripheral hole spacing: Class III surrounding rock 40cm, Class IV 35cm, Class V 30cm; Charge structure: continuous uncoupled charge (charge density 0.25kg / m³); Pluging length: ≥20cm (mechanically compacted using clay gunning mud).

[0076] During the dynamic control of blasting effects, over-excavation monitoring is carried out. The cross-section after blasting is scanned using a Trimble SX10 3D scanner to generate an over-excavation cloud map. Then, the average over-excavation depth is calculated based on the number of detection points and the over-excavation amount corresponding to each detection point. If the average over-excavation depth is less than or equal to 15cm, the construction target is met.

[0077] S102, Based on the target concrete performance indicators, determine the material mix ratio of the concrete, wherein the concrete materials include: base materials and nano-elasticity inhibitors.

[0078] Nanoparticles of elastic modifiers have extremely small particle sizes, allowing them to be uniformly dispersed within the micropores of concrete. These nanoparticles can fill the tiny pores formed during cement hydration, optimizing the internal microstructure of the concrete and making it more compact. For example, between cement hydration products, nanoparticles act like tiny "wedges," enhancing the interaction forces between particles, thereby effectively improving the compressive strength of the concrete and enabling tunnel linings to withstand greater pressure from the surrounding rock.

[0079] Ordinary concrete is brittle and prone to cracking under impact or dynamic loads. Nano-bearing elastic agents can chemically react with cement hydration products to form a flexible interfacial transition zone. When concrete is subjected to external forces, these flexible zones can absorb energy, preventing rapid crack propagation and giving the concrete better toughness. For example, in the event of sudden dynamic loads such as earthquakes, concrete with added nano-bearing elastic agents can effectively delay crack propagation and maintain the integrity of the tunnel structure.

[0080] Nano-scale elastic modifiers typically contain multiple components. Common ones include nanospheres, zeolite powder, and nano-calcium silicate. Some formulations also contain nano-silica, which can react with calcium ions in the cement matrix to generate more calcium silicate hydrate, increasing concrete strength. Additionally, magnesium fluorosilicate may be a component; it reacts with free calcium in concrete to form calcium silicate and calcium fluoride, filling capillary pores and enhancing surface structural strength and wear resistance. This improves the adhesion and bonding of concrete, reduces rebound during shotcrete application, and increases construction efficiency and material utilization.

[0081] In this embodiment of the invention, the concrete performance indicators include: slump, initial setting time, and 28-day compressive strength; the base materials include: cement, sand, crushed stone, water-reducing agent, quick-setting agent, and water; and step S102 includes:

[0082] The nano-elasticity inhibitor was dry-mixed with cement at a ratio of 1:25 to obtain a mixed material.

[0083] The mixed material and other basic materials are mixed and stirred according to the candidate preset ratio of the basic materials to obtain candidate concrete.

[0084] In this embodiment of the invention, the weight ratio of each cubic meter of concrete material is initially determined as a candidate preset ratio for the base material based on engineering specifications and requirements.

[0085] Based on the slump, initial setting time, and 28-day compressive strength of the candidate concrete, the material mix proportions of the concrete that meet the target concrete performance indicators are determined.

[0086] In this embodiment of the invention, a silane coupling agent is used to modify nano-silica (particle size 50~80nm, specific surface area ≥200m² / g).

[0087] In this embodiment of the invention, relevant parameters of the base material, nano-elastic resist agent and steel fiber are analyzed and extracted, and then performance tests are conducted. Finally, it is determined that the nano-elastic resist agent and cement are dry-mixed at a ratio of 1:25 to obtain a mixed material.

[0088] Specifically, adding nano-bullet-damping agents to concrete increases the material's toughness, improving its bulletproof and explosion-proof properties. It forms a dense structure, increasing overall tensile strength and extending the concrete's service life. It significantly reduces permeability, enhancing waterproofing. It also makes the concrete denser, improving its wear resistance and corrosion resistance.

[0089] The use of steel fibers in concrete can reduce slump loss and improve its fluidity. The addition of steel fibers can significantly improve the tensile, flexural, and shear strength of concrete, making it less prone to cracking and fracture when subjected to complex external forces.

[0090] In the comparative test, the dosage of nano-elasticity agent was 32 kg / m³, and the dosage of steel fiber was 40 kg / m³. The resulting concrete compressive strengths were 31.6 MPa and 30 MPa, respectively, and the rebound rates were 7.2% and 12%, respectively.

[0091] Therefore, in this embodiment of the invention, a nano-elastic resist agent was ultimately selected to prepare the modified concrete.

[0092] In this embodiment of the invention, the material weight ratio per cubic meter of concrete is initially determined as follows, based on specifications and requirements:

[0093] Cement : Water : Crushed stone : Water-reducing agent : Air-entraining agent : Quick-setting agent Sand = 429kg : 193kg : 912kg : 774kg : 858kg : 2.574kg : 30.03kg = 1 : 0.45 : 2.12 : 1.80 : 0.020 : 0.0060 : 0.07.

[0094] In this embodiment of the invention, the concrete mix with the initially determined mix proportion was tested, and the results met the requirements: good fluidity, cohesiveness, and water retention; after trial mixing, the wet apparent density was measured to be 2300 kg / m³, and the slump was 193 mm, indicating that no adjustment of workability was needed. The preliminary selected C25 mix proportion is shown in the table below:

[0095]

[0096] The performance results of the trial concrete mixed according to the mix proportions in the table above are shown in the following table:

[0097]

[0098] The mechanical properties obtained after seven days of curing are shown in the table below:

[0099]

[0100] The final selected combinations are as follows:

[0101]

[0102] In this embodiment of the invention, the mixed materials (nano-based elastic modifier and cement) and other basic materials (aggregates and admixtures) can be simultaneously added to a mixer for mixing according to the candidate preset ratio of the basic materials, and the aggregates and admixtures are mixed to obtain candidate concrete. That is, candidate concrete can be obtained by conducting experiments first, and the optimal material ratio can be determined based on the slump, initial setting time and 28-day compressive strength of the candidate concrete, so as to obtain the final concrete material ratio for actual engineering application.

[0103] In this embodiment of the invention, the concrete mix with the initial mix proportion can be measured, and the results are required to meet the requirements of good fluidity, cohesiveness, and water retention. After curing for 7 days, the mechanical properties of the concrete are measured, and the mix proportion is finally selected after meeting the requirements.

[0104] In this embodiment of the invention, experiments can also be conducted in actual engineering studies based on the selected final concrete material mix ratio to further analyze the concrete performance.

[0105] In this embodiment of the invention, in order to verify whether the method of incorporating nano-bulk resist agent meets the standard, different areas were selected in the tunnel and 5 cycles of test were carried out. The first 3 cycles were incorporating nano-bulk resist agent, and the last 2 cycles were incorporating nano-bulk resist agent. The average rebound rate was compared by actual comparison.

[0106] For example, in this embodiment of the invention, based on the selection of the above-mentioned mix ratio, a 14-meter-long area from GH39+260 to GH39+274 was selected on the upper step of the Takata Tunnel, and a total of 5 cycles were conducted for the test. The first 3 cycles did not contain nano-bulk resist agent, while the last 2 cycles contained nano-bulk resist agent.

[0107] Actual comparisons showed that the average rebound rate was 33.77% for products without nano-resistive agents and 13.97% for products with nano-resistive agents, a difference of 19.8%. See the table below for detailed data:

[0108]

[0109] S103, complete the drilling and blasting according to the target drilling and blasting parameters.

[0110] In this embodiment of the invention, the drilling and blasting of an ultra-long underground tunnel is completed according to the optimal target drilling and blasting parameters determined by simulation in step S101.

[0111] S104. Based on engineering requirements, determine the construction parameters of the hydraulic wet spraying machine, and complete the concrete spraying construction based on the construction parameters and the layered spraying process.

[0112] The most important factor in selecting shotcrete equipment for tunnel construction is that the designed spraying volume (m³ / h) must meet or exceed the average spraying volume required by the project, while also considering equipment utilization. Based on this, the size of the equipment, as well as the size and length of the robotic arm, are determined according to the cross-sectional dimensions of the construction site. Finally, the durability and economy of the equipment are considered. In this embodiment of the invention, a hydraulic wet shotcrete machine is selected. First, the calculated average spraying volume reaches 23-24 m³ / h. Considering that the perfect construction conditions for meeting the designed spraying volume cannot be achieved during construction, it is necessary to round up. Therefore, an equipment with a designed spraying volume of 30 m³ / h is selected. Second, the tunnel cross-section has a bottom width of 5m and a height of 8m. The robotic arm must be able to spray concrete onto the work surface at a 90°-70° angle (full 90° is optimal) within this cross-section, and its length and joint freedom must also meet the requirements.

[0113] Specifically, based on project requirements, the construction parameters of the hydraulic wet spraying integrated machine are determined, including:

[0114] Determine the amount of concrete to be sprayed based on project requirements;

[0115] The model, robotic arm length, and joint degrees of freedom of the hydraulic wet spraying machine are determined based on the amount of concrete sprayed.

[0116] In this embodiment of the invention, the amount of concrete sprayed can be determined according to actual engineering needs, thereby determining the model, robotic arm length, and joint degrees of freedom of the hydraulic wet spraying machine.

[0117] In this embodiment of the invention, it is necessary to optimize the spraying equipment and process parameters to ensure that the rebound loss is controlled within 15%.

[0118] Specifically, the required shotcrete construction efficiency is greater than 25 m³ / h. In addition, based on the actual needs of the site construction, the YL3016 automatic feeding hydraulic wet shotcrete machine is selected.

[0119] Specifically, the layered spraying process includes:

[0120] The initial spraying layer is completed within 2 hours after the blasting. The thickness of the initial spraying layer is 3-5 cm, and the wind pressure is 0.3 MPa. It is used to seal the rock surface cracks.

[0121] The re-coating layer is completed by spraying in 2 to 3 times to the designed thickness, with a single layer thickness of 5 to 8 cm and an interval of 20 to 30 minutes between layers.

[0122] The finishing layer is completed using a spiral superposition spraying method, with the nozzle advancing spirally at a speed of 0.3m / s to ensure that the surface flatness is ≤3cm / m.

[0123] In this embodiment of the invention, the initial spraying layer process is designed to be completed within 2 hours of blasting and is used to seal rock surface fissures; the secondary spraying layer process is designed to be sprayed in 2-3 times to the designed thickness, with a single layer thickness of 5-8cm and an interval of 20-30 minutes between layers (based on the "sweating" of the concrete surface as the criterion); the finishing layer process is designed to finally adopt the "spiral superposition spraying method", which advances spirally at a certain speed to ensure that the surface flatness is ≤3cm / m.

[0124] Specifically, the nozzle propels itself in a spiral motion at a speed of 0.3 m / s.

[0125] Figure 3 This invention illustrates a flow chart of a layered spraying process for a construction method to reduce shotcrete loss in ultra-long cut-and-cover tunnels, as provided in an embodiment of the present invention. Specifically, in this embodiment, the layered spraying process is carried out according to the following steps:

[0126] Preliminary preparations: First, complete the construction preparations, treat the sprayed surface, embed the spray layer thickness markers, and at the same time, inspect the incoming raw materials, select the concrete mix ratio, ensure that the equipment is in place and connect the ventilation, water and electricity, and test the machine to prepare all conditions for the spraying operation.

[0127] Initial spraying: The concrete is automatically metered and mixed, and the mixer truck transports the sprayed material to carry out the initial spraying operation. This step is the first time to establish a concrete layer on the sprayed surface.

[0128] Intermediate process: After the initial spraying, steel mesh is embedded to provide a structurally reinforced foundation for subsequent spraying.

[0129] Re-spraying and related adjustments: Carry out the re-spraying concrete operation. If additional spraying or mix ratio adjustment is required during the process, perform the corresponding operations to ensure the spraying effect. Afterwards, carry out the finishing layer operation to improve the concrete surface.

[0130] Final inspection: A final quality inspection is conducted to confirm that the quality of each step meets the standards. The process is then completed. Each step is interconnected, and the quality control of tunnel shotcrete construction is achieved through layered spraying and timely adjustments.

[0131] In this embodiment of the invention, a layered spraying process is adopted. During layered spraying, each layer of concrete is relatively thin, allowing the sprayed concrete to better fill the unevenness of the sprayed surface and the tiny pores of the previous layer of concrete. For example, after the initial spraying, the re-sprayed concrete can penetrate into the tiny gaps of the initial sprayed layer, making the overall concrete more compact, thereby effectively improving the compressive and shear strength of the concrete and better withstanding the pressure of the surrounding rock.

[0132] Applying excessively thick layers of concrete in a single application can lead to shrinkage cracking due to the large accumulation of heat from cement hydration and the resulting temperature difference between the inside and outside of the concrete. Layered spraying reduces the thickness of each layer, ensures more even distribution of heat from cement hydration, and minimizes the shrinkage stress generated during the setting process of each layer. Subsequent sprayed layers can also constrain the shrinkage deformation of the previous layer to a certain extent, greatly reducing the possibility of cracks caused by shrinkage and ensuring the integrity of the concrete structure.

[0133] Layered spraying allows construction workers to more easily control the smoothness and thickness of the shotcrete. By setting thickness markers before each layer is sprayed, the thickness of each layer can be precisely controlled, thus ensuring that the final shotcrete layer achieves the design requirements for smoothness and thickness, and improving the construction quality of the tunnel lining.

[0134] During the layered spraying process, after each layer is completed, the construction personnel can promptly check the quality of the sprayed concrete, such as whether there are any missed areas or excessive concrete rebound, and can make timely repairs and adjustments. If localized areas of non-compacted concrete are found in a certain layer, measures such as increasing the spraying volume can be taken to compensate for this during the construction of subsequent sprayed layers, preventing the problems from accumulating and affecting the overall construction quality.

[0135] The process involves initial spraying, followed by embedding a steel mesh, and then spraying concrete again. This layered spraying technique allows the steel mesh to be better encapsulated in concrete, ensuring good adhesion and bond between the mesh and the concrete. The steel mesh and concrete work together to withstand external forces, enhancing the overall load-bearing capacity and deformation resistance of the tunnel lining.

[0136] For different surrounding rock conditions, the layered shotcrete process allows for flexible adjustment of shotcrete parameters and sequence. In soft surrounding rock, initial shotcreting can promptly seal the rock to prevent weathering and loosening, and then repeated shotcreting can gradually increase the concrete thickness to improve support strength. In hard surrounding rock, the thickness and number of layered shotcretes can be reasonably controlled according to the rock surface condition after blasting to ensure support effectiveness.

[0137] Specifically, in this embodiment of the invention, the concrete spraying construction is completed based on the construction parameters and the layered spraying process, including:

[0138] During the spraying process, the spraying distance is determined based on the condition of the rock surface.

[0139] Specifically, if the rock surface is dry, the spraying distance should be controlled at 1.0-1.2m; if the rock surface is wet, the spraying distance should be controlled at 0.8-1.0m; if the rock surface has linear water flow, the spraying distance should be controlled at 0.6-0.8m.

[0140] The spraying angle is determined within the preset deviation, and the uneven rock surface is filled in the order of first filling the concave and then filling the convex.

[0141] Specifically, maintain a 90° vertical spray angle (allowing ±5° deviation) and fill uneven rock surfaces in a "concave first, convex later" sequence.

[0142] Adjust the air pressure in real time according to the spray distance.

[0143] In this embodiment of the invention, the wind pressure is adjusted in real time according to the following formula:

[0144] ;

[0145] Where P is the wind pressure (MPa) and D is the jet distance (m).

[0146] In this embodiment of the invention, during construction, the spraying distance and spraying angle can also be monitored and controlled in real time based on a cloud controller, specifically including:

[0147] The spray distance is detected using a laser rangefinder;

[0148] The spray angle is detected based on a sensor;

[0149] Upload the detection data to the cloud console.

[0150] In this embodiment of the invention, a laser rangefinder and integrated sensors can be installed on the hydraulic wet spraying machine to complete the intelligent upgrade of the equipment and realize the real-time monitoring of construction status parameters (spraying distance and spraying angle).

[0151] S105 is used to detect over-excavation and recycle the rebound material.

[0152] In this embodiment of the invention, the detection of over-excavation includes:

[0153] Using a Trimble SX10 3D scanner, the cross-section is scanned after each blasting cycle to generate an over-excavation cloud map;

[0154] The over-excavation volume is calculated using PointCab software, and the over-excavated areas are marked to guide the spraying operation.

[0155] In this embodiment of the invention, the recycling of rebound material includes:

[0156] A waterproof tarpaulin is laid under the sprayed surface, with an overlap of ≥30cm at the joints. The rebound material is screened to remove particles larger than 10mm, and then mixed into the fresh concrete at a ratio of 10%~15%.

[0157] The amount of concrete used in each truck is tracked by RFID tags, and the actual rebound rate is calculated by combining the amount collected by the canvas.

[0158] The calculation formula is:

[0159]

[0160] in, Rebound rate (%) The weight of the rebound material is in kg. This represents the actual weight of the sprayed concrete (kg).

[0161] Although preferred embodiments of the present invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present invention.

[0162] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0163] The above provides a detailed description of a construction method for reducing the loss of shotcrete in ultra-long underground tunnels. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the invention. Therefore, the content of this specification should not be construed as a limitation of the invention.

Claims

1. A construction method for reducing the loss of shotcrete in ultra-long cut-and-cover tunnels, characterized in that, The method includes: Based on preset drilling and blasting parameters, the blasting effect is dynamically controlled through three-dimensional modeling and simulation. The rock mass fracture range under different charge amounts is simulated to determine the target drilling and blasting parameters. The preset drilling and blasting parameters include: contour line blasting hole offset, hole spacing, single hole charge amount, and plugging length. The contour line blasting hole offset is used to offset the contour line blasting hole towards the tunnel center to form a reserved buffer layer. Based on the target concrete performance indicators, the material mix proportions of the concrete are determined. The concrete materials include: base materials and nano-elasticity inhibitors. Complete the drilling and blasting according to the target drilling and blasting parameters; Based on engineering requirements, the construction parameters of the hydraulic wet spraying machine are determined, and the concrete spraying construction is completed based on the construction parameters and the layered spraying process. Over-excavation is detected, and rebound material is recycled. The concrete performance indicators include slump, initial setting time, and 28-day compressive strength. The base materials include cement, sand, crushed stone, water-reducing agent, accelerator, and water. Based on the target concrete performance indicators, the concrete mix proportions are determined, including: The nano-elasticity resist agent and cement were dry-mixed at a ratio of 1:25 to obtain a mixed material. The mixed material and other basic materials are mixed and stirred according to the candidate preset ratio of the basic materials to obtain candidate concrete; Based on the slump, initial setting time, and 28-day compressive strength of the candidate concrete, the material mix proportions of the concrete that meet the target concrete performance indicators are determined. Based on project requirements, the construction parameters for the hydraulic wet spraying integrated machine were determined, including: Determine the amount of concrete to be sprayed based on project requirements; The model, robotic arm length, and joint degrees of freedom of the hydraulic wet spraying machine are determined based on the amount of concrete sprayed. The layered spraying process includes: The initial spraying layer is completed within 2 hours after the blasting. The thickness of the initial spraying layer is 3-5 cm, and the wind pressure is 0.3 MPa. It is used to seal the rock surface cracks. The re-coating layer is completed by spraying in 2 to 3 times to the designed thickness, with a single layer thickness of 5 to 8 cm and an interval of 20 to 30 minutes between layers. The finishing layer is completed using a spiral superposition spraying method, with the nozzle advancing spirally at a speed of 0.3m / s to ensure that the surface flatness is ≤3cm / m.

2. The construction method for reducing shotcrete loss in ultra-long cut-and-cover tunnels according to claim 1, characterized in that, The method further includes determining the contour line burst hole offset using the following steps: For Class III to V surrounding rock, calculate the offset of the blast hole outline according to the offset calculation formula: ； in, Q is the offset, L is the charge per hole, k is the surrounding rock coefficient (0.8 for Class III, 1.0 for Class IV, and 1.2 for Class V), and S is the safety margin.

3. The construction method for reducing shotcrete loss in ultra-long cut-and-cover tunnels according to claim 1, characterized in that, Concrete spraying is completed based on the aforementioned construction parameters and layered spraying process, including: During the spraying process, the spraying distance is determined based on the condition of the rock surface; Determine the spraying angle within the preset deviation, and fill the uneven rock surface in a sequence of first filling the concave and then filling the convex; Adjust the air pressure in real time according to the spray distance.

4. The construction method for reducing shotcrete loss in ultra-long cut-and-cover tunnels according to claim 3, characterized in that, The method further includes: The spray distance is detected using a laser rangefinder; The spray angle is detected based on a sensor; Upload the detection data to the cloud console.

5. The construction method for reducing shotcrete loss in ultra-long cut-and-cover tunnels according to claim 3, characterized in that, Adjust the air pressure in real time according to the injection distance and the following formula: ； Where P is the wind pressure (MPa) and D is the jet distance (m).

6. The construction method for reducing shotcrete loss in ultra-long cut-and-cover tunnels according to claim 1, characterized in that, The over-excavation volume is detected, including: Using a Trimble SX10 3D scanner, the cross-section is scanned after each blasting cycle to generate an over-excavation cloud map; The over-excavation volume is calculated using PointCab software, and the over-excavated areas are marked to guide the spraying operation.

7. The construction method for reducing shotcrete loss in ultra-long cut-and-cover tunnels according to claim 1, characterized in that, Recycling of spring-loaded materials includes: A waterproof tarpaulin is laid under the sprayed surface, with an overlap of ≥30cm at the joints. The rebound material is screened to remove particles larger than 10mm, and then mixed into the fresh concrete at a ratio of 10%~15%. The amount of concrete used in each truck is tracked by RFID tags, and the actual rebound rate is calculated by combining the amount collected by the canvas.

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