Construction method of replacement core soil excavation shaft

Abstract

The application provides a construction method of replacing core soil excavation shaft, adopts inverted shaft wall method to construct the shaft, and each layer of earthwork is excavated twice, first, half-section earthwork is excavated, 3mm-5mm plain concrete is sprayed, steel mesh is hung, half-section I18 steel frame is erected, vertical connecting rib is welded, steel mesh is hung, and concrete is sprayed; then, the other half-section earthwork is excavated, the other half of the shaft primary support is constructed, the shaft primary support is closed into a ring, then the next layer of earthwork is excavated, and the next cycle is entered, the excavation footage of each layer of earthwork in the range of miscellaneous fill is 0.5m, and the excavation footage of each layer of earthwork after entering the medium weathered limestone is 1m; after the shaft is excavated to the base, the bottom plate steel bar should be bound in time, and the bottom plate concrete is poured. Through the technical scheme, the construction progress is accelerated, the construction period is shortened, and the construction efficiency is improved; the degree of mechanization is high, the manual work is reduced, and the labor intensity of the operators is reduced; the significant influence of the blasting method on the surrounding environment is avoided.

Description

Technical Field

[0001] This invention relates to the field of shaft excavation technology, and more particularly to a construction method for excavating shafts by replacing core soil. Background Technology

[0002] With the deepening research and application of underground engineering, the application scope of vertical shafts is becoming increasingly wide. Traditional vertical shaft construction uses the ordinary shaft sinking method, which is slow in excavation, has low mechanization, poses high safety risks to construction personnel, and has high construction costs. Highly mechanized and intelligent vertical shaft tunneling machines are a development trend, enabling unmanned underground construction, intelligent operation and monitoring, high construction precision, and fast construction speed.

[0003] In existing technologies, blasting can be used for suburban projects under medium-hard rock geological conditions, but this method is severely limited in urban areas with heavy traffic and proximity to important buildings; ordinary rock drilling methods have too low construction efficiency, which seriously restricts the progress of the project. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a construction method for excavating vertical shafts by replacing core soil.

[0005] This invention is achieved through the following technical solution: a construction method for excavating a vertical shaft with replaced core soil, specifically including the following steps: Step S1: Measure and mark the core sampling point, use a Zoomlion ZR420 rotary drilling rig to drill cores within the excavation area of ​​the working well, and backfill the original crushed stone at the core sampling point; Step S2: Constructing the lock-in ring beam: The construction of the lock-in ring beam includes surveying and setting out, earthwork excavation, rebar tying, formwork support, and concrete pouring. The lock-in ring beam foundation pit is 9.5m long and 7.5m wide. It is excavated by manual labor and excavators, with the excavation depth reaching 100mm below the bottom elevation of the lock-in ring beam. Step S3: The truck crane installs a bucket to lift and remove the slag; Step S4: Once the concrete strength of the lock ring beam reaches 70% of the design strength, the shaft excavation can begin. The shaft is constructed using the inverted shaft wall method. Each layer of earthwork is excavated in two stages. First, half of the earthwork is excavated, 3mm-5mm of plain concrete is sprayed, steel mesh is installed, I18 steel frame is erected for half of the shaft, vertical connecting bars are welded, steel mesh is installed, and sprayed concrete is applied. Then, the other half of the earthwork is excavated, and the initial support for the other half of the shaft is constructed to close the initial support into a ring. Then, the next layer of earthwork is excavated, and the next cycle begins. Within the miscellaneous fill area, the excavation advance for each layer of earthwork is 0.5m. After entering the moderately weathered limestone, the excavation advance for each layer of earthwork is 1m. After the shaft is excavated to the foundation, the bottom slab reinforcement should be tied and the bottom slab concrete should be poured in a timely manner. Step S5: Construction of the shaft and the gate: Excavate downwards to the front of the gate arch, and reinforce three steel frames; continue to excavate the shaft downwards, and add two corner braces within the gate demolition area. After the construction at the bottom of the shaft is completed, backfill the soil to the gate construction site. Draw the gate excavation outline on the shaft wall according to the design position. Apply φ42, l=3m, t=3.25mm advanced small guide pipe grouting at a spacing of 400mm on the outer outline of the top initial support. After the grout solidifies and reaches the design strength, remove the concrete of the inner shaft wall of the gate section in sections, in the order of first the arch, then the side walls, and finally the bottom plate. After the first steel frame is erected at the shaft wall and the φ20 connecting bar is reliably welded to the shaft wall after cutting, the tunnel is excavated. Step S6: Shaft excavation and transportation. The excavated soil inside the tunnel is transported by electric tricycles measuring 2.3*1.1*1 meters. Once transported to the shaft opening, it is lifted out by a truck crane with a 1.2*1*0.8m bucket. As a preferred option, the formwork support template in step S2 is made of bamboo plywood, the support adopts a full-span scaffolding support system, the concrete pouring height is 1.3 meters, the horizontal upright spacing is 0.6 meters, and the formwork is supported by steel pipes for horizontal bracing.

[0006] As a preferred option, in step S2, the concrete pouring is as follows: the interlocking ring concrete is poured in one go; when pouring the concrete, steel grid connecting bars are reserved to ensure the excavation of the well body; φ42mm steel pipes are pre-embedded; the concrete is poured using a 5cm vibrator; the interlocking ring is poured in one go, in layers, with the thickness of each layer controlled between 300mm and 500mm, and the height difference between the concrete pouring surfaces on both sides does not exceed 0.5 meters.

[0007] As a preferred option, in step S4, the I18 I-beam steel frames are welded together with φ20 longitudinal connecting bars, with a circumferential spacing of 1m between the connecting bars; during shaft excavation, grooves for connecting plates are reserved at each connection point of the steel frame, and wooden wedges are driven into the grooves during initial shotcreting; the steel frame is installed according to the design position, and during the installation process, if there is a large gap between the steel frame and the initial shotcrete layer, it should be wedged with precast concrete blocks every 2m, and the back of the steel frame is filled with shotcrete; the longitudinal connection of the steel frame uses steel bars with a circumferential spacing of 1m, arranged in a staggered quincunx pattern; the shotcrete is applied in layers, starting from the arch foot or wall corner and spraying upwards.

[0008] As a preferred option, the vertical connecting ribs in step S4 are directly welded to the I-beam steel frame as a whole, and the welding is performed at the intersection of the vertical connecting ribs and the main ribs of the I-beam steel frame.

[0009] As a preferred option, the steel mesh in step S4 is made of Grade I φ8 steel bars. The steel mesh is laid along the undulations of the initial sprayed surface, tied and fixed to the components constructed in the early stage, and then the steel bars are welded into a mesh with an overlap length of 1 to 2 grids.

[0010] As a preferred option, when using wet spraying technology for shotcrete in step S4, the nozzle should be perpendicular to the sprayed surface, and the distance between the nozzle and the sprayed surface should be 1.5 to 2.0 m. The nozzle should be moved continuously and slowly to ensure uniform spray thickness. When there are large depressions on the rock surface, the depressions should be leveled first. The spraying operation should be carried out in sections and pieces in sequence, and the spraying order should be from bottom to top. The length of each section should not exceed 6 m. When spraying in layers, the thickness of each spray should not be less than 40 mm. The subsequent layer should be sprayed after the previous layer of concrete has set. If spraying is carried out 1 hour after the final setting, the surface of the sprayed layer should be cleaned with water first. The thickness of each spray of re-sprayed concrete is 50 to 100 mm for the arch and 70 to 150 mm for the sidewalls.

[0011] Furthermore, the rebound rate of shotcrete is: no more than 15% for sidewalls and no more than 25% for arches.

[0012] As a preferred option, two corner braces are added within the scope of the horse-head gate demolition in step S5; when the horse-head gate is demolished to enter the tunnel, the steel arch frame should be cut in sections according to the step sequence, one steel frame for the tunnel should be erected, and welded to the steel frame cut off at the tunnel entrance to ensure reliable connection, and three steel frames should be closely arranged; the longitudinal connecting bars of the steel frame should be densified and arranged at 0.5m in the circumferential direction.

[0013] By employing the above technical solutions, this invention has the following beneficial effects compared to existing technologies: 1. It accelerated the construction progress, shortened the construction period, and improved construction efficiency; 2. High degree of mechanization reduces manual labor and lowers the labor intensity of operators; 3. It avoids the significant impact of blasting methods on the surrounding environment.

[0014] Additional aspects and advantages of the invention will become apparent in the following description or may be learned by practice of the invention. Attached Figure Description

[0015] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the process of the present invention; Figure 2 This is a flowchart of the construction process for the lock-joint ring beam. Figure 3 This is a plan view of the lock ring beam; Figure 4 This is a schematic diagram of the formwork support system for the lock-joint ring beam. Figure 5 This is a schematic diagram of the replacement method construction; Figure 6 A construction sequence diagram for the horse-head gate; Figure 7Diagram showing the arrangement of corner bracing at the horse-head gate. Detailed Implementation

[0016] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0017] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0018] The following is combined Figures 1 to 7 The construction method of excavating a vertical shaft for replacing core soil according to an embodiment of the present invention will be described in detail.

[0019] This invention proposes a construction method for excavating a vertical shaft with replaced core soil, specifically including the following steps: Step S1: As Figure 1 As shown, the measurement and layout were carried out at the core drilling site. A Zoomlion ZR420 rotary drilling rig was used to drill cores within the excavation area of ​​the working well. The original crushed stone was backfilled at the core drilling site. Step S2: Construct the lock ring beam: (e.g.) Figure 2 As shown, the construction of the interlocking ring beam includes surveying and setting out, earthwork excavation, rebar tying, formwork erection and support, and concrete pouring. The foundation pit for the interlocking ring beam is 9.5m long and 7.5m wide, and is excavated manually in conjunction with an excavator, with the excavation depth reaching 100mm below the bottom elevation of the interlocking ring beam. The excavation cross-section is as follows. Figure 3 .

[0020] like Figure 4 As shown, the formwork support is made of bamboo plywood, and the support adopts a full-span scaffolding support system. The stress system is mainly supported by the counter-bracing. The concrete pouring height is 1.3 meters, the horizontal upright spacing is 0.6 meters, and steel pipe horizontal bracing is used behind the formwork to avoid uneven stress on the formwork. For details of the support system, please refer to the schematic diagram of the lock ring formwork support system.

[0021] The allowable deviations for template installation are shown in the table below.

[0022] Table 1. Allowable Deviations for Template Installation Concrete Pouring: The interlocking ring concrete is poured in one go; during concrete pouring, steel grating connecting bars are reserved to ensure the excavation of the well body; φ42mm steel pipes are pre-embedded for welding the wellhead protective railing. A 5cm vibrator is used for concrete pouring, following the principle of quick insertion and slow withdrawal; the interlocking ring is poured in one go, but in layers, with each layer's thickness controlled between 300mm and 500mm, and the time between layers is minimized to avoid cold joints. During concrete pouring, the height difference between the concrete pouring surfaces on both sides is ensured not to exceed 0.5 meters to avoid excessive deviation causing overall shifting of the scaffolding support system.

[0023] The normal vibration time at each vibration point should be such that the concrete surface shows a layer of slurry and does not sink. When using an immersion vibrator, the distance between vibration points for ordinary concrete should not be greater than 1.5 times the radius of action of the vibrator, and collisions with reinforcing bars, formwork, embedded parts and waterproofing membranes should be avoided. The depth to which the vibrator sinks into the concrete should not be less than 50mm.

[0024] Step S3: The truck crane is used to install a bucket to lift and remove the slag; after drilling and core sampling using a rotary drilling rig (Zoomlion ZR420, 1000mm diameter), the holes are temporarily backfilled. After backfilling, the edges of the foundation pit and areas not broken by the rotary drilling rig are crushed using a drilling rig in conjunction with a small crusher. The amount of earthwork excavated each time is not large. The earthwork inside the tunnel is transported by electric tricycles (2.3*1.1*1m). The earthwork is then lifted and removed from the shaft opening by a truck crane with a bucket of 1.2*1*0.8m. Strict measures are taken to prevent slag from falling from the shaft opening.

[0025] Step S4: Once the concrete strength of the lock ring beam reaches 70% of the design strength, the shaft excavation can begin. Due to the small cross-section of the vertical shaft (7.5m × 5.5m) and its location primarily in moderately weathered limestone layers with an average rock strength of approximately 75MPa, large-scale mechanical demolition and blasting are not feasible. To ensure the project schedule, a rotary drilling rig (Zoomlion ZR420, 1000mm diameter) was used for core drilling, followed by temporary backfilling of the boreholes. After backfilling, the edges of the pit and areas not yet demolished by the rotary drilling rig were broken using a drilling rig in conjunction with a small crusher, and then the inverted shaft wall method was employed. The construction shaft is completed in two stages, with each layer of earthwork excavated in two phases. First, half of the earthwork is excavated, followed by 3mm-5mm of plain concrete spraying, installation of steel mesh, erection of the half-section I18 I-beam steel frame, welding of vertical connecting bars, installation of steel mesh, and spraying of concrete. Then, the other half of the earthwork is excavated, and the initial support for the other half of the shaft is constructed to close the shaft into a ring. Then, the next layer of earthwork is excavated, and the next cycle begins. Within the miscellaneous fill area, the excavation advance for each layer of earthwork is 0.5m, and after entering the moderately weathered limestone, the excavation advance for each layer of earthwork is 1m. After the shaft is excavated to the foundation, the bottom slab reinforcement should be tied and the bottom slab concrete should be poured in a timely manner. The I18 I-beam steel frames are welded together with φ20 longitudinal connecting bars, with a circumferential spacing of 1m. To ensure accurate installation of the steel frames, grooves for connecting plates are pre-reserved at each connection point of the steel frames during shaft excavation. During the initial shotcrete application, wooden wedges are driven into the grooves to create space for the connecting plates. The steel frames are installed according to the design position. During installation, if there is a large gap between the steel frames and the initial shotcrete layer, precast concrete blocks should be used to wedge them tightly every 2m. The back of the steel frames is then filled with shotcrete. The longitudinal connections of the steel frames use reinforcing bars with a circumferential spacing of 1m, arranged in a staggered, quincunx pattern. Shotcrete application should be carried out as soon as possible after the steel frames are erected so that the steel frames and shotcrete share the load. Shotcrete is applied in layers, starting from the arch foot or corner and working upwards to prevent the upper layer of shotcrete from being insufficiently compacted, resulting in instability of the arch foot (corner).

[0026] The vertical connecting bars are directly welded to the I-beam steel frame as a whole, and the vertical connecting bars are welded at the intersection with the main bars of the I-beam steel frame.

[0027] The reinforcing mesh is made of Grade I φ8 steel bars and is centrally processed in the steel bar processing yard. First, the steel bars are straightened using a steel bar straightening machine, then cut into steel bars. The size of the reinforcing mesh is determined by considering the arch spacing and the overlap length between mesh panels. The processed reinforcing mesh panels are hung at the positions marked on the drawings, laid following the undulations of the initial sprayed surface, and tied and fixed to the previously constructed components. The steel bars are then welded into a mesh, with an overlap length of 1-2 grids.

[0028] When using wet spraying technology for shotcrete, the nozzle should be perpendicular to the surface being sprayed, with a distance of 1.5–2.0 m between the nozzle and the surface. The nozzle should be moved continuously and slowly to ensure uniform thickness. If there are large depressions on the rock surface, these depressions should be leveled first. Spraying should be carried out in sections and patches sequentially, from bottom to top, with each section no longer than 6 m. When spraying in layers, the thickness of each layer should be no less than 40 mm. Each subsequent layer should be sprayed after the previous layer has fully set. If spraying is carried out 1 hour after final setting, the surface of the sprayed layer should be cleaned with water first. The thickness of each layer of shotcrete in repeated applications is 50–100 mm for arches and 70–150 mm for sidewalls. The rebound rate of shotcrete is no more than 15% for sidewalls and no more than 25% for arches.

[0029] Step S5: Shaft Excavation of the Horse Head Arch: Excavate downwards to the front of the horse head arch, and reinforce the three steel frames; continue excavating the shaft downwards, and add two corner braces within the horse head arch demolition area. After the bottom of the shaft is completed, backfill the soil to the horse head arch construction site, and draw the horse head arch excavation outline on the shaft wall according to the design position, such as... Figure 6As shown, φ42, l=3m, t=3.25mm advanced small guide pipes are used for grouting on the outer contour line of the top initial support, with a spacing of 400mm. After the grout solidifies and reaches the design strength, the concrete of the inner wall of the horse head gate section is removed in sections. The concrete is removed in the order of first arch, then side wall, and finally bottom plate. The first steel frame is erected at the well wall. After the steel frame is reliably welded to the vertical shaft wall after cutting, the tunnel is excavated. like Figure 7 As shown, two corner braces are added within the scope of the demolition of the horse-head gate; when the horse-head gate is demolished to enter the tunnel, the steel arch frame should be cut in sections according to the steps, one steel frame for the tunnel should be erected, and welded to the steel frame cut off at the tunnel entrance to ensure reliable connection, and three steel frames should be closely arranged; the longitudinal connecting bars of the steel frame should be densified and arranged at 0.5m in the circumferential direction.

[0030] Step S6: Shaft excavation and transportation. The excavated soil inside the tunnel is transported by electric tricycles measuring 2.3*1.1*1 meters. Once transported to the shaft opening, it is lifted out by a truck crane with a 1.2*1*0.8m bucket to prevent soil from falling out of the shaft opening. In the description of this invention, the term "a plurality of" refers to two or more. Unless otherwise explicitly defined, the terms "upper," "lower," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. The terms "connection," "installation," "fixing," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0031] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0032] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A construction method for excavating a vertical shaft with replaced core soil, characterized in that... Specifically, it includes the following steps: Step S1: Measure and mark out the core drilling area, use a Zoomlion ZR420 rotary drilling rig to drill cores within the excavation area of ​​the working well, and backfill the original crushed stone at the core drilling area; Step S2: Constructing the lock-joint ring beam: The construction of the lock-joint ring beam includes surveying and setting out, earthwork excavation, rebar tying, formwork erection and support, and concrete pouring. The lock-joint ring beam foundation pit is 9.5m long and 7.5m wide, and is excavated manually in conjunction with an excavator, with the excavation depth reaching 100mm below the bottom elevation of the lock-joint ring beam. Step S3: The truck crane installs a bucket to lift and remove the slag; Step S4: Once the concrete strength of the lock ring beam reaches 70% of the design strength, the shaft excavation can begin. The shaft is constructed using the inverted shaft wall method. Each layer of earthwork is excavated in two stages. First, half of the earthwork is excavated, followed by 3mm-5mm of plain concrete spraying, installation of reinforcing mesh, erection of a 118 I-beam frame for the half-section, welding of vertical connecting bars, installation of reinforcing mesh, and spraying of concrete. Then, the other half of the earthwork is excavated, and the initial support for the other half of the shaft is constructed to close the initial support into a ring. The next layer of earthwork is then excavated, and the next cycle begins. Within the miscellaneous fill area, the excavation advance for each layer is 0.5m; after entering the moderately weathered limestone, the excavation advance for each layer is 1m. After the shaft excavation reaches the foundation, the bottom slab reinforcement should be tied and the bottom slab concrete poured promptly. Step S5: Construction of the Shaft and the Gate Arch: Excavate downwards to the front of the gate arch, and reinforce the three steel frames; continue excavating the shaft downwards, and add two corner braces within the gate arch removal area. After the bottom of the shaft is completed, backfill the soil to the gate arch construction site. Draw the gate arch excavation outline on the shaft wall according to the design position. Apply Φ42, l=3m, t=3.25mm pre-grouting pipes at 400mm intervals along the outer outline of the top initial support. After the grout has solidified to the design strength, chisel away the inner shaft wall of the gate arch section in sections. Concrete is demolished in the following order: first the arch, then the side walls, and finally the bottom slab. The first steel frame is erected at the shaft wall, using Φ20 connecting bars. After the steel frame is reliably welded to the cut shaft wall, the tunnel is excavated. Two corner braces are added within the demolition area of ​​the portal in step S5. When the portal is demolished to enter the tunnel, the steel arch frame should be cut in sections according to the step sequence. One steel frame for the tunnel is erected and welded to the steel frame cut off at the entrance to ensure a reliable connection. Three steel frames are then closely spaced. The longitudinal connecting bars of the steel frames are densely arranged at 0.5m intervals around the perimeter. Step S6: Shaft excavation and transportation. The excavated soil inside the tunnel is transported by electric tricycles measuring 2.3*1.1*1 meters. The soil is then lifted out of the shaft by a truck crane with a 1.2*1*0.8m bucket.

2. The construction method for excavating a vertical shaft with replacement core soil according to claim 1, characterized in that... In step S2, the formwork support template is made of bamboo plywood, the support adopts a full-span scaffolding support system, the concrete pouring height is 1.3 meters, the horizontal upright spacing is 0.6 meters, and the formwork is supported by steel pipes for horizontal bracing.

3. The construction method for excavating a vertical shaft with replacement core soil according to claim 1, characterized in that... In step S2, the concrete pouring is as follows: the interlocking ring concrete is poured in one go; when pouring the concrete, steel grid connecting bars are reserved to ensure the excavation of the well body; φ42mm steel pipes are pre-embedded; the concrete is vibrated with a 5cm vibrator; the interlocking ring is poured in one go, and then poured in layers, with the thickness of each layer controlled between 300mm and 500mm, and the height difference between the concrete pouring surfaces on both sides not exceeding 0.5 meters.

4. The construction method for excavating a vertical shaft with replacement core soil according to claim 1, characterized in that... In step S4, the I18 I-beam steel frames are welded together with φ20 longitudinal connecting bars, with a circumferential spacing of 1m. During shaft excavation, grooves for connecting plates are reserved at each connection point of the steel frame. When the initial shotcrete is applied, wooden wedges are driven into the grooves. The steel frame is installed according to the design position. During the installation process, if there is a large gap between the steel frame and the initial shotcrete layer, it should be wedged with precast concrete blocks every 2m. The back of the steel frame is filled with shotcrete. The longitudinal connection of the steel frame uses steel bars with a circumferential spacing of 1m, arranged in a staggered quincunx pattern. The shotcrete is applied in layers, starting from the arch foot or corner and spraying upwards.

5. The construction method for excavating a vertical shaft with replacement core soil according to claim 1, characterized in that... In step S4, the vertical connecting ribs are directly welded to the I-beam steel frame as a whole, and the vertical connecting ribs are welded to the main ribs of the I-beam steel frame at the intersection.

6. The construction method for excavating a vertical shaft with replacement core soil according to claim 1, characterized in that... In step S4, the steel mesh is made of Grade I φ8 steel bars. The steel mesh is laid along the undulations of the initial sprayed surface, tied and fixed to the components constructed in the early stage, and then the steel bars are welded into a mesh with an overlap length of 1 to 2 grids.

7. The construction method for excavating a vertical shaft with replacement core soil according to claim 1, characterized in that... In step S4, when using wet spraying technology for shotcrete, the nozzle should be perpendicular to the surface to be sprayed, and the distance between the nozzle and the surface to be sprayed should be 1.5 to 2.0 m. The nozzle should be moved continuously and slowly to ensure uniform thickness of the sprayed layer. When there are large depressions on the rock surface, the depressions should be leveled first. The spraying operation should be carried out in sections and pieces in sequence, and the spraying sequence should be from bottom to top. The length of each section should not exceed 6 m. When spraying in layers, the thickness of each spray should not be less than 40mm. The next layer should be sprayed after the previous layer of concrete has set. If spraying is carried out 1 hour after the previous layer has set, the surface of the sprayed layer should be cleaned with water first. The thickness of each spray of the re-sprayed concrete is 50-100mm for the arch and 70-150mm for the sidewall.

8. The construction method for excavating a vertical shaft with replacement core soil according to claim 7, characterized in that... The rebound rate of the shotcrete is: no more than 15% for the sidewalls and no more than 25% for the arches.

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