A method for block-by-block oblique symmetrical excavation of large-diameter vertical shafts suitable for gravel formations

Abstract

The present invention relates to a method for obliquely symmetrical excavation of a large-diameter vertical shaft in a gravel stratum, and belongs to the technical field of large-diameter circular vertical shaft body excavation technology. The method excavates the large-diameter vertical shaft in sections vertically from top to bottom, and divides each excavation section into four arc blocks, namely arc block A, arc block B, arc block C, and arc block D, wherein arc block A and arc block D, arc block B and arc block C are obliquely symmetrical. After excavation of each arc block in the first excavation section and the last excavation section, steel bars are tied, formwork is installed, and concrete is poured to form a lock mouth of the first excavation section and a bottom ring beam of the last excavation section. Each intermediate excavation section is symmetrically excavated in four blocks and supported by a double-layer steel mesh. In each excavation section, each block is overlapped by 15-20 cm in the circumferential direction. Connecting steel bars are used to connect the first layer of steel mesh and the second layer of steel mesh. Exposed connecting bars are reserved at the bottom of each excavation section.

Description

Technical Field

[0001] The invention relates to a large-diameter circular vertical shaft excavation process, and in particular to a large-diameter circular vertical shaft excavation construction method applied to gravel formations. Background Art

[0002] Currently, large-diameter circular shaft construction in my country generally employs a "manual full-section drilling and blasting" process, manual slag loading, and winch hoisting equipment. Alternatively, raise boring is used. Before shaft construction, a hydrogeological borehole is drilled in the center of the shaft, and a water pressure test is conducted within the borehole to measure the rock permeability. Based on the hydrogeological borehole data, a plan for pre-grouting deep holes from the surface to block water flow is determined. After grouting, a raise boring rig is used to drill a pilot hole. Once the pilot hole reaches the bottom of the shaft, a reverse cutterhead is replaced and the pilot shaft is drilled from the bottom up. The pilot shaft is drilled upwards to the lower line of the strongly weathered layer, and the raise boring rig is removed to complete the raise boring operation. Based on the water flow within the pilot hole, a determination is made as to whether deep hole grouting from the bottom of the shaft upwards is necessary. The water blockage range extends from the lower end of the shaft (20 meters above the horizontal water curtain to the bottom of the shaft). Excavation and support are carried out from the surface from top to bottom, with additional grouting carried out as excavation progresses to prevent significant groundwater loss and ensure rapid and safe construction. If reverse boring is used to construct a vertical shaft, a shaft passage beneath the shaft must be constructed in advance. However, the purpose of constructing a large-diameter subway shaft is to enter the shaft passage and then proceed to the section tunnel excavation, so the pilot shaft method cannot be used. For large-diameter circular shafts in gravel strata, due to the lack of a distinct bedding structure in the gravel sedimentary layer, the strength of the gravel connection is low, and the overall stability is average. This makes full-section excavation prone to landslides, which not only threatens the safety of construction workers but also makes over-excavation and under-excavation difficult to control. Summary of the Invention

[0003] In view of the defects of the above-mentioned existing methods, the technical problem to be solved by the present invention is to provide a safe, reliable, and highly operable block excavation method suitable for large-diameter circular shafts in gravel formations, which can not only ensure construction quality, but also improve equipment utilization, accelerate construction progress, and improve construction efficiency.

[0004] To solve the above technical problems, the present invention adopts the following technical solutions: a method for the obliquely symmetrical excavation of a large-diameter vertical shaft in a sandy and gravel stratum, wherein the large-diameter vertical shaft is vertically excavated in sections from top to bottom, and each excavation section is divided into four arc blocks, namely arc block A, arc block B, arc block C, and arc block D, wherein arc block A and arc block D, and arc block B and arc block C are obliquely symmetrical; after the excavation of each arc block in the first excavation section and the last excavation section, steel bars are tied, formwork is installed, and concrete is poured, thereby forming a lock joint of the first excavation section and a bottom ring beam of the last excavation section;

[0005] Each intermediate excavation section is excavated symmetrically in four sections and supported by double-layer steel mesh, which includes the following steps:

[0006] Step 1: Excavate the arc block A. After the excavation is completed and the slag is removed, the working surface is vacated and the initial spraying of concrete is carried out. After completion, the first layer of steel mesh is installed and sprayed concrete is used to complete the first layer of steel bar coverage.

[0007] Step 2: After the excavation of arc block D and the lifting of the slag to vacate the working surface, the second layer of steel mesh construction of arc block A begins, and the initial spraying of concrete for arc block D begins. After the spraying of arc block D is completed, the second layer of steel mesh of arc block A is tied and sprayed concrete is used to complete the second layer of steel bar covering.

[0008] Step 3: The first layer of steel mesh is constructed in arc block D, and the first layer of steel bars is covered with sprayed concrete. After the excavation of arc block B and the lifting of slag to vacate the working surface, the second layer of steel mesh is constructed in arc block D, and the initial spraying of concrete is started in arc block B. After the spraying of arc block B is completed, the second layer of steel mesh in arc block D is tied and sprayed concrete is used to cover the second layer of steel bars.

[0009] Step 4: Arc block B is constructed with the first layer of steel mesh and sprayed with concrete to complete the first layer of steel cover; Arc block C is excavated, and after the slag is hoisted to vacate the working surface, Arc block B begins to construct the second layer of steel mesh, and Arc block C begins to be sprayed with concrete to complete the first layer of steel cover; After the spraying of Arc block C is completed, the second layer of steel mesh of Arc block B is tied and sprayed with concrete to complete the second layer of steel cover;

[0010] Step 5: The first layer of steel mesh is constructed in the arc block C, and the first layer of steel bars is sealed with sprayed concrete. After completion, the second layer of steel mesh is constructed in the arc block C, the second layer of steel mesh is tied, and the second layer of steel bars is sealed with sprayed concrete.

[0011] Step 6: Excavate the core soil reserved for this stage, and use a tower crane and a slag bucket to lift the core soil out of the circular shaft, and then use a slag truck to transport the slag to the slag yard.

[0012] In each excavation section: ensure that each block overlaps 15-20cm in the circumferential direction; use connecting steel bars to connect the first layer of steel mesh and the second layer of steel mesh to fix the second layer of steel mesh; reserve exposed connecting bars at the bottom of each excavation section, and do not use sprayed concrete to cover it, so as to facilitate the overlap with the steel bars of the next excavation section, so that the steel bars of the upper and lower excavation sections are connected into a whole.

[0013] Preferably, after step three is completed, the tank truck exits the site for the first time, and after step four is completed, the tank truck exits the site for the second time.

[0014] Preferably, each block overlaps by 18 cm in the circumferential direction.

[0015] The thickness of the initial sprayed concrete of each arc-shaped block is 5 cm, the thickness of the first layer of steel mesh covering is 12 cm, and the thickness of the second layer of steel mesh covering is 13 cm.

[0016] Preferably, all intermediate excavation sections are reinforced with steel bars.

[0017] Preferably, other construction is strictly prohibited during the process of lifting the debris.

[0018] The present invention provides a clear, economical, and rational method for excavating large-diameter circular shafts in gravel formations for urban subway systems. The block-by-block excavation method effectively avoids the unsafe conditions of full-section excavation in gravel deposits, which can easily lead to shaft collapse, resulting in casualties, and uncontrollable over-excavation and under-excavation. By adopting the block-by-block oblique symmetrical excavation method, each arc block only needs to be sealed with sprayed concrete to complete the first layer of steel bar covering before excavating another arc block. Symmetrical arc blocks are excavated first, and the construction of two arc blocks can be carried out at the same time. The on-site preparation work is reduced and the construction progress is accelerated. Each stage of construction can reduce the number of tank trucks going back and forth by at least four times. Compared with the sequential excavation method, the construction of each excavation section can not only save half a day of construction time, but also save tank truck transportation costs. At the same time, the utilization rate of equipment such as tower cranes is also improved. In each excavation section, it should be ensured that each block overlaps 15-20cm in the circumferential direction, and connecting steel bars are used to connect the first layer of steel mesh and the second layer of steel mesh to fix the second layer of steel mesh. Exposed connecting bars are reserved at the bottom of each excavation section, which are not covered with sprayed concrete, so as to facilitate the overlap with the steel bars of the next excavation section, so that the steel bars of the upper and lower excavation sections are connected into a whole, thereby improving the overall structural stability of the entire large-diameter shaft after excavation, and improving safety during construction and subsequent operations. The present invention has the characteristics of being safe and reliable, easy to operate and implement, having good construction quality, fast construction progress and little disturbance to surrounding rocks. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the large-diameter vertical segmented excavation sequence;

[0020] Figure 2 This is a schematic diagram of the excavation construction steps;

[0021] Figure 3 This is a schematic diagram of the first layer of steel mesh shotcrete in the middle excavation section;

[0022] Figure 4 Schematic diagram of the second layer of steel mesh sprayed concrete in the middle excavation section. DETAILED DESCRIPTION

[0023] In order to better understand the improvements made by the present invention over the prior art, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0024] like Figure 1 As shown in Figure 4, a block excavation method for a large-diameter circular shaft in a gravel formation is used. Compared with the traditional large-diameter circular full-section shaft excavation construction method, in order to save project costs and ensure the milestones are completed on time, the large-diameter circular shaft is excavated in four obliquely symmetrical blocks.

[0025] The large-diameter shaft is excavated vertically in sections from top to bottom, with each excavation section divided into four arc blocks, namely arc block A, arc block B, arc block C, and arc block D. Arc block A and arc block D, as well as arc block B and arc block C, are obliquely symmetrical. During construction, after the excavation of each arc block in the first and last excavation sections, reinforcement is tied, formwork is installed, and concrete is poured, thereby forming the locking mouth of the first excavation section and the bottom ring beam of the last excavation section. The locking mouth 5 of the first excavation section is to prevent the wellhead from collapsing and protect the construction safety of subsequent excavation workers, while the bottom ring beam 6 of the last excavation section can prevent the adverse effects of uneven foundation settlement or large vibration loads, thereby enhancing overall rigidity.

[0026] Each intermediate excavation section is excavated symmetrically in four sections and supported by double-layer steel mesh, including the following steps:

[0027] Step 1: Excavate curved block A. After excavation and slag removal, clear the working surface and perform the initial spraying of concrete 7. This spraying process follows the working surface quickly, shortening the interval between excavation and support. This effectively fills cracks and defects on the gravel surface, preventing the loosening of fragments cut through the cracks and improving the stress state of the gravel. Once this is complete, install the first layer of steel mesh 1, and spray concrete to complete the first layer of reinforcement 2.

[0028] Step 2: Due to the obliquely symmetrical excavation construction sequence, the bordering area of the two arc blocks is small. Therefore, after arc A completes the first layer of steel bar coverage, arc block D can be excavated, and there will be no collapse caused by insufficient steel mesh support during the excavation of both arc blocks. After arc block D completes the lifting of slag to vacate the working surface, arc block A begins the second layer of steel mesh construction, and arc block D begins the initial spraying of concrete to seal it. After the spraying of arc block D is completed, the second layer of steel mesh 3 of arc block A is tied, and the second layer of steel bar coverage 4 is completed by spraying concrete. At this point, the excavation of arc block A and the combined support of double-layer steel mesh are completed.

[0029] Step 3: Construct the first layer of steel mesh in arc block D and spray concrete to complete the first layer of reinforcement. Subsequently, arc block B is excavated. After the excavated soil is hoisted and the work surface is cleared, construction of the second layer of steel mesh begins in arc block D. Simultaneously, the initial spray concrete is applied to arc block B. After spraying arc block B, the second layer of steel mesh in arc block D is tied and spray concrete is applied to complete the second layer of reinforcement. This concludes the excavation of arc block D and the combined double-layer steel mesh support.

[0030] Step 4: The first layer of steel mesh is constructed on arc block B, and the first layer of steel bar coverage is completed by spraying concrete; arc block C is excavated, and after the slag is lifted to vacate the working surface, arc block B starts the second layer of steel mesh construction, and arc block C starts the initial spraying of concrete to cover it; after the spraying of arc block C is completed, the second layer of steel mesh of arc block B is tied, and the second layer of steel bar coverage is completed by spraying concrete, and the excavation of arc block B is completed in combination with the double-layer steel mesh support.

[0031] Step 5: The first layer of steel mesh is constructed in arc block C, and the first layer of steel bar coverage is completed by spraying concrete. After completion, the second layer of steel mesh is constructed in arc block C. After the second layer of steel mesh is tied, the second layer of steel bar coverage is completed by spraying concrete. The excavation of arc block C is completed in combination with the double-layer steel mesh support.

[0032] Step 6: After the excavation of the four arc-shaped blocks and the support of double-layer steel mesh are completed, the core soil reserved for this stage is excavated and lifted out of the circular shaft using a tower crane and a slag bucket. The slag is then transported to the slag yard using a slag truck. At this point, the construction of an intermediate excavation section is completed.

[0033] In each excavation section, it should be ensured that each block overlaps by 15-20cm in the circumferential direction; connecting steel bars are used to connect the first layer of steel mesh and the second layer of steel mesh to fix the second layer of steel mesh; exposed connecting bars are reserved at the bottom of each excavation section and are not covered with sprayed concrete to facilitate overlapping with the steel bars of the next excavation section, so that the steel bars of the upper and lower excavation sections are connected into a whole.

[0034] At the same time, after step 3 is completed, the tank truck will be withdrawn for the first time, and after step 4 is completed, the tank truck will be withdrawn for the second time. Reinforced steel support should be provided in all intermediate excavation sections.

[0035] In the circumferential direction, each block should preferably overlap by 18 cm.

[0036] Preferably, the thickness of the initial sprayed concrete of each arc block is 5 cm, the thickness of the first layer of steel mesh covering is 12 cm, and the thickness of the second layer of steel mesh covering is 13 cm.

[0037] In order to ensure the safe management of shaft construction, other construction is strictly prohibited during all processes of lifting debris.

[0038] Compared with general block excavation, the general block excavation is based on the block, and each block is excavated separately until the sprayed concrete is sealed and the second layer of steel bar is covered before the construction of the next arc block can be carried out; when using the block oblique symmetrical excavation construction method, each arc block only needs to be sealed with sprayed concrete and the first layer of steel bar is covered before the excavation of the next arc block can be started, and two arc blocks can be constructed at the same time. The block oblique symmetrical excavation method can reduce the preparation work on site and speed up the construction progress. The construction of each excavation section can reduce the number of round trips of tank trucks. In comparison, it not only saves construction time but also reduces the transportation cost of tank trucks. At the same time, the utilization rate of equipment such as tower cranes is also improved.

[0039] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for the obliquely symmetrical excavation of a large-diameter vertical shaft in a gravel formation, characterized in that: The large-diameter shaft is excavated vertically in sections from top to bottom, and each excavation section is divided into four arc blocks, namely arc block A, arc block B, arc block C, and arc block D. Arc block A and arc block D, arc block B and arc block C are obliquely symmetrical. After the excavation of each arc block in the first excavation section and the last excavation section, steel bars are tied, formwork is installed, and concrete is poured to form the lock beam of the first excavation section and the bottom ring beam of the last excavation section. Each intermediate excavation section is excavated symmetrically in four sections and supported by double-layer steel mesh, which includes the following steps: Step 1: Excavate the arc block A. After the excavation is completed and the slag is removed, the working surface is vacated and the initial spraying of concrete is carried out. After completion, the first layer of steel mesh is installed and sprayed concrete is used to complete the first layer of steel bar coverage. Step 2: After the excavation of arc block D and the lifting of the slag to vacate the working surface, the second layer of steel mesh construction of arc block A begins, and the initial spraying of concrete for arc block D begins. After the spraying of arc block D is completed, the second layer of steel mesh of arc block A is tied and sprayed concrete is used to complete the second layer of steel bar covering. Step 3: The first layer of steel mesh is constructed in arc block D, and the first layer of steel bars is covered by sprayed concrete. After the excavation of arc block B and the lifting of slag to vacate the working surface, the second layer of steel mesh is constructed in arc block D, and the initial sprayed concrete is started in arc block B. After the spraying of arc block B is completed, the second layer of steel mesh in arc block D is tied and sprayed concrete is used to cover the second layer of steel bars. Step 4: Arc block B is constructed with the first layer of steel mesh and sprayed with concrete to complete the first layer of steel cover; Arc block C is excavated, and after the slag is hoisted to vacate the working surface, Arc block B begins to construct the second layer of steel mesh, and Arc block C begins to be sprayed with concrete to complete the first layer of steel cover; After the spraying of Arc block C is completed, the second layer of steel mesh of Arc block B is tied and sprayed with concrete to complete the second layer of steel cover; Step 5: The first layer of steel mesh is constructed in the arc block C, and the first layer of steel bars is sealed with sprayed concrete. After completion, the second layer of steel mesh is constructed in the arc block C, the second layer of steel mesh is tied, and the second layer of steel bars is sealed with sprayed concrete. Step 6: Excavate the core soil reserved for this stage and use a tower crane and a slag bucket to lift the core soil out of the circular shaft, and then use a slag truck to transport the slag to the slag yard; In each excavation section: ensure that each block overlaps 15-20cm in the circumferential direction; use connecting steel bars to connect the first layer of steel mesh and the second layer of steel mesh to fix the second layer of steel mesh; reserve exposed connecting bars at the bottom of each excavation section, and do not use sprayed concrete to cover it, so as to facilitate the overlap with the steel bars of the next excavation section, so that the steel bars of the upper and lower excavation sections are connected into a whole.

2. The method for excavating a large-diameter vertical shaft in a sandy and gravel formation in a block-by-block, obliquely symmetrical manner according to claim 1 is characterized by: After step three is completed, the tank truck exits the site for the first time, and after step four is completed, the tank truck exits the site for the second time.

3. The method for excavating a large-diameter vertical shaft in a sandy and gravel formation in a block-by-block, obliquely symmetrical manner according to claim 1 is characterized by: Each block overlaps 18 cm in the circumferential direction.

4. The method for excavating a large-diameter vertical shaft in a sandy and gravel formation in a block-by-block, obliquely symmetrical manner according to claim 1 is characterized by: The thickness of the initial sprayed concrete of each arc-shaped block is 5 cm, the thickness of the first layer of steel mesh covering is 12 cm, and the thickness of the second layer of steel mesh covering is 13 cm.

5. The method for excavating a large-diameter vertical shaft in a sandy and gravel formation in a block-by-block, obliquely symmetrical manner according to claim 1 is characterized by: All intermediate excavation sections must be reinforced with steel bars.

6. The method for excavating a large-diameter vertical shaft in a sandy and gravel formation in a block-by-block, obliquely symmetrical manner according to claim 1 is characterized by: During the process of lifting debris, other construction is strictly prohibited.

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