The following is what Zhongda Consulting brings to you about eleven common urban underground space construction methods for your reference.
1 New Austrian method
Design basis: rock bearing theory (1950's)
Stable surrounding rock itself has the ability to bear load and self-stabilize; unstable surrounding rock Loss of stability is a time process;
If necessary support and restrictions are provided during this period, the surrounding rock can still return to a stable state.
Focus on process and control, emphasizing full utilization of the self-bearing capacity of rock mass.
Technical elements: Shotcrete (mesh) support, flexible support and permanent lining constitute a composite lining and monitoring measurement
Design theory - construction method - the state of the support structure is more in line with reality Condition.
2 Drilling and blasting method
Design basis: Relaxation load theory (1920's)
Stable surrounding rock has self-stabilizing ability;
Unstable surrounding rock will collapse and requires supporting structures to support;
{Support load}〓{The weight of the rock mass that may collapse due to relaxation within a certain range}
Attention Results and treatment methods
Technical elements: rigid support (steel and wood component support), which generally needs to be replaced with an integral thick lining (permanent support).
The design of temporary support and permanent lining based on the most unfavorable combined load of surrounding rock is not consistent with the actual working conditions.
3 Full-section boring machine method
Equipment: Full-section boring machine (TBM)
Principle: The motor drives the main shaft to rotate → pressurizes the cutterhead tightly Rock wall → Use the disk-shaped hob on the cutter head to break the rock → The entire tunnel section is formed at one time
Advantages: The monthly footage is 1.5 to 2.0 times that of the drill and blast method, the over-excavation amount is less than 5%, and the lining cost Significant savings, construction safety and good rock layer adaptability
Applicable objects: long hard rock tunnels (especially suitable for tunnel excavation in areas with harsh climate conditions such as rock fragmentation, high mountain hypoxia, severe cold)
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4 Shield method
Equipment: The main body of the shield machine is a movable high-strength steel casing (shield shell)
The shield machine is used in soft soil, Special equipment for building tunnels in soft rock and broken water-bearing strata. The shield shell supports the ground before the permanent lining is constructed and does not require temporary support.
The shield machine is designed, manufactured or modified according to the tunnel and foundation conditions.
Construction cross-section: mostly circular, but also rectangular, horseshoe-shaped, semi-circular and special-shaped.
Applicable objects: urban subways, underwater tunnels, hydraulic tunnels, etc.
5 Immersed Pipe Method
Construction method: Prefabricated reinforced concrete pipe section → floated to the tunnel site of pre-excavated underwater foundation trench → the pipe section is positioned and then injected with water ballast and sunk to the designed position → Underwater connection with adjacent pipe sections → Foundation treatment → Backfilling with soil → Pavement inside the tunnel.
Applicable objects: underwater tunnels. It has low foundation requirements and is especially suitable for project sites with shallow water depths such as soft foundations, river beds or sea beds, where it is easy for dredging equipment to excavate foundation trenches.
Commonly used cross-section types: circular and rectangular
6 Open excavation method
Construction method: Excavation of earth from top to bottom from the surface to the design elevation → from The main work of the tunnel is carried out from bottom to top → backfilling the foundation pit or restoring the ground
Key processes: lowering the groundwater level, earth and stone excavation, slope support, structural construction, waterproofing engineering, etc.
7 Cover and Excavation Method
Construction method: First use continuous walls, bored piles, etc. as the enclosure structure and intermediate piles, and then construct reinforced concrete cover plates. Earth excavation and structural construction are carried out under the protection of walls and intermediate piles.
Reverse approach: Earth excavation and structural construction are carried out from top to bottom.
Follow the method: After all earth excavation is completed, structural construction will be done from bottom to top.
8 Shallow Burial and Undercover Excavation Method
When constructing shallow buried tunnels, sometimes due to the surrounding environment, the underground excavation method must be used for construction, which is called shallow burial and undercover excavation method. Based on the NATM theory, various auxiliary construction measures are used to strengthen the surrounding rock during excavation. Immediate support and sealing after excavation will form a ring, so that they can work together with the surrounding rock to form a joint support system, effectively inhibiting excessive deformation of the surrounding rock.
The essence of the construction: "Pipeline is advanced and strict The eighteen-character policy of grouting, short excavation, strong support, quick closure, and frequent measurement.
9 Underground Diaphragm Wall Method
Construction method:
Use special trenching equipment to drill in the mud along the boundary of the foundation pit of the proposed underground structure or high-rise building. In the state of protecting the wall, a trench of designed length and depth is excavated from the ground; then the steel cage is hoisted into it, and concrete is poured in the trench filled with mud using the conduit method; the concrete is poured upward from the bottom to displace the mud. Reinforced concrete wall segments are formed underground; special joints connect each unit wall segment to form an integral underground continuous wall.
Applicable objects:
Special underground structures such as deep and large foundation pits for high-rise buildings, large underground shopping malls and parking lots, subway stations, underground pump stations, substations, and oil depots.
The length of the foundation pit constructed using the underground continuous wall method has reached several hundred meters, the excavation depth has reached more than 30m, and the depth has exceeded 50m.
10 Pipe Jacking
Construction method
Use a hydraulic cylinder to push the prefabricated pipe section into the borehole formed by the cutting cutterhead or tunnel boring machine A trenchless construction method that constitutes the lining.
Applicable objects
Crossing roads, railways, buildings, rivers, and underground areas where excavation is not allowed or cannot be done in downtown areas, historical protection areas, farmland and environmental protection areas, etc. Engineering construction.
11 Freezing method
Freezing is an artificial freezing technology for the soil layer. It relies on liquid nitrogen, etc. to directly vaporize and absorb heat in the freezing tube to take away the heat in the ground layer, thus realizing the freezing of the soil layer. of quick freezing.
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