What is the method for tunnel excavation? There are various methods for tunneling Tunnel excavation involves various methods, depending on factors such as geology, tunnel size, and project requirements. Here are some common methods used in tunnel excavation:

　　Ⅰ. Drill and Blast Method

　　1.Description : This traditional method is commonly used in hard rock conditions. It involves drilling holes in the tunnel face, filling them with explosives, and detonating the charges. After blasting, the debris (muck) is removed, and the process is repeated.

　　2. Applications : Used for longer tunnels in mountainous or rocky areas.

　　3. Advantages : Cost-effective for hard rock and adaptable to different conditions.

　　4. Disadvantages : Slow and produces vibrations that can affect nearby structures.

　　5. Construction steps :

　　- Drilling : According to the design requirements, arrange blast holes on the tunnel face. The position, depth, and angle of the blast holes need to be precisely calculated to ensure the blasting effect. Usually, pneumatic drills or hydraulic drills are used for drilling operations.

　　- Charging and blasting : Load explosives into the blast holes and conduct blasting. The type and amount of explosives should be selected according to the nature of the rock and the design requirements of the tunnel. After blasting, ventilation and smoke exhaust are required to remove harmful gases and create a safe environment for subsequent operations.

　　- Mucking : Use loaders, excavators, and other equipment to load the blasted slag onto transportation vehicles and transport it out of the tunnel.

　　- Supporting : To prevent the tunnel surrounding rock from collapsing and other unstable situations after blasting, timely support is needed. Support methods can be bolt support, shotcrete support, or a combined support of both.

　　Ⅱ. Shield method

　　1. Principle : A shield is a special equipment with a shield cover. It advances in the underground through the thrust of shield jacks. The cutter head at the front end of the shield machine rotates to cut the soil, and at the same time, the cut soil is transported out through the mucking system. At the rear end of the shield machine, lining segments are assembled to form a tunnel.

　　2. Scope of application : Mainly applicable to soft soil strata, such as the construction of urban subway tunnels. Because the stability of soft soil is poor, the shield method can effectively control stratum deformation during excavation and reduce the impact on surrounding buildings and underground pipelines.

　　3. Construction steps :

　　- Shield machine launching : Install the shield machine in the shield working shaft and make it ready for tunneling. In the launching stage, measures such as strengthening the tunnel entrance need to be taken to ensure the smooth cutting of the shield machine into the stratum.

　　- Tunneling construction : The shield machine advances forward according to the designed route and slope. During the tunneling process, by controlling parameters such as the cutter head rotation speed, thrust, etc., the excavation effect and the attitude stability of the shield machine are ensured. At the same time, operations such as mucking and synchronous grouting should be carried out in a timely manner to fill the gap between the shield machine and the surrounding soil to prevent stratum settlement.

　　- Lining assembly : After the shield machine advances a certain distance, at its rear end, prefabricated concrete lining segments are assembled one by one into a circular lining structure by using a segment erector. The lining segments are connected by bolts and provided with sealing devices such as waterstop strips to ensure the waterproof performance and overall structural strength of the lining.

　　- Receiving construction : When the shield machine reaches the receiving shaft, receiving construction is carried out. This includes handling the receiving tunnel entrance and adjusting the attitude of the shield machine to ensure the safe and accurate entry of the shield machine into the receiving shaft.

　　Ⅲ. Tunnel Boring Machine (TBM)

　　1. Description : A TBM is a massive, cylindrical machine equipped with rotating cutting heads. The TBM advances through the ground, simultaneously excavating the material and installing tunnel linings.

　　2. Applications : Used for long tunnels in urban or densely populated areas, as it minimizes surface disruption.

　　3. Advantages : Faster than drill and blast, less impact on the environment, and safer for workers.

　　4. Disadvantages : High initial cost and limited flexibility in varying geological conditions.

　　5. Construction steps :

　　- TBM assembly and debugging : Assemble the various components of the TBM at the tunnel portal or in a dedicated assembly tunnel and conduct comprehensive debugging to ensure the normal operation of the equipment.

　　- Tunneling operation : After the TBM starts, the cutter head starts cutting rocks under the strong thrust. During the tunneling process, according to the hardness and integrity of the rock, reasonably adjust parameters such as the cutter head rotation speed, thrust, and torque. At the same time, precisely control the tunneling direction. Through equipment such as laser guidance systems, ensure that the TBM tunnels according to the designed route.

　　- Mucking and supporting : The broken slag is transported out of the tunnel through conveyor belts and other means. During the tunneling process, according to the situation of the surrounding rock, support methods such as bolts, steel arches, and shotcrete can be used to ensure the stability of the tunnel. However, the TBM itself also has certain support functions. For example, the shield structure can prevent the surrounding rock from collapsing to a certain extent.

　　- Equipment maintenance and overhaul : Since the TBM is a large and complex equipment, regular maintenance and overhaul of the equipment are required during the tunneling process, including tool replacement and equipment maintenance to ensure the performance and tunneling efficiency of the equipment.

　　Ⅳ. Cut-and-Cover Method

　　1. Description : This method involves excavating a trench, constructing the tunnel inside, and then covering it up. It is often used for shallow tunnels.

　　2. Applications : Commonly used in urban areas for metro systems or road tunnels.

　　3. Advantages : Simple and cost-effective for shallow tunnels.

　　4. Disadvantages : Disrupts surface activities and is not suitable for deep tunnels.

　　5. Construction steps :

　　- Excavation of excavation pit : First, carry out preliminary work such as construction enclosure and dewatering (if the groundwater level is high). Then, excavate the excavation pit in layers and sections according to the design requirements. The excavation method can be a combination of mechanical excavation (such as excavators) and manual excavation. During the excavation process, attention should be paid to supporting the slopes to prevent soil collapse.

　　- Tunnel structure construction : Construct the main tunnel structure at the bottom of the excavation pit, such as pouring concrete floor, side walls, and roof. During the structure construction process, ensure that the concrete pouring quality and the arrangement of steel bars meet the design requirements.

　　- Backfilling and restoration : After the tunnel structure construction is completed and reaches a certain strength, conduct backfilling. The backfill soil should be compacted in layers to restore the ground facilities such as roads and greenery.

　　Ⅴ. Shallow-buried subsurface excavation method

　　1. Principle : In shallow-buried strata, on the premise of transforming geological conditions and focusing on controlling surface settlement, using grids (or other steel structures) and shotcrete as the initial support means, following the principle of the "New Austrian Tunneling Method", and adopting various auxiliary construction measures to strengthen the surrounding rock and fully mobilize and exert the self-bearing capacity of the surrounding rock.

　　2. Scope of application : Applicable to tunnel projects in weak surrounding rock and shallow-buried strata, especially in tunnel constructions in busy urban areas where surface traffic cannot be interrupted and underground pipelines are complex. Such as the interval tunnels of urban subways.

　　3. Construction steps :

　　- Advanced support : Before excavation, reinforce the surrounding rock in front of the tunnel through methods such as advanced small pipe grouting and pipe shed to improve the stability and self-bearing capacity of the surrounding rock.

　　- Excavation operation : Use short footage, weak blasting (if blasting is allowed) or manual excavation for tunnel excavation. The footage of each excavation should be strictly controlled according to the situation of the surrounding rock, generally around 0.5 - 1.5 meters.

　　- Initial support : Immediately after excavation, conduct initial support, mainly including shotcrete, installing grid steel frames, and setting bolts. The initial support should closely follow the excavation face and timely seal the surrounding rock to prevent excessive deformation of the surrounding rock.

　　- Secondary lining : After the deformation of the initial support is basically stable, conduct secondary lining construction. The secondary lining generally uses cast-in-place concrete to improve the overall safety and waterproof performance of the tunnel structure.

　　Ⅵ. New Austrian Tunneling Method (NATM)

　　1. Description : NATM is a flexible approach that uses the surrounding ground for tunnel support. It involves continuous monitoring and adjusting of support systems (like shotcrete, steel ribs, and rock bolts) during excavation.

　　2. Applications : Effective in soft or variable ground conditions.

　　3. Advantages : Reduces construction costs by adjusting to actual conditions and allows flexibility.

　　4. Disadvantages : Requires constant monitoring and expert knowledge to manage ground conditions.

　　Ⅶ. Immersed Tube Method

　　- Description : Pre-fabricated tunnel sections are floated to the construction site, sunk into a dredged trench, and then connected underwater. The trench is later backfilled to secure the structure.

　　- Applications : Suitable for underwater tunnels, such as river or harbor crossings.

　　- Advantages : Cost-effective for underwater applications and allows for large tunnel diameters.

　　- Disadvantages : Requires complex underwater operations and site preparation.

　　Ⅷ. Earth Pressure Balance (EPB) Shield

　　- Description : The EPB shield is a specialized TBM that supports the tunnel face using excavated material (earth). It balances the pressure to prevent ground collapse during excavation.

　　- Applications : Often used in soft soils or urban areas with high groundwater levels.

　　- Advantages : Maintains ground stability and controls surface settlement.

　　- Disadvantages : Expensive and complex to operate.

　　Ⅸ. Pipe Jacking

　　- Description : In this method, sections of concrete or steel pipes are pushed (jacked) into the ground, creating a tunnel without the need for excavation from the surface. The jacking process is usually done through an access shaft.

　　- Applications : Typically used for utility tunnels or small-diameter tunnels in urban areas.

　　- Advantages : Minimizes surface disruption and is suitable for confined spaces.

　　- Disadvantages : Limited to small diameters and requires access shafts at both ends.

　　Each method is chosen based on the specific conditions of the site, including geological features, environmental impact, and project size.