1, shield shell
The shield shell is composed of notch ring, support ring, steel plate bundle, shield tail and other parts through welding, riveting and bolting. The main functions are: to withstand formation pressure, provide temporary support, protect the safety of equipment and operators, withstand the horizontal thrust of the jack, and enable the shield to advance in the soil layer. It is also the skeleton and foundation of each mechanism.
2, notch ring
It is a cast steel or welded ring with stiffness and strength at the front of the shield. The front end is cut into a sharp angle to facilitate cutting into the ground, and there are reinforcement ribs around the circumference to transmit the horizontal thrust of the jack to the steel shell.
3, support ring
Similar to the notch ring, it is the main force-bearing part of the shield. It is a steel casting with a certain thickness and consists of annular reinforcements, longitudinal reinforcements, and a shell. The annular reinforcements are welded at both ends of the support ring, the longitudinal reinforcements are welded between the annular reinforcements, and the shield jack is mounted on it.
The support ring is equipped with vertical and horizontal columns and beams to form a well-shaped partition, and a working platform is set on the second floor.
4, steel plate bundle
The main function is to protect excavation, tunneling and lining devices. It is made up of two layers of steel plates riveted together. The blocks are wrapped outside the support ring and the notch ring. The extended part is the shield tail.
5, shield tail
The shield tail consists of an annular shell and a sealing device installed on the inside. Its function is to support the periphery of the tunnel and prevent groundwater, excavation surface mud, soil and grouting materials from being squeezed into the tunnel. The shield tail is where the lining assembly takes place and its length depends on the lining form.
6, shield tail seal
The shield tail seal is set up to prevent grouting materials, groundwater, and excavation surface mud and soil from flowing into the shield machine from the periphery of the steel shell panels and segments. As the shield keeps advancing, the friction between the inner wall of the shield tail and the outer ring of the lining segment is very large, and the seal is easily damaged.
The shield tail seal adopts three wire brush and sealing grease sealing methods. Seal grease is pressed between the wire brushes to withstand high-pressure underground mud and water. Before starting the 10 ring, sealing grease is injected into each ring, and then every 10 ring is injected into the 100 ring. After the test section, sealing grease is injected into every 50 ring or 100 ring. In special circumstances, such as when the sealing is not good, care should be taken during construction to ensure that sealing grease is replenished at any time.
7, excavation mechanism
The excavation mechanism consists of a cutting cutterhead, cutterhead support and sealing system, cutterhead drive system, soil bin and other parts.
8, cutting cutterhead
The shield cutterhead is the main component of the excavation mechanism. It is in direct contact with the soil on the excavation surface. Through the action of the hydraulic cylinder, the shield cutterhead is pushed forward. The cutter cuts into the soil layer. The driving device rotates the cutterhead. The cutterhead cuts the soil and the tunnel is driven forward.
9, cutting tool
Cutting tools are key parts of the excavation mechanism. In order to adapt to the soil in this area, improve strength, increase efficiency, and facilitate replacement, two types of cutters are designed and installed on the shield.
One is an ordinary cutter, which is fixed on the cutterhead rib plate with bolts. The cutter is equipped with carbide to increase the wear resistance of the cutter, so that the cutter does not need to be replaced during construction in a section.
The other is the super digging knife, which is mainly suitable for special situations.
10, cutter head support and sealing system
The cutterhead support adopts intermediate support type.
The cutterhead rotary seal is mainly used to maintain bearing grease and prevent sediment, groundwater, and additives from invading the cutterhead bearings. It consists of two inner and outer groups of multiple lip seals.
11, cutterhead drive system
The cutterhead drive is the main drive of the shield machine, which is driven by 8 hydraulic motors. The hydraulic motor has the characteristics of being able to adapt to the instantaneous torque necessary for starting and excavation.
12, sealed bulkhead and airlock
The cutting chamber is a sealed chamber. A sealed partition is set up between the cutting chamber and the operating chamber. The sealed partition is equipped with air pressure pipelines, mud pipelines, excavation gates and other devices to facilitate drainage and maintenance.
A human gate is set up on the upper part of the sealed partition. When personnel need to enter the sealed chamber to troubleshoot or replace tools, they should first pressurize the sealed chamber (maximum compressed air of 0.25Mpa) to make it easy to drain the muck, stabilize the excavation surface and stop water. Gradually pressurize or depressurize through the human gate.
13, segment transportation and assembly mechanism
As the shield advances, the reinforced concrete segments, the tunnel's permanent support, need to be assembled simultaneously. The reinforced concrete segments prefabricated on the ground are transported to the tail working surface of the shield through working shafts and rail transport vehicles, and are installed by the segment installation robot. The segments are 6 pieces per ring, and the maximum block weight is 3.2 tons.
The segment installation manipulator is powered by hydraulic pressure and has 6 degrees of freedom. It can adjust each segment to the appropriate position to ensure assembly accuracy and ensure that the bolt holes of the segments to be assembled are aligned with the bolt holes of the assembled segments to facilitate bolt installation and fixation.
14, promotion mechanism
A shield tunneling machine advances through soil mainly through a thrust mechanism installed within its support ring. The mechanism comprises hydraulic cylinders or jacks and associated hydraulic equipment, reacting against lining segments. Because internal space is restricted, installation conditions are difficult and operating conditions differ from other machinery, cylinders must be compact, light, simple, easy to install and arrange, and well synchronized. Suitable protective devices must prevent dust, muddy water and mortar entering the oil or jacks.
The propulsion cylinders are symmetrically and evenly distributed along the circumference, with a total of 22 sets. The thrust of each cylinder is 1500kN, and the total thrust is 33000kN. The pushing stroke of 3 long cylinder is 1860mm, and the pushing stroke of 18 short cylinder is 1200mm.
The propulsion cylinders can be divided into 4 groups. The four cylinder groups operate at the same time, and the shield moves forward in a straight line.
If you act separately according to the regulations, you can obtain the direction adjustment action of the shield.
15, discharge mechanism
The discharge mechanism is mainly composed of screw conveyors, belt conveyors, excavated rail cars, lifting and upper transportation equipment, mud (foam) injection equipment and other major components.
The screw conveyor is driven by a hydraulic motor with a power of 74kw. Its diameter is 702mm, and it is tilted. The soil inlet is at the lower part of the cutting bin, and the soil discharge port is at the upper part of the belt conveyor. The soil discharge port is equipped with a hydraulically controlled soil discharge gate to control the speed of excavation and the amount of soil discharged, thereby controlling the excavation speed and surface settlement.
The belt conveyor plays the role of intermediate transmission and is hydraulically driven. The power is 15kw, the belt speed is 1.2m/s, and the total length is 52 meters.
The mud (foam) injection equipment pumps the mud (or foam) configured on the ground into the cutting chamber to improve the water tightness and fluidity of the sandy muck.
16, wall back grouting system
The behind-the-wall grouting system mainly consists of ground behind-the-wall mud manufacturing equipment, transport vehicles, docking pumps, shield automatic behind-the-wall grouting equipment, etc.
Behind-the-wall grouting mainly prevents foundation displacement around the tunnel, improves the water-stopping performance of the tunnel, and ensures the early stability of the segment lining.
17, electric, hydraulic power station
The power devices of shield machinery are mainly electric and hydraulic power devices. These devices are located in the power station, which is located on the follow-up trolley following the shield. The power station consists of a transformer, switchboard, console, hydraulic oil pump unit and hydraulic oil tank, hydraulic control valve, cooling system, etc. The hydraulic system converts electricity into hydraulic power, and accurately controls excavation, segment installation, and other actions through control components such as hydraulic pressure, flow, and directional valves.
Since the shield machine requires large electric power and the tunnel excavation is long, in order to prevent the input voltage drop outside the tunnel from increasing, the main transformer must follow the shield machine into the tunnel and move forward together. The capacity of the main transformer is 800KVA.
18, auxiliary equipment
Shield starting and turning frame
The shield starting frame is placed in the starting shaft and is mainly used when installing the shield and just starting to enter the hole after installation.
The shield turning frame is placed in the receiving shaft and is mainly used for the shield turning around in the station.
Follow-up trolley equipment
Subsequent trolley equipment includes: power unit trolley, operation control equipment, synchronous grouting equipment, centralized lubrication and sealing grease pumps, etc. These are connected with the shield.
Shield machine monitoring system
In order to prevent foundation displacement and large settlement, an automatic monitoring system is used to monitor the environment of the shield machine and its working area.
A laser measurement device is used to determine whether the shield machine has pitch, deflection, roll, etc.
Prevent the shield machine from deflecting in horizontal, vertical and other directions.
Ventilation and transportation equipment
Ventilation adopts axial flow fan.
Tunnel transportation uses rail cars and consists of electric locomotives, slurry trucks, earth trucks, segment trucks, material trucks, etc.
Other equipment
Other auxiliary equipment include underground communication equipment, lighting devices in the cave, etc.
Shield boring machines can be divided into closed type and open type according to the excavation mode.
The open type is suitable for strata with good self-reliance and no groundwater. The closed excavation mode is suitable for strata with poor self-support conditions and rich groundwater, because the use of closed excavation can effectively ensure the self-reliance and stability of the excavation surface.
Sealed shield machines are divided into two types: mud-water pressurized type and earth pressure balanced type, which represent the characteristics of different excavation methods and soil balance methods on different working surfaces.
These two types of shields are currently the two most commonly used and advanced forms of shields in the world, but their applicable geology and scope are quite different. The large amount of mud produced by mud-water pressurized shield construction must be processed by ground equipment. The mud treatment equipment is relatively large and covers a large area. Many urban buildings are dense and it is difficult to provide large and open construction sites.
Currently, earth pressure balance shield machines are mostly used to build subway tunnels in urban soft soil strata.
Earth pressure balance shield machines accommodate a wide range of soil types and geological conditions and can work in various complex strata. They offer relatively high construction speeds, cost less than slurry shields, make settlement easier to control and support automatic monitoring and control. For soils with a high sand content, the soil-conditioning system of an earth pressure balance shield can select additives such as bentonite, CMC, clay, superabsorbent polymers and foaming agents according to soil conditions and inject them into the excavation face and soil chamber. A mixing mechanism vigorously blends the additives with the excavated soil and sand, turning the excavated material into a plastic, flowable and impermeable soil mass. This material fills the soil chamber and screw conveyor. Thrust from the shield's hydraulic cylinders pressurizes it to balance the earth and water pressures at the excavation face, stabilizing the face.
The basic working principle of earth pressure balance shield is:
1) Excavation of shield machine
A hydraulic motor drives the cutting head while the shield's hydraulic cylinders (jacks) are activated to advance the shield. The excavated soil enters the soil chamber. As the cylinders extend and the cutting head continues rotating, the chamber fills with soil. Whether additives are injected to improve soil flowability and impermeability depends on the geological conditions. The screw conveyor is then started to discharge the excavated soil onto the transport belt. The belt conveys it to muck rail cars, which transport it through the shaft to the surface.
2) controls the amount and speed of soil discharge
Control of the soil discharge volume and rate is essential to excavation-face stability. When a sufficient amount of spoil accumulates in the earth chamber and screw conveyor, resistance increases as the cut soil passes through the cutter openings into the chamber. When this resistance is sufficient to counter the earth pressure of the surrounding ground and the pressure of groundwater, the excavation face remains relatively stable without collapsing. Excavation can then proceed smoothly as long as the volume of spoil discharged through the screw conveyor from the earth chamber remains balanced with the volume being cut and entering the chamber.
The earth pressure balance shield works by maintaining the relative balance and stability of the earth pressure or the amount of soil residue through earth pressure management.
The relative balance between the earth pressure and the amount of soil residue is ensured in three ways: first, the speed of the propelling cylinder remains unchanged, and the rotation speed of the screw conveyor and the opening of the gate are changed; second, the rotation speed of the screw conveyor and the opening of the gate remain unchanged, and the propelling speed of the propelling cylinder is changed; third, both are adjusted appropriately at the same time.
(Source: Internet)