What determines and affects the earth pressure of shield propulsion

Thrust calculations. The thrust of the shield machine is composed of the friction resistance of the outer periphery of the shell, the earth pressure and water pressure of the chest plate, the traction force of the follow-up equipment, and the friction resistance of the segment and the shield tail seal.

Thrust f1 to overcome the frictional resistance of the outer periphery of the shell

f1 = ·d·l·p·f = 7764 kn thrust f2 to overcome the earth and water pressure on the chest plate

F2 = A·(P2+PW) = 10314 kn Thrust f3 to overcome the traction of the follow-up equipment

f3 = gb·μ441 kn

Push F4 to overcome the frictional resistance of the segment and the shield tail seal

f4 = ·ds· s·n(pt+ ·pw·lt) = 1632 kN maximum thrust required for hob = f5

f5 = nc·pc=5880 kn

The thrust required for propulsion f

f = f1 + f2 + f3 + f4 + f5 = 26019 kn equipment thrust.

Although it is better to have a large number of propulsion cylinders for curve construction and direction control, the size and quantity are limited by space.

The number of thrust and cylinders equipped with this shield machine: 1715 kn 22 (only) equipped with thrust f0

f0 = 1715 22 = 37730 kn propulsion when using 22 cylinders.

fs = 1715 22 = 37730 kN safety rate = fs f = times.

From the calculations, it can be seen that the shield machine is equipped with sufficient thrust.

Determined by the formation and burial depth, the earth pressure is affected by water and gas!

Let's introduce this concept with a [retaining wall] as an example, and for the sake of illustration, let's first agree:

1) The side of the wall in contact with the soil is called the "frontal surface", which is what we usually call the "back of the wall";

2) The side of the wall that does not come into contact with the soil is called the "back soil surface".

3) Whether active or passive earth pressure, it refers to the pressure on the [frontal surface];

4) The [equilibrium state] mentioned below is judged by the failure of the soil.

Active earth pressure].

In the case of wall instability, the wall is pushed by the soil and displacement occurs (the wall moves in the direction away from the soil or rotates around the wall root), and in the process of moving, the soil is constrained by the wall and becomes weaker and weaker, at this time, in order to prevent its own further decline, the internal shear stress of the soil body increases, and is used to maintain its own stable state until the soil itself no longer slides;

Finally, the wall moves to a certain position, at this position, the internal force of the soil to maintain its own balance has reached the maximum (the wall can not maintain its own stability if the soil is moved), this equilibrium state is called [(active) limit equilibrium state], in this state, it is easy to think that the wall is subjected to the least force of the soil.

Therefore, when the above equilibrium state is reached, the pressure of the soil on the wall [frontal surface] is called "active earth pressure".

Passive earth pressure].

On the contrary to the above situation, when the wall [back soil surface] is subjected to external force, so that the wall moves towards the soil, causing extrusion to the soil, at this time, the soil still has to maintain its own stability, so the internal force will also increase, resist the occurrence of deformation, until a stage, when the limit value of the soil internal force is still unable to prevent the deformation, the soil is damaged, and when it is not bad [critical state], it is the so-called [passive] limit equilibrium state].

In this equilibrium state, the pressure of the soil on the [facing surface] of the wall is called the [passive earth pressure].

In short: the wall is pushed away by the soil, and finally balanced, which is called [active earth pressure];

The soil is squeezed by the wall and finally balanced, which is called [passive earth pressure];

The so-called active and passive are actually for [soil].

The concept is placed in the shield method].

With the previous introduction, we can think that the shield cutterhead is a wall, the face of the tunnel is the face of the wall, and the driving effect of the shield cylinder (jack) on the shield can be regarded as the external force of the retaining wall facing the soil extrusion.

Answer] :d earth pressure has static earth pressure, active earth pressure and loose soil with strong pressure, or Zheng is used differently according to the stratum conditions. Controlling the earth pressure according to the static earth pressure setting is the most ideal earth pressure value for the excavation face without deformation, but the control of the earth pressure is quite large, and the equipment capacity must be increased.

Active earth pressure is the critical pressure at which the excavation face does not collapse, and the controlled earth pressure is minimal. When the geological conditions are good, the soil is covered deeply, and the soil arch can be formed, the relaxed earth pressure can be used.

Answer] :d shield construction site setting:

1) When the construction of the working well needs to take precipitation measures, a considerable scale of precipitation system (pump room) should be set up.

2) When the pneumatic shield construction is adopted, an air compressor room should be set up at the construction site to supply sufficient compressed air.

3) When the slurry balance shield is used for construction, the mud treatment system (** attitude and sail control room) and mud pool should be set up at the construction site.

4) When using earth pressure balance shield construction, facilities such as electric locomotive battery charging room should be set up.

Answer]: cMeasures to reduce the deformation of the early formation caused by the prolapse of the shield tail: use synchronous grouting to fill the tail void in time; According to geological conditions, engineering conditions and other factors, the single liquid grouting or double liquid grouting is reasonably selected, and the grouting material and mix ratio are correctly selected, so as to stabilize the assembled lining structure in time; Strengthen the control of grouting volume and grouting pressure; Carry out the second injection of the big argument in a timely manner.

Answer]: A test point should be earth pressure (balance) shield construction knowledge. The construction control of earth pressure shield is mainly based on the improvement control of earth pressure and plastic fluidity, supplemented by the control of soil discharge volume and shield parameters.

EPB shield has long been known as soil cutting closed or soil pressurized shield. The EPB shield boring machine is to use the full-section cutting cutterhead installed in the front of the shield to cut down the frontal soil into the storage and sealing bin behind the cutterhead, and make the cabin have an appropriate pressure and the water and soil pressure balance of the excavation face, so as to reduce the disturbance of the shield advancement to the formation soil, thereby controlling the surface settlement, and continuously discharge the soil ballast to the soil discharge port by the screw conveyor installed at the bottom of the sealing bin when unearthing; Construction features: Auxiliary construction measures such as soil reinforcement are basically not used in the construction, saving the cost of technical measures, and there is no pollution to the environment; According to the change of earth pressure, the excavation and shield propulsion speed are adjusted, which is easy to achieve the stability of the working face and reduces the surface deformation; Automatic control and management can be formed for the amount of excavated soil, with a high degree of mechanical automation and fast construction speed.

Different from the earth pressure balance shield, the slurry shield construction mode: through the sealing bin of the supporting ring front device partition, inject the mud of appropriate pressure to form a mud film on the excavation face, support the front soil, and cut the surface mud film of the soil body by the large cutterhead installed on the front, mix with the mud water, form a high-density mud, and transport it to the ground for treatment by the slurry pump and pipeline, and the whole process is uniformly managed by the automatic control system of slurry balance established in the ground ** control room; Construction features: the excavation surface can be stabilized in the stratum prone to quicksand, and the construction operation can be carried out under normal atmospheric pressure, without the need for pneumatic construction; The slurry pressure transmission speed is fast and uniform, the control accuracy of the balanced earth pressure of the excavation face is high, the interference to the soil around the excavation face is less, and the control accuracy of ground settlement is high. The shield excavation is transported by the slurry pipeline, which is fast and continuous; The transportation volume of electric locomotives is reduced, and the construction of the landing hall is fast; The cutter and cutterhead wear are small, and it is easy to construct long-distance shields; The torque of the cutterhead is small, which is more suitable for the construction of large-diameter tunnels; However, slurry shield requires large-scale slurry treatment equipment and a site for setting up slurry treatment equipment.

Among the four options, permeability, moisture content and water-glue ratio have nothing to do with shield construction, and are all quietly interfering.

Answer] :d Hu Wuli assessed in this question is a closed shield to control the deformation of the formation. When the earth pressure shield is excavated in weak or loose formations, when the viscous resistance or friction between the outer periphery of the shield and the surrounding soil is large, drag reduction measures should be taken.