Shield in and out of the hole overburden is too shallow construction scheme 70

The soil near the entrance and exit hole is to support and reinforce.

The commonly used reinforcement methods mainly include: grouting method, high-pressure jet stirring method and freezing method.

1.Grouting method.

According to its principle, it can be divided into two types: the osmotic grouting method that does not change the arrangement of soil particles, only makes the injected material penetrate into the gap between the soil particles and consolidates; Vein-like cracks are formed along the grouting layer, the grouting material reduces the gap between soil particles, and the soil is compacted. The former is suitable for sandy soil layers, and the latter is suitable for cohesive soil layers.

2.High-pressure jet stirring.

High-pressure jetting of reinforcing materials to mix them with the stirred soil and sand, or to replace the stirred soil and sand, to form an improved formation with a certain strength.

3.Freeze the construction method.

The soft stratum or the groundwater-bearing soil layer is frozen, and the frozen soil has high strength and water-stopping properties, especially suitable for large-section shield construction and groundwater pressure high occasions.

In fact, what you are talking about is entering the hole, entering the hole is mainly divided into several stages, that is, according to the form of your end reinforcement, the shield enters the hole door ring sealing device, and the shield enters the end reinforcement, generally first enters the jet grouting pile, and then enters the three-axis stirring, if the area is watery, it is generally necessary to take refrigeration, and first enter the freezing area, and then enter the jet grouting pile or mixing pile. Then the shield tail is completely detached from the door ring sealing device and starts synchronous grouting. In the construction process, the main attention is to the bottom analysis, the selection of the end reinforcement method, the horizontal exploration core to check the broken reinforcement results, the vertical coring to check the end of the mixing pile reinforcement results, if the area allows, the water is large at the bottom layer, and precipitation measures should be taken.

Pay attention to the precipitation level. Pay attention to the settlement after the reinforcement section, etc. Pay attention to the lubrication of the door sealing device.

According to the different forms of the shield, choose the sealing device of the door knocker. . . The total time of initiation is not easy to be too long, but the single-ring propulsion speed should be controlled at about 10mm per minute, mainly considering the disturbance to the bottom layer. If there is frozen reinforcement, do not stop the cutterhead for a long time.

There are many details to be aware of...

Well, one by one, the question of the opponent is called out of the hole, according to the Japanese parlance. We usually call it a hole.

When entering the hole, you need to assemble the negative ring segment, and the negative ring segment is to know the ring segment from the reaction frame, which we generally call 0 ring.

When you just enter the hole, the contact between the concrete and the soil is not too close at this time, and it is easy to collapse, so the hole generally maintains a little earth pressure, and we generally maintain the pressure of kilograms, and the speed should be slower at this time. After entering the tunnel, the speed gradually increases after passing through a certain adaptation stage to the formation - test tunneling.

In the process of entering the hole, the rubber curtain installed on the door of the cave plays the role of stopping water and maintaining pressure. However, it should be noted that after the cutterhead is all in the rubber curtain, the fan-shaped plate should be lowered and fixed.

Oh, if you don't understand something, you can ask me again.

Answer]: a, c, d

This question assesses the technical points of the excavation technology of the soil reinforcement section of the tunnel in the initial construction of the shield. Key points of tunneling technology in the soil reinforcement section of the tunnel entrance: (1) When installing the shield base and reaction frame, it is necessary to ensure that the shield tunneling direction conforms to the tunnel design axis; (2) Before dismantling the entrance enclosure structure, it is necessary to confirm the soil reinforcement effect of the hole, and if necessary, carry out grouting reinforcement, and ensure that the soil collapse and stratum deformation do not occur when the hole entrance enclosure structure is removed, and the stability of the excavation face during the initiation of the shield structure should be ensured; (3) After the shield tail enters the hole, seal the hole and close the ring segment tightly to prevent muddy water and grouting slurry from leaking from the cave door.

Option B and E belong to the technical points of shield receiving construction.

1. The grouting method is also divided into two kinds according to the principle: the osmotic grouting method that does not change the arrangement of soil particles; The grouting material reduces the particle gap and the soil is compacted. The former is suitable for gravel soil layers, and the latter is suitable for sand soil layers.

2. High-pressure jet stirring method, high-pressure jet reinforcement material, so that it is mixed with the stirred soil and sand to form an improved soil layer.

3. Freezing method, the weak stratum or groundwater soil layer is frozen, so that the soil has high strength and water retention during working hours.

It can be constructed by adding high-pressure jet grouting piles to the three-shaft mixing plant, and can be frozen.