Construction method of ultra-shallow overburden and large longitudinal slope starting construction method of shield machine in coastal dredging and reclamation stratum

Abstract

The invention discloses a construction method for a shield tunneling machine to start from a coastal blow filling stratum with ultra shallow covering soil and a large longitudinal slope. The construction method comprises the following steps that (1) a starting end soil body is strengthened, specifically, the starting end soil body is strengthened by adopting high pressure jet grouting piles with the coordination of tri-axial mixing piles; (2) hole door pre-buried steel rings and external rings are installed, and grouting holes are reserved; (3) a starting concrete base is prefabricated, positioned and installed; (4) a starting bracket and a counter-force frame are positioned, installed and strengthened; and (5) the shield tunneling machine starts to enter a hole and perform tunneling, specifically, the starting state of the shield tunneling machine is reasonably selected, and the center line of the shield tunneling machine is kept coincident with the center line of the tunnel design. The construction method is suitable for the coastal blow filling stratum with the ultra shallow covering soil (the starting section covering soil thickness is less than or equal to 5 m) and the large longitudinal slope (the designed longitudinal slope is larger than or equal to 2%), the shield attitude control is good, ground deformation and uneven settlement can be effectively prevented, the segment assembling quality at a starting stage is ensured, the defects of dislocation, breakage, water leakage and the like are reduced, and the smooth starting of the shield tunneling machine is escorted.

Description

technical field [0001] The invention relates to a starting construction method of a shield machine, and is particularly suitable for coastal dredging formations with ultra-shallow covering soil (thickness of covering soil in the starting section ≤ 5m) and large longitudinal slope (design longitudinal slope ≥ 20‰). Background technique [0002] Shield initiation is a key link in tunnel shield tunneling construction and one of the difficulties in shield tunneling construction. The success or failure of shield tunneling will have a decisive impact on tunnel construction quality, progress, safety, construction period and economic benefits. However, the large slope of the shield machine and the start of shallow covering soil have always been difficulties in engineering construction. [0003] Due to the requirements of the project design line, it is necessary to apply the shield construction to the coastal dredger reclamation formation. The starting segment of the shield is the c...

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Problems solved by technology

[0004] Due to the particularity of the coastal dredging and reclamation strata, the starting construction of the shield machine is even more difficult, which is specifically manifested in the following four difficulties: 1. Geological difficulties: the thickness of the covering soil at the starting section is 4.6m, and the shield machine cutterhead The diameter is 6.986m, and the tunneling of the shield machine has a great impact on the ground surface. In addition, the overburden layer is dredged fill and plain fill. The groundwater level is high, the water content of the formation is high, and the stability of the formation is poor. The head of the shield machine is easy to float. It is easy to cause surface subsidence, slurry channeling or roof collapse

2. The starting positioning accuracy is high and difficult: the design longitudinal slope is 25‰, the segment width is 1.5m, and the height difference between the front and rear of the segment ring reaches 37.5mm for each excavation ring. During the starting positioning process, the reaction frame is tilted If the angle is not controlled accurately, it will cause the force-bearing surface of the reaction frame to be different from that of the shield body, resulting in excessive deviation of the shield attitude.

3. It is difficult to control the starting attitude of the shield machine: before entering the hole, the vertical curve is 25‰ downhill, and the shield machine is prone to "kowtow"; The vertical component force may cause the reaction frame to float up as a whole; after entering the tunnel, starting from the downhill slope of 25‰ along the tunnel design axis, the shield machine is easy to fall, and the component force in the vertical direction is likely to cause tunnel Floating of the slices, resulting in misalignment of the slices and water seepage

4. It is difficult to establish the pressure of the soil warehouse in time: the length of the shield body of the shield machine is generally about 9m. Before the shield body completely enters the ground, it is difficult to establish the pressure of the soil chamber. Continuous underpressure excavation will easily lead to the collapse of the excavation surface. It is a dredger-filled soil layer with poor stratum stability, and shield tunneling disturbance will increase stratum collapse and ground subsidence

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