Construction method for improving shield soil in composite sand gravel stratum

Abstract

The invention provides a construction method for improving shield soil in a composite sand gravel stratum. Water, foam and bentonite slurry are used as composite improvement additives; and different additives are selectively injected to the front of a cutter head, the inside of a soil barn or a screw conveyor according to the actual working condition during shield driving with the aid of special improvement equipment and processes so as to play a role in improving the plastic fluidity of the soil, reducing the torque of the cutter head, stabilizing the excavation face and improving the driving efficiency.

Description

technical field [0001] The invention relates to a shield tunnel soil improvement construction method, in particular to a shield tunnel soil improvement construction method in a composite sand and gravel stratum. Background technique [0002] The earth pressure balance shield machine is widely used in tunnel engineering, and its ability to adapt to different geological conditions (cohesive soil, sandy soil, gravel and even soft rock) is the strongest. But not all formations have good plastic fluidity, low permeability and internal friction angle. For example, in Chengdu, my country, the geological conditions are medium sand and gravel, medium-dense to dense pebble soil, and the maximum particle size of boulders is The unique Chengdu clay has low natural water content w and natural pore ratio e, small compressibility coefficient a and high shear strength. It is easy to cause the following problems: [0003] 1) The excavation surface is unstable: the sand and gravel stratum ...

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Problems solved by technology

[0005] 3) Cake formation and occlusion of the soil silo: Due to the lack of fluidity of the excavated soil, under the action of the advancing pressure and temperature of the shield machine, the soil is consolidated and dehydrated to form a hard "mud cake", and the inner wall of the soil silo is arched. If there are no other remedial measures, the entire soil tank will be blocked, resulting in excessive torque of the cutter head, difficult or impossible excavation, causing the temperature of the main bearing of the cutter head to rise, accelerating the damage of the main bearing, and even "sintering" and "sintering" of the main bearing. The serious consequences of "locking up" will cause huge construction risks

[0006] 4) Heavy load on mechanical equipment: the coefficient of friction between the cutter, cutter head and soil is large, so the torque and thrust increase accordingly, resulting in increased current consumption and oil pressure load, high frequency of mechanical failures, and long service life of mechanical equipment. shorten

[0007] 5) Jamming event: If the excavation surface cannot be balanced, the upper part of the excavation face collapses, or there are many pebbles, a jamming event will occur, making the shield machine cutter head unable to rotate

[0008] 6) Tool wear: The excavation of the shield in the gravel stratum will inevitably lead to an increase in the torque of the cutter head, which in turn will lead to the wear of the tool, increasing the difficulty and cost of construction

[0011] 1) The porosity in the sand and gravel stratum is large, and during the construction of shallow covering soil, the foam injection pressure is too high to easily break down the ground;

[0012] 2) The sand and gravel strata in the Chengdu area are dense soil layers with high cutting strength. A high foam injection rate is required to meet the requirements of the excavation speed. A large amount of foam injected into the cutter head and the soil bin will cause a certain amount of pressure inside the soil bin. Fluctuations bring difficulty to the operation and control of shield tunneling and easily cause construction risks;

[0013] 3) The groundwater level of the Chengdu formation is greatly affected by seasons and construction precipitation, and the moisture content of the soil layer changes rapidly. The use of foam is greatly affected by the moisture content of the soil layer, and the foam injection rate is not easy to control;

[0014] 4) The cost of foam improvement is expensive. The amount of foam agent used for construction and excavation of the first ring (segment width 1.5m) is about 80-120L, and the cost is 1000-1500 yuan / ring, and the construction cost is high

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