Construction method for high artesian area ultra-deep foundation pit

Abstract

The invention relates to track traffic and tunnel categories, in specific to a super-deep foundation pit construction method for high pressure water areas. The method adopts underground continuous walls (or drilling piles, drill biting piles and corresponding waterproof curtains) as enclosure structures and inner supports as support structures; in the premises of complying with pressure water safety factor that is required in specifications, perform open excavation down to a certain elevation; during the course of open excavation method, carry out casting for surrounding purlins, supports and upper side walls; then, add water into the foundation pit, and the water injection height should guarantee the excavation to the bottom can resist pressure water and meet certain safety factors; perform underwater excavation down to the baseplate elevation and overbreak a certain depth for underwater bottom closing concrete cast; then, pump water out of the foundation pit before casting baseplate and back-casting remaining internal structures.

Description

technical field [0001] The invention relates to rail transit and tunnels, in particular to a construction method for ultra-deep foundation pits in areas with high confined water. Background technique [0002] In the prior art, the design and construction methods for tunnel working wells and intermediate air well foundation pits in confined water areas are as follows: [0003] The first is the top-down method of open-cut open-cut frame with reduced pressure. The design idea of ​​this method is: use the underground diaphragm wall (or bored pile, occlusal pile and corresponding water-proof curtain) as the enclosure structure, and the internal support (steel support or concrete support) as the support structure, after the enclosure structure is completed, the confined water construction in the foundation pit will be carried out first, and the foundation pit excavation will be carried out after the pressure water head drops to the design required level, and the internal support w...

AI Technical Summary

Problems solved by technology

The disadvantage of this method is that the depth of the water-proof curtain is large, especially when the confined water layer is thick and buried deep, the water-proof curtain is inserted into the deep bedrock, and the requirements for construction technology and construction machinery are very high. The construction is difficult, and the construction quality may not be guaranteed; the project cost is relatively high

[0005] The third method is the caisson method. There are caissons with closed bottom and unsealed caissons. The sinking speed of the closed caisson is relatively slow. If the closed caisson is used in ultra-deep foundation pits, the construction period will be longer

The disadvantage of this method is that in areas with high confined water head, it is very difficult to seal the bottom of the caisson without reducing the confined water head; during the sinking process of the caisson, sudden subsidence and sand gushing are prone to occur (especially when the water content is low). Abundant sandy soil or sand layer), inclination and offset, and unsinkable conditions; the sinking elevation of caissons is not easy to control, and super-sinking is prone to occur. In projects with high precision requirements, there are certain risks. For example, when the slope of the subway line is large, the over-sinking of the caisson has a greater impact on it; in addition, the construction of the caisson has a greater impact on the surrounding environment, and the impact range is wider, and the surrounding ground is prone to subsidence, cracking, etc., which is harmful to the surrounding environmental protection. less effective

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