What are the common support methods for deep foundation pit support?

Before excavation, concrete cast-in-place piles shall be set around the foundation pit. Piles are arranged continuously in two rows at intervals, and concrete tie beams or anchor piles and pull rods are arranged at the top of the piles. Convenient construction, good safety and low cost.

2. Soil nailing wall support

Soil nailing (also known as mortar anchor) is set in natural soil by drilling, inserting steel bars and grouting, and combined with shotcrete panel to form a soil nailing wall similar to gravity retaining wall, so as to resist the earth pressure behind the wall and maintain the stability of the excavation surface. Also known as shotcrete-anchor net reinforcement slope or shotcrete-anchor net retaining wall.

3. Bolt support

It is suitable for excavating large and deep foundation pits in hard soil or broken rocks, and it is used when there are buildings nearby to ensure slope stability.

4. Combined support of retaining cast-in-place pile and soil anchor

There are no anchor piles and tie rods at the top of the pile, but they are dug to a certain depth, and anchor rods are driven obliquely behind the pile at regular intervals. After reaching the strength, install the cross brace, tighten it and fix it. Excavate in the middle of the pile to the designed depth, which is suitable for large-scale deep foundation pit. The construction period is long, and there are buildings nearby, which are not allowed to support, and the adjacent foundation is not allowed to have settlement and displacement.

5, steel sheet pile support

When the foundation pit is deep, the groundwater level is high and there is no precipitation, using sheet pile as supporting structure can not only retain soil and prevent water, but also prevent quicksand. Sheet pile support can be divided into anchored sheet pile (cantilever sheet pile) and anchored sheet pile. The commonly used steel sheet pile is U-shaped steel sheet pile, also called Larsen steel sheet pile.

6, underground continuous wall support

First, the reinforced concrete diaphragm wall is built. After reaching the strength, mechanical excavation is adopted between the walls. The supporting method has high rigidity and strength, can retain soil, bear load, stop water and prevent seepage, can be used in narrow sites, and is suitable for large-area deep foundation pit construction with groundwater.

7. Retaining wall+internal support

When the depth of foundation pit is deep, the strength and deformation of cantilever retaining wall can not meet the requirements, and the reliability of anchor pulling outside the pit is low, the support inside the pit can be used. It is suitable for all kinds of foundation soil layers, but the disadvantage is that the internal support will occupy a certain construction space. Commonly used are steel tube internal support and reinforced concrete frame internal support.

Compared with ordinary steel support and concrete support, the new prestressed fish-bellied steel support occupies less space and has a short construction period, which has a good application prospect.