Foundation pit classification

Urban bridge engineering foundation pits are mainly used for the construction of caps, abutments and enlarged foundations, and are generally divided into two types: unsupported and supported.

1. Unsupported foundation pit


1. The foundation is not deeply buried, the construction period is short, and the safety of adjacent buildings will not be affected when the foundation pit is excavated.

2. The groundwater level is lower than the base, or the penetration is small, which does not affect the stability of the pit wall.

Main forms: The pit wall forms of unsupported foundation pits are divided into vertical pit walls, slope and stepped pit walls, and variable slope pit walls.

2. Supporting foundation pit


1. The soil quality of the foundation pit wall is unstable and affected by groundwater.

2. The amount of sloping earthwork excavation is too large and uneconomical.

3. It is easy to be restricted by the construction site or neighboring buildings, so slope excavation is not allowed.

Foundation pit classification level one: Important projects or supporting structures are part of the main structure, and the excavation depth is greater than 10 meters, and the distance from adjacent buildings and important facilities is within the excavation depth. There are historical cultural relics within the scope of the foundation pit. , Modern excellent buildings, important pipelines and other foundation pits that need strict protection.

Level II: Foundation pits located between Level I and Level III.

Level 3: Excavation depth is less than or equal to 7 meters and the surrounding environment has no special requirements.

Support method
Shallow hole

Common forms of support:

(1) Anchor support

(2) Inclined column support

(3) Continuous vertical support

(4) Intermittent horizontal support

(5) Intermittent horizontal support

(6) Short column transverse support

(7) Temporary retaining wall support

Deep pit folded

Common forms of support:

(1) Soil nail wall support

(2) Steel sheet pile support

(3) Cement soil wall support

(4) Support and support in the row of piles

(5) Anchor support for row piles and soil layer

(6) Retaining pouring piles or underground continuous wall support

Summary: There are many ways to support foundation pits, and they are flexible and need to be selected based on specific conditions. The specific scheme to be adopted depends on factors such as the soil quality of the foundation pit, groundwater level and other factors, and a conclusion can be made based on the “exploration report” provided by the exploration department.