First, the structure type of foundation pit supporting construction

1, slope excavation

Slope excavation is also known as slope rate method. When there are possible sites for slope excavation around the foundation pit, the geological conditions of the site are good, and the groundwater level is deep, the slope excavation should be given priority.

The slope rate of slope excavation should be determined by calculation according to the requirements of slope stability.

2, supporting support structure

Sheet pile, column pile, diaphragm wall and other supporting bodies belong to this category. Retaining piles and walls are inserted into the pit bottom soil to a certain depth(Generally, it is inserted into a hard soil layer), the upper part is a suspended wall or an anchor support system is set to form a beam type stress member, which is solved according to the vertical elastic foundation beam inserted into the soil.

This kind of supporting structure is widely used, has strong applicability, and is easy to control the deformation of the supporting structure. It is especially suitable for deep foundation pit with large excavation depth, and can adapt to various complex geological conditions. The design and calculation theory is relatively mature, and the engineering experience in various regions is also more, which is the main form often used in foundation pit engineering.

3, gravity support structure

Soil-cement mixing pile retaining wall, high-pressure rotary jet pile retaining wall, soil nail wall and so on are similar to gravity retaining wall. This kind of supporting structure has a large section size and relies on the gravity of the solid wall to retain soil. The wall body can also be designed into lattice structure, or step form and other forms, the wall body mainly bear pressure, generally do not bear tension, according to the gravity retaining wall design principle calculation. No wrong pull or internal support system, earth excavation construction is convenient. When the soil condition is poor, the excavation depth of foundation pit should not be too large. Suitable for small foundation pit engineering. Adopt soil nail wall structure, adaptability is larger. There have been a lot of engineering experience in the application of solid gravity support structure.

Soil NAILING can be combined with prestressed bolt, micro pile, waterproof curtain wall, etc., to form composite soil nailing wall, composite soil nailing wall has good supporting performance and a wide range of application.

4, combined support structure

On the basis of the above two retaining and gravity supporting structures, the combination of several supporting structures can be adopted, such as pile row-Composite soil nailing, or upper slope followed by composite soil nailing wall, lower row pile+The composite form, such as internal support, is called combined support structure.

Second, the structure choice of foundation pit supporting construction

The selection of supporting structure should be based on the geological conditions of the site, the depth and function of the foundation pit, construction conditions, environmental factors and regional engineering experience, etc. The following factors should be comprehensively considered:

1Foundation pit depth;

2, soil properties and groundwater conditions;

3, the bearing capacity of the surrounding environment of the foundation pit to the deformation of the foundation pit and the consequence of the failure of the supporting structure;

4, the main underground structure and foundation form and its construction method, the plane size and shape of the foundation pit;

5, the feasibility of construction technology of support structure:

6, construction site conditions and construction season;

7, economic indicators, environmental performance and construction period.

The applicable conditions of various support structures can be referred to the following table:

Three, foundation pit supporting groundwater control

When choosing the type of foundation pit, it is necessary to consider the treatment of groundwater, that is, how to control groundwater, which is an important content in the design and construction of foundation pit engineering. Especially in sandy soil and silt soil, when the water is shallow and abundant, sometimes there is confined water layer in the lower aquifer, it becomes an important factor affecting the stability of foundation pit.

The excavation of foundation pit in the area with high groundwater level requires dewatering, and pumping groundwater for a long time will cause the surrounding land subsidence. Therefore, when the environmental conditions do not allow dewatering, it is necessary to set a water stop curtain around the foundation pit to cut off the connection between the aquifer inside and outside the pit, so as to avoid the impact on the environment caused by the dewatering in the pit. Water stop curtain can be used underground diaphragm wall, cement soil mixing pile curtain wall or rotary jet grouting pile water stop curtain and other methods.

In the design of foundation pit, the seepage stability of foundation pit should be checked, which is also an important content of groundwater control. It is necessary to prevent the influence of flowing sand, flowing soil, piping and confined water layer on the foundation pit bottom.

Shanghai Qiangqiang Foundation Engineering Co., LTD. 's business covers foundation pit engineering, pile foundation engineering, land and waterFoundation treatment, slope treatment and other engineering fields. around "Excellent technology, reliable process, fast construction" technical requirements, is to provide customers with land, water foundation engineering technical consultation, construction services and other comprehensive solutions of the entity enterprise. Contact Number:400-100-2850