What is foundation pit engineering and what is foundation pit engineering knowledge

In order to ensure the safety and stability of the underground space formed by the ground downward excavation during the construction of the underground structure, the retaining structure, groundwater control, environmental protection and other measures required are called foundation pit engineering.

Foundation pit engineering is a systematic engineering integrating geological engineering, geotechnical engineering, structural engineering and geotechnical testing technology. Its main contents: engineering survey, supporting structure design and construction, earthwork excavation and backfill, groundwater control, information construction and surrounding environmental protection.

The simplest and most economical way for foundation pit construction is to enlarge the slope excavation, but it is often limited by the site conditions and the surrounding environment, so it is necessary to design the support system to ensure the smooth progress of the construction and can better protect the surrounding environment.

To put it simply, the foundation pit is when the underground part of the main structure needs to be constructed, in order to provide space for underground construction, protect the surrounding environment and the building from being affected, and take a series of measures, including 1. Carry out support (support structure), the role is to serve as a retaining support structure to maintain the balance of soil inside and outside the pit; 2. Reduce the groundwater level, so that the water level is lowered to 1m lower than the pit, so as to prevent the leakage of water and destroy the soil balance during the excavation process; 3. Excavate the soil in the pit, dig out the soil in the pit according to the construction sequence, and then construct the retaining structure to ensure the balance of the soil. Among the aspects involved, geological exploration, design of supporting structures, construction, monitoring of foundation pit deformation, detection, in general, the above is called foundation pit engineering, is a very comprehensive system engineering.

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1. Foundation pit engineering is a comprehensive discipline in geotechnical engineering.

Foundation pit engineering not only involves engineering geology, soil mechanics, seepage theory, structural engineering, construction technology and monitoring design, but also involves the intersection between these disciplines, such as: the influence of groundwater seepage on earth pressure and soil stability: consider the influence of the interaction between soil and supporting structure on the magnitude and distribution form of earth pressure; the influence of different processes of unloading and loading of soil on the support system; spatio-temporal effects in foundation pit construction; Adopt the monitoring and information construction of groundwater level, earth pressure, deformation of support and support systems, etc.; Foundation pit engineering causes the influence of the surrounding soil stress field, displacement field, and groundwater level changes on the surrounding environment.

2. Temporary and risky.

Under normal circumstances, foundation pit support is a temporary measure, the safety reserve of the supporting structure is small, the risk is large, and the economic indicators of the foundation pit engineering are particularly demanding, and sometimes even unreasonably low safety. In the deep foundation pit project in the dense building complex of large cities, the surrounding environmental conditions are strict, the foundation pit project must be safe and reliable, and the cost of the foundation pit project is often high, therefore, the contradiction between temporary and economic indicators is prominent.

3. There are large regional differences in foundation pit engineering.

The geological conditions of the engineering in various regions are different, such as the engineering geology and hydrogeological conditions of the soft soil area and the loess area, resulting in great differences in foundation pit engineering. There are also differences in different areas of the same city, so the design should be adapted to local conditions and cannot be simply copied.

4. The environmental conditions around the foundation pit are strict.

Adjacent tall buildings, underground structures, pipelines, subways, etc. have strict deformation restrictions caused by foundation pit excavation, and the construction factors are complex and changeable, and changes in climate, season, surrounding water bodies and other factors can lead to changes in the environmental conditions around the foundation pit.

The above characteristics determine the complexity of foundation pit engineering design and construction. A variety of uncertain factors can easily lead to some conceptual errors in the design and construction of foundation pit engineering, which is the main reason for foundation pit accidents.

Characteristics of foundation pit engineering: The foundation pit support system is a temporary structure, with a small safety reserve and a greater risk. Foundation pit engineering has a strong regional character.

Foundation pit engineering has a strong personality. It is difficult to classify foundation pit engineering and stipulate unified standards for the allowable deformation of supporting structures. The foundation pit project is comprehensive.

Foundation pit engineering includes: engineering survey, supporting structure design.

and construction, earthwork excavation.

and backfilling, groundwater control, information construction and surrounding environmental protection.

There are generally two kinds of construction technology: slope excavation (excavation without support) and excavation under the protection of the support system (excavation with support).

1. Deep foundation pit.

It refers to the excavation depth of more than 5 meters (including 5 meters), or the depth of the excavation is not more than or trembling 5 meters, but the geological conditions, the surrounding environment and the underground pipeline are particularly complex.

2. According to the Ministry of Housing and Urban-Rural Development of the People's Republic of China on May 13, 2009 issued the "Measures for the Safety Management of Dangerous Sub-project Projects" in the subsidiary documents, the deep foundation pit project is: the earthwork excavation of the foundation pit (groove) with an excavation depth of more than 5m (including 5m).

Support and dewatering projects. (Although the excavation depth does not exceed 5m, the earthwork excavation and support of the foundation pit (groove) that affects the safety of adjacent buildings (structures) due to the geological conditions, surrounding environment and underground pipelines of the banquet sedan chair.)

In the construction of buildings, we will encounter a variety of terms of installation and repair, today I want to introduce to you is the foundation pit, let's take a look at the definition of the foundation pit, the difference between the foundation pit and the foundation groove, and what are the ways of foundation pit support.

Definition of foundation pit.

The building foundation pit refers to the space below the ground excavated for the construction of the foundation and basement of a building (including structures). A temporary pit excavated for the foundation of a building is called a foundation pit. The foundation pit is a temporary project, and its function is to provide a space for the masonry of the foundation to be carried out according to the location specified in the design.

The difference between the foundation and groove of the foundation of the pit and the foundation groove of the foundation of the foundation

Dig a single foundation earthwork, when the length is 3 times the width and above, and the width is not more than 3m is the foundation groove, when the bottom area is less than 20 is the foundation pit. When digging the entire house foundation, it is called a large excavation foundation pit, and when digging a depth of more than 5 meters, it is called a deep foundation pit.

The way of foundation pit support.

According to the division of deep and shallow foundation pits, it can be divided into:

Shallow pit support: (1) anchor pull 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 support: (1) soil nail wall support, (2) steel sheet pile support, (3) cement soil wall support, (4) pile inner support support, (5) pile layer anchor support, (6) retaining cast-in-place pile or underground diaphragm wall support.

Deep foundation pit, as the name suggests, is an underground excavation project, which can be divided into two situations.

1. Earthwork excavation, support and dewatering engineering of foundation pits (grooves) with an excavation depth of more than 5m (including 5m). 2. Although the excavation depth does not exceed 5m, the geological conditions, surrounding environment and underground pipelines are complex, or the earthwork excavation and support of the foundation pit (groove) that affects the safety of adjacent buildings (structures). **Deep foundation pit engineeringDeep foundation pit, as the name suggests, is an underground excavation project, which can be divided into two situations.

1. The earthwork excavation, support and dewatering workshop of the foundation pit (groove) with an excavation depth of more than 5m (including 5m). 2. Although the excavation depth does not exceed 5m, the geological conditions, surrounding environment and underground pipelines are complex, or the earthwork excavation and support of the foundation pit (groove) that affects the safety of adjacent buildings (structures).

Foundation pit engineering mainly includes the design and construction of foundation pit support system and earthwork excavation, which is a very comprehensive system engineering. It requires close cooperation between geotechnical and structural engineering technicians. The foundation pit support system is a temporary structure, which is no longer needed after the completion of the underground engineering construction.

Both the pit and the trench are used to build the foundation of the building, but the shape of the plan is different. The foundation pit is square or relatively close to square; The grooves are long in shape and sometimes longer. To grasp the difference in their shape.

Foundation pit refers to the bottom area within 27 square meters (not 20), and the bottom long side is less than three times the short side of the foundation pit.

The base groove refers to the base groove with the width of the bottom of the groove within 3 meters and the length of the groove is more than 3 times the width of the groove.

That is to say, the general definition of deep foundation pit is: the bottom area is within 27 square meters (not 20), and the long side of the bottom is less than three times the short side, the excavation depth is more than 5 meters (including 5 meters) or more than three floors of the basement (including three layers), or the depth is not more than 5 meters, but the geological conditions and surrounding environment and underground pipelines are particularly complex (vice versa, it is a shallow foundation pit).