Expert’s argument for deep foundation pits

Article 6 A construction enterprise shall organize an expert group of no less than 5 people to conduct demonstration and review of the prepared special construction plan.

(2) Familiar with laws, regulations, technical standards, norms and procedures in the field of engineering construction;

(3) Engaged in relevant professional survey, design, construction and supervision work for more than ten years and Have senior technical titles or above.

Article 8 The preparation, expert argumentation, review and approval of special construction plans that comply with the provisions of Article 5 of these detailed rules shall be carried out in accordance with the following procedures:

(1) The construction enterprise shall organize relevant Professional engineering and technical personnel shall prepare a special construction plan and attach a calculation sheet, which shall be reviewed by the technical person in charge of the enterprise;

(2) The construction enterprise shall invite relevant experts who meet the conditions specified in Article 7 of these Detailed Rules to review the completed work. The prepared special construction plan shall be subject to demonstration and review. The technical director and plan preparation personnel of the construction enterprise, as well as the project professional supervision engineer and chief supervision engineer of the supervision unit shall attend the demonstration meeting.

(3) The construction unit should specify an expert to serve as the team leader. The expert team should evaluate whether the special construction plan is reasonable and feasible, whether the content is complete, whether the calculations are accurate and complete, and whether it meets the relevant mandatory standards for project construction, etc. Conduct a demonstration review and submit written demonstration review opinions. Members of the expert group should sign the demonstration review opinion, and the expert group's written demonstration review opinion should be included as an attachment to the special construction plan.

(4) The construction enterprise shall modify, supplement and improve the original special construction plan based on the demonstration and review opinions put forward by the expert group, review it by the person in charge of the technical department of the enterprise, approve it by the technical person in charge of the enterprise, and report it to the supervision unit It can only be implemented after review by a professional supervision engineer and signature by the chief supervision engineer.

(5) When the expert group believes that the special construction plan needs major modifications, the construction company shall reorganize expert evaluation and review after the special construction plan is modified and improved.

(6) The expert review and argumentation letter for the special construction plan should be filled out in the attachment.

Article 9 Construction enterprises should strengthen the management of sub-projects with greater risks, and identify sub-projects with greater risks when reviewing drawings and preparing construction organization designs. .

Prepare a special construction plan before construction, and strengthen technical briefings before construction (including safety and quality technical briefings), inspections during the construction process, and acceptance after construction is completed; professional production safety management personnel and Quality personnel should strengthen the full-process tracking and supervision of sub-projects with greater risks.

Extended information:

A deep foundation pit refers to an excavation depth exceeding 5 meters (including 5 meters) or a basement with more than three floors (including three floors), or the depth does not exceed 5 meters. meters, but the geological conditions, surrounding environment and underground pipelines are particularly complex.

According to the attached documents in the "Safety Management Measures for Partial Projects with Greater Danger" issued by the People's Republic of China and the Ministry of Housing and Urban-Rural Development on May 13, 2009, Deep foundation pit projects include:

(1) Earth excavation, support and dewatering projects for foundation pits (troughs) with an excavation depth exceeding 5m (including 5m). ?

(2) Although the excavation depth does not exceed 5m, the geological conditions, surrounding environment and underground pipelines are complicated, or the earthwork excavation of the foundation pit (trough) affects the safety of adjacent buildings (structures), Support and dewatering projects.

The foundation pit project mainly includes the design and construction of the foundation pit support system and earth excavation. It is a highly comprehensive and systematic project. It requires close cooperation between geotechnical and structural engineering technicians. The foundation pit support system is a temporary structure that is no longer needed after the underground engineering construction is completed.

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Both foundation pits and foundation trenches are used to build the foundation of buildings, but their plane shapes are different. The foundation pit is square or close to a square; the foundation trench is long in shape and has It takes a long time. What you need to master is the difference in their shapes.

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

A foundation trench refers to a foundation trench where the width of the trench bottom is within 3 meters and the trench length is greater than 3 times the trench width.

In other words, a deep foundation trench is generally defined It 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 exceeds 5 meters (including 5 meters) or the basement has more than three floors (including three floors), or the depth is not More than 5 meters, but the geological conditions, surrounding environment and underground pipelines are particularly complex. (On the contrary, it is a shallow foundation pit)

Features:

1) The foundation pit support system is a temporary structure with a small safety reserve and high risks. During the construction of foundation pit projects, monitoring should be carried out and emergency measures should be taken. Once a danger occurs during the construction process, timely rescue is required. When excavating deep foundation pits, pay attention to strengthening drainage and anti-irrigation measures. If the risk is greater, emergency plans should be made in advance.

2) Foundation pit engineering has strong regional characteristics. Foundation pit projects with different engineering geological and hydrogeological conditions such as soft clay foundations and loess foundations have great differences. There are also differences in different areas of the same city. The design and construction of the support system and earth excavation of the foundation pit project must be adapted to local conditions and carried out according to local conditions. Experience from other places can be used for reference, but it cannot be simply transferred.

3) Foundation pit engineering has strong individuality. The design and construction of the support system and earth excavation of the foundation pit project are not only related to the engineering geological and hydrogeological conditions, but also to the location, ability and importance of the adjacent buildings (structures) and underground pipelines of the foundation pit, as well as Surrounding site conditions, etc.

Sometimes protecting the safety of adjacent buildings (structures) and municipal facilities is the key to the design and construction of foundation pit engineering. This determines that the foundation pit project has a strong personality. Therefore, it is difficult to classify foundation pit projects and set unified standards for allowable deformation of supporting structures.

4) Foundation pit engineering is highly comprehensive. Foundation pit engineering requires not only geotechnical engineering knowledge, but also structural engineering knowledge. It requires a combination of soil mechanics theory, testing technology, computing technology, construction machinery, and construction technology.

5) Foundation pit engineering has strong spatial and temporal effects. The depth and plane shape of the foundation pit have a great influence on the stability and deformation of the foundation pit support system. When designing the foundation pit support system, attention should be paid to the spatial effect of the foundation pit project.

Soil, especially soft clay, has strong creep properties, and the earth pressure acting on the supporting structure changes with time. Creep will reduce the strength of the soil and reduce the stability of the soil slope. Therefore, sufficient attention must be paid to the time effect of foundation pit engineering.

6) Foundation pit engineering is a systematic engineering. The foundation pit project mainly includes two parts: support system design and earth excavation. Whether the construction organization of earth excavation is reasonable will play an important role in the success of the support system. Unreasonable earth excavation, steps and speed may lead to displacement of the pile foundation of the main structure, excessive deformation of the supporting structure, and even cause instability of the supporting system, leading to damage. At the same time, during the construction process, monitoring should be strengthened and efforts should be made to implement information-based construction.

7) Foundation pit engineering has environmental effects. Foundation pit excavation will inevitably cause changes in the groundwater level and stress field of the surrounding foundation, leading to deformation of the surrounding foundation soil, affecting surrounding buildings (structures) and underground pipelines, seriously endangering their normal use or safety. A large amount of earthwork will also have an impact on transportation and the environment of the spoil site.

Founder pit retaining structure system

1. The foundation pit enclosure structure system includes plate (pile) walls, purlins (crown beams) and other ancillary components. The sheet (pile) wall mainly bears the earth pressure and water pressure generated by the excavation and unloading of the foundation pit, and transmits this pressure to the support. It is a construction temporary retaining wall structure that stabilizes the foundation pit.

2． There are many forms of enclosure structures used in subway foundation pits, and their construction methods, techniques and construction machinery are also different; therefore, special considerations should be taken according to the depth of the foundation pit, engineering geology and hydrogeological conditions, ground environmental conditions, etc. The characteristics of urban construction are determined after a comprehensive technical and economic comparison.

Reference: Baidu Encyclopedia-Deep Foundation Pit