? Paper Keywords: building foundation construction technology quality

? Abstract: Based on the author's working experience for many years, this paper briefly discusses the construction technology of modern building foundation engineering.

1 Construction characteristics of building foundation engineering

1. 1 complexity

China has a vast territory and complex engineering geological conditions, including muddy soil, miscellaneous fill, collapsible loess, frozen soil and seasonal frozen soil. In addition, karst geology is mainly located in southwest China, but it is also distributed in other areas; At the same time, China is a country with many earthquakes and high magnitude, and earthquakes have great influence on the foundation. This complicated geological condition increases the difficulty of basic engineering survey, design and construction, and puts forward a lot of complicated technical problems.

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Examples of houses cracking and collapsing due to improper foundation design or construction scheme have occurred from time to time, resulting in serious losses, and the malignant and huge waste caused by engineering construction is really amazing.

1.3 potential

Judging from the complicated process connection of the main structure itself, the latter process covers the former process to varying degrees, and the process quality is obviously concealed, which is why the main structure project must strengthen the inspection and acceptance of concealed works and save complete concealed acceptance data.

1.4 severity

To a certain extent, once a building project is completed and put into use, foundation quality accidents are often irreversible, and the losses caused by them are far greater than the cost of foundation engineering construction. Regardless of site selection, survey and design, or construction quality problems, once quality problems occur in foundation engineering, it will often lead to foundation instability and the destruction of the overall structure of construction engineering. It is a fatal and devastating major quality accident in construction engineering, which not only causes huge economic losses, but also directly endangers people's lives and property safety. Because the foundation bears all the loads of the superstructure, once local damage occurs, its damage degree will spread rapidly, and accidents are often sudden and often difficult to be found by people, further aggravating its harmfulness and severity.

1.5 difficulty

The difficulty in handling quality accidents of foundation engineering means that compared with other parts of construction engineering, its reasons are closely related to its position and function: ① The foundation engineering is underground, and the construction operation of accident handling is more difficult; (2) Once the foundation bears the upper load, the treatment of it will inevitably affect the performance of the superstructure of the building, especially for the completed and delivered projects, which bear all the loads of all construction projects, and the chain nature of foundation engineering quality accidents is very difficult to deal with.

2 to ensure the effectiveness of building foundation engineering construction

2. 1 Pay attention to the accuracy of engineering exploration.

The engineering investigation report shall fully reflect the engineering geology and hydrogeology of the construction site. To prevent engineering accidents of foundation, we must first have a comprehensive and correct understanding of the engineering geology and hydrogeological conditions of the site. The key is to do a good job in engineering investigation, and reasonably determine the task and purpose of engineering investigation according to the characteristics of the construction site and the use requirements of the building. Exploration provides a decisive reference for the design of buildings, so it must not be ignored and not done, nor can it be falsified without considering whether it is applicable. Especially for complex and weak foundations, we should be more cautious.

In addition, attention should be paid to the selection of drilling depth during exploration. Because the drilling depth must meet the design requirements, if it does not meet the design requirements for compression thickness or the soil layer where the pile is located, it will be impossible to correctly calculate the settlement of the foundation or the correct bearing capacity of the pile, and it will also fail to meet the design requirements of the foundation. Therefore, the appropriate drilling depth must be determined according to the design requirements. If the number of exploration is insufficient, the number of drilling holes and exploration pits is small, and the depth of drilling holes is not enough, so that the unevenness of excavation and the inconsistency of bedding can not be expressed, it may cause warping, bending and cracking of buildings, resulting in serious quality accidents and huge economic losses.

2.2 Improve the rationality of structural design

The foundation design should be based on the use requirements of buildings, structural forms and geological conditions of the site, combined with the specific conditions of the site. On the premise of applicability and economy, it is necessary to ensure that the main load-bearing structure of the building will not crack or be damaged during normal use.

Designers should be cautious about the recommended value of foundation bearing capacity provided by the engineering investigation report and strictly calculate the actual earth pressure of foundation. If they have questions about the recommended value of the survey report, they can conduct load test verification again. When building large and medium-sized projects on natural foundations, the constructors should check the rationality of the design foundation bearing capacity. Once the foundation settlement is found to be large or inclined, it is necessary to stop work immediately and study with the survey, design and use units to take necessary measures to prevent catastrophic damage to the foundation and buildings.

3. Strengthen the construction technology of building foundation engineering.

Taking a residential project as an example, this paper discusses how to do well the construction quality of building foundation engineering. This project is a frame structure with 7 floors, including overhead floors, with the height of 2. 1m and the upper floors of 3.0m The soil layers of the site are filled soil, silt, silty clay, muddy coarse sand and sandy clay from top to bottom.

3. 1 basic selection

The foundation is the connection between the building and the foundation, and the foundation transfers the load of the vertical system of the building to the foundation. If the bearing capacity of foundation is sufficient and the distribution of foundation is the same as that of vertical structure, independent foundation can be used; If the foundation is weak and the building is high, the raft foundation should be used. The advantage of raft foundation is that the contact surface of foundation is large and the cost is higher than that of independent foundation. If the foundation soil is good and the underground water level is low, manual digging cast-in-place piles are used as support.

Assuming that the foundation has insufficient bearing capacity and belongs to soft soil foundation, measures must be taken to treat soft soil foundation. Soft soil foundation is composed of muddy soil, collapsible loess, miscellaneous fill or other foundations, so its composition is uniform, and its distribution range is similar.

Soil and sediment provide corresponding parameters for the foundation treatment scheme adopted. In the preliminary calculation, it is best to calculate the approximate load of the building structure first, assuming that it is evenly distributed in the whole area, so as to get the average load level, which can be compared with the bearing capacity of the foundation itself. If the allowable bearing capacity of foundation is more than four times the average load level, it may be more economical to use independent foundation than mat foundation. If the allowable bearing capacity of foundation is less than 2 times of the average load level, raft foundation can be used, and if it is between the two, pile foundation or open caisson foundation can be used.

3.2 Foundation construction technology and measures

When the local foundation soil is silt and the upper soil layer is thin, measures should be taken to avoid the disturbance of silt and muddy soil during construction. If it is filled soil and construction waste, it can be used as bearing layer under the condition of good uniformity and compactness. Miscellaneous fill such as domestic garbage with high organic matter content and industrial garbage corrosive to foundation cannot be used as bearing layer without treatment. When selecting the foundation treatment method, factors such as engineering geological and hydrogeological conditions, building requirements for foundation, building structure and foundation type, surrounding environmental conditions, material supply and construction conditions should be comprehensively considered, and the best scheme should be selected after comparative analysis of technical and economic indicators.

In foundation treatment, effective measures must be taken to strengthen the stiffness and strength of local structures, so as to increase the adaptability of buildings to uneven deformation of foundation, and necessary tests must be carried out on the determined foundation treatment methods to provide relevant basis for construction quality. After foundation treatment, the deformation of the building should meet the requirements of current relevant codes, and settlement observation should be carried out during construction.