Research paper on concrete application of geotechnical engineering construction technology

Research paper on concrete application of geotechnical engineering construction technology

1 technical characteristics of geotechnical engineering construction

1) has strong uncertainty. In the construction site investigation, it is difficult to explore the overall situation of rock and soil, and some rock and soil structures may be unstable, which will change with the changes of external factors and affect the construction progress.

2) There are strong regional differences. China has a vast territory, and the natural conditions in different regions are quite different. There are many kinds of rocks, and the properties of rock and soil are also very different. The emphasis of construction technology design is quite different.

3) strong concealment, not easy to be found. Many geotechnical engineering projects are located underground, such as foundation treatment, pile foundation grouting and underground continuous wall construction. The construction process and operation of the project are hidden, even if there are problems, it is difficult to find them.

4) Strong correlation with surrounding rock and soil structures. The choice of geotechnical engineering construction technology will be greatly influenced by the specific construction environment, such as the structure and nature of geotechnical engineering, and the stability of engineering buildings is also closely related to the geotechnical structure of the construction site.

2 Application status

2. Application of1in foundation treatment

1. Various mature foundation treatment technologies are widely used in geotechnical engineering construction in China, and many of them have reached the world leading level. Second, according to the characteristics of its own geotechnical structure, China has independently developed a series of foundation treatment technologies, which greatly improved the level of foundation treatment and the overall construction quality. In recent years, China has independently developed a new type of foundation between pile foundation and composite foundation-reinforced concrete composite foundation with sparse piles. The application of this foundation can improve the bearing capacity of rock and soil between piles and the stability of buildings. Thirdly, on the problem of dealing with the deviation of buildings, China has adopted the methods of reaction release, water flushing and core pulling and core lowering, which have well dealt with the deviation of inclined buildings.

2.2 Application in Foundation Engineering Construction

First of all, various pile-forming technologies have been widely used in geotechnical engineering construction all over China, and post-grouting technology of cast-in-place pile has been developed, which separates cast-in-place pile from grouting technology, greatly improves the bearing capacity of pile foundation and reduces the settlement of pile foundation. Secondly, geotechnical construction technology, attention to the influence of surrounding environment, pre-drilling and static pressure are adopted to broaden the application scope of reinforced concrete precast piles. At present, the construction technology of immersed cast-in-place pile is widely used because of its low cost and convenient construction.

2.3 Application in Slope Reinforcement

First, China's geotechnical anchoring technology has been applied in the last century, and it is relatively mature at this stage, and the secondary grouting technology has been adopted, which greatly improves the bearing capacity of anchor rods in soft soil. At present, China's geotechnical anchoring technology has been at the leading level in the world. Secondly, in the deep foundation pit support technology, soil nailing technology has developed rapidly in China. Combining other technologies with soil nailing technology to form composite soil nailing support has greatly improved the support strength and broadened the application scope of soil nailing support.

2.4 Application of Trenchless Technology

This construction technology does not need to excavate the surface of the construction site, which can ensure the smoothness of the construction site, and can also be used for the detection, replacement, maintenance and construction of underground pipelines without excavating the surface. These technologies started relatively late in China and are still in the initial stage.

3 the specific application of geotechnical engineering

Taking the concrete construction of a section of Hanyi high-speed railway as an example, the post-grouting technology of cast-in-place pile in geotechnical engineering construction technology is studied and analyzed.

3. 1 project overview

First, the soil quality. Geotechnical engineering construction area is mainly composed of artificial fill layer and lake accumulation layer. Artificial fill layer mainly includes miscellaneous fill, silt and cultivated soil, and its soil characteristics are grayish brown, loose, concrete and domestic garbage. Sludge is mainly organic matter and pond sludge; Farming soil is mainly cohesive soil. Second, the water content. The main aquifer in this area is Quaternary Holocene silty soil, and there is shallow groundwater under the project section, so the water quantity is not very large and the water quality is not very good. In addition to this water layer, there is also a slightly confined water, which belongs to sealed fresh water and can be used as drinking water.

3.2 Geotechnical engineering concrete design and construction technology

According to the actual needs, the diameter of the bored pile is 1.5m, and the top of the pile should pass through the silt layer 10m to ensure the stability of the pile. Because the length of the pile is very long, it is necessary to determine in advance how much pressure a pile needs to bear. The designer's estimate is about 4500KN. Because the local geological conditions are not very good, it is necessary to choose the grouting technology suitable for the local area to protect the bearing capacity of the pile.

First, determine the grouting pressure. Through the analysis of grouting parameters, it is concluded that the grouting pressure should not exceed 2.5MPa, and it is best to control it in the range of 1~2MPa during concrete construction. When grouting, the installation sequence of grouting pipes must be determined. Generally, the check valve is connected first, and then the high-pressure grouting hose is connected. After grouting is completed, the closing sequence of valves is also very important. Generally, close the check valve first.

Second, the grouting quantity. After many calculations in this project, the designers have come to the conclusion that the cement demand is 3.5t, the water-cement ratio in grouting is preferably between 0.5 and 0.6, and the grouting speed should be moderate. In the post-grouting process of cast-in-place pile, if slurry returns, the grouting machine should be stopped immediately, and grouting should be carried out after about half an hour.

Thirdly, the control of grouting time. Through years of working experience, we know that the initial setting period of concrete will officially start after about 10, so if grouting can maintain the best effect, it needs to start after 10. If the grouting time is too early, the concrete has not completely solidified at this time, which will lead to low concrete strength and destroy the influence of the pile itself; If the grouting time is too late, it is difficult to form a smooth concrete channel between the solidified concrete. Therefore, the grouting time must be well controlled in practical engineering to improve the overall level of the building.

3.3 Test of post-grouting technology for geotechnical engineering cast-in-place pile to improve engineering effect

The purpose of this test is to verify the strengthening effect of grouting reinforcement on the bearing capacity of cast-in-place piles. The radius of the test pile is 1.0m, and the pile length is 50m. The specific experimental steps are as follows: 1. Preparation before the experiment. Step 1: Select the poured test pile, carry out corresponding treatment, keep the top surface of the pile clean and flat, and set up four layers of steel mesh, with the direct spacing of each layer of mesh being 15cm. Step 2: Make sure that the main reinforcement in the column is at the same level, and reset the grid according to the above standards. Step 3: Set the reference column, keep the top surface of the column flat, and set the grid as above. Step 4: Set steel plates for wrapping within a distance of one pile length from the top of the pile. The experimental site should be flat and large vehicles can pass normally. Step 5: Excavate the foundation pit in advance and do a good job of drainage. Second, the installation of field equipment. According to the requirements of the load in the test, select the appropriate jack specifications to ensure that the output of the jack is not more than 80% of the top weight in each test. The benchmark pile is used to support the benchmark frame, and the linear distance between the benchmark pile and the test pile should meet the requirements of the specification. The settlement measurement is analyzed and measured by a dial indicator.

4 conclusion

With the continuous progress of China's economy and society and the continuous improvement of people's living standards, people put forward better requirements for geotechnical engineering construction technology. In order to meet the needs of the development of the times, the construction technology of geotechnical engineering has been continuously reformed and developed. In order to better apply construction technology, construction workers must first understand their own characteristics.

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