1 construction technology of concrete cutoff wall
The application of concrete cutoff wall in building construction mainly originated in Italy in the 20th century, and then the concrete cutoff wall technology was gradually popularized and widely used in other countries. The application of concrete cutoff wall technology in China's construction projects began in the 1950s, and then it was widely used in China's projects, which also provided a certain guarantee for the quality of construction projects. So far, China's concrete cutoff wall technology has reached a certain level of development. Concrete cutoff wall contains different types, which can be divided into the following types according to the structural form.
1. 1 slotted concrete cutoff wall
This type of cutoff wall is called slotted concrete cutoff wall because its cross section is slotted. When fixing the wall, mud and other forms are mainly used, and then holes are drilled at appropriate positions and concrete is backfilled to form the cutoff wall. In general, the seam length of slotted concrete cutoff wall is about 7m. According to different connection modes, there are two different connection modes: interlocking and overlapping.
1.2 Pile-column concrete cutoff wall
The cross section of this type of concrete cutoff wall is a circular hole, and the concrete cutoff wall is formed by backfilling with conduit and mud retaining wall. According to the different connection methods, the layout of cutoff wall is also different. For example, on the basis of ensuring the seepage prevention of earth-rock dams, builders usually adopt two different connection methods: interlocking and overlapping.
1.3 mixed concrete cutoff wall
Mixed concrete cutoff wall is a combination of slotted hole and pile-column concrete cutoff wall. In addition, in the foundation construction of water conservancy projects, due to the scarcity of clay resources around water conservancy projects, the requirements for environmental protection are relatively high. At present, bentonite slurry is widely used in the relevant requirements of cutoff wall construction materials. In mud wall protection and reinforcement, drilling mud mainly includes water, clay and additives. For the preparation of drilling mud, the consistency of mud needs to be determined according to the drilling method and the actual situation of the formation. If the mud is too thin, it will affect the drilling speed. The following aspects should be paid attention to in the configuration of drilling mud: First, control the liquid level of mud, and the liquid level elevation in the slot should be about 1m higher than the river elevation, and it should be supervised by someone; The second is to control the specific gravity of mud, which is not more than1.15; The third is to control the viscosity of mud. High mud viscosity will lead to a decrease in displacement, which is generally controlled between 32 and 50.
2 Key points of construction technology of concrete cutoff wall in foundation treatment of water conservancy project
2. 1 Construction technology of concrete cutoff wall in building facilities
In the foundation treatment of hydraulic engineering, construction equipment is one of the more important elements in the construction of concrete cutoff wall, especially the application of drilling equipment. Due to the huge drilling equipment, special attention should be paid to the transportation and maintenance of the equipment during use. If it is necessary to use a wire rope drilling rig during foundation construction, the construction personnel need to repeatedly break the ground with an impact drill before construction until the ground is completely broken, and then pump out the mud and sand chips on the ground with a sand pump. If this method is used to drill holes, it will not only consume a lot of resources, but also reduce the construction efficiency. If the impact reverse circulation drilling rig is used, the construction personnel should change the slag discharging mode of the equipment to the pumping continuous slag discharging mode to avoid the damage of the drilling rig to the particles during the working process, thus affecting the working effect of the drilling rig. This form is more efficient, but it requires more equipment. When using grab bucket for construction, constructors can remove the soil, use the bucket teeth of the equipment for cutting, and completely crush the soil and gravel on the ground before cleaning.
2.2 Construction technology of concrete cutoff wall
2.2. 1 construction of underground continuous wall by drilling and splitting method
In the construction of concrete cutoff wall, the drilling and splitting method is mainly used in sandy pebble stratum. During the construction, the axis needs to be divided into several grooves, and each groove is different in length according to the design requirements. During construction, the two tanks are divided into the first-stage tank and the second-stage tank, and then the slot hole construction is carried out. Wire rope impact drilling rig and impact reverse circulation impact drilling rig shall be used, and layered drilling shall be adopted during drilling. For drilling holes with adjacent depths between holes, the hole inclination needs to reach a certain standard when drilling. After the main hole and the corresponding auxiliary hole are hacked repeatedly, the mud and debris should be cleaned up after chopping.
2.2.2 Construction of cut-off wall by drilling and grasping method
In the foundation construction of water conservancy project, faced with some relatively tight ground slotting, the construction personnel need to combine punching machine with grab. When the punching drill goes deep into the bedrock and boulder layer in the main hole, the grab punching drill should be used to grab the auxiliary hole. The captured auxiliary hole is located in the middle of the adjacent main hole, and the slotted hole construction should be carried out by using the method of three drills and two grabs according to the size of the slotted hole.
2.3 Construction process of concrete cutoff wall
First, after the trench excavation is completed, the trench should be fixed with building materials such as soil, and on this basis, the stability of the inner wall of the trench should be ensured. In the process of organizing the construction, the construction personnel should choose loose clay and make mud to ensure that the density of the mud is 1.05g/cm3. The second is to set guide wall to protect the pipe trench. In actual construction, the drilling rig should be used as the foundation guide device to protect the pipe trench. Because the construction period of the concrete cutoff wall is short, for this reason, in order to save the construction cost, the constructors can adopt the repeatedly modified steel structure guide wall and other forms of concrete structure guide wall. Thirdly, when pouring concrete, we should choose the way of straight conduit, and the main premise to ensure the uniformity of concrete pouring is the inner diameter of the conduit. In addition, when choosing concrete, it is necessary to choose appropriate concrete gradation and concrete with appropriate strength in combination with the actual situation of construction projects, which requires that concrete has strong impermeability, and the impermeability coefficient can reach 1× 10-6 cm/s Fourth, in order to ensure the quality and effectiveness of the connection, the construction personnel need to use the cutting method to construct the concrete cutoff wall, because the wall
3 Conclusion
To sum up, influenced by economic development, water conservancy projects have gradually become the focus of attention of relevant personnel in recent years, especially in Gansu. Foundation construction is the basic link of water conservancy project, and its quality affects the whole water conservancy project. This paper mainly expounds the technical points of concrete cutoff wall construction in foundation treatment of water conservancy projects, hoping to help improve the construction quality of water conservancy projects in Gansu and even the whole country, so as to better promote the development of water conservancy in China.
I believe that after the above introduction, everyone has a certain understanding of the technical points of concrete cutoff wall construction in water conservancy projects. Welcome to Zhong Da for more information.
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