A preliminary investigation on the construction technology of concrete impermeable walls of dam shoulders in water conservancy and hydropower projects

  With the increasing number of water conservancy and hydropower construction projects, its significance for the economic development of China is becoming increasingly heavy, as a project that is beneficial to the improvement of people’s living standards and the country, its quality is the focus of attention during the construction process. The construction of hydropower construction also contains the construction of the dam base, the construction of the dam shoulder, the construction of the reservoir construction of different parts of the construction, these construction processes will involve the concrete impermeable wall construction technology, so as a water conservancy and hydropower construction designers, mastering the basics of concrete impermeable wall, and understand its characteristics is particularly important.

  1 Concrete seepage control wall technology

  1.1 The development status of concrete seepage control wall

  The concept of concrete impermeable walls has emerged in the 20th century and is being used more and more in the development of water conservancy and hydropower projects.

  1.2 Types of concrete impermeable walls

  1.2.1 Slotted slab type impermeable wall.

This type of impermeable wall is a channel type impermeable wall with cross section. It is mainly reinforced with mud, etc., and requires holes at suitable locations for backfilling with concrete. Usually, according to the different sizes of the slots and holes, this type of seepage control wall can also be divided into interlocking type and lap type.

  1.2.2 Pile and column type impermeable wall.

The cross section of this type of seepage control wall is in the shape of round holes, mainly assisted by casing or mud, and the large diameter round holes are filled with concrete, and the link work of seepage control wall is reached by this technique, where the difference is that the pile holes can be linked in different ways, and the arrangement of each type of seepage control wall is also different.

  1.2.3 Mud tank seepage control wall.

It is known by name that this type of seepage control wall is mainly reinforced with mud in order to make the hole wall upright. This kind of seepage control wall should be filled with a mixture of practical mud, sand, clay, etc., so as to form a solid seepage control wall.

  1.2.4 Sheet pile infill impermeable wall.

This type of impermeable wall mainly uses the attached small tubes to carry out the construction work. The attached small tubes are driven into the foundation and the concrete material is driven into the space made by the small tubes using the pile itself, thus forming an impermeable wall.

  2 Concrete seepage control wall construction characteristics

  In the process of concrete seepage control wall construction, it not only includes the construction of hole guide wall and power supply system, but also the mixing and filling work of concrete, and various mixing and material transportation work, which are only some of the work in the construction of concrete seepage control wall. These jobs often use a bit of temporary equipment to carry out the work, and the actual scope of the construction process is very wide, which leads to the importance of the interface between each construction process.

Concrete impermeable walls, as a hidden project in construction, need to ensure that they are not polluting to the environment. Concrete impermeable walls have good adaptability to the elasticity as well as depth of water and hydropower construction, and are load-bearing as well as waterproof.

  3 dam shoulder concrete seepage control wall construction equipment and technology

  3.1 Selection of equipment for dam shoulder concrete seepage control wall

  This equipment can be used to repeatedly impact the ground surface into pieces and mud, which is practical for some soft ground as well as gravel and cobble ground operations. There is another kind of equipment often used in the construction of impermeable walls, is the grapple trencher, this machine does not rely on mud and other media, only the use of their own teeth can be completed for the ground cutting separation work, can be directly broken through the soil layer, for a variety of particles of uneven size of the soil layer, into the slot effect is very high. In the actual construction process, two kinds of equipment are often used to cooperate with the construction to achieve the highest construction efficiency.

  3.2 Construction process

  3.2.1 Drilling and splitting method.

This process is mainly applicable to cobblestone and sandstone ground. When carrying out construction, the size of the slot hole is set beforehand, and the ground is operated according to the set size, and after drilling operation by the equipment and reaching a certain depth, the drilling and splitting work is carried out directly on the secondary hole, and the waste generated by the drilling and splitting is disposed of.

  3.2.2 Drill and grab method.

When trenching in tight strata using the combined construction method of grab and percussion drill for construction, after the center-strike drill drills into the bedrock and drifting pebbles of the main hole using the grab to dig the amplitude hole between the two main holes according to the size of the slot hole, you can use three drills and two grabs or two drills and one grab method for construction.

  3.2.3 Grabbing method.

The construction of impermeable walls is carried out by using a grapple to dig the slots using a subsoil layer or a layer of sand and pebbles with a relatively small particle diameter, thus improving the construction efficiency.

  3.3 Production process of clay-doped concrete impermeable wall

  The dry production process of clay-doped concrete is complicated, costly and less stable in terms of soil properties and composition, but the dosing is more accurate, while the wet production process is simple, easy to operate, and produces a stable slurry with a large dosing error but within the allowable range of the clay-doped concrete ratio.

  4 dam shoulder concrete impermeable wall construction difficulties

  4.1 Difficulties in the construction of the loose bottom layer

  For the slots loose soil oil in the fill quality or poor soil quality resulting in the slots of the soil is relatively loose, in the excavation of the slot, it is easy to collapse and split, so to take the necessary precautions.
(1) The length of the slot hole of the first phase should be scribed smaller.
(2) Use powder spray piles and deep mixing piles for reinforcement of the soil 4-7m deep under the guide wall.
(3) To reduce the height of the solid wall mud surface, and to use cement-clay slurry filling and excavation backfill for cases where slump pits and cracks have appeared.
(4) Use the method of jump excavation for excavation, and leave two phase slots plus one phase slot when excavating for the same phase slot hole.

  4.2 Difficulties in dealing with lost ground in the trench

  When Xiao encounters a medium-strong missing layer or overburden layer during trenching, the mud will be lost rapidly, causing the hole wall to collapse Generally, when dealing with missing strata, we should quickly use soil material to backfill into the trench and squeeze and mix it before excavation For strata with more serious missing, pre-fill the cement bentonite slurry before excavating the trench hole.

  4.3 Difficulties in embedded rock

  Generally use cast steel to make heavy chisel embedded tools, use containing impact-resistant alloy edge angle welded to the bottom of the Kam forbearance angle length of 1-1.4m, width to be slightly lower than the width of the wall, height of 3m cross section for rectangular weight of 3-5t using 30-50t crawler crane to drive heavy chisel impact host construction needs to pay attention to the following aspects.

  4.3.1 When Xiao encounters hard rock in the excavation of the trench hole, first use the heavy chisel for impact crushing, and then fish out the rock chips and rock pieces to form a cycle of back times after many back times, it can reach the expected depth.

  4.3.2 When using the drilling method for trenching, the overburden of the entire slot hole can be dug first and then operated.} Avoid the situation of unstable trench wall.

  4.3.3 Heavy chiseling determines the efficiency of embedded rock. In the process of operation, the operator should use heavy chiseling to enhance the number of impact points, impact height and the number of strokes according to the construction experience Zhuang to avoid excessive crushing.

  4.4 Manual construction should pay attention to the problem

  The outstanding problem of narrow channel construction is safety, to prevent accidents must be in accordance with the operating procedures. Hanging wall concrete should be vibrated and compacted, and the formwork should be removed according to the specified time. When backfilling concrete, to fill while cutting the buttress beam, in addition, we should pay attention to drainage and falling objects to injure people, etc.

  5 Conclusion

  The shoulder of the dam needs to bear the pressure of the dam and the surrounding facilities in the hydropower project, so it is especially important to ensure the load-bearing capacity and pressure resistance of the shoulder during the construction process. A good shoulder is the basis for the safety of the dam, so how to perfectly integrate the concrete impermeable wall technology in the construction process of the shoulder is a test for the dam designers, but also the more important part of the entire construction process. Only to ensure the quality of the construction of the shoulder, in order to better protect the useful life of the dam, and better contribute to the improvement of living standards of the surrounding people.

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