What Is Panel Construction?

Reinforced concrete faced rockfill dams use a rockfill body as a supporting structure, and a concrete faceplate is placed on the upstream surface of the rockfill dam as an impervious structure. It belongs to earth-rock dam type, and its typical structure is shown in Figure 1. Face rockfill dams can be divided into roller compacted rockfill dams and cast-back rockfill dams according to the different dam body filling construction methods; depending on the material of the dam body, they can be divided into face rockfill dams and concrete face gravel dams. The most common is the rockfill dam. ^[1]
Reinforced concrete faced rockfill dam

Reinforced concrete faced rockfill dams use a rockfill body as a supporting structure, and a concrete faceplate is placed on the upstream surface of the rockfill dam as an impervious structure. It belongs to earth-rock dam type, and its typical structure is shown in Figure 1. Face rockfill dams can be divided into roller compacted rockfill dams and cast-back rockfill dams according to the different dam body filling construction methods; depending on the material of the dam body, they can be divided into face rockfill dams and concrete face gravel dams. The most common is the rockfill dam. ^[1]

Chinese name

Reinforced concrete faced rockfill dam

Foreign name

Reinforced concrete face rock-fill dam

Also known as

Face rockfill dam

Development process of reinforced concrete faced rockfill dam

The face rockfill dam first appeared in the western United States, which was related to the development of the mining and gold mining industry in the western United States at that time: mining needed water, and miners were familiar with blasting technology, so this type of dam came into being. It was initially impervious to water panels and later replaced by concrete panels to withstand higher water pressure.

The development of face dams has gone through three stages: 1850-1940. The rockfill construction method is rockfill, supplemented by the high-pressure water gun compaction process. The rockfill body is not dense enough, and the amount of settlement and horizontal displacement is large. Rockfilling is generally only applicable to low and medium dams with a dam height of less than 70 meters. From 1940 to 1965. During the transition period from the rockfill dam to the compacted rockfill dam, during this period, due to the increasing height of the dam, the rigid concrete panel could not adapt to the deformation of the rockfill and cracked, and the number of dams with severe leakage increased significantly. On the contrary, the clay core wall with an anti-filtration layer can adapt to the large deformation of the rockfill, and ensure its anti-seepage performance. Therefore, the face rockfill dam is gradually replaced by the clay core wall or the inclined wall rockfill dam. Replaced. After 1965. Due to the emergence of large-scale vibratory rollers and the technology of layered compaction of rockfills becoming more mature, the quality of rockfills has been significantly improved, and faced rockfill dams have once again shown their superiority. By the end of the 20th century, the world s highest panel rockfill dam had reached a height of 190 meters, and it was the Aguamirba dam in Mexico. The construction of concrete faced rockfill dams of modern significance in China began in 1985 and has developed rapidly. By the end of the 20th century, it ranked first in the world in terms of both quantity and height. The highest concrete faced rockfill dam in China is the Tianshengqiao first-level dam, with a height of 178 meters. ^[1]

Main features of reinforced concrete faced rockfill dam

The stability of the dam slope is good. The slope angle of the dam slope is roughly equal to the natural angle of repose of the loosely filled rockfill, which is lower than the internal friction angle of the compacted rockfill. The anti-seepage panel is located on the upstream side of the rockfill body, and has good performance in bearing water pressure; the dam body has good water permeability and is hardly affected by the permeability. The dam body has good seismic performance, small earthquake deformation, and no pore water pressure caused by the earthquake; although the earthquake may cause cracks in the panel and increase the leakage of the dam body, it will not cause the dam to break. The construction diversion and flood season are convenient. During the construction of the rockfill body, the rockfill body can be used to block the water directly when the panel is not poured; the upstream dam slope cushion material is protected by rolling cement mortar and other protective measures; The dam body can pass water after the rocks. It is less affected by climatic conditions during construction. ^[1]

Structure of reinforced concrete faced rockfill dam

Panel: a thin plate impervious structure located on the upstream surface.

Dam body: According to the working characteristics of each part of the rockfill body, different requirements are set for the properties of the material, maximum particle size, particle gradation, compaction density, deformation modulus, water permeability and application process to make full use of the local Material performance, reduce engineering cost and facilitate construction. The dam body is generally divided into three main areas: area is the anti-seepage reinforcement area, area is the semi-permeable cushion area, and area is the main rockfill area.

Area is composed of impermeable cover and cover weight. The impermeable cover is filled with clay or non-adhesive fine sand. It is set on the peripheral joints and panels at lower elevations. Its role is to bring the impervious earth material into the joints when the joints and panels crack. Through the anti-filtration effect of the underlay of the panel, the blocking cracks restore the anti-seepage performance. In order to prevent the instability of the impervious earth material, cover it with any material as a cover weight. The setting of the anti-seepage reinforcement area depends on the specific requirements.

Area is the cushion area, which is directly under the panel. It is required to provide a uniform, flat and reliable support surface for the water stop of the panel and the bottom of the joint; when the water stop of the panel or joint is cracked, a second anti-seepage can be achieved. The role of the defense line; during the construction period, when the panel is not poured, it can meet the requirements of the temporary dam body for flood protection. Therefore, the cushion material should have high shear strength, low compressibility, semi-permeability and good construction performance. The cushion material is made of fresh, hard, weather-resistant stone, which can be processed stone, natural sand gravel, or a mixture of the two. The grading requirements of the cushion material are relatively strict, the maximum particle size is 75 ~ 100 mm, and the particle content of less than 5 mm is 30% ~ 55%. The permeability coefficient of the cushion material is required to be 1 × 10 ~ l × 10 cm / s.

The width of the cushion area is determined according to the infiltration stability and construction technology. The horizontal width is 2 to 4 m. When backhoes, loaders, etc. are used in conjunction with manual auxiliary paving, 1 to 2 m can be used. The cushion layer is generally arranged with a uniform width, and is appropriately enlarged in the base contact area.

Area is the main rockfill area and is the main body of the face rockfill dam. It is the main support for bearing water and other loads. It is required that the dam material in the soil rockfill area has low compression, high shear strength, good water transport and Durability. In order to make full use of local materials, according to the deformation characteristics of different parts of the dam, the III area is divided into three areas: IIIA (transition area), IIIB (mound rockfill area) and IIIC (secondary rockfill area). Hydraulic transition requirements and the principle of decreasing deformation modulus. Among them, because the IIIC area is far away from the panel, the water load it bears is small, and it can be filled with poor materials.

Seat cushion: a concrete structure that is arranged around the panel and sits on the foundation, also known as toe board. ^[1]

Joints: Expansion joints and construction joints to eliminate harmful cracks and facilitate construction. According to the position and function of the seam, it can be divided into peripheral seams, vertical seams on the panel, expansion joints on the toe board, horizontal seams between the panel and the wave wall, expansion seams on the wave wall, and construction seams. The most important seams are the vertical seam and the panel. Seam. The schematic diagram of the joint of the face dam is shown in Figure 2.

(1) Peripheral seams. It is the joint that connects the panel and the toe board. The reinforcement in the joint is broken. It is provided with caulk compressible material and 2 to 3 stops of water. Due to the huge difference in the deformation modulus of the structural foundation on both sides of the peripheral joint, the relative displacement of the face plate and toe plate under the action of water load is the weakest link in the face plate dam.

(2) Vertical seam of panel. It is the indirect joint of the panel board perpendicular to the axis of the dam, and the reinforcing steel does not pass through the joint. According to the stress characteristics of the panel, the vertical seam located in the middle of the river bed will be squeezed, which is called compressive seam. Generally, there is only one bottom water stop, and compressible material is embedded in the seam. Some works have 2 water stop and No caulking material is provided; the vertical seam located on the bank of the dam is stretched due to the stagnation of the panel to the middle. . The spacing of the vertical joints is determined by the shape of the valley, the temperature difference, the uneven settlement of the rockfill under the panel, and the construction conditions. It is generally 12 ~ 18 m. To reduce the deformation gradient and absorb more deformation, the shore is stretched. The seam spacing is often taken as half of the pressure seam spacing.

(3) Toe board expansion joint. To prevent irregular and harmful cracks on the toe plate caused by uneven settlement of the foundation and strong restraint of the foundation, toe plate expansion joints can be provided. Recently, most of the face dams that have been constructed have eliminated the toe-blade expansion joints, and instead divided the facility joints according to the concrete construction, and the steel bars penetrate the joint surface.

(4) Horizontal seam between panel and wave wall. The horizontal joint between the panel and the wave wall is provided with 2 water stops at the bottom and top. Due to the accident of the face dam behind the ditch in Qinghai Province, China, relevant Chinese regulations stipulate that the elevation of this horizontal joint between the face plate and the wave wall should be higher than the highest static water level.

(5) Expansion joint of wave wall. This joint is provided to prevent the uneven settlement of the rockfill at the bottom of the wave-proof wall and affect the normal use of the wave-proof wall. Its spacing is generally the same as the vertical gap of the panel, and water-stop is set in the gap.

(6) Construction joints. When the slabs of high dams are poured, they are often constructed in stages, so the slabs are provided with horizontal construction joints, and the steel bars pass through the joint surface.

Rockfill: a granular material with a certain gradation, usually refers to artificial blasting mining materials and coarse-grained materials piled up at the natural foothills. The definition itself does not include sand and gravel, but from the rockfill materials of face dams, due to sand and gravel It also has similar properties to stone, and typically also includes gravel. ^[1]

Reinforced concrete panel rockfill dam panel construction

For low dams, the slab is constructed in the first stage, that is, after the filling of the rockfill dam is completed, the slabs are concentrated. For the middle dam, the slabs should be constructed in stages, that is, the slabs are poured after the rockfill reaches a certain height. At the same time as the panel is poured, rockfill can be filled. When the dam is tall and the amount of work is large, the panels can be poured in stages. Otherwise, the dam slope will be too long, which will cause greater difficulties in construction diversion and construction technology, and it is not convenient to organize flow operations.

Face-cast concrete pouring is generally carried out by sliding formwork, but there are also some that use flip-up formwork or fixed formwork, and some panels are even constructed by sprayed concrete. ^[1]