**4.3. Connection to concrete face slabs**

If the toe plinth of a concrete face rockfill dam is built on overburden layers and a concrete wall is used to cut off the underground seepage, then a reliable connection between the face slabs

**Figure 9.** Connection techniques in the Yele ACRD. (a) Section A-A. (b) Section B-B.

and the cutoff wall should be guaranteed. Now, it is a standard way to use one or two linking slabs to connect the cutoff wall with the toe plinth, as exemplified in **Figure 10**. Water stops are installed at the connection points of different components. The width of the toe plinth and the linking slab(s) should be determined based on the allowable hydraulic gradient of the underlying overburden, and on the permitted three-dimensional displacements that are sustainable for the water stop structures. The designing features of connection systems in typical CFRDs are shown in **Table 4**. In these CFRDs, the width of the linking slab(s) usually ranges from 2 to 4 m.

plate and fixed at the top of the joints. The gap between the different concrete components is

Practices in Constructing High Rockfill Dams on Thick Overburden Layers

http://dx.doi.org/10.5772/intechopen.78547

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After removing the surficial loose layers, most overburden still requires some additional treatment before using as a dam foundation. Commonly used techniques include compaction, consolidation grouting, vibro-replacement stone columns, high-pressure jet grouting, and so

To provide a firm foundation, vibrating rollers are always used to compact the overburden retained. Dynamic compaction is also commonly used to increase the stiffness and strength of the overburden layers. The authors recommend the Miaojiaba CFRD as an example [9] for dynamic compaction, which was performed before constructing the dam. The average settlement achieved by dynamic compaction was 26.4 cm, and the measured settlement of the overburden during dam operation is about 35–50 cm, indicating that the total settlement may be considerably larger if dynamic compaction has not been performed. Prior to dynamic compaction operations, it is, however, necessary to lower the underground water table.

Consolidation grouting is always performed to provide a sound foundation for the seepage barrier of dams (e.g., clay core and toe plinth). The depth of grouting generally ranges from 5 to 10 m. The distances between grouting holes and rows range from 2 to 3 m. A concrete plate is usually cast before conducting the consolidation grouting works, serving as a working

For weak layers such as sand lenses that are difficult to remove, vibro-replacement stone columns are usually used to densify the soils to form a composite foundation. The stone columns also serve as vertical drainage paths that are beneficial to dissipate the pore pressure within the surrounding soils. In the Huangjinping ACRD [14], vibro-replacement stone columns with a diameter of 1.0 m were set to improve the sand lenses buried more than 25 m below the ground surface.

High-pressure jet grouting is a ground improvement and soil stabilization method, where a stabilizing fluid is injected at a high velocity into the treated soil under a high pressure. The grouted fluid hardens within the soil, forming well-cemented jet grouted columns. Highpressure jet grouting is a very versatile foundation improvement method and has been used not only in building temporary cutoff wall for cofferdams (e.g., **Figure 1**), but also in treating

deeply buried sand lenses within the overburden layers (e.g., **Figure 2**).

20 mm, and 12-mm wooden plates are placed in between these components.

**5. Foundation improvement techniques**

**5.1. Compaction**

**5.2. Consolidation grouting**

platform for grouting.

**5.3. Vibro-replacement stone column**

**5.4. High-pressure jet grouting**

on. These treatment techniques are briefly summarized below.

The watertight structure for the perimetric joints used in most CFRDs (e.g., Aertash) consists of three layers. A "W"-shaped copper water stop is used at the bottom, and a wavy watertight stripe is used as the middle sealer. Plastic filling material is enclosed by a "Ω"-shaped rubber

**Figure 10.** Connection techniques in the Aertash CFRD.


**Table 4.** Designing features of the connection systems of typical CFRDs.

plate and fixed at the top of the joints. The gap between the different concrete components is 20 mm, and 12-mm wooden plates are placed in between these components.
