## 2 A New Idea for the Construction of the Protection and Seepage Control Layer for the CSGR Dam  
The construction of the protection and seepage control layer for the CSGR dam must fulfill the objectives of anti-seepage effectiveness and durability and strength, while also addressing challenges such as minimizing construction interference between CVC, RCC, and CSGR components within the dam body, as well as overcoming difficulties related to accessibility for rolling machinery near the boundary areas. Combined with the construction experience from Tangba Protection Dam and Shaping I Hydropower Station, a novel approach has been devised: employing vibrated grout-enriched CSGR as the protection and seepage control layer for the CSGR dam, as illustrated in Figure 1. This method also introduces a redesigned water stop structure. Additionally, to address challenges encountered in constructing CSGR dams on non-rock foundations, it is proposed to relocate the cutoff wall to the upstream side of the dam. The key features of this innovative concept include:  
(1) The anti-seepage and drainage zoning design of the CSGR dam. The protection and seepage control layer of the CSGR dam includes the upstream, downstream and top areas. Its function is considered according to the concrete face rockfill dam, which undertakes the anti-seepage under the action of high-pressure water. The dam body is designed according to the bearing body, which mainly meets the requirements of stability against sliding and compressive strength. Drainage is set between the protection and seepage control layer and the bearing body, and it is discharged in time when water leakage occurs, which can further relax the restrictions on the dam material. When the CSGR dam is constructed on the sandy pebble foundation and the dam height is low, the drainage can be canceled because the sandy pebble foundation itself has drainage capacity. (2) The vibrated grout-enriched CSGR is used as the material of protection and seepage control layer. Combined with the sand, gravel and rock of the Tangba protection dam riverbed, according to the design requirements of the protection and seepage control layer, a suitable admixture was selected to develop a vibrated grout-enriched CSGR with a 90-day compres  
Figure 1: New cross-section of CSGR dam. sive strength greater than 15 MPa, an impermeability grade of W8 and a frost resistance grade of F100 (Fn, F represents the frost resistance grade of concrete and n represents the frost resistance grade value. Fn indicates that the specimen is damaged after n freeze-thaw cycles of concrete, where n = 100) Combined with the sand, gravel and rock of the Shaping I Hydropower Station riverbed, a suitable admixture was selected based on a series of laboratory trial compatibility tests to develop a vibrated grout-enriched CSGR that can meet the compressive strength of more than 20 MPa, the impermeability grade of W12 (Wp, W represents the impermeability grade, \(p\) represents the concrete impermeability grade value. Wp indicates that the test sample can withstand hydrostatic pressure of P/10 MPa without any water seepage, where \(p\) = 12), and the frost resistance grade of F225, as shown in Table 1. The properties of the vibrated grout-enriched CSGR material can reach the indexes of CVC and RCC materials, and it is safe and reliable as the protection and seepage control layer material of the dam body. Because it is CSGR, the construction technology is consistent with the bearing body of the dam body, so the construction equipment and construction technology have been further simplified, avoiding the interference caused by the simultaneous construction of conventional concrete as the protection and seepage control layer and CSGR as the dam body material. It is proposed to add a slurry rate of 8-12% in the fresh CSGR materials, so that its workability can be changed from dry and rolling CSGR to slump and vibratable CSGR, whose compactness can be further improved by full vibration.