## 3 New Method for Dam Construction Combining Cemented Sand, Gravel, and Cemented Rockfill  
The maximum allowable grain size of the cemented sand and gravel aggregates is 150 mm, with any oversized aggregates needing to be removed or crushed. A certain number of aggregates with a grain size greater than 150 mm occurs in cemented material dams. For example, the proportion of oversized natural sand and gravel materials in the Dashixia Water Conservancy Project in Xinjiang exceeded 20%, and there was a certain amount of natural alluvial pebbles with a size of more than 150 mm and a maximum size of 500 mm in the Qianwei Hydropower Project. Since it is difficult to evenly mix aggregates larger than 150 mm in the mixture and production of cemented sand and gravel, the separation of aggregates larger than 150 mm is a serious problem during the laying process, which poses a challenge for the current construction methods to solve. In this study, a structural design model and construction method combining cemented sand and gravel and cemented rockfill in a three-layer sandwich form is proposed to solve the problem of a large proportion of large-sized (150-300 mm) aggregates, which leads to a considerable amount of waste materials and an increase in project costs due to the crushing of oversized aggregates in some projects. The model and method have since been granted invention patents in China [14], the United States [15], and Japan [16]. The new cemented rockfill dam structure proposed in this invention is shown in Figure 6a. The construction layers laid and stacked from bottom to top comprise a lower layer of cemented sand and gravel, a cemented rockfill layer, and an upper layer of cemented sand and gravel. The aggregates of the cemented rockfill layer have a size in the range of 150-300 mm, and the aggregates of the cemented sand and gravel layer have a size of 150 mm or less. The large-sized block stones are laid before the lower layer of cemented sand and gravel is crushed, initially set and, after slurry spraying, covered by the upper layer of cemented sand and gravel, which is compacted as the bearing structure of the dam core. The anti-seepage surface layer is constructed simultaneously upwards. Additionally, this study proposes a construction method for whole-process quality control. First, the water/cement ratio for the mixing of sand and gravel materials is determined through simulation tests; when the lower layer of cemented sand and gravel is laid, it is controlled, such that the rockfill is laid prior to the initial setting of the lower layer. During this process, an image scanner is used to collect visual data of the rockfill to statistically calculate the maximum, minimum, and mean grain sizes as well as the spacing of the rockfill material. Second, the rockfill with a maximum grain size of less than one-quarter of the minimum side length of the dam section is selected and the spacing is controlled to meet the design requirements. Then, cement slurry is sprayed on the rockfill such that the cement slurry fills the gaps between the rockfill and covers all the rockfill, and the laying of the upper layer of cemented sand and gravel is completed when the cement slurry is initially set. Finally,the construction layer is laid and rolled, and the rolling is stopped when the thickness of the construction layer decreases by 10% or when any value of the apparent density satisfies the conditions. In the present study, the rockfill material was directly laid without mixing, which prevented the problem of the existing mixing equipment not being able to mix excessively large aggregates; the rockfill aggregates increased the strength of the dam and reduced the cement consumption per unit, resulting in a lower increase in hydration heat temperature and fewer cracks, thus improving the construction quality of the dam.