## 1 Introduction  
The Jinjigou Reservoir is approximately 35 km from Yingshan County, Sichuan Province, China, and is a key water conservancy project of the Qujiang River system. This reservoir has a maximum design dam height of 33.0 m, with a total storage capacity of 11.2 million m\({}^{3}\)[1], and is responsible for supplying water to a 37.87 km\({}^{2}\) irrigation area in Yingshan County and to 22,200 people and 112,200 heads of livestock in this irrigation area. There is no large fault zone or seismic structure in the reservoir area. The mountains on both sides of the dam site are composed of interbedded thin-to-thick laminated sandstone and sandy mudstone with different thicknesses, essentially forming a narrow valley with symmetric V-shaped walls, with weak intercalated layers and poor continuity at the base of the dam. Since the project is located in the red bed area of Southwest China, sandstone is the main material available for dam construction because of a mine near the dam site. The sandstone has an average saturated uniaxial compressive strength of 32.8 MPa, with the lowest value being less than 29 MPa, and a softening coefficient of 0.71, which suggests that it is a soft rock [2]. Among the natural building materials near the project, the pebble aggregates are of a high strength but involve a long transportation distance, with an average of approximately 60 km, and are restricted in both mining activity and supply [3]. Therefore, a construction method that would allow for the full use of the existing soft rock aggregates for dam construction was the primary challenge in the construction of the Jinjiigou Reservoir.  
Among the existing dam types, earth-rockfill dams can be constructed by making full use of local soft rock materials, which can deliver a safe structure under proper design conditions [4]. However, since the materials constituting the dam body are loose and granular, earth-rockfill dams have a poor resistance to flood overtopping [5] and hence can collapse quickly when subjected to overtopping flood flow under overdesign conditions such as major earthquakes, landslides, and floods. For example, in August 1975, the Banqiao earth-rock core dam in Henan, China, collapsed during an overtopping flood, resulting in 26,000 deaths [6]. In May 2020, the Edenville Dam and the downstream Sanford Dam over the Tittabawassee River in the United States collapsed successively due to widespread and sustained rainfall [7]. The Jinjiigou Reservoir has good dam foundation conditions, and important towns lie downstream. To reduce public risk and make full use of local resources, an earth-rockfill dam did not seem to be the appropriate choice in this instance.  
As large-volume concrete structures, concrete dams have a strong ability to resist collapse under overtopping flooding [8]. Regarding the material parameters of concrete artificial aggregates, the Code for Investigation of Natural Building Material for Water Resources and Hydropower Project (SL251-2015) [9] clearly stipulates that the original rock has a saturated compressive strength \(>\) 40 MPa and a softening coefficient \(>\) 0.75. The sandstone material at the Jinjiigou project site has a low compressive strength and softening coefficient, such that the material indexes are unable to meet the specification requirements for concrete aggregates, and the mining and supply of pebble aggregates near the project are restricted. Therefore, the concrete dam solution is constrained by local materials and thus not an ideal choice of dam type.  
To ensure the safe, economical, and environmentally friendly construction of the Jinjiigou Reservoir, this study proposes for the first time the construction of cemented soft rock dams and a cemented rockfill dam to make full use of the excavatable rock materials near the dam, further deepening the concept of the construction of cemented dams while developing relevant dam construction technology.