## 1 Introduction  
The Korean government established a long-term roadmap in 2022 called S-construction 2030 for digital construction and automation in order to increase productivity and safety. The roadmap consists of 46 topics in 10 categories, including the expansion of BIM (Building Information Modeling), autonomous construction machines, OSC (Off-Site Construction), and smart devices. The goal is to transition the construction industry from traditional paper drawings and labor-intensive work to advanced technology-centered work that is digitalized and automated. The plan aims to increase the productivity and the quality of construction while also enhancing safety on site. To achieve this goal, the Korean government has set up 3 major tasks under 10 basic tasks and 46 detailed tasks. The plan includes the introduction of BIM for the digitalization of the construction industry. The smart device includes drones for measurement and monitoring over the life cycle of construction and management. As drones gain popularity for construction management, many studies have been carried out to assess their accuracy and applicability over the last decade. Some of this literature is presented below. UAV (Unmanned Aerial Vehicle) data acquisition and processing has shown its value in the earthwork of large infrastructure projects [1]. Drones were used to improve workplace safety in construction [2; 3]. Drones were proposed for cable monitoring, such as power lines, showing a few centimeters of accuracy [4]. A drone was used for construction progress monitoring by visualizing the created 3D model via color-coding the building elements [5]. The effect of distribution and the number of control points was studied on the achievable accuracy for the drone mapping of corridors, such as roads and pipelines [6]. The volume change of a landfill stock was calculated using drone photogrammetry in Malaysia, and its potential was confirmed [7]. UAV was tested for waste landfill settlement monitoring, and 10 cm accuracy was reported [8]. A model for construction error analysis of RC (Reinforced Concrete) pile foundation using a drone was proposed [9]. In the study, RC piles were detected using image processing, and the distance between the pile centers was computed. A thermal camera was used to monitor an urban landfill and its potential for detection of hazardous gas emissions [10]. A roughness analysis of paved roads was carried out using drone LiDAR and photogrammetry [11], reporting 6 and 7.2 cm vertical accuracy in RMSE, respectively. A study used UAV-LiDAR and MPS to obtain geometric parameters (such as road longitudinal profile and cross-slope) by using digital terrain model surfaces derived from the point cloud data [12]. A study was conducted on earthwork volume calculation, and vertical accuracy of 5.4 and 2.5 cm were reported for photogrammetry and LiDAR, respectively [13]. A standard work type was developed in Korea to utilize drones at expressway construction sites [14]. UAV was used for damage inspection of bridge infrastructures and the benefits of safety, cost sustainability, and repeatability, as well as the limitations of battery issues and the presence of obstacles were all discussed [15]. In the field of ground settlement measurement, drones have recently gained more interest for their ability to access remote and dangerous areas with accurate measurement sensors [8; 16; 17; 18]. It is anticipated that multiple drones and fixed wing type drones should increase the applicability [19; 20]. As listed above, drones are widely tested in many fields, such as road, landfill, and construction progress monitoring, but few studies have been carried out for long-term ground settlement measurement at soft ground near harbor facilities. Conventionally, the task was performed using manual surface settlements using engineering levels only for limited points.