## 5 Conclusions  
Methods for measuring retaining wall displacements using inclinometers had the following problems: difficulties in installing them, in identifying the 2D local lateral displacement of the retaining wall, and in measuring using manpower. In order to address these problems, a 2D LiDAR sensor-based retaining wall displacement measurement system  
Figure 17: Sensitivity analysis results regarding the LCC analysis variables and assumptions. (**a**) Present worth analysis; (**b**) benefit/cost (B/C) ratio analysis; (**c**) annual measurement cost-saving effect analysis; (**d**) ROR analysis; (**e**) breakeven point analysis. was developed in this study. The performance of the developed system was evaluated, and an economic analysis was performed in order to analyze the reliability of the measurement results and the economic feasibility of the system. The following conclusions were drawn. 1. The retaining wall displacement measurement system comprised: (1) a retaining wall displacement measurement hardware, (2) a software for controlling the hardware, and (3) a displacement analysis device. As compared to TLS, a 2D LiDAR sensor which is economical was applied to the retaining wall displacement measurement hardware. This hardware was developed to collect the point cloud data of the retaining wall by rotating the 2D LiDAR sensor at 360\({}^{\circ}\) at a constant speed using a servomotor. The hardware was designed so that wireless control can be performed using software for hardware control, and a displacement analysis device. 2. A testbed was constructed to evaluate the displacement measurement performance of the developed system. A deformation of approximately 7.15 mm was considerably recognizable and the RMSE between the ground truth and lateral displacement predicted using the developed system was 2.82 mm. The system was considerably accurate with Korea's lateral displacement threshold, thus revealing a high applicability in the construction sector. 3. The results of the LCC analysis revealed that the developed system had a present worth of $56,075.91, a B/C ratio of 3.52, an annual measurement cost-saving effect of 71.59%, an ROR of 61.48%, and a breakeven point of 2.71 years, revealing that it had high economic feasibility. The sensitivity analysis results showed that the developed system was economically feasible in the analysis ranges of five selected variables. Among the five variables, the economic feasibility of the system was lowest when the number of inclinometers was 1. The effects of the system construction and system repair costs, as well as the discount rate on the variability of the economic analysis results were insignificant. Since the economic feasibility of the system aggravated when the system construction cost increased by 351.96% ($42,183.82), the commercialization model of the system had to be developed to avoid exceeding this cost level. This study however had a limitation: the displacement measurement performance of the system was evaluated using a discontinuous deformation simulation model. Hence, it is necessary to verify the displacement measurement performance and set the rotation speed and number of rotations by constructing a testbed that can simulate the continuous deformation of an actual retaining wall. In the future, displacement analysis software that can easily analyze and confirm the results will be developed. If the developed system is used for retaining wall displacement measurements--particularly at small- and medium-sized construction sites--it is expected that problems with the conventional manpower-based measurement methods will be resolved. Additionally, the applicability of the system is expected to considerably improve using the economic feasibility analysis results obtained in this study. Conceptualization, J.-S.K. and Y.S.K. ; Data curation, J.-S.K. and G.-y.L. ; Investigation, J.-S.K. ; Methodology, J.-S.K. and G.-y.L. ; Project administration, Y.S.K. ; Validation, J.-S.K. ; Visualization, J.-S.K. ; Writing--original draft, J.-S.K.