## 4 Performance and Economic Feasibility of a Retaining Wall Displacement Measurement System
### Economic Feasibility of System
#### 4.2.2 Setting of LCC Analysis Variables and Assumptions  
Since different construction sites have different measurement plans, the measurement site was assumed, as shown in Figure 14 and Table 4, in order to analyze the LCC for the conventional and automated measurement methods under similar conditions. In the conventional method, the measurement cost increased with the excavation depth. However, the excavation depth was set at 3 m for a conservative economic analysis. Further, it was assumed that displacement measurements on both sides of the retaining wall were performed using two inclinometers. An interview with a company that specialized in measurement revealed that the measurement period for small- and medium-sized construction sites with excavation depths of <10 m was six months. Measurements were conducted twice weekly over a six-month period based on the technical guidelines on measurement and management for excavation construction in Korea, for a total of 48 measurements. To evaluate the variability of the LCC analysis results under the aforementioned conditions, a sensitivity analysis was conducted on the assumptions for the number of inclinometers and measurement period, which are expected to have a considerable variability among construction sites. The work cost (labor, material, and equipment) of the conventional measurement method was calculated using the standard quantity per unit of Korea's ground survey published by the Korea Engineering and Consulting Association [31]. Since the hardware must be mounted under the corner strut for the automated measurement method, the input of one corner strut installation person (ordinary worker, steelworker, or welder) and equipment (tower crane) was applied [32]. The quantity was then calculated with the input of an intermediate technician, which is similar to the calculation for the inclinometer casing installation work. Since the retaining wall displacement measurement work can be performed more conveniently compared to the conventional method, the quantity was  
Figure 14: Measurement-site assumptions for LCC analyses. Figure 13: Life cycle cost (LCC) analysis scope. calculated with the input of a beginner technician in a similar manner as the calculation for one inclinometer measurement. Regarding the unit price for the above quantity, the labor cost was derived from the wage survey report of Korean engineering companies [33], the report on the wage status of Korean construction industries [34], the material cost based on the price information magazine of Korea [35] and estimates from related companies, as well as the equipment cost based on the cost calculation table for construction machinery in Korea [36]. The work costs for the conventional and automated measurement methods (Tables 5-7) were calculated as $9870.93 and $1466.85, respectively, showing that the cost benefit of the automated measurement method compared to the conventional measurement method was $8404.08 per year. The system construction cost for the automated measurement method was calculated as the cost invested in constructing the system (Table 8), while the system repair cost was calculated to be 5% of the system's construction cost every year. The service life of each component was determined based on the service life table of the Public Procurement Service of Korea [37] and interviews with system manufacturers, while the component replacement cost was set by considering an entire replacement depending on the service life. To evaluate the variability of the LCC analysis results based on the changes in the system input cost, a sensitivity analysis was conducted regarding the changes in system construction and repair costs. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Parameters**} \\ \hline Excavation depth & 3 m \\ Boring depth & 5 m \\ (Excavation depth + 2 m) & 2 units \\ Inclinometer & 1 unit \\ Measurement period & 6 months \\ Number of measurements & 48 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Assumed measurement site parameters.