The estimated cost of work and K3 construction of retaining walls

One of the methods used to control the stability of the soil so as not to experience a landslide is to build a retaining wall. In carrying out the work, of course, it is necessary to pay attention to occupational safety and health for all those involved in a project, including the community around the project, therefore, it is important to calculate costs before starting work, so that the project can be carried out properly according to regulations, objectives, functions, benefits, impacts, costs, quality, time, and K3 or occupational safety and health. This study aims to determine the cost of retaining a cliff wall using the main material of mountain stone/split stone, including labor costs, materials, tools, and occupational safety and health (K3) costs. This research uses quantitative descriptive method. To complete this research, we need data on the budget plan for the construction project for the construction of retaining walls, and factual costs at the project site. The data sources consist of project documents, contract documents, and direct observations on site. This research has identified the cost of materials, tools, labor, and K3 in units converted to cost/m 3 , and produced a coefficient of unit price analysis for retaining wall work. The results of this study can contribute to estimating the cost of retaining wall work using mountain/split stone specifications at an early stage during planning, using unit costs/m3 of work, both by planners, contractors and the general public.


Introduction
The land is a foothold and a place for a building to stand, so land is an important aspect that needs to be reviewed in construction planning, therefore, it is very important to pay attention to the soil stability factor [1]. One of the methods used to control the stability of the soil so as not to experience a landslide is to build a retaining wall [2]. A retaining wall is a structure built to hold soil that has a slope where the stability of the soil cannot be guaranteed by the soil itself [3]. Retaining wall buildings are used to withstand lateral soil pressures caused by fill soils or unstable original soils due to topographic conditions [4]. The construction of retaining walls must be based on the calculation of stability and safety factors because errors that occur in the construction of retaining walls can have fatal consequences, namely property loss and loss of life [5]. Therefore, we need a retaining wall design that is really stable and efficient, stable in terms of strength to support the magnitude of the overturning and shearing forces. The need for costs in making retaining walls directs us to the importance of having a Budget Plan (RAB), so there needs to be an estimate of costs in planning a job [6].
Cost estimation is a calculation carried out to plan the needs that will later be needed to complete a job [7]. In planning a construction project, cost estimation plays an important role in project implementation [8]. In the early stages, cost estimation is used to find out how much it will cost to realize a project [9]. Cost estimates on a construction project must be prepared before a project is implemented, to determine the possible costs of a project [10]. Cost estimation is closely related to cost analysis, namely work that involves assessing the costs of previous activities that will be used as material for preparing cost estimates [11]. In other words, preparing a cost estimate means looking into the future, calculating, and making estimates of things that will and may happen. While the cost analysis focuses on the assessment and discussion of past activity costs that will be used as input [12]. In practice, the estimation of construction costs requires several different estimates based on the intended use or designation [13]. In the early stages of the project such as during concept preparation, feasibility studies, and preliminary design, it is clear that it is not possible to estimate based on the calculation of the quantity (volume) of work because usually job descriptions and specifications do not exist [14]. However, at these stages, an estimate is already needed in order to take into account project financing [15].
The importance of cost estimation does not make contractors forget the importance of occupational safety and health (K3), because occupational safety and health is the supervision of people, machines, materials, and methods that include the work environment so that workers do not get injured [16]. The cost of implementing SMK3 construction in the field of public works is allocated in general costs which include: preparation of RK3K, promotion of K3, work protective equipment, personal protective equipment, insurance and licensing, K3 personnel, health facilities, signs, and others related to risk control K3 [17].
The main purpose of this study was to determine the need for labor costs, material costs, tool costs, and the cost of the need for equipment for occupational health and safety equipment on retaining wall work. In addition, this study also aims to find out how long the work will take, and how much it will cost, and to produce a unit cost analysis coefficient in retaining wall work using mountain stone/split stone as the main material. The expected contribution of this research, for government agencies, planning consultants, project owners, contractors, and the community, it becomes easier to estimate the cost of retaining wall work, so that they can determine and prepare a budget before project implementation.

Method
This study uses a quantitative descriptive method. The research was carried out on the work of making retaining walls with a case study on the Cibaraja -Kadudampit road segment, Selajambe village, Cisaat sub-district, Sukabumi district with a volume of 204.82 m 3 , using the main material of mountain stone/split stone. The equipment used in this study is a measuring instrument, stationery, and some other handyman equipment. To find out the costs used in the work of retaining walls, namely by making direct observations at the project site, and supported by other data, then analyzed using a mathematical formula into a unit of cost/m 3 . This unit cost/m 3 includes the cost of materials, tools, labor, and K3 (Occupational Health and Safety) costs, and produces a coefficient of Work unit price analysis.

Research Data
The data used in this study is in the form of contract documents from the Public Works Department consisting of (SPK, HPS, drawings, tender documents, and others). The main data that need to be obtained during direct observation are:  Volume/quantity of each work item  The workforce that is employed includes workers, builders, head builders, foremen, and drivers  Labor wages include workers, handymen, head craftsmen, foremen, and drivers  The ingredients used, as well as the quantity  Prices of materials used  Equipment used in the work and its price  Equipment used to control occupational safety and health (K3) and their costs.

Research Flow
There is a problem in financing the retaining wall work, especially related to the cost of occupational safety and health (K3), so this research begins with problem formulation, literature study, identification of research data needs, data collection, data analysis, interpretation of analysis results, and so on. An illustration of the flow of this research is presented in Figure 1.

Retaining Soil Wall Works
The retaining wall referred to in this study is a retaining cliff due to the steep land elevation between the vacant land and the road, where there is drainage on the side of the road, and after drainage is a slope/cliff with a height of 2 m. The condition of the retaining wall is visualized in Figure 2. The technical specifications used in this retaining wall work consist of rock/split stone, sand, gravel, and cement. The work volume of this retaining wall is 204.82 m 3 . Based on the results of observations and construction drawing data as shown in Figure 2, it is known that the quantity of each work item in the installation of this retaining wall, as explained in Table 1.

Retaining Wall Work Cost
The cost of retaining wall works reviewed in this study consists of material costs, equipment costs, labor costs, and occupational safety and health (K3) costs, so this discussion is discussed in further discussion sections.

Material Cost
In identifying material costs, it is necessary to know what materials are used, how many quantities of materials are, and what the unit price of the material is [18]. After being identified, the total costs incurred for the purchase of materials are calculated, then the material costs are calculated in units/m 3 of retaining wall work. The results of the survey and observation show that the material, quantity, and unit price of the material are as shown in Table 2. It is known that the total material cost is Rp. 108,768,739 as described in Table 2, while the volume of retaining wall works is 204.82 m 3 as described in Table 1, so the material cost/m 3 of retaining wall work can be calculated using Equation 1 as follows: = Rp. 531.046 (1) After being analyzed so that it can be stated that the cost of retaining wall work/m 3 is Rp. 531.046.
After knowing the material cost/m 3 of retaining wall work, then it is necessary to explain how much material is used/m 3 . How to calculate the amount of material used in each volume of retaining wall work is to divide the amount of material used by the total volume of retaining wall work, as exemplified in calculating stone materials using Equation 2 as follows: Based on the analysis using Equation 2, it can be seen that the use of mountain stones/split stones in each volume of retaining wall work is 1.17 m 3 . The use of rock material/split stone, cement, and sand in every 1 volume of retaining wall work is presented in Table  3.  With the results of this analysis, it can be determined that the coefficient of material for the retaining wall is 1.17 m 3 of mountain stone, 176 kg of cement, and 0.4531 m 3 of sand.

Tool Cost
To calculate the cost of tools, it is necessary to identify what tools are needed, in what quantity, and at what cost. Ownership of equipment in retaining wall works consists of direct purchases of simple tools, and by way of rental for heavy equipment, such as concrete mixers, dump trucks, water tankers, and tampers. Based on the observations that the tools used, the quantity, and the price of the tools are as described in Table 4. The results of the analysis show that the total cost of the tool is Rp. 26,767,079, and the cost/m 3 of retaining wall work, calculated using Equation 1, and the result is Rp 130,686/m 3 . The need for tools/m 3 for retaining wall work, which can then be used as a calculating coefficient, as shown in Table  5.

Labor Costs
Labor productivity is very influential on the costs incurred, the higher the productivity of the workforce, the cheaper the cost, and the lower the productivity, the more expensive the labor costs [19]. In general, in construction projects, the workforce that he employs consists of workers, builders, head builders, foremen, and drivers. In the retaining wall work, it is known that the manpower employed consists of workers, builders, and foremen, without using the head of a handyman, while the driver's financing has been included in the cost of equipment.
To find out the cost of labor, first, it is necessary to know the number of workers employed, wages/hours or daily wages, and length of work, and based on observations it is known as described in Table 6. Based on the information presented in Table 6, it is known that the total labor cost is Rp. 45,578,748, while the volume of retaining wall work as described in Table 1 is 204.82 m3, so the labor cost/m 3 of retaining wall work is calculated using Equation 1 is Rp. 222,531.
Next, it is necessary to calculate the productivity of the workforce daily. Based on observations of labor productivity from day 1 to 30, there are differences, so it is necessary to calculate the average productivity in each day. The retaining wall work is carried out daily by 10 workers, 5 craftsmen, 1 foreman, and is completed within 30 days, therefore the average daily productivity can be calculated using Equation 3.
The results of the analysis using Equation 3, it can be seen that the average daily labor productivity is 6.943 m3. Based on this information, the contribution of labor in completing the retaining wall work can be calculated using Equation 4 as follows: , the contribution of labor in retaining wall work is described in Table 7. The next step is to determine the labor coefficient. This labor coefficient can then be used to analyze the cost of labor wages on retaining wall work in the next project. This coefficient will be determined for workers, builders, and foremen. It is known that the average daily productivity is 6.943 m 3 , carried out by 10 workers, 5 craftsmen, and 1 foreman, so the labor coefficient can be determined using Equation 5 as follows: Based on the results of the analysis using Equation 5, the labor coefficient on retaining wall work is summarized in Table 8.

Cost of Occupational Safety and Health (K3)
The work of retaining walls (TPT) has a potential hazard to the workforce, and the results of the investigation identified that the potential hazards consist of:  Injured if crushed by a tidal stone  Buried by the ground  Injured by digging tools, hoes, crowbars, and others  There was an accident due to traffic  An accident or injury occurs due to the distance between workers is too close  Hurt by a fallen tree branch.
With these potential hazards, steps to anticipate and prevent the dangers caused by the work of laying and compacting the HRS-WC work, namely:  Prepare and provide medical equipment in a first aid kit  Builders and workers must wear clothing and equipment (safety clothing, safety boots, gloves) that comply with the standard  Maintain and care for each other between workers  Ensure that no outsiders or other workers are in the place where the car is unloading the material  Install temporary signs and regulate traffic to keep it running smoothly by wearing appropriate clothing  Maintain a safe distance between workers from one another Given the potential hazards, then taking steps to anticipate occupational safety and health on retaining wall work, it can be seen that the costs incurred for K3 are as described in Table 9. By referring to Table 9, the K3 coefficient is as described in Table 10.

Time and Cost of Retaining Soil Wall Works
Completing work on time as specified can benefit various parties, both service providers or service users, or contractors or developers [20]. This retaining wall works to hold the cliff on the side of the road because if it is not reinforced the soil can slide and damage the road, which will eventually disrupt the smooth transportation [21], [22]. The volume of retaining wall works is 204.82 m 3 which was completed in 29.5 days. The workforce employed are 10 workers, 5 handymen, and 1 foreman. It is also known that the average daily productivity is 6,943 m 3 . After discussing the cost of retaining wall work which consists of the cost of materials, tools, labor, and K3 (Occupational Health and Safety) costs, the total cost and percentage of the cost of this work are as described in Table 11. In addition to costs, it is also known that the coefficients of materials, tools, labor, and K3 are summarized in Table 12.