Cost and Duration Analysis on the Variation of Soil Improvement Method on Port Development at West Java

Several port facilities, including a container terminal, was built in a port reclamation project in Subang Regency, West Java. The soil improvement method employed in most reclamation projects usually involves prefabricated vertical drains, deep cement mixing (DCM), pile method, etc. This study aims to analyze the varying soil improvement methods, specifically deep cement mixing method and the pile method using bamboo piles and compare them for work efficiency based on time and cost. The methodology used in this study included literature studies, and qualitative analysis based on keyword. Based on the analysis results on the aspect of duration, the preparation, installation/design, and installation of barriers with geotextile reinforcement, backfilling, and pavement for the DCM and pile method required 743.15 days and 763 days respectively. The cost review, which referred to the unit price of Minister of Public Works and Housing Regulation No. 1 year 2022, found that the DCM method requires higher costs than piles. The analysis results also shown that the DCM method is more efficient due to the process in the DCM method has a fast installation duration, does not require many human resources on one job, and the materials used are environmentally friendly and more durable in water.


Introduction
Along with significant economic growth in Indonesia, export-import activities can be transported by land, water, and air, especially in water areas namely at the port [1,2].The need for limited land requires reclamation which is the result of expanding the coastal area through improvement methods into a land affected by sea level based on the Minister of Public Works Regulation No. 40/PRT/M/2007 which can be used as regional development [3].A few researchers [4][5][6][7] conducted soil investigation before construction as well as for reclamation planning , soil condition is something that needs to be studied first because it is the initial foundation to maintain stability in withstanding the loads it receives [8][9][10]To determine the condition of the soil, laboratory and field tests are conducted and then the soil improvement method is determined [10,11] The soil improvement method that can be used in reclamation is deep cement mixing [8] which is a new technology invented in the late 1980s-1990s to improve embankment materials developed by the 1324 (2024) 012043 IOP Publishing doi:10.1088/1755-1315/1324/1/012043 2 Port Research Institute of the Japanese Ministry of Transport and has been proven as an environmentally friendly soil improvement method for water ecological systems [8].The use of deep mixing method is often used in stabilizing soil by mixing binders such as cement or lime injected by special machines without the need to be continuously compacted in the soil to a certain depth and deep cement mixing is able to increase [8,9].This method of soil improvement with deep cement mixing has been applied to the reclamation of Tung Chung East, Hong Kong by considering factors on soil conditions, binder characteristics, mixing conditions and curing conditions [8].
Many researchers conducted the soil improvement using deep cement mixing and bamboo piles.Both of two methods have a result has a good material for stability in construction.In addition, a soil improvement method that is often encountered and used is piling using bamboo cores as reinforcement combining bamboo cores and bamboo mats that can increase the bearing capacity of the soil in tensile strength comparable to wood, superior in elasticity and the material is easy to find [2].To achieve the completion of construction, a time and cost plan is needed.The problem of these methods is not yet considering the time and cost in project management.These two things are interrelated so that each job has a specified duration and costs incurred.

Methodology
This research methodology is started from identification of the problem, data collection, analyse the parameter such as climate data to know the how influence in the implementation work, calculated the volume of each method in the area layout that obtained from Google Earth, determine the duration and input to Microsoft Project, and bathymetry map to know the depth of reclamation area for volume.

Data processing
Data processing started from making the work item of each soil improvement method.Later on, calculate the volume of each work item required and calculate the unit price analysis to obtain cost in one work item.Then, the volume is multiplied by unit price to obtain the cost estimated.For time estimates, the data uses from literature studies and productivity manpower, which this data will proceed with Microsoft Project; the result in unit days and see the relationship among of each work item.

Literature study 3.1. Planning and implementation project
Every construction project begins with planning.To ensure that this process runs well, the major objectives must be established upfront.Planning is essential for completing a good project; therefore, it necessitates recognizing several possibilities and then selecting the best one while taking into account all potential restrictions [13].During project planning, the necessary implementation information, such as drawing plans and specifications, must be prepared [13].
According to [13], the following actions were carried out during the planning stage: create the overall project's the completion item, examining the project's engineering issues, seeking final overall permission from the project owner, planning as well as pre-design drawings for cost estimates, extensive design, scheduling, requirements, and working drawings, create a list of the amounts needed, estimate the ultimate cost, and create a time schedule.
The following data required in the project implementation framework by [13] can be considered as a target, namely: a. Establish the start of the project and its end in date format; b.
Arrange the types of work performed; c.
Determine the duration required to complete the type of work performed; d.
Creating a relationship between a job and other jobs; e.
Establishing a work calendar containing working days and working hours; f.Include the necessary costs; g.
Supervise the construction process in case of overlapping.

Determine the duration
Duration determination, based on PMBOK is the process of estimating the duration of work time required with available resources to complete a job.The time unit of duration can use minutes, hours, days, weeks, or other time units [13].This duration determination is based on the amount of work.The number of jobs is the amount of work done by workers in a certain period of time [13].By using the formula of the amount of work divided by work productivity as follows: Description: Qi = amount of work in work units Pi = work productivity in units of work or units of time Based on equation above, the greater the duration of work indicates that the amount of work is directly proportional so that the greater the amount of work [6].

Cost estimation planning
In cost budget planning, a detailed understanding of the plans and specifications used is required.The result is to know how much material is used and its quality based on the specifications [13].The information needed to plan the cost is the amount of material used, the working labor or working hours, the duration of the use of tools used in each job.The purpose of designing a cost budget is to obtain funds for the work and a reference in controlling the entire project [13].The following are factors that affect the cost budget described by [13] as follows: x The type of tool and its needs; x Availability of materials; x Availability of equipment; x Labor productivity; x Weather factors; x Type of contract; x Quality issues; x Ethics; x Control system; x Management skill.
Hereby, the cost estimation with the following formula:

) Cost for all items
Total cost estimated = Ʃ Total Cost of work item (4)

Climate Data
In climate data, rainfall taken in this planning is used to determine the amount of rainfall intensity in one month.Figure 6 is the monthly average rainfall data taken from the Ciherang Station of the Meteorology Climatology and Geophysics Agency (BMKG) in 1992 -2014.

Figure 6 Average rainfall monthly
Based on Figure 6, the highest monthly average rainfall is in January which is about 360 mm, the other highest rainfall is in March and April.With high rainfall, mobilization of materials from land can take time.The small rainfall indicates that June to September is the dry season so that construction can begin in June.A research stated that too much rainfall can inundate reclamation materials and construction [14].

Wind Data
Wind data is used to determine the direction, height, and period of waves.Wind speed was measured using an anemometer.Characteristics of the Java Sea which has a monsoon climate that blows from the east coast of Java to the west in May to September with low rainfall based on data taken from Qui et al

Wave Data
Waves are an important factor in protecting coastal buildings in reclamation planning.Based on Figure 7, the wave direction tends to the west with heights from 0 to 0.5 meters, then 0.5 to 1 meter, then 1 meter to 1.5 meters and between 2 meters and 2.5 meters.Based on the Beaufort scale by Stewart (2008) in [15] in Analysis of Wind Speed and Wave Height Characteristics using Altimetry Satellite Data (Case Study: Java Sea) it is classified that the planning location can run smoothly because the smaller the wave height the safer the reclamation construction process.

Figure 7. Wind Rose at Tanjung Priok Coastal
The highest rainfall in January, followed by March and April indicates that there are factors that can affect work productivity such as taking materials from other places by land.Rainfall other than in these months tends to be less high so that the implementation is smoother.In the wind factor, the research location tends not to have a high speed of 10 m/ s so that it does not cause high waves that can enter the construction process.

Implementation work
The following implementation work is planned and adapted from literature review.For this study has eight steps to achieve the soil improvement.It starts with preparation work, dredging work, deep cement mixing that divides into three: testing in laboratory, trial and error analysis, and implementation, installation of rubble rock for stability of embankment, deep cement mixing in use of piping system, and pavement works in Table 1 The implementation of bamboo piles, same as the deep cement mixing conducted.The difference is the dredging disposed to dumpsite, and after installation of rubble rock is continued with pavement works in Table 2

Work volume
The work volume is obtained from the calculation based on the layout area.For the preparation work volume is presented as unit of Ls.The layout area is 300x445 meters that has a depth of 13 meters that obtained from bathymetry map in Figure 4.For the deep cement mixing as shown in Table 3 is obtained from calculations of material needed from laboratory testing, trial and error, and implementation of determined layout area and geometry based on theoretical study.The rubble rock installation and geotextile are calculated by volume formula in unit of m 3 and area formula in unit of m 2 .Also, the DCM's volume calculation applied to cement pipe mixing in unit of m 3 .Lastly, the pavement works based on area calculation multiplied by height of work item as well as for the bamboo piles method work item in Table 4. Bamboo piles with a diameter of 10 cm, a distance of 1.5 meters, and an area of 445 meters necessitate 297 sets with a total of 1 bond comprising 5 bamboos, which necessitates 1485 sticks.Then, for vertical 300 meters, 200 sets with a total of 1 bundle including 5 bamboos are required, requiring 1000 sticks.As a result, the total number of bamboo stakes required is 2485 stems.Bamboo mattress installation totals 133500 m 2 of complete reclamation.It is the same as the amount of work in the deep cement mixing method for the volume of other task descriptions.

Duration
Based on the results of work planning according to the duration of 743.14 days, with the preparation stage requiring 23 days in which mobilization of heavy equipment takes time to facilitate work before it starts, temporary stockpiles filled with sand material which will be used as backfill, then backfilling in 357.14 days.In the duration of the deep cement mixing work at the laboratory test stage until the coring test a total of 58 days, this duration is calculated based on the laboratory testing time and the curing time of the sample which requires 28 days to achieve a certain compressive strength.Then in the experimental area to determine the quality of the sample based on the coring test.Embankment work with a phased process of rubble rock installation was 165 days, followed by 2 days of cement pipe mixing work, and reclamation work, namely 60 days for sand stockpiling and 50 days for asphalt installation.
The duration of the reclamation method using bamboo slips takes 763.15 days with the following information.In the backfill work is still carried out as in the backfill work in the deep cement mixing method, but in the bamboo niche method, the backfill is not used so it is disposed of at the dumpsite which takes 120 days because it passes through the waterway and passes in January which has high rainfall at that location.Furthermore, the duration of sand stockpiling takes 100 days because the volume of stockpiling is so large that it takes a long time, the tools used are dump truck and excavator.

Cost estimation
The cost estimation can be calculated using Equation 2. Hereby the estimated cost for deep cement mixing method as shown in Table 5.Based on the results of the calculation of the cost budget plan as shown in Figure 5, based on the unit price analysis of Minister of Public Works and Housing Regulation No. 1 year 2022, the total cost was obtained at Rp 318,723,076,197.49.This method requires more costs due to laboratory testing, the tools used are barges, excavators, drilling machines, and grab dredgers, and the materials used are very large.Hereby, the cost estimation for bamboo piles as shown in Table 6.Based on the results of the cost analysis using the bamboo pile method in Table 6, this method costs Rp 251,176,827,989.05.With the tools used mainly in hammers, dump trucks, excavators and other heavy equipment.

Comparison of two methods
Based on the calculation of the cost and time required to complete the reclamation phase using the deep cement mixing method and bamboo piles, there is a significant difference.This difference is distinguished by the use of tools used.Also, its beneficiaries for construction in using deep cement mixing based on the past researchers has been sustained, there are safe for marine ecosystems, maximalised the maintenance work, and minimized the waste of soil.The bamboo piles method uses tools that are familiar in construction, while the deep cement mixing method uses tools that are not familiar and have not been included in the unit price analysis.Based on duration, reclamation work with bamboo piles takes longer than reclamation work using deep cement mixing due to the use of materials used and the installation process that needs to be careful in the water.The weather factor, with the highest rainfall in January, March and April, affects the reclamation work so care needs to be taken in its implementation.

Conclusions
In conclusion, the duration of reclamation work using the deep cement mixing method is 743.14 days faster than the bamboo pile method which requires 763.15 days because the material formation process is faster and the tools used are more practical.Then, based on the costs incurred, the deep cement mixing method is more expensive, namely Rp 318,723,076,197.49compared to bamboo stakes, namely Rp 251,176,827,989.05from the unit price analysis of Minister of Public Works and Housing Regulation No. 1 year 2022 and the efficiency of the two methods based on cost, time, and quality uses deep cement mixing because the work process is faster and the material used is able to increase the bearing capacity which is greater and can last a long time.Comparing based on sustainability, the deep cement mixing is more sustainable than bamboo piles because of DCM safe for marine ecosystems, maximalised the maintenance work, and minimized the waste of soil.

Figure 1 Figure 2
Figure 1The area used for port development

Figure 3
Figure 3 Illustration of bamboo piles installation

Figure 4
Figure 4 Bathymetry map

Figure 5
Figure 5 Illustration of deep cement mixing installation based on DCM barge specification in Sea Surface Temperature and Its Variability in Indonesian Region.Changes in wind direction at 07:00 and 17:30, and the results of the monthly wind averages have wind speeds less than 10 m/s which indicates this area is calmer.

Table 1 .
. Deep Cement Mixing Work Implementation

Table 3 .
Deep Cement Mixing Work Implementation

Table 4 .
Bamboo Piles Work Implementation

Table 5
Cost Estimation for Deep Cement Mixing Method

Table 6
Cost Estimation for Bamboo Piles