Analysis of Pavement Dimension at The Hang Nadim International Airport in Batam City, Indonesia

It was acknowledged that, the Hang Nadim International Airport’s aircraft movements increased significantly at recent 10 years period. The shift in aircraft dimensions and weights have raised questions whether or not the existing apron pavement dimensions are sufficient for accommodating the increase aircraft parking demands and to bear aircraft load changes. The purpose of this research is to evaluate and analyze the apron dimensions and pavement thickness at Hang Nadim Airport. This research was used two relevant methods as guidelines for calculating this apron dimension and thickness; ICAO (International Civil Aviation Organization) Anex 14 2013 and FAA (Federal Aviation Administration) 150/5320-6d. It was calculated that the apron dimension needs to be expanded to 1600 m x 150 m for accommodating 31 aircraft parking in 2025 (11 units B747300 + 16 units B737-900 + 4 units F27). The apron thickness would be 46.2 cm of base course and 10 cm of subbase course.


INTRODUCTION
Due to a huge increase in the air traffic over the past decade, and with further growth forecast, air traffic congestion on the airport surface is a major constraint on efficient use of airport resources [1]. The Hang Nadim International Airport's aircraft movements increased by an average of 7.30% every year started from 2007.
The capacity of an airport depends on the capacities of its landside and airside components [2]. Based on data from 2007 to 2016, the population, GDP and per capita income of Batam City have increased every year. GDP is the most sensible to air traffic growth in region where only international airports are located, that is for region that exhibit the highest level of development [3].
A runway is a rectangular area on the airport surface prepared for the takeoff and landing of aircraft. Taxiways are defined paths on the airfield surface which are established for the taxiing of aircraft and are intended to provide a linkage between one part of the airfield and another. Apron is an area where the aircraft instrument and engine operation can be checked prior to takeoff [4].
Hang Nadim International Airport is located in Batam City, Riau Archipelago, Indonesia. In 2016, Hang Nadim Airport has a single runway with dimensions of 4015m x 45m, 2 exit taxiways with dimensions of 150m x 23m and 2 rapid exit taxiways with dimensions of 300m x 23m. The existing apron has dimensions of 690.5 x 76.8m and 240m x 150m. This apron has a capacity of 13 aircrafts with the largest type of aircraft operating is Boeing 737-900, while Hang Nadim airport have to accommodate 19 aircrafts in 2016. Therefore, the existing apron has to be expanded.
Airport pavements should satisfy safe and regular aircraft operations thus, it is necessary to monitor these surfaces [5]. This research also designed the pavement thickness in the apron expansion for 2026.

METHOD
The Hang Nadim International Airport (coordinates of 01 '07 '15 "NL and 04˚06'50" EL) is located in Batam City, Riau Archipelago, Indonesia which has a distance of ± 7 km from the downtown of Batam City. (Figure 1).  There are four steps to determine the pavement dimension. First, forecasting of the airport capacities in the future using linear and multi linear regression. Second, evaluating the existing landing movement area. Third, analyzing and planning the requirement of the landing movement area in the future. Fourth, designing the pavement dimensions and thickness.

Forecasting
Forecasting is a process of predicting some future event or events [6]. In planning and decision making processes, prediction of future events is very critical and forecasting can help in making rational decisions [7]. Therefore, forecasting is required for the development of air facilities. Airside facilities forecasting include passengers, aircraft movements, population, GDP, per capita income, and cargo. The data of this forecasting are shown in the table below: The passengers and aircraft movement in 2026 are projected with the multi-linear and linear regression approaches. It was shown that the number of passengers increased 300 times, and aircraft movements increased by 200% in 10 years

Linear Regression
Linear regression analysis is one of the most commonly used statistical methods for modeling cross section data. In regression modeling there are two kinds of variables, dependent variable (variables that are influenced or value depend on other variables) and independent variable (variable that is suspected to affect dependent variable) [8]. The linear regression shown in the equation below:

Multi-Linear Regression
Regression models with one dependent variable and more than one independent variables are called multilinear regression [9]. The multilinear regression shown in the equation below:

Landing Movement Area
Aircraft characteristics have an important role on airport planning. Both the airport airside and landside planning are based on operating characteristics of the aircraft which will be operated at the airport according to the available pavement strength especially the dimension of the apron thickness [10]. The airport's airfield component includes all the facilities located on the physical property of the airport to facilitate aircraft operations [11].

Apron
An apron will accommodate number of aircrafts according to the calculation of the amount of each type of aircraft movements during peak hours [12]. Area of apron are planned depend on the wingspan and the length of each type of aircraft referring to ICAO Annex 14 2013. The apron must have sufficient slope so there is no waterlogging on the surface of the apron.
According to ICAO, the maximum allowable slope is 1%.
An aircraft stand should provide the following minimum clearances between an aircraft using the stand and any adjacent building, aircraft on another stand and other objects:

Pavements
The application of concrete pavements for apron in this airport has been rigid pavement slabs. This rigid pavement slab spreads and distributes the overall aircraft wheel load over the pavement layer more efficiently.
The concentrated wheel load of an airplane is spread out over a large area keeping pressure on the subgrade low. A subbase at least 4 in. Thick is recommended for airport pavements. The principal factors that affect concrete thickness of airport pavements are gross weight and type of landing gear of aircraft, concrete strength, soil support [13].
The pavement design consists of flexible pavement (high quality asphalt and aggregate) and rigid pavement (concrete slabs).

Subgrade
The subgrade is an important part in the design of the runway because this layer is the lowest layer that supports construction and loads. Investigation of subgrade is needed to determine the type of soil and soil bearing capacity.

Subbase Course
Subbase course is a part of runway pavement construction between the subgrade and base course.

Base Course
Base course (high quality split stone) is a course between the surface course and the subbase course.

Surface Course
Surface course is in direct contact with the aircraft wheel load. This course should have high stability, waterproof, and be able to distribute the loads to the base course.

Subgrade Modulus (K)
Subgrade is one of the important factors in the pavement structure. Compaction is needed to obtain a good quality of subgrade. The strength of the bearing capacity of the subgrade in a rigid pavement structure is expressed by the modulus of the subgrade reaction (K) through plate bearing testing. According to the AASHTO T222-86 method the test is carried out on an area that represents the foundation material that will support the pavement. If the K value in the plan cannot be measured, then the K value from the correlation with the CBR value can be used, but this correlation value must be tested again in the field. Subgrade modulus (k) is determined using the formula below: To establish the flexural strength for the thickness design the designer needs to consider several factors, such as: A. Capability of the industry in a particular area to produce concrete at a particular strength B. Flexural strength vs. cement content data from prior projects at the airport C. The need to avoid high cement contents, which can affect concrete durability D. Whether early opening requirements necessitate using a lower strength than 28-day.

Maximum Take Off Weight
Maximum Take Off Weight (MTOW) value is required to determine the thickness of the concrete slab. The MTOW will determine the aircraft that has the largest MTOW to be used as the planned aircraft.

Equivalent Annual Departure
Equivalent Annual departure (EAD) value is the annual departure of the planned aircraft, which is the aircraft with the largest MTOW.
The slab thickness is determined based on the curves below:

RESULTS AND DISCUSSION
The results will be discussed in 3 subsections, including forecasting results, evaluation and projection of the movement area, and pavement.

Forecasting Results
The forecasting results are shown in the table below: The increase in the number of passengers and aircraft movements from 2017 to 2026 indicate that air-side facilities require to be developed.

Movement Area
Movement area is the part of an aerodrome to be used for the take-off, landing and taxiing of aircraft, consisting of the maneuvering area and the apron [14]. The characteristics of operating aircrafts at Hang Nadim International Airport are shown in the table below: This research uses two types of operating aircraft. First, B 737-800, the operating aircraft with the longest ARFL, which has a runway length requirement of 2256 m. Second, B 747 -300, the assumed aircraft in 2026 with the longest ARFL where the runway length needs 3320 m.

Apron
Hang Nadim Airport has an apron with capacities of 13 aircrafts including B747-SP, B737-900, dan F27 while the apron has to accommodate 19 aircrafts. Calculation of existing apron requirements is shown in the table below:   The Equivalent Annual Departure (EAD) is calculated using the A320 aircraft. The Equivalent Annual Departure of A320 is 67,087.01 movements.

Thickness of The Rigid Pavement
Slab thickness is determined from Figure 2 by plotting flexural strength of 613.54 psi then being drawn horizontally until it intersects the subgrade modulus of 118.8 pci, from the intersection point of flexural strength and subgrade modulus then pulled vertically upwards to intersects the MTOW and then pulled horizontally again with annual departure 67,087.01.
Based on Figure 4, the slab thickness is determined of 17.15 inches. Because the annual departure result is more than 25,000, therefore the thickness of the pavement have to calculate the factor of pavement thickness of 1,054, so the designed slab thickness is determined as below:  Based on the 11 inch subbase course thickness with a 118.8 pci subgrade k modulus value, the subbase modulus k value is 322 lb / inch3 as shown in Figure 5. A subbase at least 4 in. (100mm) thick is recommended for airport pavements [15]. Therefore, the equivalent thickness of the rigid pavement is determined of 56,2 cm. Concrete slabs are connected by transverse joint reinforcement or dowel. The connection is in the centre of the plate thickness and parallel to the axis of the road. The dowel planning criteria are determined based on the thickness of the concrete slab plan as shown in the Table 11.

CONCLUSIONS
The evaluation results of Hang Nadim International Airport's apron dimensions (690,5 m x 76,8 m and 240 m x 150 m) has a capacity to accommodate 13 aircrafts require to be expanded to become 1600 m x 150 m in order to accommodate 31 aircraft in 2026 (11 units B747-300 + 16 units B737-900 + 4 units F27). The apron thickness would be 46 cm of slab thickness and 10.2 cm of subgrade thickness.