Green open space implementation on the underground building

Green Open Space (GOS) as described as an open place to grow plants both naturally or intentionally planted. The arrangement of GOS on the underground building is of a similar type to the green roof design on buildings located at ground level. This is due to the similarity in the characteristics of the park on top of a building. Using a quantitative approach, the study presented the GOS visually, showed the area, the percentage of green plants, and the number of shade trees. This research used the model of Underground Gas Insulated Substation (GIS) as a representative of the underground building that can be further reviewed to be applied in DKI Jakarta. Underground GIS requires land in a natural environment but tries to maintain part of that environment with green space applied to the roof of the underground building. GOS is applied on the Underground GIS roof by implementing the intensive green roof. By considering public activity spaces and arranging vegetation layout, it is hoped that this Underground GIS can become a built environment that can reduce the ecological footprint, enhance benefits for the environment, and make the growth of urban space more sustainable and livable.


Introduction
Green Open Space (GOS) as described in spatial planning regulation, as stated in Law of the Republic of Indonesia no. 26/2007, is an extended open area/pathway and/or group, to grow plants naturally or purposely planted [1]. GOS in urban area (urban forests, parks, green lines) is broadly considered to be an important factor to the health and well-being of urban residents [2][3] [4][5] [6]. GOS systems that are suitable for their function can provide essential rainwater infiltration and water purification services for urban residents [7]. GOS is also associated with sustainable cities because of its various functions, namely as a carbon capture area (carbon sink), maintenance of biodiversity, location of aquifers, and air pollution control. [8] [9]. Contribution of GOS to the quality of the urban environment in accordance with the objectives of organizing RTH in accordance with the Guidelines for the Clause and Application of GOS in Urban Areas as stated in the Regulation of the Minister of Public Works (Permen PU) No: 05 / PRT / M / 2008, namely maintain land availability as water catchment areas, creating urban planning feature, that can achieve a balance condition between the built and natural environment. That condition is useful for increasing the conformity of the urban environment, making community's benefit, and creating safe, comfortable, fresh, beautiful, and clean environment.
The function of GOS in DKI Jakarta, with the typology of urban areas with densely populated areas, is a unit of ecological, social, and hydrological functions [10]. Based on the underground building development plan, the type of GOS is determined from the estimated surface area that can be converted into its function of GOS, above the underground building. Using a quantitative approach, the study presented the GOS visually, showed the area, the percentage of green plants, and the number of shade trees. This research used the model of Underground Gas Insulated Substation (GIS) as a representative of the underground building that can be considered to be applied in DKI Jakarta. The specific function of the building, and the potential location in the high-density population, could be an attractive object to be a further consideration. As a comparison, if the average construction requirement of land area of an Underground GIS in the DKI Jakarta area is 1,500-2,000 m 2 , so the provision of green open space can be an economic value that needs to be considered in the development of an Underground GIS [11].

Literature Review
The arrangement of GOS in the Underground GIS area is of a similar type to the green roof design on buildings located at ground level. This is due to the similarity in the characteristics of the park on top of a building. A green roof typically consists of several layers which are described in Figure 1. Green Roof Layers, including building roof, insulation layer and waterproofing; protective layer and shelter; drainage layer; plant root boundary layer; plant growth media; plants and vegetation [12]. Each component has a specific role in the green roof system and the selection of each material is adjusted according to the geographical location and climatic conditions [13]. In general, the Green roof also has several roles [14] [15], including regulate flow and improve rainwater quality, can increase the green space area of the city by maintaining the original habitat and ecosystem, lower the city temperature, lower energy consumption costs, reduce noise distraction and enhance visual appearance, improve air and water quality, carry out social functions and add value to an urban environment. Figure 2. Popular Plant Species Grown in Cities with Source: [12] High, Moderate, and Low VOC Levels Source: [23] [18]

Figure 1. Green Roof Layers
Types of Green Roof are divided into 2 (two) types, namely: a. Intensive Type: this type of green roof has a thick planting layer and soil layer so that more types of plants can be planted. b. Extensive Type: a simpler type of green roof and each has a thinner layer. The types of plants that can be planted are generally sedum. Vegetation that may be applied on a Green Roof in a tropical climate according to several previous studies, is described in Although there is no further question that green open space have many advantages to urban residents, as long as a city produces a large amount of NOx, green open space must be designed optimally in terms of vegetation and tree selection. Certain tree species that are known as high producers of Biogenic Volatile Organic Compounds (BVOC) as listed in Figure 2. Popular Plant Species Grown in Cities with High, Moderate, and Low VOC Levels, should not be planted in large quantities in green open space [18]. The reduction of grass cover is also necessary as BVOC emissions occur on grass that is routinely mowed [19] [20]. This is contrary to the opinion of Amani-Beni, Zhang, Xie, & Xu (2018) [21] which states that grassy areas can reduce urban temperatures and increase humidity. This research tries to optimize the number of trees and still provide a minimal grassy area for the needs of population interaction and evacuation gathering points according to the GOS' function described in the research of Nikolaïdou, Klöti, Tappert, & Drilling (2016) [22].

Method
The research used a quantitative approach. Table 2. Process of Quantitative Data described data processing for the provision of green open space was carried out using Autocad and Sketchup software with the help of the Google Earth application to determine the area of GOS, the percentage of green vegetation, and the number of shade trees. Based on how to obtain the data, quantitative data on the variable of GOS provision and investment feasibility are included in discrete data. Discrete data is data in the form of integers or fractions obtained by counting [24].

Result and Discussion
GOS in Underground GIS is designed using a green roof structure. The soil layer is divided into 6 (six) layers to provide a growing medium for plants but still protect the structure of the building underneath. The type of green roof used is the intensive type, based on the advantages of the types of vegetation. An insulating and waterproofing layer is applied to the underground structures to protect against the different water depths and pressures, static and dynamic style, temperature variations, and gas movement of plants including roots.
The conditions mentioned above can affect the concrete structure, such as cracking or evaporation. Therefore, the Underground GIS design will be coated with a combination of pre-application (1) and post-application (2) waterproofing layers in accordance with Figure 3 Waterproofing Layers.

Measurement Tools
Area of GOS [10] The minimum area of GOS "Taman Rukun Warga" in urban areas is 0.5 m2 per resident, with a minimum area of 1,250 m 2 m 2 -Google Earth -Autocad -Sketchup Type of GOS [10] GOS "Taman Rukun Warga" serves one resident in the form of 70% -80% green space, and the rest can be in the form of a hardened yard as a place to implement activities. There are at least 10 (ten) shade trees of small or medium tree species.
-% green space -unit of shade trees -Google Earth -Autocad -Sketchup  The designation of land is in accordance with Figure 5. Land Surface Allocation, which explains that the proportion of the built-up area for the entire Underground GIS land is planned to be 26%. This built-up area includes the main equipment mobilization area (transformer and GIS), the mobilization of supporting equipment, the workers 'evacuation area, the workers' entry and exit area, and the air circulation area. Most of the land is used for access by considering the size of the main equipment transportation vehicle [25]. The use of entry access can also be optimized again so that vegetation space can be increased and is designed to be planted with small vegetation if there is no equipment mobilization activity. The materials used, such as paving and natural stone, are used as pavement materials for access because they can absorb rainwater so that they are not flooded.

Conclusion
Underground GIS also requires land in a natural environment but tries to maintain part of that environment with green space applied to the roof of the underground building. GOS is applied to the Underground GIS roof by implementing the Intensive Green Roof. Based on Figure 6. Design Aspects of RTH Underground GIS, this study finds that the aspects that are considered in the Green Roof and Underground GIS, by adding public activity spaces and layout arrangements, are the aspects that must be considered for designing green open space above underground buildings. It is hoped that this Underground GIS can become a built environment that can reduce the ecological footprint, generate benefits for the environment, and make the growth of urban space more sustainable and livable.