Comparative Analysis of Multi-Utility Tunnel and Conventional Methods: Evaluating Cost Efficiency, Soil Stability, and Sustainability for Infrastructure Development in IKN, Nusantara

The Multi-Utility Tunnel (MUT) designed to integrate various utilities within a single tunnel network. The implementation of MUT provides benefits such as integrated utility networks, improved efficiency, longer infrastructure lifespan, support for urban sustainability, easier maintenance, and enhanced safety by reducing physical disruptions [1]. Moreover, MUT systems can be easily integrated with modern innovations and technologies [1, 2], in contrast with traditional utility system places each utility separately, often lacking coordination and neglecting the integration of modern technologies [3, 4]. Traditional systems create several issues, including: (1) high space demand, (2) high operational and maintenance costs, (3) disorganized network management, (4) environmental disturbances from frequent digging, (5) low disaster resilience, (6) low energy efficiency, (7) challenges in integrating new technologies, and (8) negative impacts on the urban economy [5]. Currently, no major city in Indonesia has widely adopted the MUT system. However, the upcoming Nusantara Capital City (IKN), slated for habitation by 2028, offers a unique opportunity to design modern infrastructure, including the MUT. With largely undeveloped land, implementing MUT in IKN is expected to improve sustainable urban functions, optimize space utilization, and provide long-term infrastructure solutions.

This research aims to compare the MUT method and conventional method in terms of sustainability and cost efficiency, focusing on the Core Government Area (KIPP) of IKN Nusantara. It examines long-term sustainability and cost efficiency, using geotechnical data from five KIPP zones, which may not fully represent IKN. The study relies on technical parameters such as cost, soil, and structure, with analysis based on model simulations and real-time tests. Cost estimates are projected over 10 years, excluding contingency and construction-related risks.

This section presents the analysis of the data, focusing on the performance, efficiency, and space utilization of the MUT in comparison to conventional infrastructure. Key findings and their implications are discussed.

3.1 Results

This section presents key findings from the study, focusing on the performance, efficiency, and space utilization of the MUT system. The results are categorized into: (1) Utility Management System; (2) MUT; (3) Long-Term Sustainability.

3.1.1 Utility management system

The evaluation shows that MUT scored 5/5 for integration, indicating optimal coordination across utilities, while the traditional system scored 1 due to disorganized layouts and poor adaptability. Key findings include: (1) UMS enhanced MUT dimensional efficiency, (2) reduced utility overlap, and (3) enabled IoT-based real-time monitoring (see Table 6).

Table 6. Key advantages of MUT system over traditional systems

The high integration performance confirms that the Utility Management System, especially through the use of MUT, significantly enhances the MUT’s technical design, operational reliability, and long-term sustainability.

3.1.2 MUT

This section is organized into three key parts: (1) Integrating Geotechnical Data into the MUT Design, (2) Vertical Load Considerations, and (3) Enhancing Space Efficiency, each of which is explained in detail as follows:

Integrating Geotechnical Data into MUT Design. The geotechnical investigations in the KIPP IKN Nusantara region provided essential soil classification and critical data that directly influenced the structural and geometric design of the Multi-Utility Tunnel (MUT). The soil tests conducted across various zones were tied to specific design parameters, such as tunnel depth, wall support requirements, foundation type, and necessary soil improvements. Table 7 summarizes how each geotechnical test result contributed to key design decisions.

Table 7 links test results to design actions, ensuring MUT alignment avoids unstable layers, optimizes structural components, and anticipates ground behavior. For instance, weak soils in Zone 5, identified through CPT and qu tests, prompted deeper tunnels and stronger retaining materials. Modulus values from PMT and Triaxial tests informed finite element modeling, which guided the dimensioning of side walls and base slabs. These data-driven adjustments enhance tunnel performance and reduce construction risks.

The design assumes the Multi-Utility Tunnel length is 1 km (1,000 meters) for consistency with the conventional system comparison. The MUT design includes five scenarios: (1) Joint Duct Utility (JDU) “a shared duct system for various utilities like high-voltage cables and water pipes, aimed at optimizing space and reducing environmental impact.” [23, 24]; (2) Hydrant Pipe “A Hydrant Pipe is a specialized pipeline connected to the city's hydrant system, providing quick access to water for firefighting” [25]; (3) Gas Pipe is a pipeline used to transport natural gas or other gases, typically for residential, industrial, or commercial purposes [26]; (4) Joint Duct Pipe (JDP) is a channel or pipe designed to accommodate multiple types of cables or pipes within the same conduit, aimed at space efficiency and infrastructure management [27]; (5) Fiber Optic Cable (FO) functions to support high-speed telecommunication networks for internet, telephone, and data services [28, 29].

Table 7. Relationship between geotechnical tests and MUT design parameters

The design for IKN Nusantara is based on international best practices and is divided into three types: (1) MUT for main roads (MUT Type 1), (2) MUT for branch roads (MUT Type 2), and (3) MUT for tapping points (Tapping MUT). Figure 4 illustrates the cross-sectional diagram of a MUT, with a total width of 4.5 meters, a height of 4 meters, and a wall thickness of 0.2 meters. The effective width is 3.7 meters (after accounting for boundary walls), and the effective height is 2.6 meters (considering boundary floors) (see Figure 5).

MUT Type 1 has the following dimensions: total width of 4.5 meters, height of 4 meters, and wall thickness of 0.2 meters. The effective width is 3.7 meters (after accounting for boundary walls), and the effective height is 2.6 meters (considering boundary floors) (see Figure 5).

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Figure 4. Cross-sectional diagram of the MUT Type 1

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Figure 5. 3D cross-sectional view of the MUT Type 1 with utility annotations

MUT Type 2 is an extension of MUT Type 1 (see Figure 6 and Figure 7).

MUT Type 3 or Tapping MUT is designed for connections to the main utility tunnel, enabling utility distribution to various areas without the need for separate tunnels (see Figure 8 and Figure 9).

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Figure 6. Cross-sectional diagram of MUT Type 2

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Figure 7. 3D cross-sectional view of MUT Type 2

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Figure 8. Top view and cross-sectional diagram of tapping MUT

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Figure 9. 3D cross-sectional view of tapping MUT

The following table compares the specifications of different MUT types, including MUT Type 1, MUT Type 2, and Tapping MUT (see Table 8).

Table 9 outlines the main components of the three MUT types, detailing utilities. These components ensure efficient space usage and support essential services in urban infrastructure.

Table 8. The dimensions proposed design for MUT in IKN

Table 9. The main components proposed design for MUT in IKN

To maintain consistency with traditional systems, this study focuses on MUT Type 1, designed for main roads in IKN Nusantara. It offers a more integrated solution with three chambers: (1) the Drainage Chamber for water flow, (2) the Utility Chamber for JDU, Hydrant Pipe, Gas Pipe, JDP, and Fibre Optic Cable, and (3) the Electricity Chamber for electricity cables. This design contrasts with conventional systems that require multiple separate installations and more space.

In alignment with global best practices, we will benchmark the system against successful international standards from countries like China, Japan, and the European Union [30, 31]. The MUT design varies across China, Japan, and the European Union in three key aspects: (1) China prioritizes space optimization, rapid construction, and disaster resilience with smart monitoring for improved utility management; (2) Japan focuses on seismic safety, using high-strength materials to withstand earthquakes; (3) The European Union emphasizes sustainability, energy efficiency, and minimal environmental impact, incorporating advanced monitoring and maintenance technologies.

Comparison highlights: (1) Tunnel dimensions in all regions range from 3 to 6 meters in width and 3 to 4 meters in height, with separate compartments for utilities; (2) All regions use high-strength reinforced concrete and corrosion-resistant materials for durability, especially for water and gas pipelines; (3) Structural designs: China focuses on optimization and resilience, Japan on seismic safety, and the EU on sustainability and energy efficiency; (4) Proper ventilation and drainage are ensured across all regions; (5) Utilities are separated to avoid interference, with access provided via manholes and shafts.

Vertical Load $(\mathbf{P})$. The vertical load $(\mathbf{P})$ $\left(\mathbf{k N} / \mathbf{m}^2\right)$ is divided into three as follows: Firstly, The Weight of The MUT Structural Concrete ($\boldsymbol{W}_{\boldsymbol{Concrete}}$): $\boldsymbol{W}_{\boldsymbol{Concrete}}$ refers to the weight of the concrete used in the construction of the MUT structure itself, which contributes to the overall vertical load [32]. $\boldsymbol{W}_{\boldsymbol{Concrete}}$ specific weight of concrete per square meter. It is a measure of the weight of concrete applied over an area of 1 square meter ( $\mathrm{kN} / \mathrm{m}^2$ or $\mathrm{kg} / \mathrm{m}^2$ ). $\boldsymbol{W}_{\boldsymbol {Concrete}}$ calculates as follows:

$W_{ {Concrete }}=V_{ {Concrete }} \times \rho_{ {Concrete }} \times g$          (1)

where, (1) $W_{{Concrete}}=$ Weight of the concrete per 1 meter $\left(\mathrm{kN} / \mathrm{m}^2\right)$; (2) $V_{{Concrete }}=$ specific weight of concrete per square meter $\left(k N / m^2\right), V_{{Concrete }}=b(m) \times h(m) \times t(m)$; (3) $\rho_{{Concrete }}=$ Density of the utilities $\left(\frac{\mathrm{kg}}{\mathrm{m}^3}\right)$.

Substituting the values: $\mathrm{W}_{\text {Concrete}}=(4.2 \mathrm{~m} \times 2.6 \mathrm{~m} \times$ $0.3 \mathrm{~m}) \times 25 \frac{\mathrm{kN}}{\mathrm{m}^3}=3.276 \mathrm{~m}^3 \times 25 \frac{\mathrm{kN}}{\mathrm{m}^3}=81.9 \mathrm{kN}$. The density of the concrete is already expressed in kN/m³ (kilonewtons per cubic meter), which inherently includes the effect of gravity. Therefore, there is no need to multiply by gravitational acceleration  (9.81 m/s²).

Secondly, the Load of the Utilities ($\mathrm{W}_{\text {utility}}$): $\mathrm{W}_{\text {utility}}$ represents the load generated by the utilities within the MUT, including pipes, cables, and other equipment actively used during operation. The total weight of utilities ($\mathrm{W}_{\text {utility}}$) is calculated by summing the individual weights of each utility system installed in the tunnel. The formula is as follows:

$\begin{gathered}\mathrm{W}_{\text {utility }}=\mathrm{W}_{\mathrm{JDU}}+\mathrm{W}_{\mathrm{H}}+\mathrm{W}_{\mathrm{GP}}+\mathrm{W}_{\mathrm{JDP}}+\mathrm{W}_{\mathrm{EC}}+\mathrm{W}_{\mathrm{D}}+\mathrm{W}_{\mathrm{V}}+\mathrm{W}_{\mathrm{FO}}\end{gathered}$          (2)

where, (1) $\mathrm{W}_{\text {utility }}$ = total weight of utilities within the MUT (kN/m²); (2) $\mathrm{W}_{\mathrm{JDU}}$= wiegth of Joint Duct Utility (kN/m²); (3) $\mathrm{W}_{\mathrm{H}}$= weight of Hydrant Pipe (kN/m²); (4) $\mathrm{W}_{\mathrm{GP}}$= Gas Pipe (kN/m²); (5) $\mathrm{W}_{\mathrm{JDP}}$= weight of Joint Duct Pipe (kN/m²); (6) $\mathrm{W}_{\mathrm{EC}}$= Weight of Electricity Cable (kN/m²); (7) $\mathrm{W}_{\mathrm{D}}$ = Drainage Contains (kN/m²); (8) $\mathrm{W}_{\mathrm{V}}$= Ventilation Contains (kN/m²); (9) $\mathrm{W}_{\mathrm{FO}}$= weight of Fibre Optic (kN/m²).

Substituting the values: $\quad W_{{utility }}=17.035+10.630+6.791+3.822+4.245+0.95+0.95+0.577=45 \mathrm{kN} / \mathrm{m}$.

Lastly, Total Vertical Loads ($P$) per meter length (kN/m²) are calculated as follows:

$\mathrm{P}=\mathrm{W}_{\text {Concrete}}+\mathrm{W}_{\text {utility}}$          (3)

where, (1) $\mathrm{P}=$ Total vertical loads $\left(\mathrm{kN} / \mathrm{m}^2\right)$; (2) $\mathrm{W}_{\text {Concrete}}=$ specific weight of concrete per square meter ($\mathrm{kN} / \mathrm{m}^2$); (3) $\mathrm{W}_{\text {utilitas}}=$ Weight of utility inside the MUT ($\mathrm{kN} / \mathrm{m}^2$).

Substituting the values: $P=W_{ {Concrete}}+W_{{utilitas }}=81.9 \frac{\mathrm{kN}}{\mathrm{m}}+45 \frac{\mathrm{kN}}{\mathrm{m}}=126.9 \frac{\mathrm{kN}}{\mathrm{m}}$. In other words, for every square meter of MUT, the vertical load $(P)$ is $126.9 \frac{\mathrm{kN}}{\mathrm{m}^2}$.

Space Efficiency. Relative space efficiency is calculated using the ratio between the MUT (Multi Utility Tunnel) system and the conventional system by comparing the total space used by each system, as formulated in Eq. (4) as follows:

$R_e=\frac{L_{ {Conventional }}-L_{M U T}}{L_{{Conventional }}} \times 100 \%$          (4)

where, (1) $R_e$= Relative space efficiency (in percentage); (2) $L_{Conventional}$= Total utility space length in the conventional system (in meters); (3) $L_{M U T}$= Total utility space length in the MUT system (in meters).

Yielding the following value: $\begin{aligned} \mathrm{R}_{\mathrm{e}}=\frac{\mathrm{L}_{\text {Conventional }}-\mathrm{L}_{\mathrm{MUT}}}{\mathrm{L}_{\text {Conventional }}} \times 100 \%=\frac{7.5 \text { meter }-4.5 \text { meter }}{7.5 \text { meter }} \times 100 \%=40 \%\end{aligned}$. The MUT system can save up to 40% of space (Re = 40%) compared to conventional methods. 

The value of $R_e$ indicates the level of efficiency of the new system compared to the conventional system, as follows: (1) $R_e$  > 1: The new design is less efficient, using more space than the conventional design (space wasted); (2) $R_e$  = 1: The new design and conventional design are equally efficient, with no space saving; (3) $R_e$ < 1: The new design (MUT) is more efficient, saving space compared to the conventional design.

3.1.3 Long-term sustainability (dependent variables)

Long-term sustainability divides into two aspects: (1) sustainability from a physical perspective; and (2) cost efficiency.

Sustainability from a physical perspective can be viewed from two aspects: (1) Soil Stability and (2) Structural Stability. The explanations for each are as follows: Firstly, Soil Stability analyse using three 3 parameters which is Modulus Elasticity (E), Poisson's Ratio (ν), Maximum Stress ($\sigma_{\max }$) [33]. First, the explanation regarding soil stability is addressed through Modulus of Elasticity (E). Modulus of Elasticity (E) is used to measure the stiffness of the soil, providing insights into how much the soil can deform under stress [34, 35]. Reference [36] indicates the soil’s ability to resist elastic deformation (Ɛ) when subjected to stress ($\sigma$)  [37]. The higher the soil stiffness (E), the smaller the elastic deformation (Ɛ), which indicates better stability [32, 38] (see Eq. (5)).

$\varepsilon=\frac{\sigma}{\mathrm{E}}$          (5)

where, (1) $\varepsilon=$ the ratio of the change in length $(\Delta L)$ to the original length $(L)$, or $\frac{\Delta L}{L}$; (2) $\sigma=$ force per unit area (kN/m²) or Pascal (Pa); (3) $E=$ modulus of elasticity.

In this research, Modulus of Elasticity (E) measured using Triaxial Test and Cone Penetration Test [39, 40]. Table 10 summarizes the elastic modulus (E), tested stress $\left(\sigma_{ {Test }}\right)$, and calculated stress $\left(\sigma_{ {calc }}\right)$ for various soil types at different depths in the KIPP zones.

Table 9 highlights key findings:

(1) Elastic Modulus (E) increases with depth, ranging from 500-600 kN/m² in West KIPP and 550-650 kN/m² in South KIPP;

(2) Test Stress $\left(\sigma_{ {Test }}\right)$ is higher in denser soils, e.g., 200 kN/m² in clayey sand to 250 kN/m² in compact sand in West KIPP;

(3) $\sigma_{{Test }}$ and $\sigma_{ {calc }}$ are consistent, validating the model;

(4) Relative Deformation (Ɛ) increases slightly with depth but remains within limits, with denser soils deforming less;

(5) Soil type significantly affects mechanical properties, with denser soils showing higher E and $\sigma_{{Test }}$ values.

Table 10. Elastic modulus, tested stress, and calculated stress for various soil types in KIPP zones

Second, the explanation regarding soil stability is addressed through Poisson's Ratio (ν). Poisson's Ratio (ν) measures the ratio of lateral to axial strain under stress and is crucial for assessing lateral pressure and volumetric deformation in soils [41, 42]. A high ν (near 0.5) indicates nearly incompressible saturated soils, while lower values (0.2–0.3) suggest better stability in granular soils. It’s determined via lab tests like Triaxial and Uniaxial Compression. For this study, a soil length of 10 m (L) is assumed to calculate deformation. Table 11 lists ν and Elastic Modulus (E) values across KIPP zones, essential for evaluating soil stability and MUT design suitability.

Table 11. Elastic Modulus (E) and Poisson's Ratio (ν) for various soil types in the KIPP zones

Based on Table 10, Poisson’s Ratio (ν) and Elastic Modulus (E) generally increase with depth across all KIPP zones. For instance, in West KIPP (Zone 1), ν rises slightly from 0.30 to 0.32 while E increases from 500 to 600 kN/m². Similar upward trends are observed in North, South, East, and Central KIPP zones, with denser soils consistently showing higher values. This indicates a positive correlation between Poisson’s Ratio and Elastic Modulus, where denser soils exhibit greater elasticity and reduced deformation under stress.

Thirdly, the explanation regarding soil stability is addressed through Maximum Stress $\left(\sigma_{\max }\right)$. Maximum Stress $\left(\sigma_{\max }\right)$ represents the maximum stress the soil can withstand before failure, essential for understanding the soil’s load-bearing capacity. It directly evaluates soil bearing capacity and defines the safe load limit for structures like MUT, ensuring stability. Measured through Direct Shear, Triaxial, or Unconfined Compression Tests.

$\sigma_{\max }=\frac{\text { Force }(\mathrm{N})}{\text { Area }\left(\mathrm{m}^2\right)}$          (6)

where, (1) $\text {Force}$ = total external load or force applied to the soil $(\mathrm{N})$ (taken from test result. Force (N) $=\sigma_{\max } \times$ Area $\left(\mathrm{m}^2\right)$ $\times 1000$ (1000 is the conversion factor from kPa to N/m² (1 kPa = 1000 N/m²)); (2) $\text {Area}$ = contact area between the soil and the applied force $\left(\mathrm{m}^2\right)$. Contact area assume for 10.92 m² for soil loading analysis. Maximum Stress $\left(\sigma_{\max }\right)$ presented in Table 12.

Table 12. Data of maximum stress, force, and area for various soil types in different test zones

Table 12 shows that maximum stress (σ_max) increases with depth across all KIPP zones. In West KIPP (Zone 1), Sand-Clay soil stress rises from 200 kPa at 0-5 m to 250 kPa at 10-15 m. North KIPP (Zone 2) follows a similar trend, increasing from 180 kPa to 240 kPa. South KIPP (Zone 3) has the highest stress values, reaching 300 kPa at 10-15 m, indicating stronger soil suitable for heavier structures.

East (Zone 4) and Central KIPP (Zone 5) show lower stress levels, with gravelly soils having the lowest bearing capacity, requiring reinforcement or design adjustments.

Secondly, sustainability from a physical perspective can be assessed through structural stability, which refers to a structure's ability to endure loads and forces without failure, deformation, or collapse [43, 44]. To analyse structural stability, three key factors are considered: (1) Total Stress ($\sigma_{t o t}$); (2) Maximum Deformation (∆); and (3) Safety Factor (FS).

First, sustainability from a physical perspective can be assessed through structural stability using the indicator of Total Stress ($\sigma_{\text {tot}}$). Total Stress ($\sigma_{\text {tot}}$) applied to the soil by structural elements above it. Total stress ($\sigma_{\text {tot}}$) results from external loads. It is calculated using Eq. (7):

$\sigma_{t o t}=\frac{\mathrm{P}}{\mathrm{A}}$          (7)

where, (1) $\sigma_{t o t}=$ Total stress $(\mathrm{kPa})$; (2) $P=$ Vertical load $\left(\mathrm{kN} / \mathrm{m}^2\right) ;(3) A=$ Base area of the structure ($\mathrm{m}^2$).

Total Stress on soil by test ($\sigma_{\text {Test}}$). Total Stress determined through tests such as the Direct Shear Test, Triaxial Test, or Unconfined Compression Test [45, 46]. It is used to assess soil stability by comparing the applied pressure to the soil's bearing capacity. If the total stress $\sigma_{tot}>\sigma_{Test}$, the soil risks being overloaded and may fail, requiring reinforcement for safe MUT support. If $\sigma_{\text {tot }}<\sigma_{{Test}}$, the soil has higher bearing capacity than tested, offering potential cost savings in foundation design. When $\sigma_{\text {tot }}=\sigma_{{Test}}$, the soil is stable, confirming it can safely bear the expected loads and ensuring reliable MUT foundation design (see Table 13).

Table 13. Soil stability evaluation based on total stress $\left(\sigma_{t o t}\right)$ and test stress $\left(\sigma_{Test}\right)$ comparison across KIPP zones

As the conclusion on the analysis of total stress ($\sigma_{t o t}$) and field test results ($\sigma_{{Test}}$) across various KIPP zones, the following conclusions can be drawn: In all KIPP zones, total stress ($\sigma_{\text {t o t}}$) is consistently lower than tested stress ($\sigma_{\text {Test}}$), indicating that soil strength exceeds laboratory test results. This confirms soil stability across all zones, meaning the soil can safely support applied loads. Consequently, structural designs can be more efficient with less need for reinforcement, and the soil may support greater loads if required in the future.

Second, sustainability from a physical perspective can be assessed through structural stability using the indicator of Maximum Deformation ($\Delta$). Maximum Deformation ($\Delta$) is the change in shape (strain) of the soil due to the stress applied by vertical loads This parameter is used to assess the stability of the soil beneath structures and utilities. It is calculated using Eq. (8):

$\Delta=\frac{P . L}{E . A}$          (8)

where, (1) $\Delta$ = Maximum deformation (m); (2) $P$ = Vertical load ($\mathrm{kN} / \mathrm{m}^2$); (3) $L$ = Length of the soil element (m); (4) $E$ = Soil stiffness (kPa); (5) $A$ = Cross-sectional area of the soil element ($\mathrm{m}^2$). The Maximum Deformation ($\Delta$) results are presented in Table 14.

Table 14. Soil characteristics by zone and depth at KIPP

Table 14 shows Maximum Deformation (∆) for various soil types across five KIPP zones, factoring in vertical load (P), cross-sectional area (A), elasticity modulus (E), and soil length (L). Soils with higher elasticity, like Compact Sand and Clay, exhibit smaller deformations, indicating better stability, while Fine Sand and Gravel show larger deformations, signaling vulnerability. For example, Gravelly Sand in Zone 5 has ∆=0.031 m, higher than Fine Sand in Zone 4 (∆=0.022 m). Maximum Deformation is crucial for structural stability as higher deformation reduces soil bearing capacity and increases settlement risk.

Third, sustainability from a physical perspective can be assessed through structural stability using the indicator of Safety Factor (FS). Safety Factor (FS) is the ratio between the soil's maximum stress ($\sigma_{\max}$) assume equal ($\sigma_{{Test}}$) and the total stress ($\sigma_{\text {t o t}}$) assume equal applied by the structural load [47-49]. The formula is:

$F S=\frac{\sigma_{\max }}{\sigma_{t o t}}$          (9)

Interpretation of results is as follows: (1) FS > 1.5 (Safe) – The soil is sufficiently stable to support the load; (2) FS = 1.0 (Marginal) – The soil is close to its stability limit and requires attention; (3) FS < 1.0 (Unsafe) – The soil is unstable and at risk of failure. Safety Factor (FS) results are presented in Table 15.

Table 15. Safety Factor (FS) for different zones and soil types

The Safety Factor (FS) analysis across KIPP zones indicates that most soils, particularly in West, North, South, and East KIPP, can support applied loads safely, with FS values above 1. South KIPP (Zone 3) exhibits the highest stability (FS = 2.36), while East KIPP (Zone 4) also shows safe FS values ranging from 1.26 to 1.57. However, Central KIPP (Zone 5), particularly the Gravelly Sand at 0-5 m depth, has a marginal FS of 1.10, indicating a higher risk of structural failure. This highlights the need for soil improvement or design modifications in Central KIPP to ensure stability and prevent failure.

Structural analysis confirms that most KIPP soils can bear applied loads, with bearing capacities surpassing lab assumptions. Soils with higher elasticity, such as compact sand and clay, deform less and exhibit better stability. Conversely, fine and gravelly sands deform more, which could pose risks if unsterilized. While the majority of zones exhibit FS values greater than 1, Central KIPP’s FS of 1.10 signals potential failure risks and the necessity for reinforcement. Therefore, most zones are suitable for MUT construction, with Central KIPP requiring soil strengthening for secure foundations.

Long-term sustainability, in terms of cost efficiency, can be assessed through Total Cost and Asset Depreciation. Total Cost (∆C) combines Capital Expenditure (Capex) and Operational Expenditures (Opex) for both the traditional and MUT systems, as defined in Eq. (7).

$\Delta C=C_{ {Capex }}+C_{{Opex }}$          (10)

where, (1) $C_{ {Capex}}$ = Capex (IDR); (2) $C_{{Opex}}$ = Opex (IDR).

Firstly, long-term sustainability in terms of cost efficiency assessed through aspects of $C_{ {Capex}}$ as part of the total cost. $C_{ {Capex}}$ refers to the funds spent to acquire, upgrade, or maintain physical assetss [50]. In this research, $C_{ {Capex}}$ is measured per 1,000 meters. $\mathrm{C}_{\text {Capex}}$ calculated by summing all costs incurred during the construction of both systems (see Eq. (11)).

$\begin{aligned} C_{{Capex }}=C_{J D U}+ & C_H+C_{G P}+C_{J D P}+C_{E C}+C_D  +C_{F O}+C_{E C}+C_{C C}\end{aligned}$          (11)  

where, (1) JDU installation cost ($C_{J D U}$) (IDR); (2) Hydrant cost ($C_H$) (IDR); (3) Gas Pipe cost ($C_{G P}$) (IDR); (4) JDP cost ($C_{J D P}$) (IDR); (5) Electricity Cable cost ($C_{E C}$) (IDR); (6) Drainage cost ($C_D$); (7) FO $\left(C_{F O}\right)$. Plus, two additional new costs, namely: (8) Excavation (5 lanes) Cost ($C_{E C}$) (IDR); and (9) Construction Cost ($C_{C C}$) Excavation (5 lanes) Cost (IDR).

Capex efficiency (CEE) between the traditional system and MUT is calculated using the following equation.

$C E E=\frac{C_{{Capex\ Traditional }}-C_{{Capex\ MUT }}}{C_{ {Capex\ Traditional }}} \times 100 \%$          (12)

where, (1) $CEE$ (IDR); (2) $C_{Capex\ Traditional}$ (IDR); (3) $C_{{Capex\ MUT}}$ (IDR).

The Capex for both methods is presented in Table 16.

Table 16. Capex for conventional and MUT methods

Long-term sustainability in terms of cost efficiency assessed through aspects of $\mathrm{C}_{\mathrm{Opex}}$ as part of the total cost. $\mathrm{C}_{\mathrm{Opex}}$ refers to the ongoing, recurring costs incurred during the operation an infrastructure or system after its construction [50]. The operational costs of each utility calculate as follows (see Eq. (13)).

$\begin{gathered}C_{{Opex }}=O_{J D U}+O_H+O_{G P}+O_{J D P}+O_{E C}+O_D +O_{F O}+O_{U M}\end{gathered}$          (13)

where, (1) JDU cost $\left(O_{J D U}\right)$ (IDR); (2) Hydrant cost $\left(O_H\right)$ (IDR); (3) Gas Pipe cost ($O_{G P}$) (IDR); (4) JDP cost ($O_{J D P}$) (IDR); (5) Electricity Cable cost ($O_{E C}$) (IDR); (6) Drainage cost $\left(O_D\right)$ (IDR); (7) FO $\left(O_{F O}\right)$ (IDR). Plus, one additional new cost; (8) utility maintenance cost ($O_{U M}$) (IDR).

The calculation of $C_{{Opex }}$ efficiency (OEE) between the traditional system and MUT is calculated using the following equation:

$OEE =\frac{C_{{Opex\ Traditional }}-C_{{Opex\ MUT}}}{C_{{Opex\ Traditional }}} \times 100 \%$          (14)

where, (1) $OEE$ (IDR); (2) $C_{{Opex\ Traditional}}$ (IDR); (3) $C_{{Opex\ MUT}}$ (IDR).

If the value of CEE MUT or OEE MUT is positive, it indicates that the MUT method is more cost-efficient compared to the conventional method, and the other way around. The Opex for both methods are presented in Table 17.

As summary, the total costs over a 10-year period are summarized in Table 18.

Secondly, long-term sustainability in term of cost efficiency can be assessed through aspects of Asset Depreciation. Asset depreciation is the systematic allocation of the initial cost of a fixed asset used in an entity’s operations over its useful life. Depreciation reflects the decrease in asset value over time due to wear and tear, damage, usage, or other external factors [51].

Table 17. $C_{{Opex}}$ for conventional and MUT methods

Table 18. A comparison of cost parameters and efficiency between the conventional method and the MUT system

 Depreciation is calculated using the Straight-Line Method [52], see equation as follows:

$A D=\frac{C_{{Capex }}-R V}{U L}$          (15)

where, (1) Annual Depreciation (AD) = asset value decreases each year (IDR); (2) $C_{Capex}$ is the cost of building or purchasing the asset (IDR); (3) Residual Value (RV) is the expected value remaining after the asset’s useful life (IDR); (4) Useful Life (UL) is the duration the asset is expected to be in service (Years).

The annual depreciation rates were derived from an interview with the Ministry of Public Works of the Republic of Indonesia. The Ministry noted that, after years of observing utilities in tropical regions like Indonesia, they concluded that the Traditional Method experiences a higher depreciation rate of 5% annually, resulting in faster asset value reduction. Conversely, the MUT Method has a lower depreciation rate of 1.25% per year, leading to slower depreciation and better retention of asset value over time. The annual depreciation can be calculated as follows:

$\mathrm{AD}=C_{{Capex }} \times \mathrm{ADR}$          (16)

where, (1) Annual Depreciation (AD) = asset value decreases each year (IDR); (2) $C_{{Capex }}$ is the cost of building or purchasing the asset (IDR); (3) Annual Depreciation Rate (ADR) (%).

Total Depreciation over n years is calculated by multiplying the annual depreciation by the number of years (n) being analysed [53, 54], as follows:

$T D=A D R \times N$

where, (1) Total Depreciation (TD) is the total value decrease over the observation period (IDR); (2) Annual Depreciation Rate (ADR) is the depreciation percentage applied each year (%); (3) Number of years ($N$) of observation (10 years, 20 years, …).

Asset Value After Depreciation: Asset Value After Depreciation calculates as follows:

$A V A D=C E-T D$          (18)

where, (1) Asset Value After Depreciation (AVAD) is the remaining value of the asset after n years.

Table 19 compares the asset depreciation values over 10, 20, and 30 years for both the Conventional Method and the MUT System. The data, sourced from interviews with the Ministry of Public Works and calculations based on observed depreciation rates for various utilities, highlights the differences in Capex and depreciation over time. The table demonstrates that the MUT system experiences slower depreciation, resulting in higher retained asset value compared to the conventional method.

Table 19. Compares asset depreciation over 10, 20, and 30 years for the conventional method and the MUT system, showing slower depreciation and higher retained value for the MUT system

 The MUT system excels in performance with a perfect utility integration score of 5/5, combining multiple networks into one tunnel. It offers 40% land-use efficiency compared to conventional methods, crucial for space-limited areas like IKN Nusantara. While MUT has a higher initial Capex (13.25 billion IDR), its lower operational costs and space-saving benefits make it more cost-effective in the long run, with a total cost of 12.775 billion IDR over 10 years, compared to 14.25 billion IDR for the conventional system.

3.2 Discussions

This section analyses the results and links them to the research goals, emphasizing the broader implications. The Utility Management System, particularly MUT, offers key advantages over traditional methods, such as integrating multiple utilities into a single tunnel and saving up to 40% of urban space—critical for land-scarce areas like KIPP Nusantara. MUT also supports smart management through SCADA and IoT for real-time monitoring, with the added benefit of allowing future utility expansion without the need for major new infrastructure.

Geotechnical analyses show that soil variability across KIPP zones impacts MUT design; stable zones support the tunnel well, while weaker zones require reinforcement. Environmentally, MUT reduces land disruption, improves safety, and enhances accessibility. Financially, despite higher initial costs, MUT results in long-term savings through reduced maintenance, better space utilization, and slower asset depreciation (1.25% annually), leading to a higher ROI compared to conventional methods.