Results in Engineering

PentaPod: A New Type of Concrete Armor for Coastal Protection

--Manuscript Draft--

Manuscript Number:

Full Title: PentaPod: A New Type of Concrete Armor for Coastal Protection

Short Title:

Article Type: Research paper

Section/Category: Civil Engineering

Keywords: PentaPod; A New Concrete Armor; A New Insight for Coastal Protection; Kd Values
of PentaPod

Corresponding Author: Dantje Kardana Natakusumah, Bsc, MSc, PhD, Ir

Bandung Institute of Technology Faculty of Civil and Environmental Engineering
Bandung, West Java INDONESIA

Corresponding Author Secondary

Information:

Corresponding Author's Institution: Bandung Institute of Technology Faculty of Civil and Environmental Engineering

Corresponding Author's Secondary

Institution:

First Author: Dantje Kardana Natakusumah, Bsc, MSc, PhD, Ir

First Author Secondary Information:

Order of Authors: Dantje Kardana Natakusumah, Bsc, MSc, PhD, Ir

Hendra Achiari, Dr. Eng., B.Sc., M.Sc.

Eka Oktariyanto Nugroho, Dr. Eng., B.Sc., M.Sc.

Syarif Hidayatulloh, B.Sc., M.Sc.

Jonathan Angelo Ishakputra, B.Sc., M.Sc.

Fitra Adinata, B.Sc.

Order of Authors Secondary Information:

Abstract: This paper explores PentaPod, an invention in concrete armor units developed to
protect coastal areas from damage caused by waves and currents. Until now, there
hasn't been an armor unit intentionally designed to enhance its stability through
connections with neighboring units. PentaPod provides a novel perspective,
suggesting that the stability of armor units can be significantly improved not only by
having substantial weight and effective interlocking but also by securely connecting
them to each other. With this in mind, PentaPod concrete armor can be installed in a
random or regular manner without the need for fasteners. Alternatively, it can also be
installed regularly in layers with fasteners. Compared to conventional concrete armor
installations, the overall stability of structures is significantly improved with
interconnected PentaPod, either partially or entirely. In this paper, the results of testing
the Stability Coefficient (Kd) for two variations of armor, namely PentaCone and
PentaOcta, tested in a Wave Tank are also presented. The objective of this testing is to
ascertain the stability coefficient for both variations of armor when installed randomly or
regularly without any tying involved. The PentaPod arrangement allows for the
implementation of both Grey Protection (using concrete armor) and Green Protection
(conservation of mangrove areas) simultaneously, showcasing its versatility and
integrated approach to coastal protection.

Suggested Reviewers: Muhammad Syahril Badri Kusuma, Prof, PhD

Professor, Bandung Institute of Technology Faculty of Civil and Environmental
Engineering
msbadrik@lppm.itb.ac.id

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 M Mustain, Prof., Drs., M.Sc., Ph.D.
Professor, Sepuluh Nopember Institute of Technology Department of Ocean
Engineering
mmustain@oe.its.ac.id

Adi Prasetyo, Dr.

Head, Ministry of Public Works and Public Housing
madjutakgentar@yahoo.com

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Declaration of Interests Statement

Declaration of interests

☐The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.

☒The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests:

Dantje Kardana Natakusumah reports financial support and article publishing charges were provided
by Bandung Institute of Technology. Dantje Kardana Natakusumah reports a relationship with
Bandung Institute of Technology that includes: employment, funding grants, speaking and lecture
fees, and travel reimbursement. The Author is a member of Faculty of Civil and Environmental
Engineering
Highlights

Some Highlights

1) Design and Arrangement: PentaPod features four horizontal legs and one vertical leg, forming a square-

based pentahedral pyramid. This design can be arranged in either a random or regular manner, with holes

along the center of the legs for the insertion of binding ropes.

2) Interconnection and Stability: PentaPod was specifically developed to enhance stability through

interlocking with neighboring units. When installed in a regular layer, PentaPods can either be interconnected

using ropes or installed without interconnections, depending on the application requirements.

3) Simplified Planning and Placement: The geometric design of PentaPods simplifies the counting of units

and enables precise planning for their placement in specific areas. Additionally, the use of binding ropes

streamlines the installation process on diverse surfaces and aquatic environments, adding to the practicality

of the PentaPod system in coastal protection.

4) Installation Flexibility: For random installations, interconnections between units are not necessary,

eliminating the need for holes. This flexibility allows for cost-effective and adaptable installation in various

coastal protection projects.

1) Cost Efficiency and Practicality: Regular installation of PentaPods without binding reduces armor unit

requirements, leading to cost savings. Conversely, regular installation with binding not only enhances

stability but also allows for a reduction in armor unit size, further cutting down costs.
Manuscript Click here to access/download;Manuscript;Manuscript -
Pentapod.docx
Click here to view linked References

1 PentaPod1: A New Type of Concrete Armor for Coastal Protection

2 Dantje Kardana Natakusumah*
3 Expertise Group in Water Resources Engineering, Faculty of Civil and Environmental Engineering
4 Institut Teknologi Bandung (FCEE-ITB), *Email: dknpub@gmail.com
5 Hendra Achiari
6 Marine Engineering Study Program, FCEE -ITB, Email: achiarihendra@gmail.com
7 Eka Oktariyanto Nugroho
8 Expertise Group in Water Resources Engineering, FCEE -ITB, Email: nugrohoeka@itb.ac.id
9 Syarif Hidayatulloh
10 Alumnus of the Master's Program in Civil Engineering, Institut Teknologi Bandung, Email:
11 syarif.cmh@gmail.com
12 Jonathan Angelo Ishakputra
13 Alumnus of the Master's Program in Water Resources Management, Institut Teknologi Bandung, Email:
14 jonathanangelo82@gmail.com
15 Fitra Adinata
16 PT. Sapta Ahi Pratama, Email: fitra240484@gmail.com
17
18 Abstract: This paper explores PentaPod, an invention in concrete armor units developed to protect coastal

19 areas from damage caused by waves and currents. Until now, there hasn't been an armor unit intentionally

20 designed to enhance its stability through connections with neighboring units. PentaPod provides a novel

21 perspective, suggesting that the stability of armor units can be significantly improved not only by having

22 substantial weight and effective interlocking but also by securely connecting them to each other. With this in

23 mind, PentaPod concrete armor can be installed in a random or regular manner without the need for fasteners.

24 Alternatively, it can also be installed regularly in layers with fasteners. Compared to conventional concrete

25 armor installations, the overall stability of structures is significantly improved with interconnected PentaPod,

26 either partially or entirely. In this paper, the results of testing the Stability Coefficient (Kd) for two variations

27 of armor, namely PentaCone and PentaOcta, tested in a Wave Tank are also presented. The objective of this

28 testing is to ascertain the stability coefficient for both variations of armor when installed randomly or regularly

29 without any tying involved. The PentaPod arrangement allows for the implementation of both Grey Protection

30 (using concrete armor) and Green Protection (conservation of mangrove areas) simultaneously, showcasing its

31 versatility and integrated approach to coastal protection.

32 Keywords: PentaPod, A New Concrete Armor, a New Insight for Coastal Protection, Kd Values of PentaPod

1
PentaPod is a concrete armor unit patented in Indonesia under the registration number P00202305213,
attributed to the Institute of Technology Bandung, a government-funded university in Indonesia.

1
33 1 Introduction

34 Wave action is one of the factors that contributes to erosion. When storms occur the force of waves, on the

35 coastline gradually erodes the land. Carries away sediment. This erosion primarily occurs at the coastline

36 resulting in erosion and wearing down of the land. The intensity and frequency of wave action can vary

37 depending on factors like wind speed and wave height. Over time this erosion can significantly change the

38 shape of the coastline leading to habitat loss and alterations in the ecosystem. Additionally erosion can directly

39 impact activities by posing a threat, to coastal infrastructure and decreasing land value. It is crucial to

40 implement coastal management strategies to minimize these effects and protect the integrity of areas.

41 Wave currents are a significant cause of coastal erosion, as they create intense local currents that move

42 sediments and contribute to the loss of land along the shoreline. This process occurs when waves approach the

43 coast at a certain angle before returning to the sea while carrying sediment near the coastline. Over time, this

44 cycle repeats, causing erosion in a zigzag pattern along the coastline. Wave currents tend to be more

45 pronounced in areas with currents or where the coast is not aligned with the dominant wave direction

46 (Encyclopedia Britannica, Erosion, 2023, December 14).

47 Rising sea levels contribute to coastal erosion, impacting coastal habitats and communities. As the Earth's

48 temperature rises, ice melting and water entering the oceans lead to the recession of coastlines and intensified

49 wave impact, accelerating erosion. Adapting to rising sea levels is crucial in coastal management. According

50 to Bouchahma, Yan, and Ouessar (2019), sea level rise and coastal erosion have drawn increasing attention

51 due to their significant impact on coastal infrastructure, vegetation, and disasters . Additionally, a study funded

52 by NERC, BGS, and ANSTO confirms that sea level rise will dramatically speed up the erosion of rock

53 coastlines by 2100 (ScienceDaily, 2022).

54 The impact of human activities on coastal erosion is a well-documented phenomenon. According to

55 Bouchahma, Yan, and Ouessar (2019), Human activities can exacerbate erosion. The construction of structures

56 such as harbors, docks, and sea walls can disrupt the natural movement of sediment along the coast, resulting

57 in local erosion. Dredging and sand mining also remove sediment from areas, reducing sand supply and

58 worsening erosion. Coastal development driven by climate change—such as the construction of structures and

59 infrastructure in certain areas—can contribute to erosion by altering coastal processes and increasing

60 vulnerability to storms and rising sea levels.

2
61 The United States Geological Survey (USGS) provides an overview of coastal land loss, highlighting that

62 coastal erosion is initiated by the movement of water in the form of high waves and strong currents (USGS,

63 2003). Concrete protection units are often used in coastal protection to provide a high level of protection

64 against wave action and erosion. the use of concrete protection units in coastal areas is vital for mitigating

65 wave action and erosion. These units are commonly employed to safeguard harbor and coastal structures such

66 as breakwaters, sea walls, and bridge foundations. They are specifically designed to absorb energy and endure

67 erosive forces, thereby upholding slope stability and safeguarding critical infrastructure.

68 1.1 Aplication of Armor Concrete Protection Unit

69 Coastal structures are designed to mitigate wave energy, reduce wave height, or redirect wave energy away

70 from vulnerable coastal areas. Examples of coastal structures that can enhance wave protection include

71 breakwaters, seawalls, groynes, revetments, and offshore artificial reefs. These coastal structures are usually

72 constructed using rough and irregular rock blocks, known as rubble mounds, made from natural stone, often

73 consisting of igneous rocks with large stones or various types of manufactured concrete armor (Marine and

74 Coastal Management Victoria, 2023).

75 Here are some potential applications of Armor Units globally:

76 1) Coastal Protection: A primary application of Armor Units is to protect beaches from coastal erosion

77 caused by sea waves. In areas with long coastlines prone to erosion, Armor Units can be utilized to

78 strengthen and shield beaches from abrasion.

79 2) Harbors and Docks: Armor Units can effectively safeguard harbors and docks against strong wave

80 action. By installing Armor Units around these critical structures, it's possible to provide robust protection,

81 keeping vital infrastructure secure from damage caused by waves and seawater.

82 3) Artificial Islands and Coastal Beaches: The construction of artificial islands and the development of

83 coastal beaches, common in many coastal regions, can benefit from Armor Units to maintain stability and

84 protect against erosion and sea waves.

85 4) Flood Control and Water Conservation: Armor Units are advantageous in flood control and water

86 conservation projects. They serve an essential role in directing water flow and providing robust protection

87 for areas vulnerable to flooding.

3
88 5) Reclamation Projects: In regions undertaking reclamation projects to develop new lands by the sea,

89 Armor Units can safeguard these areas from erosion and disturbances due to sea waves. Moreover, in such

90 reclamation projects where new ecosystems and habitats are being established, Armor Units can play a

91 crucial role in ensuring the stability of these new environments.

92 6) Tourism: Coastal tourist destinations can employ Armor Units to preserve the beauty of beaches and

93 tourist infrastructure from damage caused by sea waves. This application is particularly beneficial in

94 preserving the natural charm and attractiveness of tourist spots, which are often a region's economic

95 lifeline

96 7) Marine Infrastructure Projects: Marine infrastructure projects, such as bridges spanning straits or

97 shipping channels, can gain significant advantages from using Armor Units. These units offer protection

98 against damage caused by adverse weather conditions. By absorbing and dissipating the energy of waves

99 and storms, Armor Units enhance the durability and lifespan of these critical structures.

100 8) Disaster Recovery: Following natural disasters like tsunamis, Armor Units are vital in recovery efforts,

101 reinforcing and safeguarding coastlines from additional damage. Their deployment is crucial for quickly

102 rebuilding and stabilizing affected coastal ecosystems and communities, ensuring a more resilient

103 infrastructure against future catastrophes.

104 Given the topography of regions with extensive coastlines, straits, and water bodies, the use of Armor Units

105 can significantly benefit the protection of infrastructure, the environment, and other valuable assets from the

106 adverse impacts of sea waves and coastal erosion..

107 1.2 Pre-existing Concrete Armor

108 Figure 1 and Figure 2 showcase various types of existing concrete armor commonly used for coastal

109 protection. The earliest recognized armor unit is the Tetrapod, initially developed in 1950 by Pierre Danel and

110 Paul Anglès d'Auriac at Laboratoire Dauphinois d'Hydraulique (now known as Artelia) in Grenoble, France.

111 It is a specialized wave-dissipating concrete block, primarily used to counter erosion in coastal infrastructures

112 like breakwaters and seawalls. The design of the Tetrapod, effective in dissipating wave forces and reducing

113 displacement through its interlocking structure, has led to its widespread adoption worldwide. This innovation

114 marked a significant advancement in coastal engineering.

4
115

116 Figure 1: Wave protection units made of concrete. (Smith, 2016, Chapter 3)

117

118 Figure 2: Overview of Breakwater Units (Muttray and Reedijk, 2008)

119

5
120 In addition to Tetrapod, the most common concrete armor blocks used for coastal protection include Dolos,

121 Accropode, Core-Loc, Xbloc, A-Jacks and Crablock, are all types of concrete armor units used for coastal

122 protection. They are designed to dissipate wave energy and resist erosion in coastal and hydraulic engineering

123 applications. Here are some details about each:

124 1) Dolos : The Dolos is a wave-dissipating concrete block used in coastal management. It was invented in

125 1963 and first deployed in 1964 on the breakwater of East London, a South African port. Dolosse are

126 commonly employed for the protection of shorelines and rubble structures, and their design is

127 primarilybased on hydrodynamic stability (Burcharth, H. F., & Liu, Z., 1987).

128 2) Accropode: The Accropode is a single-layer concrete armor unit introduced in 1980. It is designed to

129 provide hydraulic stability through interlocking and structural strength. The blocks are placed in a single

130 layer in a predefined grid, with the orientation of the blocks typically specified. Accropode units are

131 known for their excellent structural strength and are used in coastal protection projects. (Hall, K. R. (1997).

132 3) Core-Loc: The Core-Loc concrete armor unit was developed in 1996 by the US Corps of Engineers (USA)

133 with the initial objective of repairing armor facings made with Dolos units. The ERDC Coastal and

134 Hydraulics Laboratory (CHL) developed and patented CORE-LOC Concrete Armoring in 1996 to provide

135 reliable navigation and shore protection structures in high wave-energy environments. It offers an

136 optimized concrete armor solution for coastal erosion control and wave energy dissipation.

137 4) Xbloc: The Xbloc is a compact, randomly placed, interlocking concrete armor unit. It offers large

138 structural strength and hydraulic stability similar to that of Accropode. Xbloc units are applied in

139 breakwaters and shore protection projects, providing an efficient solution for coastal erosion control. The

140 Xbloc model was designed and developed in 2001 by the Dutch firm Delta Marine Consultants, now

141 called BAM Infraconsult, a subsidiary of the Royal BAM Group (Wikipedia contributors, 2023).

142 5) A-Jacks: The A-Jacks, also known as A-Jacks 3, is a three-dimensional interlocking concrete block

143 system. The A-Jacks concrete armor units were developed by Contech Engineered Solutions. It is designed

144 to resist wave energy and prevent erosion in coastal structures. A-Jacks are commonly used in breakwater

145 and revetment applications, offering a stable and durable solution for coastal protection (Contech., A-

146 Jacks Installation Guide, 2018).

6
147 6) Crablock: The Crablock is a new single-layer concrete protection unit used in the repair of damaged

148 breakwaters. The concrete armor unit Crablock was recently invented in the UAE. It is described as a new

149 and symmetrical single-layer concrete armor unit. It has been developed to provide efficient coastal

150 protection by dissipating wave energy and resisting erosion. The design and placement pattern of Crablock

151 are important factors in its effectiveness as a coastal protection (van der Meer, J. W., Verhagen, H. J., &

152 Reedijk, J. S., 2015).

153 2 PentaPod, A New Concrete Armor for Coastal Protection

154 The PentaPod was developed recently in 2023 by the first author of this paper, D.K. Natakusumah. It was

155 developed at the Ocean Engineering Laboratory and the Water Resources Engineering Laboratory at the

156 Institute of Technology Bandung Second Campus in Jatinangor, Indonesia. PentaPod was first presented at the

157 40th Annual Scientific Meeting of the Indonesian Association of Hydraulic Engineers in Bandar Lampung,

158 Indonesia (D.K. Natakusumah et al., August 2023). It was subsequently published in the Journal of Water

159 Resources Engineering managed by the Indonesian Association of Hydraulic Engineers (D.K. Natakusumah

160 et al., December 2023).

161 2.1 Distinctive Feature of the PentaPod

162 The term "PentaPod," or more precisely “PentaPod Square Pyramidal (PentaPod-SP)," is characterized by

163 distinctive features: it has four horizontal legs and one vertical leg, forming a square-based pentahedral

164 pyramid when these legs are connected with imaginary lines. This form enhances stability and allows for

165 stronger, more regular connections between units, with the option of binding through holes in all four legs.

166 This design is aimed at absorbing wave energy and enhancing structural stability, making it ideal for coastal

167 protection applications that prioritize stability.

168 Prior to the emergence of PentaPod, there were no armor units specifically designed to enhance stability

169 through connection with neighboring units. PentaPod offers a new perspective with the idea that the stability

170 of armor units can be significantly enhanced, not only through the weight of individual units and effective

171 interlocking of the outer surface but also by securely connecting them to one another. The overall stability of

172 coastal structures is determined by the combined stability of these interconnected armor units, ensuring much

173 greater stability compared to conventional installations.

7
174 Emphasizing the use of holes along the leg axes for rope installation, the PentaPod method offers a safer way

175 to connect PentaPod units in three different directions: x, y, and z. PentaPods rely not only on their own weight

176 but also on the combined weight of the interconnected units, connected in both horizontal and vertical

177 directions. Furthermore, this paper will examine how PentaPod Concrete Armor can be considered a new

178 innovation in the context of coastal protection, by identifying significant differences between PentaPod and

179 other existing concrete armors.

180 2.2 Is pentapod a New Invention?

181 Some concrete armor units depicted in Figure 1 and Figure 2 share similar topologies. For instance, Tetrapod

182 and Quadripod are similar, as are Hexaleg and Hexapod, Ajack and Xblock, and StaBar and Dolos. Despite

183 their shared topologies, each type of armor has a unique detailed shape that sets it apart as a distinct form of

184 concrete armor for coastal protection. Hence, the specific detailed shapes are what differentiate concrete armor

185 types with similar topologies.

186 Figure 3 shows various forms of PentaPod (PentaOcta, PentaCone, PentaSquare, and PentaCube) from left to

187 right. Each leg of the PentaPod has a hole with a diameter of at most 10% of the leg cross section size. These

188 holes are used for inserting binding ropes that secure one PentaPod to another in the same coordinate axis.

189 This method of binding ensures that PentaPod units are securely connected in the x, y, and z directions.

190 The reasons for classifying PentaPod as a new invention are as follows. Compared to the concrete armor

191 depicted in Figure 1 and Figure 2, the following observations can be made:

192 1) In Figure 1 and Figure 2, there are various types of existing concrete armor commonly used for coastal

193 protection. The existing concrete armor differs significantly, both in topology and detailed shape, from

194 any of the PentaPod variants shown in Figure 3.

195 2) None of the existing concrete armor units were deliberately designed with holes along the leg axes of the

196 armor to insert binding ropes, ensuring a secure connection of PentaPod units in the x, y, and z axis

197 directions.

198 3) The term 'PentaPod,' or more precisely 'PentaPod Square Pyramidal (PentaPod-SP),' is not related to any

199 concrete armor units seen in Figure 1 and Figure 2. This indicates that this name has not been previously

200 used for concrete armor.

8
201
202 Figure 3: Forms of PentaPod from left to right: PentaOcta, PentaCone, PentaCube, PentaSquare.

203 With PentaPod armor, inter-unit binding is facilitated due to the shape of its legs, which naturally align with

204 the x, y, and z axes. By creating holes through the legs of the PentaPod and threading ropes through these holes

205 in different orientations, a PentaPod arrangement can be formed, creating a grid with binders installed along

206 the horizontal and vertical leg axes (x, y, and z directions). Binding ropes between PentaPod Concrete Armor

207 can be made of nylon ropes, reinforcing steel, or steel fiber slings (sling), preferably made of corrosion-

208 resistant and durable materials. The binding ropes in the holes can be pegged at the ends or partially or entirely

209 grouted.

210 3 Testing Pentapod in the Wave Flume

211 Although the initial intention focuses on using PentaPod in configurations with interconnected units,

212 understanding the stability of PentaPod armor units installed without binding slings is crucial. This testing

213 ensures PentaPod meets the technical requirements for protecting revetments, groins, and other sloping

214 breakwaters made of rock mounds, where PentaPod is typically installed without binding.

215 The research in this area forms part of the thesis work by Graduate Students in Civil Engineering

216 (Hidayatulloh, 2023) and Water Resources Management (Ishakputra, 2023) at the Faculty of Civil and

217 Environmental Engineering, Institut Teknologi Bandung, Indonesia. The forthcoming sections will detail the

218 results of testing PentaPod concrete armor in a Wave Flume. In this study, both types of armor will undergo

219 testing in the Wave Tank available at the Ocean Engineering Laboratory at ITB Jatinangor Campus.

220 The typical configuration of sloping breakwaters can be found in the Shore Protection Manual (1984) and

221 Triatmojo's book "Teknik Pantai" (2006), as illustrated in Figure 4. The Kd coefficient value, indicating the

222 stability of concrete armor units, can only be determined through testing in a wave tank. This test is important

223 as it simulates the conditions of waves and sea currents that can influence the behavior and stability of armor

224 units in actual coastal environments.

9
225

226 Figure 4: Design of sloping breakwater structures.

227 3.1 Experimental Setup

228 This process typically involves using a specific scale model of sloping breakwaters. The laboratory testing

229 process begins by creating a scale model that aligns with the design of the intended real-life breakwater

230 structure. This 1/25 scale model comprises a core made from mound reef rocks and a protective outer layer

231 guarded by PentaPod, set on a uniform slope of 1:1.5. The model stands 0.75 meters tall, designed to prevent

232 water from overflowing its top during tests, as depicted in Figure 5.

233

234 Figure 5: Dimensions of the 1/25 Scale Breakwater Model

235 The experiment occurs in the Wave Flume at the Ocean Engineering Laboratory at Institute of Technology

236 Bandung (ITB ), Jatinangor Campus, Indonesia. Figure 6 depicts the layout of wave sensor placement and

237 breakwater model in the wave flume. In this experiment five wave sensors were installed in the tank to capture

238 the characteristics of waves throughout the experiment. Figure 7 shows. The wave tank, which is 40 meters

239 long, 0.75 meters wide, and 1 meter deep, features a wave generator that can create both regular and irregular

240 waves. For this study, the generator settings create wave heights from 7 cm to 15 cm, with wave periods

241 ranging from 0.8 to 1 second and a wave depth of 0.50 cm

10
242

243 Figure 6: Layout of wave sensor placement and breakwater model in the wave flume

244

245

246

247 Figure 7: Image showing the placement of the breakwater model in the wave flume.

11
248 In each experiment series, a cycle runs until reaching the damage criteria, which is deformation or damage to

249 3 armor units from their original position. In a single cycle, the experiment is conducted by gradually

250 increasing the wave height from 0.5 cm to 1 cm, depending on the hypothesis about the critical wave. As the

251 experiment approaches the critical wave, the increase in wave height is reduced to 0.5 cm. Each wave height

252 is tested for 30 minutes in one experimental cycle. In this study, it is found that non-breaking waves have a

253 period of 1 second, while for breaking waves, the wave period is reduced to 0.8 seconds.

254 3.2 Testing the Kd Value

255 The Kd value measures the ability of coastal protection layers to remain stable under the influence of waves

256 and other sea water forces. In 1950, Robert Y. Hudson developed the Hudson Formula, used in coastal

257 engineering to calculate the weight of coastal protection units, such as rocks, concrete blocks, or other

258 structures, based on the known Kd value. Conversely, the Hudson Formula can also determine the Stability

259 Coefficient (Kd) value based on existing characteristics and conditions. According to Hudson's Formula

260 (1950), the Kd value for a specific armor unit can be expressed as follows:

γr ∙ H 3
261 Kd =
W. (Sr − 1)3 . cot θ

262 Where

𝛾𝑟
263 𝑆𝑟 =
𝛾𝑎

264 Kd = Stability Coefficient

265 W = weight of the protective armor

266 𝛾𝑟 = specific weight of the rock/concrete

267 𝛾𝑎 = specific weight of seawater

268 H = wave height

269 θ = angle of inclination of the breakwater side.

270 3.3 Types of PentaPod Armor Tested

271 In Figure 8, two variants of PentaPod concrete armor, PentaCone and PentaOcta, are visible. In this study,

272 both types of armor will undergo testing in the Wave Tank available at the Ocean Engineering Laboratory at

273 ITB Jatinangor Campus.

12
274
275 (a) PentaCone (b) PentaOcta
276 Figure 8: Shapes of PentaPod types a) PentaCone and b) PentaOcta

277 3.4 Placement of PentaPod Armor Tested

278 Figure 13, illustrates that PentaPod units can be organized in either a random or a structured pattern. Random

279 placement is opted for when the topography or the bathymetry of the area presents complexities. On more

280 uniform surfaces, whether flat or sloped, regular installation of PentaPod is feasible, thanks to the ability of

281 the four lower legs of each unit to create a flat base. The experiment employs two distinct placement methods:,

282 as depicted in Figure 9.a and 9.b (or originally Figure 13,a and 13.b)

283

284 a). Random Configuration b). Tightly Packed Single Layer Unbound

285 Figure 9: The experiment uses this method for both types of placements

286 Future testing for the Sparsely Packed Single Layer Unbound and Sparsely Packed Double Layer Unbound

287 installations of PentaPod, as depicted in Figure Figure 13.c and 13.d, is on the agenda. These tests, intended

288 for academic purposes, aim to ascertain the stability coefficient (Kd) specific to PentaPod installations in these

289 configurations.

13
290 However, the aforementioned installation technique is not suitable for sloped breakwaters. The recommended

291 installation for such breakwaters is depicted in Figure 13.e and 13.f, which include e) Sparsely Packed Single

292 Layer Interconnected and f) Sparsely Packed Double Layer Interconnected configurations. This approach is

293 based on preliminary test findings that indicated the wave flume's force was insufficient to displace

294 interconnected PentaPods. Consequently, further testing of interconnected PentaPods will be carried out on

295 the Check Dam model at the River and Sedimentation Laboratory.

296 4 Results and Discussion

297 The main parameter to know in assessing the stability of a breakwater is the damage to the protective layer

298 units when certain waves occur. Before determining this main parameter, it is necessary to know the values of

299 supporting parameters from the protective layer unit model and the breakwater to be tested. Here are the testing

300 parameter characteristics for the PentaPod model, as listed in Table 1 below:

301 Table 1: Characteristics of the PentaPod Test Model Specimen

Parameter PentaCone PentaOcta
W 117.70 gr 116.49 gr
ϒr 1.89 gr/cm3 1.91 gr/cm3
ϒa 1 gr/cm3 1 gr/cm3
Sr 1.89 1.91
cot (α) 1.50 1.50
302
303 In this experiment, three testing scenarios take place: the first scenario involves uniform/single-layer

304 placement with non-breaking waves; the second scenario involves random single-layer placement with non-

305 breaking waves; and the third scenario involves random single-layer placement with breaking waves. During

306 the wave tests, researchers assess the stability of PentaPod armor by observing the proportion of armor units

307 that shift. When this proportion exceeds 5 percent, the test stops, and the wave height associated with this

308 damage is considered the design wave for calculating the stability coefficient.

309 4.1 Scenario 1: Uniform Single-Layer Placement with Non-Breaking Waves

310 The overall stability of the protected coastal structures in this experiment depends on the individual weight of

311 each armor unit and the interlocking of surfaces between neighboring armor units. PentaPod aims to overcome

312 these limitations, where the overall stability of coastal structures is determined by the combined stability of

313 interconnected armor units, resulting in a very high Kd value for all types of PentaPod armor.

14
314 Testing results with uniform single-layer placement and non-breaking waves show remarkable ability in

315 withstanding wave forces, primarily due to the weight of the armor units themselves and the interlocking

316 between units. The orderly and compact placement of armor units further enhances the overall resilience of

317 the arrangement. The weight adhering between units contributes significantly to their ability to counteract the

318 impact of wave splash.

319 Moreover, the interconnected nature of the units increases stability by distributing the load and preventing

320 displacement. As a result, uniform single-layer placement of armor units offers significant strength against

321 wave splash, effectively protecting coastal structures from potential damage. The test Stability coefficient

322 results for uniform single-layer placement with non-breaking waves are available in the following Table 2:

323 Table 2: Stability coefficient results for uniform single-layer placement with non-breaking waves

PentaCone PentaOcta
Cycle Number
Waves Height (cm) KD Waves Height (cm) KD
1 12.54 30.21 11.11 19.77
2 14.31 44.83 13.53 35.71
3 13.96 41.64 14.1 40.39
4 13.50 37.64 - -
5 14.18 43.64 - -
6 13.03 33.82 - -
Average 13.58 38.58 12.91 31.96
324

325 4.2 Scenario 2: Random Single-Layer Placement with Non-Breaking Waves

326 Experimenting with random placement is essential, given the dynamic nature of sea depth and wave

327 fluctuations in real-world scenarios, where uniformly or orderly installing armor units on breakwaters often

328 poses significant challenges. Testing the random placement of armor units is, therefore, a necessary step in the

329 research process. Evaluating the performance of randomly installed armor units not only provides insights into

330 optimizing the design and placement strategies of coastal protection structures but also helps in understanding

331 their adaptability and robustness. This understanding is key to ensuring the resilience and effectiveness of

332 these structures under varying and often unpredictable field conditions.

333 The test results from the scenario involving random single-layer placement with non-breaking waves are

334 comprehensively detailed in Table 3. The information provided in Table 3 is crucial for assessing the

335 effectiveness of the PentaPod units in a random single-layer arrangement when subjected to non-breaking

336 wave scenarios, contributing valuable insights to the hydraulic performance of the PentaPod.

15
337 Table 3: Stability coefficient results for random single-layer placement with non-breaking waves

PentaCone PentaOcta
Cycle Number
Waves Height (cm) KD Waves Height (cm) KD
1 12.41 29.26 7.00 4.96
2 9.64 13.70 8.73 9.61
3 12.82 32.25 9.21 11.31
4 12.92 33.01 9.67 13.09
5 12.96 33.33 10.35 16.04
Average 12.15 27.45 8.99 10.52
338

339 4.3 Scenario 3: Random Two-Layer Placement with Breaking Waves

340 The type of wave depends on the depth and height of the wave, leading to its classification as either breaking

341 or non-breaking waves. In field conditions, breaking waves are commonly encountered in shallow coastal

342 areas, making the assessment of coastal structures' resistance to the forces generated by breaking waves

343 extremely important. Coastal structures, such as buildings along the shoreline, require rigorous testing to

344 determine their ability to withstand the impact and forces associated with breaking waves. This testing is

345 crucial to ensure the strength and stability of coastal structures when exposed to the challenges posed by

346 breaking waves. The results from this scenario are presented in Table 4 below:

347 Table 4: Stability coefficient results for random single-layer placement with breaking waves

PentaCone PentaOcta
Cycle Number
Waves Height (cm) KD Waves Height (cm) KD
1 11.50 23.28 7.94 7.22
2 9.76 14.23 9.46 12.19
3 11.61 23.95 10.45 16.45
4 10.50 17.69 9.97 14.29
5 9.42 12.80 10.20 15.30
6 9.97 15.17 8.40 8.56
7 9.90 14.85 7.91 7.13
Average 10.56 18.01 9.19 11.59
348

349 4.4 Discussion of Results

350 While PentaPod is typically favored in arrangements where its units are interconnected, the purpose of this

351 testing is to determine the coefficient stability (Kd) of PentaPod armor units when installed conventionally

352 without being interconnected. This ensures that PentaPod meets the technical requirements for use as a

353 protective rouble mount in structures such as sloping breakwaters, revetments, groins, and reef breakwaters.

354 Key findings of this testing include:

16
355 1) Uniform Single-Layer Placement with Non-Breaking Waves: Uniform single-layer placement offers

356 strong resistance to wave impact. Armor units placed in an orderly and compact manner tend to be more

357 resistant to deformation and damage. However, very precise placement is needed, and the strength of the

358 locking between units plays a crucial role in maintaining stability. When units are damaged, the potential

359 for failure increases.

360 2) Random Single-Layer Placement with Non-Breaking Waves: Random single-layer placement shows

361 that some units may experience temporary deformation but eventually return to stability over time. This

362 phenomenon occurs due to the continual pressure and dynamic forces generated by the wave impact.

363 Factors such as frictional strength between deformed units and their neighbors influence their stability.

364 3) Random Two-Layer Placement with Breaking Waves: In this scenario, it is important to assess the

365 resistance of coastal structures to breaking waves. Coastal structures require rigorous testing to determine

366 their ability to withstand the impact and forces associated with breaking waves. Initially, deformation

367 occurs as a result of the interaction between the waves and the loosely interlocked units in a random

368 arrangement. Over time, however, the units have the ability to adjust their positions and form a new stable

369 equilibrium.

370 4) Testing Results for Stability Coefficient (Kd): For PentaCone, the Kd value was found to be 18.01,

371 while for PentaOcta, the Kd value is 11.59. This is due to the circular cross-section of PentaCone, which

372 experiences lower wave resistance compared to the octagonal cross-section of PentaOcta (Hidayatulloh,

373 2023; Ishakputra, 2023).

374 5) Comparison of Kd Values for Tetrapod: Various researchers have obtained different Kd values for

375 Tetrapod, namely Kd=10 to 25 (Kinog et al., 2018), Kd=12.57 (Wardhani, et.al., 2021), and Kd=7.8

376 (Setyandito et al., 2014), with these differences due to varying damage criteria. Compared to PentaCone

377 (Kd=31.51-39.4) and PentaOcta (Kd=13.04-33.30), the Kd values of PentaPod are higher.

378 6) Since the forces generated by waves were insufficient to displace interconnected PentaPod armor units,

379 their testing did not take place in the wave tank. Instead, the evaluation of these interconnected units was

380 conducted using a PentaPod-applied check dam model. This testing was carried out at the River and

381 Sedimentation Laboratory, offering a more relevant and challenging environment to assess the stability

382 and effectiveness of the interconnected PentaPod units under different hydraulic conditions.

17
383 4.5 Testing of Interconnected PentaPod in the River Laboratory

384 From the outset, PentaPod was designed with the concept of interconnected units in mind. The overall stability

385 of coastal structures is determined by the combined stability of these interconnected armor units, which

386 significantly increases stability for all armor types. Since the wave-generated forces were not strong enough

387 to displace interconnected PentaPod armor units, their testing of PentaPod interconnected units applied to a

388 check dam model at the River and Sedimentation Laboratory, ITB Campus in Jatinangor.

389 The results of the physical model tests of the PentaPod check dam are displayed here to demonstrate how the

390 interconnection between PentaPod units can enhance the structural stability of the check dam against strong

391 currents, which cannot be resisted by relying solely on the individual weight of each unit. These presented

392 results are just a supplement to this paper, while the complete testing results will be published in another

393 paper related to the application of PentaPod for riverbank protection.

394 Figure 10 displays the plan and section of the Cibitung check dam, constructed using interconnected

395 PentaPods at a 1/25 scale. Each unit interlocks through ropes made of concrete rods or steel slings, with options

396 for full-length grouting or anchoring only the ends. This interconnected design leverages not just the individual

397 weight of each PentaPod but also the collective strength of all connected units, significantly enhancing

398 stability. The units are anchored securely to both the structure and a concrete base plate, forming a robust

399 foundation on several steel-reinforced concrete bore piles, drilled to standard geological engineering

400 specifications.

401
402 Figure 10: Plan and section of the Cibitung check dam made from interconnected PentaPods.

18
403 Figure 11 illustrates the 3D model of a check dam composed of interconnected PentaSquare units, a variant

404 of the PentaPod. The hydraulic testing of this Cibitung check dam model, which utilized interconnected

405 PentaSquare units, entailed channeling flood discharges calibrated for a 1/25 scale model. During the testing,

406 the model underwent flood discharges simulating return periods of 2, 5, 10, 25, 50, and 100 years, allowing

407 for a comprehensive assessment of the dam's resilience and performance under various hydraulic scenarios.

408
409 Figure 11: 3D model of the check dam made from interconnected PentaPods.

410 Figure 12 illustrates the model's state when subjected to the designated flood discharge of 2 years return

411 period. The During all test scenarios, no armor unit or any combination of armor units was displaced. However,

412 if the bindings were removed, the water would sweep away the armor. The testing results of the concrete units

413 bound in the check dam model are sufficient to estimate the effect of unit binding in both river and coastal

414 applications.

415 The drag force received by PentaPod units in the wave tank is much less than the drag force received by

416 PentaPod units in the check dam model. When tested in the wave flume, no armor units were dislodged from

417 the interconnected PentaPod arrangement. This highlights the effectiveness of the binding system in

418 maintaining structural integrity under wave action. The interconnected design significantly enhances stability,

419 proving the PentaPod's efficiency in withstanding various hydrodynamic conditions without displacement or

420 failure.

19
421
422 Figure 12: Hydraulic model test of the check dam made from interconnected PentaPods.

423 5 Basic Forms for Installing PentaPods

424 PentaPod Concrete Armor can be arranged randomly or in a structured manner. Regular installation is usually

425 done on relatively flat or sloping surfaces, made possible because the four bottom legs of a PentaPod can form

426 a flat surface. Regular installation can be done tightly or loosely. Tight installation provides maximum

427 protection, while loose installation reduces the number of PentaPod armor units, making it more economical.

428 PentaPods arranged in a regular single layer are installed without being interconnected (as shown in Figure

429 13.a, 11.b, 11.c, and 11.d).

430 However, PentaPods can also be arranged regularly in one or two layers (as in Figure 13.e and 11.f), where

431 all armor units are interconnected with ropes passing through the holes in the legs, both horizontally and

432 vertically. When all armor units are interconnected, the overall stability of the coastal structure determined by

433 the combined stability of these interconnected armor units. Testing results of interconnected PentaPods, tested

434 with strong water currents at a speed much greater than that in the wave tank, show that no armor units came

435 loose, due to the very high stability coefficient of the interconnected PentaPod armor.

20
436
437 a). Random Configuration b). Tightly Packed Single Layer Unbound

438
439 c). Sparsely Packed Single Layer Unbound d). Sparsely Packed Double Layer Unbound

440
441 e). Sparsely Packed Single Layer Interconnected f). Sparsely Packed Double Layer Interconnected
442 Figure 13: Various basic forms for installing PentaPods.

443 6 Comparison of TetraPod and PentaPod Installation

444 To demonstrate the armor arrangement and coastal protection results using PentaPod, this section compares

445 PentaPod installation methods with those of the commonly used Tetrapod. Figure 14 displays a side-by-side

446 comparison of TetraPod and PentaPod shapes. Following this, the installation methods of both TetraPod and

447 PentaPod in coastal protection are compared.

448 1) TetraPod (Pierre Danel and Paul Anglès d'Auriac, 1950) has four protruding legs forming a tetrahedral

449 pyramid, with each leg elongated cylindrical in shape and rounded at the ends. Its design allows unit

450 interlocking when placed together, although not always tightly or regularly, and is designed to absorb

451 wave energy, making it ideal for breakwaters and coastal protection.

21
452 2) PentaPod (D.K. Natakusumah, 2023) has five protruding legs forming a pentahedral pyramid, has a

453 design of one vertical leg and four horizontal legs, enhancing stability and allowing stronger, more regular

454 connections between units with the option of binding through holes in all four legs. This design is aimed

455 at absorbing wave energy and enhancing structural stability, making it ideal for coastal protection

456 applications prioritizing stability.

457 TetraPod (P. Danel and Paul A. d'Auriac, 1950) PentaPod (D.K. Natakusumah, 2023)
458 Figure 14: Comparison of TetraPod and PentaPod shapes.

459 6.1 Random Installation

460 This comparison explores how TetraPod and PentaPod closely pack together in a single layer format, as Figure

461 15 illustrates. In Figure 15.a, TetraPods are arranged randomly, a common sight in coastal areas. Meanwhile,

462 Figure 15.b shows PentaPods also arranged randomly, a sight that may become more common in coastal areas

463 in the future. This shift may lead to an increased use of PentaPods in coastal areas, offering a new approach to

464 managing wave action and coastal erosion.

(a) (b)
465 Figure 15: Random Installation of Tetrapod and PentaPod

22
466 6.2 Dense Single Layer Installation

467 This comparison delves into the dense installation of TetraPod and PentaPod arranged in a single layer format,

468 as depicted in Figure 16. In Figure 16.a, TetraPods are placed in a coastal area, forming a dense single layer

469 where each unit is independent. The geometric shape of TetraPods creates a somewhat chaotic appearance,

470 making it challenging to count the units easily. Shifting focus to Figure 16.b, there is a compact arrangement

471 of PentaPods in a single-layer configuration. In this arrangement, each PentaPod stands independently,

472 allowing for easy counting and precise planning of PentaPod unit placement in an area, an advantage not

473 shared by Tetrapod.

(a) (b)
474 Figure 16: Dense Single Layer Installation of Tetrapod and PentaPod

475 6.3 Loose Single Layer Installation

476 In Figure 17, there are two images showing the loose single layer arrangement of TetraPod and PentaPod

477 placed in relatively flat coastal areas. Figure 17.a shows a loosely arranged single layer of TetraPods. This

478 arrangement is somewhat random due to the triangular shape of the lower legs of TetraPod, making it difficult

479 to arrange them regularly, thus complicating the counting and planning of TetraPod unit placement accurately

(a) (b)
480 Figure 17: Loose Single Layer Installation of Tetrapod and PentaPod

23
481 In Figure 17.b, a loosely yet structured single layer arrangement of PentaPods is visible. In this configuration,

482 PentaPods exhibit a regular arrangement thanks to their geometric shape, facilitating easy counting and

483 enabling precise planning of PentaPod unit placement in an area. Each PentaPod unit can be tied to others

484 using plastic or anti-rust metal ropes passed through holes along the PentaPod leg axes or left independent.

485 This image depicts PentaPod units along the outer perimeter tied in either the horizontal x or y direction, with

486 the central units remaining untied. In this arrangement, none of the PentaPods are tied vertically. Furthermore,

487 it demonstrates that the square-shaped spaces created by the convergence of two legs from four neighboring

488 PentaPods can serve as habitats for mangrove plants. This feature illustrates the dual functionality of

489 PentaPods, where they not only provide robust coastal protection (Grey Protection) but also support

490 environmental conservation efforts through mangrove habitat creation (Green Protection). The integration of

491 these two approaches underscores the versatility and ecological sensitivity of the PentaPod design in coastal

492 management.

493 6.4 Compact Double-Layer Installation

494 In Figure 18, there are two images demonstrating the compact double-layer arrangements of TetraPod and

495 PentaPod placed in relatively flat coastal areas. Figure 18.a displays a compact double-layer arrangement of

496 TetraPod. Despite the triangular shapes at the lower legs of the TetraPods, this arrangement is orderly, allowing

497 for easy counting and precise planning of PentaPod unit positioning in a specific area.

498 Figure 18.b shows a compact double-layer arrangement of PentaPods. The PentaPods in this setup exhibit an

499 orderly arrangement due to their geometric shapes, facilitating easy unit counting and accurate placement of

500 PentaPod units in the designated area. Each PentaPod in this arrangement remains unconnected from the

501 others.

(a) (b)
502 Figure 18: Compact double-layer installation of Tetrapod and Pentapod

24
503 6.5 Compact Multi-Layer Installation

504 Figure 19 presents two images showing the compact, multi-layer arrangement of TetraPod and PentaPod in

505 relatively flat, shallow coastal areas. Figure 19.a illustrates a compact, multi-layer arrangement of TetraPods.

506 In this configuration, the number of TetraPods per layer decreases as the height increases, and as the water

507 depth increases, the width of the bottom layer widens.

508 In Figure 19.b, on the other hand, the PentaPods maintain consistent upper and lower dimensions while

509 securely interlocking. The vertical locking can be securely tied to the base grid. When stacked in several layers,

510 the bottom segments of the PentaPods join to create a flat surface. This surface allows for the placement of

511 plates, positioning the layers of PentaPods between the bottom grid and top plates, serving as support points.

512 By adding flat concrete plates on the top surface, these concrete layers can also act as practical working spaces.

513 Additionally, heavy equipment like backhoes and trucks transporting PentaPod units can use these concrete

514 paths, facilitating operations in shallow coastal areas.

(a) (b)
515 Figure 19: Installation of more than two layers of Tetrapod and Pentapod

516 7 Conclusions

517 Here are the conclusions drawn based on a comprehensive series of experiments and in-depth evaluations

518 conducted as part of this extensive experiment. These findings provide valuable insights into the effectiveness

519 and adaptability of the PentaPod system in various coastal protection scenarios. They highlight the innovative

520 aspects of PentaPod usage in enhancing coastal armor stability and offer guidance for future applications and

521 1) PentaPod was developed to address limitations of commonly used concrete armor in coastal structures,

522 which could only be arranged randomly or orderly without binding. Therefore, the overall stability of

523 protected coastal structures largely depends on the individual stability of each armor unit.

25
524 2) PentaPod concrete armor can be arranged both randomly and orderly and can be installed without binding.

525 However, PentaPods can also be organized in one or more layers, where all armor units are horizontally

526 and vertically interconnected, enhancing the overall stability of coastal structures.

527 3) Inter-unit connections among PentaPods can reduce the size of individual PentaPods as the stability of the

528 PentaPod arrangement is not based on the individual weight of PentaPods but on the combined weight of

529 several interconnected PentaPod units and the stronger connections facilitated by ropes connecting the

530 PentaPod units.

531 4) Simple and Precise Placement: PentaPod allows for more direct and measurable placement, simplifying

532 armor count and providing transparent construction cost estimation.

533 5) Enhanced Stability through Inter-Unit Connection: The presence of inter-unit connections significantly

534 increases the stability of the PentaPod arrangement, providing much higher stability than TetraPod. This

535 stability results from the combined weight of interconnected PentaPod units and the binding facilitated by

536 ropes among them.

537 6) Potential Size Reduction: Inter-unit connections in the PentaPod arrangement can lead to a reduction in

538 the size of individual PentaPods. Stability stems not only from individual weight and surface friction but

539 also from combined weight and binding created by ropes connecting PentaPods.

540 7) Integrated Grey and Green Protection: PentaPod arrangements allow the implementation of Grey

541 Protection (using concrete armor) and Green Protection (mangrove area conservation) simultaneously,

542 demonstrating diversity and an integrated approach in coastal protection.

543 8) Wave flume testing involved determining the Stability Index (Kd) for two PentaPod Concrete Armor

544 variants, namely PentaCone and PentaOcta. The experiment shows that the stability coefficient for both

545 PentaPod Concrete Armor variants is quite high.

546 9) PentaCone showed a higher stability coefficient than PentaOcta in all scenarios, with a Kd value of 18.01

547 for PentaCone and 11.59 for PentaOcta. This increased stability can be attributed to the circular cross-

548 section of PentaCone, which experiences lower wave resistance compared to the octagonal cross-section

549 of PentaOcta.

26
550 10) Different Kd values for concrete armor (e.g., Tetrapod) obtained by various researchers are due to

551 differences in damage criteria. As a comparison, different Kd values for TetraPod obtained by various

552 researchers include Kd=10 to 25 (Kinog et al., 2018), Kd=12.57 (Wardhani, et.al., 2021), and Kd=7.8

553 (Setyandito et al., 2014), with these differences being due to different damage criteria. Compared to

554 PentaCone (Kd=31.51-39.4) and PentaOcta (Kd=13.04-33.30), the Kd values of PentaPods are higher

555 than TetraPods. Standardization is needed for breakwater sections affecting the percentage of damage.

556 11) To avoid confusion in comparing Kd values for specific concrete armor (e.g., Tetrapod), PentaPod testing

557 should be conducted simultaneously with comparative armor like Tetrapod. Thus, Kd values for tested

558 armor and comparative armor are obtained based on the same damage criteria and calculation formulas.

559 12) The novelty of PentaPod lies in the fact that concrete armor can be installed both randomly and in an

560 orderly manner. An orderly installation without binding reduces the number of armor units and costs,

561 while orderly installation with binding increases stability and allows for a reduction in armor size, thus

562 lowering costs. Binding ropes facilitate the installation of armor on surfaces and in water.

563 8 Recommendations

564 In the future further research could greatly enhance our knowledge, about the characteristics and uses of

565 PentaPods. The focus of this research would be in the following areas;

566 1) Experimenting the long term durability and structural integrity of PentaPods under conditions, including

567 extreme weather events and prolonged exposure to seawater.

568 2) Investigating the impacts of PentaPod installations on marine ecosystems and coastal biodiversity. This

569 research would assess their ability to support life and contribute to habitat restoration.

570 3) Exploring materials or coatings for PentaPods that could improve their durability, eco friendliness or

571 effectiveness in dissipating wave energy.

572 4) Conducting studies to optimize the design parameters such as shape, size and interlocking mechanisms of

573 PentaPods for applications like stabilizing riverbanks protecting harbors and reinforcing shorelines.

574 5) Performing evaluations that compare the costs and benefits of installing PentaPods with traditional coastal

575 protection methods. This evaluation would consider factors such as installation costs, maintenance

576 requirements and environmental benefits.

27
577 6) Investigating the integration of PentaPods with energy systems like wave energy converters to harness

578 additional benefits from these coastal protection structures.

579 7) Researching the scalability of PentaPod installations for large scale projects as exploring opportunities,

580 for customization to adapt them to specific local conditions and requirements.

581 8) Hydrodynamic Performance Testing; Conducting tests, in controlled settings to gain an understanding of

582 how PentaPods perform in different hydrodynamic conditions with a specific focus on minimizing the

583 impact of waves and currents on shorelines.

584 Dedicating research efforts to these areas can broaden knowledge and practical applications of PentaPods,

585 fostering the development of efficient solutions for safeguarding coastal environments. This approach

586 encourages innovative practices in coastal defense, directly impacting the resilience of shorelines against

587 erosion and environmental degradation.

588 9 Highlights

589 Before closing this paper, it's essential to highlight some key features of PentaPod. Understanding these

590 highlights can provide deeper insights into the potential impact and applications of PentaPod in coastal

591 engineering.

592 1) Design and Arrangement: PentaPod features four horizontal legs and one vertical leg, forming a square-

593 based pentahedral pyramid. This design can be arranged in either a random or regular manner, with holes

594 along the center of the legs for the insertion of binding ropes.

595 2) Interconnection and Stability: PentaPod was specifically developed to enhance stability through

596 interlocking with neighboring units. When installed in a regular layer, PentaPods can either be

597 interconnected using ropes or installed without interconnections, depending on the application

598 requirements.

599 3) Simplified Planning and Placement: The geometric design of PentaPods simplifies the counting of units

600 and enables precise planning for their placement in specific areas. Additionally, the use of binding ropes

601 streamlines the installation process on diverse surfaces and aquatic environments, adding to the

602 practicality of the PentaPod system in coastal protection.

28
603 4) Installation Flexibility: For random installations, interconnections between units are not necessary,

604 eliminating the need for holes. This flexibility allows for cost-effective and adaptable installation in

605 various coastal protection projects.

606 5) Cost Efficiency and Practicality: Regular installation of PentaPods without binding reduces armor unit

607 requirements, leading to cost savings. Conversely, regular installation with binding not only enhances

608 stability but also allows for a reduction in armor unit size, further cutting down costs.

609 10 Acknowledgments:

610 The authors extend their gratitude to the Ocean Engineering Laboratory staff, particularly Muhammad Asad,

611 for assisting Graduate Students in Civil Engineering and Water Resources Management with their master's

612 thesis research. Special thanks are also directed to the Water Resources Engineering Laboratory staff - Soka

613 Wiangga, Anwar Abdurahman, Darmanto Ady Saputra, and technicians Jajang and Ade Sarigan. Their

614 invaluable assistance in constructing the 1/25 scale breakwater model, and in developing the PentaCone and

615 PentaOcta models of the same scale, was instrumental to this work’s success. Finally, we would like to extend

616 our thanks to Jovian Javas for numerous small corrections and for uploading this paper to Results in

617 Engineering Journal website.

618 11 References

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