PERFORMANCE OF VERTICAL COMPOSITE BREAKWATER MODEL OF BOX-BEAMS, ROCK AND PILES

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 13, December 2018, pp , Article ID: IJCIET_09_13_135 Available online at aeme.com/ijciet/issues.asp?jtype=ijciet&vtype= =9&IType=13 ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed PERFORMANCE OF VERTICAL COMPOSITE BREAKWATER MODEL OF BOX-BEAMS, ROCK AND PILES Frans Rabung Doctoral Student of Civil Engineering Department, Hasanuddin University, Indonesia Muhammad SalehPallu Professor, Civil Engineering Department, Hasanuddin University, Indonesia Muhammad Arsyad Thaha Associate Professor, Civil Engineering Department, Hasanuddin University, Indonesia Achmad Bakri Muhiddin Senior Lecturer, Civil Engineering Department, Hasanuddin University, Indonesia ABSTRACT To overcome the problem lack of protection for ports and coasts in marginal locations of Indonesia, a new type breakwater was proposed. It was specially designed for internal waters of Indonesia. Physical modelling tests proved that the designed models effectively absorbed incoming wave energy, therefore reduced wave transmission and reflection. The models stood as vertical breakwaterr but performed like conventional rubble-mound breakwater. The main novelty of the new design is use of box-beams as fill rock support and wave water focuser. Besides superiority in wave energy absorption, this breakwater would also be efficient in use of material and easy to build because the size of rock can be adjusted in accordance to available heavy equipment on site. In turn the cost would be much reduced which is the main problem for marginal areas in Indonesia archipelagoes. Key words: Breakwater, Waves, Rubble-mound, Wave transmission, Wave probes. Cite this Article: Frans Rabung, Muhammad SalehPallu, Muhammad Arsyad Thaha and Achmad Bakri Muhiddin, Performance of Vertical Composite Breakwater Model of Box-Beams, Rock and Piles, International Journal of Civil Engineering and Technology (IJCIET) 9(13), 2018, pp et/issues.asp?jtype=ijciet&vtype=9&itype e= editor@iaeme.com

2 Frans Rabung, Muhammad SalehPallu, Muhammad Arsyad Thaha and Achmad Bakri Muhiddin 1. INTRODUCTION Archipelagoes of Indonesia have 95,181 km in length of coast line and more than 17,500 islands. There is an extensive damage to the coasts because there is no maintenance (protection) for most of them. For the islands, less than ten are big (main islands) and only few of them have ports protected by breakwaters. Most of the islands are small islands which are unmanned; the rest are intermediate islands which are manned with poor port facilities, no breakwater protection. The reason for the lack of coastal and port protection is high cost due to limitation of material and heavy equipment for construction. This is the main grounds for this research. It is required a new type of breakwater which is cheap, easy to construct, hydrodynamically efficient and if possible multifunction as quay wall. For that purpose, this study was conducted. But first, because of wind-wave conditions are very different, the coasts/waters must be distinguished between external and internal. Most of ports are located in the internal waters, therefore this study focused on these areas. Makassar coast, in South Sulawesi province, was chosen as the representative for prototype conditions as it faces the longest fetch length and fastest wind speed nearly along a year. Twenty years wind data recorded hourly were used for wave predictions. Results of the wave predictions were twopairs of significant wave heights Hs and periods Ts, i.e. Hs = 3.6 m with Ts = 10 s and Hs = 1.38 m with Ts = 3.8 s. The former came from daily average wind speed, while the latter came form daily highest wind speed processed by fastest mile wind speed method (Rabung et al, 2018)[1]. Thus, these circumstances shall be understood as the scope of these study. Rubble-mound breakwaters, from conventional one until berm type and natural slope (Rabung and Hinwood, 1993) [2], are well-known for their effectiveness in transforming incoming wave energy into wave transmission, reflection, and energy absorption, but requirements for huge amount of materials and heavy equipment to handle armor stones and transportation make them nearly impossible to build in these remote areas. Vertical breakwaters such as vertical wall, wave screen etc. are efficient in use of material but unavailability of suitable equipment and difficulties in construction cause them not a popular choice. Development in use of rock as filler for vertical breakwater, such as in Rageh (2009) [3], Liu and Li (2012) [4], Liu and Faracci (2014) [5] among others, paved the path way to this study. Physical model experiments were conducted to test a new type of breakwater proposed to solve the problems,i.e. vertical composite breakwater of box-beams, rock and piles. The main objective in this paper is to know its effectiveness in absorbing incoming wave energy in the forms of wave transmission and reflection. 2. MATERIALS AND METHODS 2.1. Equipment The experiments were conducted in the Hydraulic and Coastal Engineering Laboratory, Department of Civil Engineering, Hasanuddin University. The main equipment is Armfield S6MKII-15M type wave flume and Armfield H40 type wave probes, a set of three with wave monitors (Figure 1).Eagle Technology data acquisition board was used to convert analog data to digital to be saved in a computer. Wave View software was used to control data saving in. csv extension which is MS Excel compatible file. A highspeed camera was also provided on a static tripod to make videos as well as still photographs. The flume has 15 m long, 300 mm wide and 450 mm deep. It is facilitated with a flap type wave paddle moved by a variable speed motor. An additional wave absorber made of artificial fiber was installed at the other end of flume to make sure that no water reflection in sufficient time could reach the model which was positioned at 12 m from wave paddle editor@iaeme.com

3 Performance of Vertical Composite Breakwater Model of Box-Beams, Rock and Piles 2.2. Model Materials Rocks Two group sizes of basalt rockwere used to know effects of porosities. The materials, taken from concrete quarry, had good shape (about cubic) and carefully selected by sieving. The first group (rock I) passed through square sieve having 20 mm wide of hole side and detained on 10 mm one; thus, the average size of rock I is 15 mm (D n50 ). Rock II passed through sieve 30 mm and detained on 20 mm holes, so D n50 = 25 mm. The purpose of strictly procedure in selecting rock materials was aimed to simulate the expected procedure of selection of rock materials on the prototype. As results very homogeneous gradation materials were got with high porosities n 1 = 0.57 and n 2 = Sizes of the rocks were chosen so that mass in the prototype will be about 250 kg and 1000 kg respectively; these sizes still can be handled by small mobile crane. Figure1 Armfield S6MKII wave flume and other sets of equipment Box-Beams This material is the innovation of this study. In prototype they would be made by concrete, but in the model they were made by hollow steel bars, cut every 40 mm (w) and then stick together side by side to make beams so that the hollows were facing the incoming waves. In prototype there would be hooks on bottom side and hook-holes on top side so that lower boxbeams would hold upper box-beams on their position strongly to make walls on front and back sides of a breakwater (Figure 2). Figure 2 Details of the box-beams and breakwater There are two main functions of the box-beams, the first is to hold the fill rocks on their places, and the second is to direct wave water into and out of fill rocks. On Figure 2 it is editor@iaeme.com

4 Frans Rabung, Muhammad SalehPallu, Muhammad Arsyad Thaha and Achmad Bakri Muhiddin shown that number of box-beam holes are three only, in practice the number can be added as long as available small crane still can handle them; the number determines the length of boxbeams. The important thing to remember is positions of hook and hook-holes, they always have to match each other leaving an empty space between consecutive beams. Width w of box-beams was made just the same for model I and model II, i.e. 40 mm, because effects of width variation of fill rock B were more important to watch. Dimensions of box-beam holes depend on the size of fill rock. In the models, dimensions of square holes were 15 mm for model I and 25 mm for model II, just follow the sizes of rock. During experiments it was found that no single rock could pass the box-beam holes. The dimensions of box-beam holes were not included in dimensional analysis because preliminary experiments showed no effects on waves (Figure 3). Figure 3 No effects of box-beams on water wave hydrodynamics Piles and tie beams Piles and tie beams are to support the box-beams from all kinds of forces acting on them. Dimensions of piles and tie beams depend on analyses requirements. Distance between piles, as same as tie beams, depends also on analyses requirements but maximum one third of the length of box-beams so that every box-beam will be supported by at least two piles. Frames of model I and model II are shown in Figure 4.Space of width B between box-beam walls was for fill rock, it varied from 100 mm, 200 mm to 300 mm to study the effect of width of rock. Figure 4 Frames of model I and model II editor@iaeme.com

5 Performance of Vertical Composite Breakwater Model of Box-Beams, Rock and Piles 2.3. Theoretical Bases Waves parameters involved The two pairs of design waves given above were checked for theoretical wave categories following USACE (2008, Fig. II-1-20) [6]. It was found that the first pair was located on the boundary area between Stoke s 2 nd Order and 3 rd Order, while the second pair was in the Linear Wave area. For the Linear or Airy Wave and Stoke s 2 nd Order Theory, equations that consisting required parameters are (USACE, 1984, pp 2-34 to 2-35) [7]: = tanh ( ) (1) = tanh ( ) (2) Meanwhile, for Stoke s 3 rd Order the equations are: = tanh = tanh 1+! 1+! " #$% (&/ (%)*! " +, (3) " #$% (&/ (%)*! " +, (4) From the equationsa bove we find wave parameters: wave height H, celerity C, length L, period T and water depth h involved. Parameter C can be substituted by T and T by L, thus the parameters left are H, L, and h. These parameters became variables in the experiments. T and L are interchangeable, T was used as input for wave paddle mechanism, whereas L was measured along wave flume for analyses Dimensional Analysis, Froude Similitude, Reynold Number As the main objective of the study is to find out hydrodynamic effectiveness of the new system in the forms of wave transmission and reflection, we have first to define the coefficient of transmission C t and coefficient of reflection C r as follows: - =. / and 0 = 1 / (5) where H i is incoming wave (design wave) height, H t is transmission wave height and H r is reflection wave height. Relation of H i and H r is given in the following equation: 2 ) = 345 3/6 and 2 0 = /6 where Hmax and Hmin are maxima at anti node and node points, L/2 and L/4, in front of the models as result of combination of H i and H r (Figure 5 from Kamphuis, 2011, Fig and 2.14) [8]. These points became locations of wave probe no. 1 and no. 2 respectively. Wave probe no. 3 for measuring wave transmission H t was positioned at one meter behind the models. (6) editor@iaeme.com

6 Frans Rabung, Muhammad SalehPallu, Muhammad Arsyad Thaha and Achmad Bakri Muhiddin Figure 5 Locations of H max and H min for wave measurements and analyses To find the relation between H i, H t and H r we have to analyze it in the form of C t, C r and energy loss coefficient C L =E L /E i from conservation of wave energy: 8 ) = substituted into =1-0 (7) Now, all involved parameters required to perform dimensional analysis have been known. From wave action there are L, h and H in the forms of H i, H t,h r or C t, C r and C L, whereas from structural reaction there are B, w, and n. Using Buckingham s theorem, the parameters are processed with multiplication factor k = 2π/L, we find: 0, -, =;(<2 ),<=,<h,=?,a) (8) Mass density of rock and mass density of water ratio ρ b /ρ w, gravity acceleration in prototype and in model ratio g p /g m = 1 are not included in the process as they become nondimensional constants. As already mentioned above, dimensions of box-beam holes are not included in the dimensional analysis because from many videos made during preliminary experiments, both models did not show any effects of holes existence. Model scale was determined based on Froude s dynamic similitude rule, i.e. the same Froude Number in the model and prototype. Following guides from Hughes (1995, p.130) [9] for 2-d Wave Transformation 1:10 to 1:50 and Breakwater Stability 1:30 to 1:50 as well as learning from wave flume facilities, it was decided to use Geometric Scale λ = 30, Time Scale = λ = 5.48 and Force Scale = λ 3 = 27,000. Another condition important to hold in doing coastal physical model is Reynold Number. To be constantly in gravity hydrodynamic conditions, especially for flow between rock grains, Reynold Number must be higher than 10 4 (van der Meer, 1988, p.41) [10].This can be achieved if rock gradation has D 90 > 4 6 mm (Hijum and Pilarczyk, 1982) [11] and porosity is high (van Gent, 1995) [12]. All these criteria are satisfied in these models Experimental setup The two pairs of extreme waves were used as boundaries of experiments, the first had H = ± 120 mm and T = ± 1.8 s in the model, the other had H = ± 46 mm and T = ± 0.69 s. All experimental runs laid in between these two extrema. For main experiments, which were to determine wave transmission and reflection, there were two models (n 1 and n 2 ), three rock mound widths (B = 100, 200, 300 mm), three water depths (h = 200, 250, 300 mm) and five periods/strokes; thus, there were 90 runs. Other runs were preliminary runs for wave flume calibration, some for studying effects of model frames without fill rock, some to study runup and toe erosion, and some to know duration of run before causing wave re-reflection from wave paddle; total runs in this laboratory work were about 200. Models height was 400 mm, so all water depths were below top of the models (no overtopping waves). Models were located 12 m in front of wave paddle. At this location, it s editor@iaeme.com

7 Performance of Vertical Composite Breakwater Model of Box-Beams, Rock and Piles required 28 to 35 s of various runs for wave reflection to reach the wave paddle and caused unwanted re-reflection waves. Therefore, each main experiment ran for only 30 s; the first 10 s was used to correct the first and second wave probe locations (although the locations were actually already predicted from wave flume calibration), the second 10 s was the main data to analyze and the last10 s was kept for backup. The frequency of data acquisition was 1000 Hz. 3. RESULTS AND DISCUSSION 3.1. Wave Transmission Not all results can be presented in this paper because limitation of space, but it is tried to present graphs that can convey as many parameters as possible. Figure 6 shows relation between transmission coefficient C t, water depth kh, ratio of rock mound width B to boxbeam width w, and porosities n. It should be remembered that C t is H t /H i, kh is 2πh/L, n = 0.57 is porosity for rock of model I and n = 0.55 is porosity for rock of model II. So, all parameters are presented in these graphs. The graphs show that the deeper the water the more effective C t. It is also shown that wider rock mound B will give more effective C t ; effectiveness can reach C t = Figure 6 Relation between C t, kh, B/w and n Wave Reflection Figure 7 shows relation between reflection coefficient C r, water depth kh, ratio of rock mound width B to box-beam width w, and porosities n. Similar to transmission graphs, the deeper the editor@iaeme.com

8 Frans Rabung, Muhammad SalehPallu, Muhammad Arsyad Thaha and Achmad Bakri Muhiddin water the more effective C r ; this is a character of rubble-mound breakwater, different from perforated vertical wall where the more effective wave transmission the more ineffective wave reflection. From graphs we also can see similar character to the previous ones, i.e. higher porosity gives slightly better C r, but wider B is less effective than narrower one Energy Loss Figure 8 shows characters of coefficient of energy loss. In contrast to C t and C r, the energy loss coefficient becomes higher as water deeper. This is another characteristic of rubblemound breakwater, which means by more body of breakwater is under water more incoming wave energy is absorbed. Figure 7Relation between C r, kh, B/w and n 3.2. Comparisons Figure 9 shows C t, C r and C L with combined B/w in one plate. It shows while C t and C r go down, C L go up, it means this type of breakwater is effective in absorbing wave energy. This characteristic is typical to conventional ruble-mound breakwater, not for full protection neither for partial protection vertical breakwater where usually C r increase as C t decrease meanwhile C L is flat or go to zero absorption. Figure 10 shows C t, C r and C L graphs from a pile-rock break water prototype simulation [4], a very close breakwater type to these models. The graphs show that while C t goes down sharply, C r goes up slowly and C L slightly goes down; this implies that the pile-rock editor@iaeme.com

9 Performance of Vertical Composite Breakwater Model of Box-Beams, Rock and Piles breakwater is not as effective as box-beams models, but it should be reminded that Figure 10 graphs are resulted from numerical model works, not confirmed by physical models yet. 4. CONCLUSION This study has developed a new type vertical breakwater model whose hydrodynamic characteristics are close to conventional rubble-mound breakwaters. It has been proved that this new type is effective in absorbing wave energy and reduce wave transmission as well as reflection height. The study also implies that use of rock material is less both in volume and size which will affect cost and easiness to build. It is expected that this type of breakwater is appropriate for marginal ports and islands in internal waters of Indonesia. Figure 8Relation between C L, kh, B/w and n editor@iaeme.com

10 Frans Rabung, Muhammad SalehPallu, Muhammad Arsyad Thaha and Achmad Bakri Muhiddin Figure 9 Relation of C t, C r, C L with B/w combined REFERENCES Figure 10 C t, C r and C L from nearly similar pile-rock breakwater [4] [1] Rabung, F., Pallu, M. S., Thaha, M. A., Muhiddin, A. B. Wave Predictions and Deformations Along Makassar Coast. Proceedings HATHI 5 th International Seminar on Water Resilience in a Changing World, Bali, 2016, pp [2] Rabung, F. and Hinwood, J. B.Scale Model Tests on a Rubble-Mound Breakwater Trunk. 11th Australasian Conference on Coastal and Ocean Engineering. Townsville: Institution of Engineers Australia, 1993, pp [3] Rageh, O.S. Hydrodynamic Efficiency of Vertical Thick Porous Breakwaters.13th International Water Technology Conf. Hurghada, Egypt.: IWTC 13, 2009, pp editor@iaeme.com

11 Performance of Vertical Composite Breakwater Model of Box-Beams, Rock and Piles [4] Liu, Y. and Li, H. Analysis of Wave Performance through Pile-Rock Breakwaters. Journal of Engineering for the Maritime Environment, Vol. 228(3), 2014, pp [5] Liu, Y. and Faraci, C. Analysis of Orthogonal Wave Reflection by a Caisson with Open Front Chamber Filled with Sloping Rubble Mound. Coastal Engineering 91, 2014,pp [6] USACE. Coastal Engineering Manual, 2008, Figure II [7] USACE. Shore Protection Manual, 1984, pp [8] Kamphuis, J.W. Introduction to Coastal Engineering and Management, 2nd ed. World Scientific Publishing Co. Pte. Ltd.: Singapore, 2011, Fig and 2.14 [9] Hughes, S.A. Physical Models and Laboratory Techniques in Coastal Engineering. World Scientific Publishing Co. Pte. Ltd.: Singapore, 1995, p. 130 [10] Van der Meer, J. W. Rock Slopes and Gravel Beaches under Wave Attack. Delft: Delft Hydraulics, 1988, p. 41 [11] Hijum, E. V. andpilarczyk, K. W. Equilibrium Profile and Longshore Transport of Coarse Material Under Regular and Irregular Wave Attack. Delft, the Netherland: Delft Hydraulics. 1982, p.105 [12] Van Gentt, M.R. Porous Flow Through Rubble-mound Material. Journal of Waterway, Port, Coastal and Ocean Engineering, Vol.121, 1995,pp editor@iaeme.com