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Sri Lanka
Experimental Study on Underwater Sediment Accumulation During Bow Spraying of Trailing Suction Hopper Dredger
Liu, Gongxun (CCCC National Engineer Research Center of Dredging Technology and Equipment) | Xie, Kang (CCCC National Engineer Research Center of Dredging Technology and Equipment) | Liang, Xin (CCCC National Engineer Research Center of Dredging Technology and Equipment) | Yin, Jifu (CCCC National Engineer Research Center of Dredging Technology and Equipment) | Lu, Chuanteng (Nanjing Hydraulic Research Institute) | Jin, Peng (CCCC National Engineer Research Center of Dredging Technology and Equipment) | Wu, Yawei (College of Civil Engineering, Tongji University) | Xie, Liquan (College of Civil Engineering, Tongji University)
ABSTRACT Based on the Colombo Port City project in Sri Lanka, the effects of water depth, spray angle and sediment volume on underwater sediment accumulation were systematically studied through the indoor bow spray physical model test, and the physical model test results were compared with the field measured results. The physical model test results show that the sediment accumulation range is relatively concentrated, which is in an irregular conical shape. The slope and the maximum height increase with the increase of sediment volume. Under most working conditions, the slope of accumulation formed by 45 ยฐ spray angle is greater than that formed by 30 ยฐ spray angle. The maximum height of sediment accumulation increases with the increase of spray angle, but the variation amplitude is relatively small. The slope of sediment accumulation gradually slows down with the increase of water depth, and the maximum height of sediment accumulation also shows a downward trend. The measured results of the field bow spray verified the accuracy of the model test results. This study has important guiding significance for the determination of construction parameters and improvement of construction technology of trailing suction dredger bow spray. INTRODUCTION At present, with the gradual improvement of environmental protection and engineering design requirements, higher requirements are put forward for the fine construction technology such as underwater flatness or hydraulic fill of dredging ship sediment treatment (Gao & Meng, 2006; Li & Wang, 2009; Cheng, 2012). During the construction of dredging vessels, it is necessary to master the underwater diffusion distribution and accumulation of sediment in the unloading operation, so as to facilitate the timely adjustment of the construction plan, reduce the secondary handling, slope management and other workload generated in the later stage, and thus reduce the project cost. At present, there are relatively few studies on the bow spray of trailing suction dredgers at home and abroad. Among them, the numerical simulation and analysis on bow spray trajectory curve and flow field characteristics of trailing suction hopper dredger (TSHD) were carried out based on the control of bow spray distance and loss (Yin et al, 2016). The influence of air resistance coefficient, sediment density and spray angle on mud motion trajectory was analyzed and studied, which is helpful for a TSHD to have an optimum standing point and control points in the rainbowing construction (Wang et al. 2017). Compared with the theoretical analysis formula, the particle method numerical simulation (Lucy, 1977; Gingold & Monaghan, 1977; Monaghan, 1994) can better describe the dynamic process of spray and the force on the pipe(Yu et al, 2018). Based on the jet-flow theory, a new method (which is called jet-momentum model) for calculating trajectory and extension of liquid jet in air was established by inducing the entrainment assumption and momentum analysis method and the model with the measured data of the trailing suction dredger bow spray and the dredging pipeline was verified and analyzed (Wang et al, 2018).
- Research Report > New Finding (0.85)
- Research Report > Experimental Study (0.85)
- Transportation > Marine (0.72)
- Transportation > Infrastructure & Services (0.72)
Abstract In situ nondestructive pull out tests have been done in the Power House and Transformer caverns of the Uma Oya Multipurpose Development project which lies in the south-eastern part of the central highland region of Sri Lanka. Performed based on ISRM and ASTM, the nondestructive pull out tests purpose is to control quality of installed Double Corrosion Protected (DCP) fully grouted rock bolts and approve the considered working load capacity of DCP rock bolts. Load-displacement graph of the loaded end of DCP rock bolts have been recorded to check boltgrout and grout-rock contacts shear strength as well as corrugated sheath contact surface bonding. The test results indicate that load bearing capacity of the bonded length meets the design criteria. The obtained displacements of tests were also compared with analytical method displacement predictions which are generally much less than the test results. This indicates that some debonding should have been happenned during pull out tests. 1 Introduction It is usual to do pull out tests in underground excavations such as power house caverns to control the quality of installed rock bolts. This is mainly done according to the ISRM suggested method and ASTM standard (Brown 1981; ASTM, n.d.) as well as other references (Farmer 1975; G. S. Littlejohn and Bruce 1975; S. Littlejohn 1993; Zou 2004; Aydan 2018), based on which the load-displacement graph of the rock bolt loaded head is obtained. Pressure grouting (about 2 bar pressure) was done for installation of rock bolts. The increase in pullout resistance from pressure grouting was likely caused by a combination of several factors, including higher rock-grout contact stresses, and grout injected under pressure into the fractures/ fissures preexisting in the rock mass (Park, Qiu, and Kim 2014). Most of the references adress the pull out test results done in laboratory (Blanco Martรญn et al. 2013). Althouth the results of the in situ pull out test are usually less accurate in comparison with the laboratoy pull out tests (due to the field difficaulties in measurments), it was tried to get results as accurate as possible. In this regards, all the test equipments and their calibrations were controlled. The tests were done in roofs (after finishing the excavation and rock support of the roof and befor constinuing the excavation) and walls (after finishing the bench excavation and befor loosing the access) of the power house and transformer caverns (PHC and TC).
- Geology > Rock Type (0.31)
- Geology > Geological Subdiscipline > Geomechanics (0.31)
ABSTRACT To hindcast the wave climate at a particular study area in North-western Coast of Sri Lanka, Wave Transformation Matrix and MIKE 21 Spectral Waves (SW) models were used. Directional wave data recorded at 15m ~ 16m depths in Colombo Port during 1998 โ 2015 periods was transformed to the study area by using numerical simulation techniques. Thus, representative nearshore wave climate was established at 20 m water depth in the study area (i.e. Wennappuwa in North-western coast). Transformed wave data was analyzed in both annual and seasonal basis. From our analysis, highest percentage of annual waves at 20 m depth in study area has been identified between 250N โ 260N directional range. Seasonal wise, southwest monsoon season was recognized as dominant season. Finally, design wave heights for breakwater structures of a proposed harbour were predicted by extreme wave analysis. INTRODUCTION The coastal wave climate of Sri Lanka has been investigated during the past few decades for the design and construction of many coastal structures and large scale major projects along the coastline. One of a major step forward was the directional wave measurement program off the south-west corner of Sri Lanka by Scheffer et al. (1994). In this program, wave measurements were carried out at 70 m water depth offshore location in Galle. However, successive wave analysis and publication were based only on the first three and a half years data from the program. Since available field measure wave data is limited along the coastline, wave data are transformed from the measurement location to the location where the wave conditions are required, using wave transformation models. Further, wave data measured in early time does not contain wave directions, those data cannot be used for the transformation process. Additionally, underestimation of wave heights due to the limitations of wave measuring instruments questions about the reliability of the recorded data in the past (e.g. due to the rigidity of the mooring, Wave-Rider buoys which was used between 1983 and 1997 in Sri Lanka in near-shore were not able to measure the higher waves (Wikramanayake et al., 2003)). Hence, there is a necessity to carry out wind wave modeling by using the state-of -the-art modeling methodologies for the Sri Lankan coastlines. In the scientific literature, there are some wave climate studies focusing the southern coast of the Sri Lanka (e.g. Thevasiyani & Perera (2014); Laknath & Sasaki (2011), Ranasinghe et al, (2011)). However, similar studies have been done rarely covering the North-western coast line of Sri Lanka (e.g. Bamunawala et al (2015)). Before implementing the Coastal Resource Management Project (CRMP) in Sri Lanka between 2000 โ 2006 periods, significant amount of coastal erosion was observed in some coastal stretches in the North-western coast line of Sri Lanka. However, lacks of understanding about the existing coastal processes and high risk have become hindrances for development projects such as fishery harbour construction in North-western coast of Sri Lanka. Consequently, it has been adversely affected to the larger fishery community of the same region. On the other hand, directional wave data has been being recorded for a considerable duration in West coast since 1998, mainly focusing the development and improvements of the main commercial harbour in Sri Lanka (i.e. Colombo Harbour). Hence, use of existing wave data in West coast for the development projects in North-western coast is identified as a wise approach. Accordingly, transformation of recorded wave data in West coast to the Northwestern coast to understand the wave climate in North-western coast of Sri Lanka is the main objective of this study.
- Information Technology > Data Science (0.48)
- Information Technology > Modeling & Simulation (0.34)
1. Introduction 1.1 Main challenge and purpose of the abstract After finalizing the excavation and support installation in the main caverns of the Uma Oya MPDP (Multi-Purpose Development Project), cracks in the shotcrete lining of the caverns and in the connecting galleries occurred. This happened during the ongoing work on the inner concrete structure of the caverns. The designers had to give proof to the client that these events will not endanger the integrity of the structures during construction and service life. As one of the main hazard scenarios potential buckling failure along pre-defined rock slabs in the cavern's side walls was recognized. The potential slabs were formed by the specific discontinuity pattern with sub-vertical joints almost in parallel to the caverns. In case of buckling failure, additional load would have been transferred into the rock pillar between the caverns. The decisions taken on site during construction were based on long-term monitoring data of which actual examples can be presented. The focus is on readings from load cells on anchors, extensometers and crack meters. 1.2. General outline of the project The Uma Oya MPDP in Uva province of Sri Lanka is a classical hydro power plant with the additional benefit conveying water from the central mountain region to the dry south part of the island. The scheme consists of two catchment areas confined by each a dam. These areas are linked via a low pressure conveyance tunnel of 3.9 km length. A 15.3 km long headrace tunnel starting from the Dyraaba dam guides the design discharge of 19.5 m/s past a surge shaft, a valve chamber, a vertical pressure shaft with a length of 630 m, an underground powerhouse with an adjacent transformer cavern both bearing an overburden of almost 700 m and a tailrace tunnel of 3.7 km length.
- Asia > Sri Lanka (0.25)
- Europe > Switzerland > Zรผrich > Zรผrich (0.21)
Abstract Accurately prediction of storm surges is beneficial for protecting life and property safety of residents who living along the coast. Using a curvilinear grid, a two-dimensional Delft3D-FLOW hydrodynamic model was setup to investigate the effect of storm track and tidal stencil on storm surge on the northeast coast of Sri Lanka, where has attracted little study. Results showed that storm track and tidal stencil have a significant influence on storm tide. The closer of typhoon center to study area, the more serious storm surge will be caused. In addition, the encounter of cyclone and spring tide can result in a super high storm tide. The simulated potential storm surge in this paper can be used for engineering design and coastal flooding protection. Introduction Natural hazards, such as storm surge associated with severe tropical cyclones, are adversely affecting vulnerable communities in Sri Lanka. During the months of November to December, numerous cyclones forming in the southwest or southeast Bay of Bengal at low latitudes tend to intensify into tropical storms and approach even across the coast of Sri Lanka. Although Sri Lanka is affected only occasionally by the storm surge (Dube et al., 2008; Jayawardena, 2014), the coastal regions especially eastern province of Sri Lanka indeed suffer extensive loss of life and property, as evidenced by historical cyclones including tropical cyclones of November 1964, November 1978 and November 1992. For instance, the cyclone occurred in November 1964 induced a severe storm surge about 4.5 m in Mannar (Jayawardena, 2014), which inundated and destroyed low-lying coastal settlements. According to Dinamina newspaper of December 25, 1964, this cyclone resulted in about 650 dead and 400 missing in the Northern Province of Sri Lanka. Effective prediction of storm surges can help public officials and planners develop with the desire to lower the vulnerability to storm surge. Since the hazardous intensity of storm surge is related to storm intensity, storm track, tidal stencil and influencing duration. Consequently, the research of storm surge response to different storm tracks and tidal stencil has certain scientific significance and application value.
Applying Rock Physics Analysis to De-Risk Exploration Prospects in Mannar Basin, Sri Lanka
Malkani, Anil (Cairn India Limited) | Routray, Prabir (Cairn India Limited) | Majumdar, Pinaki (Cairn India Limited) | Kumar, Prem (Cairn India Limited) | Ghosh, Biswanath (Cairn India Limited) | Chacko, Soman (Cairn India Limited)
Abstract The study area, block SL-2007-01-001, operated by Cairn India Ltd., is located in the Mannar basin of NW offshore Sri Lankan (blue polygone in Figure-1) and contains a sedimentary section exceeding 7km, the age of which ranges from Jurassic to Recent. The large number of oil and gas discoveries in the contiguous Cauvery Basin, both in Cretaceous and Tertiary sections, makes this frontier basin an attractive candidate for exploration. In 2010 Cairn Lanka acquired 1753 sq km of 3D seismic data in order to assess the exploration potential of this deep water block. This paper focuses on the role that rock physics analysis played in the assessment, risking, and ranking of the key leads identified in the basin. Of the numerous leads identified, three were high-graded in large part due to their DHI characteristics, resulting in the Dorado and Barracuda gas discoveries (Well-A & Well-C in Figure-1, respectively), the first hydrocarbons to be discovered in the Mannar Basin. The third well, Well-B, was a dry hole. De-risking of exploration prospects was based on quantitative seismic interpretation supported by rock physics analysis. This paper emphasizes how rock physics can add value in an exploration project to influence business decisions by reducing subsurface uncertainties. The nearest well, CY-DWN-2, that provided data for depth trends and rock physics analysis is located approximately fifty kilometers south west of the study area. Although this was a dry hole, it provided significant information on the sedimentary sequence, rock properties, and their associated seismic responses. Various "what if" scenarios were created to understand associated seismic responses. The analsyis explained the dry hole at CY-DWN-2 and highgraded the prospectivity of the Dorado lead. The latter was subsequently drilled, leading to the Dorado discovery.
- Asia > Sri Lanka > Palk Strait (0.86)
- Asia > Sri Lanka > Laccadive Sea (0.86)
- Asia > Sri Lanka > Bay of Bengal (0.86)
- Asia > India > Tamil Nadu > Bay of Bengal (0.25)
- Phanerozoic > Cenozoic (1.00)
- Phanerozoic > Mesozoic > Cretaceous > Upper Cretaceous (0.48)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Geological Subdiscipline > Stratigraphy (0.95)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.48)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.34)
- Asia > Sri Lanka > Palk Strait > Mannar Basin (0.99)
- Asia > Sri Lanka > Laccadive Sea > Mannar Basin (0.99)
- Asia > Sri Lanka > Bay of Bengal > Mannar Basin (0.99)
- (3 more...)
Velocity Model Update Via Inversion of Non-Parametric RMO Picks Over Canyon Areas Offshore Sri Lanka
Fruehn, Juergen (ION GX Technology) | Valler, Victoria (ION GX Technology) | Stevens, Noah (ION GX Technology) | Adhikari, Subhrashis (Cairn India) | Phani, Maheswara (Cairn India) | Sarkar, Swarup (Cairn India) | Rao, C.G. (Cairn India) | Kumar, Prem (Cairn India) | Routray, Prabir (Cairn India)
Abstract Conventional 2 and 4 order RMO picking of moveout on CRP gathers for a complex sea-floor canyon area, offshore Sri Lanka, failed to capture the short wavelength velocity variation associated with the buried canyons, thus limiting the ability of subsequent ray-based tomographic inversion to resolve the required level of complexity. In this study, we show results from autopicking performed using a new non-parametric scheme which in-part captured the complex residual moveout behaviour in CRP gathers, thus enabling the tomographic inversion to resolve more detail in the velocity model, and thereby facilitate improved imaging.
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.91)
Resolution of Internal Basalt Structures Offshore Sri Lanka
Stevens, Noah (ION GX Technology) | Valler, Victoria (ION GX Technology) | Fruehn, Juergen (ION GX Technology) | Adhikari, Subhrashis (Cairn India) | Sarkar, Swarup (Cairn India) | Chatterjee, Priyabrata (Cairn India) | Rao, C.G. (Cairn India) | Kumar, Prem (Cairn India) | Routray, Prabir (Cairn India)
Abstract Offshore Sri Lanka, basaltic flows and other intrusive bodies (sills and dykes) hamper efforts to image deeper structures. In this study, we demonstrate the ability of hi-resolution hybrid gridded tomography to resolve the internal structure of an extensive basaltic flow, revealing intercalated sedimentary units within the basalt. Given the exploration potential of sediments trapped either beneath or within basalt flows, these findings are of particular interest for this region. These findings are supported by well log measurements which penetrate one of the flows.
- Geophysics > Borehole Geophysics (0.71)
- Geophysics > Seismic Surveying > Seismic Processing (0.48)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.33)
Elucidation of Seasonal Sediment Transport Processes In Kirinda Fishery Harbour In Sri Lanka Using XBeach Model
Laknath, D.P.C. (Hydraulic and Environmental Engineering Research Section, Civil Engineering Research Institute, Technology Center, Taisei Corporation) | Sasaki, Jun (Estuarine and Coastal Engineering Laboratory, Department of Civil Engineering, Yokohama National University)
ABSTRACT: Seasonal sand accumulation processes in Kirinda Fishery Harbour was studied using field data and numerically reproduced results. In order to explain the bottom topography variation occurred during February 2005 - February 2006 period in the vicinity of the harbour, a 2DH numerical model, XBeach was successfully used. XBeach model was executed for the selected dominant wave conditions of southwest and northeast monsoons. On the basis of reproduced longshore current patterns, sand transport directions and resultant accretion and erosion areas for both southwest and northeast monsoons were explained. Considering the topography variations and current directions, main sand movement direction from south to north directions during the southwest monsoon was explained. Sand deposition inside the basins and entrance resulted from the sand inflow through the entrance by flow currents during the sand transport process from south to north direction. Further, during the northeast monsoon, accretion and erosion areas nearby harbour were explained based on the mean currents direction from north to south directions. INTRODUCTION Sri Lanka is an island country, situated off the southeastern coast of the Indian subcontinent in the Indian Ocean. The exploitable fishery resources of the country can be broadly categorized into fresh water, brackish water and marine water, of which marine water provides more than 85 percent of the total fishery resources. Among the many factors which reduce the operational efficiencies of the existing harbours, seasonal sand accumulation is identified as one major, common and unsolved problem of many fishery harbours of the country. Out of all fishery harbours, conditions of Kirinda Fishery Harbour are recognized as severe because of the huge amount of sand accumulation and resultant seasonal closure of its entrance (Laknath and Sasaki, 2011a). On sedimentary coasts, the sediment transport caused by waves and currents often presents major problems in harbour operations.
Wave Climate Study Around Kirinda Fishery Harbour In Sri Lanka Using SWAN Model
Laknath, D.P.C. (Department of Civil Engineering, Graduate School of Engineering, Yokohama National University) | Sasaki, Jun (Department of Civil Engineering, Graduate School of Engineering, Yokohama National University)
ABSTRACT: Seasonal sand accumulation problem in Kirinda fishery harbour is well known problem among the harbours in Sri Lanka. To elucidate the possible sand transport patterns close to the harbour area, wave climate study was carried out using SWAN modeling system. After analyzing global reanalysis wind data, SWAN model was executed for the selected representative simulation periods of southwest and northeast monsoon by wind forcing. On the basis of estimated wave parameters, sea and swell waves and longshore sand transport directions were investigated. During the southwest monsoon, sea and swell wave propagation from southwest direction is identified. For northeast monsoon, two distinct wave directions corresponding to the sea and swell waves were recognized. Finally, longshore sand transport process occurs during the southwest monsoon season, from southwest direction is recognized as the main cause for the seasonal closure of the entrance. INTRODUCTION The small natural harbour, which had been used by the fishermen in Kirinda and neighbouring villages, was expanded as "Kirinda Fishery Harbour" in 1985. The major objective of this harbour development project was to provide facilities for the local and migrant fishermen to engage in fishing industry throughout the year, irrespective of conditions such as the impact of monsoon climate. However, as a result of inadequate considerations on physical phenomena such as wave climate, sediment transport and littoral drift processes around the harbour area, harbour operations were suspended in 1986 due to the severe sand accumulation inside the harbour basin (ECL, 1992). In spite of the harbour being rehabilitated with proposed layout modifications in 1994, the sand accumulation process was not completely solved. At present, it occurs throughout the year and becomes severe during the southwest monsoon season. As a result, the harbour entrance is often blocked, diminishing the safe and convenient navigation access.