Browsing by Author "Tulsi, Kishan Ramesh"
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- ItemThree dimensional method for monitoring damage to dolos breakwaters(Stellenbosch : Stellenbosch University, 2016-12) Tulsi, Kishan Ramesh; Schoonees, J. S.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Ports are frequently protected by breakwaters which are designed to withstand harsh environmental conditions over long periods of time. However, in most cases, they gradually or suddenly deteriorate before they reach their design life. In order to extend the design life of breakwaters, regular damage investigations and timeous repairs are required. One of the important aspects is calculating the severity of damage to breakwaters. Traditionally, breakwater inspection has been done using aerial photographs and underwater imaging to accomplish these investigations. Breakwaters are systematically divided into inspection stations and photographs are taken to inspect and assess the damage. The photographs are then visually compared with the previous inspection photographs to identify changes. This is difficult to achieve as it is not always possible to get the helicopter exactly in the same position on every survey and highly dependent on the skill of the helicopter pilot. Another difficulty is taking underwater images near the breakwater due to poor visibility and wave breaking. A major disadvantage of the aerial photographic method is that it only provides a two dimensional (2D) picture of the breakwater above water. The inter-tidal zone on a breakwater slope is where damage usually occurs. It is difficult to capture data in this zone, particularly due to wave action, which results in poor visibility. Ideally, a method is required to capture and assess damage above and below water. High resolution laser scanning and acoustic technologies are available to inspect breakwaters above and below water. These are light detection and ranging (LIDAR) and multibeam echo sounders respectively. The South African coastline has few significant embayments’ that can provide natural shelter from the high energy wave regime on the coastline. Consequently, South African ports require protection in the form of heavy armoured breakwaters and seawalls. Maintenance of these defences is critical for the safe functioning of these ports. Rapid assessment of damage to breakwaters and seawalls which is cost e↵ective is necessary to ensure that repairs are undertaken timeously. This study explores the use of LIDAR and multibeam echo sounders, instead of the traditional aerial photography, to assess damage to breakwaters in general. Three dimensional (3D) data analysis using LIDAR and multibeam echo-soundings (as investigated in this thesis) is aimed at providing a more realistic method to quantify damage above and below water rather than two dimensional (2D) photographs. The objective of this study was to evaluate the accuracy of a 3D method using the LIDAR and multi-beam echo sounder data to quantify damage to dolos breakwaters above and below the water surface (including the inter-tidal zone). This was aimed towards the development of the 3D eroded volume method (3D method). The investigation began with an idealized undamaged model breakwater slope in a laboratory experiment comparing the repeatability of the 3D method with sequential scans and the photographic method in an attempt to compare the deviation in repeatability of data captured. Thereafter three degrees of artificial damage were created to the slope of the model breakwater in the form of settlement, intermediate damage and failure of a localized area of the dolos armour layer. The 3D method was then applied to a 3D physical model study of the spur breakwater at the root of the Table Bay main breakwater. Field data of the spur breakwater were then captured with the 3D method and compared with the most recent 2D aerial photographic survey. More than two decades of 2D aerial photography damage assessment data of the spur breakwater were available to establish a baseline. The 3D method data captured were compared with the visual 2D field data to determine the 3D methods accuracy. The comparison of the cumulative damage progression monitored by the visual 2D photographic method with that calculated by the 3D method, showed that there is a good correlation between the two damage quantification methods. The cumulative percentage damage obtained from the 2D visual analysis records has a mean di↵erence of 10% in comparison to the 3D method. The results of the 2D and 3D methods di↵er in cases of small settlements and larger displacements. This study has led to an advance in the quantitative 3D assessment of di↵erent degrees of damage to breakwaters with dolos armour units above and below water. The 3D method used to assess the extent of damage to a breakwater was compared against the conventional visual method described by Phelp (1995). A marginal variation between the two methods was found, however the 3D method which quantifies 3D eroded volume is recommended for future breakwater investigations to provide a better quantifiable above and below water assessment.