Print Email Facebook Twitter Breakwaters under construction exposed to oblique waves Title Breakwaters under construction exposed to oblique waves Author Mulders, P.H.M. Contributor Stive, M.J.F. (mentor) Verhagen, H.J. (mentor) Uijttewaal, W.S.J. (mentor) Smith, G.M. (mentor) Faculty Civil Engineering and Geosciences Department Hydraulic Engineering Date 2010-06-23 Abstract During the construction of breakwaters contractors often encounter undesired reshaping of exposed core material. This reshaping is comparable to the deformation process of berm breakwaters in which the outer profile reshapes into a more stable s-curve. In the case of oblique waves this deformation is enhanced by a longshore transport of stones leading to even more loss of material and damage. Throughout the years few formulas were derived for both processes which describe the behaviour of berm breakwaters as well as gravel beaches reasonably well. These formulas however turned out to be inadequate when it comes to describing the behaviour of core material. In particular the influence of the wide grading of quarry run, commonly used as core material, is to a large extent unknown and generally not described in the available relations. To investigate this influence of the stone grading on both the two-dimensional deformation and longshore transport new physical model tests were carried out in the wave basin at Delft University of Technology. In total 12 tests were executed in which two different gradings, three different angles of wave attack and two different wave spectra were tested. Data collected from the tests included wave and profile measurements together with the displacements of stones, originating from two colour beams which were applied in the middle of the trunk. These data along with visual observations eventually led to a conceptual model describing stone movements in both transverse and longshore direction. Using Matlab three-dimensional profile and erosion models were generated from which the different profile parameters were determined. With respect to the distance from origin, for each test an exponential relation was derived to describe the stone displacements. After determination of the area of uniform transport these exponential relations were used to calculate the total longshore transport by means of extrapolation and multiple integrations. Subsequently all parameters found were compared to the formulas currently available for both processes. Regarding the deformation parameters the test results produced the best fit with the formulas derived in [MERLI 2009]. Still on several occasions a deviant relation was found concerning the influence of wave obliquity. In addition, the formulas became less accurate for the narrow grading used in the tests, which fell outside the range tested by Merli. However, for the crest height of the deformed profile test results deviated completely from the available formula as no influence was found whatsoever for all tested parameters. Here the deviation was contributed to a higher instability of the part above the initial deformation, partly due to the steepness of the slope. On the subject of the longshore transport clear trends were found describing the influence of the varying parameters. Both a higher wave load and wider grading lead to an increase of the longshore transport. For the wider grading, however, this increase gave a rather distorted image, as not all fractions in the mixture were transported evenly. Due to segregation the coarsest fractions were mostly transported in the transverse direction while the finer fractions were transported further away in the longitudinal direction. Alternatively, computation of the longshore volume transport proved to be more representative. Regarding the effect of wave obliquity an increase in angle of wave attack of 30 to 45 degrees was accompanied by a decrease in longshore transport; though this decrease was less than already available formulas indicated. However despite the fact that it describes a completely different trend concerning this particular influence, the best fit was found after multiplying the relation derived by [ALIKHANI 1996] with a factor 100. Subject gradingbreakwatercorereshapingtwo-dimensional deformationlongshore transportstone displacementphysical model testwave obliquity To reference this document use: http://resolver.tudelft.nl/uuid:cc04f91a-4f2d-4c6c-9c8e-a803a258f500 Related item http://data.3tu.nl/repository/uuid:784e88ae-079d-4882-83f4-a5d565760dd1 Part of collection Student theses Document type master thesis Rights (c) 2010 Mulders, P.H.M. Files PDF MSc-Thesis_P._Mulders.pdf 4.24 MB PDF Appendices_MSc-Thesis_P._ ... ulders.pdf 24.47 MB Close viewer /islandora/object/uuid:cc04f91a-4f2d-4c6c-9c8e-a803a258f500/datastream/OBJ1/view