Sedimentologische Untersuchungen an Grimmelfinger Graupensanden

Zusammenfassung Die Untersuchung von Korngrößenverteilung und Rundungsgrad der Grimmelfinger Graupensande an zwei durch 150 km Transportweg unterschiedenen Aufschlüssen gibt Hinweise auf die Einwirkungen auf das verfrachtete Sedimentmaterial unter gleichförmigen, fluviatilen Bedingungen.Am Anfang des untersuchten Rinnenabschnittes besteht das Sediment überwiegend aus je einer Modalfraktion im Mittelsandbereich, Grobsandbereich und Feinkiesbereich¹.Auf dem Transport wird die Mittelsandfraktion — vermutlich infolge der Schlagwirkung des Feinkieses — aufgerieben und fortgeführt. In den beiden gröberen Fraktionen wird am Ende des untersuchten Abschnittes keine Korngrößenabnahme und damit verbunden auch keine Rundungsgraderhöhung beobachtet. Dieses Ergebnis wird verglichen mit den in der Literatur mitgeteilten Untersuchungen in Abriebmühlen und Feldbeobachtungen. Danach dürfte der Rundungsgrad in der Feinkiesfraktion seinem unter den gegebenen Umständen erreichbaren Grenzwert sehr nahe sein und sich auch bei weiter fortgesetztem Transport kaum noch ändern. In der Grobsandfraktion wird der Anteil, dessen Rundung verbessert wird, infolge der damit verbundenen höheren Kugeligkeit bevorzugt fortgeführt.Die Untersuchungen bestätigen, daß die Abrundungseffekte an Sedimentmaterial in strömendem Wasser in Abhängigkeit von der Korngröße betrachtet werden müssen.

---

The mechanical effects of fluvial transport over a distance of 150 km were studied by means of size frequency distributions and analysis of roundness in a Tertiary flow channel in Southern Germany filled by sand mixed with fine gravel.When entering the-channel the deposited material shows characteristic trimodal size frequency distributions. During transport the finer modal fraction (0.2...0.63 mm) is destroyed — probably through breakage by the gravel — and removed, while the sizes of the two coarser fractions remain unaffected. The roundness of the coarser fractions also remains unchanged by transport. This suggests that the roundness of the gravel material has approached its limiting roundness which is the optimum that can be achieved under the prevailing conditions. That part of the coarse sand fraction which becomes better rounded by transport may be removed preferably, because the grains getting higher sphericity by being rounded are transported more easily.Grain sizes have to be considered when abrasion effects are studied.

---

---

Herrn Professor Dr. H. Aldinger danke ich für die Möglichkeit, die vorliegende Arbeit im Geologisch-Paläontologischen Institut der Technischen Hochschule Stuttgart anzufertigen, Herrn Dr. D. Elwert, Kiel, für die Überlassung von Probenmaterial.     

Dynamic Response Analysis of Interaction System of R.C. Gravity Single-Leg Platform

In this paper, the responses of the interaction system of R.C. gravity single-leg platform to seismic excitation are mainly analysed. A set of nonlinear equations for the interaction system are established by using the wave, one is the soil-structure interaction and the other is the fluid-structure interaction. The seismic response of the interaction system is analysed for the influence of the asymmetric structure, fluid action, etc. with the input of seismic SH waves in any direction. The numerical results are given for a simple example.     

Submarine canyon development in the Izu-Bonin forearc: A SeaMARC II and seismic survey of Aoga Shima Canyon

SeaMARC II sidescan (imagery and bathymetry) and seismic data reveal the morphology, sedimentary processes, and structural controls on submarine canyon development in the central Izu-Bonin forearc, south of Japan. Canyons extend up to 150 km across the forearc from the trench-slope break to the active volcanic arc. The canyons are most deeply incised (1200–1700 m) into the gentle gradients (1–2°) upslope on the outer arc high (OAH) and lose bathymetric expression on the steep (6–18°) inner trench-slope. The drainage patterns indicate that canyons are formed by both headward erosion and downcutting. Headward erosion proceeds on two scales. Initially, pervasive small-scale mass wasting creates curvilinear channels and pinnate drainage patterns. Large-scale slumping, evidenced by abundant crescent-shaped scarps along the walls and tributaries of Aoga Shima Canyon, occurs only after a channel is present, and provides a mechanism for canyon branching. The largest slump has removed >16 km³ of sediment from an 85 km² area of seafloor bounded by scarps more than 200 m high and may be in the initial stages of forming a new canyon branch. The northern branch of Aoga Shima Canyon has eroded upslope to the flanks of the arc volcanoes allowing direct tapping of this volcaniclastic sediment source. Headward erosion of the southern branch is not as advanced but the canyon may capture sediments supplied by unconfined (non-channelized) mass flows.Oligocene forearc sedimentary processes were dominated by unconfined mass flows that created sub-parallel and continuous sedimentary sequences. Pervasive channel cut-and-fill is limited to the Neogene forearc sedimentary sequences which are characterized by migrating and unconformable seismic sequences. Extensive canyon formation permitting sediment bypassing of the forearc by canyon-confined mass flows began in the early Miocene after the basin was filled to the spill points of the OAH. Structural lows in the OAH determined the initial locus of canyon formation, and outcropping basement rocks have prevented canyon incision on the lower slope. A major jog in the canyon axis, linear tributaries, and a prominent sidescan lineament all trend NW-NNW, reflecting OAH basement influence on canyon morphology. This erosional fabric may reflect joint/fracture patterns in the sedimentary strata that follow the basement trends. Once the canyons have eroded down to more erosion-resistant levels, channel downcutting slows relative to lateral erosion of the canyon walls. This accounts for the change from a narrow canyon axis in the thickly sedimented forearc basin to a wider, more rugged canyon morphology near the OAH. About 9500 km³ of sediment has been eroded from the central, 200 km long, segment of the Izu-Bonin forearc by the formation of Aoga Shima, Myojin Sho and Sumisu Jima canyons. The volume of sediment presently residing in the adjacent trench, accretionary wedge, and lower slope terrace basin accounts for <25% of that eroded from the canyons alone. This implies that a large volume (>3500 km³ per 100 km of trench, ignoring sediments input via forearc bypassing) has been subducted beneath the toe of the trench slope and the small accretionary prism. Unless this sediment has been underplated beneath the forearc, it has recycled arc material into the mantle, possibly influencing the composition of arc volcanism.     

Effect of Berm Width and Elevation on Irregular Wave Run-Up

This paper discusses the effect of berm width and elevation of composite slope on irregular wave run-up. Based on the data obtained from model tests, the formula and distribution of irregular wave run-up on composite slope are derived. The changing of wind speed, width and elevation of the berm are considered comprehensively. The wave run-up with various exceedance probability can be es-timated utilizing the distribution curves of irregular wave run-up.     

Shear Failure of a Clamped Dented Tubular Beam Under Lateral Impact

- The shear failure of a rigid-plastic dented clamped tubular beam under the lateral impact of a mass is investigated. Both the denting and the impact point are in the middle span of the beam. It is assumed that denting does not spread during the shear sliding. Numerical results show that the axial force and lateral deflection of the beam are very small at the moment of the occurence of shear failure, which means that the finite deformation effect can be neglected in the shear failure analysis. Also, some aspects of the initial impact energy are investigated.     

Siltation Prediction for Navigation Channels and Harbour Basins on Muddy Beach

- This paper, after briefly reviewing the experimental research on sediment transport on muddy beach since the 1950s, improves and perfects the method for forecasting siltation in navigation channels and harbour basins which was first put forward in China by the authors. In consideration of silty sediment and sand, some factors in forecasting methods have been changed and modified. Consequently, the modified methods can be used either to compute siltation in navigation channels and harbour basins on muddy beach or to compute siltation and scouring in navigation channels and harbour basins on both silty beach and sandy beach. The verification of field data from eleven large, medium and small natural harbours shows a good agreement between the forecasting by the modified method and the natural conditions. Finally, the paper deals with the rational utilization of water area after the construction of the West Dyke in Lianyungang, the maintenance of water depth of the navigation channel at the entrance, siltation distribution, siltation in the navigation channel and harbour basin for ships of 100 thousand tonnnage. Results once again prove that the prospect of constructing Lianyungang Harbour into a deepwater harbour is bright.     

Calculating Method and Verification of Wave Pressure Distribution on the Breast Wall of Mound Breakwater

In this paper, the calculating charts and formulae about wave pressure on the breast wall are derived with seven parameters on the basis of physical model study. The verification shows that the charts agree with the example, and are adopted in the Specifications of Fishery Harbours Breakwater by the Ministry of Agricultures.     

Sea-floor observations in the tongue of the ocean,Bahamas: An Argo/SeaMARC survey

SeaMARC side-scan sonographs and Argo video and photographic data suggest that the recent sedimentary environment of the floor of the Tongue of the Ocean is controlled by an interplay of turbidity current flow from the south, sediment spill-over from the carbonate platform to the east (windward side), and rock falls from the west carbonate escarpment (lee side). The spill-over forms a sandy sedimentary deposit that acts as a topographic obstruction to the turbidity current flow from the south. This obstruction is expressed by the westward migration of a northwest-southeast oriented turbidity-current-cut channel.     

Ship hull drag reduction using bottom air injection

The idea of bottom air injection to reduce ship hull resistance is not new. Early patents envisioned planing hull applications. Recent planing hull tests speed realized an increase of 7–12 knots. River barges and ship fitted with an air injection system results are presented to show a 10–15% reduction in the frictional resistance. Graphs for making initial estimates for displacement hulls with bottom air injection are presented. It is clear from these results that improvements in high speed planing catamarans and full form hull resistance can be realized by using bottom air injection.