Test data to compare the resulting behavior with that observed under cyclic loading triaxial test conditions are presented. It is concluded that the liquefaction characteristics observed in the two types of tests are qualitatively similar. However, under cyclic simple shear conditions, which provide a close simulation of the stresses induced under field conditions, the cyclic shear stresses required to cause liquefaction were only about 35% of those determined by more approximate triaxial test procedures. It is suggested, however, that limitations of the simple shear test procedure induce liquefaction at stress levels perhaps 40% to 50% lower than those corresponding to actual field conditions, and that a correction factor of this order of magnitude should be applied to laboratory simple shear test data intended for use in the analyses of field problems. The test program also showed that frequency effects, within the range from 1/6 cps to 4 cps, are small.

Closure to “Sand Liquefaction Under Cyclic Loading Simple Shear Conditions”

Investigations on the porous media equations and resistance coefficients for coastal structures

Physical modeling of local scour development around a large-diameter monopile in combined waves and current

This paper presents the results of an experimental investigation of the complete sequence of sediment behaviour beneath progressive waves. The sediment was silty with d50 = 0.060 mm. Two kinds of measurements were carried out: pore-water pressure measurements (across the sediment depth), and water-surface elevation measurements. The process of liquefaction/compaction was videotaped from the side simultaneously with the pressure and water-surface elevation measurements. The video records were then analysed to measure: (i) the time development of the mudline, (ii) the time development of liquefaction and compaction fronts in the sediment and (iii) the characteristics of the orbital motion of the liquefied sediment including the motion of the interface between the water body and the sediment. The ranges of the various quantities in the tests were: wave height, H = 9–17 cm, wave period, T = 1.6 sec, water depth = 42 cm, and the Shields parameter = 0.34–0.59. The experiments reveal that, with the introduction of waves, excess pore pressure builds up, which is followed by liquefaction during which internal waves are experienced at the interface of the water body and the liquefied sediment, the sequence of processes known from a previous investigation. This sequence of processes is followed by dissipation of the accumulated excess pore pressure and compaction of the sediment which is followed by the formation of bed ripples. The present results regarding the dissipation and compaction appear to be in agreement with recent centrifuge wave-tank experiments. As for the final stage of the sequence of processes (formation of ripples), the ripple steepness (normalized with the angle of repose) for sediment with liquefaction history is found to be the same as that in sediment with no liquefaction history.

The sequence of sediment behaviour during wave-induced liquefaction

Experiments have been conducted in a large oscillatory flow tunnel to investigate the effects of acceleration skewness on oscillatory boundary layer flow over fixed beds. As well as enabling experimental investigation of the effects of acceleration skewness, the new experiments add substantially to the relatively few existing detailed experimental datasets for oscillatory boundary layer flow conditions that correspond to full-scale sea wave conditions. Two types of bed roughness and a range of high-Reynolds-number, Re~O$({10^6})$ , oscillatory flow conditions, varying from sinusoidal to highly acceleration-skewed, are considered. Results show the structure of the intra-wave velocity profile, the time-averaged residual flow and boundary layer thickness for varying degrees of acceleration skewness, β. Turbulence intensity measurements from particle image velocimetry (PIV) and laser Doppler anemometry (LDA) show very good agreement. Turbulence intensity and Reynolds stress increase as the flow accelerates after flow reversal, are maximum at around maximum free-stream velocity and decay as the flow decelerates. The intra-wave turbulence depends strongly on but period-averaged turbulent quantities are largely independent of β. There is generally good agreement between bed shear stress estimates obtained using the log-law and using the momentum integral equation, and flow acceleration skewness leads to high bed shear stress asymmetry between flow half-cycles. Turbulent Reynolds stress is much less than the shear stress obtained from the momentum integral; analysis of the stress contributors shows that significant phase-averaged vertical velocities exist near the bed throughout the flow cycle, which lead to an additional shear stress, -puw; near the bed this stress is at least as large as the turbulent Reynolds stress.

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Experimental study of the turbulent boundary layer in acceleration-skewed oscillatory flow

Wave boundary layer over a stone-covered bed

This paper summarizes the results of an experimental investigation on wave scour around a circular pile in three kinds of soil, namely in dense silt with a relative density of Dr = 0.74, in medium dense silt with Dr = 0.38, and in sand with Dr = 0.23. The dense silt was achieved by wave liquefaction. Upon the completion of the liquefaction/compaction process, the pile was subjected to wave induced scour. The range of the Keulegan-Carpenter number KC, tested in the experiments is from practically 0 to approximately 20. The Shields parameter in the experiments was such that the bed was live. The scour depth was increased by a factor of 1.6-2 when the bed soil was changed from medium dense silt or sand to dense silt. This is partly due to an increase in the angle of friction. The time scale of scour also was influenced by the density of the soil. The time scale was largest for the dense silt case, and smallest for the sand case in the experiments.

Wave Scour around a Pile in Sand, Medium Dense, and Dense Silt

This paper summarizes the results of an experimental and theoretical investigation of: (1) pipeline flotation in a soil (liquefied under waves); and (2) density of the liquefied soil. In the experiments, the soil was silt with d50 =0.078 mm . Pipeline models of 2 cm diameter were used. They were buried in the soil at different depths in the range 3–15.5 cm . The total depth of the silt layer was 17.5 cm . Waves (with 17 cm wave height and 1.6 s wave period, the water depth being 42 cm ) were used to liquefy the soil. The pipes with specific gravity smaller than 1.85–2.0 floated when the soil was liquefied, the critical specific gravity for pipe flotation. The lower bound of the above range corresponds to the initial pipe position near the surface of the bed, and the upper bound to that near the impermeable base. Furthermore, the pipe floated (or sank) to a depth where the pipe specific gravity was equal to the previously mentioned critical specific gravity for flotation. The density of liquefied soil was ...

Figen Hatipoglu

Papers

The sequence of sediment behaviour during wave-induced liquefaction

Wave boundary layer over a stone-covered bed

Wave Scour around a Pile in Sand, Medium Dense, and Dense Silt

Critical Flotation Density of Pipelines in Soils Liquefied by Waves and Density of Liquefied Soils

The cycle of soil behaviour during wave liquefaction