The identification of triggering agents for soft-sedimentation structures is an enigmatic geological problem. Mainly seismic-induced soft-sediment structures have been recognized in ancient sediments, rather than those resulting from storm waves. We analyse soft-sediment deformation structures in Upper Miocene calcarenitic tempestites of the Guadalquivir Basin (Southern Spain). The most common structures are load-casts which vary in height and width from 10 centimetres to several metres. The structures are always restricted to a small part of the stratigraphic sections, in exclusive association with tempestites. The analysed soft-deformation structures are interpreted to be the result of liquidization processes. Chiefly from their inferred depositional environment, and subordinately from the deformation style, we have devised basic criteria to identify the trigger mechanism. In these soft-sediment deformation structures the liquefaction was triggered by pore pressure changes induced by cyclic and residual stress of storm waves.

Soft-sediment deformation structures induced by cyclic stress of storm waves in tempestites (Miocene, Guadalquivir Basin, Spain)

Upper Cambrian limestones and dolostones of western Newfoundland, Canada, display conspicuous synsedimentary mud cracks. Cracks occur in carbonate mudstone interbedded with ooid and peloid grainstone (unwashed oolite and ribbon rock lithofacies). The traditional interpretation is that these are desiccation cracks. The weight of evidence supports an alternative e explanation: cracks resulted from the differential mechanical behaviour under stress of stiff mud interlayered with loose ooid/peloid sand. The processes envisaged to cause such diastasis cracks may be applicabl e to a wide variety of both carbonate and terrigenous clastic deposits composed of interlayered sediments of contrasting material properties, and may be a viable alternative to synaeresis

Diastasis cracks: mechanically generated synaeresis‐like cracks in Upper Cambrian shallow water oolite and ribbon carbonates

Quasi‐static field equations for fully saturated porous elastic media, based on Biot's theory (1972‐1973), established in the writer's previous works (1989‐1990) are used in order to describe the behavior of such materials under wave ocean loading. A brief description of cross anisotropy with a vertical axis of symmetry (orthotropy) is given. The five independent elastic parameters of anisotropic materials are clarified. The field equations are modified and adapted for application to anistropic cases. A numerical procedure (finite element discretization) for the motion equations of an orthotropic saturated poro‐elastic seabeds is presented. The accuracy of the chosen algorithm is discussed. The wave‐induced pore pressures, effective stresses and displacements in an anisotropic submarine sediment are investigated. The results illustrate a significant influence of elastic anisotropic parameters on the wave‐induced pore pressures, effective normal stresses, shear stresses, horizontal and vertical displacemen...

Response of cross-anisotropic seabed to ocean waves

In this paper, shear, effective stress and pore pressure distributions of two-layer porous soils subjected to harmonic waves are presented. The instability of the porous soil because of wave loading is investigated in terms of instantaneous liquefaction. The governing equations are written in their fully dynamic form, and possible simplifications are introduced. Finite-element models are developed for each formulation, and numerical results are verified with their corresponding analytical solutions, which are also developed here. Then, the problem of a two-layer soil under waves both in an open domain and in front of a vertical wall is studied in terms of dynamic response variations and regions of instantaneous liquefaction. Both linear and nonlinear waves are considered. Finally, a number of parametric studies to investigate the effect of a surface clay layer, inertial terms in the equations, various soil and wave parameters, and wave nonlinearity on the dynamic behavior and instability are carri...

Pore Pressure, Stress Distributions, and Instantaneous Liquefaction of Two-Layer Soil under Waves

Wave pressures and uplift forces on and scour around submarine pipeline in clayey soil

This note describes the determination (for a wide class of wave pressure forms) of the response to waveloading of an infinite half-space consisting of a porous elastic soil skeleton. Under such loading, no volumetric strains occur in the soil mass, and there is no coupling between the pore water and the skeleton. Also, an analytical relationship has been established between stresses and pore pressures, so that the computation of the pore pressures is sufficient to solve the complete effective stress problem. The paper gives an integral formulation for the pore pressure as a function of the wave pressure.

L Dormieux

Papers

Effective stress response of a plane sea-bed under wave loading