The vertical distribution pattern of the fine suspended sediment concentration (SSC) plays an important role in the aquatic ecosystem of shallow water. To investigate the SSC profile in submerged vegetated river flow, a series of indoor flume experiments was conducted. Glass spherical balls of three different diameters (40, 77, and 90 μm) with a uniform specific gravity of 2.5 were used for the model sediments. A set of sampling devices was designed for the simultaneous measurements of SSCs at multipoints along a vertical line. Experimental results show that the SSC profile was re‐distributed in the vegetated region, gradually forming a new equilibrium pattern in the overcanopy flow layer with its maximum occurring near the canopy top. From this maximum point near the canopy top, the suspended sediment formed a dynamic balance between upward turbulent diffusion and downward gravitational settling. Meanwhile, the momentum diffusivity was observed to linearly decrease upward from the maximum‐SSC elevation toward the water surface, thereby allowing us to deduce an empirical negative linear formula. Based on the convection‐diffusion equilibrium mechanism and with assistance of the empirical formula of flow momentum diffusivity, a new form of the Rouse formula was derived for the overcanopy flow layer. In general, this equation agrees well with the measured data. Some undercalculated deviations appear in the well‐above canopy zone due to the upskewed turbulence and the weak upward secondary flow. This deviation decreases with increasing sediment diameter. The bed deposition mainly comes from the deep part of canopy‐occupied flow layer.

In this paper, uniaxial compression tests on layered rock specimens are numerically modelled using the discrete element method to investigate the effect of a soft interlayer on the strength and deformation of rock specimens. For these simulations, the thickness and dip angle of the soft interlayer were varied. Thirty-five numerical models for different cases were established after calibrating the micro-mechanical parameters of the hard and soft rock materials. The computational results were analysed in terms of three aspects: the stress–strain curves, micro-crack propagation patterns, and particle velocity fields. The stress–strain curves indicate that increasing the thickness and dip angle of the soft interlayer causes the peak stress and ultimate strain to drop by up to 42% and 34%, respectively. The thickness of the soft interlayer has a greater influence than that of the soft interlayer dip angle on the uniaxial mechanical behaviour of the rock specimen. Additionally, crack propagation patterns and particle motion in the layered rock models indicate that the cracks develop preferentially along the soft interlayer and that the notable failure features of the layered rock models are stepped failure modes that occur at greater dip angles.

The resistance of an open-channel flow under the influence of bending deformation of submerged flexible vegetation canopy was experimentally studied in an indoor water flume. Altogether, 27 tests under the cross-combinations of three bulk flow velocities ($V$ ), three vegetation elastic moduli ($E$ ), and three vegetation stem thicknesses ($b$ ) were conducted. The total drag force experienced by the vegetation stem was accurately calculated based on the measured vertical profiles of flow velocity and the second order turbulent momentum in front of an individual plant, and this enabled the estimation of the overall drag coefficient ($C_D$ ) for bulk flow. The results show that the bending deformation of vegetation helps to transfer momentum downward toward the channel bed, thus helping to reduce the overall resistance to flow. The Cauchy number ($C_Y$ ) is an important parameter representing the bending property of the vegetation in open-channel flow; it’s functionally related to the resistance of flow. For small deformation configurations, the bending angle ($\theta$ ) and the relative bending displacement (${\delta }_z/h_p$ ) are linearly dependent on $C_Y$ and ${(C_Y)}^2$ , respectively. The $C_D$ and Manning’s $n$ for the bulk flow are both power law functions of $C_Y$ . The semiempirical formulas of $C_D$ and $n$ proposed in this study are expected to apply to further experimental studies and river engineering.

Underwater pipelines are vital to the oil industry. Extending the service life of these pipelines is a key issue in improving the sustainability of oil transportation. A geotextile mattress with floating plate (GMFP) is a novel and sustainable countermeasure for scour and erosion control and is herein introduced to protect a partially buried pipeline from local scour in steady currents. A series of experiments was designed to verify the protection capabilities of the GMFP and investigate its parametric effects on protection. The average seepage hydraulic gradient under the pipeline was adopted to depict the protection effects of the GMFP, and was calculated with the pore pressure readings under the pipeline. The test results show that the GMFP is capable of protecting a pipeline from the onset of local scour in a unidirectional current. The average seepage hydraulic gradient below the pipeline decreases remarkably after a GMFP is installed. The average hydraulic gradient shows a descending trend with increased sloping angle α when 0.64 < sinα < 0.77. The hydraulic gradient hits a nadir at sinα = 0.77 and climbs with the increasing sloping angle when sinα > 0.82. The hydraulic gradient ascends when the bottom opening ratio δ increases from 0.167 to 0.231, due to the decreased intensity of the bottom vortex. The hydraulic gradient drops with a rising plate height, except for a fluctuation at H_p = 0.12 m. An approximate negative correlation is found between the obstruction height of the floating plate and the average hydraulic gradient under the pipeline. This could be partially attributed to the extension and amplification of the bottom vortex on the leeside of the pipeline due to the increased plate obstruction height.

To study the effects of underwater terrain on plane seismic waves (P-SV wave) propagation, the theoretical solution of ground displacement, strain, rocking, and energy for the underwater terrain is derived based on Biot’s theory. Numerical results in terms of incident angle and Poisson’s ratio are illustrated for various porosities and degrees of solid frame stiffness. The results show that the response of a saturated-fluid porous soil under overlying water is controlled by the solid frame stiffness and Poisson’s ratio. Considering the effect of complex site amplification, the scattering theoretical solution of plane SV wave by a circular-arc canyon with overlying water is first derived based on the free-wave field above obtained. The effects of the incident frequencies, the incident angles, and the circular arc canyon on the ground motion of the soil-water interface are investigated parametrically. In particular, the effect of overlying water on ground motion is studied, and the results indicate that the existence of an overlying water layer absorbs the energy of a seismic wave to a certain extent. Meanwhile, the accuracy of the results is also verified by reducing the complex site to that without an overlying water layer and no canyon. Finally, based on the theoretical solution derived above, the coherence functions and the underground variable seismic motion of the site also are simulated, respectively. Compared with ground motions, the numerical results show that underground motions are smaller, which indicates that the canyon has a certain amplification effect on the seismic motions.