Saturated Sand Bed Research Articles

Predicting the penetration depth and towing resistance of beam trawl fishing gears in sand

Accurate characterization of mechanical perturbations on the seabed is essential for developing models assessing the environmental impacts from physical disturbances. Furthermore, understanding the relationship between (1) seabed resistance and (2) penetration depth, can also facilitate the development of more efficient and less impactful fishing gears. This study examines these two aspects of tickler chain rigged beam trawling via large-scale physical experiments. Three scaled down models (“light,” “medium,” and “heavy” designs) were developed to represent the impacts from typical beam trawl configurations used in the North Sea and were towed at various speeds on a saturated sand bed. Results reveal that increasing the towing speed reduces the mean penetration depth and the steady-state towing resistance of the gears. Smaller scale physical model tests incorporating tickler chains in sand, demonstrate that the towing resistance is significantly influenced by the soil compaction and particle sizes. Moreover, our study offers a simple and efficient method to estimate the penetration depth and towing resistance of prototype beam trawl gears in sand. This approach, along with the associated research, may be valuable for marine scientists assessing trawling impacts and demersal fishing gear designers seeking to optimize efficiency while minimizing seabed disturbance.

Experimental investigation on seabed response characteristics considering vibration effect of offshore monopile foundation

Monopile foundations are currently the most significant support form for offshore wind turbines. An experimental investigation of the vibrating monopile was conducted inside the cohesionless saturated sand bed to examine the pore water pressure oscillation response law and amplitude variation features around the monopile under the vibration effect. The experimental results indicate that the vibration loading force Fp, vibration frequency fv and vibration amplitude Av have remarkable impacts on the various characteristics of the pore pressure response around the monopile foundation. The lower the vibration frequency, the more prominent is the delayed attenuation process during the oscillation cycle, and a succession of pore pressure sub-peaks develop near the phase end of the cycle period. Additionally, the pore pressure amplitude decay rate increases with increasing frequency as the depth of the seabed grows, and the pile side pore pressure shows a trend of increasing and then decreasing with frequency.

Effects of seawater on the infiltration behavior of bentonite slurry into sand

As a support fluid, bentonite slurry has been extensively used in slurry shield tunneling to stabilize the tunnel face by forming a low-permeable filter cake. However, the infiltration behavior of bentonite slurry in complex conditions such as when suffering from seawater intrusion has not been fully understood. In order to investigate the infiltration behavior and filter cake formation under seawater intrusion, seawater-based bentonite slurries with increased salt content were prepared to represent different seawater intrusion severities. The rheological properties and physical stability of these slurries were evaluated. A series of infiltration column tests were conducted on two saturated sand beds with different particle sizes. Scanning electron microscope (SEM) was performed to unravel the microstructure of the filter cake. The infiltration column test results show that the low-permeable filter cake can be formed on the fine sand bed regardless of the salt content of the slurry. The salt shortened the time span of the mud spurt and made the filter cake more permeable to water. For the medium sand, the filter cake cannot be formed when the salt content exceeds 1%, because the deterioration of rheological properties of the slurry weakened its rheological blocking effect when infiltrating the sand. Based on the SEM images, it was found that the filter cake under seawater intrusion contained many well-connected inter-agglomerate channels that reduced its sealing quality. The obtained results can provide guidance and reference for the application of bentonite slurry when tunneling in a sea environment.

How vertical oscillatory motion above a saturated sand bed leads to heap formation.

We show how oscillations in fluid flow over a fluid-saturated and porous sediment bed leads to the development of a bedform. To understand the role of pressure fluctuations on the bed associated with flow oscillations, we analyze how the flow penetrates into and through the bed. We then calculate the corresponding vertical pressure gradients within the bed that tend to expand the bed along the vertical direction. When these pressure gradients are large enough, they facilitate small irreversible rearrangements of the grains within the bed, and so cause granular creep. We conjecture that this granular creep alternates with jamming to produce a granular ratchet that slowly lifts the surface of the bed locally where pressure gradients dominate, and depresses the surface where shear stresses dominate. We observe that the shape of the resulting heap exhibits a constant characteristic width. The height of this heap evolves approximately as the square root of time, in agreement with dimensional arguments predicated on a coarse-grained viscous deformation of the bed. The surface of the heap contracts initially with the square root of time, consistent with an incompressible analysis of the flow of grains within the heap. Near its peak the heap grows due to a dilatation of the bed, to inward radial flux, or to a combination of the two.

Effect of model scale on helical piles response established from shake table tests

This paper investigates the effect of model scale on seismic response of prototype helical pile (HP) groups employing finite element modelling approach verified by the results of single gravity shaking table models of piles installed in dry and saturated sands. The prototype shaking test configuration was established from model shake table tests by adopting a set of similarity and dimensional laws. The results demonstrated that the scaled models exhibited generally similar responses. The HPs' response in the saturated sand bed was dominated by the rocking behaviour, while the flexural behaviour dominated the response in the dry tests. In addition, the HPs' lateral response followed the lateral soil uniform deformation in the dry tests, while they did not follow the nonuniform soil deformation in the saturated tests. However, the prototype models' axial and lateral responses were different from the results of the shaking table scale. The HP exhibited less scaled lateral deformation, bending moments, and settlement in the prototype models than those at the shaking table scale in the dry and saturated tests. Meanwhile, the prototype helices’ stress was higher than the shaking table helices in the saturated tests and less than them in the dry tests. A set of scaling factors was suggested for extrapolating the soil and HP responses from 1 g shake table model tests. Based on the obtained results, the soil and HP responses may be extrapolated from 1 g shake table model tests employing the following scaling factors: soil displacement increase factor, SDIF = 0.8n in the saturated tests, and SDIF = 0.6n in the dry tests, while the pile displacement increase factor, PDIF = 0.7n in the saturated test and 0.5n in the dry test.

Reliquefaction Assessment Studies on Saturated Sand Deposits under Repeated Acceleration Loading Using 1-g Shaking Table Experiments

ABSTRACT In this paper, reliquefaction studies of saturated sand deposits prepared at 40% and 60% relative density were tested using a uni-axial shaking table at repeated incremental acceleration loading conditions. The repeated acceleration loading was selected similar to continuous earthquake and associated foreshock/aftershock shaking events observed in recent earthquakes. For experimental testing, sinusoidal acceleration of 0.1 g, 0.2 g, 0.3 g, and 0.4 g loading with 5 Hz frequency was selected and applied sequentially to the model ground after dissipation of generated excess pore water pressure from the previous loading. The generated excess pore water pressure, pore pressure ratio, liquefaction time, variation in soil density, soil displacement and foundation settlement were estimated. The reliquefaction potential of saturated sand bed subjected to repeated acceleration loading was reported.

Experimental Observations on the Initiation of Sand-Bed Erosion by an Upward Water Jet

AbstractErosion of a saturated sand bed by a vertically upward water jet was studied experimentally. Direct observations on the behavior of sand-bed erosion were obtained by increasing the flow rat...

Centrifuge Seismic Test on Seismic Behavior of Pile Group in Liquefiable Soil

A series of grouped-model piles (2×2) centrifuge shaking table tests at an acceleration of 80 g was conducted to simulate seismic responses of a grouped-piles embedded in liquefiable sandy soil subjected to different magnitudes of earthquake loading. The tested grouped-piles connected with a pile cap are used to support 4 sets of model dry storage tank.Different test conditions including elevations of pile cap, elevations of ground water table, and dry and saturated sand beds all are reported in the study. Sensors (i.e., strain gauges along the depths of pile for measuring the bending moments, accelerometers for measuring the accelerations at different depths, LVDTs and pore water pressure transducers) densely instrumented in the piles and the surrounding soils provide valuable information for examining their evolution at various degrees of liquefaction. The magnitudes of bending moment along pile depths would increase with the increases of base shaking. The lowest bending moments were measured for the grouped–piles with the pile cap embedded in the dry sand bed while the largest lowest bending moments for the grouped–piles with the pile cap embedded in the saturated sand bed with the water table at the surface. The test results can be used to validate the results derived from the numerical simulation.

Pore Water Pressure and Liquefaction in Saturated Sand Bed Induced by Tsunami

Pore Water Pressure and Liquefaction in Saturated Sand Bed Induced by Tsunami

Shaking table tests to investigate the influence of various factors on the liquefaction resistance of sands

This paper presents the shaking table studies to investigate the factors that influence the liquefaction resistance of sand. A uniaxial shaking table with a perspex model container was used for the model tests, and saturated sand beds were prepared using wet pluviation method. The models were subjected to horizontal base shaking, and the variation of pore water pressure was measured. Three series of tests varying the acceleration and frequency of base shaking and density of the soil were carried out on sand beds simulating free field condition. Liquefaction was visualized in some model tests, which was also established through pore water pressure ratios. Effective stress was calculated at the point of pore water pressure measurement, and the number of cycles required to liquefy the sand bed were estimated and matched with visual observations. It was observed that there was a gradual variation in pore water pressure with change in base acceleration at a given frequency of shaking. The variation in pore water pressure is not significant for the range of frequency used in the tests. The frequency of base shaking at which the sand starts to liquefy when the sand bed is subjected to any specific base acceleration depends on the density of sand, and it was observed that the sand does not liquefy at any other frequency less than this. A substantial improvement in liquefaction resistance of the sand was observed with the increase in soil density, inferring that soil densification is a simple technique that can be applied to increase the liquefaction resistance.

Effect of overburden stress and surcharge pressure on the liquefaction response of sands

The physics and mechanism of soil liquefaction is understood sufficiently well by researchers now. However, the effect of various external factors such as the weight of the structure and overburden pressure on the liquefaction behavior of cohesionless soils is still under investigation. This paper presents a comprehensive study consisting of shaking table experiments on saturated sand beds to understand the effect of overburden pressure for free field conditions and the effect of surcharge weight for under the structure conditions on the liquefaction response of the sand beds. Pore water pressure was monitored continuously and the loss of effective stress with dynamic time was calculated for all the tests. Liquefaction occurred for shaking under specific ground motion conditions, which was visibly seen in the shaking table tests when the sand bed started to shake like a liquid and sand boils were formed on the bed. The number of cycles of dynamic shaking required for liquefaction and the pore water pressure were compared for different models. It was observed that increase in overburden pressure increases the liquefaction resistance of the soil. For sand beds under building pressure, the liquefaction response was observed to depend a great deal on the dynamic loading parameters. In the case of sand beds under surcharge loads, the response was complicated because of the complex soil–structure interaction under dynamic loading conditions.

PREDICTION OF THE RETENTION VOLUME OF SEDIMENT DURING WATER-BASED SEDIMENT INJECTION

The aim of this study is to propose a model for describing the pressure changes due to the retention of sediment (organic matter adsorbed on fines, diameter range 1−100 µm) inside saturated sand beds. Such model makes it possible to predict the retention volume of sediment, which is useful for considering the biodiversity of tidal flats. On the basis of Poiseuille's law and the hydraulic radius concepts, two models could theoretically be proposed to predict the pressure drop in the absence or presence of sediment retention. From one of the proposed models, the retention volume of sediment is determined, and is verified by comparing the predictions with experimental data. It was found that the friction coefficient determined based on the proposed model was in good agreement with that determined from the measured pressure drop, suggesting that the measured pressure drop can be reproduced by the proposed model. Moreover, the retention volume predicted by the proposed model well matches the measured retention weight. It was found that the properties of organic matter bonded onto sediment particles strongly affected the retention behavior of sediment. Sediment that is absorbed by decomposed organic matter travels more easily through sand beds, resulting in a low reduction of permeability.

Deposition Behavior of Mud in Sand Beds Under the Effects of Organic Properties

Mud transport in sand fractures has yielded a large body of information which is used to understand the sludge-ization of tidal flats, to improve the tidal flat environment, and to design artificial tidal flats. Over the past decades, studies of particle transport in saturated and unsaturated porous media provide a very clear understanding of the processes that govern particle transport. It has been reported that the particle transport and capture in porous media are significantly governed by hydraulic pressure gradient, porosity, and permeability distribution. The objective of this research is to present a study of mud transport in saturated sand beds, aiming to delineate the effects of the organic properties of mud on the general behavior of mud transport and deposition condition in pores. Laboratory experiments were undertaken to look into the effects of the organic properties. The experiments were conducted at a flow rate of 1.3 cm3/s. Many types of muds that have differences in the organic properties were injected into different sand beds at a concentration of 120 mg/L. It was observed that the deposition condition of mud in the beds was mostly due to the organic properties of mud. Mud containing high amounts of organic matter easily remained in sand beds. Furthermore, it was found that mud deposited in the pores as clusters rather than being separately adsorbed onto the surface of soil particles.

Oxidation processes and clogging in intermittent unsaturated infiltration

Intermittent infiltration of wastewater through a non saturated sand bed is an extensive treatment process aimed at eliminating organic pollution, oxidizing ammonia and removing pathogens. A 1D numerical model, IPOX, has been worked out to simulate the transfer and oxidation of dissolved organic matter and nitrogen in unsaturated sand beds. IPOX was calibrated after real scale tests performed in Spain and Burkina Faso. Simulations allowed us to point out the influence of (i) kinetics on oxidation performances and (ii) biomass development on the process sustainability. These results brought a new light on the sizing and operation of infiltration percolation and soil aquifer treatment (SAT) plants.

Plant water relations and mineral nutrition of containerized nursery plants in relation to irrigation method

Cotoneaster dammeri C. K. Schneid. 'Coral Beauty' and (Forsythia ovata × Forsythia europaea Deg. and Bald.) Forsythia 'Northern Gold' were grown in 3.8-L containers in a softwood bark–peat–sand medium, using overhead, pulse, drip or subirrigation methods. N, P and K were supplied from Nutricote 16N-4.4P-8.1K (type 140) controlled-release fertilizer. Overhead sprinklers irrigated containers during two 45-min periods each day. Daily pulse irrigation was from sprinklers for four 7-min periods, and drip irrigation to individual containers occurred during two 5-min periods. For subirrigation, plants were placed on permanently saturated sand beds. Subirrigation resulted m significantly higher plant dry weights at the end of the growing season than all other treatments. Measured daily leaching volumes were greatest from overhead-irrigated containers, followed by drip- and then pulse-irrigated containers. Leaching from the subirrigated treatment was small and sporadic, occurring only after moderate rainfall. Shoot water potential (ψT) was measured at weekly intervals through the middle of the growing season. There were no differences in predawn or dusk ψT values between treatments, but midday ψT was generally lower in subirrigated plants. At the end of the growing season, electric conductivity of the medium was highest for subirrigation, intermediate for drip and pulse irrigation, and lowest for overhead irrigation. This pattern was repeated for foliar K levels. It appears that superior growth of subirrigated plants is due more to better nutrient retention in the medium than to any effect on plant water status. Key words: Capillary irrigation, nutrient leaching

Centrifuge modelling of tower structures on saturated sands subjected to earthquake perturbations

The dynamic behaviour of a tower structure founded on a saturated sand bed subjected to model earthquakes was investigated using the bumpy road-shaking system of the Cambridge centrifuge. Excess pore pressure was generated and effective stress reduced. When the initial natural frequency of the tower–soil system exceeded the driving frequency of the earthquake, the reduction in effective stress caused a degradation in the soil stiffness and a lowering of the natural frequency. The generation of excess pore pressure caused a jump in the natural frequency of the tower-soil system to a discrete frequency at which the energy of the earthquake was concentrated. When the initial natural frequency was either equal to or less than the driving frequency of the earthquake, the excess pore pressure did not cause any change in the natural frequency of the tower–soil system. Le comportement dynamique de la structure d'une tour fondée sur un lit de sable saturé et soumise à des simulations seismiques a été étudié à l'aide du système de génération de secousses de la centrifugeuse de Cambridge. Les séismes se traduisent par l'apparition d'un excès de pression interstitielle et par la diminution de la contrainte effective. Lorsque la fréquence propre initiale du système tour–sol devient supérieure à la fréquence imposée par les séismes, la diminution de contrainte effective entraîne une dégradation de la raideur du sol ainsi qu'une réduction de la fréquence propre. L'apparition d'un excès de pression interstitielle se traduit par un saut de la fréquence propre du système tour–sol vers une fréquence discrète pour laquelle l'énergie du séisme est la plus forte. Lorsque la fréquence propre initiale est inférieure ou égale à la fréquence imposée par les séismes, l'excès de pression interstitielle ne génère aucune modification de la fréquence propre du système tour–sol.

Thermal Stability And Application Of Emulsion Composed Blocking Agents For Steamflooding

Abstract The investigation into mobility control and blocking agents to improve steamflood conformance has been of ongoing interest. This paper examines the thermal stability and application of oil-in-water macroemulsions to block high permeability channels created by steam injection. The stability of 5% (by volume) Primrose and Lloydminster heavy oil-in-water emulsion was screened using both an anionic (Vista 250) and a nonionic (Triton X-100) surfactant. Surfactants were used in active concentrations of 25 to 5000 ppm to create the emulsions. Visual observations of the droplet character and the emulsion pH behaviour at different surfactant concentrations, over cure temperatures of 25 °C to 225 °C. were the criteria used to determine stability. Results of this work indicate the Vista 250 was superior to the Triton X-100 with respect to maintaining emulsion stability at high temperatures. The optimal surfactant concentration for creating 5% oil-in-water emulsions and maintaining their stability was found to be in the range of 50 to 300 ppm jar the surfactants used here. Recovery and steamflood behaviour were observed in an unscaled linear model containing an oil saturated single size sand. Comparative results using a heterogeneous model containing two parallel oil saturated sand beds of different permeabilities show early breakthrough and reduced recovery due to steam channelling. Externally prepared emulsion (5% oil content. 100 ppm Vista 250) was then injected to block the more permeable channels. Blockage was tested using the emulsion injected as a slug followed by steam and with the emulsion co-injected with steam. During slug injection the emulsion was injected at a constant pressure with a permeability reduction on the order of 90% inferred from a change in flow rate data, Emulsion slug injection was more effective with respect to improved blocking and recovery than was the co-injection of emulsion and steam for both heavy oils. The strategy behind this research was to examine from a mechanistic standpoint if the application of a stable heavy oil emulsion as a high temperature blocking agent would result in improved oil recovery in an unsealed physical model- No attempt was made to assess the economic viability of the process for implementation in the field. Laboratory assessment of the process for field implementation would require a scaled physical model. Currently, the integration of scaled emulsion criteria with scaled reservoir criteria for physical and numerical simulation poses a challenging problem. The authors believe this process would warrant further investigation for potential application to a heavy oil reservoir with a bottom water zone as well as stratified or heterogeneous reservoirs. Introduction In the application of steam injection to heterogeneous reservoir there is a tendency for steam and steam condensate to channel through high-permeability zones, thus leaving a significant amount of oil unrecovered. Many techniques have been proposed from controlled permeability reduction to outright plugging of channel zones through the use of blocking agents(1,2). However, to be successful the blocking agent must withstand the harsh environment associated with hightemperature steamflooding. The use of oil-in-water macroemulsions as the blocking agent for steamflood application is examined here.

Transient Stresses Induced in Sandbed by Wave Loading

Waves propagating over a permeable seabed will alter the stresses and fluid pressures within the bed and affect the erodibility and stability of bottom sediments. This paper examines the cyclic stresses which occur within a rigid bed subjected to wave loadings by means of a rational pseudo‐static approach. The results of this study suggest that wave loadings on a saturated sand bed can alter the effective stress state throughout the bed. Cyclic stress ratios are maximum at the sediment surface and decrease with sub‐bottom depth. Laboratory and field experimentation are needed to verify existing theories and to better understand the stressing mechanisms involved in this complicated problem.