Simplified-robust geotechnical design of soldier pile–anchor tieback shoring system for deep excavation

The shoring system that consists of soldier piles and anchor tiebacks is often used in deep excavations in sandy deposits. However, uncertainties often exist in the design of such shoring systems. In this article, a simplified-robust geotechnical design method is proposed to account for these uncertainties in the shoring system design. Specifically, for a given deep excavation, uncertain soil parameters and surcharges are treated as noise factors, and the parameters of soldier piles and tieback anchors are treated as design parameters. Robust design is then implemented as a multiobjective optimization problem, in which the design robustness is sought along with cost efficiency and safety requirements. A trade-off between design robustness and cost efficiency exists and the optimization usually leads to a Pareto front. By applying the knee point concept, the most preferred design that meets the safety requirements and yields the best compromise between design robustness and cost efficiency can be identified on the Pareto front. Improvements made to the existing robust geotechnical design method include an efficient formulation of the design robustness and a new procedure for finding the most preferred design in the design pool. The new simplified-robust geotechnical design method is illustrated with a real-world excavation case study.     

Development of the cyclic p–y curve for a single pile in sandy soil

Pile foundations that support transmission towers or offshore structures are dominantly subjected to cyclic lateral load induced by wind and waves. For a successful design, it is crucial to investigate the effect of cyclic lateral loads on the pile behavior that is loaded laterally. Although the p–y curve method is generally utilized to design the cyclic laterally loaded pile foundations, the effect of cyclic lateral loads on the pile has not been properly implemented with the p–y curve. This reflects a lack of consideration of the overall stiffness change in soil–pile interaction. To address this, a series of model pile tests were conducted in this study on a preinstalled aluminum flexible pile under various sandy soil conditions. The test results were used to investigate the effect of cyclic lateral loads on the p–y behavior. The cyclic p–y curve, which properly takes into account this effect, was developed as a hyperbolic function. Pseudo-static analysis was also conducted with the proposed cyclic p–y curve, which showed that it was able to properly simulate cyclic laterally loaded pile behavior in sandy soil.     

A method for detecting the breaking of wind-generated waves in deep water

The breaking of wind-generated waves is an important phenomenon in the ocean, having close relation to many aspects of the ocean, such as air-sea interaction, ocean wave dynamics, oceanic remote sensing and ocean engineering. The first problem encountered in both its theoretical study and practical measurement is how to detect the breaking of waves.     

The processes of semi-enclosed basin–ocean water exchange across a tidal mixing zone

To assess each of the two possible mechanisms responsible for the fortnightly modulation of semi-enclosed basin–ocean water exchange (‘density tides’), a set of numerical experiments is carried out using a vertically two-dimensional numerical model with realistic situations in Puget Sound in mind. It is found that, although the localized vertical viscosity (or the localized vertical diffusivity) enhanced in the entrance sill region primarily controls the bottom-water transport (or the bottom-water density) during spring tides, it does not lead to any appreciable variations of bottom-water density (or bottom-water transport). This indicates that the fortnightly modulation of vertical viscosity and that of vertical diffusivity both play important roles in creating density tides. In the real ocean, the vertical viscosity and diffusivity are enhanced simultaneously during spring tides, so that it is difficult to discriminate between both effects on density tides. This causes the widespread misunderstanding that density tides are mainly caused by the decreased advection of dense bottom-water from outside due to the enhanced vertical viscosity during spring tides.     

Time–frequency spectral signature of Pelotas Basin deep water gas hydrates system

Pelotas Basin has the largest gas hydrate occurrence of the Brazilian coast. The reserves are estimated in 780 trillion cubic feet, covering an area of 45,000 km². In this work we apply spectral decomposition technique in order to better understand a gas hydrate deep water system, performing a continuous time–frequency analysis of seismic trace, where frequency spectrum is the output for each time sample of the seismic trace. This allows a continuous analysis on the effects of the geologic structures and lithology over frequency content of the seismic wave. Spectral anomalies found were interpreted as variations of hydrates concentration inside the Gas Hydrate Stability Zone (GHSZ), as well free gas accumulations beneath and Below the GHSZ and gas chimneys. We concluded that this technique has a good potential to assist seismic study of structures associated with gas hydrates accumulations.     

Assessment of hydrodynamic competence in extreme marine events through application of Boussinesq–Green–Naghdi models

Here in present work, rotational Boussinesq–Green–Naghdi models were applied to assess the hydrodynamic intensity through the study of the boulder transport in east coast of Philippines during typhoon Haiyan and damage to coastal residences in New Jersey coast due to hurricane Sandy. The hydrodynamic forces were quantitatively analyzed and correlated to both boulder transport distance and the structural damage state in the two cases. The boulder transport was found initiated at vicinity of infragravity swash bores. Inertial force generated by the acceleration in front of the bore was found increasingly large as boulder sizes increased therefore far from negligible as in some other literatures. Besides, transport distances were highly sensitive to wave-heights and boulder sizes, so that onshore positions might be a viable approach of identifying rough magnitudes of paleostorm before other information is available. Fragility functions to predict the damage state of coastal residences due to runups was derived and preliminary validated. Water velocity and the shielding parameter were identified as major predictors of damage while free board and water depth are relatively insignificant. Due to the relative lack of wind damage observed, nearshore hydrodynamics featuring instantaneous nonhydrostatic impact might be the persistent cause of massive littoral processes and low-level structural failure in coastal regions during extreme marine events. Nonhydrostatic phase-resolving models such as Boussinesq-type models would be necessary complements for the intermediate-scale assessment of marine hazards in coastal ocean.     

Characterisation of nano magnesia–cement-reinforced seashore soft soil by direct-shear test

Abstract

In this study, the mechanical behaviour of nano magnesia–cement-reinforced seashore soft soil (NmC3S) was evaluated and characterised by the direct-shear testing of seashore soft soil (3S), cement reinforced seashore soft soil (C3S) and NmC3S. The comparison among these three types of soils indicates that NmC3S has greater shear strength and deformation modulus than C3S and 3S. The shear stress of both C3S and NmC3S increase significantly prior to a shear displacement of 1.0?mm, followed by a sharp decline before reaching the critical state. The failure displacement increases as the applied normal stress increases. NmC3S demonstrated greater friction angle than both C3S and 3S; however, the magnitude of its cohesion lies between that of C3S and 3S. Moreover, a mathematical model that describes the shear stress–displacement curve was proposed, which can effectively model the strain-hardening and strain-softening curves of these three types of clays. Finally, a generalised formula for capturing the stress–displacement behaviour of these three materials is presented with the explanations for the physical meaning of each parameter.     

Effect of sulphates and curing period on stress–strain curves and failure modes of soil–lime–natural pozzolana mixtures

Abstract

An experimental investigation was undertaken in order to assess the effect of sodium (Na₂SO₄) and calcium (CaSO₄·2H₂O) sulphates and curing period on stress–strain curves and failure modes of grey (GS) and red (RS) clayey soils stabilised by lime (L), natural pozzolana (NP) and their combinations (L–NP). Several soil–L–NP mixtures were studied to be used as subgrade soils for road pavements. Stress–strain curves were obtained from unconfined compressive strength (UCS) test made on several soil–L–NP specimens after curing for 7 and 120 days. Tests results showed that the use of L or L–NP without sulphates produced a significant increase in peaks stress of both clayey soils and then modified their stress–strain curves from nonlinear to linear behaviour almost up to 70% of peak stress after a longer curing period. However, the presence of 2% Na₂SO₄ or any CaSO₄·2H₂O content provided beneficial effects on peaks stress and stress–strain curves of both stabilised clayey soils and then improved their linearity almost up to 95% of peak stress after curing for 120 days. In contrast, the presence of 6% Na₂SO₄ caused undesirable effects. In addition, both sulphates greatly affected the failure modes of soil–L–NP specimens, particularly at a later stage.     

Evaluation of hydraulic conductivity through particle shape and packing density characteristics of sand–silt mixtures

Abstract

This study aims to evaluate the relationship between saturated hydraulic conductivity with particle shape and packing density characteristics of silty sand soils. The article presents a series of hydraulics tests performed on three kinds of sand with different particles shapes (Chlef rounded sand, Fontainebleau sub-rounded sand and Hostun sub-angular sand) mixed with low plastic rounded Chlef silt in the range of 0–30% fines content. The sand–silt mixture samples were tested in the constant-head permeability device at a loose relative density (D_r = 18%) and a constant room temperature (T?=?20?°C). The obtained results indicate that the measured saturated hydraulic conductivity (K_s) correlates very well with the fines content (F_c), packing density in terms of [maximum void ratio “e_max,” minimum void ratio “e_min,” predicted maximum void ratio “e_max”_pr and predicted minimum void ratio “e_min”_pr] and particle shape characteristics ratios in terms of roundness ratio (R_r = R_hs/R_mixture) and sphericity ratio (S_r = S_hs/S_mixture) of the silty sand materials under consideration. Moreover, the analysis of the available data show a noticeable success in exploring the prediction of the saturated hydraulic conductivity (K_s) based on the particle shape and packing density characteristics (R_r, S_r, e_max, and e_min) of the studied sand–silt mixture samples.     

A Technique for Photogrammetric Estimation of Albedo of Snow–Ice Surfaces

Izvestiya, Atmospheric and Oceanic Physics - New ways to improve the original technique for assessing the albedo of snow–ice surfaces with the use of ground measurements of incoming solar...     

Modelling of the bottom water flow through the Romanche Fracture Zone with a primitive equation model––Part 2: Comparison of vertical mixing parameterisations with observations

Three parameterisations of the vertical mixing of a primitive equation model that uses a geopotential coordinate system are tested against observations in the context of the Antarctic Bottom Water flow through the Romanche Fracture Zone. On an increasing complexity scale, the three parameterisations are a convection algorithm, a vertical diffusivity depending on a Richarson number, and a vertical diffusivity calculated from a turbulent kinetic energy (TKE) equation. The model uses a high vertical and horizontal resolution.It is shown that the convection algorithm does not produce enough vertical mixing compared to observations. This results in the propagation of a too dense water mass in the downstream basin. On the opposite, the Richardson number-dependent algorithm as well as the TKE algorithm produce a mixing comparable to the observations. With these two parameterisations, the main region of intensification of the vertical mixing is located downstream of the main sill that was also described as the major region of turbulence from observations. The mixing length of the TKE parameterisation is consistent with calculation of Thorpe scales from the fine structure of CTD data. Hence, the two successful parameterisations initially designed for the surface mixed layer also give satisfying results for overflows as soon as the hydraulic control and its associated downstream intensified vertical shear are correctly represented in the model.     

Algorithms for automatic,real-time tsunami detection in wind–wave measurements Part I: Implementation strategies and basic tests

Several, although not all, wind–wave gages are equipped with sensors capable of detecting sea-level oscillations within the tsunami frequency band. The present paper looks at the algorithms to be implemented in the software of these gages in order to automatically perform the real-time detection of a possible tsunami within recorded signals. In particular, a new algorithm is proposed and tested. The first part of the paper concentrates on the algorithms' characteristics, implementation strategies and basic testing. First of all, the situations in which wind–wave measurements are either essential, or useful for real-time tsunami detection are discussed. In the second place, already existing algorithms are recalled, specifying their characteristics and fields of application. Then, the characteristics of the new proposed algorithm – mainly based on an infinite impulse response, time domain filter – are illustrated and analyzed. Performance and efficiency of the considered algorithms are compared using synthetic time series. The second part of the paper discusses the algorithms' use in the framework of Tsunami Early Warning Systems (TEWS), testing them in actual cases.     

Proof of the equivalence of Tanizawa–Berkvens’ and Cointe–van Daalen's formulations for the time derivative of the velocity potential for non-linear potential flow solvers

Dealing with freely-floating bodies in the framework of non-linear potential flow theory may require solving Laplace's equation for the time derivative of the velocity potential. At present, there are two competing formulations for the body boundary condition. The first one was derived by Cointe [1] in 2D. It was later extended to 3D by van Daalen [2]. The second formulation was derived by Tanizawa [3] in 2D. It was extended to 3D by Berkvens [4]. In this paper, a proof is given that the Cointe–van Daalen's and the Tanizawa–Berkvens’ formulations are equivalent. It leads to a simplified version of Cointe–van Daalen's formulation. The formulation is validated against the analytical solution for a moving sphere in an unbounded water domain.     

Reanalysis of seasonal and interannual variability of Black Sea fields for 1993–2012

A retrospective analysis has been done for the hydrophysical fields of the Black Sea for 1993–2012 with the assimilation of undisturbed monthly average profiles of temperature and salinity that were obtained by using an original procedure of joint processing of satellite altimetry and rare hydrological observations. The accuracy of the reconstructed fields of temperature and salinity of the Black Sea is evaluated by comparison with the data of sounding from the hydrological stations and the Argo floats. A comparative analysis is performed for the integral characteristics of the fields of temperature, salinity, and kinetic energy with the same characteristics of the reanalysis for 1992–2012 that assimilated the average annual profiles of temperature and salinity, surface temperature and altimetry level of the sea after being adjusted with respect to climate seasonal variability. The proposed procedure of the reanalysis execution allows a more precise reconstruction of the interannual variability of temperature and salinity stratification in the main pycnocline. The correlation between the annual and seasonal variability of the eddy of the wind friction tangential stress and the average kinetic energy at the levels is revealed.     

A Eulerian–Lagrangian method for the simulation of wave propagation

A Eulerian–Lagrangian method (ELM) is employed for the simulation of wave propagation in the present research. The wave action conservation equation, instead of the wave energy balance equation, is used. The wave action is conservative and the action flux remains constant along the wave rays. The ELM correctly accounts for this physical characteristic of wave propagation and integrates the wave action spectrum along the wave rays. Thus, the total derivative for wave action spectrum may be introduced into the numerical scheme and the complicated partial differential wave action balance equation is simplified into an ordinary differential equation. A number of test cases on wave propagation are carried out and show that the present method is stable, accurate and efficient. The results are compared with analytical solutions and/or other computed results. It is shown that the ELM is superior to the first-order upwind method in accuracy, stability and efficiency and may better reflect the complicated dynamics due to the complicated bathymetry features in shallow water areas.     

A parameterization of ice shelf–ocean interaction for climate models

Model results from a regional model (BRIOS) of the Southern Ocean that includes ice shelf cavities and the interaction between ocean and ice shelves are used to derive a simple parameterization for ice shelf melting and the corresponding fresh water flux in large-scale ocean climate models. The parameterization assumes that the heat loss and fresh water gain due to the ice shelves are proportional to the difference in freezing temperature at the ice shelf edge base and the oceanic temperature on the shelf/slope area of the adjacent ocean as well as an effective area of interaction. This area is proportional to the along-shelf width of ice shelf and an effective cross-shelf distance, which turns out to be rather uniform (5–15 km) for a variety of different ice shelves. The proposed parameterization is easy to implement and valid for a wide range of circumstances. An application of the proposed scheme in a global ice ocean model (CLIO) supports our hypothesis that it can be used successfully and improves both the ocean and sea ice component of the model. This parameterization should also be used in models of the climate system that include a coupling between an ice sheet and an oceanic component.     

Seeing the ocean through the eyes of seabirds: A new path for marine conservation?

Seeing the ocean through the eyes of seabirds could help meet the challenges of managing common-pool marine resources both in protected and unprotected areas. First, seabirds are top-predators, exposed to all threats affecting the oceans, and this makes them ideal sentinel organisms for monitoring changes within marine ecosystems. Second, seabirds cross both ecological and political boundaries, and following their movements should help making interdependencies within and between marine ecosystems more visible. Third, seabirds are conspicuous and often charismatic animals, which interact differently with different groups of stakeholders and provide the opportunity to acknowledge and discuss each other's values and interests. In this paper, we present these research avenues using a seabirds’ view, for tackling marine conservation and management issues, and we give operational examples of implementation based on our work in the English Channel.     

Application of Remote-Sensing Observations for Detecting Patterns of Localization of Cu–Ni Mineralization of the Norilsk Ore Region

Izvestiya, Atmospheric and Oceanic Physics - The methods of a complex analysis of materials of space, gravimetric, and magnetometric surveys were developed on the basis of a study of reference...