Sand Load Research Articles

Lateral Performance for Long Pile Subjected to Simultaneous Axial and Lateral Loads in Dense Sand: An Experimental Study

The present study focus on the investigation ofthe response of single pile when subjected to both axial and lateral loads simultaneously in dense sand. To study this issue, laboratory model was locally improved to examine the piles under this kind of loading. The dense sand provided using raining technique. The slenderness ratio of the tested pile is ( L/D=45). On the other hand, the vertical and horizontal loads are divided into 5 stages to assess the influence of load intensities on the lateral pile response. It can be concluded that the lateral pile response is affected by changing the load intensities

Combined loading capacity of skirted circular foundations in loose sand

Skirted foundations are an attractive foundation concept in the offshore energy sector, both for wind turbines and oil and gas platforms. Most of the evidence of skirted foundation behaviour under combined vertical, horizontal and moment (VHM) loading in sand has been collected from small-scale model experiments conducted at unit gravity on the laboratory floor. This paper presents results from a series of centrifuge experiments of skirted foundations on loose silica sand at relevant prototype stress levels. The vertical load-penetration curve is shown to be predicted well using established analytical methods. Centrifuge modelling results provide experimental evidence of the complex effects of the interaction of skirt aspect ratio and relative stress level on the VHM yield surface. A conservative and design-oriented solution based on the yield envelope approach describes available foundation capacity within the established framework of strain-hardening plasticity theory.

Erosion and corrosion resistance of plasma electrolytic oxidized 6082 aluminum alloy surface at low and high temperatures

This paper embodies the findings of a study on improving the surface tribology of Al alloy 6082-T6 through plasma electrolytic oxidation (PEO) process. The surface macro/microstructure and composition were investigated. Electrochemical measurements were performed at temperatures of 20 and 80°C using an inductively coupled plasma and open circuit potential tests after immersion in 3.5%NaCl solution. The erosion tests were performed with water carrying sand particles at different sand loadings (200 and 1000mg/l) and temperatures (20 and 80°C). After erosion experiments, the weight loss measurements were recorded, and the worn surfaces were assessed through SEM study and profilometry analysis. The micro-hardness of the coated layer and the substrate were measured before and after the erosion test. The formed PEO layer of 40μm thick was almost sound, uniform, well adhered to the substrate and consisted mainly of alumina phases (α-Al2O3, γ-Al2O3). The relative proportions of α-Al2O3 to γ-Al2O3 were 31: 79%. The PEO coating shows much better corrosion and erosion resistance and less surface damage compared to the aluminum substrate, especially at elevated temperature and high sand loading. The PEO hardness increases as the distance from the substrate increases until near the middle of the coating.

Islands of the upper River Ob: morphometric characteristic, evolution and dynamics

The studied reach of the upper River Ob is quite complicated in the morphological aspect and characterized by very low channel stability and high discharge of sand load. Unconstrained conditions for lateral channel migration promotes active channel deformations not only at long-term scale, but also seasonally. Channel deformations contribute to the transformation of the channel and its morphodynamic type in time. The upper River Ob is intensively used as a water course, so any reorganization of the channel and river islands should be taken into account to support navigation.
 Morphometric and morphodynamic analysis of the islands made it possible to develop their morphological classification. Morphometric parameters of islands, being associated with the characteristics of the channel itself, are one of the main classification features. Empirical relations were obtained that link the dimensions (Lo, Bo) and shape of islands (Lo/Bo) with the morphodynamic channel type and its stability, the degree of branching of the channel (number of islands no per 1 km of channel length x). The features of island dynamics are also determined by the morphodynamic type of the channel and are associated with the morphometric characteristics of the islands themselves and their position in the channel, which determines the transgressive, regressive and transverse shift or their stable position in time.

Empirical approach based on centrifuge testing for cyclic deformations of laterally loaded piles in sand

A systematic study into the response of monopiles to lateral cyclic loading in medium dense and dense sand was performed in beam and drum centrifuge tests. The centrifuge tests were carried out at different cyclic load and magnitude ratios, while the cyclic load sequence was also varied. The instrumentation on the piles provides fresh insights into the ongoing development of net stresses, bending moments and deflections as cycling progresses. Parallels between the test results and corresponding cyclic triaxial tests are drawn. The paper combines the results from this study with those from previous experimental investigations to provide empirical design recommendations for monopiles subjected to unidirectional cyclic loading.

Sandbraking. A technique for landing large payloads on Mars using the sands of Phobos

The basis of a novel braking technique by using the Phobos sands for landing large payloads on Mars is outlined. Here consideration is given to the utilization of the Phobos or Deimos regolith as material for aerobraking by discharging a load of sand at certain distance in front of the spacecraft during the descent manoeuver. Although immediately after getting rid the load of sand in front of the spacecraft they have a null relative velocity with the spacecraft, however, because the stronger atmospheric drag acting on the tiny particles of sand they will be promptly decelerated. As a result, the particles of sand will impact onto the front of the spacecraft with a velocity close to the terminal velocity of the spacecraft itself. By using a pusher-disc – or akin damping system, in front of the spacecraft the momentum exchange from the sand collisions will result in a braking force acting on the spacecraft. Due to the very small delta-v budget required to lift material from the surface of Phobos or Deimos to their transfer orbits, then a small amount of dedicated rocket chemical propellant brought from Earth could be transformed into a huge amount of sand lifted from the surface of Phobos of Deimos to their transfer orbits. The large thrust generated by the Sandbraking makes this technique propitious for landing of planetary bodies struggling against gravity.

A multi-technique approach for evaluating sand dynamics in a complex engineered piedmont river system

A multi-technique approach is proposed to study sand dynamics in an engineered piedmont river. Only a few studies focused on such systems and innovative methodological protocols still need to be designed to better understand sand transport in piedmont rivers where bedload dynamics has been largely modified with nowadays a residual sand transport on a fixed gravel matrix. The proposed methodology is based on an analysis of bathymetry and turbidity measurements and on modelling, including the development of sediment rating curves and 2D numerical modelling, and using sediment budgeting for cross-validation. Its application to the Isère-Rhône confluence (France) provided some insights of sand fluxes in this complex river system where few sediment flux data are available. Indeed, a substantial amount of sand sporadically reaches the downstream part of the Isère River because of the presence of a series of dams, and jeopardizes navigation and flood management at the confluence. Based on the analysis of the 2015 flushing event, it was found that the sediment transport capacity was reached during the event whereas sand supply can be considered as null when dam bottom gates are closed. Suspended load of sand was prevailing downstream of the last dam but quickly settled down at the confluence. The sand deposit was eventually evacuated from the confluence during the small floods occurring after the flushing event with a minimum discharge of approximately 500 m3/s in the Isère River and 1000 m3/s in the headrace canal of the Rhône River. The presented methodology can be transferred to other sites with similar issues.

Behavioural analysis of vertical and batter pile groups under vertical and lateral loading in sand

Laboratory model tests were carried out to study the behaviour of vertical piles and batter pile groups under vertical and lateral load. The model pile groups were made up of mild steel rod of 8-mm diameter. Parameters such as degree of batter and different length to diameter ratios of 7.50, 15.00 and 22.50 were considered in this study. The size of the model tank was 1000 mm × 1000mm × 800 mm. Experiments were performed on 3 × 3 model pile groups with a row of batter piles both positive and negative in addition to vertical pile groups with batter angle 0° in sandy soil subject to vertical and lateral loads. It was observed that the behaviour of vertical pile groups and group of piles with batter piles were similar but it showed substantial variation in the capacity of pile groups. Results indicated that the load–settlement relationships were non-linear for all model pile groups both under vertical and lateral loading. Numerical FEM analysis using ABAQUS/CAE 6.11 was also used to compare and validate the load carrying capacity of pile groups obtained from the experimental model tests.

The response of suction caissons to multidirectional lateral cyclic loading in sand over clay

Offshore wind turbines and their foundations experience loading from varying directions, yet understanding of the effect of changes in the direction of applied cyclic loading on foundation response remains limited. This study investigates the behaviour of a suction caisson foundation in sand over clay under various types of multidirectional cyclic loading. The findings are significant: although the caisson rotation (or tilt) is affected by changes in load direction, the caisson rotation is less than that in a unidirectional test with the same cyclic load magnitude and symmetry, meaning that a unidirectional test may serve as a conservative estimate of caisson rotation for multidirectional loading. This contrasts with previous findings for monopiles in sand, where prediction of the accumulated displacement based on unidirectional cyclic loading was substantially un-conservative for multidirectional loading. Changes in unloading stiffness due to changes in load direction are slight, varying by an amount that is no greater than the change measured over the course of a unidirectional test. Foundation stiffness and ultimate capacity following multidirectional cyclic loading are largely unaffected, unlike unidirectional cyclic loading, where consolidation of the clay layer improves both the stiffness and capacity.

Long‐Term Evolution of Sand Transport Through a River Network: Relative Influences of a Dam Versus Natural Changes in Grain Size From Sand Waves

AbstractTemporal and spatial nonuniformity in supplies of water and sand in a river network leads to sand transport that is in local disequilibrium with the upstream sand supply. In such river networks, sand is transported downstream as elongating waves in which coupled changes in grain size and transport occur. Depending on the magnitude of each sand‐supplying event and the interval between such events, changes in bed‐sand grain size associated with sand‐wave passage may more strongly regulate sand transport than do changes in water discharge. When sand transport is controlled more by episodic resupply of sand than by discharge, upstream dam construction may exacerbate or mitigate sand‐transport disequilibria, thus leading to complicated and difficult‐to‐predict patterns of deposition and erosion. We analyzed all historical sediment‐transport data and embarked on a 4‐year program of continuous sediment‐transport measurements to describe disequilibrium sand transport in a river network. Results indicate that sand transport in long river segments can evolve over ≥50‐year timescales following rare large sand‐supplying events. These natural changes in sand transport in distal downstream river segments can be larger than those caused by an upstream dam. Because there is no way to know a priori whether sand transport in a river has changed in response to changes in the upstream sand supply, contemporary continuous measurements of sand transport are required for accurate sand loads and budgeting. Analysis of only historical sediment‐transport measurements, as is common in the literature, may lead to incorrect conclusions with respect to current or future sediment‐transport conditions.

Mapping and measuring aeolian sand dunes with photogrammetry and LiDAR from unmanned aerial vehicles (UAV) and multispectral satellite imagery on the Paria Plateau, AZ, USA

The Paria Plateau is a potentially important but relatively unstudied aeolian sand source area in the Grand Canyon region of Arizona, USA. This study used unmanned aerial vehicle (UAV) - based LiDAR and structure-from-motion (SfM) photogrammetry to produce high-resolution topographic models of aeolian dunes on the plateau. We combined the dune topography data with a high-resolution satellite image maximum likelihood classification (producer's accuracy = 87.2%) to quantify potential aeolian sand source areas across the 958 km2 plateau. We mapped all the unvegetated active aeolian dunes on the plateau and estimate they contain 24 Tg of sand, and could, therefore, be a proportionately important regional sand source considering the annual sand loads of the downwind Paria River at its confluence with the Colorado River are generally <1 Tg. The results and data from this study could be useful for future investigations that wish to explicitly link aeolian sand on the Paria Plateau to downwind sediment dynamics in the region. The methodology for UAV and satellite remote sensing that we demonstrate could be applied to quantify sand at large geographic extents in other aeolian environments around the world.

Development of Test Equipment for Evaluating Hydraulic Conductivity of Permeable Block Pavements

The use of permeable block pavement has been acknowledged as one of the promising Low Impact Development (LID) strategies to mitigate the harmful effects of depletion of natural surfaces, due to the uncontrollable development of infrastructure and buildings. Numerous studies, associated with drainage properties and long-term performance of this traditional pavement alternative, have been conducted in the past 30 years. Nevertheless, standardized equipment and methodologies are still limited, specifically for small-scale laboratory models. This paper suggests equipment that is capable of evaluating the hydraulic performance of permeable pavement materials in a laboratory set-up, by monitoring permeability and simulating the physical clogging process. Constant head permeability tests with systematic application of fine clogging particles were conducted on three identical permeable block systems (PBS), composed of four stone pavers. Each test system received an equivalent amount of eight years’ particle loading of silica sand, with different size distributions. The experimental results revealed that all the models showed permeability degradation trends similar to those presented in other literature.

Near-ground impurity-free wind and wind-driven sand of photovoltaic power stations in a desert area

The ground mounted photovoltaic panel in desert areas is one of the best methods to get the solar energy. Unfortunately, there are no existing wind codes and standards to show the effect of impurity-free wind loads and wind-driven sand loads on ground mounted photovoltaic panels. It is necessary to investigate the characteristics of the impurity-free wind and wind-driven sand flow in desert areas. The characteristics of mean and fluctuating wind data are obtained from a 10 m-high tower set up in a desert photovoltaic power station, Zhongwei, China. The wind-driven sand flow fields in sandstorm climate are built to obtain the sand concentration profile and the impact pressure profile of sand particles using the wind tunnel testing. The sand concentration decreases exponentially with height under the lower wind speed and appears in the form of reverse “S” when the wind speed increases. The sand particles movement in the wind-driven sand flow reduces the wind speed and increases the turbulence intensity. To improve the output power and service life of photovoltaic panels in sandstorm climate, it is recommended that the installation height of photovoltaic panels should be 2 m.

Simplified p-y curves under dynamic loading in dry sand

The behavior of soil-pile systems subjected to dynamic loads in dry sand was investigated using experimental tests. The focus of this study was to quantify the simplified dynamic p-y curve for pseudo-static analysis from model tests under various loading frequencies. A framework for determining the p-y curve on the basis of 1 g shaking table tests was introduced. Based on the results of the model tests, the dynamic p-y curve is highly dependent on the relationships between the natural frequency of the soil-pile system and the loading frequency, the acceleration amplitude and the relative density of soil. The simplified dynamic p-y curve is a hyperbolic function. The initial slope and the ultimate soil resistance were proposed as functions of the properties of the pile and soil. The proposed p-y curves were determined to be more appropriate than the existing p-y curves for representing the soil-pile interaction for a single pile under dynamic loads in dry sand.

Effect of embedment on the vertical capacity of bucket foundation in loose saturated sand: Physical modeling

ABSTRACTBucket foundations have been widely used for a variety of offshore applications. The effects of skirt length on ultimate bearing capacity of bucket foundation have been studied and reported in published scientific papers. However, few studies have addressed the behavior of bucket foundations in loose saturated sand. In this paper, a series of experimental investigations were performed to determine the bearing capacity of bucket foundation under uniaxial loading. The experiments were conducted on small-scale foundations under vertical loading in loose saturated sand. It was found that increasing the skirt length would enhance the bearing capacity of bucket foundation. As reflected in the present study, bearing strength might be enhanced more than 5 times in loose saturated sand in comparison to surface footing with equivalent diameter. Based on the experimental investigation, a depth factor was proposed to approximate bearing capacity of bucket foundations in terms of those for surface footing and embedment ratio. Moreover, the corresponding settlement of foundation at the failure load was found to increase with skirt length.

Front of unimpeded infiltrated sand moving as sediment transport through immobile coarse gravel

ABSTRACTA simple model for the front of unimpeded infiltrated sand, moving as sediment transport through immobile coarse gravel particles is proposed. The theoretical celerity of the front computed by the model matched the celerity in novel experiments made in a laboratory flume. The dimensionless infiltrated sand load through gravel, estimated from the present experiments and published data, is a function of the Shields parameter and the ratio of the sand front height minus the gravel height to the gravel diameter. No effect of the ratio of sand and gravel diameters was observed. Finally, the experimental bed resistance relationship changes from hydraulically macro-rough of the gravel particles, when the infiltrated sand front is much less than the gravel layer, to a mixture of the sand and gravel roughness, when the sand layer is on the same order of magnitude of the gravel. A new resistance law is proposed.

Improved trade-offs of hydropower and sand connectivity by strategic dam planning in the Mekong

Dams in the Mekong Basin are mostly planned project-by-project and without strategic analysis of their cumulative impacts on river processes such as sediment connectivity. We analyse missed and future opportunities for reducing hydropower impacts on sediment connectivity through strategic planning of dams in the Se Kong, Se San and Sre Pok (‘3S’) tributaries of the lower Mekong, which are critically important as a source of sand for the Mekong Delta. With strategic planning, 68% of the hydropower potential of the 3S Basin could have been developed while trapping 21% of the basin’s sand load. The current dam portfolio resulting from project-by-project planning uses 54% of the hydropower potential while trapping 91% of the sand load. Results from the 3S demonstrate that strategic network-scale planning is crucial for developing lower-impact hydropower, a relevant finding given the at least 3,700 major dams that are proposed worldwide. Dams in the Mekong Basin are built without considering impacts on river processes. This study shows that with strategic planning in the lower Mekong, 68% of the basin’s hydropower potential could have been developed while trapping 21% of the basin’s sand load.

The response of suction caissons to long-term lateral cyclic loading in single-layer and layered seabeds

Suction caissons are being increasingly considered as an alternative foundation type to monopiles for offshore wind turbines. Single caisson foundations (or monopods) for offshore wind turbines are subjected to lateral cyclic loading from wind and waves acting on the structure. Recent studies have considered the response of suction caissons to such loading in sand, but have generally been limited to a few thousand cycles, whereas offshore wind turbines will generally experience millions of loading cycles over their lifetime. This paper presents the results from a programme of caisson tests in sand, clay and sand over clay seabed profiles, where each test involved about one million cycles of lateral load. The capacity and rotation response is shown to approach that measured in the sand seabed when the sand–clay interface is located at or beneath the caisson skirt tip. In contrast to previously published studies in sand, one-way cyclic loading is the most onerous loading symmetry for a layered seabed with a sand thickness equal to half the skirt length. However, the rotation for this seabed profile is essentially identical if the load is sustained or cyclic, provided that the cyclic loading remains one way. Lateral cyclic loading was seen to increase caisson capacity by up to 30% – with a bias towards clay-dominated seabed profiles – and stiffness by up to 50%. Such stiffness increases need to be considered when assessing the system dynamics for the offshore wind turbine, as demonstrated in the paper.

Sand erosion of solar glass: Specific energy uptake, total transmittance, and module efficiency

Surface roughness, RZ, normal transmittance, ΤN, total transmittance, ΤT, and photovoltaic (PV) module efficiency, ηS, were measured for commercial solar glass plates and PV test modules identically sandblasted with different loads of quartz sand (200–400 μm), impact inclination angles, and sand particle speed. Measured data are presented versus the specific energy uptake during sand blasting, E (J/m2). Cracks, adhering particles, and scratch-like textures probably caused by plastic flow phenomena could be observed after sand blasting. Their characteristic size was much smaller than that of sand particles. After blasting and subsequent cleaning, the glass surface was still covered with adhering glass particles. These particles, cracks, and scratch-like textures could not be removed by cleaning. For sand blasting with α = 30° inclination angle and E = 30 000 J/m2, normal transmittance, total transmittance, and relative module efficiency decreased by 29%, 2% and ∽2%, respectively. This finding indicates that diffusive transmission of light substantially contributes to PV module efficiency and that the module efficiency decrease caused by sand erosion can be better estimated from total than by normal transmittance measurements.

Analysis of laterally loaded bucket foundation with external skirt in sand using a Winkler model approach

An investigation is made to present analytical solutions provided by a Winkler model approach for analysis of a bucket foundation with external skirt subjected to lateral loads in sand. The bucket foundation with external skirt consists of an internal compartment and an external short skirted compartment. The lateral stiffness coefficient along the skirt of the bucket foundation in nonhomogeneous soils employing the Mindlin solution for lateral loads is presented. The relationship between horizontal displacement, rotation, moment and shear force of the bucket foundation subjected to lateral loads in nonhomogeneous soils is obtainable in the form of the recurrence equation. The vertical, lateral and rocking stiffness coefficients on the base of the bucket foundation are presented considering the solutions of a hollow rigid cylindrical punch acting on the surface of a soil. An envelope of the combined ultimate horizontal and moment load capacities of the bucket foundation in sand is shown. The relationship between ultimate lateral and moment load capacities and aspect ratios (internal and external skirt-lengths to diameter) is presented. Behavior of the bucket foundation with external skirt in sand up to failure is clarified from the relationship between lateral loads and displacement and that between depth and lateral pressure.