Sand Containers Research Articles

Physical Model Studies on Stability of Geotextile sand Containers

Coast parallel submerged breakwaters made of Geotextile Sand Containers (GSCs) are increasingly being incorporated into coastal management solutions because of their cost effective and environmentally friendly characteristics. These reduce the wave action on the lee side by forcing wave breaking and their stability is a function of the relative crest width, crest height, and the damage. The present work involves a physical model study on 1V:2H sloped trapezoidal submerged reefs constructed with 485 gm GSCs with different alignments like Perpendicular, Parallel, and Flemish. They have a height (h) of 0.25 m and varying crest widths (B) and are tested for stability for wave heights (H) of 0.1 m and 0.12 m and wave periods (T) of 1.5 s to 2.5 s in a water depth (d) of 0.3 m.

Research on Reclamation and Activation of Moulding Sands Containing Water-Glass Hardened with Microwaves

Abstract Presented are results of a research on usability of an innovative reclamation process of microwave-hardened moulding sands containing water-glass, combined with activation of binder. After each subsequent stage of reclamation, quality of the reclaimed material was determined on the grounds of measurements of permeability and results of screen analysis. The reclaimed material was next used again to prepare new moulding sand. The sandmix based on high-silica sand prepared with water-glass grade 145, was subject to the following cyclical treatment operations: mixing components, consolidation, microwave hardening, cooling, heating the mould up to 800 °C, cooling to ambient temperature, mechanical reclamation dry and wet. It was found that the used-up and reclaimed sandmix containing water-glass is susceptible to the applied activation process of thermally reacted film of binder and, in addition, it maintains good quality and technological properties of high-silica base. Observations of surfaces of reclaimed high-silica grains with activated film of reacted inorganic binder were carried-out using a scanning microscope. Thanks to properly selected reclamation parameters, the high-silica base can be reused even five times, thus reducing demand for fresh aggregate and inorganic binder.

HYDRAULIC STABILITY OF COASTAL STRUCTURES MADE OF GEOTEXTILE SAND CONTAINERS (GSCS): EFFECT OF ENGINEERING PROPERTIES OF GSCS

Due to their numerous advantages, Geotextile Sand Containers (GSCs /or Geobags) are getting increasingly popular as an alternative to conventional hard (rock / concrete) structures. This study attempts to evaluate the significance of the most important engineering properties and their influence on the hydraulic stability of GSC-structures. The most important engineering properties of GSCs are the mechanical properties of the geotextile material, the sand fill ratio, type of the fill material, the interface friction, etc. In fact most of these properties will affect the deformation of GSCs and the movement of sand inside the container. More importantly, these properties are interrelated. The importance of these aspects has been highlighted in many studies and projects worldwide. However, the knowledge about the influence of the sand fill ratio, the properties of fill material and the interface friction of GSCs on the hydraulic stability of GSC-structure is still very poor. Therefore, a series of experimental investigations were conducted, in order to better understand their effect on the hydraulic stability and to develop a computational tool and simple formulae for the hydraulic stability of different types of GSC-structures subject to different wave conditions. This paper contains some selected findings from these experimental investigations, which were performed at Leichtweiss-Institute for Hydraulic Engineering and Water Resources (LWI). Furthermore, the sensitivity of each GSC property on the hydraulic stability and new hydraulic stability nomograms are presented, including the implications for the engineering practice.

INVESTIGATIONS ON SCOUR DEVELOPMENT AROUND A GRAVITY FOUNDATION FOR OFFSHORE WIND TURBINES

Due to insufficient insights about the scour development around the STRABAG gravity foundation, the Franzius-Institute conducted small- and large-scale physical model tests in wave flumes on a scale of 1:50 and 1:17 in order to investigate the wave-induced scouring phenomena around the foundation and to design a scour protection system. The tests on scour development without a scour protection system show that the main areas which are vulnerable to scour are the contact areas of the foundation. Furthermore, the experiments show that a scour protection system is necessary for the given and investigated wave boundary conditions; the performance of the selected protection system using geotextile sand containers is verified. Additional numerical simulations indicate an amplification of the resulting flow around the foundation under combined loads (waves and current), but without significant change of the flow pattern

Hydraulic Stability of Submerged GSC structures

Geotextile Sand Containers (GSCs) are used for the construction of coastal structures as a low cost and softer alternative to expensive and hard structures made of concrete or rubble. However, the hydraulic stability of GSC-structures still needs to be investigated for a better understanding of the processes and the parameters of GSCs, which cause the failure. This study focused on the effect of the geotextile material, the sand fill ratio, and the inclination in GSC placement towards the hydraulic stability of submerged GSC structures. Four sets of specifically designed laboratory model experiments were carried out to study the influence of aforementioned parameters on the GSC stability. A new failure mode of GSCs was identified through the model experiments and named as “uplift and drift”. From the test results (wave and damage analysis), new stability curves were developed and compared with each test scenario. The influencing parameters were quantified and the relative importance of each parameter for the hydraulic stability of submerged GSC structures was assessed. Finally, it was concluded that the sand fill ratio is the key influencing parameter among all considered parameters. For the tested sand fill ratios, the hydraulic stability increases, when the sand fill ratio increases. Furthermore, it was concluded that the stability of inclined GSCs is higher than horizontally placed GSCs. However, stability decrement was concluded for GSC made from the woven geotextile material comparative to the nonwoven GSCs. Hence, the type of the geotextile material and the inclination of GSC placement were found to be two important aspects that need to be considered, when designing GSC-structures.

Engineering Properties of Geotextile Sand Containers and Their Effect on Hydraulic Stability and Damage Development of Low-Crested / Submerged Structures

Despite the considerable development of Geotextile Sand Container (GSC) technology, no proper design guidelines are yet available for the design of GSC-structures on a sound scientific base. This on-going research study aims to focus on developing simplified formulae and a computational tool for the design of GSC-structures. The significance of important engineering properties including the type geotextile material, the sand fill ratio, the interface friction, and their influence on the hydraulic stability of GSC-structures will also be evaluated. For this purpose and in order to better understand the effects of these properties on the hydraulic stability of GSC-structures, a series of systematic laboratory experiments were conducted. In this paper some of the most important findings are discussed, including the implications for the design practice.

Evaluation of the efficiencies of helical anchor plates in sand by centrifuge model tests

The uplift capacity of helical anchors normally increases with the number of helical plates. The rate of capacity gain is variable, considering that the disturbance caused by the anchor installation is generally more pronounced in the soil mass above the upper plates than above the lower plates, because the upper soil layers are penetrated more times. The present investigation examines the effect of the number of helices on the performance of helical anchors in sand, based on the results of centrifuge model tests. Uplift loading tests were performed on 12 different types of piles installed in two containers of dry sand prepared with different densities. The measured fractions of the uplift capacity related to each individual helical plate of multi-helix anchors were compared with the fractions predicted by the individual bearing method. The results of this investigation indicate that in double- and triple-helix anchors, the contributions of the second and third plate to the total anchor uplift capacity decreased with the increase of sand relative density and plate diameter. In addition, these experiments demonstrated that the variation of the anchor load–displacement behavior with the number of helices also depends on these parameters.

Liquefaction Resistance of Sands Containing Plastic Fines with Different Plasticity

Soils in the field or at reclaimed sites commonly contain some amount of silt or clay rather than clean sand only. The effect of a low fraction of plastic fines within sand matrix on liquefaction resistance is not clearly understood. In this study, clean sand was mixed with 10% plastic fines having different plasticity indexes (PIs), and the effect on liquefaction resistance was evaluated in terms of cyclic stress ratio. A series of undrained cyclic triaxial tests were carried out on loose, medium, and dense specimens that were reconstituted in the laboratory by the undercompaction method. The results showed that liquefaction resistance tended to decrease as the PI of 10% fines in the specimens increased. Liquefaction resistance of loose specimens was marginally influenced by the plasticity of fines. However, in the case of dense specimens, liquefaction resistance decreased up to 40% as the PI of 10% fines increased. It was shown that even though a low fraction of plastic fines was included within sand matrix, it still had a significant effect on the liquefaction resistance of sandy soils.

Technology of Sand Level Detection Based on CCD Images

Heavy oil takes advantage of proportion in world petroleum resources. Thermal recovery technology, the chief means of heavy-oil exploitation, has been widely applied in development of world heavy-oil reservoir. To study the effect of sand-control technology in the process of heavy-oil thermal recovery, A HTRSTS (Heavy-oil Thermal Recovery Simulation Testing System) has been build. The detection of sand level in sand container is very important. The sand level detection technology adopted in this system is image processing technique based on CCD. Sand container image is taken by CCD, and then HTRSTS locks the interface between sand and liquid through CCD scanning. The preliminary experimental result shows that the standard deviation is about 0.02 liter, which could satisfy practical requirement quite well.

Measurement of Small-Strain Shear Moduli of Partially Saturated Sand During Infiltration in a Geotechnical Centrifuge

Abstract This paper describes the use of bender elements to measure changes in small strain shear modulus, Gmax, of sand layers due to the change in degree of saturation during centrifuge tests. The goal of the measurements is to verify that steady-state infiltration is an appropriate technique to control the effective stress in centrifuge physical modeling of partially saturated sands. Specifically, the suitability of infiltration is assessed by checking if the measured values of Gmax of partially saturated sand layers follow a similar trend to dry and saturated sand layers when the effective stress is defined from the suction and degree of saturation profiles during steady-state infiltration. Three pairs of bender elements were installed at different depths in a container of Ottawa sand, and the shear wave velocities of the sand were measured during steady-state infiltration into the sand layer. The applied infiltration rate was varied to obtain different uniform distributions of degrees of saturation with depth. Consistent with results from suction-controlled resonant column tests performed on the same sand, the values of Gmax measured from the bender element tests varied nonlinearly with degree of saturation with a peak value at a degree of saturation between 0.3 and 0.4. When interpreted in terms of mean effective stress, the values of Gmax from the bender element tests on partially saturated sands followed a unique trend consistent with measurements for dry and saturated sands.

Geotextile sand container shoreline protection systems: Design and application

The use geotextile sand containers (GSCs) as shoreline protection systems, has grown moderately since the first applications in the 1970s. This slow growth can be attributed to two factors; firstly, the lack of understanding of coastal processes and design fundamentals by the larger geosyntheticcommunity in order to provide coastal engineers with suitable solutions, and secondly; there has been very little rigorous scientific wave flume testing with which to analyse the wave stability of geotextile sand containers. The application of geotextile containers in coastal protection works can be traced back to early works carried out in 1970s. The application of these types of structures was somewhat haphazard as very little was understood about the wave stability and durability of the structures. Early wave stability work was carried out Ray (1977) and Jacobs (1983) with small containers, however, the testing programs were limited and did not provide sufficient confidence in the product to carry out exhaustive engineering design. As a result, the technology until recently has relied on manufacturers’ design suggestions based on monitoring of actual structures. Over the past five years, coastal population pressure, extreme events and concerns over climate change and sea level rise have resulted in more emphasis being placed on shoreline protection systems. Geotextile manufacturers have responded to the challenges put forward by design engineers and intensive research has been carried out in the field. This paper outlines the current “state of the art” in terms of the design and specification of geotextile sand containers (GSC). This paper covers the key issues which will ensure the long term integrity of a geotextile shoreline protection system is maintained, these issues include: • Container stability; • Detailed analysis of recent large scale wave flume testing which assess filling capacity, size of container, structure slope and scour protection etc.; • Container/geotextile durability; • Methods and specifications used to limit the effects of the fundamental factors affecting the life span of geotextile containers such as vandal resistance, UV degradation and abrasion resistance etc.

Core made of geotextile sand containers for rubble mound breakwaters and seawalls: Effect on armour stability and hydraulic performance

A systematic armour stability and the hydraulic performance, including wave reflection, wave transmission, experimental study in the twin-wave flumes of Leichtweiss-Institute (LWI) is performed on a geocore breakwater and a conventional rubble mound breakwater in order to comparatively determine the wave run-up and wave overtopping. The geocore breakwater consists of a core made of sand-filled geotextile containers (GSC) covered by an armour made of rock. The geocore is more than an order of magnitude less permeable than the quarry run core of a conventional breakwater. As expected, the core permeability substantially affects the armour stability on the seaside slope, the wave transmission and the wave overtopping performance. Surprisingly, however, wave reflection and hydraulic stability of the rear slope are less affected. Formulae for the armour stability and hydraulic performance of the geocore breakwater are proposed, including wave reflection, transmission, run-up and overtopping.

Greywater reuse for irrigation: Effect on soil properties

A controlled study of the effect of greywater (GW) irrigation on soil properties was conducted. Containers of sand, loam and loess soils were planted with lettuce, and irrigated with fresh water, raw artificial GW or treated artificial GW. Greywater was treated using a recirculating vertical-flow constructed wetland. Soil samples were collected every 10 days for the 40-day duration of the study, and plant growth was measured. Soils were analysed for physicochemical and biological parameters to determine changes caused by the different treatments. It was demonstrated that raw artificial GW significantly increased the development of hydrophobicity in the sand and loam soils, as determined by water droplet penetration time. No significant changes were observed for the loess soil under all treatments. Observed hydrophobicity was correlated with increased oil and grease and surfactant concentrations in the soil. Zeta (ζ) potential of the soils was measured to determine changes in the soil particle surface properties as a result of GW irrigation. A significant change in ζ-potential (less negative) was observed in the raw artificial GW-irrigated sand, whereas no difference was observed in the loam or loess. Soils irrigated with fresh water or treated GW exhibited no increase in hydrophobicity. Fecal coliform bacteria were absent or < 10 CFU g − 1 in soils irrigated with fresh water or treated GW, but at least 1 order of magnitude higher in raw artificial GW irrigated soils. Only in the last sampling event and only for the loess soil was plant growth significantly higher for fresh water irrigated vs. raw or treated GW irrigated soils. This study demonstrates that treated GW can be effectively irrigated without detrimental effects on soil or plant growth; however, raw GW may significantly change soil properties that can impact the movement of water in soil and the transport of contaminants in the vadose zone.

How does long-term odor deprivation affect the olfactory capacity of adult mice?

BackgroundUnilateral naris occlusion (UNO) has been the most common method of effecting stimulus deprivation in studies of olfactory plasticity. However, despite the large corpus on the effects of this manipulation, dating back to the 19th century, little is known about its behavioral sequela. Here we report the results of standard olfactory habituation and discrimination studies on adult mice that had undergone perinatal UNO followed by adult contralateral olfactory bulbectomy (bulb-x).MethodsThe olfactory performance of UNO mice was compared to matched controls that had unilateral bulb-x but open nares. Both habituation and discrimination (operant) experiments employed a protocol in which after successful dishabituation or discrimination to dilute individual odors (A = 0.01% isoamyl acetate; B = 0.01% ethyl butyrate; each v/v in mineral oil), mice were challenged with a single odor versus a mixture comparison (A vs. A + B). In a series of tests the volume portion of Odor B in the mixture was systematically decreased until dishabituation or discrimination thresholds were reached.ResultsFor the habituation experiment, UNOs (n = 10) and controls (n = 9) dishabituated to a 10% mixture of Odor B in Odor A after being habituated to A alone, while both groups failed to show differential responding to a 2% mixture of B in A. However, the UNO group's increased investigation durations for the 2% mixture approached significance (p < 0.06). A replication of this study (7 controls & 8 UNOs) confirmed that controls did not differentiate Odor A and a 2% mixture of B in A but UNOs did not (p < 0.05). For the discrimination experiment, 4 UNOs and 4 controls were shaped to dig in one of two containers of sand that contained the S+ odor (Odor B) to obtain sugar pellet rewards. As in the habituation experiment, UNOs displayed greater olfactory capacity than controls on this task. Controls and UNOs had an average mixture discrimination threshold of 1.6% (± 0.4) and 0.22% (± 0.102) respectively, a difference that was statistically significant (p < 0.02).ConclusionsAdult mice relying on an olfactory system deprived of odor by naris occlusion from near the time of birth display enhanced olfactory capacity compared to control mice. This counterintuitive result suggests that UNO is neither an absolute method of deprivation nor does it diminish olfactory capabilities. Enhanced olfactory capacity, as observed in the current study, that is a consequence of deprivation, is consistent with recent molecular and physiological evidence that stimulus deprivation triggers compensatory processes throughout the olfactory system.

Shear Strength and Stiffness of Sands Containing Plastic or Nonplastic Fines

This paper presents the results of a systematic laboratory investigation on the static behavior of silica sand containing various amounts of either plastic or nonplastic fines. Specimens were reconstituted using a new technique suitable for element testing of homogeneous specimens of sands containing fines deposited in water (e.g., alluvial deposits, hydraulic fills, tailings dams, and offshore deposits). The fabric of sands containing fines was examined using the environmental scanning electron microscope (ESEM). Static, monotonic, isotropically consolidated, drained triaxial compression tests were performed to evaluate the stress-strain-volumetric response of these soils. Piezoceramic bender element instrumentation was developed and integrated into a conventional triaxial apparatus; shear-wave velocity measurements were made to evaluate the small-strain stiffness of the sands tested at various states. The intrinsic parameters that characterize critical state, dilatancy, and small-strain stiffness of clean, silty, and clayey sands were determined. All aspects of the mechanical behavior investigated in this study (e.g., stress-strain-volumetric response, shear strength, and small-strain stiffness) are affected by both the amount and plasticity of the fines present in the sand. Microstructural evaluation using the ESEM highlighted the importance of soil fabric on the overall soil response.

Process based stability formulae for coastal structures made of geotextile sand containers

Geotextile Sand Containers (GSC) are increasingly used worldwide for shore protection structures such as seawalls, groins, breakwaters, revetments and artificial reefs. However, reliable design formulae for the hydraulic stability based on a good understanding of the processes involved in the wave-structure interactions are still needed. Although the effect of the deformations of the sand containers on the hydraulic stability is significant, no stability formula is available to account for those deformations and the associated processes leading to the observed failures. Therefore, based on the results of extensive experimental and numerical studies ([Recio J. 2008, Hydraulic Stability of Geotextile Sand Containers for Coastal Structures – Effect of Deformations and Stability Formulae – PhD Thesis, Leichtweiss Institute for Hydraulic Engineering and Water Resources, www.digibib.tu-bs.de/?docid=00021899]), analytical stability formulae are developed that account for the effect of the deformations of the individual GSCs for sliding and overturning stability. The required drag, inertia and lift coefficients are determined experimentally from hydraulic model experiments specially designed for this purpose. Several types of GSC configurations which are representative for a wide range of GSC-structure types are investigated under wave action. Moreover, deformation factors to account for the deformation of the containers on the stability are analytically derived and implemented in the stability formulae. Finally, Stability formulae for each type of coastal structures made of geotextile sand containers such as breakwaters, revetments, sea walls, dune reinforcement and scour protection systems are proposed and recommendations are given with respect to the practical application of the proposed hydraulic stability formula, including their limitations.

Processes affecting the hydraulic stability of coastal revetments made of geotextile sand containers

Softer and flexible protection alternatives, such as structures made of geotextile sand containers (GSC) are often used instead of hard coastal structures made of concrete or rubble material. Although the effect of the deformations of the sand containers is significant, no stability formula is available to account for those deformations. To achieve a better understanding of the processes that affect the stability of GSC-structures several types of hydraulic model experiments and analyses were performed. The processes investigated were: (i) wave-induced loads on the sand containers, (ii) wave induced flow on GSC-structures, (iii) internal movement of sand in the containers, (iv) variation of contact areas among neighbouring GSCs during wave action, (v) types of displacement of GSCs within a coastal structure and finally (vi) the effect of the deformations on the stability of GSC-structures. In addition, a flow model and two structural dynamic models were further developed, validated and applied towards a better understanding of the processes involved in the wave structure interaction. Based on these results a better understanding of the processes that affect the stability of coastal structures made of sand containers has been achieved.

Learning with Nature: A Sand Dune System Case Study (Portugal)

Abstract The implantation of a submarine outfall pipe in 1995 for the cellulose pulp and paper companies Celbi and Soporcel, Portugal, led to some changes in the Leirosa sand dunes system. The use of heavy machinery and the close proximity of a breakwater aggravated the long-term problems of erosion in this coastal ecosystem. Sand accretion was the first step in the reconstruction of the Leirosa dunes. Subsequently, to stabilize the sand, we carried out revegetation, planting the grass Ammophila arenaria (L.) Link. In February 2001, after a particularly severe winter, most of the ocean-facing side of the Leirosa rehabilitated sand dune system was severely damaged. In spite of this problem, the monitoring plan to assess sand erosion and vegetation growth continued. In 2005, after balancing several alternatives, the Leirosa sand dunes were reconstructed with layers of geotextiles filled with sand. Once the sand containers were in place, this protective barrier was covered with sand and planted with A. arena...

Hydraulic permeability of structures made of geotextile sand containers: Laboratory tests and conceptual model

The permeability values were obtained for more than 15 different geotextile sand container (GSCs)-structures. The influence of the size of the sand containers (four different sizes were tested), arrangement and geometry was investigated. First results show that the size of the container represents one of the primary factors influencing the permeability but the method of placement of the GSCs also plays a significant role (different methods of placing resulted in a permeability with more than a 50% difference). The results show that the flow through the GSC-structure is solely governed by the gaps between neighbouring containers and that the flow through the sand fill in the containers can be neglected. In addition, several GSC-structures with the same geometry and the same size of containers but with different arrangements (and thus different permeabilities) were tested under wave action in the twin wave flume of LWI. The results show that the mode of placement of elements strongly affects the permeability and the stability of GSC-structures. Placement of the containers in such a way that the contact areas among containers are maximized resulted in the largest overall stability against wave action. A conceptual model for the determination of the permeability of GSC-structures is proposed.

Australian and German experiences on the use of geotextile containers

Geotextile containers and tubes are used for flood emergency protection in dams and dikes, and also as construction elements for erosion control, bottom scour protection and scour fill artificial reefs, groynes, seawalls, breakwaters and dune reinforcement. New shore protection structures, especially at sandy coasts, are increasingly needed. However, due to the increasing storminess associated with climate changes some of the existing dunes must be protected/reinforced. Hydraulic model investigations were carried out at Leichtweiss-Institute for Hydromechanics and Coastal Engineering (LWI) of the Technical University of Braunschweig, to establish reliable stability formulas for sand containers applied as dune protection/reinforcement subject to storm waves.