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.     

Effect of deformations on the hydraulic stability of coastal structures made of geotextile sand containers

The hydraulic stability of geotextile sand containers (GSCs) for dune reinforcement, seawalls, revetments and artificial reefs for shore protection against storm waves has been studied within an ongoing extensive research program at Leichtweiß Institute. Although the effect of the deformation of the sand containers on the hydraulic stability is significant, no stability formula is available to account for this effect and the associated processes which have led to the observed failures. To achieve a better understanding of these processes and to analyze the influence of the deformations on the stability of coastal structures made of GSCs, different types of scale model tests have been performed. Results from a variety of scale model tests on: (i) wave-induced forces on the sand containers, (ii) internal movement of sand in the containers and (iii) underlying processes leading to the deformations and displacement of the containers have clarified many of the hydrodynamic processes involved, showing that indeed the deformations of the geotextile sand containers substantially affect their stability.     

Physical model studies on damage and stability analysis of breakwaters armoured with geotextile sand containers

Harnessing the advantages of geotextile sand containers (GSCs), numerous submerged breakwaters and shoreline protection structures have been constructed worldwide. But an emerged breakwater structure with geotextile armour units, capable of replacing the conventional structures, is rarely discussed. A 1:30 scaled physical experimentation is chosen as a preliminary investigation to test the feasibility of using GSCs as breakwater armour units. Structural design is evolved based on a comprehensive literature survey. The paper focuses on the stability parameters and damage characteristics of the proposed structure. Four different configurations are subjected to waves, confining to Mangaluru's wave parameters. Effect of armour unit size and sand fill ratio on the stability of the structure is analysed and it is concluded that changing sand fill ratio from 80% to 100% shot up the structural stability to a maximum of 14%. Increasing bag size also resulted in the increased stability up to 8%. Experiments revealed that the best performing configuration could withstand wave heights up to 2.7 m. Stability curves for all tested configurations are discussed and can serve as an effective guideline for designing GSC breakwaters.     

Performance of mortar and concrete made with a fine aggregate of desert sand

At this moment there is no national specification concerning the application of desert sand with very fine grain. To be able to apply desert sand to mortar and concrete in civil engineering, mortar and concrete made of Tenggeli desert sand and Maowusu sandy land sand have been tested in order to clarify their engineering characteristics. Based on the determined chemical composition and the physical characteristics of desert sand, the mechanical properties of mortar and concrete made of two types of desert sand as fine aggregate were investigated. The results of the tests indicate that desert sand can be used as a fine aggregate in mortar and concrete for general civil engineering.     

Shear banding in drained and undrained triaxial tests on a saturated sandstone: Porosity and permeability evolution

Detailed analysis of shear band formation and shear band microstructure formed in drained and undrained triaxial tests on Fontainebleau sandstone is presented. It is shown that under globally undrained conditions, local fluid exchanges inside the sample occur at shear banding resulting into a heterogeneous damage pattern along the shear band. At high confinement, pore pressure generation inside the band leads locally to fluidisation of the crushed material, which results into the formation of connected channels in the heart of the band. Image processing analysis is used for evaluation of porosity inside the shear band and estimation of the permeability is performed using the Walsh and Brace [The effect of pressure on porosity and the transport properties of rock. J Geophys Res 1984; 89 (B11): 9425–31] model. It is shown that, porosity increase as observed in the band at low confining pressure and porosity decrease as observed at high confining pressure are both accompanied by a reduction of permeability inside the shear band due to the increase of tortuosity and specific surface. However, this permeability reduction is much more important at high confining pressure and can reach values three orders of magnitude smaller than the permeability of the intact material.     

Comparison of bearing capacity of a strip footing on sand with geocell and with planar forms of geotextile reinforcement

Comprehensive results from laboratory model tests on strip footings supported on the geocell and planar reinforced sand beds with the same characteristics of geotextile are presented. The various parameters studied in this testing program include the reinforcement width, the number of planar layers of geotextile and height of the geocell below the footing base. Contrary to other researches, the performance of the geocell and planar reinforcement is investigated at the range of low to medium settlement level, similar to those of interest in practice. The results show that the efficiency of reinforcement was decreased by increasing the number of the planar reinforcement layers, the height of the geocell reinforcement and the reinforcement width. For the same mass of geotextile material used in the tests at the settlement level of 4%, the maximum improvement in bearing capacity (IF) and percentage reduction in footing settlement (PRS) were obtained as 2.73 and 63% with the provision of geocell, respectively, while these values compare with 1.88 and 47% for the equivalent planar reinforcement. On the whole, the results indicate that, for the same quantity of geotextile material, the geocell reinforcement system behaves much stiffer and carries greater loading and settles less than does the equivalent planar reinforcement system. Therefore, a specified improvement in bearing pressure and footing settlement can be achieved using a lesser quantity of geocell material compared to planar geotextile.     

黄河特细砂瓷砖粘结砂浆的配制及影响因素研究

以黄河特细砂为集料制备水泥基瓷砖粘结砂浆,研究胶粉和纤维素醚用量对砂浆流动度、砂浆力学性能以及抗冻性能的影响.结果表明:砂浆稠度随着胶粉用量的增加而增大,当胶粉用量为胶凝材料质量的0.7％时,砂浆的抗压、抗折强度及抗冻性能最佳;随着纤维素醚用量的增加,砂浆稠度逐渐增大,黄河特细砂瓷砖粘结砂浆的强度逐渐降低,拉伸粘结强度逐渐增大.利用黄河特细砂制备的粘结砂浆性能符合JC/T 547-2005《陶瓷墙地砖胶粘剂》标准要求.为黄河特细砂资源的有效利用提出了一条经济可行的途径.     

Constitutive model for monotonic and cyclic responses of loosely cemented sand formations

This paper presents a model to simulate the monotonic and cyclic behaviours of weakly cemented sands. An elastoplastic constitutive model within the framework of bounding surface plasticity theory is adopted to predict the mechanical behaviour of soft sandstone under monotonic and cyclic loadings. In this model, the loading surface always passes through the current stress state regardless of the type of loading. Destruction of the cementation bonds by plastic deformation in the model is considered as the primary mechanism responsible for the mechanical degradation of loosely cemented sands/weak rock. To model cyclic response, the unloading plastic and elastic moduli are formulated based on the loading/reloading plastic and elastic moduli. The proposed model was implemented in FLAC2D and evaluated against laboratory triaxial tests under monotonic and cyclic loadings, and the model results agreed well with the experimental observations. For cyclic tests, hysteresis loops are captured with reasonable accuracy.     

Steady state strength of sand:concepts and experiment

残余强度或稳态强度的确定是砂土液化研究中的重要课题。饱和砂土有３种典型的不排水剪切特征：稳态性状、准稳态性状、和加工硬化性状。在三轴不排水剪切中,大部分松砂表现出准稳态性状。新近的研究表明,“准稳态性状”不是砂土的固有性状,而是三轴试验中的边界条件所导致。本文通过试验研究发现,饱和砂土在三轴不排水剪切中通常表现出４个明显不同的阶段：初始阶段、坍塌阶段、临界状态应力阶段、和后破坏阶段。稳态强度只有在坍塌阶段中才会较好地表现出来。文中还对变形稳态的定义作了修正和补充,并根据修正的变形稳态定义给出了Ｕｎｉｍｉｎ砂的稳态强度及其它的一些试验性质。     

Vibratory pile driving in water-saturated sand: Back-analysis of model tests using a hydro-mechanically coupled CEL method

The development of a hydro-mechanically coupled Coupled-Eulerian–Lagrangian (CEL) method and its application to the back-analysis of vibratory pile driving model tests in water-saturated sand is presented. The predicted pile penetration using this approach is in good agreement with the results of the model tests as well as with fully Lagrangian simulations. In terms of pore water pressure, however, the results of the CEL simulation show a slightly worse accordance with the model tests compared to the Lagrangian simulation. Some shortcomings of the hydro-mechanically coupled CEL method in case of frictional contact problems and pore fluids with high bulk modulus are discussed. Lastly, the CEL method is applied to the simulation of vibratory driving of open-profile piles under partially drained conditions to study installation-induced changes in the soil state. It is concluded that the proposed method is capable of realistically reproducing the most important mechanisms in the soil during the driving process despite its addressed shortcomings.     

Influence of thermal damage on physical properties of a granite rock: Porosity, permeability and ultrasonic wave evolutions

In this paper, parameters for characterization of connected porosity and overall damage in the thermally-cracked rock of granite in order to assess, respectively, its transport properties and its mechanical strength are identified and quantified. Samples were heated to a range of peak temperatures up to 600 °C at ambient pressure. Characterizations were made by measurement of porosity, gas permeability, velocity and attenuation of ultrasonic waves. Our study confirms the strong influence of thermal damage on physical properties, and shows clearly the potential of the above techniques in connection with this type of damage. Typically, we show that the porosity measurement only informs about open porosity, which is distributed and available at rock surface, whereas the gas permeability measurement characterizes the connected porosity. As for the ultrasonic wave propagation, it is sensitive to overall damage in the material. Nevertheless, we observed that the three techniques are complementary and similarly describe the rock behavior in each stage of heat treatment; they show a good consistency between them.     

Stability assessment of the Three-Gorges Dam foundation, China, using physical and numerical modeling—Part I: physical model tests

Foundation stability is one of the most important factors influencing the safety of a concrete dam and has been one of the key technical problems in the design of the Three-Gorges Project. The major difficulties lie in two facts. The first one is that the dam foundation consists of rock blocks, with joints and so-called ‘rock bridges’ and the gently dipping joints play a critical role in the foundation stability against sliding. The second one is that, even in the regions where the gently dipping fractures are most developed, there are no through-going sliding paths in the rock mass due to the existence of the rock bridges; so the dam could slide only if some of the rock bridges fail, so as to create at least one through-going sliding path. To date, due to unavoidable shortcomings in physical and numerical modeling techniques, there is not a single satisfactory method to solve the problem completely. For this reason, the integration of multiple methods was adopted in this study and proved to be an effective and reliable approach.This Part I paper describes work based on the results of geological investigations and mechanical tests, relating to the geological and geomechanical models of the Three-Gorges Dam, and then a systematic study procedure was developed to carry out the stability assessment project. Then, 2D and 3D physical model tests for some critical dam sections were performed. In the physical tests, based on similarity theory, various testing materials were selected to simulate the rock, concrete, fracture and rock bridge. The loading and boundary conditions were also modeled to meet the similarity requirements. The failure mechanism was derived through a progressive overloading that simulated the upstream hydrostatic pressure applied to the dam, and the factor of safety was defined as the ratio between the maximum external load inducing the start of sliding instability of the dam foundation and the upstream hydrostatic load. The experimental results indicated that the stability of the Three-Gorges Dam foundation satisfies the safety requirements. Nevertheless, further discussions demonstrated that because of the incomplete definition of factor of safety adopted in the physical model tests, it is also essential to study the stability of the Three-Gorges Dam foundation using numerical modeling, which will be presented in the companion Part II paper.     

Ultimate compressive strength design methods of aluminum welded stiffened panel structures for aerospace, marine and land-based applications: A benchmark study

The high strength-to-weight advantage of aluminum alloys has made it the material of choice for building airplanes and sometimes for the construction of land-based structures. For marine applications, the use of high-strength, weldable and corrosion resistant aluminum alloys have made it the material of choice for weight sensitive applications such as fast ferries, military patrol craft, luxury yachts and to lighten the top-sides of offshore structures and cruise ships. And while, over the last two decades, the ultimate limit state (ULS) design approach has been widely adopted in the design of aerospace and land-based (steel) structures, it is just recently being considered as a basis for the structural design and strength assessment of ships and offshore structures. Practical ULS methods or design codes are available in the aerospace and civil engineering industries, but they are just now being developed for use by the marine industry. The present paper compares some useful ULS methods adopted for the design of aerospace, marine and land-based aluminum structures. A common practice for aerospace, marine and civil engineering welded stiffened panel applications is discussed.     

Removal of heavy metals from storm and surface water by slow sand filtration: the importance of speciation

The removal of heavy metals from storm and surface waters by slow sand filtration is described. The importance of speciation as a technique for exploring and improving the mechanisms of removal is identified. Laboratory-scale slow sand filters operating at conventional flow rate and depth were shown to be able to reduce concentrations of selected heavy metals (Cu, Cr, Pb and Cd) found in road runoff, surface water and sewage effluents to drinking water standard. Nitrogen, volatile solids and modified Stover speciation were used to differentiate between the potential mechanisms of removal, i.e. active biomass, organic adsorption and simple adsorption or precipitation on the surface of the sand. The data presented show that adsorption via organic ligands was the predominant mechanism for metal removal at the surface of the filter but chemical adsorption was the more important deeper in the filter. In the lower layers the adsorbed metals were more easily exchanged than the organically bound metals. The precise chemical ligands were not identified and varied from metal to metal. The most important operational factors affecting performance were therefore the concentration of organic matter, filter depth and the flow velocity.     

Cost estimation, optimization and competitiveness of different composite floor systems—Part 1: Self-manufacturing cost estimation of composite and steel structures

This paper presents self-manufacturing cost estimation, cost optimization and competitiveness of different composite floor systems: composite I beams, composite trusses produced from rolled channel sections and composite trusses made from cold formed hollow sections.Part 1 of this two-part series of papers presents the estimation of the self-manufacturing (direct production) costs for composite and steel structures. The self-manufacturing costs are proposed to be defined as the sum of the material, the power consumption and the labour costs. The material costs of the structural steel, concrete, reinforcement, the shear connectors, electrodes, the anti-corrosion, fire protection and top coat painting, the formwork floor-slab panels and gas consumption are presented in detail. The power consumption costs comprise costs of sawing the steel sections, edge grinding, drilling, welding, stud welding and vibrating the concrete. The labour costs (times) presented define the costs of metal cutting, edge grinding, preparation, assembling and tacking, welding, welding of shear connectors, steel surface preparation and protection, drilling, cutting, placing and connecting the reinforcement, concreting, consolidating and curing the concrete. New approximation functions are proposed for the calculation of some manufacturing times and material consumptions. As the discussed costs vary significantly around the world, the proposed cost expressions are given in the open form to be used for cost estimation in different economic conditions. A numerical example of the estimation of the self-manufacturing costs for a composite I beam floor system shows the suitability of the proposed approach.On the basis of the defined self-manufacturing costs, introduced in Part 1, the cost optimization and the competitiveness of different composite floor systems are discussed in Part 2.     

Dual-phase steel rebars for high-ductile r.c. structures, Part 1: Microstructural and mechanical characterization of steel rebars

The considerable influence of steel’s mechanical behaviour on the dissipative capacity of r.c. structures has led to increasing interest in optimizing the mechanical properties of the reinforcing bars used for seismic applications.

The work presented herein is part of a broad-ranging study on the potential utilization of highly innovative types of steel for reinforced concrete earthquake-resistant structures. In particular, we present the main results obtained in experimental trials on a low-C, Mn–Si steel in the form of concrete reinforcing bars subjected to intercritical tempering treatment in a temperature range between 740 and 820 C to obtain various dual-phase ferrite–martensite structures. The samples were characterized via mechanical tests and metallographic analyses in order to correlate the bars’ characteristics with the microstructure of the steel itself.

Experimental characterization of this steel has allowed for the development of a mathematical model to enable the evaluation of the ductility performance of concrete structural elements reinforced with dual-phase steel bars.     

The development of IT-supported residential services: a conceptual model of influences and constraints

An understanding of the potential and the complexity of IT-supported residential services is essential in order to realize it, especially if one will foresee some of its implications, such as constraints by and influences on the institutions, the markets and the power structure in society. Since our society appears to us as mainly artificial, the creation of IT-supported residential services can be seen as a matter of design. Design in that sense to study how things ought to be and not how they are. The paper describes a conceptual model, and the methodology behind it, of the complex domain of IT-supported service infrastructures for residential living. The model indicates how the residents and the institutions, such as the municipalities, the housing companies, the service providers and the IT-industry, will sanction, prevent or modify the market of residential services.     

Analysis of structural failures in timber structures: Typical causes for failure and failure modes

Collapses of timber structures are negative for the competitiveness of timber on the construction market. The question is what can be done to reduce the risk for failure in timber structures in the future. For this purpose a comprehensive survey and analysis of failures in 127 timber structures have been made. The present paper summarises the results from this survey with an analysis of the underlying causes and associated conclusions and recommendations. The most common cause of failure is related to weaknesses in or lack of strength design (41.5%), followed by poor principles during erection (14.1%), on-site alterations (12.5%) and insufficient or lack of design with respect to environmental actions (11.4%). In total, about half of the failures are caused by the designer and about one fourth of the failures are caused by the personnel working at the building site. Wood quality, production methods and production principles only cause a small part (together about 11%) of the failures.     

Natursyns model: A conceptual framework and method for analysing and comparing views of nature

This article presents a conceptual framework and methodology by which stakeholders’ views of nature can be investigated, explained, compared and ‘ideal types’ distilled based on qualitative interviews and, plans, laws and other texts analysed. The aim of such studies is to increase the knowledge about personal, social and cultural aspects of landscape and their relations in general to improve the basis of countryside planning and management in particular. Within the Natursyns model (the Danish word ‘natur’ corresponding to “nature” in English and “syn” implying perceived, imagined, cognized and culturally agreed interpretations) landscape is understood simultaneously as: ‘habitat’, unrealised sense impressions; ‘area’, all the ways in which nature is cognised; and as ‘symbol’, all types of representations of nature and its parts. The use of the model is illustrated; its epistemological foundation, the semiotics and phaneroscopy (phenomenology) of the American philosopher Charles S. Peirce, is described; the content of its fields explained; and benefits and shortcomings discussed.     

Sources of elastic deformation in steel frame and framed-tube structures: Part 1: Simplified subassemblage models

Three simple models for including the effect of beam-column joint deformation in the analysis of steel moment resisting frame and framed tube structures are presented. The first model, called the Fictitious Joint model, is based on two-dimensional frame analysis and is useful for preliminary analysis only. The second model, called the Krawinkler Joint model, and the third model, known as the Scissors Joint model, use an assembly of rigid links and rotational springs to represent the joint, and may be used in preliminary and final analysis of full structural systems. All derivations are provided in the form of “displacement participation factors”, which allow a detailed breakdown of the various components of subassemblage displacement.When applied to isolated beam-column subassemblages, it is shown that all three modeling approaches produce the same general expression for computing deflections arising from shear deformations in the panel zone region. However, the Krawinkler and Scissors models do not include the effects of flexural deformation within the beam-column joint, whereas the Fictitious Joint model does. While not the dominant source of deformation, it is shown in the paper that the effects of flexural deformations in the beam-column joint should not be ignored.It is also shown in this paper that the overall displacements predicted by the simplified models correlate very well with displacements computed from detailed three dimensional finite element analysis of the same subassemblage. However, the finite element analysis approach, taken alone, is not capable of providing a breakdown of the subassemblage displacements into components, such as panel zone shear, or column joint flexure. Part 2 of the paper presents a method for providing this information from the results of detailed finite element analysis.