Artificial Blocks Research Articles

Reinforcement requirement of breakwaters to counteract future sea level rise

The sea level rise due to climate change requires to consider reinforcement solutions for coastal protection structures in order to preserve their initial stability behaviour and overtopping conditions. Tests carried out with a wave flume were performed on a breakwater, set as a reference, with artificial blocks for the armour. It appears that a variation of the still water level greatly affects the overtopping. Two test scenarios of sea level rise have been studied: 0.5 m and 1 m. In those conditions, different solutions of structure reinforcement have been tested, aiming to keep the initial overtopping conditions. For a rise of 0.5 m of the still water level, increasing the height of the crest wall by 1.5 m is allows to maintain the initial overtopping. For a rise of 1 m of the still water level, the reinforcement of the armour with a third layer of artificial blocks and increasing the height of the crest wall is necessary to keep the initial overtopping and the stability of the armour.

BEACH EROSION COUNTERMEASURE USING NEW ARTIFICIAL REEF BLOCKS

Two-dimensional and three-dimensional laboratory experiments were conducted to investigate not only the flow mechanism near the submerged breakwater but the performance of two newly developed eco-friendly artificial reef blocks. The results of two-dimensional experiments proved that new artificial blocks (EREEB) showed a better performance than TTP in terms of wave attenuation due to wave breaking turbulence near the crest of the structure. Three-dimensional experiments convinced that installing another type of new artificial block (WERF) in between submerged breakwater reduced the return flow velocity more than 50% compared with the gap between the breakwaters is empty. Therefore, these two types of newly developed artificial reef block can contribute the counter measure of beach erosion and habitat of sea lives.

ChemInform Abstract: Towards High‐Performance Bioinspired Composites

AbstractReview: 217 refs.

A laboratory fracture shear cell used for simulation of fracture reactivation

Fault reactivation is an unfavourable incident during drilling and production that may occur due to changes in situ stresses and reservoir pressure. Only a few studies, in their analyses, have included the effects of fault geometrical properties—these are important parameters controlling fault slippage and damage around it. In this paper, the significant influence of fracture morphology on the mechanical behaviour of rock fractures was investigated through experimental studies of shearing rock fractures in the lab. The experiments carried out using a fracture shear cell (FSC): the cell that was modified by adding a number of components to an existing true triaxial stress cell (TTSC) and designing a duplex high pressure cylinder that is capable of applying large normal stresses to the sample at a constant rate. A number of artificial blocks made of mortar material were subjected to shear tests using FSC under a wide range of normal stresses and at different shearing directions. The outputs of uniaxial compressive strength and fracture shear tests in the lab were used to plot the failure envelope of the fractured rock mass and discuss the failure mechanism through shearing. Accordingly, a calibrated, numerical discrete element method (DEM) was used to simulate the shear behaviour of fractures previously tested in the lab. The results of lab tests and DEM simulations will be presented and different failure mechanisms that are expected during shearing will be explained. The results show the significant influence of surface roughness on shear strength and extent of damage zone along the fracture. It was found that the shearing response of fractures depends on the magnitude of normal stress, which indicates the importance of having a good knowledge of in-situ stresses when modelling fault reactivation and damage near the fault zones. The results of lab experiments and numerical simulations were compared and good agreements were observed.

The assessment of shear stress and bed stability in stream ecology

Summary1. Substratum stability and shear stress exerted by flowing water can have a strong influence on the structure of benthic communities. Bed stability can be characterised in a variety of ways, e.g. flow competence, threshold of particle entrainment, measures of erosion and deposition, particle transport distance, abrasion and bedload transport rate. This paper reviews methods for the quantification of bed stability and shear stress in streams and rivers that are relevant for the examination of the relationships between stream biota and bed stability.2. The most suitable method for a research project depends mainly on the objectives. The targeted group of biota, spatial and temporal scale of investigation, as well as hydraulic conditions and substratum characteristics at the study site(s) determine the choice of a technique for the assessment of bed stability.3. Indirect measurement of shear stress can be more accurate than calculations based on the DuBoys equation. However, the latter is preferred for reach‐wide applications within the limits imposed by hydraulic conditions. The entrainment of the substratum is most effectively assessed using a combination of shear stress and competence equations, but the latter require careful parameterisation. At the patch‐scale, direct measurement of entrainment force is a valid alternative.4. Morphometric budgeting is the most comprehensive and least invasive technique for the assessment of rates of erosion and deposition. The transport of substratum particles is efficiently monitored with in situ marked or active tracer particles which allow for rapid and non‐invasive identification and high recovery rate. As the assessment of bedload transport rate by formulae can be inaccurate, direct measurement is preferred. However, bedload traps interfere with the substratum and continuity of measurement with samplers is limited. Thus developments in the sector of acoustic and piezoelectric devices offer a potential alternative.5. The abrasive forces by suspended sediments on stream biota are effectively evaluated with artificial blocks that are fixed on the stream bed. Descriptive surveys that assess bed stability offer an alternative to direct measurement and calculations. They are straightforward and non‐invasive but can be observer‐biased. If single methods do not provide useful links with biological data this may be improved by the application of a multivariate approach.6. Many of the methods assessed have not yet been applied in research on benthic communities, but these hydraulic and geomorphologic techniques offer considerable potential for the assessment of bed stability in stream ecology.

A comparison of sampling techniques in the assessment of burrowing crab abundance in saltmarsh and mangrove environments.

Many researchers have recognised the importance of crabs in the mangrove ecosystem. However, very little is known about burrowing crab species living in temperate Australian saltmarsh. In the present study four different survey techniques were employed to investigate the diversity and abundance of crabs in the saltmarsh and mangrove at Towra Point. The four techniques yielded different results for species abundance and diversity. Four different species Heloecius cordiformis, Sesarma erthrodactyla, Helograpsus haswellianus and Paragrapsus laevis were found in saltmarsh. Three of these species H. Cordiformis, S. Erthrodactyla and P. Laevis were also found in the mangrove. A higher diversity of crabs were found in the Sarcocornia and Sporobolus saltmarsh communities than those dominated by Jancus kraussii. Pit traps were an effective means of capturing crabs though under-represented H. Cordiformis, and S. Erthrodactyla but was ineffective at identifying crabs in the more heavily vegetated Sporobolus and Juncus communities. Surveying crabs underneath artificial blocks may have over-represented the density of S. Erythrodactyla. Burrow counting is a quick and effective means of estimating crab density, though gives no information on assemblage diversity. The results of the study recommended a combination of pit-trap and visual census as a means of efficiently sampling crab assemblages.

Fuzzy control of a swells canal system

This work forms a part of the research undertaken on the maritime developments behaviour submitted to the action of sea waves. To succeed in this objective, we have conceived and achieved a system of artificial wave generation in a swells channel (channel of 37.5 m of length, 1 m of width and 1 m of depth). Indeed, the simulation of swells on scale model has many advantages. We can mention the construction of dykes for the protection of ports, the didactic interest of conception and generation of new models of waves and the construction of boat shells. The installed canal has to achieve tests of developments stability in the domain of the maritime hydraulics. Every work or scale model is constituted of several layers of ripraps of shapes and well-determined relative density. Thus, the survey of stability consists in reproducing in similitude (scale 1/20) in the swells canal to observe their effects on the holding of riprap (accumulation of boulder) or the artificial blocks of the scale model. Otherwise, the modelling of the process of swell generation is described by complicated physical laws and requires important means of computation. To solve this problem, we have conceived a system based on fuzzy logic permitting to assure the generation of coherent command data with the statistical parameters characterizing the oceanic waves, and to guarantee its conformity to the model of Pierson Moskowich spectrum.

Incorporating GIS Building Data and Census Housing Statistics for Sub-Block-Level Population Estimation

This article presents a deterministic model for sub-block-level population estimation based on the total building volumes derived from geographic information system (GIS) building data and three census block-level housing statistics. To assess the model, we generated artificial blocks by aggregating census block areas and calculating the respective housing statistics. We then applied the model to estimate populations for sub-artificial-block areas and assessed the estimates with census populations of the areas. Our analyses indicate that the average percent error of population estimation for sub-artificial-block areas is comparable to those for sub-census-block areas of the same size relative to associated blocks. The smaller the sub-block-level areas, the higher the population estimation errors. For example, the average percent error for residential areas is approximately 0.11 percent for 100 percent block areas and 35 percent for 5 percent block areas.

Several Genes Expressed During Morphogenesis of Lentinus edodes (ImHyup-1)

Differential display of reverse transcription (DDRT)-PCR was conducted to have a profile of the differentially expressed genes during the formation of fruiting body of Lentinus edodes. The lines of L. edodes (ImHyup-I) employed were cultivated in the artificial blocks of sawdust, and the fruiting body was induced from the mycelia or the mass protruded from the brown surface of the sawdust blocks. RNAs were prepared from the four different developmental stages; mycelial, primordial, and stipes and pileus of fruiting body. The fragments of cDNA were synthesized from the combinations of the arbitrary primers and 3' one anchored Oligo-dT primer. Twelve combinations using the primers have been tested, and among them nineteen bands were identified as differentially expressed. Those genes were further analyzed by DNA sequencing and followed by homology search. Characterization of one clone was conducted as a preliminary data and more are under investigation.

A probabilistic model of rubble mound armor stability

Two fundamental problems of breakwater armor layer stability — the behavior of interlocking resistance and the random nature of breakwater stability — are examined through laboratory experiments and a probabilistic model. Based upon laboratory experiments of static pull-out tests, it is found that the interlocking resistance of artificial blocks when randomly placed is, more or less, proportional to the weight of the units. Only for tightly packed blocks, arranged in a pattern, does the interlocking resistance show a possible deviation from the weight proportionality. The resistance of the armor layer is shown to be a random property that can be adequately described by a log-normal distribution. A probabilistic stability equation is developed. The final equation contains six random variables; their behaviors are not all known at present. However, with the partial knowledge we have, the equation is used to bring out a number of salient features in breakwater design.

Laboratory Formulation for Transmission and Reflection at Permeable Breakwaters of Artificial Blocks

Dimensionless empirical formulas of wave transmission through and reflection from permeable breakwaters are presented. Data are collected from laboratory tests by the author and also from those reported by several investigators. Results obtained in this study give a near good approximation under a practical condition that the ratio of wave length to depth is smaller than 0.25.

An Ecological Study of Arthropod Populations on Apple in Northeastern Wisconsin: Phytoseiid Mite Species on the Foliage

Populations of phytoseiid mites on apple foliage were studied in a natural (unsprayed) and 2 artificial (captan and DDT-captan) environmental blocks in a “Northwestern Greening” apple orchard in Door Co., Wisconsin, from 1959 through 1962. Twelve species of phytoseiids were found of which Typhlodromus caudiglans Schuster, Amblyseius fallacis (Garman), Typhlodromus longipilis Nesbitt, and Amblyseius zwoelferi (Dosse) were the most common in that order. T. caudiglans was far the most common species annually in the check and captan blocks and A. fallacis in the DDT-captan. The latter species' tolerance to DDT increased annually.

Experimental Studies on Wave Transmission of a Permeable Breakwater Constructed by Artificial Blocks

Experimental Studies on Wave Transmission of a Permeable Breakwater Constructed by Artificial Blocks

Hydraulic Resistance of Artificial Concrete Blocks

Hydraulic Resistance of Artificial Concrete Blocks

Determination of the stone and concrete block weight in protective linings of structures subject to wave action

1. Formulas of different authors for the determination of stone or concrete block weight in slope-type riprapped structures contain different noncomparable safety coefficients. Analysis of experimental conditions permitted establishing the boundaries of limit states, absolute stability and total riprap destruction and obtaining an evaluation criterion for the safety factor. 2. Block stability is determined by two characteristics-distancel from the center of gravity of the element to the possible axis of rotation and angle α0. Stability calculation of different shaped blocks only as a function of these two characteristics showed that the weight decrease of artificial blocks compared with stone weight is the same as in experiments. Wave impact must be considered as the dumped stone destroying force, with a certain phase retard. Insignificant changes in impact pressure with slope angle (pressure decrease in steep slopes is partially compensated with the downslope velocity increase) permit considering that destructive forces do not depend on the slope angle. 3. From the stability equation My=Mo, a stone-weight formula was derived including in its general form three coefficients which can be obtained by calculation and an impact pressure transmission coefficient which is determined experimentally. 4. Numerical coefficients obtained by calculation determine the order of magnitudes. Introducing a safety factor K≈1.5,f(α) according to formula (20) it lies on the border of the absolute stability zone. This gives a certain assurance of safety in the stone and block weight determination for all slope angles between 15° and 45°. 5. The formula for determining the necessary block weight will have the final form: Open image in new window where K is the safety factor 1.5 (according to p. 7.24 SN 288-64).

Transhepatic portal venography: a new method of portal vein visualization.

Technics for visualization of the portal venous system in man have been available for the past ten years. They consist of direct injection into the portal vein at operation or injection into the splenic pulp (splenoportography). The first method requires direct operative exposure and the second does not permit visualization of the intrahepatic portal system in the face of a blocked splenic or main portal vein, or with high portal pressure and reversal of flow; nor can this method be applied for intrahepatic portal vein visualization in the patient who has had a splenectomy or operative shunting of the portal venous system. In 1951, Rappaport (1) published his original and extensive study of hepatic venography in the dog. He described hepatic venous anastomotic channels which communicated freely with one another and permitted diffuse hepatic vein filling from a single large injection of contrast material. We have studied a large number of injection-corrosion casts of dog livers and have failed to demonstrate the presence of such anastomoses in the normal animal. A comparison of our studies with the anatomic distribution of the channels described by Rap-paport, with direct portal venous injections in dogs, led us to believe that in his experiments there was reflux of contrast material from the hepatic vein into the portal system. The purpose of this paper is to report our preliminary investigation of the possibilities of utilizing retrograde hepatic vein injections for the visualization of the portal venous system in animals and man. Method: An open-end opaque catheter is passed from a peripheral vein, through the right atrium, and into a wedged position in an hepatic vein. Pressures are then recorded and the catheter withdrawn approximately 1 cm. from the wedge, a procedure confirmed by a drop in pressure. A forceful hand injection of 20 c.c. sodium diatri-zoate is then made and serial filming carried out (2). In man we have used a No. 10 Cournand or a No. 280 polyethylene catheter and 40 to 50 c.c. of contrast material. ResultsThe examination was successfully performed in 20 normal mongrel dogs. In each of these animals complete visualization of the intrahepatic portal system was accomplished. Subsequent direct injection of the portal vein in vivo and in vitro confirmed the fact that the structures visualized were indeed portal veins. Artificial blocks of the portal veins were made by in vivo injection of vinyl plastic material through a Hales needle guide (3) attached to the portal vein. Transhepatic portal venograms demonstrated the failure of these blocked veins to fill with contrast material. Nine patients have been studied by this method, with satisfactory filling of the entire portal venous system of the lobe injected. To this date we have been unable to achieve reflux of the contrast material past the porta hepatis in man.

THE "TETRAPOD"

The Tetrapod was invented twelve years ago and the first breakwater with a Tetrapod protection was built eleven years ago. It is felt that a review of the results since obtained with these artificial blocks may be of some interest, preferably in the form of an objective practical examination of the behaviour of Tetrapod-protected structures during the past few years, and of the way in which they have stood up to bad weather during the period. First, however, a brief description will be given of the development of the Tetrapod and the Tetrapod technique.
 Most breakwaters are of the rubble-mound type, because of the very good hydraulic properties of this type of design ; the seaward slope, roughness and "porosity" of their facings are generally such as to ensure the gradual destruction of wave energy, reduce wave overtopping and reflection and minimize toe erosion risks.