جستجوی مقالات مرتبط با کلیدواژه « compaction » در نشریات گروه « عمران »

One of the key factors that reduce the bond strength between repair mortars and concrete substrate is improper compaction of the repair layer when applied to concrete. Due to the fact that compacting has a direct effect on the adhesion of the interface of two layers, so the lack of proper compaction causes small cavities between the two layers and as a result causes a decrease in bond strength. Therefore, in this paper, by applying semi-destructive tests, by applying initial compression for 24 hours on the mortar applied to the concrete substrate, the effect of compression on bond between the repair layer and the concrete has been studied. The effect of one week of curing on the dry shrinkage of repair mortars is also presented. In the following, the compressive strength of repair mortars was evaluated using the "twist-off" and "pull-off" tests. In this regard, calibration diagrams were drawn between laboratory tests and semi-destructive tests and linear equations were presented to convert the original results from semi-destructive tests to the compressive strength of mortars. ABAQUS software was used to investigate cracks and stresses in mortars. The results show an increase in bond strength between the repair mortar and the concrete substrate by applying initial compression. Applying initial compression of 0.5 kg/cm2 on unhardened mortar increased the shear and tensile strength between the repair and concrete layers at the age of 90 days by 36.9% and 31.4%, respectively. Also, a linear relationship with high correlation was observed between the readings obtained from the above tests with the compressive strength of repair mortars.

In a majority of methods used for designing asphalt pavements, the base and sub-base layers have not received enough attention; instead, most researches have focused on the asphalt layers. These layers play a key role in reducing stress on the base layer. Light Weight Deflectometer (LWD) test is commonly used for assessing the bearing capacity of unbound layers of pavements. The present study aims to investigate the simultaneous effects of different variables such as sample thickness, wet content, weight, and compaction on the base layer surface modulus and deflection through LWD test results on the 150times150times60 cm sample. The results indicated that the maximum compaction value was 97% with a thickness of 40 cm and the minimum compaction value was 10 Kg weight with 20 cm thickness. Furthermore, according to the findings, an increase in the compaction and thickness of the layer led to a decrease in the deflection and an increase in the mass of weight; however, moisture did not significantly influence the mentioned factor.

By 2070, approximately 140 million of the world's population will have resided in coastal areas and in the vicinity of rivers and, thus, economist forecast that around 30000 million euro of assets could be dependent on flood protection. A large part of these flood protection systems is old and need replacement and / or adjusted to match safety standards. It requires a significant investment in addition to an increase in population pressure in coastal areas. Eembankment structures are built of erodible (earthen) and/or non-erodible (Concrete) material by humans or formed naturally. These are used as in the flood protection system and water storage for drinking and irrigation, energy production, and recreation purposes. Due to various reasons, such as overtopping, seepage, internal erosion and piping, and slope instability earthen embankments may fail. However, more than 34% dam, 35% earth dams throughout the world, and 30% dam failure in USA during the last 80 years are consider due to overtopping. More than 60% of human casualties resulted from the failure of dams due to the failure of the three large dams (Vajont dam (Italy), John Storm dam (USA) and Mucho dam (India) due to overtopping flow. Heavy rainfall and consequent dramatic increase in water level, or wave attack caused by hurricane and earthquake are regarded as the primary factors in creating overtopping flow. Inadequate free height, limited capacity of weirs, and inaccurate prediction of the most likely flood are among the most well-known human factors. Laboratory experiments are carried on overtopping of embankments consisting of silty sand constructed with different levels of compaction. Digital image processing was employed to investigate the surface variation in embankment due to overtopping erosion with time. The results show that a direct relationship exists between the relative density of soil and erosion duration. It is also an inverse relationship between density and rate of erosion. On other hand, relative compaction has a key role in headcut erosion and is clearly evident that in the rate of erosion.

Flexible Pavement has the most share for road construction in most countries. Iran also follows this rule. In most asphalt pavements design methods, there is less focus on base and subbase layers and most of the researches are focused on the asphalt layer. Since the behavior of these materials is different in the short and long term due to the elastoplastic properties, it’s so important to examine their behavior before using in the pavement layers and also behavioral comparison between different types of materials. This leads to the choice of the best type of pavement materials and the best conditions for grading, moisture and compaction. In results, it is important to select the test conditions that can accurately simulate the actual stresses on the pavement. Light weight deflectometer (LWD) test is usually used to determine the bearing strength of the unbound layers of the pavement. The purpose of this study is to examine simultaneously the role of the effective factors associated with the base layer on the behavior of this layer using of LWD test. The selected effective factors include compaction, thickness, and moisture content of the layer. The results show that increasing of compaction from 87% to 97%, and layer thickness from 20 to 40cm, the surface modulus of layer is significantly increased and deflection is reduced. Also, the results show that the changes in the moisture content of the layer did not have effect on the modulus and deflection of the layer.

Chemical stabilization by cement is among the factors of optimizing the soil performance. Numerous studies have been performed in the field of using cement as a stabilizing material (Naderi Nia- Naeini SA, 2009; Dupas J, Pecker A, 1979). The results of this research show that the addition of cement to the soil increases stiffness and improves soil’s failure behavior and its engineering properties. Improving the engineering properties of the soils stabilized with cement is essentially due to hardening of cement as a result of hydration of cement and forming additional cementitious materials between the hydrated cement and clay particles in the soil (Shihata SA, Baghdadi ZA, 2001). On the other hand, although cement industry has adopted the most modern technologies to reduce pollution, different stages of cement production and transportation have a great share in the environmental pollution. Studies indicate that to produce one ton of cement and clinker in Iran 0.655 and 0.79 tons of CO2 greenhouse gas are emitted respectively (Milika Bildrici 2019). Therefore the cement mix optimization is such that the lowest amount of energy is used to produce it with the least damage to natural resources and finally the best performance possible is provided which is considered as a main goal (Khaleghi, M. H. 1990).

Bridge failures are fortunately rare, but every year a number of bridge collapse that has occurred somewhere in the world. In many cases these collapses could have been avoided by an adequate bridge management regime that included good inspection, assessment and maintenance procedures. One specific type of failure that from time to time causes sudden catastrophic collapse of bridges is the undermining of foundations due to bed scour. Bed scour is the transport of bed material by the flow of water and is present to some degree where the river bed is formed of granular material. Scour increases as flow rates increase and therefore the actual collapse of structures due to scour often occurs during periods of extreme flow due to flooding. Of course, this is exactly the time that direct observation of the foundations of a structure is not possible and therefore a collapse may be put down to an ‘act of God’. A good inspection regime that includes bed measurement and engineering analysis can find indications of developing scour before the situation becomes critical. If this is followed up with well-designed remedial works, undermining of the structure, even in extreme conditions, may be prevented. The formation of scour holes around bridge piers or abutment is one of the main causes of bridge foundation collapse. Local scour at bridge piers and abutment may be defined as a local lowering of the bed elevation. This lowering is mainly caused by the horseshoe vortex combined with the downflow in front of the pier and abutment, the vortex shedding at the back of the pier, abutment and the flow contraction. Bridge failure due to the effects of local scour associated with the structure of the local flow field around piers and abutment involves a considerable interest in scour prediction and scour protection measures. Two basic procedures may reduce the scour depth. The first consists in enhancing the ability of the bed material to withstand erosion. This is generally done by placing an armoring device on the bed, such as riprap. The riprap provides a physical obstacle that resists the erosive power of the flow. The second procedure consists in reducing the downflow in front of the pier and the horseshoe vortex scouring the bed material. The local scour around bridge pier and abutment in recent years has been widely studied by different authors. They proposed different methods to control the scouring depth. The most dominant concern about bridges stability is the occurrence of local scour around foundations. The local scour around bridge piers and abutments has been widely studied by different authors in recent years. They proposed different methods to control the scour depth. In order to reduce scouring around bridge piers and abutments one of the methods is the soil compaction. Compaction rise the relative density and soil resistance which mitigates scour and produce a time delay in scour hole development process. This paper focuses on the effect of clay content percentage and compaction ratio on scour reduction around bridge piers. Hence, 5%, 10%, and 15% clay was added to soil and then compacted. According to the experimental results, when 15% clay was added to non-cohesive sediment materials in saturated bed conditions with a relative density of 70%, the scour process was completely controlled after 24 hours around the bridge pier.

It is widely known and well emphasized that the cemented sand is one of economic and environmental topics in soil stabilization. In some instances, a blend of sand, cement and other materials such as fiber, glass, nano particle and zeolite can commercially available and effectively used in soil stabilization in road construction. In this investigation, zeolite and its effect on compaction studied as one of pozelan additive material to cement. Therefore, cilinopiolite kind of zeolite, Neka cement type II and Babolsar sand are used. Compaction poroctor tests were carried out on 24 combination type of cement and zeolite with include different cement percentages 2, 4, 6 and 8 percent of total dry weight of samples and replacement percent’s of 0, 10, 30, 50, 70 and 90 cement with zeolite. Results show that by replacement cement material by zeolite, the maximum dry density increased 2 to 2.5% in comparison with cemented samples and 14% optimum water content approximately concluded. At the end, a function fits Based on Voltra series presented to relate maximum dry density and zeolite-cement-soil parameters.

The lack of accessibility of high- quality materials and the increased costs associated with the use of these materials will finally necessitate engineers to use local soils. In such cases, ground improvement behaved satisfactorily in many conditions. Ground improvement can be defined as the procedure of increasing shear strength parameters and decreasing the permeability and compressibility of the soil. Different methods can be used to improve the geotechnical properties of the problematic soil, one of which is using additives. Additive stabilization is achieved by the addition of proper percentages of cement, lime, fly ash, bitumen, or combinations of these materials to the soil. The selection of type and determination of the percentage of additive to be used are dependent upon the soil classification and the degree of improvement in desired soil quality. It is known that, when using soil-cement as a compacted layer over low bearing capacity soil, the system failure usually happens under tensile stresses at the base of the improved layer. Then, it would seem more reasonable to use the tensile strength as a direct measure of the soil-cement strength. In this investigation, zeolite and its effect on compaction are studied as one of addictive material to cement. Therefore, Kilinopiolite kind of zeolite, Neka cement type 2, and Babolsar sand are used. 24 combination types of cement and zeolite include different cement percentages: 2, 4, 6, and 8 percent of the total dry weight of samples and replacement percent's of 0, 10, 30, 50, 70, and 90 zeolites with cement. In this article, first, soil mixture and producing samples based on standard compaction test have been done. Results show that by increasing the replacementpercentages of zeolite with cement, decreasing maximum dry density and 14% optimum water content approximately concluded. Also, by replacing 30 percentage of cement by zeolite material, the tensile strength increased up to 40 % in comparison with cemented samples.

I‌n‌t‌e‌g‌r‌a‌l b‌r‌i‌d‌g‌e‌s a‌r‌e g‌a‌i‌n‌i‌n‌g i‌n‌c‌r‌e‌a‌s‌i‌n‌g p‌o‌p‌u‌l‌a‌r‌i‌t‌y b‌e‌c‌a‌u‌s‌e o‌f e‌c‌o‌n‌o‌m‌i‌c‌s a‌n‌d t‌h‌e‌i‌r f‌a‌s‌t c‌o‌n‌s‌t‌r‌u‌c‌t‌i‌o‌n p‌r‌o‌c‌e‌s‌s, a‌s‌s‌o‌c‌i‌a‌t‌e‌d w‌i‌t‌h t‌h‌e o‌m‌i‌s‌s‌i‌o‌n o‌f b‌e‌a‌r‌i‌n‌g s‌u‌p‌p‌o‌r‌t‌s a‌n‌d e‌x‌p‌a‌n‌s‌i‌o‌n j‌o‌i‌n‌t‌s. I‌n t‌h‌e p‌r‌e‌s‌e‌n‌t s‌t‌u‌d‌y, t‌w‌o o‌b‌j‌e‌c‌t‌i‌v‌e‌s a‌r‌e f‌o‌l‌l‌o‌w‌e‌d: F‌i‌r‌s‌t, i‌n‌v‌e‌s‌t‌i‌g‌a‌t‌i‌o‌n o‌f c‌y‌c‌l‌i‌c e‌a‌r‌t‌h p‌r‌e‌s‌s‌u‌r‌e b‌e‌h‌i‌n‌d i‌n‌t‌e‌g‌r‌a‌l b‌r‌i‌d‌g‌e a‌b‌u‌t‌m‌e‌n‌t‌s b‌e‌i‌n‌g c‌o‌m‌p‌a‌r‌e‌d w‌i‌t‌h t‌h‌a‌t i‌n‌d‌u‌c‌e‌d b‌e‌h‌i‌n‌d t‌h‌e a‌b‌u‌t‌m‌e‌n‌t o‌f t‌r‌a‌d‌i‌t‌i‌o‌n‌a‌l b‌r‌i‌d‌g‌e‌s (w‌i‌t‌h i‌s‌o‌l‌a‌t‌e‌d d‌e‌c‌k a‌n‌d a‌b‌u‌t‌m‌e‌n‌t, w‌h‌i‌c‌h a‌r‌e c‌a‌l‌l‌e‌d s‌e‌p‌a‌r‌a‌t‌e‌d b‌r‌i‌d‌g‌e‌s i‌n t‌h‌i‌s s‌t‌u‌d‌y). C‌y‌c‌l‌i‌c t‌r‌a‌f‌f‌i‌c l‌o‌a‌d i‌s u‌s‌e‌d a‌s t‌h‌e s‌u‌r‌c‌h‌a‌r‌g‌e i‌n t‌h‌e a‌n‌a‌l‌y‌s‌i‌s. S‌e‌c‌o‌n‌d, i‌n‌v‌e‌s‌t‌i‌g‌a‌t‌i‌o‌n i‌s u‌n‌d‌e‌r‌t‌a‌k‌e‌n o‌f c‌h‌a‌n‌g‌e‌s i‌n t‌h‌e d‌i‌s‌t‌r‌i‌b‌u‌t‌i‌o‌n a‌n‌d t‌o‌t‌a‌l t‌h‌r‌u‌s‌t o‌f e‌a‌r‌t‌h p‌r‌e‌s‌s‌u‌r‌e, d‌u‌e t‌o d‌i‌f‌f‌e‌r‌e‌n‌t s‌o‌i‌l d‌e‌n‌s‌i‌t‌i‌e‌s. T‌h‌r‌e‌e n‌u‌m‌e‌r‌i‌c‌a‌l m‌o‌d‌e‌l‌s a‌r‌e d‌e‌v‌e‌l‌o‌p‌e‌d u‌s‌i‌n‌g t‌h‌e F‌L‌A‌C p‌a‌c‌k‌a‌g‌e. T‌h‌e f‌i‌r‌s‌t m‌o‌d‌e‌l i‌s a r‌e‌t‌a‌i‌n‌i‌n‌g w‌a‌l‌l. T‌h‌e c‌h‌a‌r‌a‌c‌t‌e‌r‌i‌s‌t‌i‌c‌s o‌f t‌h‌i‌s m‌o‌d‌e‌l a‌r‌e t‌h‌e s‌a‌m‌e a‌s a p‌h‌y‌s‌i‌c‌a‌l m‌o‌d‌e‌l m‌a‌d‌e i‌n t‌h‌e s‌o‌i‌l l‌a‌b‌o‌r‌a‌t‌o‌r‌y t‌o s‌t‌u‌d‌y t‌h‌e e‌a‌r‌t‌h p‌r‌e‌s‌s‌u‌r‌e o‌n r‌e‌t‌a‌i‌n‌i‌n‌g w‌a‌l‌l‌s u‌n‌d‌e‌r c‌y‌c‌l‌i‌c s‌u‌r‌c‌h‌a‌r‌g‌e‌s. T‌h‌e f‌i‌r‌s‌t m‌o‌d‌e‌l i‌s u‌s‌e‌d t‌o c‌o‌m‌p‌a‌r‌e t‌h‌e r‌e‌s‌u‌l‌t‌s o‌f n‌u‌m‌e‌r‌i‌c‌a‌l a‌n‌d e‌x‌p‌e‌r‌i‌m‌e‌n‌t‌a‌l m‌o‌d‌e‌l‌i‌n‌g a‌n‌d i‌n v‌a‌l‌i‌d‌a‌t‌i‌n‌g t‌h‌e p‌r‌o‌c‌e‌s‌s o‌f t‌h‌e n‌u‌m‌e‌r‌i‌c‌a‌l m‌o‌d‌e‌l. T‌h‌e s‌e‌c‌o‌n‌d a‌n‌d t‌h‌i‌r‌d m‌o‌d‌e‌l‌s a‌r‌e m‌o‌d‌e‌l‌s o‌f i‌n‌t‌e‌g‌r‌a‌l a‌n‌d s‌e‌p‌a‌r‌a‌t‌e‌d b‌r‌i‌d‌g‌e‌s. T‌h‌e i‌n‌d‌u‌c‌e‌d e‌a‌r‌t‌h p‌r‌e‌s‌s‌u‌r‌e i‌s e‌v‌a‌l‌u‌a‌t‌e‌d o‌n t‌h‌e a‌b‌u‌t‌m‌e‌n‌t o‌f b‌o‌t‌h b‌r‌i‌d‌g‌e‌s, u‌n‌d‌e‌r s‌t‌a‌t‌i‌c a‌n‌d c‌y‌c‌l‌i‌c c‌o‌n‌d‌i‌t‌i‌o‌n‌s o‌f t‌r‌a‌f‌f‌i‌c s‌u‌r‌c‌h‌a‌r‌g‌e. P‌r‌e‌s‌s‌u‌r‌e d‌i‌s‌t‌r‌i‌b‌u‌t‌i‌o‌n b‌e‌h‌i‌n‌d t‌h‌e w‌a‌l‌l, a‌s w‌e‌l‌l a‌s t‌h‌e p‌o‌i‌n‌t o‌f a‌p‌p‌l‌i‌c‌a‌t‌i‌o‌n o‌f t‌h‌e t‌o‌t‌a‌l t‌h‌r‌u‌s‌t, w‌a‌s d‌e‌t‌e‌r‌m‌i‌n‌e‌d a‌n‌d c‌o‌m‌p‌a‌r‌e‌d b‌e‌t‌w‌e‌e‌n t‌w‌o b‌r‌i‌d‌g‌e‌s. T‌h‌e r‌e‌s‌u‌l‌t‌s h‌a‌v‌e s‌h‌o‌w‌n s‌i‌g‌n‌i‌f‌i‌c‌a‌n‌t c‌h‌a‌n‌g‌e‌s i‌n b‌o‌t‌h t‌h‌e q‌u‌a‌n‌t‌i‌t‌y a‌n‌d d‌i‌s‌t‌r‌i‌b‌u‌t‌i‌o‌n o‌f e‌a‌r‌t‌h p‌r‌e‌s‌s‌u‌r‌e b‌e‌h‌i‌n‌d t‌h‌e a‌b‌u‌t‌m‌e‌n‌t, i‌n t‌h‌e c‌a‌s‌e o‌f i‌n‌t‌e‌g‌r‌a‌l b‌r‌i‌d‌g‌e‌s. I‌n a‌d‌d‌i‌t‌i‌o‌n, t‌h‌e e‌f‌f‌e‌c‌t o‌f s‌o‌i‌l d‌e‌n‌s‌i‌t‌y o‌n c‌y‌c‌l‌i‌c e‌a‌r‌t‌h p‌r‌e‌s‌s‌u‌r‌e i‌s i‌n‌v‌e‌s‌t‌i‌g‌a‌t‌e‌d a‌n‌d c‌o‌m‌p‌a‌r‌e‌d b‌e‌t‌w‌e‌e‌n t‌h‌e t‌w‌o b‌r‌i‌d‌g‌e‌s. T‌h‌r‌e‌e d‌i‌f‌f‌e‌r‌e‌n‌t s‌t‌a‌t‌e‌s o‌f s‌a‌n‌d, i‌n‌c‌l‌u‌d‌i‌n‌g l‌o‌o‌s‌e, m‌e‌d‌i‌u‌m a‌n‌d d‌e‌n‌s‌e, a‌r‌e u‌s‌e‌d f‌o‌r m‌o‌d‌e‌l‌i‌n‌g t‌h‌e g‌r‌a‌n‌u‌l‌a‌r b‌a‌c‌k‌f‌i‌l‌l b‌e‌h‌i‌n‌d t‌h‌e a‌b‌u‌t‌m‌e‌n‌t. R‌e‌s‌u‌l‌t‌s o‌f e‌a‌r‌t‌h p‌r‌e‌s‌s‌u‌r‌e b‌e‌h‌i‌n‌d t‌h‌e s‌e‌p‌a‌r‌a‌t‌e‌d a‌b‌u‌t‌m‌e‌n‌t s‌h‌o‌w a s‌i‌m‌i‌l‌a‌r t‌r‌e‌n‌d t‌o r‌e‌t‌a‌i‌n‌i‌n‌g w‌a‌l‌l‌s, w‌h‌i‌c‌h e‌x‌p‌e‌r‌i‌e‌n‌c‌e i‌n‌c‌r‌e‌a‌s‌i‌n‌g p‌r‌e‌s‌s‌u‌r‌e d‌u‌e t‌o i‌n‌c‌r‌e‌a‌s‌i‌n‌g d‌e‌n‌s‌i‌t‌y. U‌n‌l‌i‌k‌e r‌e‌t‌a‌i‌n‌i‌n‌g w‌a‌l‌l‌s a‌n‌d s‌e‌p‌a‌r‌a‌t‌e‌d a‌b‌u‌t‌m‌e‌n‌t‌s, t‌h‌e i‌n‌t‌e‌g‌r‌a‌l b‌r‌i‌d‌g‌e e‌x‌p‌e‌r‌i‌e‌n‌c‌e‌s l‌e‌s‌s l‌a‌t‌e‌r‌a‌l p‌r‌e‌s‌s‌u‌r‌e d‌u‌e t‌o i‌n‌c‌r‌e‌a‌s‌i‌n‌g d‌e‌n‌s‌i‌t‌y. M‌o‌r‌e d‌e‌t‌a‌i‌l‌s o‌f t‌h‌e f‌i‌n‌d‌i‌n‌g‌s a‌n‌d t‌h‌e‌i‌r c‌a‌u‌s‌e‌s w‌i‌l‌l b‌e d‌i‌s‌c‌u‌s‌s‌e‌d i‌n t‌h‌e n‌e‌x‌t s‌e‌c‌t‌i‌o‌n‌s.