Effect of Stress Conditions on Collapse Deformation Behavior of a Rockfill Material

Ali Akbar Heshmati,Ahmadreza Tabibnejad,Hossein Salehzadeh,Saeed Hashemi Tabatabaei 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.6

A set of saturated and dry-saturated large-scale triaxial tests were conducted in order to explore the effects of stress conditions on the saturation-induced collapse deformation behavior of a rockfill material. Specimens were tested in different confining pressures and for dry-saturated tests the specimens were submerged in various shear stress levels. The results indicate that in all of the drysaturated tests a sudden reduction in the volume of the specimens was observed during the submerging process. The ratio of the minimum axial strength of a submerged specimen (at the end of the saturation process) to the shear strength of the specimen before saturation is defined as the coefficient of stress recovery, Csr. Results of the dry-saturated tests showed that this ratio increases as the confining pressure increases and decreases by increasing the shear stress level. According to the results of dry-saturated tests the values of internal friction angle reduction caused by saturation (Δφc), the ratio of the elasticity modulus of the material after saturation to its elasticity modulus in dry condition, i.e., Ewet/Edry, and also the saturation induced sudden volumetric strain (εvc) decrease as the confining pressure increases. However the shear stress level does not have any meaningful effect on the variation of Dfc, Ewet/Edry and (εvc).

Effect of Gradation Curve and Dry Density on Collapse Deformation Behavior of a Rockfill Material

Ahmadreza Tabibnejad,Ali Akbar Heshmati,Hossein Salehzadeh,Saeed Hashemi Tabatabaei 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.3

Rockfill material, such as other coarse grained materials, undergoes rapid or sudden settlements of relatively large values, withoutany changes in the applied loads and only because of submerging. In the literature this phenomenon is called collapse deformation. The effects of gradation curve and dry density on the collapse deformation behavior of a rockfill material were explored and thechanges in the strength and deformability parameters of this material caused by submerging were determined. Two large scale triaxialequipments with three different sample diameters of 20, 30 and 80 cm were employed and a set of dry-saturated tests wereconducted. Specimens with different gradation curves and various initial dry densities were tested. The results indicate that in all ofthe dry-saturated tests, sudden reductions in the shear strengths and volumes of the specimens were observed during the submergingprocess. The effects of material maximum particle size, fines content and initial dry density on the value of sudden shear strengthreduction, internal friction angle reduction caused by saturation (Δφc), the change in elasticity modulus of the material due tosubmerging, i.e., (Ewet/Edry), and also the saturation-induced sudden volumetric strain (εvc) were evaluated and discussed.

Effect of Cyclic Pre-straining on the Dynamic Behavior of Very Dense Sand

Habib Shahnazari,Ali Akbar Heshmati,Hossein Sarbaz 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.1

Earthquakes, including the main shock, fore-shocks and after-shocks, are among the most devastating natural disasters. Mostbuilding structures that are damaged due to a main shock then experience more damage when they are subjected to aftershocks. Anystrong shock may decrease the strength of a steel or concrete structure. However, depending on its magnitude, a foreshock may eitherincrease or decrease the shear strength of an earth-fill structure. A loose granular specimen usually gains some shear strength whensubjected to pre-loading. This behavior is mainly due to an increase in relative density and experience of shear history. For a verydense granular material, it is unclear whether fore-shocks and main shocks increase or decrease its shear strength. However, theanswer to this uncertainty is vital when evaluating the safety factor of a well-compacted granular earth-fill dam after an earthquake. The objective of this study is to study the effects of cyclic pre-straining on the dynamic behavior of saturated and very dense sandspecimens. The major findings from the laboratory study are the following: (a) under small pre-strain, the microstructure remainsessentially unchanged, but an increase in density leads to an increase in the soil strength; and (b) under large pre-strain, themicrostructure is completely altered to a new form. In this case, if the loading amplitude is identical to the one in the previous prestrain,the soil strength increases; however, if the loading amplitude is less than the previous pre-strain, the strength decreases in thenext stage. Such a decrease occurs even though the relative density increases.

Perceptions of Iranian Cancer Patients Regarding Respecting their Dignity in Hospital Settings

Avestan, Zoleikha,Rahmani, Azad,Heshmati-Nabavi, Fatemeh,Mogadasian, Sima,Faghani, Safieh,Azadi, Arman,Esfahani, Ali Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.13

Background: There are several factors that threaten the dignity of cancer patients in hospital settings. However, there is limited literature regarding the degree to which dignity of cancer patients is actually respected in daily clinical practice. The aims of this study were therefore to explore cancer patient perceptions of respecting their dignity and related variables in an Iranian cancer specific center. Materials and Methods: This descriptive-correlational study was carried out among 250 cancer patients admitted to a cancer specific center in East Azerbaijan Province, Iran. These patients were selected using a convenience sampling method. The Patient Dignity Inventory (PDI) was used for data collection. Descriptive and inferential statistics were used for data analysis. Results: The patients' scores in 18 out of 25 items of PDI were 3 or greater which indicate the importance of considering these items in clinical settings. Also, the score of patients in three sub-scales of PDI including illness-related concerns, personal dignity, and social dignity were 74, 65 and 57, respectively (based on a total 100). The overall score of PDI was statistically associated with age, history of disease recurrence, education, employment and economic status of participants. Conclusions: According to the study findings the dignity of Iranian cancer patients is not completely respected in clinical settings which require special considerations. As nurses spend more time at patients' bedsides, they have an important role in maintaining and promoting dignified care.

The Occurrence and Risk Assessment of Exposure to Aflatoxin M1 in Ultra-High Temperature and Pasteurized Milk in Hamadan Province of Iran

Amir Sasan Mozaffari Nejad,Ali Heshmati,Tayebe Ghiasvand 질병관리본부 2019 Osong Public Health and Research Persptectives Vol.10 No.4

Objectives: Aflatoxins are a category of poisonous compounds found in most plants, milk and dairy products. The present research was carried out to detect the presence of aflatoxin M1 (AFM1) in samples of milk collected from Hamadan province, Iran. Methods: Twenty five samples of ultra-high temperature (UHT) and 63 samples of pasteurized milk were collected and the amount of AFM1 was measured by an Enzyme-Linked Immunosorbent Assay method. In addition, the estimated daily intake (EDI) and hazard index (HI) of AFM1 was determined by the following equations:(EDI= mean concentration of AFM1 × daily consumption of milk/body weight; HI= EDI/Tolerance Daily Intake). Results: AFM1 was detected in 21 (84%) UHT milk samples and in 55 (87.30%) pasteurized milk samples. Seven (28%) samples of UHT and 21 (33.33%) pasteurized milk samples had higher AFM1 content than the limit allowed in the European Union and Iranian National Standard Limits (0.05 μg/kg). None of the samples exceeded the US Food and Drug Administration limit (0.5 μg/kg) for AFM1. EDI and HI for AM1 through milk were 0.107 ng/kg body weight/day, and 0.535, respectively. Conclusion: A significant percentage of milk produced by different factories in Iran (84% of UHT and 87.3% of pasteurized milk) was contaminated with AFM1. Therefore, more control and monitoring of livestock feeding in dairy companies may help reduce milk contamination with AFM1. As the HI value was lower than 1, it can be assumed that there was no risk of developing liver cancer due to milk consumption.

Investigation of Failure Behaviour of Soil Nailed Excavations under Surcharge by Centrifuge Model Test

S. Mohammad Shoari Shoar,Ali A. Heshmati R.,Hossein Salehzadeh 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.1

A series of centrifuge tests were performed to evaluate surcharge effects on the behavior of nailed vertical excavations. The primary purpose was to observe the mechanism of failure surface development and to compare the test results with software results based on equilibrium limit analysis. In this experiment, four different surcharges were applied to both samples with and without nails. Applying surcharge and the following excavation were performed in 40 g acceleration. At the beginning of the test, the excavation was maintained using a water-filled membrane, right next to it. At the target acceleration, the surcharge was modelled by filling the loading tank over the sample with water, and finally, with water draining from the membrane, soil excavation was simulated. Eventually, failure surfaces resulted from the experiment were compared with the ones calculated by the equilibrium limit analysis-based software. Results revealed that the shapes of failure surfaces are bilinear in all tests and that the surcharge has its effects on the development of failure surfaces. In the meantime, the pull-out mechanism was observed in the nails during failure, with no bending. The equilibrium limit analysis also estimates the width of failure wedge well and its depth conservatively.