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RISS 인기검색어
- 검색키워드
- 저자 : Ali Akbar Heshmati (검색결과 3 건)
- 무료
- 기관 내 무료
- 유료
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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).
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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.
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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.
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