Amir Akbari Garakani | Niroo Research Institute (original) (raw)

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Papers by Amir Akbari Garakani

E3S Web of Conferences, 2016

International Journal of Geomechanics, 2016

Treatment of soft or weak foundation in a rockfill dam is of importance due to being susceptible ... more Treatment of soft or weak foundation in a rockfill dam is of importance due to being susceptible to the large settlements, which may cause the dam body subjected to undesirable deformations and even, catastrophic failures. In this papers the stress-strain behavior of a 58m rockfill dam in Iran, namely Gerdehbin dam, and its soft and weak alluvial thick foundation has been assessed numerically and, the effect of consolidation grouting of the basement (as a remediation method) on the dam deformations and stress levels, is investigated. For this purpose, a finite difference based software (FLAC 2D ver. 4.00) has been used to evaluate the effects of the governing mechanical parameters on the dam body behavior. Results show that for certain values of the mechanical properties of the grouted zone, the dam body deformations reaches to the minimum level. The mechanical properties of the grouted zone materials are dependent on the grouting pattern. Hence, an optimized grouting pattern has be...

Engineering Geology, 2015

A conventional triaxial test device was modified to characterize the hydro-mechanical behavior of... more A conventional triaxial test device was modified to characterize the hydro-mechanical behavior of a loessial soil during isotropic and shear loadings. This device is capable of precise and continuous measurements of water outflow during the application of loading. The tests were performed on "undisturbed" cylindrical specimens, which were taken from loessial deposits in Gorgan, a city in the northeast of Iran. Experimental measurements indicate that the hydro-mechanical behavior of loess is highly affected by the extent of applied mean net stress and the level of suction. During both isotropic and shearing stages of loading, the tested specimens may exhibit collapse, abrupt decrease in volume or sudden positive volumetric strain, upon wetting or applied loading. However, the magnitude and extent of collapse are different depending on the applied state of the stress and the hydromechanical loading path. The results of the experiments reveal that the peak shear strength of the soil increases, as the applied mean net stress during isotropic loading or the applied matric suction increases. The shearing test results are also used to investigate the efficiency of suction stress in describing the state of stress for unsaturated loessial soils. The outcome indicated a unique critical state line for unsaturated specimens under different stress paths and loading conditions. Furthermore, considering the effective stress concept, a hardening constitutive law is presented in this study to demonstrate the hardening/softening behavior of the collapsible loessial soils. Abbreviations: b, Double-hardening parameter; b 1 and b 2 , Fitting parameters of the hardening model; d 200 , Percent passing sieve No. 200; d 4 , Percent passing sieve No. 4; d c , Percentage of clay fraction; de p , Increment of plastic change in void ratio; dS e , Increment of change of effective saturation; e, Void ratio; e o , Initial void ratio; M, Slope of critical state

Unsaturated Soils: Research & Applications, 2014

Highly collapsible loessial soils are characterized by an open void structure that can experience... more Highly collapsible loessial soils are characterized by an open void structure that can experience significant settlement upon loading. In the field, these partially saturated Aeolian deposits are particularly susceptible to wetting-induced collapse. Due to difficulties in preparing undisturbed specimens from highly collapsible soils, previous studies have generally performed laboratory tests on reconstituted specimens with different water contents and densities, and the effect of disturbance on the initial state of the soil was ignored. Disturbance in highly collapsible soil specimens may significantly affect the natural composition of the soil matrix, the non-homogeneous distribution of macro-or micro-pores, and the weak inter-particle bonding between the grains. The current study utilizes a new experimental approach to assess the effect of disturbance on the hydro-mechanical behavior of a highly collapsible loessial soil. Results from tests on undisturbed and reconstituted specimens prepared at the same water content and dry density indicate that disturbance can in some cases significantly affect the observed hydro-mechanical behavior of a collapsible soil during the wetting process. For low mean net stress testing, for tests conducted on specimens at the same values of mean net stress, the deformation measurements for undisturbed specimens were lower than those that were observed when testing reconstituted specimens. At higher values of mean net stress, both undisturbed and reconstituted soil specimens showed very similar wetting-induced volumetric strain behavior. This observation is believed to be due to the effect of the mechanical stress on the natural composition of the soil matrix, which can break cemented bonds between soil particles and reduce the effect of non-homogeneity in the distribution of pores on the deformation behavior of the soil.

Unsaturated Soils: Research and Applications, 2012

Loessial collapsible soils are in the group of problematic soils and have been encountered in man... more Loessial collapsible soils are in the group of problematic soils and have been encountered in many parts of the world such as some regions in Iran. In these soils, sudden and large volume changes occur while the water content, overburden stress or both are passed a threshold limit. In this paper the collapse potential of a loessial soil taken from Gorgan; a city in Golestan province in North of Iran; has been investigated on both undisturbed and remolded specimens by using oedometer tests. For both types of samples, the effect of initial moisture content and also inundation stress have been investigated on the collapse potential and permeability behavior of the aforementioned soil. The results show that the type of specimen, initial water content, initial dry density and inundation stress have strong affect on collapse potential and permeability coefficient of the studied loess.

Geotechnical Testing Journal, 2014

Unsaturated loessial Aeolian deposits tend to experience significant volumetric compression when ... more Unsaturated loessial Aeolian deposits tend to experience significant volumetric compression when subjected to loading. This behavior is generally attributed to their open, unstable soil fabric and their weak inter-particle bonding forces, which together yield a soil void structure that is susceptible to collapse. The current study examines two possible mechanisms of pore collapse in a loessial soil: pore collapse induced by an increase in net confining stresses under constant matric suction conditions, such as what occurs when a new structure is constructed on top of a collapsible soil deposit, and pore collapse induced by a change in matric suction conditions under a constant net confining stress, such as what occurs when a collapsible soil deposit beneath an existing structure experiences significant wetting due to a large precipitation event. To accomplish this task, an innovative test approach was used to assess the hydro-mechanical behavior of a highly collapsible loessial soil. The test setup incorporates a set of electronic pressure regulators coupled with three electronic pressure sensors to measure and control the applied pressures, and two high-precision digital volume change measuring devices to measure changes in the volume of the specimen and its degree of saturation. Using this approach, "undisturbed" loess specimens are subjected to either isotropic compression at a constant matric suction, or wetting-induced collapse at a constant mean net stress. Results indicate that the hydro-mechanical behavior of collapsible soils is considerably stress-path dependent. For the same values of mean net stress, the deformation measurements of specimens subjected to isotropic compression were often larger than those subjected to wetting-induced collapse. For the isotropic compression tests, it was shown that the soil water retention curve of the soil depends on the mean net stress. Less sensitivity to the mean net stress was observed for specimens subjected to wetting-induced collapse.

Failures, undesirable deformations and crack propagation through the concrete lining of the water... more Failures, undesirable deformations and crack propagation through the concrete lining of the water conveying Canals are of kinds of common problems in the regions covered by the swelling clayey soils. In this paper, an under construction water conveying Canal, namely Jaldian Canal which is located in West Azerbaijan province in Iran, and its highly swelling soil base has been selected to study the efficiency of six different base improvement methods. For this purpose, a 42 m length test Canal in seven equal segments at the project site is constructed and base improvement methods applied to each segment, followed by visual and quantitative inspections and surveying. Also one segment has been constructed without any base improving as a comparative bench mark. Improving methods consist of execution of drainage layers with different thicknesses beneath the Canal base, mixing the base soil with lime and Portland cement and, increasing the ductility of the Canal concrete body to overcome the Canal deformations which cause cracking through the Canal side walls and base. By recording the Canal deformations and cracks the efficiency of each method has been evaluated and reported in this paper. Results show that placement of a drainage layer beneath the Canal base with appropriate thickness could be the best choice to improve the swelling potential. Also this method is the most economical method for improvement.