| 1. |
- Ahmadi-Naghadeh, Reza, et al.
(författare)
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A new isotropic specimen preparation method from slurry for both saturated and unsaturated triaxial testing of a low-plasticity silt
- 2019
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Ingår i: ASTM geotechnical testing journal. - : ASTM International. - 0149-6115 .- 1945-7545. ; 42:4, s. 854-879
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Tidskriftsartikel (refereegranskat)abstract
- A new procedure for the preparation of low-plasticity silt specimens that are isotropically reconstituted from slurry is developed for use in both saturated and unsaturated soil testing. Spatial variations of the water content and grain size distribution were examined to confirm the uniformity of the specimens (regarding void radio and segregation). The new preparation method results in a homogeneous specimen, which has a simple stress history. The repeatability of the proposed method in preparing identical specimens was verified for both saturated and unsaturated soil testing. The strength and volumetric behavior of specimens prepared by the introduced method are compared with those of moist-tamped compacted specimens and one-dimensionally reconstituted slurry specimens by performing consolidated drained triaxial tests. The microstructure of the specimens prepared with different methods was examined using Scanning Electron Microscopy and Mercury Intrusion Porosimetry. The test results indicate that silt specimens could exhibit either dilative or contractive behavior at normal consolidated conditions, depending on the microstructure.
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| 2. |
- Ahmadi-Naghadeh, Reza, et al.
(författare)
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Exponential Equation for Predicting Shear Strength Envelope of Unsaturated Soils
- 2019
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Ingår i: International Journal of Geomechanics. - : American Society of Civil Engineers (ASCE). - 1532-3641 .- 1943-5622. ; 19:7
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Tidskriftsartikel (refereegranskat)abstract
- An exponential equation is introduced to predict the nonlinear variation of shear strength with matric suction for unsaturated soils. The proposed equation involves three constant parameters, two of which are effective shear strength parameters (i.e., ′ and c′). The third parameter is the maximum capillary cohesion, c″max, which is the maximum possible increase in shear strength due to matric suction. A procedure for the determination of c″max from the soil-water characteristic curve (SWCC) is devised. The proposed equation is validated through a series of constant-suction consolidated drained triaxial tests conducted on specimens reconstituted by isotropic consolidation from the slurry state. In addition, the validity of the equation is investigated by applying it to the test results of five other soils that were available in the literature for the low-suction range (i.e., up to 1,500 kPa). A comparative study on the prediction of shear strength was carried out between the proposed equation and six other shear strength equations found in the literature. The results show that the proposed equation provides reliable predictions of the shear strength of unsaturated soils when the shear strength converges to an asymptotic value at the residual water content.
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| 3. |
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| 4. |
- Ahmadi-Naghadeh, Reza, et al.
(författare)
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Volume change measurement in triaxial tests by monitoring cell fluid volume based on viscoelastic behavior of the test setup
- 2017
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Ingår i: ASTM geotechnical testing journal. - : ASTM International. - 0149-6115 .- 1945-7545. ; 40:4, s. 683-697
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Tidskriftsartikel (refereegranskat)abstract
- A novel procedure was developed to measure the total volume change of the unsaturated soils in triaxial testing. The principle of the proposed method was based on cell fluid volume measurements corrected by the assumption of viscoelastic behavior for the triaxial setup. Calibration and parameter determination procedures of the model are devised, and the presented model is implemented into a MATLAB code. The proposed method was validated through a series of consolidated drained triaxial tests on saturated specimens, by comparing the changes in volume measurement of proposed method and conventional measurement (pore fluid). The accuracy in volume measurement during consolidation and shear stages of these tests was between 0.09 and 0.32 cm3, which is on par with or better than more complex and expensive alternatives found in the literature. Repeatability of the proposed technique in measurement of the volume change was also investigated through a series of suction controlled unsaturated soil tests.
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| 5. |
- Ahmadi-Naghadeh, Reza, et al.
(författare)
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Water content controlled instead of suction controlled strength tests
- 2013
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Ingår i: Life Science Journal. - 1097-8135 .- 2372-613X. ; 10:1, s. 2023-2030
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Tidskriftsartikel (refereegranskat)abstract
- Most soils that concern geotechnical engineering are in the state of partial water saturation. Current practice tries to predict engineering properties of cohesionless soils using data from tests on saturated specimens, regardless of the saturation in the field. Due to complexity of test setups and high technical requirements, unsaturated soil tests are not among the common equipment of soil mechanics laboratory. One of these problems is the existence of suction, which is a function of water content and affects the strength behavior of unsaturated soils. Procedures to keep the water content of the partially saturated specimens constant and homogeneous in conventional soil tests are not well-established. The exception to this is unsaturated test setups, which are costly, complicated and found only in research institutions, hence prohibiting the industry from keeping up with the developments in this field. This study explores simple modifications to conventional methodologies of triaxial and direct shear tests, with the ultimate aim of preventing temporal and spatial variability of specimen water content throughout test duration. For different modifications, specimens of each test are dissected at the end of the test, and water content profiles of the specimens are obtained.
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| 6. |
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| 7. |
- Maghsoudloo, Arash, et al.
(författare)
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Numerical Comparison of Retaining System Behavior for a Deep Excavation Case with and Without Ground Improvement
- 2012
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Ingår i: Proceedings of the International Conference on Ground Improvement & Ground Control. - Singapore : Research Publishing Services. - 9789810735777
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Konferensbidrag (refereegranskat)abstract
- In the construction of deep excavations in urban areas, the safety of adjacent ground and structures becomes major concern for engineers. In soft clays, the main reason for occurrence of large deflections of soil support systems in excavations is instability of the excavation base. This paper will focus on analyzing and comparing design of an excavation with and without jet grout improvement applied to the excavation base by employing the finite-element code PLAXIS. A well-documented case study is analyzed, and soil properties in the model are calibrated using available field data from inclinometers. Then the same analysis is repeated for the improved case and results are compared. The results reveal the effectiveness of jet grout blocks in decreasing lateral wall movement, base heave and surface settlement on the retained side.
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