The Dynamic Behavior of Calcite Cemented Gravelly Sand – A Case Study of Tehran Soil

Shakeri, Mohammad Reza | 2011

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 42443 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen; Sajjadi, Ali Akbar
  7. Abstract:
  8. An understanding of the effect of degree of cementation on static and dynamic behaviour of cemented soils is becoming increasingly important in design and analysis of geotechnical engineering problems. Naturally cemented coarse-grained soils are widely present in many parts of the world. Misunderstanding of the behaviour of such soils could lead to underestimate or overestimate of the soil parameters. Previous studies conducted by Haeri and his co-workers show that most of the alluvial deposit of Tehran, the capital city of Iran, has a soil with cemented nature. The amount and characteristics of the cementation of the deposit varies in different parts from highly cemented in the north to non-cemented in the south. This deposit consists of gravelly sand to sandy gravel with some cobbles and is dominantly cemented by calcite with carbonate origin. In addition, Tehran is situated in an earthquake prone area. Thus, considering Tehran cemented soil and its vulnerability to ground shakings, characterization of dynamic properties of gravelly cemented soil is inevitable. In this regard, a study on the dynamic behaviour of Tehran deposit, artificially cemented with calcite, has planed. In order to understand the cyclic response of Tehran cemented gravelly soil, more than 190 undrained cyclic and monotonic triaxial tests are performed on uncemented and 1.5, 3.0, 4.5 and 6.0% calcite cemented samples with 10cm diameter and 20cm height. Calcite crystals are chemically precipitated in specimen voids helping hydrated lime and passing CO2 gas through a special mold and curing the samples for a period of time under water. The samples are isotropically consolidated in three different effective confining pressures including 100, 300 and 500 kPa after full saturation of the specimens. Cyclic loading consists of sinusoidal load type with a frequency of 1 Hz with various double amplitude of deviator stresses under various confining pressures were carried out. In addition the cemented and uncemented specimens are statically tested with an axial strain rate of 0.01% per minute. Results obtained from the tests, show that dynamic and static strength of calcite cemented gravelly sands increase with cement content and confining pressure, in the same cyclic stress and strain levels. Also, increase in deviator strain results in the increase in damping ratio and decrease in shear modulus. On the other hand, the decrease in stiffness (degradation) with the number of load cycles is observed. A decremental linear relationship between cyclic stress ratio and the logarithm of the number of cycles associated with the failure can be established. Membrane compliance is also considered especially for uncemented specimens and required corrections are suggested and made for the loading cycles required for initial liquefaction as well as, the cyclic excess pore water pressure ratio during cyclic loading
  9. Keywords:
  10. Cemented Soil ; Calcite ; Dynamic Behavior ; Gravely Sand ; Cyclic Triaxial Test

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