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An Investigation on the Effects of Liquefaction Induced Lateral Spreading on Deep Foundations and Development of Mitigation Measures Using 1g Shake Table Tests

Kavand, Ali |

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 44153 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen; Rahmani, Iraj
  7. Abstract:
  8. Liquefaction induced lateral spreading is defined as the lateral displacement of mildly sloping grounds or those ending in free faces as a result of liquefaction in subsurface soil layers. Damages imposed by lateral spreading on pile foundations supporting different types of structures such as ports, bridges and buildings are usually observed in large earthquakes. These potential damages are of high degree of importance in southern and northern coastal areas of Iran where several ports and critical facilities are located. River banks all over the country where bridge piers exist are also among the areas prone to potential damages. Evaluation of the effects of lateral spreading on existing structures, using safe analysis and design methods and also development of mitigation measures are among the main steps towards reduction of the hazards associated with this destructive phenomenon. This study aims to investigate the behavior of deep foundations under the lateral loads due to lateral spreading utilizing 1g shake table tests and introducing mitigation measures against lateral spreading. The investigations are divided in two main parts i.e. experimental evaluation of pile response to lateral spreading and evaluation of mitigation methods (stone columns and micropiles) to reduce the lateral spreading effects on piles. For this purpose, a series of large scale shake table experiments are performed. During the experiments different parameters of the soil response including soil acceleration and displacement in free field and variations of excess pore water pressure in free field as well as in areas close to the piles and also those parameters relating to pile response such as pile acceleration, displacement and bending moments were recorded and analyzed. Besides, the lateral pressures on the piles due to the lateral spreading were obtained by back calculation of the bending moments in the piles. The results show that the pattern and magnitude of bending moments and lateral pressure on piles due to lateral spreading are affected by a number of factors including the geometrical and mechanical parameters of the soil layers (soil density, presence of upper non-liquefiable crust layer) as well as those of the piles including being single or group, presence of pile cap, location of the pile within the group, number of piles in the group and rigidity or flexibility of the piles. The effects of super structure are also found to be important in this respect. Another finding is that the maximum values of bending moments in piles and soil pressures on different piles of a group are also affected by shadow and neighboring effects. Some of the aforementioned factors are not given full consideration in current codes of practice. In most of the tests, the magnitude of lateral forces on model piles due to lateral spreading was found to be more than that specified by JRA (Japan Road Association) design code. These facts reveal the necessity of revising current methods of analysis and design of the piles against lateral spreading considering the aforementioned parameters. In case of using stone columns, different aspects of the soil behavior (acceleration, pore water pressure, surface displacement and pattern of lateral displacement) and also force (bending moment and lateral pressure in piles) and deflection behaviors of piles were altered comparing to the case of not using any mitigation measure. The experimental results show that utilizing micropiles with the specifications used in our models is not able to effectively reduce lateral spreading effects on the piles. On the other hand, stone columns are able to reduce displacement and bending moment in the model piles as well as lateral soil pressures on the piles up to 10 cycles applying sinusoidal base shaking with an acceleration of 0.3g )equal to an earthquake magnitude of about M=7.0). However stone columns increase the level of accelerations recorded on the pile caps before the initiation of liquefaction. Another drawback of using stone columns is the residual displacement in the pile cap occurred at the end of shaking that was not observed in case of no mitigation measure. These facts are highly important for seismic design of the superstructures and should be given full consideration when using stone columns as mitigation measure against lateral spreading
  9. Keywords:
  10. Liquefaction ; ِDeep Foundations ; Liquefaction-Induced Lateral Spreading ; Shaking Table Test ; Mitigation Measures

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