Investigating the Influence of a Silty Layer on the Liquefaction of Saturated Sandy Soils through Numerical Methods

Moghaddam Ranjbaran, Babak | 2016

685 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49379 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Pak, Ali
  7. Abstract:
  8. One of the main geotechnical phenomena that causes severe damage during earthquake is liquefaction. This incident occurs due to the undrained behavior of loose sandy soils. In this occurrence, the interaction between the solid and liquid phases in a cyclic motion leads to an increase in pore water pressure and a decrease in interactive forces (effective forces) between grains in the solid grains. Therefore, shear strength decreases. Different aspects of the aforementioned phenomenon is investigated, namely, field, laboratory, and numerical; nevertheless, the study is largely focused on the numerical modelling. Most studies in this field are carried out on a one-layer saturated sand. However, in reality, several layers of silt and clay may also exist between sand layers. Considering real-case scenario is of paramount importance in earthquakes in which the failure of the soil ensues. Given that the nature of liquefaction is a coupled multi-mechanism phenomenon, the effect of the unforeseen layers should be taken into account in sandy layers. In this research, the effect of a possible intra-silt layer in seismic response, surface settlement, and generation and drainage of pore water pressure in saturated sandy soils during and after vibration are investigated using coupled dynamic hydro-mechanical and effective stress methods. In this regard, finite element software, OPENSEES, is used for problem solving and response estimation. OPENSEES is capable of simulating the saturated porous media while taking into account the coupled U-P formulations. To accurately grasp the behavior of sand, critical two-surface plasticity model of Dafalias and Manzari (2004), which is capable of capturing the different behaviors of saturated sands(with different relative densities), both monotonically and cyclically under drained and undrained conditions, is used. During the analyses, variable permeability coefficient (a function of excess pore water pressure ratio) has been utilized for accuracy purposes. Results indicate that existence of a silty layer among sand layers, creates a layer of water (water film) with high pressure. The movement of new layer and delayed drainage of it, brings about failure in the aftermath of earthquake. In other words, a slity layer can cause instabilities, even after earthquake
  9. Keywords:
  10. Effective Stress Analysis ; Coupled Analysis ; Liquefaction ; Silty Sand ; Layared Soil ; Intra Silt Layer

 Digital Object List