Waleed El-Sekelly

PRESHAKE: A Database for Centrifuge Modeling of the Effect of Seismic Preshaking History on the Liquefaction Resistance of Sands

Several researchers found that the behavior of natural preshaken soils can be very different from artificial recent fills. This paper presents an extensive database of two very long centrifuge experiments (CS-5-1-1 and CC-5-1-1) performed both on silty and clean sand at the geotechnical centrifuge testing facility at Rensselaer Polytechnic Institute (RPI). The two experiments test the effect of seismic preshaking history on the liquefaction resistance of sandy soils. The database described herein was generated using the NEEShub online DataStore tool under the name “PRESHAKE: Centrifuge modeling of the effect of seismic preshaking on the liquefaction resistance of sands” (DOI: http://dx.doi.org/10.4231/D38K74X78). The paper discusses the tools and materials used in the experiments along with an explanation of each item in the database. Sample analyses are also presented in the paper to give an insight on the capabilities of the database for numerical and analytical applications. The paper is concluded with some possible applications along with tips and limitations of the database.

Guyed Monopile Foundation for off-Shore Wind Turbines

Over recent years, renewable energy has become an important choice for the Egyptian government, as Egypt has been suffering severe power shortages and rolling blackouts. Egypt put an energy strategy that aims at increasing the renewable energy share to 20 percent of Egypt’s energy production by 2020. This target is expected to be met largely by scaling-up wind power projects. While most wind energy in Egypt is produced by on-shore wind farms, off-shore wind farms can be much more productive and efficient. Coastal zones in Egypt enjoy high wind energy potential. Designing foundations for off-shore wind turbines is challenging, as these structures are subjected to dynamic forces such as wind and waves. Monopiles are one of the most efficient foundation systems for offshore wind turbines, however they are mainly used in shallow water (less than 30 m deep). There is an urgent need to increase both the depth and capacity of monopiles supported wind turbines. Increasing the depth and diameter of monopiles can become uneconomic, thus a modified system needs to be adopted. This paper is the first step in studying the adoption of a system of ties (aka guys) to support the monopiles and reduce their free length above the sea level.

Recent advances in physical modeling and remote sensing of civil infrastructure systems

Natural and man-made hazards are often associated with costly damages to civil infrastructure systems, such as buildings, bridges, Levees, dams, pipelines and offshore structures of all types. The lack of high-quality field and lab data of soil system response have eluded researchers and practitioners until recently. Recent advancements in physical modeling facilities (centrifuge and full scale) and advancement in remote sensing technology are leading to a new reality for the health assessment of soil–structure systems. This new reality is leading to a paradigm shift in the evaluation and modeling of soil–structure systems. Physical modeling, remote sensing and computational simulations are destined to replace the current empirical approaches and will ultimately become the main tool for analysis and design of soil–structure systems. The paper discusses the results of recent research studies utilizing physical modeling to simulate the response of critical soil–structure systems to natural and man-made hazards.

Response of a silty sand centrifuge deposit to repeated earthquakes

The estimation of liquefaction potential of soil deposits is mainly based on field liquefaction triggering charts based on the Seed and Idriss Simplified Method. Currently these field liquefaction triggering charts seem to be generally conservative, as they do not take into account factors that tend to increase the liquefaction resistance of natural sand deposits located in seismic areas. The work presented in this paper incorporates data from the field, as well as centrifuge experiments performed at RPI. The experimental work involved simulating several decades to a century of earthquake events applied to a 6-m uniform silty sand deposit. The results show that repeated earthquake shaking generally has the effect of increasing the liquefaction resistance of soil deposits over time. This increase in liquefaction resistance does not seem to be fully accounted for by the simultaneous increase in the shear wave velocity of the soil. In other words, sites that have been subjected to hundreds of small earthquakes as well as some larger liquefying events may not liquefy again unless they are subjected to very intense earthquake shaking.