NEES: PRESHAKE: Centrifuge modeling of the effect of seismic preshaking on the liquefaction resistance of sands
AuthorsThe authors of this database are Waleed El-Sekelly (Rensselaer Polytechnic Institute), Tarek Abdoun (Rensselaer Polytechnic Institute) and Ricardo Dobry (Rensselaer Polytechnic Institute). The database was published at NEEShub on February 09 2015 and has been reproduced here to preserve the data and ensure continued access.
This effect of preshaking history on the liquefaction behavior of sandy soils is documented in this database. This database includes data from two centrifuge experiments performed on both silty and clean sand. The tests simulated the effect of several decades to several centuries of earthquake events on a 5-6 m uniform clean or silty sand horizontal deposit, including both events that liquefied the deposit and others that did not liquefy it. The two centrifuge deposits were subjected to three or four basic event types: Events A, B and C (or D). An Event A was defined as 5 sinusoidal cycles of a peak base acceleration, apb ≈ 0.035-0.045 g; an Event B was defined as 15 sinusoidal cycles of a peak base acceleration, apb ≈ 0.04-0.05 g; and an Event C (or D) was defined as 15 sinusoidal cycles of a peak base acceleration, apb ≈ 0.1-0.25 g, all in prototype units. The prototype frequency in all cases is 2 Hz. The 15-cycle duration of Events B, C and D corresponds approximately to an earthquake of moment magnitude, Mw ≈ 7.5; while the 5-cycle duration of the Events A correspond to Mw ≈ 6. An Event A represents a mild to moderate earthquake shaking; an Event B represents a mildly strong earthquake shaking; and an Event C (or D) represents a strong to very strong extensive liquefaction shaking in the field. The results of the experiments showed that the combination of mild/moderate (Events A) to mildly strong (Events B) shakings resulted in a significant increase in liquefaction resistance of the deposits over time. However, the occurrence of extensive liquefaction, caused by an Event C or D, resulted in an immediate reduction in liquefaction resistance of the deposit. This suggests a complex phenomenon, with most of the shaking events strengthening the liquefiable layer but some of them weakening it, sometimes dramatically when extensive liquefaction was involved.
The database is in the form of a table in which each row corresponds to an event in the experiment. The database is composed of two centrifuge experiments. The columns of the database table provide detailed information about the characteristics of each experiment as follows:
- Test name: The test name as reported by the corresponding reference. The first letter, C, stands for centrifuge experiment. The second letter, S or C, stands for silty or clean sand. The numbers stand for the ratio between the number of events types A, B and C, respectively.
- g-level: The gravitational acceleration of the centrifuge model in (g)s.
- Reference: The reference that include all the detailed procedures and analysis of the corresponding experiments.
- Soil Type: The soil used in each experiment. Two types of soils were used in the experiments; Ottawa F55 sand, and silty sand.
- Saturation fluid: The saturation fluid used in each experiment. All the experiments had about the same prototype permeability. In order to achieve that, centrifuge experiments on Ottawa F55 sand were saturated with viscous fluid, while centrifuge experiments on silty sand were saturated with water.
- Shaking Event # : The number of the shaking in the sequence of shakings of each experiment.
- Shaking type: The type of the base motion shaking. In all the cases the base motions were approximately sinusoidal.
- Number of cycles: The number of complete sinusoidal cycles in the corresponding shaking.
- Max. base acc. (g): The peak input acceleration at the base which is typically repeated in all the cycles
- Normalized shear Wave velocity (m/sec): The average normalized shear wave velocity estimated using bender elements generating shear waves propagating in the horizontal direction and polarized in the vertical direction and recorded after the corresponding shaking.
- Max. excess pore pressure ratio near the base: The maximum excess pore pressure recorded by the closest sensor to the base divided by the effective vertical stress at the same location.
- Max. excess pore pressure ratio near the surface: The maximum excess pore pressure recorded by the closest sensor to the surface divided by the effective vertical stress at the same location.
- Settlement, S (mm): The average LVDT settlement at the top of the deposit.
- Cumulative Settlement, S_cum (mm): The cumulative settlement at the top of the deposit from the beginning of the experiment up to the corresponding shaking.
- Model height, H (mm): The initial prototype height of the model minus the cumulative settlement at the top of the deposit.
- Density (kg/m3) : The overall density of the model after the corresponding shaking.
- Relative density (%): The overall relative density of the model after the corresponding shaking.
- Vertical strain (%): The Vertical strain (%) = (S/H) x 100 % due to the corresponding shaking.
- Max. Lat. Def. at the surface (mm): The maximum lateral deformation of the laminar box approximately at the surface of the deposit due to the corresponding shaking.
- Instrumentation: Schematic diagram of the set up and instrumentation of the each model.
- Data file (model units): The data file of each shaking. Typically the data file is composed of several columns. The first column is always the time, which typically uniformly increase with a constant time step that was set by the experimentalist. The rest of the columns are the readings of each individual calibrated sensor. It has to be noted that the results need to be corrected for g-level using the appropriate conventional centrifuge modeling scaling laws.
El-Sekelly W. The Effect of seismic preshaking history on the liquefaction resistance of granular soil deposits. Ph.D. dissertation, Rensselaer Polytechnic Institute, Troy, NY; 2014.
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