NEESR-SG: Study of Pile Foundations Subjected to Liquefaction-Induced Lateral Spreading
Test SG-1
Researchers studying earthquake-induced “soil liquefaction” and its effects on foundations that support water front infrastructure have developed an earthquake simulator to model the response of water-saturated sand under earthquake forces. During strong shaking, loose sand often turns into ‘liquid-like’ material and causes damage to structures sitting on top or embedded in the soil. The goal of the research is to learn how soil becomes “liquefied” and contribute to failure of foundations that support bridges, ports and harbor structures, or buildings.
The researchers have completed two successful level ground liquefaction experiments (3m test and LG-0) using the large-scale earthquake liquefaction simulator and will conduct additional tests in the coming months. These experiments will be web cast live.
Experiment Setup
The researchers have developed a new earthquake-induced liquefaction simulator using a 5 m long, 2.75 m wide and 6 m high laminar stack ring system capable of containing about 150 tons of sand at the NEES laboratory at the University at Buffalo, State University of New York. The rings are stacked vertically, separated by ball bearings allowing sliding between the rings. The laminar stack and its base sit on large bearings on the strong floor, and is slightly inclined 2 degrees to simulate sloping ground. After being filled with loose sand and water (approximately 20 ft), when the base is shaken using two 100-ton hydraulic actuators with strong vibrations representative of those occurring at deeper firm ground during an earthquake, the soil liquefies and spreads laterally. A robust hydraulic fill method allowing sand grains to slowly fall through water mimicking natural alluvial deposition of sands in rivers, lakes, or man-made port islands is used to build the ground inside the laminar rings, at a target density verified by density tests and cone penetration measurements. A computer controlled shaker capable of 200 ton force powered by four MTS pumps each rated at 185 gpm flow with 3.000 psi working pressure was developed to provide precise synthetic or past records of earthquake motions at the base.
Advanced instrumentation techniques using a dense sensor array of MEMS accelerometers, piezometers, potentiometers, and digital image analyzers are used to closely monitor the time-history of accelerations, dynamic water pressures, and vertical and lateral spreading within the ground. The tricky part of the problem is to understand how the ‘liquefied sand’ constantly changes its response during and immediately following the earthquake.
Updates
May 9, 2007 as a part of the NEESPiles
project sponsored by the NSF a slope-ground (2 ° incline)
liquefaction test will be conducted on Thursday, May 10 at 10:00 am EDT, using the laminar box.
In this test the laminar box
is filled with saturated loose sand up to a height of approximately 20
feet, and subjected to a sinusoidal 1-D ground motion at the base with
a peak horizontal acceleration of about 0.3g. The soil is instrumented
with a dense array of piezometers,MEMS accelerometers (shapeaccel
array), and potentiometers (for measurement of lateral displacements
of the box, and vertical settlement of the ground surafce during and
after shaking).
Previous Experiments
Sponsor
This project is supported by the George E. Brown, Jr. Network for Earthquake Engineering Simulation program of the National
Science Foundation under award number CMS-0529995.
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