Soil Improvement (2007-2011)
NEESR-SG: Soil Improvement Strategies to Mitigate Impact of Seismic Ground Failures via Novel Integration of Experiment and Simulation
Principal Investigator: Scott Olson (University of Illinois at Urbana-Champaign)
Co-Principal Investigators: Youssef Hashash (University of Illinois at Urbana-Champaign), Carmine Polito (Valparaiso University)
Seismically-induced ground failures are a pervasive and growing source of economic loss from earthquakes. Concurrently, growing infrastructure needs demand more and larger bridges with increased spans and traffic volumes, thus requiring the use of large, stiff foundations such as large diameter shaft groups or gravity caissons. When seismically-induced ground failures occur, these foundations must contend with large, but unknown, lateral forces. A common solution is to conservatively remediate large blocks of soil susceptible to failure, which involves high construction costs, increased construction time, and greater environmental impacts.
This NEESR-SG project led by investigators at the University of Illinois and Valparaiso University are evaluating novel ground improvement geometries (e.g., chevrons, arches) to “deflect” laterally moving soil thereby reducing:
- lateral loads on large foundation elements;
- ground improvement costs; and
- time and environmental impacts.
This is being accomplished via an innovative integration of centrifuge experiments (performed at RPI) and Self-Learning Simulations (SelfSim) using OpenSEES, termed “Simulation-designed Experiment – Experiment-driven Simulation” (SDE-EDS) that is at the heart of NEES’ Grand Vision. This novel integration will result in robust mitigation strategies for seismically-induced ground failure that can be implemented in a Performance-based Earthquake Engineering (PBEE) environment.
Our team is using the NEES centrifuge facility at RPI to physically model a number of caisson/ground improvement configurations to develop the methods needed to mitigate the consequences of lateral spreading on these large, rigid foundation elements. The cornerstone of lateral pressure measurement in this research is the use of tactile pressure sensors. This technology has made it possible to record total pressure on the caisson and ground improvement element at discrete areas with time. The following photos show how the tactile pressure sensor has been used on the model caisson as a means to record total earth pressure time histories during cyclic loading in the centrifuge.
The purpose of this testing program is to measure pressures induced against a rigid foundation as a result of lateral spreading-induced movement toward the caisson. Some of the tests are conducted to observe the lateral pressures developed against the caisson with soil profiles both with and without an upper clay cap (intended to be a relatively non-liquefiable stratum). Other later tests include the use of a deflection wall of varying configuration immediately upslope of the caisson. The purpose of the ground deflection wall is to observe whether there is a decrease in lateral pressures against the caisson, and to quantify the change as compared with the tests not containing a deflection wall.
Test I-B includes the caisson without a deflection wall. This test has a 2 m thick clay cap at the surface, underlain by 8 m of potentially liquefiable sand. The purpose of this test is to observe and quantify lateral pressures on the caisson as a result of the downslope soil movement induced by lateral spreading.
Test II-A includes the caisson with a “V” shaped ground deflection wall. The soil profile in this test includes 10 m of potentially liquefiable sand.
Test II-B is essentially the same as Test II-A, but has a different soil profile; a 2 m clay cap, followed by 8 m of potentially liquefiable sand.
Test II-C has the same soil profile as Test II-B, but includes a ground deflection wall of a different configuration. In this test the ground deflection wall is a semi-circle.