NEES/EERI Webinar, Oct. 31: Improving Seismic Performance of Pile Foundations in Soft Clays Using Deep Soil Mixing

A NEES/EERI Research-to-Practice Webinar: Improving Seismic Performance of Pile Foundations in Soft Clays Using Deep Soil Mixing

Presented by: K.K. "Muralee" Muraleetharan, University of Oklahoma; Sri Sritharan (M. EERI, 1994), Iowa State University; Gerald Miller, University of Oklahoma; Amy Cerato, University of Oklahoma; Arul Arulmoli (M. EERI, 1996), Earth Mechanics, Inc.; and Juan Baez, Advanced Geosolutions, Inc.

October 31, 2013, 3:00 – 4:30 p.m. (EST)

Seismic behavior of pile foundations is a complex problem. This complexity is further exacerbated when weak soils such as soft clays or liquefiable sands surround the pile foundations. The behavior of pile foundations in liquefiable sands has been studied extensively; however, similar investigations for soft clays and seismic response of piles in improved soils have received attention only in recent years. Ensuring satisfactory performance of pile foundations during earthquakes is critical for obtaining desirable seismic performance of structures that they support.

In case of weak soils, a design option is to use increased number of larger diameter piles, which are both difficult and expensive to design and construct. An innovative and perhaps more cost-efficient solution to this problem is to use Deep Soil Mixing to improve the soil surrounding the pile foundation near the ground surface, thereby increasing the pile foundation's lateral stiffness and resistance. This method has, however, not found wide usage due to lack of knowledge about the seismic behavior of piles in improved soils.

This NEES/EERI research-to-practice webinar will present results from a recently concluded NEES project called NEES-pilEs (piles in low E soils). The project included centrifuge tests, full-scale field tests, simplified analyses, sophisticated computer simulations, and formulation of seismic design recommendations for single piles and pile groups. The tests and analyses reveal that soil improvement can drastically alter the pile behavior and produce dependable response for both foundations and structures. When compared to the response in unimproved soils, depending on the extent of ground improvement around the piles, piles in improved soft clay produced 2 to 8 times larger stiffness and 4 to 5 times higher lateral force resistance. Furthermore, earthquake loading of centrifuge model pile foundations reveal the importance of incorporating the change in natural frequency of the improved foundation-soil system into the analyses.

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