Location

San Diego, California

Session Start Date

3-26-2001

Session End Date

3-31-2001

Abstract

During the 1995 Kobe earthquake widespread liquefaction occurred in fill deposits of man-made islands in the port area of Kobe. The liquefaction of thick fill deposits resulted in extensive sand boils, large lateral movement and settlement of the ground. A number of piles has been found damaged or collapsed due to the excessive ground response as above. One important observation from the Kobe earthquake was that fewer signs of liquefaction and lesser ground deformation were found in reclaimed deposits that have been treated by ground improvement measures. In order to investigate the effects of liquefaction and ground improvement on the performance of pile foundations, a detailed study was conducted on a well-documented case history from the Kobe earthquake. This paper highlights the effects of liquefaction and ground improvement by sand compaction piles on the response of an oil-storage tank supported on pile foundations. On the west part of the man-made Mikagehama Island, a 2450 kl oil-storage tank is located. The tank is supported on 69 high-strength concrete piles with a diameter of 45 cm. The surface layer at the tank site is a 13.6 m thick deposit of reclaimed gravelly soil. The loose fill deposit is fairly uniform and has rather low SPT resistance of 5 to 6 blow counts throughout the depth. Around the perimeter of the pile foundation, sand compaction piles have been installed down to a depth of 15 m, thus forming a 4 m thick belt zone of improved soil around the foundation. As a result of the ground improvement, the SPT resistance in the fill deposit significantly increased and reached values of 1 O-30 blow counts in the SCP zone and 20-40 blow counts in the foundation soil respectively. To investigate the response of the soil-pile-tank system induced by the Kobe earthquake and examine the effects of liquefaction and soil improvement, a series of effective stress analyses was carried out. In the analyses, both soil and pile were modeled as elastoplastic materials. Material parameters of the fill deposits were determined based on results from field investigations and multiple series of laboratory tests on undisturbed samples recovered by means of the ground freezing technique. The influence of oil oscillation and effects of sloshing were accounted for by a simple mass-spring system representing the dynamic action of a fluid in a tank. It was found that even though the excess pore pressures reached the effective overburden stress level in both unimproved and improved soils, the computed maximum shear strains in the ground were significantly reduced as a result of the ground improvement. The effects of ground improvement were clearly reflected on the pile response through a reduction in both displacements and bending moments of piles. Peak bending moments exceeding the yielding level were computed at the depth of the interface between the liquefied fill layer and non-liquefied silty soil layer where also the largest actual damage to the piles was observed in a close inspection of two piles of tank TA72 by bore-hole camera recordings.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conferences on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics

Meeting Name

Fourth Conference

Publisher

University of Missouri--Rolla

Publication Date

3-26-2001

Document Version

Final Version

Rights

© 2001 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Mar 26th, 12:00 AM Mar 31st, 12:00 AM

Effects of Liquefaction on Seismic Response of a Storage Tank on Pile Foundations

San Diego, California

During the 1995 Kobe earthquake widespread liquefaction occurred in fill deposits of man-made islands in the port area of Kobe. The liquefaction of thick fill deposits resulted in extensive sand boils, large lateral movement and settlement of the ground. A number of piles has been found damaged or collapsed due to the excessive ground response as above. One important observation from the Kobe earthquake was that fewer signs of liquefaction and lesser ground deformation were found in reclaimed deposits that have been treated by ground improvement measures. In order to investigate the effects of liquefaction and ground improvement on the performance of pile foundations, a detailed study was conducted on a well-documented case history from the Kobe earthquake. This paper highlights the effects of liquefaction and ground improvement by sand compaction piles on the response of an oil-storage tank supported on pile foundations. On the west part of the man-made Mikagehama Island, a 2450 kl oil-storage tank is located. The tank is supported on 69 high-strength concrete piles with a diameter of 45 cm. The surface layer at the tank site is a 13.6 m thick deposit of reclaimed gravelly soil. The loose fill deposit is fairly uniform and has rather low SPT resistance of 5 to 6 blow counts throughout the depth. Around the perimeter of the pile foundation, sand compaction piles have been installed down to a depth of 15 m, thus forming a 4 m thick belt zone of improved soil around the foundation. As a result of the ground improvement, the SPT resistance in the fill deposit significantly increased and reached values of 1 O-30 blow counts in the SCP zone and 20-40 blow counts in the foundation soil respectively. To investigate the response of the soil-pile-tank system induced by the Kobe earthquake and examine the effects of liquefaction and soil improvement, a series of effective stress analyses was carried out. In the analyses, both soil and pile were modeled as elastoplastic materials. Material parameters of the fill deposits were determined based on results from field investigations and multiple series of laboratory tests on undisturbed samples recovered by means of the ground freezing technique. The influence of oil oscillation and effects of sloshing were accounted for by a simple mass-spring system representing the dynamic action of a fluid in a tank. It was found that even though the excess pore pressures reached the effective overburden stress level in both unimproved and improved soils, the computed maximum shear strains in the ground were significantly reduced as a result of the ground improvement. The effects of ground improvement were clearly reflected on the pile response through a reduction in both displacements and bending moments of piles. Peak bending moments exceeding the yielding level were computed at the depth of the interface between the liquefied fill layer and non-liquefied silty soil layer where also the largest actual damage to the piles was observed in a close inspection of two piles of tank TA72 by bore-hole camera recordings.