Liquefaction Potential Analysis Research Articles

Updated liquefaction potential analysis eliminates foundation retrofitting of two critical structures

Developments in geotechnical engineering after 1970 prompted the reevaluation of the foundations of three large nuclear material processing buildings in 1994. Concerns were raised because the subsurface conditions beneath them contain a Miocene-age clayey sand stratum with very low standard penetration resistance values. A preliminary liquefaction potential evaluation based on Seed et al. [The influence of SPT procedures in soil liquefaction resistance evaluation. Report no. UCB/EERC-84/15, October 1984] empirical procedures for Holocene-age data showed that based on the low blowcount the formation was liquefiable, and that foundation retrofitting was in order.Analysis of the soil performance during the Charleston, South Carolina earthquake indicated that the dynamic strength of sands increases with the age of the deposit [Lewis et al. Liquefaction resistance of old sand deposits. Paper presented at the Pan American Soil Mechanics Conference held in Brazil, 1999], a finding in agreement with conclusions reached earlier by Skempton [Standard penetration test procedures and the effects in sands of overburden pressure, relative density, particle size, aging and overconsolidation, Geotechnique 36(3) (1986) 425–447], and, confirmed later, by Kramer and Arango [Aging effects on the liquefaction resistance of sand deposits: a review and update. Proceedings of the Eleventh European Conference on Earthquake Engineering, Paris 1998, Abstract vol. 184]. Because of the age of the sands at the subject sites, it was decided to test in the laboratory the potential strength gain of the site soils due to aging relative to the values derived from the empirical chart. The laboratory test results demonstrated a strength increase by a factor between 2 and 3. Based on these findings, it was concluded that there was no need to retrofit the building foundations, thus saving several million dollars.The paper describes the buildings, the geologic setting and the field and laboratory work performed in this investigation, a summary of field performance of sands during the Charleston and Northridge earthquakes, and presents a design-oriented chart to predict the dynamic strength increase with age of sand deposits older than Holocene period.

Liquefaction Evidence for the Strength of Ground Motions Resulting from Late Holocene Cascadia Subduction Earthquakes, with Emphasis on the Event of 1700 A.D.

During the past decade, paleoseismic studies done by many researchers in the coastal regions of the Pacific Northwest have shown that regional downdropping and subsequent tsunami inundation occurred in response to a major earthquake along the Cascadia subduction zone. This earthquake occurred almost certainly in 1700 a.d., and is believed by many to have been of M 8.5–9 or perhaps larger. In order to characterize the severity of ground motions from this earthquake, we report on a field search and analysis of seismically induced liquefaction features. The search was conducted chiefly along the banks of islands in the lowermost Columbia River of Oregon and Washington and in stream banks along smaller rivers throughout southwestern Washington. To a lesser extent, the investigation included rivers in central Oregon. Numerous small- to moderate-sized liquefaction features from the earthquake of 1700 a.d. were found in some regions, but there was a notable lack of liquefaction features in others. The regional distribution of liquefaction features is evaluated as a function of geologic and geotechnical factors in different field settings near the coast. Our use of widely different field settings, each in which we independently assess the strength of shaking and arrive at the same conclusion, enhances the credibility of our interpretations. Our regional inventory of liquefaction features and preliminary geotechnical analysis of liquefaction potential provide substantial evidence for only moderate levels of ground shaking in coastal Washington and Oregon during the subduction earthquake of 1700 a.d. Additionally, it appears that a similar conclusion can be reached for an earlier subduction earthquake that occurred within the past 1100 years, which also has been characterized by others as being M 8 or greater. On the basis of more limited data for older events collected in our regional study, it appears that seismic shaking has been no stronger throughout Holocene time. Our interpreted levels of shaking are considerably lower than current estimates in the technical literature that use theoretical and statistical models to predict ground motions of subduction earthquakes in the Cascadia region. Because of the influence of estimated ground motions from Cascadia subduction-zone earthquakes on seismic hazard evaluations, more paleoliquefaction and geotechnical field studies are needed to definitively bracket the strength of shaking. With further work, it should be possible to extend the record of seismic shaking through much of Holocene time in large portions of Washington and Oregon.

Magnitude Scaling Factors for Soil Liquefaction Evaluations

Energy concepts are applied to the conditions that are likely to have existed at distant liquefaction sites in past earthquakes. From this, magnitude scaling factors are derived that reflect field cyclic strength conditions. It is shown in the paper that the factors are independent of the field acceleration assumed to have existed at the sites, and are only dependent on the magnitude-equivalent number of cycles relationship. These factors are compared with others based on laboratory cyclic strengths from Seed and Idriss and on statistical regression of data from field case histories of liquefaction. The factors derived based on energy concepts are similar to those derived by Ambraseys based on a statistical analyses of extensive liquefaction data. It is concluded that the factors derived in the paper based on energy concepts, or by Ambraseys, appropriately represent field conditions and avoid the limitations and extrapolations of the laboratory-based derivation by Seed and Idriss, and they are recommended for use in the analysis of liquefaction potential.

Reduction factor for liquefaction potential analysis : Ho, C L; Kavazanjian, E Soil Dynam Earthq EngngV9, N6, Nov 1990, P313–322

Reduction factor for liquefaction potential analysis : Ho, C L; Kavazanjian, E Soil Dynam Earthq EngngV9, N6, Nov 1990, P313–322

Reduction factor for liquefaction potential analysis

A probabilistic method to evaluate liquefaction potential based on uniform cyclic laboratory tests is developed. In this method, a peak shear stress reduction factor and a number of uniform cycles of load are paired to yield probabilities of initial liquefaction equivalent to that from nonuniform earthquake loading. An illustrative analysis is presented for a hypothetical site. The method is then used to analyze a case study of a site known to have liquefied during the 1981 Westmorland, CA earthquake.

LIQUEFACTION POTENTIAL MAP IN TOKYO LOWLAND

In order to identify liquefaction susceptibility for wide area, it is necessary to have as much information as possible in the area under consideration. In this study, a computer aided system has been developed to facilitate engineering decision-making concerning liquefaction susceptibility. The man-machine interactive system and graphic display capability give an engineer not only the final evaluated result but also information needed to understand the background knowledge on the factors of liquefaction likelihood. The liquefaction potential lots map in Tokyo Lowland was compiled from the indices of liquefaction potential analysis, the information about liquefaction generated during the Kanto earthquake, and the characteristics of geography and geology.The system engineering procedure was useful for the interactive evaluation of a great amount of information and for the decision about poorly defined problems such as the assessment of liquefaction potential mapping. A result of these studies showed that the liquefiable area was about one forth of Tokyo Lowland.

Numerical analysis of liquefaction potential of partially drained seafloors

The cyclic normal and shear stresses induced in the seafloor sands by sea waves, generate transient and residual pore-water pressures. When the pore pressure becomes equal to the total normal stress the soil liquefies and loses its strength. This paper presents a numerical method for evaluating pore-water pressure build-up and liquefaction potential of offshore sites, in which partial drainage is implemented through a two-dimensional consolidation model. The effect of soil permeability, relative density and deformability on pore-pressure generation is studied and an application of the method to evaluate the liquefaction potential of a North Sea site is examined.