Discussion of "High-modulus columns for liquefaction mitigation" by James R. Martin II, C. Guney Olgun, James K. Mitchell, and H. Turan Durgunoglu

This paper presents the performance of a shopping complex in Turkey where the soils were improved with jet-grout columns and preload fills and subjected to the 1999 Kocaeli Earthquake (M=7.4). Under construction at the time of the earthquake, the Carrefour Shopping Center covers an area of 55,000m2 and is founded on shallow footings, mats, and slabs-on-grade that rest on soft, saturated alluvial sediments consisting of clays, silts, and sands. High-modulus columns constructed by jet grouting were installed at close-to-moderate spacings to reduce anticipated static settlements in the clays and mitigate liquefaction in the sands. The site was subjected to a peak acceleration of approximately 0.2g during the earthquake. Grouting had been completed for about two-thirds of the site when the earthquake struck. Following the event, a field reconnaissance found stark contrast between the performance of the improved and unimproved sections. The jet-grout-treated areas suffered no apparent damage, whereas the unimproved sections of the complex, along with nearby untreated building sites, commonly suffered liquefaction-related settlements of up to 10 cm. This is the only case history known to the authors that documents the field performance of high-modulus columns used in this manner for liquefaction mitigation and direct instrumented measurement of liquefaction-induced settlements

An overview of local site effects and the associated building damage in Adapazari during the 17 August 1999 Izmit earthquake

Two major earthquakes occurred in Turkey along the North Anatolian fault in 1999. The first one, which occurred on 17 August 1999, had a moment magnitude of 7.4 and ruptured the 140-km segment of the fault in the Marmara region. Adapazari, a city with a population of 190,000, which is mostly located on a deep alluvial basin in the near field of the ruptured fault, was among the worst-affected urban areas in the earthquake-affected region. The distribution of damage over the city was highly nonuniform, indicating the variability of the ground response to the strong motion. Five- to six-story buildings located over deep alluvial soils were most adversely affected by the earthquake. Geotechnical characteristics of the alluvial basin of Adapazari are evaluated using the deep and shallow borehole Iogs and the measured parameters from the field and laboratory. This data is used for developing representative one-dimensional site-response models for various depths of alluvium and for liquefaction assessment in saturated surface soils. Recorded data from several aftershocks are utilized for model calibration. The results of soil-response studies are found to be highly Correlated with the general trends in the intensity and distribution of building damage. Based on in situ tests, soil liquefaction is determined to have occurred extensively in Adapazari which is in conformity with the postearthquake observations of widespread liquefaction-induced foundation displacements. Evidently, liquefied soil layers served as passive isolation mechanism for numerous buildings, some of which were subjected to excessive foundation displacements of various forms without signs of significant structural damage

Just how prescient are our building damage predictions?

Adapazari was the scene of spectacular structural damage as well as widespread liquefaction after the earthquake of August 17, 1999. Damage patterns observed are re-examined to investigate whether they are indicative of a consistent trend explicable in terms of the building attributes and/or site conditions. 301 buildings that had collapsed fully have been re-evaluated from their design blueprints. An examination based solely on structural attributes, including data from other sets of building assessment projects, leads us to believe that building collapse is perhaps just too involved to reduce to a few simple guilt pointers. Site effects might have played a major role in the observed damage, because only a conflicting trend between structural attributes and the actual damage can be established

Re-examination of damage distribution in Adapazari: Structural considerations

Adapazari was the scene of spectacular structural damage as well as widespread foundation displacement that occurred in the city during the devastating earthquake of August 17, 1999. The damage patterns observed in Adapazari were quite peculiar, so these are re-examined in an effort to answer the question of whether they are indicative of a consistent trend in terms of the building attributes and/or site conditions. For this purpose two databases comprising buildings surveyed in Adapazari after the earthquake have been re-evaluated. The first data set included buildings that had collapsed fully; hence no complete data on the as-built properties have been assembled. Their examination was necessarily a desk study conducted from the design blueprints of the individual buildings that no longer existed. The second source was a larger database comprising buildings that had experienced various levels of damage and examined using conventional evaluation procedures. All buildings were rated from the viewpoint of conventional seismic performance using accepted parameters to confirm the observed damage. An examination based solely on structural attributes leads us to believe that building collapses observed in Adapazan are perhaps too involved to reduce to a few simple deficiency attributes. The site effects seem to have played a major role in the observed damage, because conflicting trends of structural attributes and the actual damage were established. A companion paper focuses on the influence of site effects on the observed building damage

Re-examination of damage distribution in Adapazari: Geotechnical considerations

The role of ground conditions in damage distribution patterns of buildings in the city of Adapazari during the 17 August 1999 Izmit (Kocaeli) earthquake (M-w 7.4) is investigated. Damage was concentrated in the central districts of the city over the alluvial basin where four to seven-story reinforced concrete buildings were most adversely affected. Two distinct and mutually exclusive modes of building damage were observed on the alluvium: structural system failures due to strong ground shaking, and foundation bearing failures apparently associated with soft or liquefiable surface deposits. To estimate the variation of surface response during the earthquake, the sites were classified as either stiff or soft, based on the amplification and de-amplification characteristics determined through analysis of one-dimensional soil response models. The results are compiled to develop an idealized codification of site-specific spectra that is utilized to assess the variation of spectral accelerations associated with the earthquake throughout the city. The outcome is consistent not only with the general trends pertaining to the distribution of building damage in terms of collapse data and post-earthquake observations, but it also predicts the respective sites of occurrence of the two distinct damage modes successfully. Accordingly, it is concluded that the buildings over soft sites benefited from significant reductions in seismic demand owing to the strong nonlinear soil response, and escaped pancake-type collapse

Site classification of Turkish national strong-motion stations

Since 1973, the General Directorate of Disaster Affairs of Turkey has deployed several strong-motion accelerographs at selected sites. Within the framework of the project entitled Compilation of National Strong Ground Motion Database in Accordance with International Standards, site conditions were investigated within the upper 30-m depth by surface seismic and standard penetration tests. Preliminary characterization of the sites is made by making use of both geophysical and geotechnical criteria of NEHRP Provisions and Eurocode-8 site classification systems. The liquefaction susceptibility of those sites which comprise saturated cohesionless deposits is also determined. Mean shear-wave velocity, mean penetration resistance, site class, and liquefaction susceptibility of each site are tabulated. The Turkish strong-motion database supplemented by detailed information on site conditions is a valuable source of information particularly for those studies that put emphasis on the relationship between site conditions and strong-motion parameters