Collapse mechanism of the Antalya Tufa deposits

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2002
Dipova, Nihat
This research aims assessment of collapse mechanism of Antalya Tufa deposits. Antalya city has settled on tufa deposits. However, it was named as travertine previously, deposition in cool water regime and biogenic origin, imply that use of tufa term is more appropriate. At the end of the eighties, the area behind the Antalya tufa cliffs started to be occupied by buildings. However, some of these high-rise buildings suffer from foundation instabilities. Cracking and fissuration of the walls and overall tiltings were typical indications of differential settlement that buildings were suffering. The settlement of foundations was a result of collapse behavior of some tufa types upon loading and/or wetting. Studies started with investigation of geological properties of tufa. An extensive field work was carried out to determine aerial distribution of the problematic material. Properties of grains, voids and bonding material were searched by using microscope and scanning electron micrograph (SEM) techniques. Disturbed and undisturbed samples were recovered and laboratory tests were performed to determine index geotechnical properties and collapse potential (Cp). mThe studies indicated that, depositional environment and micro-fabric are closely related to geotechnical behavior of tufa. Tufas are the products of physico-chemical and biogenic precipitation. In biogenic process, precipitation is the cause of decreasing partial pressure of CO2 by photosynthesis of algae or bacteria. After precipitation, tufa undergo meteoric- vadoze cementation and diagenesis. Relatively young deposits near the surface, are weakly bonded with thin films of carbonate cement. Void ratio is relatively high and around 1.00. Collapse occurs as a result of destruction of the weak bonds upon loading and/or wetting. In the collapsible Antalya Tufa, under additional load, foundation soils collapse under natural water content without additional water. However, water addition increases collapse initially triggered by pressure increase. In this study, a technique for undisturbed sampling from an excavation pit, has been introduced. Soil index parameters, collapse potential (Cp) and coefficient of volume compressibility (mv) were determined by laboratory methods. Cp and mv were correlated with index parameters and empirical predictive models were developed. For prediction of settlement of foundations resting on collapsible tufa, two laboratory techniques and one empirical method were presented. Traditional soil improvement techniques were discussed and suitable techniques for collapsible Antalya Tufa were recommended.

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Citation Formats
N. Dipova, “Collapse mechanism of the Antalya Tufa deposits,” Ph.D. - Doctoral Program, Middle East Technical University, 2002.