American Society of Civil Engineers


Decision Process for Selection of Retaining Structure for an Excavation in Soft Clay


by Turan Durgunoglu, (Zetas Zemin Teknolojisi A.S., Resadiye Cad. No: 69/A 34794 Cekmekoy, Istanbul Turkey E-mail: durgunoglut@zetas.com.tr), Fatih Kulac, (Zetas Zemin Teknolojisi A.S., Resadiye Cad. No: 69/A 34794 Cekmekoy, Istanbul Turkey E-mail: kulacfatih@zetas.com.tr), Selim Ikiz, (Zetas Zemin Teknolojisi A.S., Resadiye Cad. No: 69/A 34794 Cekmekoy, Istanbul Turkey E-mail: selim.ikiz@zetas.com.tr), Ali Gunay, (Zetas Zemin Teknolojisi A.S., Resadiye Cad. No: 69/A 34794 Cekmekoy, Istanbul Turkey E-mail: aligunay@zetas.com.tr), and Onder Akcakal, (Zetas Zemin Teknolojisi A.S., Resadiye Cad. No: 69/A 34794 Cekmekoy, Istanbul Turkey E-mail: onder.akcakal@zetas.com.tr)
Section: Research Advances and Case Histories of Deep Excavations, pp. 790-798, (doi:  http://dx.doi.org/10.1061/9780784412121.082)

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Document type: Conference Proceeding Paper
Part of: GeoCongress 2012: State of the Art and Practice in Geotechnical Engineering
Abstract: In recent years the number of shopping malls has increased rapidly parallel to development of the cities within Turkey. Due to the need for large and flat areas, many of these structures have been constructed in areas with poor subsoil conditions. The need for large underground car parks added more to the difficulty of the geotechnical problems. Kagýthane Mall Project described in this paper is a particular case having a difficult geotechnical problems to be solved. The structure is planned to have four basement levels to excavation depth of approximately 17 m. According to the soil investigations, soil profile consists of very soft Golden Horn Clay at the top overlaing bedrock sandstone which is located at a depth ranging from 10 m to 28 m below ground surface. The site is very close to Kagithane River therefore groundwater level is high. The shoring system was decided to be formed as tie back system having multilevel prestressed anchors at the original design. Pre-bidding studies have shown that, high displacements are likely at the sections which have soft clay dominated soil profile because of the low anchorage capacities and low modulus of elasticity of soft clay. Therefore, an alternative shoring system has been studied and proposed to be implemented during the bidding stage. In the proposed system the following construction steps have been implemented. Construction of the diaphragm walls, 5 m deep excavation in front of the diaphragm wall with one row of prestressed anchor, improvement of the soil with jet grouting at this level underneath the foundation and also within the temporary berm against the diaphragm wall, excavation to form a 5 m wide berm in front of the diaphragm wall and then a 1/1 slope to reach the foundation level at -17 m, construction of core part of the superstructure to zero level, level by level excavation to take out the temporary berm replacing it with steel tube struts to support the diaphragm wall from the slabs at the previously constructed core structure, construction of the remaining part of the building by integrating it to the diaphragm walls in slab levels while disassembling the steel struts from bottom to top in parallel with the rise of the building. This alternative system has shown to limit the expected displacements therefore to make a safe construction possible, to shorten the construction period and to bring cost reduction in overall project.


ASCE Subject Headings:
Retaining structures
Excavation
Clays