Case History for Soil Improvement of SETAT 2002 High Rise Residential by Jet Grouting in Istanbul

The subject site is located on steep slopes of Ortakoy valley, which has been filled with excavation materials obtained from the first Bosphorous Bridge and other nearby construction sites in time. There are two high-rise towers planned in the project, which are structurally and rigidly connected at the basement and at the upper three floor levels with a bridge type of passage. The basement of the high-rise towers lead to some 20 m (66 ft) deep excavations, partially in the fill, and partially in the original ground, which is greywacke, (alternating layers of claystone, siltstone and sandstone). As a result, the foundation level of the towers seated partially on greywacke and partially on the artificial, uncontrolled fill of varying thickness up to 15 m (49 ft). The site is seismically very active and any irregular displacement of the towers with respect to each other is intolerable. As a result, it was decided that the towers should have similar foundations with the subsoil under the towers having similar compression modulus values so that they will both contribute equally to respective displacements. For this purpose, improvement of the fill by means of jet grouting is considered to be the most appropriate procedure. Jet grouted columns are designed so that, they can provide sufficient capacity for superstructural loads i.e. load carrying members and also the improved soil would have similar modulus value with the greywacke bedrock. The quality control and quality assurance of the above criteria are done by means of jet grout loading tests, plate loading tests, and coring and compressive strength tests of the cores obtained from jet grouted columns presented in this article. The tests indicated a successful application of the improvement even in an uncontrolled artificial fill.