Haliç üstünde inşa edilen ve edilmekte olan Haliç Köprüsü, Yeni Galata Köprüsü, Haliç Metro Geçiş Köprüsü sondajlarından ve yapım sırasında elde edilen bilgiler, bu bölgedeki zeminlerin özellikleri hakkında ayrıntılı bilgiler elde edilmesini sağlamaktadır. Membadan mansaba doğru bu köprüler Haliç Köprüsü, Haliç Metro Geçiş Köprüsü, Yeni Galata Köprüsü olarak sıralanmaktadır. Yeni Galata Köprüsü kazıklarının girdiği çakıl tabakası, yaklaşık 80 m derinliktedir. Haliç Metro Metro Geçiş Köprüsü ekseninde kaya tabakasının derinliği, Azapkapı tarafında 55 metreden, Unkapanı tarafında 80 metreye alçalmaktadır. Yeni Galata Köprüsü kazıklarının oturduğu çakıl tabakası, Haliç Metro Geçiş Köprüsü yerindeki kaya tabakasına göre yatay olarak kabul edilebilir. Buna karşılık, Haliç Metro Geçiş Köprüsü’nün Unkapanı tarafında taban kayasında derin bir çukur bulunmaktadır. Böyle bir çukurun varlığı, Haliç’te kaya yüzeyinin enine ve boyuna doğrultudaki genel eğimlerine uymayan bir durum oluşturmaktadır. Kaya tabakaları çok yumuşak, kalın kil/silt tabakaları ile örtülüdür. Kıyılarda kalın şehir dolgusu bulunmaktadır. Yumuşak tabakaların üst yüzü hemen hemen yataydır ve bu durum zeminin yüksek su muhtevasını yansıtmaktadır. Likit limit kıvamında tabakalar, bir çanak şeklindeki taban kayasını doldurmaktadır. Haliç’in büyük ekseni boyunca kaya tabakasının derinliği, Haliç’in ağız kısmına doğru büyük bir eğimle alçalmakta ve 80 m kadar derinliğe ulaşmaktadır. Anahtar Kelimeler: Haliç (Golden Horn), yumuşak killi zeminler, çatlaklı ayrışmış kayalar.The Golden Horn is a seven and half kilometres long natural inlet of Boğaziçi Strait. It has a maximum width of about 700 m near its entrance. At its deepest part its depth is 40 m. The Golden Horn divides historical part of the city from the rest. The geology of the Istanbul area has been studied by many investigators. Penck was first to recognize the shales and graywackes as the oldest of the formations encountered in the area. He named them as the Thrace series. Subsequent investigations indicated the existence of various lithological and paleontological zones in Thrace series, and it is concluded that they belonged to the Early Carboniferous Period of the same era. Over centuries, the detritus brought by Alibey, Kâğıthane, and other creeks, heavy industrial and domestic wastes, and uncontrolled fills have changed drastically almost the entire cross section of the Golden Horn. Along the shores, many valleys have been levelled off by generally uncontrolled fills, and comparatively large areas have been reclaimed.The thickness of the man-made fill is over 40 m along the south shore and over 30 m along the north shore on the axis of the New Galata Bridge. The thickness of the fill decreases with increasing distance from the shore. Man-made fill is underlain by sedimentary deposits consisting of sand, silt and clay in varying proportions. In general it is described as grey-dark organic silty clay of marine origin. On the Eminönü (South) site of the New Galata Bridge, the soft layers are underlain by a few meters thick weathered shale. Over the deeper part of the waterway and towards the Karaköy side soft layers is underlain by cobbly gravel. The design of new bridges over the Golden Horn was subject to severe constraints. The New Galata Bridge is founded on large diameter tubular steel piles. Piles were driven into limestone, diabase and sandstone origined gravel which is encountered between the depths of 76 m and 88 m. Most of the piles of the New Galata Bridge were driven into the shuttered rock bottom. The adoption of a closed end pile having a diameter as large as 2000 mm is well suited to the soil conditions and the design requirements – the damage of the pile tip is prevented, settlement criteria are satisfied. The piles of the New Galata Bridge were designed to carry high working loads (up to 12 000 kN) in end bearing and to comply with severe restrictions on allowable settlement. A box girder bridge carried on temporary supports was constructed over the test pile and was loaded by ingots. Four hydraulic jacks were placed on the head of the test pile to obtain a total reaction of 2000 tonnes. The composite piles of the Metro Crossing Bridge extended to depths over 100 m. They were designed to carry even higher loads (up to 47 000 kN). Osterberg type of loading tests was made on Metro Crossing Bridge. In general dynamic measurements are not considered as a reliable substitute to static pile loading test. On the Metro Crossing Bridge site, dynamic analysis (PDA) is carried out and dynamic response during pile driving is also recorded. Results are found consistent with the exploration data. Depth of water on the axis of Metro Crossing Bridge is about 34 m. Soil profile is overlain by very soft, almost at liquid consistency, silt clay layer. The thickness of clay layer varied between 30 m and 50 m. Very soft silty clay layer is underlain by sandstone, siltstone and mudstone layers. Depth of rock is 55 m at Azapkapı (North) and 80 m at Unkapanı (South) side of the Bridge. Sea bottom at Golden Horn Bridge site is very shallow. Depth of rock is more than 70 m and is overlain by a gravel layer. The depth of exploration at Metro Crossing Bridge site was well over 100 m. Special attention was given to ascertain the level and characteristics of a suitable stratum. Form the initial data indicated existence of weathered rocks and alternating strong and weak rock formations. Soil investigations and pile driving provided ample information about the rock bottom of the Golden Horn. Rock levels at the site of Golden Horn Bridge and at the site of New Galata Bridge are almost flat in comparison with that of the Metro Crossing Bridge. Furthermore transversal profile of the rock bottom at Metro Crossing Bridge contains a deeper section near Unkapanı (South). Existence of such depression is not confirming with the general slopes of the rock strata. Keywords: Golden Horn, soft clayey soils, soft rocks
