Geotechnical Properties of Nicosia Soils, Cyprus
Total Page：16
File Type：pdf, Size：1020Kb
d 2n International Conference on New Developments in Soil Mechanics and Geotechnical Engineering, 28-30 May 2009, Near East University, Nicosia, North Cyprus Geotechnical properties of Nicosia soils, Cyprus C. Atalar Department of Civil Engineering, Near East University, Nicosia, North Cyprus, [email protected] B.M. Das D ean Emeritus, California State University, Sacramento,U.S.A. [email protected] KEYWORDS: Alluvium soils, swelling clays, Montmorillonite, water fluctuation, liquid limit. ABSTRACT: Swelling clays, Alluvial soils, collapsible soils and evaporitic bedrocks constitute the major problematic soils of Cyprus. The walled city of Nicosia and its closed surroundings are covered by fill. Alluviums of low bearing capacity and collapsible soils are present around the Pedios river in the southeast, southwest, and at the old bed of Pedios stream in the northeast. Swelling clays are extensively exposed around the city. Extensive outcrops of uncemented gravel covers part of the southeast and southwest. Calcarenite, sandstone and limestone of high bearing capacity are exposed in the south and southeast. Evaporitic bedrocks mainly gypsum are generally present on the surface or just below the surface and at the banks of the streams. Field studies, geotechnical investigations, geotechnical properties, X-ray diffraction, and scanning electron microscopy results are presented. These studies were conducted around Nicosia during the last eight years. Swelling clays of Nicosia are Nicosia Formation Clays and Kythrea Group Clays. Swelling potential of Nicosia Formation Clays are high to extremely high and Kythrea Group Clays are intermediate to high . The clay minerals contained large amounts of montmorillonite, lesser amounts of illite and kaolinite. The alluviums also contain high amount of montmorillonite. These alluviums show relatively high apparent strength in their dry state. However, with saturation their strength decreases. These clayey soils have low to medium swelling potential. 1 INTRODUCTION Cyprus with an area of 9,251 km² is the third biggest island in the Mediterranean sea, and the biggest island in Eastern Mediterranean region. North Cyprus covers an area of 3,299 km². The ancient settlements and the early building sites of Cyprus were located at the top or the slopes plateau of the rocky hills. The first Cypriot capital Enkomi (Alasya) (1700 BC) was established at a rocky plateau on the north bank of the Pedieos river near present day Famagusta (Gazimagusa). Soli (1193 BC) one of the ten city-kingdoms of Cyprus was build on pillow lavas at the northern slopes of Trodos mountains, Vuni Palace (498 BC) was build on top of a limestone cap of pillow lavas and the Limniti (Yeşilırmak) islet (7,000 BC) is on top of limestone hill all near day Lefka (Lefke). Nicosia, the present capital is one of the few island capitals that do not lie on the coast. Nicosia was a city-state known as Ledra or Ledrae in ancient times. Ledra in Hellenic and Roman times was a small, unimportant town. The city became the island's capital around the 10th century. It had grown in importance because of threats of pirates to the coastal capitals Paphos and Salamis, which made many people flee to the centrally located Nicosia. It has risen to its present importance as the 360 d 2n International Conference on New Developments in Soil Mechanics and Geotechnical Engineering, 28-30 May 2009, Near East University, Nicosia, North Cyprus administrative capital only since Lusignan times (1192). The seat of the Lusignan kings of Cyprus since 1192, it became a Venetian possession in 1489, and Ottoman Empire possession in 1570. The British Empire leased the island in 1878, with Nicosia serving as the capital of the new British possession. Nicosia was built on a thick alluvium avoiding the nearby clay hills to avoid damages from the swelling clays. However, soft alluviums also sometimes may cause major geotechnical problems. Bedestan is the oldest building suffered damages due to soft alluviums (Figure 1a). Nicosia is covered by extensive surficial deposits of soft soils. The walled city and its closed surroundings are covered by artificial fill (Figure 1b). Alluviums of low bearing capacity are present around the Pedios river in the southeast, southwest, and at the old bed of Pedios river in the northeast. Marl is extensively exposed in the eastern and western parts of the city. Extensive outcrops of uncemented gravel covers part of the southeast and southwest. Calcarenite, sandstone and limestone of high bearing capacity are exposed in the south and southeast (GSD 1982; De Coster et al. 2004). a b Figure 1. Bedesten (a) and walled city of Nicosia (b). 2 GEOLOGICAL BACKGROUND Cyprus is situated at the triple junction of Eurasia, Arabian, and African plates, and has played a very important role for the geological understanding of the Eastern Mediterranean region. The geology of Cyprus governs the topography. Cyprus may be divided into six geological zones according to geological evolution and emplacement of its geological units (Atalar 2005): (1) Troodos Zone or the Troodos Ophiolite, (2) North Cyprus (Kyrenia) Zone, (3) Mamonia Zone or Mamonia Complex, (4) South Cyprus Zone, (5) Mesaoria Zone, and (6) Alluviums. Cyprus has had an active and complex neotectonic history that includes numerous devastating historical earthquakes. There is a major rhomb-shaped graben that underlies most of northern metropolitan Nicosia. The graben preserves a section of the Late Miocene (Messinian) Kalavasos (Mermertepe) Formation, which was eroded from areas outside of the graben (Harrison et al. 2004). During periods of heavy rain, ephemeral streams will flow into some of the sinkholes, on the outskirts of the Pergamos (Pergama) village often resulting in additional collapse. Lately newly formed sinkholes have threatened recent housing developments from the expanding village. Field investigations have determined that the collapses are controlled by a fault system, which cuts through a carbonate/evaporite stratigraphic sequence (Harrison et al. 2002). 3 SEISMICITY OF CYPRUS Cyprus has been subject to earthquakes all through her history. The Bronze Age city of Alasia (Enkomi), first century Paphos, fourth and seventh century Salamis were among the areas badly damaged or virtually destroyed by earthquakes. However, despite lying in the second most earthquake stricken zone on earth, Cyprus sector of this zone at the time being is less active and it experiences earthquakes less frequently and of a lower magnitude than that of Greece and Turkey. 361 Geotechnical properties of Nicosia soils, Cyprus Atalar C. & Das B.M.. , Seismicity of Cyprus between 1890 and 1990 are presented at Figure 2. In recent years there are two fortunately non-destructive events have occurred with signifant magnitudes of 5.8-5.9 (February 23, 2005) and 6.8-6.9 (October 9, 1996). Figure 2 Seismicity of Cyprus 1890-1990 Ms≥4.5 (Ambraseys & Adams 1992) 4 SOILS OF CYPRUS Alluvial soils and overconsolidated clays constitute the most soils of Cyprus (Figure 2). Most of them especially the alluvial soils are located at a topographically low, rather flat area which occupies the central part of the island between the Troodos range to the south and the Girne range to the north. Most of the problems encountered in North Cyprus, in construction involves silty – clayey soft soils due to their low strength, durability and high compressibility, and the swell shrink nature of the overconsolidated swelling soils. Landslides occur at the steep slopes of the clayey formations (Atalar & Das 2004). There is widespread damage to the buildings, major roads and highways all over the country which were founded on swelling clays (Atalar 2002; Atalar et al. 2003; Atalar 2004b). Figure 3. Cyprus soils (Revised from GSD 1995). 362 d 2n International Conference on New Developments in Soil Mechanics and Geotechnical Engineering, 28-30 May 2009, Near East University, Nicosia, North Cyprus Alluvial soils Holocene to recent in age containing gravel, sand, silt and clay are widespread in the Mesaoria plain, especially at Nicosia and Famagusta and at the east and west coast. They comprise loose - medium dense gravel and sand, and soft - firm silt and clays. The alluviums mostly contain low amounts of clay size material. The alluviums also contain high amount of montmorillonite. These alluviums show relatively high apparent strength in their dry state. However, with saturation their strength decreases. These alluvial soils have low to intermediate and high to extremely high swelling potential. The silting of the ancient harbours created very soft soils especially at the east and west coastline of the Mesaoria plain. Old stream beds filled with alluviums are found at the coastline and at the interior. Overconsolidated swelling clays of Cyprus occurred as a result of the alteration of the Troodos ophiolite and the pelagic sedimentary cycles that followed in the post Createceous period. The calcium corbonate content of the marls originated from the limestones and dolomites of the Kyrenia zone. Cyprus clays can be divided into 5 groups. 1.Clays of Mamonia Complex, 2.Bentonitic Clays, 3.Clays of Kythrea (Değirmenlik) Group, 4.Mesaoria clay zone and 5.Alluvial clays (Table 1). Table 1. Swelling potential of Cyprus clays Clays Liquid Limit (LL) Swelling Potential Alluvium (North Nicosia) 32 - 48 Low - Intermediate Alluvium (South Nicosia) 60 - 115 High – Extremely High Nicosia Formation 53 - 119 High – Extremely High Kythrea Group 47 - 73 Intermediate – High Mamonia Complex 33 - 167 Intermediate – Extremely High Bentonitic Clays 55 - 210 High – Extremely High Compiled from Atalar (2002), Atalar (2004a), Atalar (2005), Atalar et al. (2006a), Atalar et al. (2006b), Atalar (2007), Constantinou et al. (2002) & Petrides et al. (2004) 5 SOILS OF NICOSIA Nicosia is almost flat lying at about 110 - 160m above the mean sea level and is located between the Kyrenia and Troodos ranges. Kanlı dere (Pedieos stream) is the main stream of Cyprus originates in the Troodos mountains in the south initially flowing to the north, north-east and until 1567 divided Nicosia north and south.