Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Bull Eng Geol Env (2005) 64: 433–440 DOI 10.1007/s10064-005-0008-z Sedat Türkmen Hıdayet Taga Received: 26 March 2004 Accepted: 20 June 2005 Published online: 8 October 2005 Springer-Verlag 2005 S. Türkmen (&) Æ H. Taga Department of Geological Engineering, Mersin University, Mersin, Turkey E-mail: [email protected] Tel.: +90-324-3610102 Fax: +90-324-3610032 ORIGINAL PAPER Engineering geological assessment of the Diyarbakir solid waste landfill site (SE Turkey) Abstract The paper reports a study to investigate the geological, hydrogeological and geotechnical properties of a proposed solid waste landfill site for Diyarbakır city, southeastern Anatolia. The study area is located in the vicinity of the Diyarbakır– Mardin highway and 6 km away from the city. The paper describes the topography, geology and hydrogeological characteristics of the bedrock and based on water absoprtion (Packer) and laboratory measures, gives permeability values for the firm to stiff clays on which the landfill will be placed as well as the secondary permeabilities of the basalts and the intergranular permeabilities of the sand and gravel layers within the claystone–mudrock sequence. Recommendations are made for the construction of the landfill. Résumé L’article présente une caractérisation géologique, hydrogéologique et géotechnique d’un site de stockage de déchets solides pour la ville de Diyarbakir dans le sud-est de l’Anatolie. Le site est proche de l’autoroute Diyarbakir-Mardin, à 6 km de la ville. L’article décrit le contexte géologique et hydrogéologique relatif au site. A partir d’essais d’absorption et de mesures au laboratoire, les perméabilités des argiles fermes à raides, sur lesquelles le stockage sera placé, ont été précisées, de même que les perméabilités des basaltes et celles des niveaux de sables et graviers intercalés dans la série argileuse. Des recommandations sont faites pour la réalisation du stockage. Mots clés Diyarbakir Æ Géologie de l’ingénieur Æ Propriétés géotechniques Æ Site de stockage Keywords Diyarbakır Æ Engineering geology Æ Geotechnical properties Æ Landfill site Introduction The purpose of this study was to determine the geological, hydrogeological, engineering and geotechnical properties of the new Diyarbakır landfill site. The proposed landfill site is located within the Diyarbakır Province, in south-eastern Anatolia (Fig.1), adjacent to the Diyarbakır – Mardin highway and 6 km from the Diyarbakır city centre. As seen in Fig. 2, the topography varies between 600 and 705 m asl. Landfilling constitutes a major component of solid waste disposal systems in most countries as the disposal system can be above or below ground water level. The depths of landfills vary from 2 to 13 m and depend upon the site conditions (General Elec Comp 1975). In general, there are three types of filling methods used in operating natural attenuation-type landfills: the trench, area and cell methods. Each of these methods is characterised by the way the site is excavated. Natural attenuation landfills without sophisticated barriers 434 Fig. 1 Location map of the Diyarbakır (Turkey) landfill area (liners) and leachate collection systems are used for disposing non-hazardous waste only. The basic principle of landfill operations is to spread the waste materials and compact it in layers within a confined area which is then covered completely with a thin, continuous layer (minimum 150 mm). Above this is at least 0.5 m of compacted soil designed to minimise infiltration of surface water (Abacı 1993). Solid waste, hazardous and non-hazardous materials are split into three categories according to their sources. These are industrial wastes, domestic wastes and commercial wastes. The population of the Diyarbakır increases every year. According to the 1995 census, it is almost 780,000, which is 1.7% of the Turkey’s population such that it ranks 16th among the provinces with a population of more than half a million (Anonymous 1998). The increasing population is a major problem in the city as the existing solid waste landfill site, which is a former quarry, is situated near an urban area. Located in basaltic rocks, the waste landfill is not secure and threatens the environment and also causes pollution of the ground water. As a consequence, it was decided to create a sanitary landfill site as part of the GAP 435 Fig. 2 Engineering geological map of the Diyarbakır landfill area Fig. 3 Geological cross section of the Diyarbakır landfill area 436 Assuming an increase in the amount of solid waste of 0.01 kg/person for each year, the compressed solid waste density was estimated to be 0.85 t/m3 (Anonymous 1998). Geological and Climatic Setting Fig. 4 Composition of solid waste of the Diyarbakır city (Southeastern Anotolian Project) Regional Transportation and Urban Project based on the US EPA (1978) requirements. Site selection was carried out in the following three stages (Urban Sanitation and Planning Project 1998). (a) Preliminary stage: Field investigation of proposed landfill sites. (b) Second stage: Comparison of proposed landfill sites. (c) Final stage: Landfill site selection. An estimate of population and amount of solid waste was made for each 5 year period to 2015. Fig. 5 Typical layout of Diyarbakır landfill area The study area is located on a plateau dissected by the Tigris River. The oldest geological unit in the study area belongs to the Upper Miocene–Pliocene and is composed of claystones, clayey sandstones, sandstones and loosely cemented (grain supported) conglomerates with detrital materials referred to as the Fars Formation by Türkünal (1980). The thickness of the unit ranges between 850 and 1,000 m. The Upper Miocene–Pliocene units are overlain by the Quaternary basalts and fluvial deposits. Basalt eruptions are a natural consequence of the NNE movement of the Arabian Plate and originated from the Karacadağ volcanic centre during Plio-Quaternary times (Ercan et al. 1991). The thickness of lava flows decreases from northwest to southeast. The Upper Miocene–Pliocene units are overlain by basalt lavas in the southern part of the study area which is bounded by a NW–SE trending mountain chain. Due to recent erosional processes, weathering and rock quarry operation, basalt lavas are well exposed in the northwestern part of the hills. A lowland area of the study site is composed of recent organic soils, blocky soils and sandy gravelly river bank 437 Fig. 6 Schematic block diagram of the proposed sanitary landfill area deposits (Figs. 2, 3). The proposed landfill site is composed of Tertiary units, consisting of claystones intercalated with conglomerate and sandstones. The claystones have generally weathered into a 5 m thick firm-stiff clayey soil which forms the base of the landfill site. Fig. 7 Average rainfall records of the Diyarbakır region (1950–2000) The study area is located within the southeast Anatolian region and is classified as a seismically active zone (ERD 1996). The cultivated soil of the Diyarbakır region is being eroded and transported from an inactive volcanic mountain. The summer is characterised by a hot climate, whereas the winter period is mild. 438 Table 1 Geotechnical properties of claystone (A3) Unit and map symbol Claystone: Diagenetic period incomplete hence not well-solidified Geological age Soil description Unified soil classification Unit weight Surface drainage Upper Miocene–Pliocene (Türkünal, 1980) Brown firm-stiff clay intercalated with sand and gravel CL: Clay of low plasticity. CS: Sandy clay. CG: Gravelly clay 19.42–21.56 kN/m3 Surface runoff generally high; however, on rolling topography small seepages are present on many slopes Impermeable, except in sandy and gravelly levels. Coefficient of permeability is 9.25·10)8 m/s 3.0–21.5% Generally few problems in upper 4 to 5 m, but shear zones and joints result in unstable walls especially where water is present in fractures. If drainage initated during construction period, discontinuity drainage may be insignificant Clay matrix is resistant to erosion Weathered zone at upper levels of excavation walls is soft to firm locally. Unweathered zone at depth firm to stiff . Unweathered material has shear strength values between 980–1,470 kPa If there is no water, temporary vertical cuts generally stable to depths of 3 to 4 m. Traces of landslides observed in the field. Residual strength parameters should always be used for design of permanent structures Internal drainage and permeability Natural water content w (%) Excavation properties Susceptibility to erosion Shear strength and compressibility characteristics Slope stability Table 2 Geotechnical properties of silty sandy gravel (A2) Unit and map symbol Silty sandy gravel-A2: Terrace deposits Geological age Soil description Plio-Quaternary Primarily rounded-subrounded, very coarse-grained and coarse-grained, locally fine-grained. Moderately well-sorted to well-sorted. As much as 3 m thick, averaging about 1 to 2 m. Typically has lenses of sand, silt and clay commonly up to 300 mm. Areal extent of thin beds very limited in places GS: Sandy gravel 14.00–18.00 kN/m3 Highly permeable. Surface drainage is high Permeability is high. Soil commonly wet and saturated locally 19.0–33.0% Soil is weakly cemented, easily excavated Resistant to erosion. But, sandy levels are more susceptible Effective friction angle 35 to 40. Residual effective friction angle 30 to 35 Typically compact If there is no water temporary vertical cuts generally stable to depths of 3 to 4 m Remedial works necessary for permanent slopes if water content high and soil weakly cemented locally. Residual strength parameters should always be used for design of permanent structure Unified soil classification Unit weight Surface drainage Internal drainage and permeability Natural water content, w (%) Excavation properties Susceptibility to erosion Shear strength and compressibility characteristics Slope stability Sources of waste in Diyarbakir Engineering Geology The main sources of solid waste in Diyarbakır are residential, commercial, construction and demolition, industrial, municipal services and agricultural (Fig. 4). Modern domestic waste consists of 70% biodegradable material. The amount of solid waste per person is 0.961 kg/day with some 750,000 t/day being generated in the city centre. The domestic solid waste is collected and compressed within the vehicles, following which the waste is transported to the eventual landfill site by larger trucks. A plan view of the Diyarbakır landfill indicating the site units is given in Figs. 5 and 6. Six test pits (Fig. 2) were opened to determine the engineering properties of the units and 14 samples taken for laboratory testing following ASTM (1990). The main engineering units are weathered claystone, intercalated sandstone and conglomerate. These units are reddish in colour upwards and grey to green with depth. Based on these investigations, an engineering geological map of the landfill site was prepared according to ISRM (1976) and Matula (1981). The very steep side slopes of the landfill site are composed of weathered sedimentary and volcanic units, classified into the following five engineering groups: 439 Table 3 Geotechnical properties of silty sand (A1) Unit and map symbol Silty sand-A1: Terrace deposits Geological age Soil description Unified soil classification Unit weight Surface drainage Internal drainage and permeability Plio-Quaternary Yellow-grey, poorly cemented, uniform, silty sand with some gravel SP:Poorly graded sand, SM: Silty sand, SG: Gravelly sand 16.00–19.00 kN/m3 Surface drainage is high due to high permeability High permeability. Coefficient of permeability is 2.5·10)2 cm/sc. Soil commonly wet and saturated locally 16.8–26.5% Easily excavated due to poor cementation Extremely susceptible to erosion Weathered material has shear strength values between 80–1,470 kN/m2 . Peak effective friction angle of normally consolidated soils 25–35. Residual effective friction angles commonly 17–25 Temporary slopes normally stable at 60 to depths of 3 to 4 m. Remedial works are necessary for permanent slopes if water content is high and soil weakly cemented Natural water content, w (%) Excavation properties Susceptibility to erosion Shear strength and compressibility characteristics Slope stability 1. Unit A3—Claystone—described as a firm-stiff clay. Field observations indicate the thickness of the unit near the landfill site is greater than 200 m, with the strata dips varying from 15 to 25. 2. Unit A 2—Old terrace deposit—composed of loose, well-sorted, silty, sandy gravels with no cohesion. 3. Unit A 1—Old terrace deposit—silty sand locally observed at high altitudes in the study area. The thickness of the unit is variable and reaches up to 5 m at the uppermost levels. 4. Unit B—Plio-Quaternary basalts—massive structures with flow banding. They are generally aphanitic and composed of plagioclase and mafic minerals. The massive basalt has a blocky structure as a consequence of cooling fractures. The orientations of the dominant joints are N70E/84NW, N10E/80SE, N40W/64NE and N45E/65NW. The discontinuity sets are widely spaced and their persistence decreases with depth. The rock mass has a secondary permeability with springs/water seepage through the discontinuities observed during the rainy season. Rock falls and toppling failures are commonly observed along the foot of the very steep basalt slopes. 5. Units Of and S—Unconsolidated recent units and deposits present in troughs between the sloping flanks. They consist of blocky, sandy, gravelly old embankment rock talus, colluvium and organic soils. The thickness in the uppermost level ranges from 0.20 to Table 4 Impermeability system of landfill site Protection layer 200 mm, sand-soil Drainage layer for leakage water Protection layer Geosynthetic (impermeable) Mineral impermeable layer 300 mm, pebble, grain size 8–16 mm Geotextile (600 g/cm3) 2 mm geomembrane 300 mm +300 mm, two clay layers 3.0 m below which is a blocky soil with a clayey matrix up to 10 m in depth although in general the maximum thickness of the unit is about 5 m. The thickness of the cross-bedded sandstone and conglomerates may reach up to 4 m but they are usually found as lenses within the claystone mudstone succession. The engineering properties of the units are given in Tables 1, 2 and 3 (ISRM 1978, 1979). Hydrogeological Conditions at the Landfill Site The hydrogeological data were compiled from field observations and records from previously drilled boreholes. The upper units and the bedrock are semipermeable and impermeable, respectively. The conglomerate and sandstone layers within the bedrock result in a noticeable increase in the overall permeability. The depth to the perched groundwater level varies from 6 to 10 m with elevations averaging some 585 m above mean sea level, ie similar to the water level in the Tigris River. The morphological appearance of the area is characterized by a wide valley lying between parallel hills. The units located in the middle part of the study area are generally impermeable. Groundwater is recharged from the valleys in the west and seeps through open discontinuities in the basalt rock mass (Fig. 2). Seepages are also observed along the boundary between the basalts and the Tertiary deposits. Water absorption (Packer) tests were carried out at 2 m intervals in the boreholes and indicated the Tertiary deposits have permeabilities in the order of 10)6 to 10)7 m/s (3–5 lugeons). Based on the laboratory tests the permeability coefficient of the coarse-grained soil samples collected within the impermeable strata is 2.5·10)4 m/s and that of the fine-grained soil samples 9.25·10)8 m/s. 440 The meteorological records between 1950 and 2000 indicate the maximum rainfall is in January (monthly mean total rainfall 77 mm). High precipitation is also recorded in December (74.60 mm) and April (74.0 mm) with the lowest rainfall occurring in August (1.15 mm) and July (1.47 mm) (Fig. 7). The characteristics of the various layers within the proposed landfill site are given in Table 4. Conclusions The proposed landfill area was classified into five engineering units; weathered claystone (A3), silty-sandy gravel (A2), silty sand (A1), basalt (B) and unconsolidated recent units (OF and S). Surface run off is generally high and internal drainage and permeability very low, except in the sandy and gravely levels. However, the almost horizontally bedded silty sandy gravels which make up the very steep slopes have a high permeability. The Plio-Quaternary basalts in the upper part of the area have high secondary permeabilities due to the cooling fractures/joints. It was concluded that the geotechnical, hydrogeological and topographical properties of the proposed landfill site indicated suitable conditions if some remedial measures are taken. In particular, it was recommended that the superficial and unconsolidated units should be removed from the site before landfilling is commenced as they are likely to result in differential settlement and instability problems. Acknowledgements The authors are very grateful to the YERCET Company (Adana/TURKEY) for contributing data. The authors also would like to thank Dr. Altay Acar (Cukurova University) for his help during this study. References Abacı S (1993) Relative permeability of unconsolidated materials with reference to gas migration from landfill. University of Nottingham Department of Mineral Resources Engineering, Ph D, 248 p Anonymous (1998) Urban sanitation and planning project—final report for solid waste management. Southeast Anatolian Project of Republic of Turkey ASTM Standards (1990) American Society for Testing and Materials Ercan T, Saroğlu F, Turhan N, Madsuda JI, Ui T, Fujitani T, Notsu K, Bağırsakcı S, Aktimur S, Can B, Emre Ö, Akçay AE, Manav E, gürler H (1991) The geology and petrology of the Karacadağ Volcanites. Bulletin of Geological Congress of Turkey, n. 6, pp 118–133. Ankara (in Turkish) ERD, 1996 Earthquake zoning map of Turkey. General Directorate of Disaster Affairs, Earthquake Research Department. Ankara General Elec Comp (1975) Solid waste management technology assessment. 348 p, England ISRM (1976) Engineering geological maps. The UNESCO Press, No:15, p 78 ISRM (1978) Suggested methods for the quantitative description of discontinuities in rock masses. Int J Rock Mech Min Sci Geomech Abstr 15:319– 368 ISRM (1979) Suggested methods for determining the uniaxial compressive strength and deformability of rock materials. Int J Rock Mech Min SCI Geomech Abstr 16(2):135–140 Matula M (1981) Rock and soil description and classification for engineering geological mapping. Report by the IAEG Commission on Engineering Geological Mapping, International Association of Engineering Geology Bulletin 24:235– 274 Türkünal S (1980) Geology of East and South-east Anatolian. Bulletin of Chamber of Geological Engineering of Turkey n. 8. Ankara. (in Turkish) US Environmental Protection Agency (US EPA) (1978) Geosynthetic design guidance for hazardous waste, landfill cells and surface impoundments. EPA 600/ 52 –87/097. US Environmental Protection Agency