Geotehnical conditions for construction of sanitary disposal site »Lukavacka rijeka«, B&H Nijaz Skripic1, Mirza Basagic1, Zlatko Langof1, Ferid Skopljak1 1Civil Engineering Faculty of the University ofSarajevo, Geology Institute, Stjepana Tomica st. 3, 71000 Sarajevo; E-mail: mbasagic@lol.ba Received: July 17, 2007 Accepted: July 20, 2007 Abstract: Construction of regional sanitary waste disposal site "Lukavacka rijeka" is planned on the place of internal overburden disposal site of surface coalmine, 3 km in the north of Lukavac city. In the area of 56 ha, disposed are coherent materials that were created during removal of overburden in surface mine in quantity of V~5.5106 m3. Geological structure of terrain is composed of remains of coal seams and sand of upper Pontian (Pl12), thick 150 m. In the roof, disposed are pre-consolidated clay and clayey-dusty sand. In the aim of reduction of settlement effects, that realistically cannot be absolutely removed, it is proposed to remove upper part in thickness of 5.0 m, in order to provide acceptable total settlement. Analyses of stability for the most unsatisfactory case when the water content is the highest, they resulted with stability factor F = 1.56. In case of water level at depth of 4.0 m, stability factor is F = 3.16, what proves that base of the disposal site is stabile. Researches proved that this location could be accepted for construction of sanitary disposal site. Key words: sanitary waste disposal site, research works, classes of material, construction conditions, drainage system Introduction Waste material is disposed at wild disposal sites in Tuzla Canton. One of significant steps of this acute problem and rehabilitation of wild disposal sites is proposed construction of regional sanitary disposal site. During selection of location, care was primarily taken about parameters of production of waste at present condition and also for further 20 years. Tuzla Canton is placed in the area of 2649 km2. It includes 13 municipalities with population of 500,504 citizens. In future 20 years prognoses are that population will increase to 625,630 (increase of 1.25 % annually), specific production of waste 380 kg/citizen/year, in total quantity of V = 4.8 million tons. Noted quantity of waste should be placed at sanitary disposal site in approximate surface of F = 17 - 20 ha and height h = 35m. Multidisciplinary analyses of numerous natural, economic, social-politic, administrative and other factors, out of nominated 6 potential locations, for construction of regional disposal site, selected location Lukavacka rijeka. Construction of regional sanitary disposal site Lukavacka rijeka is planned on the place of internal disposal site of overburden of surface coal mine, 3 km in the north of city of Lukavac. In the area of overburden disposal site in surface of 56 ha, disposed are loose materials that are created in process of removal of overburden of surface mine in quantity of V = 5.5-106 m3. Materials are disposed without any special requirements in aspect of regularity of surface of disposal site and without compaction. Over those materials of the fill pack, planned is construction of regional sanitary disposal site. Task and coal of researches was provision of necessary geological-geotechnical basis for preparation of the main project design for construction of Regional sanitary disposal site. In the aim of determination of geotechnical conditions of construction, research works are done together with geological-geotechnical researches. In this paper, results of performed researches are represented. Regarding detailed research of this area (for requirements of exploitation of coal) the following research works were conducted on purpose: Site and laboratory works: • Geodetic survey of terrain; • 9 research boreholes with core sampling and conduction of SPT tests, in total length of 140 m; • 24 research boreholes without core sampling and with conduction of SPT tests, in total length of357 m; • 220 SPT tests; • Laboratory tests of 33 samples of core (standard geomechanical parameters, oedometric tests and Proctor's), and • Geological mapping. Office works: • Collection and analyses of the existing data; • Preparation of geological, engineering-geological and hydrogeological maps and profiles; • Analyses of stability of the slope of mine disposal site, and • Calculation of settlement. Results and Discussion Geological structure Locality of Lukavacka rijeka in its geographic placement belongs to northwest part of Kreka north synclinal area. In terrain, determined are sediments of the upper Miocene (Pontian) and recent Quaternary materials of the fill. LowerPontian (Pli1) -Novorossianpack The floor coal seam with belonging sediments in its roof belongs to this part of Pontian (clays in close and sand in further roof). Thickness of the floor coal seam varies in wide range from 0.6 to 9.9 m. In this locality, this coal seam was not subject of exploitation. VpperPontian (Pll Zone of the main coal seam with belonging sediments (clays and sand in its floor and roof) belongs to this part of Pontian, and I and II roof coal seams that are not developed in the area of Lukavacka rijeka but they outcrop in the distant southern parts. Thickness of the main coal seam before exploitation varied in the range from 1.3 -8.8 m. In conducted researches in 22 boreholes, thickness of "unexploited cloths" of the coal seam was confirmed to 0.2 - 1.3 m. Thickness of sand in the floor of the main coal seam is 150 m. Quaternary sediments (Q) - recent anthropogenic creations of fills, are mainly of clayey, sandy, and detritus composition. Thickness of those sediments is variable and it varies in the range from 8.0 - 24.7 m, what is confirmed in conducted researches in boreholes B-9/5 and B-1.5/4. Representation of geological structure is given in geological map Figure 1. Structural - tectonic characteristics and morphology Kreka basin, to which area disposal site also belongs, is formed as depression most probably in the first stage of alpine organogenesis. Occurrences in this basin are in causal connection with general occurrences in the inner parts of Dinarides. In the basin, several plication structures are formed, among which the most significant is anticline Ravna tresnja, Krekanska and Lukavacka syncline. In Lukavacka syncline, more exactly in its northwest part (area of disposal site), seams are formed in syncline, with mild centripetal inclination of 10 In this part of basin, faults tectonics are not expressed just folding tectonics. Geological structure and structural-tectonic structure of the area of Lukavacka rijeka are represented in Figure 1. 130 Skripič, I., et al. LEGEN DA/LEGEWD: TT PI: PI: Holocen i Pleistocen Holocerie and Pleistocene G I in aj g I i ri a pjeskovita i pijesak Clay, sandy day and sand Pijesak Sand Glina i laporovita glina day and marly day Pijesak Sand Glina i laporov ita glina Clay and rm arly clay Pijesak jŠIjli nak i laporovita glina Sand, graveI and marty day G oretina Burned are (coal ash) KVARTAR QUA TERNAR Y GORNJI PONT UPPER PONTIAN DONJI PONT LOWER PONTIAN Otkopani prostor PK "Lukavacka rijeka" Excavated mirte area "Lukavacka rijeka" RSDO "LUKAVACKA RIJEKA" SANITARY LANDFILL "LUKAVACKA RIJEKA" - Izdan ci II k rovnog s loj a/0 utcrops of second roof layer - Izdan ci I krovnog s loj a/0 utcrops of first roof la yer - Izdanci glavnog ugljenog s\oja/Outcrops of main coal layer Izdanci podinskog ugljenog sloja ¡0 utcrops of substratum coal la yer -^— Osa sinklinale/Syr>e7/ne axis A Osa antiklinale//lnfi'c//ne axis c ~ > Srmjer tonjenja ose sink \ \na\e/Subsidence direction of s incline axis — n Snnjer tonjenja ose antik linale/Suisi'dence direction of anticline axis — — Pretpostavljeni izdanci ugljenog s\aja/Assumed outcrops of coal layer - Postepeni prelaz gline u pijesak/Gradual changes of clay into sand 1-1' Poprečni profi I/Transversal pro file I-1' Uzdužni profW/Longitudinal profile (§bgd-6 Bunari za odvodnjavanje/Ora/nage wells ® pgd-13 Geološke istražne bušotine/Geo/og/ca / investigation boreholes • ti Geotehnicke istražne bušotine /Geo technical investigation boreholes Figure 1. Geological map of wider area of RSDO "Lukavacka rijeka" In morphological aspect, present appearance of terrain is in the shape of amphitheatre. That is a result of techno genetic activities, more exactly formation of internal disposal s ite of surface coal mine. Inclination of terrain is relatively mild, most often 6 0 - 10°. Additional processes of pre-consolidation, erosion and denudation, and sliding of disposed material on technically unprepared slopes, have caused irregular forms, unsatisfactory for sanitary disposal of waste, and prior to construction of sanitary disposal s ite, it will be necessary to perform satisfactory preparation and shap ing of the surface base. Seismic characteristics From the aspect of macro se ismic belong ing (Se ismic map of BH for returning period of 500 years, Association for seismology SFRY, Belgrade 1987), area of disposal s ite belongs to zone of 7 ° MCS. On the bas is of determined geological structures, rocks in the basis and determined levels of underground water, regarding the fact that purposeful researches were not conducted, for determination of seismic hazard and risk, it should be considered with increase of se ism ic ity of+ 2.3-2.6 ° MCS. Hydrogeological relations Geological structure and structural terrain structure have caused specific hydrogeological relations. Cyclic change of sand in function of aquifer with clay and coal seams, as aqui kludges, resulted in formation of artes ian and sub-artes ian water bearing horizons, in each of sand layers. Sand layers in locality of Lukavacka rijeka are separated from each other in two waterbearing horizons: • I water bearing layer - sand in the floor of floor coal seam, and • II water bearing layer - sand in the floor of the main coal seam. Recharge of those water bearing layers in natural conditions is from outcropping surfaces of sand members that, depending on inclination of the layer and terrain configuration, create significant surfaces for infiltration of water into undergrounds. Due to mutual relations of water bearing layers and hydrogeological barriers, aquifers are mutually separated and under pressure. Both aquifers are characterised with intergranular porosity and good water permeability. An outcrop in the floor sand layer of the main coal seam is drained with battery of wells for drainage of the mine. Drainage reduces level of underground water to depth of 80 - 100 m under terra in surface. On the basis of data of pumping, calculations for those sand layers provided values of coefficients of filtration K = 2.98-10 m/s, transmiss ion T = 1.54-10 m2/s and piezo-permeability a = 8.58-10-2 m2/s and specific capacity X = 2.5-10-2 in average. Anthropogenic material from mining operations - fills is disposed directly over sand of II water bearing layer. Materials of fill, according to results of conducted researches, represent hydro-geological complex of poorly water permeable rock masses of intergranular porosity. Average coeffic ient of filtration for those materials is determined in the value of K = 2-10-& m/s. Even though poorly water permeable materials of fill do not fulfil bas ic criteria of water tightness towards bas is (water bearing sand) w ith Kmin = 1-10-8 m/s, what about should be taken special consideration during construction of sanitary waste disposal site. POPREČNI HIDROGEOLOSKIPROHL 1-1' TRA1\EVER?AL HÏDPO3E0IO3KIAL PROFILE M1 5 000 podkucje sanitarne deponije m Gina i Ispcrcwita clina Qa/ and marly da/ Fljescku podni podnskog sloja Sand in substratum of substratum iayer Nasuti materij d ///A (unutrašnje odlagal iste FK "Lukavacka rljeka") 30 hits (very hard material) Consistency index Ic = 1.2 (hard consistency) Natural moisture W= 9.3 % (low soil moisture) Cohesion c = 0.0 kN/m2 (without cohesion) Angle of inner frictioncp=35° (high value) Compressibility modulus Ms>40,000 kN/m2 (low compressible soil) Legenda Legend G eo tehnicka klasifikacija materijala G e o te c h nie a 1 m a te rial cla ssific atio n K l-ar-a in û ki llala M aicriai ct&ss Zdpremlna ■ P 3 - P + -□ L .. (PI - Pi OPT ■ M SO. SPT. Ik Ind ek f ko ne If It nc Ik k 'Ii.-- ■ +++ H ■ .- ladr- 456 357.0 1-10 0.5 5 ii 3 99 1 12.5 11-30 0.8 0 ma 102 657.0 >30 >50 0.88-0.94 >1 .2 Geološka granita nasip - s u p s t ra t ffeoJojicaJ ionisrs» b an h nt e nt - sv p stratum LU-li A Geološke ¡strašne bušotine Geological investigation borehole B 3/ 5 UGeotehnicke istrasne bušotine sa isvodenjem SPT ffeotecfrfîiaJifîvesttijafiofî b o rs ho Is s for i P 7 testing 1Î Figure 3. Vertical engineering geological profile of the area of RSDO "Lukavacka rijeka" Analysis of stability and value of settlement It is known that in case of disposal site that not only values of load bearing capacity of the base are authoritative but also settlement and resistance to sliding and especially unequal settling. For tension of weight goes <7 = 250 kN/m2 and condition of removal of the upper layer of class I to 5.0 m thickness, calculated was total value of settlement Su = 0.25 m and differences in settlement in different layers in value of Sr = 0.126 m. Evaluation of influence of permitted values of unequal settlements depends on rigidness of water permeable system and final evaluation will be provided only after detailed analyses. According to acknowledgements of conducted researches, those values of total settlements and differences in settlement due to different thickness of layers should not be critical for system. Analyses of stability proved that base of sanitary disposal site is stabile: F = 1.56 - stability factor for case of complete wateriness; F = 3.16 - stability factor for measured level of water at the depth of 4.0 m. Geotechnical conditions for construction Regarding geotechnical aspects of construction, the following can be summarised: • In the aspect of satisfaction for construction, terrain belongs to category of conditionally stabile terrain. • Irregular morphological forms of disposed material are unsatisfactory for sanitary disposal of waste, and before construction of sanitary disposal site appropriate preparation and shaping of the surface shall be done. • In the aspect of seismic hazard and risk, terrain belongs to category of unsatisfactory terrain with possibility of increase of seismicity, what should be considered during designing and shaping of construction of sanitary disposal site. • Disposed material is characterised with heterogeneous lithological composition and variable physical-mechanical characteristics that makes complex geotechnical conditions of construction. • Main problem that has to be solved in disposed material is related to reduction of scope of settlement, especially unequal settlement. • In the aim of reduction of the settlement effects, that cannot realistically be absolutely removed, proposed is removal of the upper part (class I) in thickness of 5.0 m, as well as construction of drainage system, what will provide consolidation of the surface and acceptable total settlement could be provided. • Floor sand represent water permeable layers (K = 2.98-10-6 m/s), and materials of the fill represent poorly water permeable rock masses (K = 2-10-7 m/s), that does not fulfil the bas ic criteria for initiation of the water towards the base (water bearing sand) of Kmin = 1 -10-8 m/s. In the aim of protection of pollution of aquifer, it is necessary to construct anti fltration structures. Conclusions It has been proved with research works that this location with complex geotechnical conditions can be accepted for construction of sanitary waste disposal site with application of appropriate techn ical measures: • In the aim of reduction of the effect of settlement it is necessary to remove upper part (class I) in thickness of 5.0 m, what can provide acceptable total settlement; • In the aim of increase of consolidation of the base it is necessary to construct drainage system; • In the aim of protection of aquifer it is necessary to construct anti filtration structure in the base. References Basagic, M., Langof, Z., Skripic, N., SKOPLJAK, F. (2006.): Elaborate about conducted research works at locality of sanitary disposal site "Lukavacka rijeka". Civil Engineering Faculty of University of Sarajevo, Institute for Geology, Sarajevo. ORUC, E., Jahic, I., ZIGIC, I. (2004): Analysis of influence of regional sanitary disposal site "Lukavacka rijeka" to development of mining operations in Coal mine company "Kreka". Mining Institute, Tuzla. Oruc, E., Jahic, I. (2002.): Main mining project desi gn for opening and exploitation of mining fields "Dobrinja", "Mramor" and "Marici" in underground mine "The main seam", Technical project of drainage of floor and roof layers of the underground mine "The main seam" in Mramor, Book 1-Text and Book 2-Attachments. D.D. Mining Institute Tuzla, Tuzla. ZuniC, M. (1987.): Elaborate about reserves of coal in the area of exploitation field "North syncline" Kreka. OOUR Institute for mining researches, Tuzla.