Mehmet Ali Hindistan

Investigation of surface and subsurface displacements due to multiple tunnels excavation in urban area

Underground structures are currently widely used and are built as urbanism develops. The interactions between perpendicularly crossing and parallel tunnels in the Tehran region are investigated by using a full three-dimensional (3D) finite difference analysis with elastic-plastic material models. Special attention is paid to the effect of subsequent tunneling on the support system, i.e., the shotcrete lining and rock bolts of the existing tunnel. Eventually, as the tunnels are excavated at certain levels, the interaction between the tunnels will certainly have a significant influence on both stress distribution and consequently deformations. Since multilayer tunneling is a three-dimensional phenomenon in nature, 3D numerical solutions must be utilized for analyzing effect of perpendicularly crossing tunnels at various levels. As Tohid twin tunnels and Line 7 pass beneath the Line 4 metro tunnel, changes in stress distribution, deformations, and surface settlements are studied for various conditions and the results are presented in this paper. Consequently, it is shown that there is a significant interaction between tunnels that necessitate certain preventive measures to maintain a stable tunneling operation.

Assessment of subsidence at Çayırhan lignite mine using aerial photogrammetry

Caving of overlying strata following the exploitation of an ore body underground might lead to severe damages on surface topography. Regular monitoring and recognition of subsidence are vitally important to overcome adverse effects, especially at the surface. In recent years, remote sensing techniques are widely used to measure and interpret these effects. This article presents the results of a multidisciplinary study incorporating mining, geodetic and photogrammetric engineering. In this study, an aerial photogrammetric technique is applied to determine the amount of displacements (subsidence) at the surface over Sector B at Çayırhan lignite mine. Digital elevation models of the study area both before and after exploitation of the coal seam were obtained from digitised aerial stereo photos by using MATCH-AT software. Changes between the profiles, especially in vertical direction (z-axis) which defines the amount of subsidence, were found to be up to 4 m. Both field observations and results determined from the models reveal that the extent of subsidence was in good agreement with the aerial photogrammetric characteristics and topographical survey measurements. As a result, use of aerial photogrammetry can be considered as a fast and reliable alternative method for the assessment of subsidence effects over large areas.

A Geostatistical Study of Tertiary Coal Fields in Turkey

The majority of lignite and sub-bituminous coal resources known in Turkey are of Tertiary age. Therefore Tertiary coals in Turkey are of great importance in terms of coal potential and production. This paper presents a study of spatial distributions of calorific value, ash content and moisture content over Tertiary fields. For this purpose data collected from 187 coal fields in Turkey are used. The experimental variograms of three quality attributes are computed from these data and models are fitted. These models are used in estimation of spatial distributions of the corresponding variables by ordinary kriging. In addition, the probabilities of calorific value being less than 1,600 kCal/kg at estimation nodes are computed by using Direct- Sequential Simulation. Finally, additional sampling locations are proposed especially for the fields in which further information are required.

Analysis of Roof Caving Characteristics at a Coal Mine by Using Full Scale 3D Numerical Modeling

Regular and efficient caving of roof strata behind is essential in maintaining a trouble free operation in underground longwall mining when especially mined area is left for caving. As the face advances, roof strata should be regularly caved forming a goaf as homogenous as possible. In case of having an uncaved roof behind the coal face, load on the face increases dramatically leading to serious fall of roof conditions. Therefore it is of paramout importance to have the roof regularly caved behind a longwall face. This paper presents the problems encountered at a coal mine in Turkey due to high face pressures and subsequent flow of roof at the face roof junction. The height of the fully mechanised longwall face is 4.5 m. Sliding of face coal and later the fall of roof strata in front of the shields created serious stability and safety problems in the mine. Stopes opened in the roof had to be filled by usign forepoling, foam and concrete. This rescue operation had to be completed securely before starting of the cutting operation at the longwall face. Obviously rate of production of the longwall face has been severly declined during this period. There were a couple of reasons for having such a difficult condition in the mine. The longwall panel was located near to a syncline axis leading to high tectonic stresses. There were lots of small faults through the working face. Longwall face was extremely loaded by a very strong limestone layer having a thickness of up to 80 m located at 120 m above the coal seam. Although the strata between the limestone layer and the coal seam has a readily caving characteristics, the limestone caved at long intervals causing high face pressures due to its cantilever beam effect. Moreover during caving of the limestone, severe dynamic loads are experienced in the vicinity of longwall face deteriorating stability conditions. Therefore it was decided to model the effect of limestone layer’s behaviour by means of numerical modelling. A full scale model was created in accordance with all geometrical conditions and operational parameters by using FLAC3D software. The face advance is also simulated on the model. Stress and deformation state of the coal face, surrounding rock and especially the problematic limestone layer are analysed. To solve the problem, a blasting pattern is selected to weaken the limestone layer by using drill holes opened from the surface. This paper presents the numerical modelling results in relation to selection of the best blasthole geometry to decrease loading on the face and hence maintain a safe, efficient and stable longwall operation.