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Some slope instability problems exist in Ankara clay along E90 highway. The purpose of this paper is to determine the mineralogical and geotechnical properties of soils, and to investigate the causes and mechanisms of three rotational landslides along a section of the highway. In order to accomplish these tasks, field studies, laboratory testing, back analyses, and limit equilibrium and finite difference analyses were performed. The landslides are formed within a soil consisting of clay and silt with a little sand and gravel. Slope stability analyses indicate that long-term stability of already failed slopes is critical. The failures are progressive, showing strain softening behavior with full saturation. Broken irrigation pipes existing near the landslides are found to be the main cause of sliding. Maintenance of the pipes, surface drainage, removal and replacement of the failed (slided) material are considered to be economical and practical solutions for the remediation of the slides. [ABSTRACT FROM AUTHOR]

Evaluation of the reliability of deep excavation support systems requires the inclusion of the soil variability in conjunction with probabilistic analysis. This is often considered a complicated process; therefore, the method is usually not followed in routine engineering practice. Recent developments in finite element modelling now enable probabilistic analyses to be performed more conveniently. As an illustrative example, the case history of a 20 m-deep excavation supported by anchored drilled shafts in the Sogutozu district of Ankara was investigated. Experimental results indicate that saturated sand-gravel bands, which are common within Ankara Clay, have the potential to cause a significant decrease in the anchor capacity. Ergo the excavation performance, including structural capacity and wall lateral displacements, was evaluated taking into regard the probabilistic nature of the effect of these bands and the variability of the soil parameters. Back-analysis was performed and compared with inclinometer readings to examine the capability of the numerical model to simulate the field behaviour. Later, additional finite element analyses were carried out through Python scripting software to investigate the reliability of the excavation. Geotechnical parameters of the Ankara Clay produced by Monte Carlo simulation method were used in these analyses. The results were evaluated within the context of recommended acceptable reliability levels. The reliability of the system was determined to be relatively low when taking into account the adverse impact of sand and gravel bands. [ABSTRACT FROM AUTHOR]

The slake durability test device was primarily designed for argillaceous rocks (clay-bearing) such as shale, claystone mudstone, and marl by Franklin and Chandra (Franklin JA, Chandra R (1972) The slake-durability test. Int J Rock Mech Min Sci 9:325–341). Later, the International Society for Rock Mechanics standardized the test method (ISRM (2007) The complete ISRM suggested methods for rock characterization, testing, and monitoring, 1974–2006. In: Ulusay R, Hudson JA, compilation arranged by the ISRM Turkish national group, Ankara, Turkey). The slake durability test is conducted to assess the durability offered by argillaceous rocks to degradation (slaking) when subjected to wetting–drying cycles (WD cycles). However, in previous decades two, various researchers also have used this test to assess non-argillaceous rocks. In this paper, the effects of the WD cycles and rock lumps abrasion (RLA) on the degradation of argillaceous and non-argillaceous rocks during the slake durability test are investigated. To this end, some marls and limestones (as argillaceous and non-argillaceous samples, respectively) were collected from rock trenches along roads in Lorestan province, west of Iran. The mineralogical studies were performed by microscopic thin sections and X-ray diffraction analyses (XRD). Also, physico-mechanical tests, including porosity (n) and point load index (PLI), and slake durability tests up to 15 cycles were carried out to characterize the samples. Results indicated that the degradation of argillaceous samples [assessed using slake durability index (SDI)] during the slake durability test was remarkably affected by WD cycles. Besides, the RLA showed less effect on the degradation of these samples. WD cycles had a preventative role in the degradation of the non-argillaceous samples, and only the RLA was responsible for the degradation of these sample types. The findings show that clay minerals in argillaceous samples make them highly susceptible to degradation by WD cycles. Moreover, the absence of these minerals in non-argillaceous samples has caused their degradation to be independent of the WD cycles. According to simple regression analyses, there is a good correlation between the degradation of the argillaceous samples with their saturated-to-dry PLI ratio (PLIr). However, no significant correlation existed between degradation and PLIr of the non-argillaceous samples. Overall, the PLIr can be considered a low-cost, rapid, and precise indicator to assess the degradation of the argillaceous samples during the slake durability test. Highlights: The effect of the wetting-drying cycles (WD cycles) on the degradation of argillaceous and non-argillaceous rocks was investigated. The degradation of argillaceous samples during the slake durability test was remarkably affected by WD cycles The absence of clay minerals in non-argillaceous samples has caused their degradation to be independent of the WD cycles. There is a good correlation between the degradation of the argillaceous samples with their saturated-to-dry PLI ratio (PLIr). The PLIr can be considered a low-cost, rapid, and precise indicator to assess the degradation of the argillaceous samples during the slake durability test. [ABSTRACT FROM AUTHOR]

Unsaturated soil shear strength is a significant topic in geotechnical engineering. The measurement of unsaturated soil properties such as shear strength and matric suction could be costly, hard, time-consuming, and often impractical to obtain. The purpose of this research is to propose a new shear strength model for unsaturated soil and to predict the shear strength by using the degree of saturation directly because the water saturation is easy to obtain. More specifically, this study focused on Bishop's shear strength theory and van Genuchten's soil–water characteristic curve to describe the effect of saturation on shear strength. The new shear strength model was expressed as a function of saturation degree, residual degree of saturation, effective shear strength indices, net normal stress, and five parameters. The performance of the presented model in this paper was verified by fitting it to data obtained by laboratory tests on silty sand including the triaxial shear test and soil–water characteristic curve test. From these two laboratory tests, we obtained the variation in the matric suction and shear strength with the degree of saturation under various dry densities. This proposed model was also validated against the shear strength results of the clayed-silty sand and Ankara clay recorded in the literature. Comparing the result of the shear strength under the variation of one parameter, this model was much more sensitive regarding parameter m, which was related to the material characteristic. The comparison between the predicted values and experimental points was particularly fine and showed the ability of this model to be applied to a wide range of soils. [ABSTRACT FROM AUTHOR]

Abstract: In the paper, a previously introduced method () is applied to the problem of estimating the rock mass properties of Ankara andesites. For this purpose, appropriate closed form (parametric) distributions are described for intact rock and discontinuity parameters of the Ankara andesites at three distinct weathering grades. Then, these distributions are included as inputs in the Rock Mass Rating (RMR) classification system prepared in a spreadsheet model. A stochastic analysis is carried out to evaluate the influence of correlations between relevant distributions on the simulated RMR values. The model is also used in Monte Carlo simulations to estimate the possible ranges of the Hoek–Brown strength parameters of the rock under investigation. The proposed approach provides a straightforward and effective assessment of the variability of the rock mass properties. Hence, a wide array of mechanical characteristics can be adequately represented in any preliminary design consideration for a given rock mass. [Copyright &y& Elsevier]

Abstract  The paper reports an assessment of the engineering geological characteristics of the rock mass to be encountered between Mecidiye and Gazino stations on the new extension of the Ankara metro and the determination of appropriate support and excavation methods. The rock mass quality was estimated using the rock mass rating (RMR), geological strength index (GSI) and rock mass quality (Q) systems and the tunnel divided into sections. The RMR, Q and NATM systems were used to determine the support and excavation methods in these areas. The deformations and stress concentrations around each tunnel section were investigated and the interaction of the support systems with the rock mass was analyzed using finite element software. It is concluded that rock mass classification systems should be used in tandem with numerical tools, although it is emphasized that the estimation of rock mass properties is not an exact science and both rock properties and numerical models should be refined based on observations and the results of instrumentation installed during the construction of a tunnel. [ABSTRACT FROM AUTHOR]

Due to the increasing population and resulting transportation needs, the number of subway and high-speed railway projects has also increased. The geometric constraints of such projects have caused many tunnels to be built in weak ground. Thus, weak ground tunnelling has attracted the attention of tunnel engineers and researchers. The main purposes of this study are to analyse the T4 tunnel excavated in weak ground and to compare the results obtained from the analytical solutions and 3D numerical analyses. This study specifically considers the T4 tunnel support system used in the Ankara İzmir High Speed Railway Project (Afyonkarahisar-Banaz Section). The T4 tunnel route encounters weak ground composed of layers of extremely weak mudstone, clayey sand, weakly cemented sandstone, and silty–clay matrix with pebbles. The tunnel overburden ranges from 10 to 35 m, which is shallow. After the excavation work of the T4 tunnel, severe deformation and critical stability problems in the shallow part (where the overburden is approximately 10 m) were encountered inside the tunnel, leading to a halt in construction. This was followed by revisions to the tunnel support system, leading to successful completion of the tunnel excavation. Numerical simulations of the low overburden section are performed using the commercially available FLAC3D program that uses the finite difference method. The characteristics of insufficient/ineffective support systems and adequate support systems for shallow tunnels excavated through weak ground are discussed in this study. Additionally, problems that pertain to the tunnel itself and its support system are discussed. The results of the 3D numerical analyses and analytical solutions are compared, and the advantages of 3D numerical analyses are discussed. The importance and necessity of tunnel face stability and roof stability for tunnel stability in weak ground is illustrated. Consequently, solutions based on analytical and numerical analyses are presented, and the analysis methodology and solutions proposed in the study can help guide weak ground tunnelling design and evaluation. [ABSTRACT FROM AUTHOR]

Ankara Citadel which is one of the important cultural heritages in Turkey settles in the oldest part of Ankara. Rockfall event has occurred around the Citadel located on a steep hill where andesite is exposed. The rockfall problem causes a great risk to the surrounding area where road, school, floral shops, car parking. Therefore, the major aim of this research is to reveal the rockfall risk around the castle. The rockfall problems around the Ankara Citadel may be linked with weathering, freezing–thawing, earthquake, and cooling joints, and effects or combination of these in the rock units. The rockfall-related hazard at the Citadel is assessed by 2-D rockfall analyses along several profiles in this investigation. Field observations and stability analyses (kinematic and limit equilibrium) of the slopes reveal that there exist many blocks ready to fall down. Four different andesite block sizes measured in the field are separately analyzed on the basis of bounce height, fall-out distance, velocity and kinetic energy of the blocks. The obtained data are evaluated to define the possible rockfall-based hazard zones. Based on the danger zones acquired from the rockfall analyses, the removal of the fallen and loosen andesite blocks and the installation of catch barriers with suggested properties are recommended. Besides, the risk integrated into rockfall hazard rating system on the basis of structural and morphological criteria of the rock mass reveals that medium risk category to be mitigated by light remedial measures for the indicative protection exists in the study area. [ABSTRACT FROM AUTHOR]

The construction of a large open air theatre having with an audience capacity of 7,000 is planned at the Beytepe Campus of Hacettepe University located near Ankara, Turkey, in the heart of Anatolia. The foundation of the open air theatre is composed of weak and heavily jointed Ankara Greywacke. An estimation of the strength and deformation of the Ankara Greywacke was required for assessments of short- and long-term stability. Accordingly, rock mass characterization of the Ankara Greywacke was investigated in detail by scan-line surveys and back-analyses of in situ tests performed on the excavated surface of the rock mass. The final version of the Hoek and Brown Criterion (Hoek et al., In: Proceedings of the north American rock mechanics society meeting, Toronto, Canada, pp 1–6, 2002) together with and improvements proposed by Sonmez and Gokceoglu (Int J Rock Mech Min Sci, 43:671–676, 2006) were considered together for the back analyses of small slope benches subjected to plate loading test loaded to failure. In addition, the plate loading test data were used with some well-known empirical equations for predicting of deformation modulus of rock masses to calculate ranges of values of the Geological Strength Index (GSI) The static and pseudostatic slope stabilities of the audience seating structures to be supported by benches excavated into the rock were also analyzed. The stability assessments revealed the unlikelihood of large rock mass failures for the short-term construction stages or for the long-term, as-constructed conditions under static or pseudo-static conditions. Additionally, the analyses showed that there was no need for anchors between the concrete seating structures and greywacke rock mass. [ABSTRACT FROM AUTHOR]