İsmail Dinçer

Models to predict the deformation modulus and the coefficient of subgrade reaction for earth filling structures

Determination of deformation modulus and coefficient of subgrade reaction of soils have major importance, whether the projects are in design, and construction or compaction assessment stage of earth filling structures. Plate load test is one of the frequently used method to directly determine the parameters but the method is both costly and time consuming. For this reason, this paper is concerned with the applications of artificial neural networks (ANN) and simple-multiple regression analysis to predict deformation modulus and coefficient of subgrade reaction of compacted soils from compaction parameters (such as maximum dry density (MDD) and optimum moisture content (OMC), field dry density (FDD), and field moisture content (FMC)). Regression analysis and artificial neural network estimation indicated that there are acceptable correlations between deformation modulus and coefficient of subgrade reaction and these parameters. Artificial neural networks model exhibits higher performance than traditional statistical model for predicting deformation modulus and coefficient of subgrade reaction.

The effects of discontinuity surface roughness on the shear strength of weathered granite joints

Surface roughness is one of the most important parameters governing the shear strength of rock discontinuities. Roughness types may vary based on genesis, physico-mechanical, and mineralogical properties of rocks. In this study, granite samples representing three different weathering degrees were selected to evaluate the effects of surface roughness and weathering degree on shear strength. To this aim, we determined the profile roughness coefficient (PRC), profile roughness angle (PRA), and joint roughness coefficient (JRC) for the selected fresh and weathered granite joint samples. Values of PRC were in the range of about 1.043–1.073, and PRA and JRC varied in the ranges of 16.67–21.45 and 12–18, respectively. Weathering led to the increment of joint surface roughness of the selected granitic joints due to the higher resistance of quartz crystals in the weathered matrix. However, the increment in surface roughness did not result in an increase in the shear strength. On the contrary, the shear strength of discontinuities dramatically decreased.

Quality Assessment of Geo-Materials for Coastal Structures (Yumurtalık, Turkey)

Rubble mound breakwater is one of the most important coastal engineering structures for shore and harbor protection. Standard rock quality evaluation processes were performed on massive basalt, vesicular basalt, crystallized limestone, and micritic limestone from southeast of Turkey. The rock types were evaluated within five different rock quality classification systems (CIRIA, CUR, CETMEF 2007; Lienhart 1998; Winkler 1986; Fookes et al. 1988; BS 812). The methods of CIRIA, CUR, CETMEF (2007) and Lienhart (1998) were shown to be more successful than other methods, which are insufficient to explain rock quality. Massive basalt and micritic limestone can be used as armourstone, filter layer, and core materials, but vesicular and crystallized limestone provided engineering requirements for only core materials. Vesicular basalt and crystalline limestone exhibited few poor features in terms of strength, such as iddingsite, stylolites, and micro cracks. These features can favorably affect rock strength, and oppositely affect rock quality.

Rockfall at the heritage site of the Tatlarin Underground City (Cappadocia, Turkey)

Abstract Cappadocia is one of the most important natural, historical and cultural heritages of Turkey. The region is seriously threatened by different instability problems, and several locations were accordingly closed to visit, mainly because of rockfalls. The aim of current study is to investigate the rockfall hazard potential near the Tatlarin Underground City. For this purpose, an extensive engineering geological investigation was performed and complemented with a set of rockfall simulations performed by means of the 3D numerical model HY-STONE. The investigation included: (1) mapping of the lithological units (tuffs and overlying basalts, talus deposits) and of unstable blocks along the cliff; (2) rock mass geomechanics and kinematic analysis of block stability; and (3) laboratory testing of tuff and basalt. These allowed to show that the instabilities are mainly controlled by different durability of tuffs and basalts. The weakness of tuffs facilitates a progressive undercutting of the basalt layer, the opening of subvertical joints and the consequent movement of large basaltic blocks. Two future potential rockfall scenarios have been produced by 3D rockfall modelling for hazard zonation and for suggesting risk management strategies. Model parameters were calibrated by back-analysis of both historical events and field tests. Different sets of parameters have been calibrated for different release volumes to consider different degrees of interaction with slope material of different size. The effect of roughness of the topography was investigated in terms of trajectories and lateral dispersion of blocks and its consequences on hazard zonation and risk management actions.

Rock Mass Instabilities in Tatlarin Underground City (Cappadocia-Turkey)

Cappadocia is one of the most important touristic sites in Turkey due to its spectacular and unique landforms, fairy chimneys, underground cities and historical heritages. Tatlarin underground city is one of the many rock-cut structures of Cappadocia. The Cappadocia Region mainly consists of Pre-Miocene basement rocks, Lower Miocene sedimentary rocks, Miocene volcano-sedimentary unit and Quaternary volcanic rocks. The underground city was built in slope consist of Miocene Tuff and it was generally threatened by rock mass instabilities. The most commonly observed stability problem at Tatlarin Underground City and its vicinity is the fall of rock blocks from the basalt outcrops. Potential rockfalls have been simulated by using the 3D model HY-STONE to recognize the most critical sectors and to provide a support for long-term urban planning and cultural heritage protection.

Evaluation of the physico-mechanical parameters affecting the deterioration rate of Ahlat ignimbrites (Bitlis, Turkey)

The paper principally focuses on the durability assessment of various stratigraphic levels of Ahlat ignimbrites collected from the eastern region of Turkey. A total of four different ignimbrite types with dissimilar color, texture and particularly welding degree were tested in laboratory. The laboratory tests performed on the ignimbrite specimens indicate that the welding degree as well as the lithic material content mainly controls the strength and capillarity properties of the ignimbrites. In addition, the durability of highly porous ignimbrites strongly depends upon the degree of welding. The effect of several weathering agents on the ignimbrites was evaluated on the basis of decay constant parameter. Accordingly, salt and ice crystallization pressures are a couple of major destructive agents acting within the micropores of the ignimbrites. Conversely, the investigated specimens are relatively durable against cyclic wetting–drying. Statistical evaluations reveal that the pore diameter is the major controlling factor on the deterioration rate of the ignimbrites after specifically recurrent freeze–thaw cycles. Moreover, the dry unit weight of the ignimbrites is more significant than the uniaxial compressive strength considering the deterioration rates during wetting–drying and salt crystallization. A less significant relationship was obtained between pore diameter and salt crystallization decay constant.

Reply to discussion by Alavi and Gandomi on Models to predict the deformation modulus and the coefficient of subgrade reaction for earth filling structures by Ismail Dinçer [Adv. Eng. Software 42 (2011) 160-171]

Alavi and Gandomi [1] indicated that there are some controversial points regarding the reliability and applicability of the presented ANN models proposed by Dincer [2]. According to these criticisms, complementary explanations, tables and figures were given.