نشریه زمین شناسی مهندسی ایران
سال یکم شماره 2 (تابستان 1387)

This paper presents the geomechanical parameters and the results of preliminary support design of the Daroongar diversion tunnel using some empirical and numerical methods. The rock mass rating (RMR), geological strength index (GSI) and rock mass quality (Q) systems were used for estimation of quality of rock masses properties for preliminary support design of tunnel. Also distinct element method (UDEC program) was used for stability analysis of the tunnel. Samples obtained from drilling were tested in the laboratory, included of uniaxial strength (UCS), deformation parameters, unit weight and porosity. In order to estimate strength parameters of rock mass (compressive strength of rock masses, tensile strength of rock masses, deformation modulus and Hoek-Brown constants) Hoek-Brown failure criterion was used.

Recent sediments of Aghajari formation are dominating parts of south and southwest of Iran. This has led to the fact that many of the important developing projects are located on this formation. Therefore a thorough understanding of geomechanical characteristics of various units of this formation could profit such projects at various stages of implementation. Furthermore, these studies would support formation of a geotechnical and geomechanical data bank that can be used in preliminary studies of engineering structures and preparing large scale engineering geological maps of the region.
To undertake the proposed research systematically, the Zagros range was divided in three district of northwest, central and southeast. Then the geomechanical characterizations of Aghajari units were undertaken based on the results of rock mechanics laboratory tests and the information acquired from the executed projects in the region. Beside this, durability test of every unit of this formation also was carried out to evaluate the weatherability. The analyses of the test results yielded a comprehensive set of coefficients to evaluate the various mechanical strengths from some simple inexpensive laboratory tests, and the geomechnical behaviors of these rocks are studied. The strength conversion factors have been presented implicitly. The detailed triaxial tests revealed the principal stress response of the total set of the representative samples with respect to various confining pressures. Meanwhile, shear strength parameters c and φ were determined and the transition condition from brittle to ductile behavior evaluated. An assessment of the results inferred that the rock units of Aghajari formation in central part of the study area have higher strength parameters compared to two other adjacent units. This conclusion may lead to this hypothesis that due to confinement in two strike slip faults restriction, Kazerun and Hendijan faults, these rocks have undergone the diagenetic process more rapidly and intensely. The detail of the undertaken studies is presented in the paper.

Dynamic probing for the assessment of engineering geology and geotechnical projects is a cheaper, quicker and easier method than other methods. The Dynamic Cone Penetrometer is a light weight type of dynamic penetrometer. This device has used to determine CBR of pavement bases and sub bases up to 1 to 1.2 m depths. The aims of this study are to extend application of DCP and assessment of the tips angle effect on repeatability of DCP results. Assessment of the repeatability results and probability distribution functions show that the results are repeatable. The coefficient of determination (R2) show the best distribution functions are lognormal and then normal for the mean of results. Assessment of the effect of tip angle on repeatability is shown the tip with 90° angle is more repeatable than other tips.

Landslides, which happen usually in rural regions of southwest Khalkhal, not only cause considerable economic loss, but also provide social and cultural damages. This may effect the development project that are going to be implement in this area. This study was conducted to understand and analyze the contributing factors to these landslides and slope movements, so that the findings could be used in planning different projects such as new construction developments, improvement of agriculture, protecting the soil resources, environmental issues, and economic activities. After identifying all the landslides of the region, based on the existing aerial photos and the compiled field data, basic geological maps, slope gradients, land use, distribution of the landslides, annual rainfall, and length of the rivers and roads, the area of the buildings and the number of the waste water wells were prepared at 1:50000 scale. Then , statistical analysis based on cross table and chi – square method were applied. The coefficient values and the correlation of each factor with the landslides and slope movements were calculated and compared with one another. The results showed that there are significant differences between different types of factors and their contribution to slope movements, and the degree of difference varied from factor to factor. The results also showed that rock composition is the main factor which contributed to landslide occurrence. Other factors such as land use, distance from major faults, slope condition and rivers’ undercutting played a role obtained in landslide occurrence. Based on the results, practical and scientific methods were recommended for lowering the amount of direct and indirect damages.

Because of the many problems associated with traditional procedures for identifying sediment sources, fingerprinting method, based on physical, chemical and organic properties of sediment and source materials, are increasingly being used as a valuable and effective alternative approach to assembling such information. In this method, a suitable composite (set) of diagnostic properties and a multivariate mixing model are employed to estimate the relative contributions of sediment sources to sediments yield. In this study, using a suitable composite of geochemical elements capable of discriminating subareas underlain by individual lithological types of the study basin and a multivariate mixing model, the contributions of lithological types to sediments yield were determined. The study basin is the main subbasin of Pouldasht water spreading station basin, located in Makoo township, West Azarbaijan province. The lithological subereas were categorized in five groups as sediment sources. Over 106 representative source material samples and 6 sediment samples were collected from lithological groups and sediments deposited in the river bed respectively. Then, the samples were analyzed to determine the concentrations of 18 geochemical elements. 12 out of the 18 geochemical elements were selected as a suitable composite fingerprint using discriminant function analysis. Mean contributions from the lithological subereas of Marl, Conglomerate, Limestone and dolomite, Shale and Slate, and Quaternary sediments were estimated to be 53.9, 29.75, 8.85, 7.5 and 0 percent respectively. Mean absolute error and model efficiency of the method were estimated to be 17.5% and 0.99 respectively. The fingerprinting approach to source ascription is seen as providing valuable information regarding sediment sources in the study basin.

Exploitation of materials from river beds changes hydraulic and geometric characteristics of rivers which increases the flow turbidity and flow energy. It consequently accelerates erosion, causes environmental hazards and also affects the bed sediment morphometyric characteristics. The present research was conducted in Vaz River located in Mazandaran Province, Iran, to study the effects of exploitation of two sand and gravel mines on morphometric characteristics of bed sediment. To achieve the study purpose, four cross sections were selected in the study river before and after each mine. The bed sediment were then sampled using combining technique and the important bed sediment characteristics viz. mean, standard deviation, skewness, kurtosis, mode, d10,d50, d90, gravel, sand, mud, large, medium and small diameters, shape factor, nominal diameter, sphericity, roundness, width ratio and sediment texture were then determined. The results of the study, despite of general similarities in hydraulic characteristics of cross sections before and after mines, revealed that the sand and gravel mining activities have had significant effects on all of the studied morphometric characteristics except sphericity and sediment texture.

This study investigates the role of tectonic activities in fluvial systems and produce of accommodation space for Plio-Quaternary sediments of Southern slope of Mishow-Dagh horst which is an important structural element within the horst-graben system of north of the Orumia Lake, northwest of Iran. The result of these activities and other environmental and geomorphologic processes has been to impose control mechanisms in quality of sedimentation in sedimentary environments of the study area. Investigations on Plio-Quaternary sediments via interpretation of geological, topographical and areal photos and especially field studies, indicate that several evolution stages are occurred in sedimentary systems in the study area. Based on all constraints, a five stage evolutionary model of deposits as moderately consolidated conglomerate, Qt1, Qt2, Qt3 and Qt4 are proposed and then, the role of tectonic activities assessed on each of them. The results of study showed that present topographic and geomorphologic landscape of study area hardly influenced by Quaternary tectonic activities and this factor was played the main role in produce of accommodation space and formation of transverse drainage network. The record of formation of transverse drainage network referred to after the Pasadanian orogeny and before the beginning of stage Qt1 sedimentation. Since there are not witnesses based on uplift movements in central part of Mishow-Dagh in recent geologic times and especially Quaternary, therefore, it should be look for the reason of the increase in sediment yield of fluvial systems and spread sedimentation in Quaternary, in other factors such as climatic changes. However, geomorphologic witnesses based on fluvial systems properties, indicate that the Orumia Lake bed subsided in Pleistocene and Holocene as the result of Sharafkhaneh fault activities, that probably synchronous to Quaternary climatic changes(?) caused falling of Orumia Lake water surface. In particular, this paper provides a case study that contributes to the understanding of landscape development within tectonically active zones.