ENGINEERING GEOLOGY
Year:2008 | Volume:1 | Issue:1|Papers Count:12

Rock materials are as natural materials which used in variety of coastal protection structures, especially in rubble mound breakwaters. Engineering properties of rocks, such as durability and resistance to degradation factors of the marine environments, are the important properties which the construction material of marine structures should be have. Rock durability is a function of rock properties and condition of environment in which the rock will be used. Regarding the economical importance of constructed coastal ports and facilities in coast lines of south Iran, it is necessary to evaluate the engineering properties of rocky construction materials in such structures in durability and degradation point of view. In this study, by investigating and sampling the used rock material in 27 constructed rubble mound breakwaters along the 1000km south Iran's coastlines, from Amery Port in western part to Pasabandar Port in 85km east Chabahar, and regarding the observations that collected in field visual investigations and engineering tests of durability examination, the experimental relationship between physical, mechanical and durability parameter of studied rocks have been concluded and consequently criterion to select the suitable rock of three group of rocks Limestone, Igneous rock and Bioclastic sedimentary rock (Lomashell) have been presented individually.

Mighan Playa or Lake, northeast of Arak, is mainly covered by marl and clay soils which lose their strengths to as low as 50 KN/m2 in rainy periods. Due to reasonable potential of this region for civil, mining and industrial activities, the stabilization of its soils with lime has been studied. The necessary tests were carried on the representative samples of soils to identify basic, index and strength parameters of materials. Then samples of soils mixed with different amount of lime and similar tests were repeated. The present study showed that presence of 7% to 9% of lime considerably reduces plasticity and increases soil strength. On the other hand 1% to 3% of lime increases soil compaction. This study showed that with 5% to 6% of lime, the optimum conditions of geotechnical properties can be achieved.

Marl units generate the most sediment yield rate among the geological formations in the watershed basins. Therefore, they notably affect on useful lifetime of dams and water electric constructions, flooding processes, sedimentation in the water transport channels and the existence of aqueous creatures. Study and classification on the effective characteristics of erodibility of marls could notably help to remediation activities on them. In this research, the amount of sediment yield in each marl units were compared using a portable rainfall simulator at field. The amounts of runoff and produced sediments in each marl units at three repetitions were measured. The relation between physico- chemical characteristics of marl units as independent variables and the amounts of produced sediments as dependant variables was analyzed using multivariate linear regression method.  Some characteristics such as SAR, EC, and K show 89, 3.5 and 1.5 percent of total variance of produced sediments at each marl units respectively. On the basis of ANOVA analysis of sediment data, the marl units have classified in four groups: A (include of Ols unit), B (include M3 unit), C (include M1 and M2) and D (include Olg and O-M units). The erodibility rate and sediment yield decrease from A to D group. Physico- chemical characteristics of four above mentioned groups have analyzed using variance analyze. The results show significant difference at level 0.5, .01, and .001 for some parameters such as SAR, EC, K+1, Na+1, Cl-1. Meanwhile, the mean amounts of sediment yield of various marl units obtained from rainfall simulator test show that evaporative marls of Neogene age (M1, M2 and M3) potentially produce sediment 27 to 100 times more than Qom formation marine marls and Kond formation lacustrine marls.

The present study attempts to classify rock behavior in Isfahan subway tunnel between Azadi square and University stop. The geomechanical classification (RMR), rock mass quality index (Q), and geological strength index (GSI) have been used. Since the most common damages in shallow tunnels and jointed rock mass have been observed in wedge sliding in the ceilings and walls, the Unwadge software was used for data analysis. The study also estimated the appropriate supporting systems for possible wedges. Obviously, the study and analyzing the supporting systems need enough understanding of geomechanical parameters and the deformability of the including rock mass. GSI has been used to determine such parameters. Following the establishment of such parameters, the numerical method together with Phase2 software was used to analyse the tunnels and their maximum displacement.

One of the most important parameters in back analysis is analysis of measured deformations of excavated tunnel. Numerical methods as a conventional method are used for back analysis. An artificial neural network that has been trained with sufficient number of examples made with numerical methods can be used instead of them. These networks are accurate enough and faster than numerical methods and an operator can utilize it without knowledge of rock mechanics or numerical methods. In this research, a multilayer artificial neural network has been presented which is able to predict deformations around a tunnel after excavation. Input parameters of this artificial network are deformation modulus, Poisson ratio, tensile strength, cohesion, friction angle, initial vertical stress and horizontal to vertical stress ratio. A tunnel model with 183 cases was executed with ''FLAC'' code and results (deformations) as a database was used for training and testing of the neural network. By training and testing of different neural networks, optimized values for layers and nods and architecture were found. According to obtained results, a neural network was selected. This network was able to predict deformation in roof and sides wall of tunnel accurately without having any knowledge about rock behavior. Relative strength of effect (R.S.E.) factor which is a mathematical relation in neural networks is presented that shows relative influence of parameter i as input on parameter k as output. With study of R.S.E., it was found that each parameter has a special influence on the deformations around the tunnel and some parameters has small influence in all conditions. So in analysis or back analysis of underground structures more attention should be paid to parameters that have more influence on results. By considering the effect of each parameter in numerical analysis, amount of effort for determination of the parameter and priority in geotechnical exploration can be fined.

This paper describes an experimental device which is used for determining radial permeability of rocks around well bore hole according to effective stress.Permeability of rocks is a very important characteristic because it controls the flow of fluid. Laboratory tests on thick-walled hollow cylinders of rock are relatively easy, economical and realistic means to understand better the mechanisms associated with wellbore failure. The experimental device used to carry out tests on thick-walled hollow cylinders under two distinct conditions which are: 1) Tests without pore fluid 2) Tests with convergent radial flow of pore fluid. Two types of tests were carried out in conditions with pore fluid: a) Tests under an increasing external pressure and a constant external pore pressureb) Tests under a constant external pressure and an increasing external pore pressure The tests were carried out on a very porous artificial material (CPIR09). The mode of rupture observed in the tests was a pair of radial rupture planes. The results obtained show that when the external pore pressure is constant the global permeability decreases with increasing external pressure. When the external pore pressure increases the convergent radial flow of pore fluid (due to the imposed pore pressure) slightly increased the global permeability samples. The convergent radial flow of pore fluid acts to remove fractured materials and to erode localization bands, therefore, the global permeability samples brutally increased.