Journal of Engineering Geology

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Abstract
(Paper pages 1059-1076)
Physical and mechanical properties of intact rocks are very important in civil engineering works that interact with rock such as underground structures, dams,foundations on rock, and rock slopes. Therefore geomechanical parameters such as compression strength and deformation modulus of rock can have fundamental importance in the different stages of design. Determination of these parameters is time consuming and costly. Since Asmary formation has broad outcrop in the west and southwest of Iran and many large projects are located in this formation, therefore it is a requirement to accomplish the present research. This paper is dealing to analyzing data from laboratory of two major projects of the Khersan 1 and 2 dam sites. In this regard, the physical, mechanical, dynamic and durability properties of intact rock and geology controlling agents of these changes has been evaluated and analyzed. Finally, new experimental relations between different parameters have been presented.

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One way of reduction of leakage from beneath of earth dams is using of one contact clay layer with very low permeability and intermediate to high plastisity and connectig it to core of dam. Since, most of fine-grained soil in environtment of dam have low plastisity and preparing it from another place is not economic, use of bentonite in order to improvement of engineering characteristic of borrowed clay is suitable way.
In this search effect of bentonite on geotechnical properties of fine-grained soils with low plastisity are evaluated. Results of this research show that hydraulic conductivity, consolidation coefficient, dry density, colifornia bearing ratio (CBR),.....are decreased with increase in bentonite content but optimum moisture , Aterberg limits , cohession and so on are increased with bentonite addition. Finally, with analysis of obtained result, optimum percent of bentonite is offered in order to improve of engineering properties of used clay in contact region.

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Introduction                               
Generally, in engineering geology physical and mechanical properties of rocks are investigated in macroscopic scale, and less attention is paid to investigate the texture and microstructure developing in rock during deformation. Salt rock, as a best example of ductile rocks, has attracted the attention of many researchers. Compared to silicate rocks, salt rock exhibits extensively ductile behavior at even low temperature and pressure. In micro-tectonics, salt is important, because of it is useful as an analogue material for understanding the microstructural processes and textural development in silicate rocks. Deformed salt rock can display microstructures developed in silicate rocks at high pressures and temperatures. Regarding the similarity between microstructures of salt rock and silicate rocks, investigation of microstructure and deformation mechanism in salt rock can be helpful in understanding the main cause of the squeezing phenomenon in tunnels.
One of the effective factors on squeezing phenomenon is the structures and microstructures of rock. Rock mass classifications that contain rock mass structures are used in the predicting methods. But, so far, no attention has been paid to the role of rock microstructure in predicting the squeezing phenomenon.
This study is aimed to identify deformation mechanisms occurring in microscopic scale in rocks and lead to tunnel convergent in large scale. To achieve this goal, the microstructures in a naturally deformed Late Pre-Cambrian to Early Cambrian Hormuz salt rock from the active Deh Kuyeh salt fountain in Fars province were investigated using Electron Backscatter Diffraction (EBSD).
Materials and Methods
Deh Kuyeh salt diapir was located at about 27 km NE of Lar city. Salt samples were taken from top of the east and west glaciers (S1 and S2) and from the middle part of diapiric stem (sample S3). Raw samples were first cut dry into slabs (approximately 3´2 ´1 cm). Thin sections were prepared following the procedure of Schleder and Urai (2005) and Urai et al. (1987).
Halite crystallographic orientation data were collected using a Zeiss SIGMAVP FEGSEM. EBSD patterns were collected using an accelerating voltage of 30 kV, beam current of ~ 100 nA and a working distance of about 30 mm. Oxford instruments AZTEC software was used for data acquisition. EBSD large step size (50 mm) mapping was used to examine the overall microstructure in each sample. EBSD data were processed using HKL Channel 5 software.
Results and Discussion
All samples showed relatively similar microstructures. Samples comprise a small number of large grains in a matrix of smaller grains. Most grains were irregular in shape with lobate boundaries and internal distortion. Microstructural study revealed that the ductile flow of the salt was accommodated by dislocation creep and dynamic recrystallization. Salt grains show lattice distortion and a prevalence of low-angle boundaries that are evidence for dislocation creep and recovery processes. Misorientation analysis suggests that (110) <110> and (111) <110> slip systems are responsible for crystal plastic deformation of salt grains. Schmid factor analysis showed that stresses acting on inclined directions lead to the maximum activity of these slip systems.
The observed microstructures in the salt are comparable with the microstructures presented for schist samples from Himalaya region. The rock along Himalaya main trusts also showed evidence of dislocation creep and development of crystallographic preferred orientation. Hence, this article suggests that the rock type and its microstructures are the most important factors in occurrence of tunnel convergent.
Conclusions
This article proposes that deformation mechanisms occurring in micro-scale control the rock behavior in large scale. All rocks can behave as a ductile material depending on the temperature and pressure. In intrinsically ductile rocks like salt rock, presence of many active slip systems facilitates rock deformation under lower pressures and temperatures than silicate rocks. High tectonic stresses in shear zones lead to development of a strong shape preferred orientation and crystal preferred orientation in rocks. These microstructures facilitate rock deformation under stresses exiting in tunnels. It can be said that rock type and tectonic history of the area play the most important role in occurrence of squeezing phenomenon. Other factors such as current stress system in the area control deformation speed in tunnel. It seems investigating microstructures of rocks from tunnel route before and after excavation can be effective in identifying places with high possibility of squeezing.