Journal of Engineering Geology

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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.

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The soil of the Arvand free zone in the north of Khorramshahr is fine cohesive and cannot be used in earth works. On the other hand, suitable materials for this purpose (coarse-grained soils) are located at the farther distances which a considerable cost requires. In this regard, it is trying to improve the soil with lime and furnace steel slag. This study is focused on improvement of the fine-grained soil by adding various contents of lime and furnace steel slag. For this purpose, after sampling and performance of compaction tests, different amounts of slag (10, 20 and 30% by weight of dry soil) and lime (2, 4 and 6% by weight of dry soil) were added to the soil and after curing for 28 days, the effect of additives on the physical and mechanical properties of soil was investigated by using several tests such as Atterberg limits, compaction, uniaxial compressive strength (UCS) and CBR as soaked and unsoaked. Based on USCS classification the study soil is CL, its plasticity index is about 25% and sulphate ion content is more than 0.5%. Experimental results show that by adding slag and lime at different contents to soil, mechanical properties of soil improve dramatically, so plastic index of soil decreased and UCS and CBR has been increased. Also, the maximum dry unit weight of soil increases and the optimum moisture content decreases. The test results also indicate that the effect of lime on soil is higher than slag and the effect of slag for less than 35% is not considerable, however the test result of unsoaked CBR show that the bearing of soil increase in the more than slag content 20% is significant. According to the previous studies, due to the relatively high sulphate ion content in the soil, the use of lime alone is inappropriate and the slag can only physically improve soil conditions but also chemically prevent the formation of large volume minerals (like Ettringite) by the reaction of lime with soil sulphate ion../files/site1/files/152/%D8%AD%D8%B3%DB%8C%D9%86_%D8%B2%D8%A7%D8%AF%D9%87.pdf

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In this study, it is attempted to analyze sensitivity and reliability in order to evaluate the liquefaction potential in soil layers in Tabriz. 62 boreholes that had possible conditions for liquefaction were selected. Seismic mapping was simulated using finite fault method and then the effect of soil layers on PGA was estimated. In continue, the liquefaction potential index was estimated and the zoning map of liquefaction risk was presented. In final, through sensitivity and reliability analysis of the Monte Carlo method, the rate of density function against safety factor of the soil layers versus to liquefaction was determined.