Journal of Geotechnical Geology
Volume:9 Issue: 4, 2014

Foundation design is conventionally practiced by deriving the allowable bearing capacity in terms of shear strength and compressibility. Shear strength refers to the individual or combined contribution of drained angle of internal friction and undrained cohesion,at one of the three instances of peak (failure),residual,or critical (softened) states. Compressibility refers to the elastic and consolidation settlements; the predominance of which is a factor of soil permeability. Soil is conventionally examined by confined stressing on the wet stress-state surface,for the coefficient of volume compressibility to be determined. Ultimate bearing capacity is then reduced to a certain total settlement,and an arbitrary factor of safety of 3 is finally applied to cover uncertainties. Such a conservative approach however does not always successfully restrict the settlements beneath foundation. Although the shear strength has become a much-practiced subject,there has been a certain lack of emphasis on a fundamental understanding of shear strength parameters,and even greater neglect of the correct choice of stress path for individual soil types so to derive such parameters in the most critical stress-hydraulic environment. For that reason,this work aims to critically review the shear strength literature for a better understanding of the internal angle of friction and c-intercept.

From these factors the tunnel form, dimensions, depth, the tunnel drilling method, presence of water, etc. can be mentioned. Achieving an optimized design requires identification of effective parameters and the relationships among them. Effective design parameters include stability of the tunnel face, horizontal and vertical displacement, seismic wave, and shrinkage phenomenon, etc. Also considering the importance of the structural stability on the ground surface above the tunnel, especially in the urban tunnels, the settlement level of the ground surface must be considered. In this study the stability of an 8m width and height horseshoe sectioned tunnel located in Tehran alluvium having been projected for water transmission has been technically analyzed using the FLAC 2D‎‏ software and the comparison wad made using empirical and analytical methods. The results showed that the maximum settlement resulting from design step using software is 14.9 mm which is almost consistent with the value obtained from the empirical relationship, and the difference estimation lies within the acceptable range (0.7%). Also the obtained horizontal displacement shows that the maximum displacement within the 25m distance from the tunnel axis (on both sides) is 2mm and the values obtained from the empirical relationship showed that the maximum horizontal displacement occurs on the 25m distance from the tunnel axis.

A series of microtremor array measurement was performed in a site of Tehran (shaghayeg park) with the aim of estimating the shear wave velocity (Vs) profile for near surface layers. The SPAC and f-k array processing technique were used and the results were compared with other information specially a 200 meters depth borehole and the down-hole and PS logging data have been done in this paper. The data of different time, day and night were processed and the results were compared with the actual Vs profile by definition the various criteria. We found that, the SPAC method is probably more convenient compared to the f-k method. SPAC method gives results as good as the f-k method while using smaller number of recording stations and shorter array dimensions.

Ground water contamination has been a matter of concern in developing agricultural areas which is prone to pollution by fertilizers such as nitrates. In arid parts of Kermanshah and Ilam provinces due to the transference of water from Sirvan River by tunnel and channel, agricultural industry especially irrigation technology has been developed in a rush. Ground water is not easily contaminated, because many aquifer systems possess a natural capacity to attenuate and thereby mitigate the effects of pollution. Once this occurs, it will be difficult to remediate. The replacement cost of a failing local aquifer is generally high and its loss may influence other water resources. Further, in the developing countries, such remediation might practically be impossible. Thus it is important to identify which aquifer systems and settings are most vulnerable to degradation. The main aim of this research was to evaluate extend of ground water contamination in some agricultural plains in arid regions of Kermanshah and Ilam based on the DRASTIC model. The electrical conductivity (EC) values are assigned to verify some parts of the DRASTIC vulnerability map; largely this arises from the lack of adequate nitrate information. In all plains, EC is in agree with vulnerability map except for Somar, due to the presence of Gachsaran Formation which increase EC dramatically.

Kangan and Dalan formations are one of main resevoir rocks in Fars structural province in Iran south. in XXP gas field available fractures in Kangan formation have main effect on drilling mud loss. Although shale rate change of reservoir rock units is a key factor in control of fractures distribution in upright direction. But lateral distinction in reservoir rock leakage is affected by opening amount of intersection fractures. During 31 wells drilling in TBK, drilling mud loss has occurred in 12 wells. Drilling mud loss in these wells has been observed in Kangan formation and in anticline axis range. On the basis of surface studies and EMI images’ interpretation, two major groups of fractures with non tectonic origin have been recognized in XXP anticline. These fractures have geometric characteristics including Dr. 150/80, Dr. 240/80. Two desired fracture groups are crossover and vertical on layered surface. These fractures are co-direction and intersection type with main fractures of southern Pars field. Desired fractures have evolved by the effect of upper layers’ weight before folding. Fracture Intersection have been stretched in fold axis range by folding effect and extra opening has been occurred on their surface. Extra opening of fractures intersection in fold axis range has caused drilling mud loss increase in this part of the field.

This research is concerned with the landslide susceptibility of Khoramabad area using Geographical Information System (GIS). Landslide susceptibility zonation (LSZ) is able to identify areas prone to failure based on the characteristics of past events. Satellite data, topographic maps, field data, and other informative maps were used as data layer in this study. These data layers are including lithology, slope, aspect, land use, distance from fault, distance from road and density of river. A numerical rating scheme for the factors was developed for spatial data analysis in GIS method. The resulting landslide susceptibility map delineates the study area are located into different zones of susceptibility classes including high, moderate and low. Based on the prepared landslide hazard zonation map some 32% of the study area shows high landslide susceptibility.

The surface sediments in Mahshahr Port area are mainly consist of soft clayey soils. These soils have considerable strength in dray condition but as their moisture content moves up to saturated level a notable decrease in their strength is observed. This reduction, in turn, leads to decrease of California Bearing Ratio (CBR) and increase in soil settlement which consequently results in vast and destructive deformation in the surrounding buildings. In this research, the addition of cement and lime to the soil is considered to evaluate their effect of the soil strength by performing unconfined compressive (UCS) and Atterberg Limits tests. In this procedure, different ratios of lime and cement mixture (0.0 %, 2 %, 4 %, 6 %, 8 %, 10 %, and 15 %) with various curing times is considered. The results of these tests revealed that compressive strength of soft clay decreases by adding lime or cement due to disturbing its initial structure. This decrease of strength is induced by high sensitivity of the soil, however as the time passes compressive strength of the cement-added samples rapidly grows; as compressive strength in modified samples with 6 % cement and curing time of above 3 days has increased compared to undisturbed samples and their plasticity index has decreased. On the other hand, compressive strength of samples modified by lime gradually increased, as adding 6 % lime to the soil and applying curing time of 28 days did not lead to increase of their compressive strength compared to undisturbed soil samples and their plasticity index decreased.