JOURNAL OF ENGINEERING GEOLOGY
Year:2009 | Volume:3 | Issue:1|Papers Count:12

This study explores crustal velocity structure in the west of Iran. Wealth of data from recorded local earthquakes creates an opportunity to image crust and upper mantle in the region and then these data use for the joint inversion method in this region. We proposed to study velocity and interface structure of the crust and upper mantle in the west of Iran using local earthquakes recorded in the Kermansha short-period seismic stations at the Institute of Geophysics, University of Tehran (IGUT), and the Sanandaj broad-band seismic station at the International Institute of Earthquake Engineering and Seismology (IIEES), since 2004. The earthquakes and stations should be directed for the travel time curve analysis. Recorded earthquakes were classified along the five separate profiles and 278 earthquakes (mb³3) separate in data (3000) and epicenter distance is 10-750 km, that corresponding travel-time curves were analyzed. Moreover, crustal velocity structure is determined based on the travel time curve of local event. So, algorithm program was written and arrival times of body waves compare with forward modeling code was written, in order to refine final model. This processing based on earthquakes with mb³4 and the error RMS is 0.01-0.26 sec. Compressional wave velocity of the crust is 6.23±0.07 km/s and the upper mantel (Moho) is 8.08±0.08 km/s. since, shear waves velocity for the crust, found to be 3.64±0.06 km/s and the upper mantel (Moho) is 4.70±0.01 km/s. Depths for Conrad and Moho discontinuities were obtained 11±2 km and 43±3 km respectively, which well correlate with the results of the previous gravimetric crustal studies .

When two solutions are mixed, concentrations in the mixture are volume-weighted averages of the two end-members, but the thermodynamic activities of the species controlling the water–mineral reactions are non-linear functions of the mixing ratio. Therefore, two end member solutions in equilibrium with carbonate phase could lead to a mixture undersaturated with respect to carbonate. A favorite place for this phenomenon is water table, where mixing of different waters is taking place. In this paper, Porosity change in freshwater lens of an island was calculated by coupling dissolution potential with a variable density flow and solute transport model. The effect of permeability enhancement on the rate of porosity change was evaluated. Dissolution due to this mixing takes place in water table and active edge of freshwater lens (40m from coastline). The results indicate an increase rate of 0.6×10-3 percent of porosity per year. Permeability enhancement increases the rate of dissolution and porosity change in fresh water lens.

In this study, seepage phenomena through the left abutment of Marun dam are investigated. The Marun dam is a 170 m high rock fill dam, which regulates the waters of the Marun River, serves power generation, and flood control and provides irrigation needs. The dam site lies in the Zagros Mountains of southwest Iran. This region presents continuous series of mainly karstic limestone, marl, shale and gypsum ranging in age from Cretaceous to Pliocene. The region has subsequently been folded and faulted. All underground excavations are sited in the left abutment. The spacing of the diversion tunnels and pressure tunnel is considered to be acceptable, meaning relatively short, thus requiring 2 row grouting curtain into both embankments. Prior the reservoir impoundment, the concrete plug was constructed into the middle section of second diversion tunnel. Upstream section of tunnel was not concreted. During the first reservoir impounding, the old karst channels along ‘Vuggy Zone’ cut by the second diversion tunnel were reactivated and leakage occurred. The total amount of water leakage through the left bank of Marun dam was about. The unlined second diversion tunnel had a key role in connecting reservoir with karst conduit system. On the basis of detailed engineering geological analysis, the concept of remedial works was carried out. The main points of this concept are one of row grout curtain extension up to the section with shaly interbeds declared as watertight Asmari sequence (close to the watertight Pabdeh formation) and plugging of accessible section of main karst channel by concrete. In order to determine the seepage direction and karstification pattern, solubility studies were done. Also pinhole, XRD and XRF tests were carried out. The major joint system and interbedding cracks have predominant role in karst evolution process. Hydrogeological role of joints, perpendicu-lar to geological structure, is not negligible. As a result of these studies, seepage paths have been identified in the karstic limestone in the left abutment of the dam.

The Zydoun plain experiences semi-arid climatic conditionو and though groundwater quality is not commonly acceptable with respect to drinking, it is used for irrigation. The water withdrawal of water and its increasing trend would probably put the study area into critical condition to meet demand. The main sources of water supply in the region are Zydoun aquifer and Zoreh River. The better quality of groundwater in the extreme southern part of the plain and lower exploitation expenses are the reasons why farmers prefer to use groundwater rather than river water. As a result of over- exploitation from the Zydoun aquifer in the last years water table has been declined. In order to impede critical situation in the area, a detailed study regarding management of groundwater including physiography, meteoro-logy, hydrology, hydrogeology, hydrochemistry and geomor-phology were undertaken. Based on these investigations, a number of ephemeral streams in the southern part of the plain were recognized to be suitable in term of water quantity and quality to secure a part of water demand of the area. One of the optimum methods for long-term use of these water resources is injection of water into ground and withdrawal in required time. to this end, the collected data, were put together and it was found that the most suitable method of artificial recharge was channel modification. At the end, considering consideration, morphological, permeability condition and water demands in the southern part of the Zydoun plain, eleven sites for execution of water resources management were suggested which would annually augment aquifer storage by over one MCM.

This paper presents a rigid circular footing model with specified properties and dimensions on a sandy-clay soil with Mohr-Coulomb material. This model is analyzed dynamically with finite difference 2D FLAC software under vertical component of ground excitations. Then the soil is improved with cement grouting and analyzed again. Consequently, the load-settlement curves under a circular footing, due to vertical component of ground accelerations through the underlying soil, are plotted. Also the dynamic bearing capacity of natural and soil cemented foundation is presented and discussed. The analysis results show that adding 2, 4 and 6 percent of cement, with certain conditions, cause 2.7, 4.2 and 7.0 times increase in dynamic bearing capacity, respectively, in comparison to normal soil.

The present study shows that the frequency of the main peak in the spectral ratio analysis of microtremores data correlates well with the sediment thickness at the many sites. In this study، based on the resonance period of microtremores in 200 points estimated by H/V spectral ratio and the shear wave velocity profile of 62 points the power relationship of between the thickness of sediments and resonance period in Mashhad city are introduced and the iso-thickness sediments map and cross sections are produced. The results show that the maximum thickness of the soft sediments is about 200 meters in south-east and central of Mashhad and its decreases to the south، south-west and north mountains area

Estimation of engineering properties of rocks and flow rate is an important issue in rock engineering. Properties of discontinuities have considerable effect on rock mass inflow, because they are the main pass of water flow in fracture rock masses. Despite the bulky research about water flow in rock mass, there is no clear evidence as to relationships between all of these parameters and water inflow in rock masses. Neural network systems have a great advantage in dealing with complicated problems such as forecasting, classification and pattern recognition. In this paper, artificial neural network techniques were used in order to forecast Lugeon amount and Hydraulic conductivity behavior of Granodioritic rock mass of Shoor-Jiroft dam site from some characterization of discontinuities such as Rock quality designation, Fracture frequency, Aperture, Weighted joint density, Fracture zone and depth. Relationships between these factors were analyzed with Simple Linear Regression, Multivariate Regression and Stepwise Regress-ion. A Multilayer Perceptron Neural Network (MLPNN) with back propaga-tion procedure was developed for training the network. A Dataset containing 304 values of water pressure test in Granodioritic rock mass of Shoor-Jiroft Dam project was used to train and test the network with the Levenberg-Marquardt training algorithm. The results indicated that neural network forecast hydraulic conductivity considerably better than regression methods do.