Khorasan Razavi province is one of the areas with many chains of Qanat and Mashhad city in the center of this province has developed on areas with Qanat in the west direction. Loads caused by tall buildings and structures that built on old Qanats can make Qanats unstable and consequently Qanat collapse can lead to ground settlement. This paper deals with identifying the exact locations of Qanat chains by aerial photographs and evaluating the main factors that cause Qanat collapsing. Moreover the stability of Qanat was evaluated in numerical modeling by plaxis software. The geotechnical data, Qanat depth, Qanat lining system and vertical load was used in modeling and after that, the extension of plastic zone around the Qanat underground tunnel was analyzed. The results of this research show that the rate of plastic zone extension and the influence of lining in Qanat stability decreases by increasing in the Qanat depth. As it is estimated while Qanat depth increases as much as one meter, it can tolerate more pressure as much as loads induced by a one-storey building.

One of the important parameters of soil properties for application in the plaxis, to analyse the behavior of earth structures and their failure mechanisms, is shear modulus of elasticity. An intensive geotechnical survey, field and laboratory tests were executed to estimate the values of this parameter and other soil properties in the body of dike and polder. To determine this parameter, 9 different methods were used. Because of large differences among the given values, characteristic values for each layers of soil, were calculated by using a statistical procedure. Then, calibration of stresses and strains were used to verify the characteristic values and appropriate soil test. Both of the calibrations resulted in values more than characteristic values of shear modulus which were close together. The comparison of results of calibrations with foregoing methods showed that the characteristic values were not reliable because of the shortage of data and utilization of triaxial test to determine the shear modulus was better than others.

One of the important parameters in design of coastal dykes is reinforcement of slope of body and base of dyke. In this paper, with pointing on two customary reinforcement methods of coastal dykes, the reinforcement of hendijan coastal dyke (with 40 kilometers length at Khozestan province) has investigated. In first method, geo-textile materials situated inside the slopes of dyke body horizontally. The length of geo-textile reinforcement materials and the spacing between layers have been investigated in more details. In second method, reinforce the dyke foundation by utilize a geo-textile layer over the foundation bed. In this method the effect of using reinforcement material in prevention the failure of dyke bed have been investigated. The results of these two methods has compared with each others. The First method is reinforcement by utilize geo-textile filaments in parallel layers in dyke body. The second method, utilize a layer of geo-textile in the bed of dyke. Presented analyzes simulated by plaxis FEM model (Developed by Delft University of Netherlands). Utilized different material parameters have used as for available materials at project site in south coasts of Iran. In this paper, decrease of lateral slope of dyke as for suitable stability, is most cared. The results of analysis indicate better efficiency and economic profit by utilize a layer of geo-textile in the bed of dyke. Because of poor soil layer material in dyke bed layer, the results show that using reinforce material in bed has more effect in final strength and endurance of the dyke.

Pore pressure, seepage and drainage discharge through in earthen dams are the most important characteristics that have to be defined in order to analysis an earth dam. These parameters have been measured since beginning of building dam. In this investigation, a physical model of homogenous earth dam created in the flume with three different angles of toe drain, then pore pressure of earth dam was measured by piezometers that put on the wall of the flume. Discharge of drainage was measured too. The seepage analysis was conducted by plaxis software then Result of the plaxis compare with physical model by SAS (Statistic software) and finally the best angle and without dimension index, p/h, propose for toe drain according to results & observations.