Pile-driving is a common method of foundation construction where the soil is not strong enough to support the load of the structure through conventional shallow footing. This method is widely used in residential and industrial building, bridges, highways and etc. Along with the benefits of using this method, pile driving is also a source of negative environmental effects. Noise and air pollution are the most commonly expressed concerns, but, ground vibrations originating from the pile driving impact also have important adverse effects. They can cause disturbances to adjacent structures and also disrupt the operation of nearby sensitive equipment and facilities. Permanent settlement, densification and liquefaction may also occur in the soil due to such vibrations.A common factor for evaluating the amount of vibrations is peak particle velocity (PPV), which is maximum velocity that soil particles reach during the pile driving process. PPV is the maximum velocity that a soil particle experiences during the driving of a pile from the ground surface to the desired depth. Ground motion due to pile driving generally depends on (1) the source parameters (method of driving, energy released, and pile depth), (2) the interaction between the driving machine, the pile and the soil, and (3) the propagation of waves through the soil.In this article, a two-dimensional finite element model is validated using a case study of pile-driving data conducted in the Chennai site in India. Then, by modeling a pile in sandy soil with different soil relative densities, Poisson ratio, moduli of elasticity, Unit weight, friction angle and damping ratio, the effects of these parameters on vibrations of the ground surface, and peak particle velocity on the surface, were studied. The results showed that the increase in friction angle and Poisson ratio in-creases the PPV. However, increase in the modulus of elasticity, damping ratio and soil unit weight, decreases the PPV. Also, scrutiny of PPV occurrence time shows that by variation of the in uencing parameters, except the modulus of elasticity, this time is almost constant.

Nowadays urban transportation is one of the most important problem in the large cities. The best way to reduce this problem is to use the underground tunnels. The excavation of tunnel and other underground structures lead to remove a part of insitu rock and soil masses and the considerable changes in stress conditions around them and surface settlement has been occurred, consequently. Therefore, estimation of surface settlement due to the tunnel excavation, especially in urban areas, is of great importance. The Niayesh subway tunnel was built in the northern part of Tehran and it includes north and south tunnels. From a geological point of view, the Niayesh highway tunnels are mostly placed in the Hezar Dareh Formation (A) and also some parts especially the eastern and middle parts of north tunnel are placed in Kahrizak Formation (Bn). The tunnels have been excavated by the New Austrian Tunnelling Method (NATM). In this method, primary shotcrete applied as a short-term support and the final lining is used to satisfy final support. In this paper, surface settlement has been studied by empirical methods, numerical analysis and real settlements. For the empirical and numerical methods, O’Reilly and New (1982) method and finite element method by PLAXIS2D software have been used, respectively. The five sections (CS-1 to CS-5) have been selected in order to study the surface settlement during Niayesh tunnel excavation. On the basis of the achieved results, the numerical method in all sections (except section 3) is in agreement with the real settlements. However, empirical methods have estimated the settlements more than real settlements in these sections. Also, the achieved results from real settlements, empirical methods and numerical analysis show that the maximum settlement due to tunnel excavation is more than allowable settlement and it places in the warning range.

A large portion of Iran railway routes are located in sandy desert areas. Therefore, paying attention to soil stabilization methods seems essential. In present study, in parallel to introducing the deep soil mixing as an efficient and economic method of soil improvement, in the frame work of a practical example, assuming loose sandy soil parameters, feasibility of the method application is investigated. For this purpose, by conducting the plate loading test (PLT) and direct shear test (DST) on the railway embankment and sandy subgrade materials, their shear strength as well as deformability parameters ware achieved. Further, by developing a two dimensional FE model using Plaxis code, the railway embankment stability on loose sandy subgrade is evaluated by using the C-F reduction method. The analysis is conducted for two separate cases of subgrade with and without soil-cement columns. The numerical results for embankment with 1.5 m height shows that for the loose sandy subgrade the embankment failure load limits to 447 kN corresponding to a safety factor of 1 while by using the soil-cement columns with diameter of 0.9 m to 1.2 m the failure load varies from 741 to 1274 KN and the safety factor varies from 1.26 To 1.66. Moreover, the total embankment settlement deceased up to 25% in the best arrangement of the columns.

With the growing population and density in metropolitan areas, higher tendency to live in high-rise buildings, and increasing demand for parking lots, it seems necessary to excavate soil to construct underground spaces. During excavation work, as the height of the wall increases, special care should be taken to the wall stabilization to avoid any consequent damage including extensive property damage or loss of life. Different methods such as performing steel or concrete pile, sheet piling, reciprocal anchorage, diaphragm wall, soil nailing, and soil anchorage can be utilized to stabilize excavation wall. As all of these methods have their own advantages and disadvantages, it is important to know the limitations and differences of each method. Besides providing more work space in the wall, using novel methods of stabilization may lead to considerable savings in cost and time. By examining the behavior of retaining structure and also predicting the value of wall displacement, resulting from existing loads such as adjacent structures of the wall, service loads, and vehicle live load, a big step can be taken to prevent any probable damage. Currently, due to the development of high speed digital computers, finite element method (FEM) can be applied to predict the behavior of retaining structure. In this paper, as a case study, the behavior of retaining structure of excavation wall of Narges Razavi 2 International Hotel, Mashhad, stabilized using steel pile and soil anchorage, has been investigated. For this purpose, the results obtained from finite difference software, FLAC2D, and finite element software, PLAXIS2D, have been compared with those obtained from the monitoring of excavation wall. It was found that there is a good consistency between the results.

In recent years, with the growing use of the nailing method for stabilizing excavation walls, there has been a need for a comprehensive investigation of the behavior of this method. In the previous studies, the behavior of nailed walls has been investigated in static and dynamic states and under different conditions. However, due to the different feature of near-field ground motions, it is necessary to study the effect of these motions on the behavior of the nailed walls. Near-fault ground motion is significantly affected by the earthquake record direction and the rupture mechanism. So, in this study, to compare the effects of near-field and far-field ground motions, a two-dimensional (2D) soil-nailed wall was considered. PLAXIS 2D was used for the modeling of the soil-nailed wall system. An excavation with a dimension of 10 meters in height was taken into the account. In this study, 10 records (Five fault-normal near-field ground motion records and five far-field ground motion records), were recorded on the rock and applied to the model. These ground motion records were derived from the near-fault ground motion record set used by Baker. These records were scaled to the Peak Ground Acceleration (PGA) of 0. 35g and then applied to the bottom of the finite element models. Mohr-Coulomb model was then used to describe the soil behavior, and Elasto-plastic model was employed for the nails. A damping ratio of 0. 05 was considered at the fundamental periods of the soil layer. The results showed that the generated values of bending moment, shear force and axial force in nails under the effect of the near-fault ground motions were more than those in the far-ault ground motions. These values were almost equal to 23% for the maximum bending moment, 30% for the shear force, and 22% for the axial force. The created displacement under the effect of near-fault ground motions was more than that in the far-fault since a higher energy was applied to the model in the nearfield ground motions during a short time (pulse-like ground motions). In contrast, in the far-fault ground motions, due to the more uniform distribution of energy during the record, such pulselike displacements were not observed in the system response. Increasing in nail length and soil densification, decreases the displacement of the soil-nailed wall but does not change the general behavior of the soil under the effect of near-field ground motions. Based on the obtained results, for a constant PGA, there were positive correlations between the values of the maximum displacement on the top of the wall and the PGV values of near-fault ground motion records. However, the mentioned correlations were not observed in the case of far-fault ground motions.

Summary Urban subways in the ground would change its seismic movements. Designing ground surface structure in far filed is related to the horizontal component of acceleration at the ground surface in that area. Therefore, an attempt has been made in this study to change the frequency of soil-tunnel systems and to calculate the maximum horizontal acceleration of the ground surface due to tunnel presence through changing in tunnel placement depth, its diameter and its lining thickness as well as changing the soil properties. The maximum horizontal acceleration of the ground surface has been calculated in the presence of the tunnel for soil type 4 based on code 2800. The relationship between the maximum horizontal acceleration of the ground surface and the frequency of the soil-tunnel systems will result in the production of a horizontal acceleration spectrum. In the frequency range studied, spectral accelerations in models without a tunnel have mainly higher values compared to those models that have a tunnel buried in the soil. Amplification and deamplification of the ground surface acceleration is dependent on the period of soil-tunnel systems, the properties of the model under study and the position of the point studied at the ground surface. Introduction 9 acceleration records of known influential earthquakes, 33 models (in presence of tunnel) and 7 models (in absence of tunnel) have been used in this study. Overall, about 360 nonlinear dynamic analyses have been carried out. These analyses have been made for multilayered soil while the nonlinear effects of the soil and its interaction with the surrounding structures have been considered. Methodology and Approaches This study has been conducted on a Delhi subway tunnel. ANSYS and PLAXIS2D software packages have been used for the study. The ANSYS software has been used for modal analysis, obtaining the frequencies and mode shape of the soil-tunnel systems, while the PLAXIS2D software has been used to analyze the time history and obtaining the acceleration values of key points of the model. Elasto-plastic Moher-Coulomb model has also been used to model the soil. Results and Conclusions In most cases (11 out of 14 cases), amplification of ground acceleration is observed at a depth of 20 m. 9 of the 14 ground acceleration amplification are related to a tunnel with a smaller radius (3. 13 m). Whatever the tunnel center image is taken away from the ground surface, we will have higher number of points in which acceleration amplification of the ground surface occurs.

Land subsidence is defined as equal to the vertical displacement of the ground over a specified time.  Declining water table elevation is one of the main causes of subsidence that can cause irreparable damage to surface and subsurface structures, especially in urban areas. In this research, the magnitude of subsidence due to water withdrawal from the pumping well has been estimated, and the factors affecting it have been determined. For this purpose, by collecting data from two water wells located in Kashan city, the subsidence analysis was performed based on the finite element numerical method using PLAXIS2D software. The results show that the water pumping during one year causes a decrease in the water table elevation and, as a result, the land subsidence by a few centimeters, but under a constant flow rate of water withdrawal from the well, the magnitude of subsidence in the studied wells is heterogeneous. Also, increasing the water withdrawal flow rate from wells up to 700 m3/day and the depth of wells up to 500 meters has increased subsidence, but after that, the amount of subsidence remains constant. Therefore, it can be concluded that the flow rate and depth of water withdrawal from the well are effective on the land subsidence and must be managed.

One of the major problems in highway and railway bridges is the settlement of the bridge abutments, which its reduction has always been set as the research target. Two methods which have been widely used for controlling the settlement are either reinforcing the abutment subsoil with geogrid orconstructing the abutments on piles. This paper describes the application of a two-dimensional finite element method (FEM) by using PLAXIS2D V8. 5 for comparing the performance of these two methods. The effect of the geogrid normal stiffness, length and depth of reinforcement on the horizontal and vertical displacement of abutment is also investigated. Data from an instrumented bridge abutment has been used for the model verification. The reduction of the bridge abutment, the vertical settlement and the horizontal displacement by pile and geogrid have been analysed and compared. It is found that constructing the abutment on piles has a better performance in reducing the vertical settlement of the bridge abutment. However, lower lateral displacement can be obtained by using a geogrid with a higher normal stiffness. It is also found that, while the vertical settlement is not affected by the geogrid stiffness, the horizontal displacement of the abutment decreases with increasing the stiffness.