The safety factor for slopes (FS) is traditionally determined using two-dimensional limit equilibrium (LEM) methods, however, the safety factor of a slope can also be calculated by FLAC Software with the technique of reducing soil shear strength in the time stages until the slope fails. In this presentation, we first describe the numerical methods of stability analysis, finite difference method and FLAC Software, and then we analyze the static stability using FLAC Software.

Observing authorized slope in the railway route makes the use of tunnel in mountainous areas inevitable. Tunnel No. 61 of the Northern railway has been constructed in the slope of Simindarah Mountains within the weathered rocks of the lower part of Qom formation consist of Sandstone, marl and shale with interlayer of gypsum, anhydride and salt in the length of 308 m and the portal width of 5m. The tunnel route is located on the north limb of a superimposed anticline cut by a strike-slip fault and is seismio-tectonically active. Considering the local landslides on the slope and the possibility of slide and security concerns on the slope where the tunnel is located are the subjects of the present study. In order to analyze the stability of the slope, a number of cross-sections were considered on the route of the tunnel and analyses were conducted on these sections. These sections were analyzed with CLARA Software (limit equilibrium method) and FLAC Software (numerical method). The sensitivity of the shear strength parameters on stability was also studied in detail. The geometry of the sections is approximately identical and from among the selected sections, the D-D section shows the critical status due to low shear strength. Considering the sensitivity analysis, if the shear strength parameters reach the limit where the slope may come close to sliding, the tunnel structure will be at serious risk in sections near the entrance and exit parts.      

Today, tunnels are one of the main vital arteries for a city, which are developing significantly. The development of today's societies has caused the need for tunnels in various sectors, including urban public transportation, intercity transportation, and water and sewage collection and transmission networks, etc. It goes without saying that for underground structures such as tunnels, the existence of faults and consequently earthquakes are serious threats among natural hazards. Although tunnels should not be located near active faults, sometimes passing through them is unavoidable. Sometimes, after the construction of the tunnel, the existence of the fault is known. In such cases, the deformation caused by the fault is considered a big concern and has a significant effect on the behavior of the tunnels. Meanwhile, due to the fact that most urban shallow tunnels are built in loose ground, the necessity of studying the behavior of tunnels and ensuring the safety of these structures against failure is of great importance. The advantage of numerical methods, in this research, the effect of different parameters such as the thickness of the piece, the depth of the tunnel placement and the fault angle on the behavior of piece tunnels has been investigated using FLAC 3D Software. The main goal of the research was to know the possible failure mechanism of segmental tunnels due to faulting. In this research, 24 numerical models were built to understand the behavior of segmental tunnels under the effect of reverse faulting. The validation of this numerical modeling is with the physical model of Kiani et al. The ways to improve the performance of segmental tunnels when faced with reverse fault movement is to increase the rigidity of the tunnel. In this research, the effect of the depth of the tunnel placement due to the reverse fault was also investigated. It was observed that increasing the depth of the tunnel placement when facing reverse faulting leads to a decrease in the deformation of the tunnel diameter. Also, the effect of changing the fault angle for the tunnel was investigated. Increasing the angle of the fault causes the change of places created on the ground surface and the displacement of the tunnel roof to decrease.

Seawalls are built for Protecting of beaches against waves and preventing the progression of water to the beach. For a proper understanding about these constructions, a suiTable information about applied loads on these constructions should be existed. One of the important load that applied on these constructions is sea wave. Others loads are included: weight force of the walls, weight force of the soil behind wall, weight force of the sea water on wall base and the forces applied on beach. Seawalls are built in different geometric shapes like vertical, Inclined and curvature walls (with variable slope). In this study, 4 geometric shape: vertical, Inclined, Convex and concave are simulated for analyzing the effect of geometry on stability of seawalls. So FLAC 3D Software are used. The results show that the minimum earth subsidence and horizontal displacement are obtained for convex wall and the maximum amount of these parameters for vertical wall.

High ground watertable is one of the main problems that can disrupt the tunnel construction. The prediction of groundwater infiltration into the tunnel is very important subject for preventing problems during drilling and designing drainage system. Therefore, it is necessary to consider the amount of water flow and drainage model in the design, thus, it is necessary to forecast quantity of water flow and the drainage model and consider them in design stage. For this purpose, to present a dewatering design in the eastern part of Tehran Metro tunnel Line 7, the cross-section of 4+ 500 + 4 +600 Kilometers, two drainage galleries with a length of 14 meters were used. Modeling and estimating the entering water into the tunnel requires detailed and accurate information about soil hydrodynamic properties. Also, the accuracy of modeling and numerical analysis and comparison with actual conditions for optimization of the design is very important. One of the best methods for evaluating these parameters in ground mass scale is back analysis according to experimental results. Ground water infiltration into two galleries was calculated for the whole length of the tunnel in steady state, using from finite element and finite difference methods in PLAXIS® and FLAC® Softwares. Then, from the data obtained from the Lefranc test, the value of the soil hydrodynamic parameters were estimated by the method of back analysis. The obtained results indicate the value of the method of return analysis compared to the Levfran method for measuring permeability with the same data. The measured value of groundwater infiltration in field tests was 600 cubic of meters per day and the error of the finite element and finite difference methods is equal to 12 and 4/8 percent, respectively, which are in a good agreement with the field measurements. The optimum value of permeability parameter obtained from back analysis equal to 4. 5  10-5 and 3. 6  10-5 meters per second was set for this area as well as optimum transmissivity equal to 117 and 214 meters per day.

In this study, the effect of near-field and far-field ground motions on the seismic response of the soil-pile system is investigated. The forward directivity effect, which includes a large velocity pulse at the beginning of the velocity time history of the ground motion is the most damaging phenomenon observed in near-field ground motions. To investigate the effect of near-field and far-field ground motions on the seismic response of a soil-pile system, a three-dimensional model consisting of the two-layer soil, liquefiable sand layer over dense sand, and the pile is utilized. Modeling is conducted in FLAC 3D Software. The P2P Sand constitutive model is selected for sandy soil. Three fault-normal near-field and three far-field ground motion records were applied to the model. The numerical results show that near-field velocity pulses have a considerable effect on the system behavior and sudden huge displacement demands were observed. Also, during the near-field ground motions, the exceeded pore water pressure coefficient (Ru) increases so that liquefaction occurs in the upper loose sand layer. Due to the pulse-like ground motions, a pulse-like relative displacement is created in response to the pile. Meanwhile the relative displacement response of the pile is entirely different due to the energy distribution during the far-field ground motions.

Summary: Tabriz metro twin tunnels in some stations are under ground water level. In addition to the loads from the weight of overburden, the load caused by pore water pressure is applied to them. To enter the current load into model certain boundary conditions must be considered that in this study, the probability of liquefaction and the impact of the earthquake on pore pressure loading structure have been investigated. Introduction: Geo-technical design of structures is encountered with a variety of different natural conditions (earthquake, liquefaction, etc.). This will be due to the complexity of behaviors and conditions. These structures during his lifetime, because dealing with different situations such as earthquake will not have fixed characteristics and behavior. Complex Mechanical behavior of the soil under statistical loads can be different and more complicated under dynamic loads. In this respect, the modeling of alternative behavior of saturated soil, especially in the interaction zone of soil – structure, has gained increasing research interest over past decades. Because the estimation of structure response in the soil liquefaction depends on pore water pressure, softening strain and decreasing of soil resistance. For correct investigating, linear dynamic analyze in effective stress is necessary. For this type of analyze couple or semi couple methods could be applied. In this regard Finn & Martin and Byrne could be regarded as semi couple models. Methodology and Approaches: From aforementioned semi couple models, Byrne model was chosen in this research. After calculation of related indexes, the model implemented in FLAC2D Software. The possibility of liquefaction take place in structure foundation was investigated by local tests results in effective stress method. For numerical modeling, the Bam earthquake acceleration was selected in DBE level among the existing acceleration and impact of earthquake dynamic load of on project structure pore pressure was investigated. Results and Conclusions: Using available data at the project structure the probability of liquefaction in the project region was investigated by cyclic stress method. It was estimated that with safety factor of 1.28 for Bam earthquake magnitude earthquake 6.5M, liquefaction will not occur. Nevertheless, due to exist of pore pressure at structure needed parameters was calculated in Byrne model to study simultaneous impact of dynamic loads and pore pressure to be used in numerical modeling. The results showed an increase in pore pressure due to dynamic loads caused by earthquakes so higher load values to the desired location (subway tunnel) is inserted and finally more effective maintenance system for the tunnel is estimated.

Gotvand dam is a rock fill dam located in Khoozestan province in Iran on Karun River. It will be constructed on weak mudstone and layers of sandstone. These layers are intermittent of medium strength with uniaxial compressive strength of 15 and 25MPa respectively. Some regional factors as continuous unloading, caused by river flood washed off and horizontal tectonic loading have created a local anticline in the base of the dam. It is estimated that such deformation will last over the time. Therefore, in order to determine creep parameters assessing the time dependent behavior of the foundation rock during the life of the dam through numerical and analytical methods is inevitable. In this research, by conducting creep tests under constant loads the strain- time graphs were produced for the two rock types. Applying the Burger rheological model for both rocks, their creep parameters were determined. In order to validate the produced data numerical modeling was conducted. A comparison between the results of numerical modeling and laboratory tests showed that the difference between the two methods is less than 6%. Also the time required for both rocks to enter the tertiary creep was determined to be 40 days for sandstone under 17.72MPa and 35 days for mudstone under 7.8MPa of load.

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.