نشریه مهندسی تونل و فضاهای زیرزمینی
سال هفتم شماره 2 (زمستان 1397)

Summary Simulating a rock fracture distribution is an important issue, which is common in various fields of geosciences. This issue is of particular importance in determination of hydraulic conductivity of rock mass and forecasting the amount of water entering the underground spaces. Theoretical studies has been demonstrated that the result of three-dimensional (3D) modeling discrete fracture network is closer to reality than other models. One of the limitations of the statistical methods for modeling fracture network is the lack of spatial behavior considerations of modeling fracture network parameters. In other words, based on Monte Carlo algorithm in statistical methods, generation of fracture network parameters are based on probability distribution functions, and are carried out randomly. In this study, a computational GFracIUT code is developed. In order to generate the 3D discrete fracture network and considering geometrical parameters of the fractures surveyed from the outcrops and boreholes, probability density functions are developed using geostatistical methods. In the mentioned code, initially the density of micro-fractures are conjectured using sequential Gaussian simulation. Then, the locations of the centres of the micro-fractures are determined by Poisson’s process. When the center locations of the micro-fractures are determined orientation components estimated using geostatistical approaches. The developed program is capable of modeling fractures with various geometrical shapes according to operator’s desired specifications. As examples in this regard, disc and quadrilateral shapes have been considered in this paper. In order to practically apply the program, an area in Gachsaran oil field has been considered as a case study.   Introduction Fracture is one of the main characteristics of the rock mass. Fracture network modeling by statistical method has some limitations. One of the limitations of the statistical methods for modeling fracture network is the lack of spatial behavior considerations of modeling fracture network parameters. Geostatistical methods can be employed to spatially characterize fracture network.   Methodology and Approaches First, using the GFracIUT code, we obtain the fracture density map by employing sequential Gaussian simulation method. Then, the location of the centre of each micro-fracture by Poisson’s process is determined using the software. Finally, the micro-fractures orientation component is estimated by geostatistical methods.   Results and Conclusions In this study, a computational GFracIUT code is developed. The GFracIUT code is composed of two steps: positioning the centers of fractures using the fractures density data by sequential Gaussian simulation, and assigning the directions (strikes and dips) of the fractures. In order to practically apply the software, an area in Gachsaran oil field has been considered as a case study.

Summary Several newly constructed tunnels, which have been damaged by earthquake loading, have led to extensive research on the evaluation of earthquake effects on tunnels. Underground structures are increasingly being built and exploited in the context of urban expansion and development. Tunnels are one of the most important underground structures. Failure of several tunnels under earthquake loading, and especially damage to these tunnels, have been the reasons to investigate the effects of earthquake on the tunnels.   Introduction Various activities, especially during earthquake, on the adjacent structures are of particular importance. This importance will be more in the vicinity of the historical building, due to their vast material and spiritual values. In this research, using the Henkel type I and three scale accelerometers related to the earthquakes in Northridge, Tabas and Kobe, and employing the expanded FESCAM program in MATLAB environment, the historical structures of thirty-three buildings have been studied.   Methodology and Approaches In this research, nonlinear time histories analysis has been used to generalize Henkel's relationship and to calculate the exact difference. The input waves have been investigated by the researchers for use in the Henkel harmonic waves function. The Henkel function of the first type using the mentioned accelerations is used considering the amount of dissociation, the degree of strain and stress around the twin tunnels as an additive parameter to the limited element analysis of the present study.   Results and Conclusions In this paper, the operation of differentiation is expanded with the use of mathematical relations. A case study of twin tunnels is Si-o-se-pol twin tunnels. The results of this study show that the mean displacement of horizontal thirty three bridges there in comparison with the failure to consider the effect of fractionation is increased by 28.8% and the displacement rate of the thirty three bridges compared to the failure includes the difference of 11 / 30%. Moreover, the displacement of underground structures during an earthquake is less than that of the ground structures. The results of the Mann-Whitney test with the SPSS software program have shown that there is no significant difference between the seismic performance of the thirty three bridges with the effect of tunneling dispersion and without the effect of tunneling dissociation (P-value≥0.05).

Summary Study on buried tunnels that are vital arteries in each country, has always been faced with many difficulties due to the implementation of these structures in the complex soil environment. On the other hand, due to increasing security threats in recent years, evaluating the behavior of these structures against blast loads has been felt more than ever. Therefore, in this study, effects of surface explosion on a buried tunnel has been investigated using nonlinear dynamic analysis in ANSYS-AUTODYN software. The effect of the blast wave propagation in soil is simulated with a full geometry in a Three-dimensional (3D) environment and after ensuring the accuracy of the results, the effects of the burial depth of tunnel protective slab and its dimensions in reducing the destructive effects of the explosion is evaluated in a Two-dimensional (2D) environment. The results indicate that better protection of the tunnel will be achieved if the slab is closer to the tunnel structure. Increasing the thickness of the slab always reduces the effects of the explosion on the tunnel but the change in the length of slabs cannot be a good indicator for prediction of the blast loads effects on the buried tunnel.   Introduction As enemy weapons are in progress in kind and power, our purpose in this research is to find some methods for making tunnels more safe facing blast loads. Security slabs are the tools that we use to guard the structures of tunnels facing blast loads. Here, we study physics of this security slabs as well as their geometries and distances from the tunnels. Evaluation of other effective parameters of a slab such as the kind of materials and its cross-section seems to be acceptable for future studies of guard slabs of tunnels.   Methodology and Approaches In this study, we simulate a complete condition of a surface blast, tunnel and its security slab, soil and air environment. An Eulerian algorithm and dynamic nonlinear analysis are used in the ANSYS-AUTODYN software to simulate the effects of blast loads on tunnel section. In this study, a 3D model is used for blast load propagation in soil while a 2D model is used when we have axial symmetry.   Results and Conclusions The results of this study show that pressures and effective strain on tunnels will increase by increasing the distances of slabs from tunnel structures, and when a security slab is placed closer to a tunnel liner, it will be more effective than when it is closer to the ground surface. The results also indicate that increscent of the length of the slab is not necessary to be more than a specified length. In addition, increscent of the thickness of the slab is always effective in reduction of destructive blast loads on the tunnel sections.

Summary In recent years, mountain tunneling method such as SEM/NATM has been used for tunnel construction even in urban areas because of its cost effectiveness. When this method is used in urban areas compared to mountainous areas, it is important to impose some constrained conditions, such as restrictions of surface settlement and ground water drawn down, because of existing constructions such as buildings, pile foundations and underground pipes around the tunnel face. It is said that the increase of the use of mountain tunneling method in the urban areas is due to the development of auxiliary methods such as face bolting and forepoling. Because of plain-strain condition in tunnel excavation along the tunnel axis direction, some two-dimensional (2D) models have been applied to evaluate the ground surface settlement generated by different phases of excavation. The deformation modes of tunneling face are different. The excavation face deformation is a three-dimensional (3D) problem. It would be more complicated considering forepoling implementation and face injection effects on deformations. The longitudinal displacement profile of the tunnel crown has been generated by 3D models and the typical proposed stress release relations in this research work have beem compared and evaluated.   Introduction A method for reducing-induced ground movements in open-faced tunneling is to use tunnel support methods such as  forepoling umbrella system. Forepoles are often used for supporting the ground ahead of the tunnel face during excavation. They also provide temporary support to unlined portion of tunnels. Forepoles are usually installed along the tunnel periphery in the longitudinal direction to form a supportive arch ahead of the tunnel face. This paper investigates the effect of forepoles on the stability of the tunnel face and ground surface settlement during a tunnel excavation in Tehran alluvium.   Methodology and Approaches This study was conducted based on 2D and 3D numerical models of Zarbalizadeh-Maddah underpass tunnel for controlling the face stability and deformation of the surrounding ground using PLAXIS finite element software.   Results and Conclusions The results of the 2D numerical modeling carried out in this research work represent the stable conditions of the tunnel due to the acceptable capacity of the support systems (primary and temporary) designed in different sections of the tunnel (e.g. side walls, middle walls, and invert) against different combinational loads. In spite of the stable condition of the tunnel, the surface subsidence obtained from the 2D numerical modeling (43 mm) represents a relatively high value of deformation of the ground surface compared to the instrumentation data (30 mm) recorded during the tunnel excavation. In order to more accurately investigate the effect of forepoling on the control of the surface subsidence, 3D modeling of the excavation stages was performed considering the longitudinal deformation profile (LDP) of the tunnel face. The results indicate a lower value of surface subsidence (32 mm) compared to the 2D modeling (43 mm). The 3D modeling results are also in very good agreement with the instrumentation data of the surface subsidence (30 mm).

Summary Implementation of infrastructure projects in a country is one of the key issues in the country economic growth. However, increasing the claim in the projects is inversely related to the objectives of the project due to the lack of understanding of the factors that create it and the impact of its factors on each other, especially in underground projects that we involve with many unknowns. In this research, for identifying the claim paths in DBF Tehran metro projects, after the library studies and review documents, we determined the main factors of the claim. Then, the effect of the causation factors on each other was analyzed using the system dynamics method, and finally, the most important paths that led to cost increases were identified as a result of development of the system dynamics model.   Introduction Claims affect the performance of projects as recently seen in DBF metro projects. Researches have been made to reduce claims, but they are still prevalent. The reason is the need for a better understanding of claims in the projects. Once this understanding has been made, strategies can be put in place to prevent the claims. The system dynamics method as a complete tool for studying the behavior of complex systems can solve this need. Therefore, this approach in this research has been used to identify the claims of the contractor and financier consortium in DBF metro projects.   Methodology and Approaches Using library studies and semi-structured interviews with experts, as well as examination of documents related to actual claims of DBF metro projects in Tehran, 30 causes of claims were identified, and then, a questionnaire was used to identify and rank the most important causes of claim. Then, by re-interviewing with the experts and re-examining the data and documents, the causes of claim were re-analyzed using the systems dynamic method, and the causal model was developed. Then, 20 paths of claims were extracted from the model and a questionnaire was used to identify and rank the most important claims paths leading to increased costs in DBF metro projects.   Results and Conclusions The results of this research show that the significance of each claim is in relation to other claims. The causal relationship between the claims and the claim paths shows the role and importance of each claim. One of the most important paths is the mistake in delivering data to the contractor and claiming unpredictable physical conditions specific to underground projects.

Summary Urmia tunnel is being constructed to convey water to the Naghadeh and Urmia agricultural plains. About 1800 m of excavations are located in the alluvial ground. In this paper, a part of Urmia tunnel that is located in the alluvial ground was modeled using the numerical modeling FLAC3D and PLAXIS3D TUNNEL software packages. For this, first, the new Austrian tunneling method (NATM) was modeled. The NATM modeling results showed high displacement and instability of the face of the tunnel. Then, the earth pressure balance (EPB) machine was modeled and the face pressure was calculated. The modeling results showed suitable conformation between the two software packages. Moreover, a short-length part of the tunnel was excavated in the alluvial structure using the NATM, however, according to the modeling results, the face of the tunnel was unstable, and thus, the excavation was stopped. The face pressure, in the tunnel boring machine(TBM) was also calculated.   Introduction Urmia tunnel is a challenging project because of its especial ground and excavation conditions. The main focus of this research is on tunneling in hard conditions like high groundwater level, high depth of tunnel, too much overburden, etc. An example of tunneling in hard conditions is the Urmia tunnel that is studied in this paper. The main objective of this paper is to select a suitable method of excavation in the tunnel.   Methodology and Approaches In this study, the NATM and its combination with soil improvement methods, and also, the EPB machine were modeled using the numerical modeling FLAC3D and PLAXIS 3D TUNNEL software packages. A short-length part of the tunnel, which was excavated in the alluvial ground using the NATM, was considered in this study.   Results and Conclusions The obtained modeling results in this study showed high displacement of both face and crown and instability of the face in the NATM modeling and combination of the NATM and soil improvement methods like jet-grouting and forepoling. Thus, the EPB machine was modeled and the face pressure was calculated.