نشریه مهندسی تونل و فضاهای زیرزمینی
سال دوم شماره 2 (زمستان 1392)

A major concern of tunnels construction is accurate prediction of ground displacement، which distort and، in severe cases، damage surface structures. Empirical Peck’s method is used commonly in many tunneling projects to predict surface settlements. Reasonable prediction by this method requires an appropriate estimation of trough width (i). This parameter can be obtained from previous case histories with similar ground conditions and excavations. A part of Shiraz subway system is constructed by twin tunnels using EPB machine. Due to the lack of relevant case histories، numerical simulations are used to predict i for the Shiraz tunnels. The longitudinal and transverse surface settlements obtained by numerical analyses are compared with empirical method. Consequently، the maximum settlement and i are predicted for a part Shiraz subway tunnels. The development of settlement profiles obtained by numerical modeling is also investigated in order to achieve the steady state condition behind the tunnel face. Methodology and Approaches: The numerical simulations are performed using PLAXIS 3D Tunnel. The tunnel construction process was done by systematic approach، in 35 phases. The empirical method suggested by Peck used to predict the transverse settlement trough. The longitudinal and transverse settlements predicted by numerical modeling are obtained during the excavation of tunnel. The development of surface settlements is studied to establish the steady state condition. The initial estimation of i is obtained by the current empirical equations. To achieve the appropriate trough width، the initial i is modified by comparison of settlement troughs obtained by empirical and numerical approaches. Results and The numerical results showed that the surface settlement directly above the tunnel face is around 45% of the maximum. Small surface settlement was induced after installation of the tunnel lining. The development of surface settlement profiles indicated that the steady state condition is reached at three times of tunnel diameter beyond the tunnel face. Comparison of the transverse surface settlement troughs indicated that trough width parameter is 1. 8 times the tunnel diameter. The current value can be used for prediction of surface settlement trough induced by tunneling in the similar ground and excavation conditions as Shiraz subway tunnels.

In this paper، a new method is presented to find tunnel target racking displacement in the earthquake considering nonlinear behavior of lining and soil and also soil- structure interaction. In the next step tunnel racking reduction factor has been evaluated for an incomplete ellipse tunnel located in two soil types، A and B، with overburden depth of 5 and 20 m by performing nonlinear static analysis. Finally، to verify the values of racking reduction factors، tunnel responses obtained by linear static analyses reduced by the calculated values of racking reduction factor are compared with responses obtained by nonlinear dynamic analyses. Design and analysis of the underground structures such as tunnels are performed on the basis of structure and ground deformations because the seismic response of such structures is very sensitive to the imposed ground deformations. In recent years، Several researches have indicated the importance of the harmful effects of earthquakes on tunnels and underground structures. Methodology and Approaches: In this paper، by combining Wang (1993) and Hashash (2000) methods in determination of tunnel target racking displacement and using the trial and error method to correct tunnel structure stiffness، possibility of redistribution of the forces and deformations became possible and it was tried to present a comprehensive method to determine the tunnel target racking displacement. In the next step، by using the force-racking displacement curve and applying the existing equations of reduction factors of the structures and their generalization for tunnels and underground structures and considering the soil-structure interaction، tunnel racking reduction factor is estimated. Then، using ABAQUS software، a comparison has been performed between dynamic and static forces in the tunnel lining. Results and Comparison of lining force (bending moment and axial force) between linear static analyses modified by tunnel racking reduction factors and nonlinear time history analyses shows that the accuracy of achieved tunnel racking reduction factors is acceptable. The studies also show that implementing linear static analyses without tunnel racking reduction factor leads to very conservative results of lining force in tunnel. Nonlinear time history dynamic analyses are time consuming and complicated in modeling procedure and analysis duration. Thus، By using the proposed racking reduction factors، Linear static analyses could be an alternative for nonlinear dynamic analyses with a suitable accuracy.

Development of subway systems is considered as an essential need in urban areas. Each line of a subway contains tunnels، stations and mid tunnel ventilation shafts. Concrete Arc Pre-Supporting System (CAPS) and Sequential Excavation، are known as standard methods for the construction of underground stations. When the process is underway، it is necessary to protect surface and underground structures from Subsidence hazards. In this paper، stability analysis and settlement evaluation of Haft-e-Tir Station of Tehran metro line no. 6 has been considered. Geotechnical investigations showed that the main layer has been formed of a very dens soil. Concrete Arc Pre-Supporting system (CAPS) is an executive construction method. In addition to tunnel stability، reduction of surface displacement can be obtained by CAPS. Numerical simulation has been deemed as a special procedure for evaluation and analysis of settlements. The optimal spacing for concrete arch is an important parameter for the success of the method that usually be determined by 3D modeling. However، 2D modeling methods can be faster to reach a optimal result. Methodology and Approaches: The optimal spacing for concrete arch of Haft-e-Tir Station was determined with Sakurai''s critical strain approach and allowable bylaws stresses. The surface subsidence was estimated by two methods namely analytical-empirical and numerical modeling. The numerical method of finite difference techniques (FLAC2D software) was used in this research. Analytical Bobet relations used for calculating of maximum subsidence. Maximum slope of subsidence curve is calculated by Peck empirical relations. Kramer criterion is used to control the maximum slope of the subsidence curve in both methods. Results and It is demonstrated that the optimal spacing for concrete arch for Rectifier tunnel، South tunnel، and sections I and II of North tunnel are 3، 2. 5، 3، and 3. 5 meters respectively.

Considering upward trend of traffic congestion in mega cities، construction of urban tunnels (road or metro) is inevitable. The reciprocal effect of tunneling-induced ground settlement and surface buildings is an important factor during shallow tunneling design procedures in urban areas. Hence، the effective factors in this reciprocal relationship need to be appraised prior to the construction phase. In this paper، the major characteristics of buildings were numerically simulated using 3D finite element approach. It has been demonstrated that weight and length of buildings have showed parallel correlation with surface settlements. However، building width have had reverse trend with surface settlements. The main purpose of this research is the study of influence of building weight and geometry on the surface settlement due to sequential excavation method، and interaction between buildings and tunnel. It investigated by simulating of systematic construction process of tunnel using numerical method. Methodology and Approaches: In this paper، the major characteristics of buildings were numerically simulated using 3D finite element method. In addition، results of a study on field data of the Nyayesh tunnel are presented. Results and The results have proved that the existence of surface buildings has reciprocal effects on ground settlement troughs. The increase of the building weight will result in increase of surface settlements. On the contrary، by ignoring building weight، presence of surface building foundations will cause a less settlement compared to the green field condition which is due to increase of the rigidity of building foundation and thereby ground improvement. The increase of building width reduces the surface settlements، and the increase of the building length leads to more surface settlement، although the building width is a more effective parameter، which controls the overall tunneling-building interaction behavior than building length. Thus، building weight and geometry effectively influences the surface settlements troughs in urban tunneling.

In recent years، tunneling with the Earth Pressure Balance (EPB) shield has been applied in urban areas in different soils types. The most common technology in the mechanized tunneling is using the EPB machine. Soil conditioning operation can be carried out through the screw conveyor. Knowing different soil conditioning agents and their affects in different soils types is quite important in selection of the most appropriate foam-polymer to be used. Selecting the most appropriate soil conditioning set needs different precise studies so that the properties of the conditioned soil can be determined and the measurable data can be specified. Selection an appropriate strategy (for soil conditioning during boring) highlights the importance of the ground risks involved so that conclusive decisions can be made regarding the type of the physical behavior of the foam and other additives. Methodology and Approaches: The soil layers in this project were divided into 6 units (ET-1 to ET-6). In this study، It was revealed that every unit needed specific additives depending on its geological and geotechnical specifications and the soil conditioning parameters for every unit would be different. The optimum amount of conditioning agents and types of additives to be used in the tunnel route (considering the geological risks that needed conditioning، and the presence and expanse of different soil units) were studied in 3 separate stages based on the guiding tables، standards، and laboratory and field tests. Results and For soil conditioning، used material was made of 3 different foam types (A، B and C: A & B for ordinary soils with medium stability and C for adhesion and impermeable soils with high stability) for respectively 60% and 30% of the tunnel route. The FIR change amplitude in the project has been estimated to be 20% to 80%; maximum consumption has been in the interval of 20% to 40% and FER has been equal to 4 to 7.

Water flow in tunnel projects is one of the main issues that can affect the plan and tunneling activity. Therefore، it is necessary to predict the location and the amount of water flowing into the tunnel. The experience has shown that the accurate prediction of water flow in excavated tunnels due to the lack of consideration all influencing factors، especially the properties and condition of discontinuity is not possible. In this paper، In order to investigate the effect of discontinuities properties on the rate of water flow، the cross section of Koohrang 3 (1+897 - 1+950) with the UDEC software has been modeled. By variation of the properties of discontinuity، the flow rate into the tunnel has been assessed. Results of this study have shown that the variation of the properties of discontinuity has significant influence on the steady state flow of water. Among these properties، the aperture of joint has the most significant effect on flow rate in the tunnel. Analysis of water flow is necessary for construction of underground structures. In this analysis، the possibility of any kind of change in the ground water behavior and flow rate should be considered. In this paper by using numerical model، the effect of discontinuity properties on the water flow rate were studied. Methodology and Approaches: The discontinuity properties have great influence on the water flow rate into tunnels. In order to investigate the effect of discontinuities characteristics on the flow rate of water، the cross section of Koohrang 3 with the UDEC software has been modeled. By variation of the properties of discontinuity، the rate of flow to the tunnel has been assessed. Finally، The water flow rate calculated by numerical modeling were compared with the values obtained from the analytical methods. Results and Results of this study have shown that the increase of the joint spacing reduced the rate of water flow into the tunnel due to the increase of formed blocks’ size. In addition، increase of the joint aperture has substantially increased the amount of water flow to the tunnel. Moreover، by increasing the joint orientation from 30 to 120 degree، the maximum water flow occurred at an angle between 50 and 70 degree. According to results of the investigation among the discontinuities properties، the joint aperture had the greatest effect on the flow rate of water to the tunnel.