Tunnel Span Research Articles

Stimulated Detached Eddy Simulation of three-dimensional shock/boundary layer interaction

The shock/boundary layer interaction experiment performed at IUSTI (Institut Universitaire des Systemes Thermiques Industriels, Universite de Provence) has been computed using the Stimulated Detached Eddy Simulation approach. This computation accounts for the whole wind tunnel span. It suggests that corner separations induced by the presence of lateral walls reduce the effective section of the wind tunnel and strengthen the interaction, making periodic computations irrelevant for strongly separated situations (shock deviation of 9.5 degrees). Furthermore, this computation evidences that the strongest wall pressure fluctuations are found in corner flows. The latter are subjected to low frequency movements which contribute to 30% of the total fluctuations. Nevertheless, it was not possible to connect statistically these movements to the ones of the main separation.

Methodology to quantify rock behavior around shallow tunnels by Analytic Hierarchy Process and Fuzzy Delphi Method

ABSTRACT For the quantitative identification of rock behavior in shallow tunnels, we recommend using the rock behavior index (RBI) by combining the analytic hierarchy process (AHP) and the fuzzy Delphi method (FDM). AHP can aid engineers in effectively determining complex and un-structured rock behavior utilizing a structured pair-wise comparison matrix. FDM can assist them to overcome the uncertainty in the expert judgment. Rock behavior types are categorized as rock fall, cave-in, and plastic deformation. Seven parameters influencing rock behavior are determined: uniaxial compressive strength (UCS), rock quality designation (RQD), joint surface condition, stress, ground water, earthquake, and tunnel span. They are classified into rock mass intrinsic, rock mass extrinsic, and design parameters. An advantage of this procedure is its ability to obtain each parameter's weighting. We applied the proposed method to the basic design of Seoul Metro Line 9 and quantified the rock behavior into RBI on rock fall, cave-in, and plastic deformation. The study results demonstrate that AHP can give engineers quantitative information on rock behavior.

Methodology to quantify rock behavior around shallow tunnels by Rock Engineering Systems

ABSTRACT For quantitative identification of rock behavior in shallow tunnels, we recommend using the rock behavior index (RBI) within the Rock Engineering Systems (RES) approach. RES can aid engineers in effectively determining complex and un-structured rock behavior utilizing interaction matrices. Rock behavior types can be classified into three groups: cave-in, rock fall and plastic deformation. Seven parameters influence rock behavior: rock mass compressive strength, rock quality designation (RQD), joint surface condition, stress, ground water, earthquake, and tunnel span. An advantage of RES is its ability to obtain each parameter's weighting. We quantified the rock behavior into RBI on fall, cave-in, and plastic deformation. The study results demonstrate that RES can give engineers quantitative information on rock behavior. The proposed model is illustrated via a case study on Seoul Metro Line 9.

Experiences of tunnelling in fragile himalayan rocks

The total hydro-electric potential of India is 84,044MW at 60 per cent load factor, out of which 65,623MW lies in the Himalayan ranges. The Himalayan region is characterized by high ridges, deep gorges, vulnerable hill slopes, complex geological and tectonic features. The complexity of the Himalayan range is attributed to superimposition and modification of the earlier tectonic phases by the last Himalayan tectonic phase. The poly-phase deformations in Himalaya has resulted in the development of numerous tectonic dislocations and structural discontinuities such as faults, thrusts, shears, joints, etc. which have a direct influence on the geomechanical properties of the rock masses at different project sites in the Himalayan region. Therefore, no two sites are exactly similar in their geological and tectonic settings. It has been experienced that tunnelling through weak, jointed, faulted and sheared rock masses in the Himalayan range is a challenging task. It becomes more challenging in the absence of detailed investigations because of high overburden, thickly vegetated surface and inaccessible terrain. Geological surprises, therefore, during tunnelling result in various tunnelling problems and failures—such as squeezing, chimney formation, face collapse, water inrush, etc. Many times the original tunnel alignment has been changed during construction because of face collapse. The experience of the TBM in the Dulhasti project tunnel of the Himalaya is also not very encouraging where, because of inadequate geological information ahead of the tunnel face and water ingress, the tunnel boring has been suspended many times. As a result, the desired progress could not be achieved. All such experiences have resulted in time and cost over-runs. The problems and the failures may be regarded as challenges and opportunities for generating a new knowledge base and thereby increasing the reliability of tunnelling methods. Information from geo-mechanical and instrumentation studies at various hydroelectric project tunnels has helped in generating information on rock mass behaviour and management of tunnelling problems. For example, the lesson obtained from the effect of tunnel size on squeezing ground conditions in tunnels at two projects has helped in developing a criterion for estimating the ground condition. In Fig. 1, the rock mass number N is defined as Barton’s Q with SRF = 1, H is the tunnel depth in metres and B is the tunnel span or diameter in metres. The tunnelling problems encountered in two Himalayan projects, along with the possible solutions of such problems, are presented in the paper. The steps to be taken to avoid such problems in future tunnelling projects in the highly varying and fragile rock masses such as in the Himalaya are also highlighted.

Experimental Observations of Wall Interference at Transonic Speeds

Lift and down wash interference on the high-aspect-ratio ONERA calibration configuration have been isolated from other variables (such as tunnel flow quality, effective Reynolds number, and model distortion under load) which are present in comparative wind tunnel data. The lift interference on the ONERA configuration was found to be related to the model to tunnel span ratio and is highly nonlinear in normal force at transonic speeds. Fighter and lifting body configurations were also studied. These lower aspect ratio configurations (/R<4) were found to be much less sensitive to wall interference. A family of curves which can be used to estimate lift and pitching-moment interference at transonic speeds is presented, and an empirical dependency of lift interference on/R2 is suggested.