Effect Of Tunnel Size Research Articles

복합지반에서의 쉴드 TBM 커터헤드의 회전속도에 따른 커터비트 손상에 관한 실험적 연구

This paper presents the cutter bit damage due to the rotation speed of shield TBM cutter head in the mixed ground. The efficient of cutter bits and disk cutter are very important for tunnelling in mixed ground. In particular, this research is focused on the performance of cutter bits during excavation in mixed ground which is consist of the weathered soil and rock formation. In order to carry out this research, the experimental works are prepared performed by using the scaled shield TBM cutter bits evaluation machine developed. The mixed ground is prepared considering with a scale effect of tunnel size. Three different rotation speeds of shield TBM cutter head (i.e. 2, 3, 4 rpm) are applied in the experimental work. The drag forces acting on the cutter bits are measured at each cutter bit during rotation of cutter head. It is also analysed the variation of drag forces due to the rotation speed of shield TBM cutter head. The results of this research are clearly shown that the drag forces acting on the cutter bits are jumped up at the boundary between weathered soil and rock. It is also indicated that the jamping drag forces are increased with increasing the rotation speed of the cutter head. It is found from the research that the higher rotation speed of shield TBM cutter head will be high risk in the mixed ground. It is, therefore, suggested that the use of lower rotation speed of shield TBM cutter head is recommended for reducing the cutter bit damage in practice.

The effect of tunnel size on stability problems in rock masses

The effect of tunnel size on stability problems in jointed rock masses is usually analyzed through the estimation of rock support pressures. The Q-system of rock mass classification has been widely used to estimate the rock support pressure from the rock mass quality Q. The empirical equation relating the support pressure and the tunnelling quality Q suggests that the unit support pressure is independent of the tunnel size. In this paper numerical experiments are conducted to investigate the effect of tunnel size on rock support pressures. It is shown that the support pressure increases significantly with tunnel size for an elastic-perfectly plastic rock mass. The maximum axial force in the shotcrete lining doubles as the diameter of the tunnel increases from 5 to 20 m. For linearly elastic rock mass the increase in support pressure with increasing tunnel size was computed to be small. These numerical results confirm the observations from instrumented tunnel sections in the Himalayas. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

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.

OH − dipole reorientability in hydroxyapatites: Effect of tunnel size

A study of calcium phosphate hydroxyapatite with the thermally stimulated currents methods (TSC) has led to the conclusion that the reorientable dipoles responsible for the dielectric properties measured are the structural OH − ions in the “tunnels”. The co-operative motions along chains of these dipoles have been followed by the identification and determination of compensation phenomena at T c = 212°C and 356°C. These phenomena correspond to physical events characterized by co-operative motions, such as the monoclinic-to-hexagonal phase transition observed in several apatites. Even in a material in which the higher temperature phase is frozen in at a lower temperature (e.g. by defects or by quenching), the TSC method can reveal the onset of those co-operative dipole reorientations which would otherwise produce a phase transition. An effect of the “tunnel” size and environment of OH − dipole reorientation movements has been investigated with two additional hydroxyapatites, strontium phosphate hydroxyapatite, Sr 10(PO 4) 6OH 2, and calcium arsenate hydroxyapatite, Ca 10(AsO 4) 6OH 2. “Tunnel size” is here defined as the distance from the center (6, axis) to the ion center less the ion radius. The larger tunnel sizes led to lower compensation temperatures.