Construction Sequence Of Tunnels Research Articles

Investigation of effects of different construction sequences on settlement and load transfer mechanism of single pile due to twin stacked tunnelling

Construction of tunnels in urban cities may induce excessive settlement and tilting of nearby existing pile foundations. Various studies reported in the literature have investigated the tunnel-soil-pile interaction by means of field monitoring, centrifuge and numerical modelling, but the influence of construction sequence of twin stacked tunnelling on an existing pile is seldom reported in the literature. This paper presents a 3D coupled-consolidation numerical parametric analysis to understand settlement and load transfer mechanism in single pile due to twin stacked tunnelling with different construction sequences in stiff saturated clay. To accurately capture the tunnelling induced ground deformation, path- and strain-dependent soil stiffness at small strains were taken into account in each numerical analysis, by adopting an advanced hypoplastic clay model coupled with the inter-granular strain formulation. Twin stacked tunnelling was simulated one after the other with the first tunnel excavated near the mid-depth of the pile shift and the second either next to the toe of the pile (case ST) or below the pile (case SB). In addition, two more analyses were performed with change of construction sequence of twin stacked tunnels (i.e. cases TS and BS). The first tunnel was excavated either near the pile toe (case TS) or below the pile (case BS) and second tunnel near the mid-depth of the pile shaft. The different construction sequence of twin stacked tunnels at different depth had a substantial effect on induced pile deflection and settlement. In contrast, no significant effect was found on load transfer mechanism in the pile due to the change in construction sequence of tunnels.

Three-dimensional response of double anchored sheet pile walls subjected to excavation and construction sequence

In this study, a three-dimensional (3D) response of anchored sheet pile walls was investigated on double-anchored sheet pile system during soils excavation and tunnel construction sequence. This construction procedure is executed in areas front and adjacent the sheet pile walls. This paper focused on both areas of construction effects on the sheet piles. This numerical study aimed at the evaluation of the variation of bottom wall bending moment, top wall lateral and vertical displacements and anchor reactions forces exerted in the sheet piles. This paper also described the variation of the total anchor's reactions forces from the upper and lower anchors rows. A parametric effect such as upper and lower anchors rows distance was also performed to evaluate the variation of the wall bending moment, displacement and anchors total forces. The analysis results indicated that the reactions forces developed in the lower anchor rods are always higher than those developed in the upper anchor rods. The higher the distance between the upper and the bottom anchors the lower the displacement of the top wall in any stage of the construction. The minimum bottom walls bending moment is developed in the case where the distance between the anchor's rows divided by the wall height is 0.51. Positioning the upper anchors at 0.15 and the lower at 0.39 the wall height from the top wall will induce minimum top wall vertical displacement during soil excavation. This paper presents the results and findings of the parametric study performed.

Effect of construction sequence on three-arch tunnel behavior-Numerical investigation

This paper concerns a numerical investigation on the effect of construction sequence on three-arch (3-Arch) tunnel behavior. A three-arch tunnel section adopted in a railway tunnel construction site was considered in this study. A calibrated 3D finite element model was used to conduct a parametric study on a variety of construction scenarios. The results of analyses were examined in terms of tunnel and ground surface settlements, shotcrete lining stresses, loads and stresses developed in center column in relation to the tunnel construction sequence. In particular, the effect of the side tunnel construction sequence on the structural performance of the center structure was fully examined. The results indicated that the load, thus stress, in the center structure can be smaller when excavating two side tunnels from opposite direction than excavating in the same direction. Also revealed was that no face lagging distance between the two side tunnels impose less ground load to the center structure. Fundamental governing mechanism of three-arch tunnel behavior is also discussed based on the results.

Research of Surface Deformation with Metro Double Tunnels Construction and the Relative Position Change

With the rapid development of our economy, the urban traffic becomes increasingly busy. To ease traffic congestion, underground rail transportation is becoming one of the main modes of transportation in city. At present in order to relieve the traffic congestion most major cities in China are accelerating the construction of subway tunnels. The relative position change of metro double tunnels and construction of the sequence will affect the surface subsidence deformation and the interaction of the tunnel lining. It is more concerned about these issues in tunnel design. It is the main purposes, in this paper, to analyze the metro double tunnels surface deformation, which affect by the position changes of new construction double and the sequence of construction. From the numerical simulating results, in order to reduce surface subsidence and ensure the structural safety over the subway tunnel, it should try to make double-tunnels at the same horizontal plane in design. If the double tunnels could not be located at the same horizontal plane, the double-hole tunnel construction sequence of the deformation of the surface subsidence effects are obvious it is obvious that the double tunnels construction sequence differently make the deformation of the surface subsidence. To reduce the deformation of the surface subsidence, it should be first excavated the shallow tunnels and then excavated the tunnel buried deeply. The ideal distance of the double tunnels center is greater than 4 times the tunnel diameter. It can make the surface subsidence reduce to the minimum during the metro tunnel construction.

An elastic stress–displacement solution for a lined tunnel at great depth

By using the complex potential theory proposed by Muskhelishvili, an elastic plane strain solution for stresses and displacements around a lined tunnel under in situ stresses is presented. The tunnel is assumed to be driven in a homogeneous and isotropic geomaterial, and the tunnel construction sequence is properly taken into consideration. Numerical analyses indicate that, in order to simultaneously meet the needs of structural strength and rigidity, the relative rigidity and thickness of liner should be in an appropriate range. Either too high or low values for these parameters are unfavorable for the structural stability. The variations of stresses in the geomaterial intensively rely on the relative rigidity and thickness of liner when the ratio between the distance of the point under investigation to the tunnel axis and the outer radius of the liner is in the range from 1 to 2. In addition, the present solutions contain previously known results as the special cases.

Three-dimensional analysis of unlined tunnels in rock subjected to high horizontal stress

An analysis of the stability of underground openings in weak rock is important to the design of the support requirements near the tunnel face. A detailed three-dimensional (3D) elastoplastic finite element study of face stability and the corresponding stresses around the face is conducted for a large-diameter tunnel in southern Ontario. The effect of the rock mass strength and high horizontal stresses on the tunnel deformation, stability, and distribution of tangential stresses at the tunnel circumference is investigated. To facilitate comparison with plane strain analysis, 3D results are presented for several cross sections across the tunnel. The effect of tunnel construction sequence on the predicted results is discussed.Key words: weak rock, tunnelling, horizontal stresses, three-dimensional, finite element, excavation, face stability, modeling.