Junsheng Yang

Mountain Railway Alignment Optimization with Bidirectional Distance Transform and Genetic Algorithm

Various challenging constraints must be satisfied in railway alignment design for topographically complex mountainous regions. The alignment design for such environments is so challenging that existing methodologies have great difficulties in automatically generating viable railway alignment alternatives. We solve this problem with a hybrid method in which a bidirectional distance transform DT algorithm automatically selects control points before a genetic algorithm GA refines the alignment. This approach solves the problems of 1 determining the appropriate distribution of control points in the GA and 2 producing alignments that deviate significantly from the DT-optimized paths. Automatic design of backtracking curves and dynamic generation of vertical points of intersection handling multiple constraints are developed to improve the GA performance. This method has been applied to a real case on the Sichuan-Tibet Railway where excessively severe natural gradients must be overcome. It automatically finds an alignment optimized for the given objectives and complex constraints, as well as various promising alternatives.

Panoramic Image Stitching for Arbitrarily Shaped Tunnel Lining Inspection

This article presents a low-cost panoramic image stitching system for tunnel lining inspection. The system can produce a high-quality layout panorama of the target lining using photographs taken freely in a tunnel with a hand-held camera and the tunnel design information as inputs. The three-dimensional (3D) freeform shape corresponding to the tunnel design geometry is used as the warping surface for photograph rectification. A newly designed random sample consensus algorithm is used to estimate the freeform tunnel shape from the 3D reconstructed point cloud, which can perform the registration between point sets with different sizes. These processes can make full use of the geometry information of a real tunnel and the reconstructed scene; thus, the photographs can be precisely rectified, and a planar motion stitching can composite them together. Two field applications demonstrate that the system can create a tunnel layout panorama with sufficient accuracy in tunnel lining inspection and that it is applicable to noncircular-shaped tunnels.

Analytical Prediction of Ground Movements due to a Nonuniform Deforming Tunnel

AbstractAn analytical solution is presented to predict ground movement induced by a nonuniformly deforming circular tunnel in a heavy elastic half-plane. Simple expression is proposed to describe the nonuniform soil deformation around the tunnel. The tunnel-deforming components (i.e., ground loss, ovalization, vertical translation) can be determined by the solution-inherent mechanism and by fitting from measured field data. The effects of tunnel-deforming components on the resulting displacement field are discussed. Case studies from various ground conditions were used to check the capacity and applicability of the proposed solution. Although elasticity is a rough representation of the soil behavior, the proposed analytical solution can serve as a simple tool for predicting a reasonable ground settlement profile in the preliminary design of tunnels.

Deformation Response of an Existing Tunnel to Upper Excavation of Foundation Pit and Associated Dewatering

AbstractDeep excavation clearly impacts existing underlying subway tunnels and threatens their operational safety. The prediction of existing tunnel deformation induced by nearby excavation is a major concern for urban construction. This research presents an analytical calculation method for predicting tunnel deformation induced by upside excavation and also discusses the role of dewatering in the deformation mechanism. First, the existing tunnel is assumed to be nonexistent in the soil, and the vertical unloading stress at the location of the existing tunnel caused by the upper excavation and associated dewatering is calculated. Second, the existing underlying tunnel is simplified as an elastic beam on a Pasternak foundation to calculate its vertical deformation. The proposed method was verified by the good agreement found between the predictions and the field measurements of the construction in the Shenzhen Chegongmiao hub project. Such an analytical method can provide fast and accurate evaluation resul...

Performance of Jet-Grouted Partition Walls in Mitigating the Effects of Shield-Tunnel Construction on Adjacent Piled Structures

AbstractProtective interventions are often needed to protect sensitive buildings from ground deformation induced by tunneling. This paper evaluates the effectiveness of underground jet-grouted partition wall in mitigating the effects of shield-tunnel construction on existing piled structures by means of numerical analysis and field monitoring. It is shown that the tunneling-induced displacements field can be modified by the underground partition wall in different ways depending on the combination of influential factors, such as wall stiffness, partition range angle, and insert depth below the tunnel invert. The results also indicate that the presence of the partition wall can relieve the existing piles from suffering from differential displacement, thereby improving the mechanical performance of pile–pier interaction. The reasonable agreement found between the observed field measurements and the numerical results demonstrates that underground jet-grouted partition wall can serve as an effective recourse o...

The Effects of Local Cavities on the Cracking Performance of an Existing Tunnel Lining

Local cavities around the tunnel lining due to imperfect construction or ground water erosion will lead to local contact loss and discontinuity in the ground-lining interaction. This paper evaluated the effect of local cavities on the mechanical and cracking performance of an existing tunnel lining. The geometry and position of the local cavity were defined according to the results of field investigation. Numerical analyses were performed to investigate how the local cavities affect the stress state of the concrete lining and to check the stability of the tunnel. Extended Finite Element Method (XFEM) was used to illustrate the development of cracking directions and patterns on the existing tunnel lining in the vicinity of the cavity. The above results was then verified by comparing with field observations. The presented study suggested an effective way for modelling tunnel lining cracking, and shown a systematic method to preliminary evaluate the cracking performance of an existing tunneling lining with local cavities behind.

Numerical Investigation on Muck Pressures During EPB Shield Tunneling with Varying Discharge Ratio Based on Coupled PFC3D/FLAC3D Method

In this study, an efficient numerical method coupled PFC3D and FLAC3D was presented to simulate the tunneling behaviors of EPB shield. Groups of tunneling cases with different muck-discharging ratios were conducted in PFC3D and FLAC3D with data exchanging each other in every step. The results show the muck pressures in the back of spokes are invariably less than those behind the opening of cutterhead. Moreover, pressure differences exist permanently not just between left side and right side in chamber, but in different longitudinal positions within the domain affected by tunneling, and the values of these pressure differences are subjected to muck-discharging ratio in chamber. These findings extend knowledge regarding the tunneling mechanisms of EPB shield. Besides, the proposed coupling method can be popularized with all studies about the interaction between engineering devices and soil as well.

Field Measurement of Stresses of Floor Slabs in Excavations

This paper presents field measurement of stresses of floor slabs in excavations. During the study, a typical measurement-section was selected, and concrete strain meters were embedded so as to make stress measurement for floor slabs. Effect of the excavation of adjacent foundation pit for existing structure was discussed deeply. What’s more, the stability of floor slabs was evaluated. Finally, it could be concluded as follows: With the increase of the excavation depth, the excavation of the Transfer Hall Foundation Pit (THFP) had large effect on the internal force of floor slabs beside it, however, such influence tended to be smaller for the foundation pit far from the Transfer Hall (TH);. According to the strain data from field measurement, safety factors of floor slabs were calculated, which turned out to meet national code (JGJ 120-2012). Meanwhile, it can be concluded that floor slabs were in the safe status. In the end, the variation relation of their internal force, which would provide some references for the design and construction of similar projects in future, was obtained.

A Jet-Grouted Wall in Mitigating Tunnelling Effects on Adjacent Structures

Technical measures, such as an underground partition wall, could serve as recourse to mitigate the ground movements induced by excavation. In this paper field monitoring and numerical analysis were used to examine the performance of an underground jet-grouted partition wall in mitigating the effects of shield tunnel construction on an existing pier of the Xin-Zhong Road viaduct in the Changsha Subway Line 1 project in China. The performance of the jet-grouted partition wall was calibrated by the reasonable agreement found between the observed field measurements and the numerical results. An underground jet-grouted-column partition wall was tested to serve as an effective measure in ground movement control given the need of tunnelling nearby piled structures.

Study of Stability of Surrounding Rock due to the Approach of Two Excavation Faces and Face Reinforcement in a Large Cross-Section Tunnel in Weak Stratum

When the two excavation faces of a tunnel constructed from both the entrance and exit simultaneously in soft surrounding rock approach, the excavation surface disturbance areas are superimposed, stress and deformation in the surrounding rock become extraordinarily complex, which results in substantial deformation and instability. By combining the study of the surrounding rock stress and displacement caused by both unidirectional and face-to-face excavation in the Shizilong Tunnel, the stability of the tunnel face with two excavation faces approaching one another in a bidirectional construction is analyzed by numerical analysis. It is shown that, with the reduction in the length of the unexcavated soil between the two excavation faces, the plastic zone and deformation significantly increase, and the arching effect gradually weaken, resulting in greatly reduced tunnel stability. When the distance between the two excavation faces is less than the limiting distance, an extended range of the surrounding rock approaches plastic failure, and only effective countermeasures can guarantee the safety of the tunnel construction. Further, bamboo anchor pipe grouting is adopted to reinforce tunnel faces with the initial support strengthened, when those two excavation faces in the construction of the Shizilong Tunnel are approaching. Field implementation indicates that the tunnel is excavated safely.