Stability Study Using Numerical Analysis for the Panel Method Applied to the Weathered Rock Section below the National Highway

In sections with poor ground conditions, it is difficult to apply the commonly used NATM tunnel method; thus, applications of the non-open cut tunneling method are increasing. This section is a tunnel crossing area under the national road in which the Panel method is to be applied to the section where a deeply buried layer and a loose weathered soil layer are distributed. Therefore, the stability of the upper road, the amount of settlement, and the stability of the tunnel structure were reviewed for each construction stage by using MIDAS GTX. Through the installation of measuring instruments in the tunnel area, the results of the numerical analysis were reviewed and the stability during and after construction was evaluated. Therefore, it is likely that the Panel method is an appropriate countermeasure in the downtown area and in areas with soft ground sections where the application of the general tunnel excavation method is difficult.

Three-Dimensional Probabilistic Analysis of The Surface Settlement Based On Spatial Variability of Soil Properties: Case Study Zarbalizadeh NATM Tunnel

Designing and the construction of a tunnel in urban areas has their own specific considerations. Usually, excessive settlement caused by tunneling during construction damages the adjacent infrastructures and utilities, especially if the tunnel is excavated by the new Austrian tunneling method (NATM). Thus, it’s important to make accurate predictions and effective control on tunneling-induced settlement. In this study, the soil’s Young’s modulus was modeled using a three-dimensional random field and coupled with a finite difference method (FDM) analysis to reveal the influence of scale of fluctuation (SOF) on the maximum surface settlement (Smax). To generate the field of soil’s Young’s modulus, the Fourier series method is employed and sensitivity studies are further performed via Monte-Carlo simulations (MCS). The results demonstrate both the mean value of Smax and its coefficient of variation (COV) increase from 28 mm to 31 mm and from 0.02 to 0.35 respectively, with an increasing horizontal SOF but they stabilize at higher values of SOF. Furthermore, the probability of failure increases as COV increases for each allowable limit greater than the verification FDM of Smax. It is observed that ignoring the spatial variability of soil’s properties leads to an underestimate of the risk of excessive surface settlement.

Performance of Flowable Concrete in Underground Structures

Flowable concrete gives special combinations of uniformity, performance and consistency requirements that cannot be possible by traditional normal slump concrete. It is superior concrete than the traditional concrete with high workability, no segregation, no bleeding, and it is also suitable for use in the structures with long-distance pumping i.e., more than 120-meter length, for example, in NATM tunnels, cross-passages, and the concrete structure of the station box. Flowable concrete can flow itself without vibration or a little bit of vibration like surface tamping at outer surface of the formwork for achieving a smooth surface finish after de-shuttering. Percentages of concrete ingredients that are used in concrete to ensure a balance between deformability and stability. Type of selected materials and the fixed ratio of concrete materials can be affected on the fresh and harden properties of the concrete. The article presents experimental techniques for mix designing of flowable concrete for grade M40 and application of the same concrete mix at the cast in situ Base slab, Roof slab Rcc walls for underground metro stations, NATM tunnel & cross passages in Mumbai Metro Project, package -UGC-07. The test results for conformity requirements of M40 grade flowable concrete such as flowability, viscosity, passing ability of fresh concrete, durability test and harden concrete tests determined, and results are included here.

Performance of Flowable Concrete in Underground Structures

Flowable concrete gives special combinations of uniformity, performance and consistency requirements that cannot be possible by traditional normal slump concrete. It is more superior concrete than the traditional concrete with high workability without segregation, bleeding, and is also suitable for use on structures with long distance pumping i.e., more than 120-meter length, for example, in NATM tunnels and cross-passages, and the concrete structure of the station box. Flowable concrete can flow itself without vibration or little bit vibration like surface tamping outer surface of the formwork for achieving a smooth surface finish after de-shuttering. The proportion of the mix is to be used in concrete, it must ensure a balance between deformability and stability. The behavior of concrete can be influenced by the properties of the selected item in the concrete, and the aspect ratio of the mixture. There is a need for the development of a methodology for the design of the flowable concrete mix. The paper presents an experimental procedure for the mix design of flowable concrete for grade M40 and implementation of the same mix at the cast in situ Base slab, Roof slab Rcc walls for underground metro stations, NATM tunnel & cross passages in Mumbai Metro Project, package -UGC-07. The test results for acceptance characteristics of M40 grade flowable concrete such as Slump flow test, compressive strength at the ages of 7, 28, and 56 days determined, and results are included here. Successful production of temperature control flowable concrete from batching plant, transportation, placement procedures, and proper planning of handling and execution of flowable concrete at the site are presented in this article.