Banca de DEFESA: Alan Ribeiro Santos

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : Alan Ribeiro Santos
DATE: 24/05/2024
TIME: 09:00
LOCAL: Sala Teams (On-line)
TITLE:

Numerical study of the behavior of tunnels in soft soils subjected to pore water pressure drawdown

KEY WORDS:

Tunnels; Soft soil; Lowering; Regional subsidence; Geotechnical centrifuge; Numerical modeling

PAGES: 127
BIG AREA: Engenharias
AREA: Engenharia Civil
SUBÁREA: Geotécnica
SUMMARY:

"The demand for tunnels has significantly increased in recent decades due to the rapid urbanization and population growth. In cities with soft soils, this need is particularly pronounced. Building tunnels in such conditions is challenging due to the unfavorable properties of strength and compressibility exhibited by this type of soil. The complexity of constructing tunnels in cities such as Bogotá, Mexico City, and Shanghai is further heightened by the potential consolidation of soft soil induced by the pore water pressure drawdown resulting from deep water pumping. This phenomenon alters the distribution of total stresses on the tunnel lining throughout the lowering process, leading to increased bending moments, compression, and shear forces in the structure.
In order to study the behavior of tunnels under these conditions, numerical analyses were developed, calibrated and validated through geotechnical centrifuge tests. Two models were simulated: one with the tunnel resting on a hard layer (Model No. 1) and another with the tunnel in the middle of a compressible layer (Model No. 2). The Hardening Soil (HS) model was used to simulate the compressible layer. After validating and calibrating the numerical models, the influence of initial conditions on the long-term behavior of the tunnel lining was investigated. Additionally, a parametric analysis was conducted to examinate the total stresses developed in this element, based on variations in the thickness of the tunnel lining, the at rest earth pressure coefficient (K0), the strength reduction factor (Rinter), and the overconsolidation ratio of the soft soil (OCR). The analyses demonstrate consistency between the results of physical and numerical simulations, indicating, in both cases, an adequate simulation of the regional subsidence phenomenon.
The total normal stresses developed in the tunnel lining in physical modeling differ from those observed in numerical models at before the pore water pressure drawdown but converge satisfactorily at the end of regional consolidation. The analysis of initial conditions shows limited influence of the calculation type of initial stress state on long-term results in most cases.
Evaluation of strains in the tunnel lining indicates a reduction in vertical diameter and an increase in horizontal diameter during the drawdown process (horizontal ellipse). Additionally, it highlights more critical structural conditions in Model Nº 1, which is also supported by the analysis of total stresses.
In the parametric analysis, K0 is identified as the parameter that most significantly influences the horizontal total stresses developed on the tunnel side walls, followed by OCR. The findings of this study provide valuable insights for the design of tunnels in soft soils subjected to the pore water pressure drawdown, and suggest avenues for future research, particularly concerning the comparison between numerical models and the investigation of the influence of K0 and OCR on the horizontal total stresses developed on the tunnel side walls."

COMMITTEE MEMBERS:
Externo à Instituição - JORGE ESTEBAN ALARCÓN GUERRERO - UEDA
Presidente - 2161425 - JUAN FELIX RODRIGUEZ REBOLLEDO
Interno - 1549489 - MANOEL PORFIRIO CORDAO NETO
Interno - 404227 - MARCIO MUNIZ DE FARIAS