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Stability assessment of roadbed affected by ground subsidence adjacent to urban railways

Abstract. In recent years, leakages in aged pipelines for water and sewage in urban
areas have frequently induced ground loss, resulting in cavities and ground
subsidence, causing roadbed settlement greater than the allowable value. In
this study, FLAC3D, which is a three-dimensional
finite-difference numerical modeling software, is used to perform stability
and risk level assessment for the roadbed adjacent to urban railways with
respect to various groundwater levels and the geometric characteristics of
cavities. Numerical results show that roadbed settlement increases as the
diameter (D) of the cavity increases and the distance (d) between the
roadbed and the cavity decreases. The regression analyses results show that,
as D∕d is greater than 0.2 and less than 0.3, the roadbed is in the status
of caution or warning. It requires a database of measurement sensors for
real-time monitoring of the roadbed, structures and groundwater to prevent
disasters in advance. As D∕d exceeds 0.35, the roadbed settlement
substantially increases and the roadbed is in danger. Since this may result
in highly probable traffic accidents, train operation should be stopped and
the roadbed should be reinforced or repaired. The effects of groundwater
level on roadbed settlement are examined and the analysis results indicate
that roadbed settlement is highly influenced by groundwater levels to an
extent greater than even the influence of the size of the cavity.
