Finite Element Analysis of Ground Response due to Tunneling in Cohesionless Soil

Tunneling in cohesionless soil leads to ground movement. In urban environment, the soil movement
due to tunneling may affect surface or subsurface constructions. The ground movement is
considered a major geotechnical challenge. The ground movements due to tunneling are predicted.
In the present study, the prediction of the ground movement under the impact of the tunnel
construction is highlighted and a model is proposed to study the soil structure interaction using a 2-D
finite element analysis. The ground movement due to tunneling is also calculated using surface
displacement equation proposed by Peck and Schmidt (1969). The surface displacement computed
by the proposed model and the surface displacement equation is studied at different sandy soil types
due to tunneling so as to examine the computed results. The study presents a case history along the
Greater Cairo Metro tunnel Line 2 to assess the accuracy of the proposed finite element model.
Based on this case history, extensive study using the finite element model and the surface
displacement equation is conducted to predict the ground movement due to tunneling. The
constitutive model for this analysis utilizes elasto-plastic materials. A yielding function of the Mohr-
Coulomb type and a plastic potential function of the Drucker-Prager type are employed. A linear
constitutive model is employed to represent the tunnel liner.
For the case study, this paper presents a comparison between the field measurements and those
obtained by the finite element analysis and the surface displacement equation. There is a good
agreement between computed and measured values. The tunnel system performance is expressed in
terms of surface settlement due to the tunnel construction. The study presents the prediction of the
surface settlement profile using the proposed model and the surface displacement equation at
different sand soil types. The study also examines the results obtained by the surface displacement
equation with those obtained by the finite element analysis. The results show that the surface
settlement profiles using the surface displacement equation have a good agreement with those
obtained by finite element analysis in loose to medium sandy soil. In addition, the surface settlement
profiles computed by the surface displacement equation do not agree well with those obtained by the
2-D finite element model in dense to very dense sand soil. However, the surface displacement
equation does not include the impact of different geotechnical parameters used to classify the
different sandy soil types.