Fabrice Emeriault

Assessment of ground surface displacements induced by an earth pressure balance shield tunneling using partial least squares regression

This paper presents a methodology to link the ground surface displacements to a tunnel boring machine (TBM) operation parameters. The approach consists at first in the exploration and description of the TBM operation parameters, recorded during the construction of the Toulouse (France) subway line B tunnel, using principal component analysis and agglomerative hierarchical clustering (AHC). Then, partial least squares (PLS) regression models were developed for the prediction of the displacements for the two groups of observations, identified by the AHC (pure settlements and heave at the center), as a function of the ten selected TBM operation parameters and the geometry parameter (X2/H2). The developed models take into account the nonlinear relationship between displacements and the operation parameters and the collinearity that exists in the parameters. In addition, the PLS regression allows identifying the parameters that affect the displacement of each group. The comparison of the predicted displacements with the measurements for the validation samples of the two groups shows good agreement.

Physical Model for Damage Prediction in Structures Due to Underground Excavations

Assessing the potential of building damage is a critical issue for existing and new building projects. Simple analytical approaches up to now are still mainly considered to assess the vulnerability of structures. This paper presents a new approach based on a small-scale physical model (1/40 scale factor on the dimensions) under normal gravity. It has been designed for developing and validating experimentally new methods of prediction of damages to masonry structures induced by subsidence (generally resulting from underground excavations of tunnels and mines). The analogical soil is homogeneous sand, allowing the realization of different simulations. The masonry structure consists of walls built with wood pieces without cohesion (mortar) and resting on an elastic foundation. The vertical displacements are applied through the use of an electro-mechanical jack. The technique of digital image correlation (DIC) is used to measure accurately the displacements and the deformations of the structure. The identification of the damage level is based on the crack width resulting from different vertical displacements. A specific algorithm has been developed to quantify the strain of joints. The total length of opened cracks appears to be a more relevant indicator of damage than the maximum width of cracks. The damage evolution with the vertical displacement can be divided into an initial linear part and a subsequent non-linear part. Guidelines are suggested for the assessment of the masonry damages due to underground excavations.

Effectiveness of a mitigation technique for buildings subjected to ground subsidence

Abstract A physical modeling has been undertaken to study the effectiveness of a mitigation technique (peripheral trench) to protect a residential house undergoing a ground surface subsidence from mining. A simple building model and a foam-material trench model are designed and implemented. Their deformations are measured by Digital Image Correlation (DIC) technique. The 3D physical model was proved very potential to qualitatively study the impact of ground movements on surface structures and the effect of soil-structure interaction. The trench technique was pointed out very effective to protect the building. The strain in the building and its surrounding ground are significantly reduced by the presence of the trench dug around the building.