Modulus Estimation of Surrounding Soils of Underground Structures in Service

Most underground structures in urban areas were built several decades ago and require diagnosis and maintenance to ensure their longevity. To ensure that diagnosis is as complete as possible, it is necessary to evaluate their state on three levels: structure lining, contact interface (soil/structure), and surrounding soil. However, at present, there is no fully appropriate technique for characterizing the parameters of surrounding soils and their variability in situ. This paper deals with a less invasive methodology used to obtain an estimation of the elasticity modulus of the surrounding soil of underground structures in service. The combined use of a dynamic lightweight penetrometric test (PANDA) and geoendoscopic tests permits estimating the deformation modulus of soils from the tip resistance (q_d) for a given material and from relations established for different soil models. The paper first presents the complete methodology proposed for in situ soil characterization, then the experimental work carried out in the laboratory for obtaining the relations linking the penetration tip resistance to the elastic modulus for four soil models and for different density and moisture conditions. Finally, the performance and adaptability of the methodology for estimating soil-deformation modulus and its variability is demonstrated by in situ testing campaigns in the Paris subway network.