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In the context of underground construction projects such as large-scale linear projects, knowledge of subsoil geotechnical properties is of major importance. An effective way to analyze and represent the variability of these properties is to use geostatistical methods. Despite the good performance of such methods, their use is not yet widespread in the field of underground projects. This paper aims to show the usefulness of geostatistics in the field of tunneling by proposing an original 3D sectoral modeling approach that allows dividing the geological formations in homogeneous geotechnical areas to better take into account the vertical and lateral variations of geotechnical properties. The approach is tested by developing a 3D geostatistical model of the pressuremeter tests on a section of a massive tunneling project in Paris (France): the Grand Paris Express. A strong focus is also made on the model input data: a methodology is proposed to overcome the limitations of the pressuremeter test in order to better study the spatial variability of the net limit pressure. A twofold analysis is conducted by comparing the modeling results obtained with and without pressuremeter data processing and those obtained with and without sectoral modeling. The results of the comparison show that: a) data processing is useful to better discern areas of extremes values of net limit pressure; b) dividing the geological units into homogeneous geotechnical sectors provides an advantage for geological units with geotechnical heterogeneities, as it leads to improved reliability of results. • An original 3D geostatistical modeling method for tunneling project is proposed. • Net limit pressure re-evaluation overcomes the pressuremeter test limitations. • Statistical methods identify homogeneous geotechnical areas within heterogeneous geological formations. • Sectorisation modeling outperforms global modeling for lateral geotechnical heterogeneities. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogeological analysis of flow is largely based on the concept of hydraulic conductivity. In numerical hydrogeological modeling, a value of hydraulic conductivity must be assigned at each element of mesh. In heterogeneous geological formations, this value governs the average behavior of groundwater flow within an aquifer. The goals of this study are twofold: (1) development of a methodology to transform the description of lithological units into local hydraulic conductivity values and (2) development of a methodology for reconstruction of hydraulic conductivity fields on a 83km2 of the Bordeaux urban area. Two approaches, a 2D approach and a 3D approach, based on geostatistical analysis are explained in details and compared. For both approaches, variographical analysis and ordinary kriging are carried out on the logarithmic of hydraulic conductivity and composite hydraulic conductivity is calculated using thickness-weighting to get horizontal and vertical hydraulic conductivities. The comparison of both approaches and the assessment of their potential and limitations suggest that the 2D approach is more appropriate than the 3D approach. [Copyright &y& Elsevier]

The Lascaux cave, located in southwest France, is one of the most important prehistoric caves in the world that show Paleolithic paintings. This study aims to simulate the 3D geological environment of the cave by geostatistical modeling based on 2D Electrical Resistivity Tomography (ERT) data. Seventeen ERT profiles were carried out resulting in 64,195 geolocated resistivity values, covering about 14,500 m 2 of the Lascaux site. From this dataset, 3D resistivity geo-model has been built by geostatistical method. We used geotechnical data from 36 boreholes and cone penetrometer tests to validate the geo-model. By modeling from 2D data, we can establish a good estimation of the 3D geological environment of the Lascaux site. Our results show that the site can be generally separated in two parts: the limestone promontory in the center and the detrital formations located in both east and west sides. There is a high contrast between resistivity of the two formations: 45 Ω·m (detrital formation) to 556 Ω·m (limestone) with a rough boundary. In the center, the limestone could also be separate into two parts: a superficial layer of weathered limestone (150 Ω·m) and a deeper layer with compact limestone (556 Ω·m). [ABSTRACT FROM AUTHOR]