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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]

Methodologies have been developed to establish realistic water-table maps using geostatistical methods: ordinary kriging (OK), cokriging (CoK), collocated cokriging (CoCoK), and kriging with external drift (KED). In fact, in a hilly terrain, when piezometric data are sparsely distributed over large areas, the water-table maps obtained by these methods provide exact water levels at monitoring wells but fail to represent the groundwater flow system, manifested through an interpolated water table above the topography. A methodology is developed in order to rebuild water-table maps for urban areas at the city scale. The interpolation methodology is presented and applied in a case study where water levels are monitored at a set of 47 points for a part urban domain covering 25.6 km close to Bordeaux city, France. To select the best method, a geographic information system was used to visualize surfaces reconstructed with each method. A cross-validation was carried out to evaluate the predictive performances of each kriging method. KED proves to be the most accurate and yields a better description of the local fluctuations induced by the topography (natural occurrence of ridges and valleys). [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 closure and shear behaviors of 3D self-affine rock joints are simulated by the Discrete Element Method using PFC3D. First, a methodology to produce rough self-affine rock joints using DEM is presented then eight self-affine rough joints, having low and high values of roughness exponent, self-affine correlation length, and height variance, are considered. After the calibration of the elastic and fracture behaviors of an elementary volume formed from spherical discrete elements bonded by elastic beams, the numerical rock joints are submitted to closure tests at 14 and 21 MPa followed by a shear test at constant velocity and under constant normal load. Each DEM joint is tested using three different mechanical models: rigid, ideally elastic and elastic-fracturing. The use of these three models allows highlighting the distinct influences of the morphology, the joint stiffness and the micro-fracturing on the closure and shear behaviors of the joints. [ABSTRACT FROM AUTHOR]

This paper presents an innovative system which adapts Electrical Resistivity Tomography (ERT) for fast investigation on long transects. The device consists in a set of on-the-go sensors allowing high sampling rate measurement for mobile prospections. The weak contact between the mobile sensors and the soil, to allow fast investigations, induces very noisy raw datasets. Kinematic Electrical Resistivity Tomography (named KERT) is then associated with a data treatment process. A two-step process reveals the information contained in the datasets. The first focuses on the procedure to remove noise through the use of a low-pass filter. The assessment of cutoff frequency for smoothing is deduced from a Fast Fourier Transform (FFT) analysis, thus the value is adapted to the site and the prospection. The second phase consists in calibration of the KERT on a conventional static ERT. At this point, a classical static ERT was used as a reference, and directed on a reduced part of the KERT transect. The estimation of a factor of calibration (Xc) to correct bias revealed the resistivity variations along the entire transect and in depth. In the last part of the paper, the validation of the investigation method and data treatment methodology is performed on a real case study: a 450 m transect is investigated in 5 min (mean speed: about 6 km/h), integrating 10 depths of investigation. The steps of data processing are detailed to show the final results, consisting in a zonation along the transect. [ABSTRACT FROM AUTHOR]

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]

A global modelling approach for estimating the climate influence on corrosion activity in reinforced concrete is developed. It combines: (a) the identification of statistical properties of climates in various temperate regions, and the development of a synthetic simulator able to reproduce its dominant patterns, (b) the identification of an empirical corrosion activity model, based on the analysis of experimental data, highlighting the respective influence of temperature and humidity. Synthetic simulations combining these two models are carried out. They show the complexity of the interactions, since the influence of temperature and humidity may be adverse, and the interest to describe both random fluctuations at daily scale and at seasonal scale. They confirm that monitoring of corrosion must account for this time variability and propose a way to estimate average corrosion even with measurements which would remain limited to a short period. Synthetic simulations are also used for estimating the influence of a global warming scenario on the corrosion activity. A global increase of about 38% of corrosion activity has been estimated in response to an average temperature elevation of 3°C. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the assessment of settlements of soft columnar inclusions when uncertainties in soil properties and geometric features are considered. Two common design methods, the analytical homogenisation method and the finite element method, are then combined with Monte Carlo simulations in order to find, using probability distributions of soil and geometrical characteristics, the probability of settlements exceeding a given value. The results show that length and modulus of granular piles are the two major sources of uncertainty and that the model uncertainty obtained from the interpretation of relevant sensitivities is smaller with the finite element model. From the outcome, this paper demonstrates that when geotechnical uncertainties and their effects on soil responses are appropriately accounted for, they can lead to an improved understanding and modelling of a practical geotechnical problem such as the ground improvement by columnar inclusions. [Copyright &y& Elsevier]

The study of karst features under a detrital cover is difficult to obtain using punctual traditional tools. This paper presents a 3D geostatistical modeling of ERT (Electrical Resistivity Tomography) data to describe undercover karst features. A case study was carried out on the karstic site of the prehistoric decorated Lascaux cave (France). Geophysical measurements were used to define the limit between outcropping Coniacian or Santonian limestones (southwest) and clayey sands (northeast), with a main orientation of N140°. A geometrical description of the scarp was also constructed; pinnacles and notches were found under the clayey sand detrital formation. By combining 3D ERT with geomorphological and geological observations, the geometry of the stratigraphic limit between the Coniacian and Santonian limestone could be determined. This stratigraphic limit separates two domains, one is a potential aquifer, and acts as a feeder for the intermittent spring at the cave entrance, while the other is less permeable, resulting in a permeability contrast with the later rock type. All these observations help define the geological cave environment and ensure better protection for the paintings. • Undercover karst features are found with 3D ERT geostatistical model. • Geomorphological features found comprises shelf, pinnacles and scarps. • The geological limits are redrawn around the ornamented Lascaux cave. • The top of the Lascaux cave develops within Santonian limestone. • The rest of the cave develops in Coniacian, e. g. the Hall of the Bulls. [ABSTRACT FROM AUTHOR]