Search

Monitoring is required when dewatering underground construction sites to anticipate unexpected events and preserve nearby existing structures and/or buildings. The most accurate and widespread monitoring method to measure displacements is leveling, a point-like surveying technique that typically allows for tens of discrete in situ sub-millimeter measures per squared kilometer. Another emerging technique for mapping soil deformation is the interferometric synthetic aperture radar (InSAR) method, which is based on SAR images acquired from orbiting satellites. This remote sensing technique can provide better spatial point density than leveling, more extensive spatial coverage and lower-cost acquisitions. This paper analyses, compares and discusses leveling and advanced multi-temporal InSAR measurements when they are used to measure the soil deformation induced by the dewatering associated with underground constructions in urban areas. This comparison, which has not been considered in previous works, is of paramount importance to ascertain the most suitable technique (or combination of techniques) in these contexts. To do so, an experiment was performed in the future railway station of La Sagrera, Barcelona (Spain), in which leveling and advanced multi-temporal InSAR were used to quantify ground deformation by dewatering. The results showed that soil displacements measured by leveling and InSAR were not always consistent. In the context of soil deformation measurements produced by dewatering in urban areas, InSAR measurements appear to be more accurate for investigating soil deformation, whereas leveling was more appropriate for quantifying the real impact on the nearby buildings. [ABSTRACT FROM AUTHOR]

Construction processes require monitoring to ensure safety and to control the new and existing structures. Traditional monitoring is based on land surveys and geotechnical instruments and only allows for point-like measurements. Ground-based synthetic aperture radar (GB-SAR) is a remote sensing radar installed in the ground that offers the possibility of acquiring measurements in 2D covering areas of up to a few square kilometers in a single acquisition. Because the GB-SAR technology measures phase shifts along the Line-of-Sight, it only allows for measurements in the longitudinal direction. Moreover, this technology requires coherence between subsequent acquisitions. These restrictions can be a limitation to the usage of GB-SAR for monitoring a construction process because in this context, the movements of soil and existing structures occur in any direction and at a very fast pace. This paper aims to test the GB-SAR suitability to measure movements during construction. To do so, an experiment was performed in the future railway station of La Sagrera, Barcelona (Spain), in which GB-SAR was used to accurately quantify wall displacements induced by dewatering and proved to be helpful to understand structural deformations and to identify vulnerable areas. The results were compared to traditional monitoring data and numerical models to confirm the reliability of the GB-SAR measurements. [ABSTRACT FROM AUTHOR]

Construction of tunnels can impact aquifers because of the changes produced in the natural groundwater behavior. The drain effect, which is one of the most important impacts, can be eliminated using a tunnel-boring machine (TBM) to drill a tunnel with an impervious lining. However, the use of impermeable linings results in aquifer obstruction, giving rise to the barrier effect, which may cause an increase and decrease of the hydraulic head upgradient and downgradient of the tunnel, respectively. This modification of the hydraulic head, which can be predicted analytically and is proportional to the natural hydraulic gradient of the aquifer perpendicular to the tunnel ( i N ) (before it is constructed), is negligible for aquifers with values of i N that are very small or null (approximately 0). In these cases, the analytical solutions are not useful to estimate the real impact because the head distribution is not largely affected. This study proposes a methodology to evaluate the hydrogeological impact produced by the construction of underground impervious structures in aquifers, which have a small or null i N . The method, which is based on the analysis of the groundwater response to pumping tests performed before and after construction, was tested in a stratified porous aquifer and was used along with numerical modeling to assess the barrier effect in an experimental site (Sant Cosme, El Prat de Llobregat, Barcelona). The impact on the head distribution was negligible. However, the reduction of the connectivity was considerable. Pumping tests can determine the changes in aquifer connectivity caused by the construction of an underground impervious structure. The behavior of the groundwater during the post-tunneling pumping changes with regard to the pre-tunneling tests. A delay in the response to the pumping and a decrease of the drawdown are observed in the piezometers located on the opposite side of the tunnel where the well is placed, whereas an increase of drawdown occurs in the piezometers situated on the same side of the well. The procedure explained in this paper reveals a useful tool for determining the impact caused by underground impermeable constructions in aquifers, where i N is small or even 0. [ABSTRACT FROM AUTHOR]

This paper presents a procedure for tracking rockfall trajectories and extracting kinematic parameters from both the impacts and the resultant fragments. A set of full scale rockfall experiments was performed in a quarry located in Vallirana, Barcelona (Spain). The study site was chosen due to the presence of a rigid discontinuity surface, inclined at 42° in the middle of the slope, whose configuration was expected to favor the breakage of the blocks. The trajectories of the blocks released and of the resultant fragments were recorded with three video cameras. A C++ program was specifically developed to track the 3D trajectory of blocks and fragments, and measure velocities before and after the impact. Two different modules were implemented, one for the blocks that break and one for those that do not. The trajectory of a non-fragmented block is obtained by comparing it to its 3D model. In this way, both the center of mass position and the orientation of the block are tracked. For fragmented blocks, the local coordinates of the fragments determined from the images are converted to terrain coordinates using the program we developed. A total of 16 blocks and 36 rock fragments after impact were tracked. The parameters obtained were georeferenced and linked to a common system of 3D terrestrial coordinates. The captured parameters allow obtaining the velocity distribution of fragments, the coefficient of restitution, and energy balance for the blocks that break. To our knowledge, this is the first attempt to capture kinematic parameters of rock fragments that result from the impact and breakage of rock blocks in full-scale tests. Although the analysis of the rockfall fragmentation phenomenon is beyond of this work, we have compared the performance of the fragmented and unbroken blocks. To this purpose, we have built 3D models of the rock fragments generated using images captured with a drone. The results indicate that blocks that fragment show higher rebound velocities and coefficients of restitution than the blocks that do not although there exists a certain overlap between the two groups. Despite the experiment is carried out on the same discontinuity surface and with small variations in the impact velocities, impact kinetic energies and impact angles, the coefficients of restitution obtained present a wide range of values, both for the blocks that break and for those who do not. The number of tested blocks is too small to draw generalizable conclusions, but they highlight the stochastic nature of the rebound process and the necessity to consider additional parameters for its understanding. Finally, the results confirm the relation between the dissipated energy and, especially the impact energy and the new area created by fragmentation. Furthermore, the blocks that hit the ground with the face are those that generate the most new area while those that hit the vertex generate less. • Characterizing block fragmentation. • Capturing block's impact-rebound characteristics. • Stereo photogrammetric analysis (3D) of block's trajectory. • Real-scale rockfall testing. • Obtaining block and fragments masses, velocities, energy balance and restitution coefficients. [ABSTRACT FROM AUTHOR]

The aim of this paper is to demonstrate how the integration of differential interferometric synthetic aperture radar (D-InSAR) and levelling improves the monitoring of ground deformation phenomena, thereby enabling their complete understanding. The complementarity between D-InSAR and levelling is illustrated through a case study of the construction of a road tunnel beneath Glòries Square, Barcelona; D-InSAR is employed to continuously monitor the works, notably the dewatering of the site. This study focuses primarily on D-InSAR data obtained from the processing of Sentinel-1A data following a persistent scatterer interferometry procedure. The spatial distribution of the deformation and its temporal evolution are analysed with detailed hydrogeological and piezometric data. The magnitude of deformation is discussed using levelling data and an analytical estimation based on the hydromechanical parameters of the ground obtained from a pre-existing hydrogeological numerical model and pumping tests. The D-InSAR results are shown to be essential for identifying the origin of ground deformation and the constraints on its spread. Such observations at the construction site and district (~2 km radius) scales with sub-centimetric deformation are precious contributions of D-InSAR data, whereas levelling offers a more accurate quantification of the deformation, although this remains an open issue to be further investigated. • Differential interferometric SAR as monitoring technique in civil works. • Ground deformation related to the dewatering of construction works. • Hydrogeological interpretation of D-InSAR results. • Complementarity of differential interferometric SAR and levelling. [ABSTRACT FROM AUTHOR]