No abstract

Satellite interferometric synthetic aperture radar (InSAR) is an operational remote sensing technique for monitoring ground deformation. Advanced techniques to process radar data like persistent scatterer interferometry (PS-InSAR) combined with recently available high-resolution radar modes such as StripMap (SM) and spotlight, permit detection and measurement of vertical displacements in a range of subcentimetre to millimetre and unprecedented ground range resolution. Such features open up new fields of application in civil engineering projects. Now many objects distributed over large areas may be monitored, typically on an object size scale of 2 to 20 m, with high measurement density and adequate accuracy. We present an application of this technique on a navigation lock that was constructed in a karst region where bedrock is locally dissolved by groundwater flow, occasionally leading to sinkholes, surface subsidence and displacement of structures. For that reason, the lock complex has been under terrestrial geodetic survey for several decades. This set of readily available geodetic data has been used to validate the processed satellite InSAR data, acquired by two satellites (ERS and Envisat) during the time period ranging from 1992 to 2010. Encouraged by good agreement of the geodetic and satellite measurements, in a second step TerraSAR-X data taken in SM mode has been processed to increase ground resolution. To assess further improvements in resolution the newly available TerraSAR-X High-Resolution Spotlight (HS) mode is investigated. It can be concluded that InSAR data (ERS and Envisat) reaching back to 1991/1992 may be used to gain information on subsidence effects like using a rear view mirror. However, significant limitations in resolution need to be taken into account. Comparing remotely sensed data using TerraSAR-X (SM) mode to in situ measurements of deformation, it is too early for a 1:1 validation of the very small deformation measured in situ based on 17 months of observation. Nevertheless, it can be stated that no conflicting measurements have been observed and that several areas associated with larger deformations were clearly detected. In our opinion, such approaches may improve the quality of site investigation by focusing further terrestrial geodetic and geotechnical monitoring on such pre-selected locations, especially for operational monitoring of civil engineering applications.

No abstract

In Dörverden musste die Schleppzugschleuse wegen zahlreicher Schäden durch einen Schleusenneubau ersetzt werden. In der Planungsphase wurden verschiedene Ausführungsvarianten unter wirtschaftlichen, technischen und betrieblichen Aspekten betrachtet. Nach intensiver Abwägung entschied sich die Wasser‐ und Schifffahrtsverwaltung des Bundes (WSV) für eine neuartige Bauweise: Die Baugrubenumschließung, bestehend aus einer überschnittenen und rückverankerten Bohrpfahlwand, wurde als statisch tragendes Element in das Schleusenbauwerk integriert. Um die üblichen Anforderungen wie Ebenheit und dauerhafte Dichtigkeit an die Kammerwandoberfläche zu erfüllen, wurde die Bohrpfahlwand mit einer Betonvorsatzschale kombiniert, die wiederum in die Bohrpfahlwand rückverankert wurde. Die Bauausführung erfolgte unter erhöhten Anforderungen an die Herstellungsqualität. Die Bundesanstalt für Wasserbau (BAW) hat die Bauausführung begleitet. Neben den üblichen Prüfungen wurden an ausgewählten Bohrpfahlgruppen zusätzlich modifizierte Crosshole‐Messungen veranlasst. Mit dieser Messmethode konnten neben den Sekundärpfählen auch die Primärpfähle sowie die Überschnittbereiche zerstörungsfrei geprüft werden. Der Inhalt dieses Beitrags ist in Teilen aus Saathoff et al. [1] entnommen. Dual use of a secant bored pile wall at the new lock of Dörverden: construction pit lining and chamber wall In Dörverden an old damaged lock needed to be replaced by a newly constructed lock. In the design phase various construction concepts were examined regarding economic, technical and practical aspects. After thorough consideration the Federal Waterway Administration decided in favour of an innovative construction concept: The construction pit lining consisting of a back‐tied secant bored pile wall was fully integrated into the chamber wall as a permanent load‐bearing element. The water‐facing part of the chamber wall was designed as a concrete shell. The concrete shell was affixed to the pile wall by bolts and is intended to secure essential practical properties and durability of the construction. During the construction phase enhanced requirements concerning quality standards were demanded. The Federal Waterways Engineering and Research Institute (Bundesanstalt für Wasserbau – BAW) ensured continued and coordinated implementation of these requirements. Additionally to routine tests modified cross‐hole measurements were performed at the bored pile wall. These non‐destructive measurements allowed to examine the quality of the primary as well as the secondary piles and in the region between two joining piles. The content of the paper is partly taken from Saathoff et al. [1]