Monitoring of Slope Deformation and Groundwater during Construction of the Lauenburg Lock

The Lauenburg Lock is located next to a highway and a 40 m high slope with homes on top. Prior to the construction of a replacement lock, a monitoring system including 4 inclinometers, 8 extensometers and 11 groundwater monitoring points was installed. All data are processed and real time available in an online monitoring system. It was observed that there are natural deformations in the slope and changes in the groundwater head before the construction started. Both are dependent on meteorological conditions. During groundworks unexpected peaks in the groundwater monitoring points were observed. At the same time, the slope deformation did not produce any exceptional readings. An elevation of the groundwaterhead of up to 2 m was observed during trenching of the slurry wall. Over night it decreased to normal level and was found to be uncritical. Later one trench collapsed. Additional temporary groundwater monitoring points were installed close to the slurry wall. The readings showed peaks in the water head of up to 4.5 m, which were an explanation for the collapse. To enable further works to be carried out, vacuum drains were installed to temporarily lower the water head close to the actual works. The water pressure was effectively reduced and trenching could be carried out without any further problems.