Permanent sheet pile walls in complex soil conditions Surveillance, monitoring and safety

Abstract

Kvaernerbyen field F1, also known as Kvaernerdammen, is part of the Kvaernerbyen project in Oslo, Norway. Kvaernerdammen consists of a 7-storey residential complex on an underground parking floor. The south-eastern part of the building cuts into the lower part of a steep slope, with soil conditions consisting of dry crust above firm silty clay, followed by quick clay/sensitive clay above a thin moraine layer over bedrock. Due to existing buildings and constructions further up the slope, the allowable deformations of the building pit during and post construction of Kvaernerdammen had to kept within very tight thresholds. Since the summer of 2017, Cautus Geo AS and Multiconsult Norway AS have been cooperating in “research and development” (R&D) focusing on deformations of sheet pile walls (SPW) in complex ground conditions and all aspects connected to interaction between engineering, monitoring, alerting and safety. Starting with surveillance during the construction period, monitoring a permanent SPW supporting the mentioned slope at Kvaernerdammen, the R&D collaboration was continued between Cautus Geo and Multiconsult with continuous surveillance of the construction for almost 2 years after completion. Throughout the project, all phases of a critical SPW-construction have been evaluated, mainly focusing on the effects of seasonal variations in a “permanent” phase. Observations and experiences made during the project with a comprehensive database derived from geotechnical instrumentation have provided an unusually detailed documentation of the development of the construction after completion. The load cells connected to anchors in two rows on the SPW show a correlation between increasing temperature and increasing anchor force in a permanent phase, most likely due to a volume expansion of the structure. This is an opposite trend to what was observed during the construction phase, where increasing force is recorded in the load cells at decreasing temperature, especially at negative degrees Celsius. The temperature in the load cells is measured to oscillate between positive and negative degrees Celsius only during the construction phase. The load may tend to increase in the upper part of the SPW during heavy rainfall, but of negligible value. Based on a slight change in load and deformation during the permanent phase, the SPW is regarded as a stable and secure construction at Kværnerdammen. For future projects, it is important to be aware that load changes in anchors may be dependent on a well-functioning frost protection.