A New Symmetrical Unit for Breakwater Armour: First Tests

A new and symmetrical single layer armour unit, the crablock, has been designed in the UAE. One breakwater was reconstructed with crablock, but very limited testing had been performed. Just to become more acquainted with this new unit, pre-competitive research at a university has been performed, which is the subject of this paper. Being a new...

Detection of Anomalies in Diaphragm Walls

If a calamity with a retaining wall occurs, the impact on surrounding buildings and infrastructure is at least an order of magnitude more severe than without the calamity. In 2005 and 2006 major leaks in the retaining walls of underground stations in Amsterdam and Rotterdam occurred. After these cases had been thoroughly studied it was concluded...

Concrete Flow in Diaphragm Wall Panels: A Full-Scale In-Situ Test

Flow processes, taking place during the concreting of diaphragm wall panels (D-wall panels), are of great importance for the quality of the wall. During this phase, the bentonite, present in the excavated trench, should be completely replaced by concrete in a controlled way. In literature several cases are described in which this process...

The Position of Geotechnical Engineering and Risk Management in Dutch Higher Education

As part of the Dutch national research program GeoImpuls an inventory has been made of the state of the education at Dutch institutes of higher education and post-graduate education in so far as this education concerns geotechncial engineering and geotechnical risk management. Significant differences have been found in the amount of time...

The impact of shallow cover on tunnelling in soft soil

On the effects of the TBM-shield body articulation on tunnelling in soft soil

When a Tunnel Boring Machine (TBM) is driven in soft soil, the TBM-shield constantly interacts with the surrounding soil profile excavated by the cutting wheel. The interaction pattern of shield-soil interface displacements determines compression and extension sectors in the surrounding soil. Soil compression is generated when the shield...

Tunnelling in Soft Soil: Tunnel Boring Machine Operation and Soil Response

Constructing tunnels in soft soil with the use of Tunnel Boring Machines may induce settlements including soil movements ahead of the face, soil relaxation into the tail void, possible heave due to grouting, long lasting consolidation processes, and potentially several other mechanisms. A considerable amount of the total soil displacements seems...

Criteria for face support of microtunneling TBMs

Face stability of microtunnelling TBMs is an important aspect for a safe and controlled project execution. Lack of proper face support can lead to sudden collapse with resulting large settlements. Guidelines for minimal and maximal support pressures in most codes do not take the infiltration of bentonite suspension in coarser soils into account....

Electrical resistivity method for the measurement of density changes near a probe

Urban Problems - Underground Solutions

Tunnel-boring in soft soil: A study on the driving forces applied to a slurry-shield TBM

Tunnel-boring in soft soil: A study on the driving forces applied to a slurry-shield TBM

Detecting defects in diaphragm walls prior to excavation

Recent incidents with leaking diaphragm walls during construction of subway lines in Amsterdam and Rotterdam (Netherlands) have led to reconsideration of the diaphragm wall as a retaining wall construction for deep excavations. In our opinion the joints between the panels are the weak spot. During concrete pouring the concrete should replace the...

Small incidents, big consequences. Leakage of a building pit causes major settlement of adjacent historical houses. Amsterdam North-South metro line project

The construction of the North-South metro line project in Amsterdam (the Netherlands) is ongoing for the last five years and until recently suffered no major construction incidents. In the summer of 2008 two leakages occurred in one of the building pits of the deep stations. These leakages caused major settlement of a number of historical houses...