site investigation at an operational port

Challenge

Due to the large tidal range in Guernsey, the current marinas at St Peter Port and St Sampsons have limited access in and out of the marinas depending on the state of the tides. Therefore, the States of Guernsey were looking into the possibility to develop an all-tide access marina; the first in Guernsey.

As a busy operational port, the site itself presented some challenges. Within the ‘pool’ area of St Peters Port, there was over 5 km of mooring chains and anchor blocks that couldn’t be cleared for the site investigation and commercial marine traffic limited access at certain times.

The States of Guernsey also had a strict completion date for fieldworks due to the fixed seasonal operational window for the harbour, when visitors would start to arrive and use the current facilities, so we had to be extremely efficient on site.

Solution

To minimise disruption for the Port, our approach to fieldwork planning was to work within the intertidal environment, carefully scheduling vessel moves with weather, tides and marine traffic. Our solutions and services included:

• Carefully planned operations taking account of tides to get access to shallow and deeper water locations

• Adapting the scope of works, drilling depths and testing to suit the geology of the harbour

• Live data delivered through our cloud-based data-sharing platform VirGeo®

• Utilising sonic drilling, which was better equipped for the site conditions, instead of planned cable percussion drilling

Project deliverables:

• 12 percussive boreholes (we undertook these as sonic drilling, replacing the cable percussive element)

• 10 vibrocores to a depth of up to 6 m (VC 01 - VC 08). These were undertaken as sonic boreholes as it was more suitable for the site

• Geotechnical and geo-environmental laboratory testing

• Factual report production with summary of data and findings

• Removal of mooring buoys and reinstatement and repair of mooring chains

Innovative Highlight

Sonic drilling

Part of the scope of work initially involved using vibrocore for the drilling requirement however, prior to arriving on site, we realised the ground conditions were not suitable for vibrocore operations or manoeuvring a vessel within the busy harbour. To provide the States of Guernsey with a swift solution and maximum recovery of ground data, we advised using sonic boreholes instead.

Sonic drilling can offer better recovery and quality of data and only requires one rig, rather than needing to change drills, so the process is much more efficient. Utilising our new sonic drilling rig, we completed 10 boreholes in replacement of the vibrocore requirement which were much better suited for the environment. A first for Fugro and our client.

Impact

• Minimal disruption to port operations as the SI was completed within the limited timeframe

• Avoided potential delays due to swift adaption of sonic drilling technology for data acquisition

• Maximised programme efficiency and access using on-site jack-up barge

• Reduced risk to the port environment with planned operations for buoy clearance and maintenance of mooring chains

• Strong local community engagement with a positive impact – our project manager delivered a presentation at two ‘sold out’ events for the local engineering community and local stakeholders on how the works were being carried out and why. This resulted in coverage in a local publication and greater co-operation and support from the community.