Ground investigation

Ground investigations: Identifying the unknown ahead

Horizontal Directional Coring

Successful project execution relies on the quality of information provided to clients, consultants, contractors and subcontractors and the information is needed as early as possible in the construction process. This is crucial for projects with high loading (such as high-rise towers) and also for tunneling schemes facing extremely difficult ground conditions, such as changing faces and faults that will be encountered along the route.

It is therefore of vital importance to know in advance the ground conditions ahead and, more importantly, the locations of faults, groundwater and large fissures with soft infill materials. This information dictates the choice of methods, which in turn defines the programme, the resources needed and the costs.

Sub-horizontal directional coring: new technologies for ground investigations

Traditional investigation methods provide only a few sets of localised information along the tunnel path, which may prove to be insufficient once tunnel excavation is under way. Traditional investigation methods provide only a few sets of localised information along the tunnel path, which may prove to be insufficient once tunnel excavation is under way.

In its quest to push the limits of construction, INTRAFOR undertook some years ago to go beyond the traditional soil investigations carried out vertically (or sometimes inclined) from ground level. INTRAFOR has already become a renowned expert in this field and has gone on to develop and successfully complete projects using sub-horizontal directional coring along the planned routes of tunnels. It has used this technique to achieve directional sub-horizontal coring lengths of more than 1,100m along the routes of tunnels.

This technique provides continuous, high quality information required to improve the safety and success of tunnels construction in complex ground conditions:

• Geological conditions are known along the whole tunnel route before the excavation process starts;
• No section of the tunnels is left unknown: traditional vertical ground investigations at specific spacing give very limited actual data which is extrapolated to give a geotechnical profile (with large margins of error);
• Problems can be anticipated and appropriate solutions developed before the difficult geological areas are reached;
• The amount of coring is minimised by targeting the exact tunnel route rather than carrying out the unnecessary boring usually required just to reach the tunnel section if the ground investigation is done from ground level.

INTRAFOR is one of the world’s leading specialists in this innovative ground investigation technique.

Among the company's references:

• Integrated Gas Development DAS Island, offshore Abu Dhabi, UAE
• Eagle Nest Tunnel, Hong Kong
• Harbour Area Treatment Scheme, Hong Kong
• Tsuen Wan Drainage Tunnel, Hong Kong

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