Why Site Investigation Matters

28th August 2019

The Institution of Civil Engineers quote “land without site investigation is a hazard”. In the 21st Century, it seems almost inconceivable not to appropriately assess what is below the ground prior to development (or is it?). Above all, safe design of housing, commercial and industrial buildings, roads, and bridges can only by achieved by site investigation. Key questions – what is beneath the ground? Is it a hazard? How can the risks be avoided?

Northpoint explore some famous examples of failures; which would have benefited from adequate site investigation.

1.Tower of Pisa, Italy

The structure is known across the world as the “Leaning Tower of Pisa”. In hindsight, early architects could have benefited from a geotechnical professional. With this in mind, a question – how many geotechnical engineers were available in the 12th to 14th Centuries?

Currently standing approximately 56m tall, and weighing 14,500 tonnes, this monster structure is imposing huge loads into the earth. Other than the famous “tilt”, the level of settlement from when the Tower was originally constructed to today is in the magnitude of 4000mm! By today’s standards, long term settlement >50mm is considered unacceptable.

The reason for the settlement? A shallow “soft-spot” in the ground on one side of the structure.

2. Millennium Tower, San Francisco

In contract to the Tower of Pisa, the Millennium Tower in San Francisco is of 21st Century construction. This ‘skyscraper’ is a mere 58 floors. Only a few years ago following construction, the structure started to settle and tilt. Investigations and monitoring have shown that this relatively new structure has settled (sunk) into the ground by approximately 400mm. Most noteworthy, if the structure is allowed to stand for a few hundred years, the tilt and degrees of settlement may out-do its Italian neighbour – a new global tourist attraction perhaps?

Consequently, with todays standards and design codes, how did this example go so wrong? In summary, investigations have shown that inadequate foundation design is responsible.

It is suggested that pile foundations should have extended deep into solid rock. Instead, the pile foundations were designed to sit within the dense sand deposits above.

Whilst the above examples are extreme and focus on significant structures, adequate site investigation at any level (for housing, roads and commerce) is essential, and should never be dismissed regardless of the size and scale of a development. Consequently, subsidence and failure of structures due to poor and hazardous ground (even with stringent and robust codes of practice) is still relevant across the UK, and this is inevitably due to substandard investigation and interpretation of data to inform recommendations.

Northpoint’s team of professional earth science specialists can assist you with your project requirements. Ultimately, Northpoint provide innovative and cost affective solutions to the safe management of hazardous ground.