Course

In this section, we will take a brief look at the Phase 1 Desk study. This forms the basis of all modern ground investigations in the UK.

Figure 2: A photograph of a site in Launceston, Cornwall - showing heavy vegetation and steep slopes

Site walkovers are an essential part of the desk-based investigation. Just look at our Launceston example, bet looking at a piece of paper couldn't have prepared you for this!

The site was difficult access, overgrown and steeply sloping, a challenge to get diggers and plant into, to say the least.

The Site Walkover can help us identify a number of things we need to know, before we break ground.

• Site Access - can we get in! We may need to get into the site with heavy machinery such as excavator and tractor, or drilling rigs.
• Any obvious features - such as quarries, obvious wet saturated land, even mine shafts.
• Signs of former land use - if the site was once used in industry, are there obvious signs of contamination such as barrels or oil spills?

Figure 3: A view into a freshly excavated Trial Pit.

In very simple terms we need to investigate the ground, sounds obvious, but we are looking for more than just rocks and soils.

Figure 4: Photograph of the soils excavated from the trial pit, these 'Arisings' give us material to look at and handle in detail.

Figure 5: A house severely affected by poor ground conditions

This building had either no or inadequate ground investigation. The consequences being serious for the structures and but worse for the owners who have to deal with the heartache of losing their precious homes.

Although this seems fairly serious, the consequences can be more dire than this and can even result in deaths.

Figure 6: View of a trial pit under excavation

The trial pit is the simplest and usually quickest way of obtaining information on the near surface. It is generally cheap too, compared to other methods. All you need is a suitable digger and experience!

It does have it's limitations including:

• Generally cannot extend beyond 5m
• only suitable in stable ground
• causes much disturbance to the ground
• can be very messy

Figure 7: A Dynamic Sampling rig, set up and ready to drill

Also called Dynamic Sampling or Windowless Sampling and colloquially window sampling. These boreholes are quick and relatively low cost to install. the rigs are small and can get to places other plant cannot. They are ideal for remote locations and tight spaces. As you can probably imagine they also have limitations.

• only suitable for smooth drilling conditions, any obstructions or strong ground will stop them
• can only drill to a limited depth, usually around 8-10m
• cant see a representation of the ground like a trial pit, only recovers small cores.

Figure 8: A Dynamic Sampling rig 'on the move' tracking from one location to another