When foundations are drilled into weak soil, especially when they are drilled into waterbeds, borehole stability becomes a much more serious consideration for piling companies. This is due to the fact that boreholes in these types of conditions are considerably weaker than in other soil types.
For these applications contractors require drilling fluid or slurry. These are required for a number of reasons. Firstly, they cool the bore hole’s rising temperatures brought about by friction from the machinery; secondly, they lubricate the hole and the drill bit to prevent overheating; and thirdly, it helps clean the hole. These are the main uses for slurry, but it is also useful in holding the boring hole open, stabilising the hole from collapse, controlling fluid loss and controlling the sub-surface pressure.
The same drilling fluid won’t be successful for every piling application or every soil type. Understanding drilling fluids and slurries is important in increasing the amount of success contractors will have across varying sites.
How does a drilling fluid create borehole stability?
Drilling fluids utilise overlapping platelets to form a barrier between the soil and the drilling fluid which is referred to as filter-cake. We can measure how effective each drilling fluid is via the amount of fluid that is allowed to pass through this barrier. There are also polymer slurries which create a polymer gel membrane barrier between soil and slurry.
Further hole stability is provided via positive pressure applied evenly against the barrier between the drilling fluid and formation. This pressure is obtained by use of a hydrostatic head; the pressure is similar to that of any vacuum-packed product where atmospheric pressure is applied evenly against the wrapper, making the content feel as though they are packed in tightly.
With the proper drilling fluid or slurry in place, boreholes can be made structurally sound for piling to be implemented.
For more information on piling in Manchester, contact the team at Rhino Piling today.
