For A Rotary Drilling Rig, The Softer The Geology, The Better, Right?

For a rotary drilling rig, the softer the geology, the better, right?

It's just not quite right. 

What we know about geological strength,

In geological exploration reports,

 there are generally two ways to describe geological intensity:

Ultimate bearing capacity kPa and uniaxial compressive strength MPa.

Ultimate bearing capacity generally reflects loose and plastic geology.

Ultimate bearing capacity: the load strength of the foundation when shear failure occurs.

What about uniaxial compressive strength?

It is used to reflect the test strength of rock test block.

Uniaxial compressive strength: the ultimate load value of a rock specimen when it is damaged under unidirectional compression.

Uniaxial compressive strength is mostly saturated test, but there are also different types of freezing, drying and natural tests.

The value obtained by the saturation test is also known as the uniaxial saturation compressive strength.

Experienced drivers should know:

Rotary digging pile is too soft, because it is easy to collapse the hole and shrink the diameter.

It's too hard. No, because as the strength increases, it gets harder to drill.

But in terms of numbers, what are they?

For loose, plastic geology,

The most suitable hardness range for rotary digging is 150kPa-260kPa,

Within 800kPa, rotary drilling rig construction, basically no problems.

What about rock geology?

When it comes to rocks, we know that there are four weathering orders: fully weathered, strongly weathered, moderately weathered, and breezily weathered.

When the strength of the rock is fully weathered and strongly weathered, the ultimate bearing capacity unit kPa is also commonly used, and the maximum will not exceed 800.

To the medium weathering, the strength unit will generally use the uniaxial compressive strength MPa, the minimum will not be less than 20.

How does this interval correspond to uniaxial compressive strength?

Then, the most suitable rotary excavation construction is generally in full weathering, of course, strong weathering, there is no problem.

However, once strong weathering is reached, rotary drilling will produce a certain resistance, which affects the construction efficiency.

Of course, this is an absolutely idealized construction scenario that does not consider the influence of other external factors.