Drill Rig stability is the rig capacity, which it would not turn over or lateral sliding during tramming and drilling. Rig stability does not only affect drills’ safety when drilling or tramming, it also influence the  drilling productivity click here and operator’s heath.

Drill rig’s performance is based on its stability, therefore, it is key for rig to perform very well. By stability Calculation, it can check rig overall configuration and layout as well as dimension of main component.

Meanwhile, it helps to confirm the maximum gradeability of tramming and feeding pressure when drilling

Drilling stability

As shown in picture, during borehole drilling, following force applied to rig: Feeding force P, Drilling Rig weight G, Jack cylinder reaction force Ra and Rb

There are two load case for drilling a) vertical borehole drilling; b) inclined borehole drilling

a) Vertical borehole drilling

If feeding force is excessive, the reaction force from feeding can make rig off ground via drilling bit go there and drill rod( Two front jack cylinder off ground) It become three point support and along with continuously drilling, the rig will turn over at two back jack cylinder as axis.

At this moment, RB =0, the balance formula is: Ga=bPcosβ

So the maximum allowable feeding force P= Ga/bcosβ

G: rig weight

a,b: distance from line of two back cylinder to borehole center and rig gravity center

The feeding force is balanced by rig weight, therefore, it equal to part of drill rig’s weight. Due to the borehole drilling position and drill gravity center is fixed when rig is designed, its maximum feeding force is fixed as well.

Taking weight factor Kz, feeding pressure P and rig weight G,

Kz = P/G, it is one of index of drilling machine stability

b) Inclined Borehole Drilling

Due to excessive feeding force, front Jack stand off ground, drill rig www. move horizontally by horizontal force from feeding force.

Jack stand reaction force Ra = G – N = G – Pcosβ

T = Psinβ

When T > Pt (horizontal component force of Ra ) Pt=PXt

t: adhesion coefficient, wet road t = 1.0 – 1.1; dry road t = 0.9 – 1.0;

Snow road t = 0.4 – 0.6; sandy road t = 0.4 – 0.6; mud road t = 0.4 – 0.6; on mine t = 0.4 – 1.1

Therefore balance formula T<Pt

Psinβ < (G – Pcosβ)t

So weight factor Kzz = P/G< t/(tcosβ + sinβ),

Now we can see that position of back two jack cylinder can influence stability very much, but front two jack cylinder’s position has nothing to do with rig stability due to they are off ground during drilling

Tramming Stability

Tramming stability is capacity of drill rig’s anti turning over during tramming

Stability angle and stability factor K will be index for tramming stability shown as in blow diagram












K=Mw / Mq

α, β are stability angle

Four load case for travelling stability calculation:

a) Mast erected – Tramming on even road

b) Mast erected – Tramming on slope

c) Mast lay down – Tramming on even road

d) Mast lay down – Tramming on slope

See picture in below,

But when tramming for long distance, the mast should be laid down to get best stability

Lateral stability

Lateral stability is the capacity of anti turning over when rig on slope laterally

tgγL= (0.5B – e)/h

E: Distance from center line of rig to gravity center

B: Distance between each track

H: Height of gravity center





Conclusion: taking the worst one among all the drilling rig see DTH(Down The Hole) Drilling Application

stability index as final one

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