The Ubzean Sfyrh

ASSIGNMENT ON

DRILLING AND PATTERN

GROUP MEMBERS:-

1.

NAME:                ANURAG BAJPAI

ROLL NO.:        10108EN018

COURSE:        BTECH     PART 2

2.

NAME:                AZHAR HUSSAIN

ROLL NO.:        10108EN047

COURSE:        BTECH PART 2

3.

Name:                PALLE RAVITEJ

ROLL NO.:        10108EN074

COURSE:        BTECH PART 2

DRILLING PATTERNS FOR BLASTING

Drilling pattern, also called shot hole patterns, are named after the type of cut holes used and the principle pattern. Various drilling patterns have been developed for blasting solid rock faces, such as:

i. Wedge cut or V cut

ii. Pyramid or diamond cut

iii. Drag cut

iv. Fan cut

v. Burn

Here we discuss only about wedge, pyramid and drag cut.

• Wedge cut:-

Wedge cut takes the form illustrated in fig. 1 in which two or four pairs are drilled to form a wedge, each pair starting from two sides of the drift centre and inclined at an angle less than 45° towards the centre almost meeting at the back of the cut along a line.

It is also named as V cut. In this type of drilling pattern, blast hole are drilled at an angle to the face in a uniform wedge formation so that the axis of symmetry is at the centre line of the face.

The cut displaces a wedge of rock out of the face in the initial blast and this wedge is widened to the full width of the drift in subsequent blasts, each blast being fired with detonators of suitable delay time.

The apex angle is as near as possible to 60°.

This type of cut is particularly suited to large size drifts, which have well laminated or fissured rocks. Hole placement should be carefully preplanned and the alignment of each hole should be accurately drilled.

• Pyramid or diamond cut:-

The pyramid or diamond cut is a variation of the wedge cut where the blast holes for the initial cavity may have a line of symmetry along horizontal axis as well as the vertical axis.

Pyramid cut consists in drilling holes (in the centre of the drift axis) at corners of square, 0.7 to 1m sides, almost to meet at a point at the back of the round. In a modified design known as cone cut, illustrated in fig.2, holes are drilled forming corner of a polygon with a centre holes, all nearly meeting at a point at the back of a cut. The depth of a pyramid cut is generally restricted to 50% to 60% of the width of the width of the drift.

• Drag cut:-

The drag cut is particularly suitable in small sectional drifts where a pull of up to 1 m is very useful. Drag cut used for small drifts, 1.8 to 2.4m wide, consists in drilling holes at an angle to the cleavage so that strata break along the cleavage planes (fig. 3). This pattern, being dependent on the direction of cleavage planes, calls for frequent changes, which are detrimental to systematic work and the pattern is, therefore, not favoured for large excavations.