Engineering Rock Mechanics

Questions and answers: fractures and hemispherical projection 1 05

This equation cannot be solved explicitly, and so we use trial-and-
error. The result is w = 6.296, from which, using h = 1.22 m-*, we obtain
x = 5.16 m. This is a substantial increase on the previous length of 3 m.

47.4 A fault plane with orientation 234/56 has been discovered
during a site investigation. Closer inspection shows that it has sur-
face lineations which have a pitch of 78O measured from the north-
west strike line. What is the trend and plunge of these lineations?

A7.4 The illustration below shows the final tracing paper diagram
obtained when answering this question. The steps followed in its con-
struction are given as follows.

for the fault plane. Rotate the tick

mark to the east-west line, count

in 56" and mark a cross for the

line of maximum dip. Draw the

great circle corresponding to the

fault plane. Rotate the tracing pa-

per back to north.

(2) The pitch of the lineation

is measured from the northwest 255/54

strike line. Rotate the tracing pa-

per so that the northwest end of 23

the great circle is north. Measure

the pitch of the lineation (i.e. 78")

along the great circle, using the small circles as a scale and mark a cross

on the great circle; this represents the orientation of the lineation.

(3) Rotate the tracing paper so that the lineation is on the east-west

line, mark a tick on the periphery opposite this, read off and mark next

to the tick the plunge of the lineation; it is 54".

(4) Rotate the tracing paper to north, and read off the trend of the lin-

eation; it is 255". The orientation of the lineation (given as trend/plunge)

is therefore 255/54.

(1) Plot and label a tick mark N

47.5 The line of intersection between two planes trends approxim-

ately northwest and plunges at 38O. The orientation of one of the

planes is 256/50, and the strike of the other is 132O. What is the

trend of the line of intersection and what is the dip of the second

plane?

AIS The illustration below shows the final tracing paper diagram

obtained when answering this question. The steps followed in its con-

struction are given as follows.

(1) Plot and label tick marks for the maximum dip of plane 1 and the

strike of plane 2. Rotate the tick mark for plane 1 to the east-west line,

count in 50" and mark a cross for the line of maximum dip. Draw the

great circle corresponding to plane 1, and rotate the tracing paper back

to north.