Environmental Engineering Reference
In-Depth Information
Head losses
in the system should be accounted for in determining the value of
H
. Since
most head losses occur in the drop pipe, they can be minimized by using as large a diam-
eter pipe as practical. Head loss can be estimated from the relationship (Davis et al., 1970)
h
f
f
(
L
/
D
)(
v
2
/2
g
)
(3.10)
where
L
is the pipe length,
D
the pipe diameter,
v
the flow velocity,
g
the gravitational
acceleration and
f
the frictional component (obtained from charts for various pipe diame-
ters, materials, and discharges).
Lugeon Test
In the Lugeon test, used commonly in Europe, the hole is drilled to test depth and a packer
installed about 15 ft (5 m) from the bottom. Flow is measured after 5 or 20 min of test
under pressure, and the test is performed under several pressures. The standard meas-
urement of pressure is 10 kg/cm
2
and the results are given in Lugeon units.
Lugeon unit
is defined as a flow of 1
l
of water/min of borehole length at a pressure of 10
kg/cm
2
(1 Lugeon unit is about 10
5
cm/sec).
Disadvantages of Pressure Testing
Values can be misleading because high pressures cause erosion of fines from fractures as
well as deformation of the rock mass and closure of fractures (Serafin, 1969).
Additional References
Dick (1975) and Hoek and Bray (1977) provide additional information.
3.4
Rupture Strength
3.4.1
Introduction
Basic Definitions
Stress (
σ
)
is force
P
per unit of area, expressed as
●
σ
P
/
A
(3.11)
System
Equivalent units for stress
English
13.9 psi
2000 psf
2 ksf
1 tsf
1 bar
Metric
1 kg/cm
2
10 T/m
2
(
≈
1 tsf)
SI
100 kN/m
2
100 kPa
0.1 MPa (
≈
1 tsf)
Strain (
)
is change in length per unit of length caused by stress. It can occur as
compressive or tensile strain. Compressive and tensile strain are expressed as
ε
●
ε
∆
L
/
L
(3.12)
Shear
is the displacement of adjacent elements along a plane or curved surface.
●
Shear strain
(
ξ
) is the angle of displacement between elements during displace-
●
ment.
