Acta Montanistica Slovaca
Ročník 19(2014), číslo 3, 111-117
Impact of mining exploitation on pipelines
Piotr Kalisz1 and Magdalena Zięba2
Article describes the issues related to the impact of underground mining exploitation on pipelines in Poland. For this purpose there
was conducted the impact analysis of horizontal strains, curvatures and tilt changes of the surface on loads and displacements of these
objects. Ground deformations can cause pipelines failures and thereby reduce their reliability. In addition, the examples of typical failures of
sewage system, water and gas supply systems in mining areas were presented.
Key words: pipelines, failures, mining areas
Introduction
The aim of the article is to present the issues concerning the impact of underground mining exploitation on
pipelines in the Upper Silesian Coal Basin in Poland. Mining exploitation causes deformations of soil layer
adjacent to the surface in which pipelines are buried. Hence these objects are subjected to additional loads and
displacements. This impact causes pipelines failures which can reduce their reliability. Sometimes it can be
important for the safety of surface users and also cause environmental hazards. Therefore, the problems related
to pipelines protection, their control during the occurring of mining exploitation impact and failures repair are
important issues in the surface protection in mining areas.
General characteristic of pipelines
Pipelines in longitudinal direction can be divided into continuous and segmental construction taking into
consideration the impact of mining ground deformations. Continuous pipelines are built of pipes with welded
joints which occur primarily in water and gas supply systems. Segmental pipelines are built of short pipes with
lengths typically up to several meters and gasket joints. These pipes are used in water supply systems (cast iron,
PVC - polyvinyl chloride, GRP - Glass Reinforced Plastic) and sewage systems (plastics, stoneware, concrete
and reinforced concrete). Such pipelines can also consist of pipe segments and compensators installed between
them and they occur in steel water and gas supply systems located in mining areas.
Pipelines can be divided into flexible (deformable) which are mainly made of plastic and low flexible (low
deformable) taking into consideration the interaction between these objects and subsoil. It concerns longitudinal
and transverse direction of pipelines.
Water supply systems are usually made of steel, plastics (polyethylene - PE80 and PE100) and also cast
iron pipes. To a lesser extent these pipelines are made of plastics such as polyester resins reinforced with glass
fibres (GRP) or polyvinyl chloride. Older water supply systems are rarely constructed of reinforced concrete,
prestressed concrete and asbestos cement pipes.
Gas supply systems are built of steel and plastics pipes. For the construction of low and medium pressure
gas pipelines in Poland is permitted to use polyethylene pipes - PE80 and PE100, and for higher medium
pressure gas pipelines with nominal pressure up to 1,0 MPa - PE100 [1]. Gas pipelines with pressure higher than
1,0 MPa are built exclusively of steel pipes.
Sewage systems are usually constructed of pipes with length from 1 m to 6 m. These pipes are mostly made
of stoneware, concrete or reinforced concrete and plastics (such as polyvinyl chloride, polyethylene,
polypropylene with full or structural walls and polyester resins). Cast iron is rarely used for the construction of
these systems. In recent years the share of plastics has increased, because pipes made of these materials are
currently the most widely used for the construction of new and the reconstruction of damaged sewage systems.
Pipes used for the construction of sewage systems have mostly circular cross-section and socket joints
(stoneware, concrete and reinforced concrete, cast iron, plastics), overlap or butt joints (concrete and reinforced
concrete) and sleeve joints (plastics, stoneware jacking pipes).
1
2
Ing. Piotr Kalisz, PhD, Główny Instytut Górnictwa (Central Mining Institute), Zakład Ochrony Powierzchni i Obiektów Budowlanych
(Department of Surface and Structures Protection), Plac Gwarków 1, 40-166 Katowice, Polska, pkalisz@gig.eu
Ing. Magdalena Zięba, Msc, Główny Instytut Górnictwa (Central Mining Institute), Zakład Ochrony Powierzchni i Obiektów
Budowlanych (Department of Surface and Structures Protection), Plac Gwarków 1, 40-166 Katowice, Polska, mzieba@gig.eu
111
Piotr Kalisz and Magdalena Zięba: Impact of mining exploitation on pipelines
Impact of mining ground deformations on pipelines
Impact of continuous mining deformations of soil layer adjacent to the surface on pipelines is considered in
two specific directions: parallel and perpendicular to their longitudinal axis as schematically shown in Fig. 1.
Oblique direction of this impact is a combination of these two directions.
Horizontal strains cause changes in earth pressure on pipes walls in their cross-section direction. In the case
of soil loosening their values decrease (Fig. 1b) and during soil thickening their values increase (Fig. 1c).
The additional axial forces (tensile and compressive) occur in longitudinal direction of pipelines, especially with
continuous constructions. In the case of segmental pipelines occur pipes displacements which are compensate in
joints or compensators (Fig. 1).
b) εmax
a) ε = 0
c) εmin
d) ε = 0
transverse
direction
longitudinal
direction
segmental construction of pipeline
continuous construction of pipeline
Β
Fig. 1. Impact of underground mining exploitation on pipelines.
Dynamic impacts of underground exploitation are also important in pipelines protection in mining areas.
They cause additional loads in the form of increased stresses as well as additional transverse and longitudinal
displacements of pipes. Mining tremors in unfavourable loads conditions of pipelines subjected to continuous
mining deformations can lead to additional failures [2]. It especially concerns pipes made of brittle materials
such as stoneware, concrete and grey cast iron. In most cases, the values of soil deformations caused by mining
tremors are much smaller than these resulting from the continuous impacts of mining exploitation [9].
Sometimes local failures of pipelines are caused by discontinuous deformations occurring in the form of fissures,
thresholds and sinkholes.
Longitudinal direction of pipelines
In determining the values of longitudinal forces N, occurring in segmental and continuous pipelines, it must
be considered tangential forces caused by the soil friction on the surface of pipelines and forces connected with
the anchorage of pipeline elements such as sockets and fittings
N = Nt + Nk =
Nk + τgl
2
(1)
where: Nt
Nk
τg
–
–
–
longitudinal force caused by soil friction on the outer surface of pipes,
longitudinal force caused by anchorage of pipeline elements such as compensators,
unitary tangential force caused by soil friction τ g = σ n f or its shearing,
σn
f
l
–
–
–
soil pressure on the side surface of pipeline,
coefficient of soil friction on the side surface of pipeline,
length of considered segment.
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Acta Montanistica Slovaca
Ročník 19(2014), číslo 3, 111-117
Limit values of tangential forces must also be taken into account in determining the forces and maximum
lengths of segments between compensators [7]. In the case of flexible pipelines, made of polyethylene or
polypropylene and joined by butt welding, electric resistance welding or extrusion welding, compensation
changes in lengths follow by their deformations. Deformations of such pipelines in mining areas are almost equal
along their entire length to the soil layer deformations. Range of permissible deformations for these materials is
not generally higher than horizontal strains of soil layer adjacent to the surface in mining areas of categories
0 ÷ V which permissible values are shown in Tab. 1.
Tab. 1. Categories of mining areas with the values of horizontal strains and radii of curvatures (in Poland).
Values of horizontal strains
Values of radii of curvatures
Category
R [km]
of mining area
ε [mm/m]
0
⏐ε⏐≤ 0,3
⏐R⏐ ≥ 40
I
0,3 < ⏐ε⏐ ≤ 1,5
40 > ⏐R⏐ ≥ 20
II
1,5 < ⏐ε⏐ ≤ 3
20 > ⏐R⏐ ≥ 12
III
3 < ⏐ε⏐ ≤ 6
12 > ⏐R⏐ ≥ 6
IV
6 < ⏐ε⏐ ≤ 9
6 > ⏐R⏐ ≥ 4
V
⏐ε⏐ > 9
⏐R⏐ < 4
Horizontal strains of soil layer adjacent to the surface induce bending moments in the vicinity of pipelines
bends and branches which can cause the exceeding of load capacity and their failures. Bending moments are also
caused by the ground curvatures [11] which are primarily important in the case of pipelines with larger diameters
(over 600 mm).
Horizontal strains of soil layer adjacent to the surface in the longitudinal direction of pipelines with socket
and sleeve joints or compensators cause the displacements of individual pipes what can lead to the loss of their
tightness. To avoid the unfavourable effects of mining exploitations, joints and compensators should have some
possibility for overtaking the length changes of pipelines in appropriate range. Deformation indicators are
characterized by a large random dispersion and therefore their absolute values in mining area can be much higher
than predicted ones. Extreme values of ground layer deformations that can impact with a certain probability on
pipeline segment with a length l, assuming a normal distribution, can be determined by the formula [10, 13]
ε ekstr = ε[1 + nM (l )]
where:
ε
n
(2)
– value of predicted extreme horizontal strains,
– factor which depends on the probability that the extreme values are not exceeded, for
probability 0,95 it equals n = 1,645,
M (l ) – variation coefficient, M (l ) =
M (l ) = M (l 0 )
s
, according to Batkiewicz [10, 13]
ε
l0
,
l
s
– standard deviation of deformation indicator,
M(l0) – variation coefficient of strains for standard measuring base,
– length of standard measuring base, usually 25 m.
l0
Variation coefficients of horizontal strains were defined for standard measuring bases on the basis of carried
out statistical analyses of measurement results of horizontal strains ε for loosening and thickening of soil. These
analyses were carried out in Polish deep mines of coal and copper ore. These variation coefficients are
respectively equal to M (l 0 ) r = 0,2 and M (l 0 ) z = 0,3 according to [13] and M (l 0 ) z = 0,26 from the
studies of [14]. Minimum length ∆l of joints and compensators with respect to random dispersion of horizontal
strains ε and appropriate probability of their reliable work can be determined by the formula [5]
∆l ≥ 2εl[1 + n
M (l0 ) 2r + M (l 0 ) 2z
2
l0
]
l
(3)
where l is the length of considered pipe segment.
Transverse direction of pipelines
Horizontal strains of rock mass layer adjacent to the surface play also central role in the impact of
underground mining exploitation in transverse direction to the longitudinal axis of pipeline. These strains cause
changes in earth pressure on pipes [5, 8] what lead to additional bending moments and circumferential forces
113
Piotr Kalisz and Magdalena Zięba: Impact of mining exploitation on pipelines
acting on their walls. Soil loosening causes the reduction of earth pressure on pipe walls and in non-cohesive soil
layer occurs almost immediately active limit state (Fig. 1b). Soil thickening causes the significant increase in
earth pressure on pipe walls (Fig. 1c) and it is more unfavourable than soil loosening in the case of mining
deformations which correspond to III and IV category of mining area (Table 1). The greater the value of soil
strains, the greater pressure.
Changes of transverse loads in the case of flexible pipes can also cause the excessive deflections of their
cross-sections. The state of soil strains around the cross-sections of pipelines is shown in Fig. 2 where a dash line
presents the state of soil strains around the flexible pipe.
Fig. 2. Distribution of horizontal strains around the cross-sections of pipelines.
In the zone directly adjacent to pipeline with low flexible walls occurs the concentration of soil strains
which can be characterized by a factor k0 ≥ 1,0. In the zone directly adjacent to pipelines with flexible crosssections the values of strains are smaller, because their walls move under the soil pressure. Coefficient k0 can be
determined by the formula
k0 =
n1 + 1 − 2α1
n1 -1
(4)
where:
multiple of pipe diameter d, according to Fig. 2,
n1 –
deflection of pipe cross-section per the unit of soil strain, coefficient dependent on the
α1 –
flexibility of pipe cross-section, for rigid pipes α1 = 0 [5, 6], for pipes with a very high flexibility α1 = 2.
Knowing the value of strains for soil thickening near pipelines walls it can be calculated the increased value
of loads which impact on them [5]:
σ 22 = σ 220 + ∆σ 22 = ξ 0 σ 11 + ∆σ 22
(5)
∆σ 22
where: ξ −
ξz –
ξ0 −
(6)
lateral earth pressure coefficient,
passive earth pressure coefficient,
at rest earth pressure coefficient,
−
critical strain during the soil thickening; above this value of strain occurs passive pressure, for
m
–
non-cohesive ground it equals 31 mm/m [8],
experimental coefficient, for non-cohesive soil it can be assumed m = 3,1 [8],
σ11
–
vertical load, σ11 =γz0 + pn ,
γ
z0
pn
–
–
–
unit weight of soil,
depth of buried pipeline,
surcharge load.
ε
114
⎡ ⎛ k ε ⎞m ⎤
= (ξ z − ξ 0 )⎢1 - ⎜⎜1 − 0z ⎟⎟ ⎥ σ 11
ε kr ⎠ ⎥
⎢⎣ ⎝
⎦
z
kr
Ročníkk 19(2014), číslo 3, 111-117
Acta Montanistica Slovaca
S
Failures of pipelines in mining
m
areas
Watter supply pip
pelines
Impaact of mining exploitation causes
c
mostlyy the failures in
n steel water supply
s
pipelinnes and to a much
m
lesser
extent in plastic ones which
w
are geneerally much younger.
b mining expploitation leadd to stresses increase
i
in walls of steel ppipes what caauses their
Forcces induced by
strength exceed. In adddition, occurrs walls deforrmation and it
i is also a faactor which inntensifies the corrosion
processess of steel pipeelines [4]. In extreme cases, in the zonees where pipeelines are subjjected to tensile forces,
occur thee cracks of theeir walls. In thhe zones wheree pipelines aree subjected to compressive forces occur frequently
f
the deforrmations and folds
f
of their walls. Crackss of tensioned
d pipelines aree noticed alm
most immediateely due to
the loss of
o their tightnness. Unfortunnately, deform
mations of com
mpressed pipeelines may bee not noticed for a long
time. Zonnes where occcur bends annd walls defoormations of steel pipelinees are more vvulnerable to corrosion
processess. In these zonnes occur the structure channges of materrial (microcraccks and plastiicization of material)
m
as
well as the
t failures of
o insulating coats. The results
r
are th
he occurrence of acceleratted corrosion and pits,
eventually the holes inn pipelines waalls. The exam
mple of abov
ve-mentioned failures of steeel pipelines in mining
3
areas is shhown in Fig 3.
Fig. 3. Damageed section of steell pipeline Ø100 - folding of wall, damaged
d
insulatiion, corrosion pitts and holes [15].
werage pipelin
nes
Sew
The results of minning exploitattion impact onn sewerage pip
pelines are the constructionn failures of sewers and
o their tightnness as well as
a their unfavvourable slopees changes. Failures of sew
wage systems are often
the loss of
detected after a long time
t
since their occurrence. In many arreas they repeat by years causing a thrreat to the
ment, because it is connecteed with the seewage outflow
w into the groound. Leaks can also be thee cause of
environm
supplyingg the sanitary sewage systeem with rainw
water and grou
undwater. Unnfavourable chhanges in sew
wers slopes
contributee to problemss with sewage and rainwater outflow and
d their backwaater. The adjusstment of sew
wers slopes
is possiblle through theeir complete rebuilding
r
whhich is often ju
ustified only after the end of mining exp
ploitation.
Example of the coursee of sewers sloopes within thhe Gliwicka Street
S
in Katow
wice after thee long period of mining
p
in Fig.
F 4.
exploitatiion impact is presented
264,50
264,1
264,02
263,86
Datum of the bottom of sewer manhole, m a.s.l.
264,001 264,05
264,01 263,9
263,98
264,03
264,00
263,75
263,50
263,6
263,58
2
263,56
263,41
263,26
263,18
263,13
263,00
263,01
262,83
262,95
2
262,83
262,63
262,56
262,50
262,6
62,68
26
262,47
262,58
262,37
262,32
262,3
262,45
262,18
262,066
262,00
2622,1
262,01
261,98
261,92
261,7
261,65
261,50
261,61
261,55
261,55
261,4
261,00
0
0,0
250,0
500,0
750,0
1000,0
1250,0
15000,0
1750,0
2000,0
2250,0
Distance, m
Fig. 4. Course
C
of sewers slopes within Glliwicka Street in K
Katowice.
115
Piotr Kalisz and Magdalena Zięba: Impact of mining exploitation on pipelines
Above-mentioned damage occurred in stoneware and concrete sewers of sewage system in the centre of
Katowice (Fig. 5). This system was mostly built in the years 1907-1935 without any protection to the impact of
mining exploitation.
Fig. 5. Damage of stoneware sewer [12].
Gas supply pipelines
Failures of gas supply pipelines in mining areas are mainly connected with these which are made of steel.
The most common failures in these systems are damaged compensators resulting from the ware of sealants [3].
Gas leak is rarely caused by the exhaustion of their compensation ability. The results of tensile forces are cracks
of welds which also takes place in connection with gas pipeline branches. In the area of compressive horizontal
strains of soil occur the walls deformations of steel pipelines which often lead to the loss of their tightness due to
corrosion. Significant deformations of these pipelines are also observed on branches and in bend zones because
of the influence of additional axial forces and bending moments.
In the compression zone exist also bucklings of gas pipelines which are usually bent toward the surface and
even pushed up above it. This mainly applies to polyethylene gas pipelines and also steel ones with small
diameters. In the case of polyethylene gas supply systems the closure of pipelines cross-sections and the loss of
their flow capacity occur as shown in Fig. 6. However, polyethylene gas pipelines rarely are damaged and
nowadays they are widely used for the construction of low and medium pressure gas supply systems in mining
areas.
Fig. 6. Deformation of medium pressure gas supply pipeline PE Ø160 [3,15]
116
Acta Montanistica Slovaca
Ročník 19(2014), číslo 3, 111-117
Conclusions
Impact of underground mining exploitation causes changes in primary conditions of pipelines foundation in
the soil layer adjacent to the surface. Ground deformations cause additional loads and displacements of these
objects which must be taken into account during their designing, protection and also resistance assessment in
mining areas. Therefore, in mining areas there should be used properly prepared pipes for pipelines constructions
and also appropriate design solutions that enable to transfer soil deformations. This will allow the safe working
of utility networks with the maintenance of proper reliability level.
The presented examples of utility networks failures concern mainly old and unprotected pipelines to the
impact of mining exploitations as in the case of above-mentioned sewage system in Katowice. In sewerage occur
adverse changes in slopes which should be considered during designing. In the case of existing networks with
incorrect slopes it is required their reconstruction but sometimes the sufficient solution is to build sewage
pumping station. The greatest failures occur in older steel water and gas supply pipelines, including those
equipped with compensators. The compensators are often the places of leak, but without them it would be
impossible the functioning of steel pipelines in mining areas as they protect them from serious failures. Water
and gas supply systems made of polyethylene pipes are rarely damaged.
To guarantee the appropriate level of utility networks reliability in mining areas is also needed the control
of occurring mining influence on the surface. For maintenance of networks usability and safety of surface users
it is important the fast detection and repair of failures what is also connected with easy access to pipelines. It
should be taken into account during resistance assessing of pipelines to the impact of mining exploitations.
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