Numerical investigation on the tunneling and mining induced geo-hazards: Case study in Quang Ninh, Vietnam

Journal of Science and Technology in Civil Engineering, NUCE 2020. 14 (3): 67–74

NUMERICAL INVESTIGATION ON THE TUNNELING
AND MINING INDUCED GEO-HAZARDS: CASE STUDY
IN QUANG NINH, VIETNAM
Nguyen Cong Gianga,∗, Nguyen Van Manhb , Nguyen Quang Phichc
a

Faculty of Civil Engineering, Hanoi University of Architecture,
Km 10, Nguyen Trai road, Thanh Xuan district, Hanoi, Vietnam
b
Faculty of Civil Engineering, Hanoi University of Mining and Geology,
No. 18 Vien street, Bac Tu Liem district, Hanoi, Vietnam
c
Faculty of Civil Construction, Van Lang University,
401C, Campus 45 Nguyen Khac Nhu street, District 1, Ho Chi Minh city, Vietnam
Article history:
Received 19/05/2020, Revised 29/06/2020, Accepted 29/06/2020
Abstract
In the field of rock mechanics, underground construction and mining, there have been many proposed methods
for studying geo-hazards and also many research results that have been published in the world. In Vietnam, the
numerical method is mainly used for analysis and design but not going deeply to predict the possible causes
that lead to geo-hazards due to complex geological conditions. On the other hand, underground constructions
and exploitation projects are often designed based on standards, regulations and experiences. The physical
mechanism as well as the possibility of geo-hazards occurred when constructing underground structures and
mining can take on various forms, depending on geological conditions and construction technology. Therefore,
using numerical methods to simulate and analyze the possible geo-hazards is essential. This article presents a
number of specific analysis cases, taking into account geological conditions and boundary conditions, and from
that, raising a number of issues to note when using numerical methods.
Keywords: underground mining; numerical method; geo-hazards; rock mechanics; FLAC2D.
/>

c 2020 National University of Civil Engineering

1. Introduction
Geo-hazards are types of disaster-related to geological processes induced by natural or human
activities. In recent years, various geo-hazard or geo-risks have occurred in tunneling and mining in
Vietnam. In the mining field, the geo-hazard is due to exploitation of natural resources from mine
including subsidence, slope stability, landslides and other related damage have been reported by numerous authors [1–4]. The prediction and management of geo-hazard are of great importance in the
mining industry [5–7].
Understanding the behaviour of rock masses has always been difficult for mining and underground
engineers because of the presence of discontinuities, anisotropic and heterogeneity. Empirical, analytical and numerical methods have been widely used for modeling the behavior of rock mass [8–10].
∗

Corresponding author. E-mail address: (Giang, N. C.)

67


Giang, N. C., et al. / Journal of Science and Technology in Civil Engineering

In recent years, numerical methods have been used in design of underground openings in the world,
Giang,
N. C.,
of Science
andand
Technology
in Civil
Engineering
Giang,
N. et
C.,al./Journal

et al./Journal
of Science
Technology
in Civil
Engineering
however,
in Vietnam, this issue has received little attention. Numerical modeling application in min
ing engineering aims to provide a better understanding of the mining and rock mechanics engineers
for solving problems related to the design of support systems [7, 11]. The numerical methods are conthis
article,
rock
mass
layers
andfor
underground
aditadit
in
Quang
Ninh
province
of of
Incostly
this
article,
the
rock
mass
layers
and
underground

in Quang
Ninh
province
venient,Inless
andtheless
time-consuming
the
analysismine
ofmine
stress
redistribution
and
their effects
Vietnam
were
selected
to
investigate
the
influence
of
underground
mine
adit
location
and
rock
layers
Vietnam
wereofselected

to investigate
the influence
of underground
mine
and rock layers
on the
behavior
rock mass
and designing
of support
system within
the adit
rocklocation
mass environment.
positions
to stress
states,
yielded
zonezone
and and
displacement
of the
rockrock
mass
surrounding
aditadit
by using
positions
to
stress

states,
yielded
displacement
of
the
mass
surrounding
using
In this article, the rock mass layers and underground mine adit in Quang Ninh province ofby
Vietnam
FLAC2D
[12].[12].
TheThe
results
suggest
thatthat
the the
subsidence
of the
surface
could
be triggered
duedue
to to
FLAC2D
results
suggest
subsidence
of the
surface

could
be triggered
were
selectedcollapse.
to collapse.
investigate the influence of underground mine adit location and rock layers positions
underground
underground
to stress states, yielded zone and displacement of the rock mass surrounding adit by using FLAC2D
2. Mechanical
and
Simulation
Diagram
2.The
Mechanical
Parameter
and
Simulation
[12].
resultsParameter
suggest
that
the
subsidence
of Diagram
the surface could be triggered due to underground
collapse.TheThe
rockrock
massmass
in the

coalcoal
mining
in Quang
Ninh
province,
Vietnam
consists
normally
of 4of 4
in the
mining
in Quang
Ninh
province,
Vietnam
consists
normally
layers:
sandstone,
siltstone,
argillite
and and
coalcoal
lying
inclined
withwith
mechanical
parameters
as in
layers:

sandstone,
siltstone,
argillite
lying
inclined
mechanical
parameters
as the
in the
following
Table
1.
following
Table
1.
2. Mechanical parameter and simulation diagram
Table
1. Mechanical
parameters
of rock
mass
Table
1. Mechanical
parameters
of rock
mass

The rock mass in the coal mining in Quang Ninh province, Vietnam consists normally of 4 layers:
Layer
Density

Angle
Modulus
Shear
Modulus
Layersiltstone,
Density
Cohesion
cFriction
Friction
Angle
Bulk
Modulus
Shear
Modulus
sandstone,
clayCohesion
and
coalc lying
inclined
with Bulk
mechanical
parameters
as
in G
the Gfollowing
K
Table 1. The constitutive
model
of
Mohr–Coulomb

is
used
for
modeling
the
behaviour
of the rock
K
r r
j
j
(MPa)
(GPa)
(MPa)
(GPa)
mass.
3
3
(g/cm
) )
(g/cm

Sandstone
Sandstone 2.612.61
Coal
Coal
Layer
Slitstone
Slitstone

Sandstone
Clay
Clay
Coal
Slitstone
Clay

Density
1.301.30ρ
(g/cm3 )
2.502.50

2.61
2.60
2.60
1.30
2.50
2.60

(GPa)
(GPa)
(degrees)
(degrees)
Table 1. Mechanical parameters of rock mass
1.001.00
40 40
11.60
11.60

Cohesion

0.010.01 c
(MPa)
1.001.00

8.708.70

Friction
Bulk
Shear modulus G
35 35 angle ϕ 2.60
2.60modulus K1.301.30
(degrees)
(GPa)
(GPa)

1.00
0.100.01
0.10
1.00
0.10

25 25

40
30 3035
25
30

10.00
10.00

11.60
9.609.60 2.60
10.00
9.60

7.007.00
2.702.70

8.70
1.30
7.00
2.70

TwoTwo
cases
are investigated
withwith
different
orders
of rock
layers:
cases
are investigated
different
orders
of rock
layers:
- Case
1: from

upper
to lower
layers
are clay-coal-clay-siltstone
layers
- Case
1: from
upper
to lower
layers
are clay-coal-clay-siltstone
layers
- Case
2: cases
from
upper
to lower
layers
are
sandstone-clay-coal-siltstone-sandstone
-Two
Case
2: from
to lower
layers
are sandstone-clay-coal-siltstone-sandstone
areupper
investigated
with
different

orders of rock layers:
TheThe
tunnel
has
a
semi-circular
and
straight-walled
shape
or D-shape
with
a width
andand
height
of 4m
tunnel
has
a
semi-circular
and
straight-walled
shape
or D-shape
with
a width
height
of 4m
- Case 1: from upper to lower layers are clay-coal-clay-siltstone
layers.
each,

excavation
in coal
layer.
TheThe
height
fromfrom
top top
of the
aditadit
to the
surface
is nearly
30m.
TheThe
each,
excavation
in coal
layer.
height
of the
to the
surface
is nearly
30m.
analysis
model
is shown
in Fig.
1. 1.
analysis

model
is shown
in Fig.

(a) Case 1

(b) Case 2

(a) Case
(a) Case
1 1

(b) Case
(b) Case
2 2

Figure
1.1.The
model
cases
study
Figure
The
model
ofthe
thetwo
two
cases
study
Figure

1. The
model
of of
the
two
cases
study

3. Simulation
results
discussions
3. Simulation
results
andand
discussions

68

Redistribution
of stress
induced
to excavation
opening
a complex
subject
in actual
Redistribution
of stress
induced
due due

to excavation
opening
is aiscomplex
subject
in actual
mining
conditions
because
of the
influence
of rock
mass
layers.
results
of the
numerical
mining
conditions
because
of the
influence
of rock
mass
layers.
TheThe
results
of the
numerical
simulation
show

all information
on the
of mechanical
changes
occurring
in the
mass
simulation
can can
show
all information
on the
lawslaws
of mechanical
changes
occurring
in the
rockrock
mass


Giang, N. C., et al. / Journal of Science and Technology in Civil Engineering

- Case 2: from upper to lower layers are sandstone-clay-coal-siltstone-sandstone.
The tunnel has a semi-circular and straight-walled shape or D-shape with a width and height of
4 m each, excavation in coal layer. The height from top of the adit to the surface is nearly 15 m. The
model was built with size of 30 × 30 m. The left and right boundary of model are fixed at horizontal
direction; the bottom boundary is fixed in both vertical and horizontal direction and the top boundary
of model is free. The analysis model is shown in Fig. 1. The initial boundary condition of the model
is in-situ rock mass stress state.

3. Simulation results and discussions
Redistribution of stress induced due to excavation opening is a complex subject in actual mining
conditions because of the influence of rock mass layers. The results of the numerical simulation can
Giang,
N.
C.,
et al./Journal
of Science
Technology
in the
Civil
Engineering
Giang,
N.on
C.,the
et al./Journal
of Science
andand
Technology
in in
Civil
Engineering
show all information
laws
of mechanical
changes
occurring
rock
mass surrounding the

adit, including the stress redistribution, displacement, deformation and the failure zones. Based on that
information the designers can analyze and choose the possibilities of support systems for reinforcing
rock
mass
keep
the stability
oftothekeep
opening.
By
introducing
the simulation
results,
the
systems
for
reinforcing
rock
mass
tounderground
keep
stability
of the
underground
opening.
introducing
systems
forto
reinforcing
rock
mass

thethe
stability
of the
underground
opening.
ByBy
introducing
thethe
advantage
of
numerical
simulation
in general
as simulation
well as in
be demonstrated.
simulation
results,
advantage
of
numerical
in general
asanalysis
well
ascould
in geohazards
analysis
simulation
results,
thethe

advantage
of numerical
simulation
in geo-hazard
general
as well
as in
geohazards
analysis
could
demonstrated.
could
be be
demonstrated.

(a) Case 1

(b) Case 2
Case
(b)(b)
Case
2 2

Case
(a) (a)
Case
1 1

Figure
2. Major

principal
stress
distribution
(Pa)
Figure
2. Major
principal
stress
distribution
Figure
Major
principal
stress
distribution

23and
3 show
the
distribution
of the
major
minor
principal
stresses
in the
the
rock
mass
2 and
3 show

distribution
the
major
and
minor
principal
stresses
in in
the
rock
mass
Figs.Figs.
2Figs.
and
show
thethedistribution
ofofthe
major
andand
minor
principal
stresses
rock
mass
surrounding
tunnel.
is easy
to see
in Fig.
2 that

general
redistribution
principles
surrounding
thethe
tunnel.
It isIt easy
to see
in Fig.
2 that
thethe
general
redistribution
principles
areare
thatthat
thethe
surrounding
the
tunnel.
It
is
easy
to
see
in
Fig.
2
that
the

general
redistribution
principles
are
that
major
principal
stresses
peak
value
occur
hard
rock
layers,
however
order
major
principal
stresses
of of
peak
value
occur
in in
thethe
hard
rock
layers,
however
duedue

to to
thethe
order
of of
thedifferent
majorrock
principal
stresses
ofbe
peak
value
in the
hard
layers,
however
due
to the
order of
rock
layers,
it can
seen
that
the
average
value
of
principal
stress
forming

different
different
layers,
it can
be
seen
that
theoccur
average
value
of rock
thethe
principal
stress
forming
different
different
rock
layers,
it
can
be
seen
that
the
average
value
of
the
principal

stress
forming
different
shapes.
case
2, as
siltstone
under
layer,
which
is mechanically
stronger
than
shapes.
In In
case
2, as
thethe
siltstone
lieslies
under
thethe
coalcoal
layer,
which
is mechanically
stronger
than
thethe
shapes.

In the
case
2,
as the
thethe
siltstone
lies
under
coal
layer,
which
isMPa
mechanically
stronger
the
clay
layer,
the
area
of
principal
stress
with
an
average
value
of 0.25
MPa
spreads
deeper

in than
the
clay
layer,
area
of
principal
stress
with
anthe
average
value
of 0.25
spreads
deeper
in the
coalcoal
than
in case
than
in
case
1. 1.
clay
layer,
the
area of the principal stress with an average value of 0.25 MPa spreads deeper in the

coal than
case

1. thethe
By
comparing
minimum
principal
stress
distribution
principles
in Fig.
3, the
findings
show
Byin
comparing
minimum
principal
stress
distribution
principles
in Fig.
3, the
findings
show
By
comparing
the
minimum
principal
distribution
principles

3,with
the
findings
show
quite
similarities
in the
distribution
areas
instress
both
cases.
However,
in case
2, Fig.
the
with
the
smallest
quite
similarities
in the
distribution
areas
in both
cases.
However,
in case
2, in
the

areaarea
the
smallest
minor
stress
components
with
values
ranging
from
toHowever,
0.05
MPa
iscase
more
than
insmallest
case
minor
stress
components
with
values
ranging
from
0 to0 0.05
MPa
isinmore
widespread
in

1 1
quite
similarities
in the distribution
areas
in both
cases.
2, widespread
the area than
with
thecase
with
the
stress
fluctuating
the
range
0.15
It smaller
is is
smaller
lower
part
of
the
with
the
stress
fluctuating
in in

thevalues
range
of of
0.15
to to
0.200.2
MPa.
is
in in
thethe
lower
part
of in
thecase
minor
stress
components
with
ranging
from
to MPa.
0.05It MPa
more
widespread
than
modeling.
modeling.
1 with the stress fluctuating in the range of 0.15 to 0.2 MPa. It is smaller in the lower part of the
Therefore,
results

showed
effect
layers
very
clear
stress
Therefore,
thethe
results
showed
thatthat
thethe
effect
of of
thethe
layers
is is
very
clear
to to
thethe
stress
modeling.
redistribution,
which
very
different
from
results
obtained

analytical
methods
with
redistribution,
which
is is
very
different
from
thethe
results
obtained
by by
analytical
methods
with
thethe
"averagation"
or “homogenization”
of the
model
rock
mass
[13]-[15].
"averagation"
or “homogenization”
of the
model
on on
thethe

rock
mass
[13]-[15].

69


clay
layer,
area
of the
principal
stress
an average
value
of 0.25
spreads
deeper
in coal
the coal
clay
layer,
thethe
area
of the
principal
stress
withwith
an average
value

of 0.25
MPaMPa
spreads
deeper
in the
than
in
case
1.
than in case 1.
comparing
minimum
principal
stress
distribution
principles
in Fig.
3, findings
the findings
show
ByBy
comparing
thethe
minimum
principal
stress
distribution
principles
in Fig.
3, the

show
quite
similarities
in the
distribution
areas
in both
cases.
However,
in case
2, the
the smallest
quite
similarities
in the
distribution
areas
in both
cases.
However,
in case
2, the
areaarea
withwith
the smallest
minor
stress
components
with
values

ranging
from
to 0.05
is more
widespread
in case
minor
stress
components
with
values
ranging
from
0 to0 0.05
MPaMPa
is more
widespread
thanthan
in case
1 1
Giang, N. C., et al. / Journal of Science and Technology in Civil Engineering
with
stress
fluctuating
in the
range
of 0.15
to 0.2
MPa.
is smaller

in the
lower
of the
with
thethe
stress
fluctuating
in the
range
of 0.15
to 0.2
MPa.
It isIt smaller
in the
lower
partpart
of the
modeling.
modeling.
Therefore, the results showed that the effect of the layers is very clear to the stress redistribution,

which isTherefore,
very
different
from
the
results
by analytical
methods
the

“averagation”
or
Therefore,
results
showed
that
effect
layers
is with
very
clear
to the
stress
thethe
results
showed
thatobtained
the the
effect
of of
the the
layers
is very
clear
to
the
stress
redistribution,
which
very

different
from
results
obtained
analytical
methods
redistribution,
which
very
different
the the
results
obtained
by by
analytical
methods
withwith
the the
“homogenization”
of istheis
model
on
the from
rock
mass
[13–15].
"averagation"
or “homogenization”
of the
model

on the
mass
[13]-[15].
"averagation"
or “homogenization”
of the
model
on the
rockrock
mass
[13]-[15].

(a) (a)
Case
11 1
(a)
Case
Case

(b) Case
Case
(b) Case
2 22
(b)

3. Minimum
principalprincipal
stress distribution
(Pa)
Figure

3.Figure
The
principle
of minimum
stress
distribution
Figure
3. The
principle
of minimum
principal
stress
distribution

Similarly, the results obtained with the principle of movement show that due to the influence of the
Giang,
N.
et al./Journal
ofmass
Science
Technology
in Civil
Engineering
rock mass layers,
theN.movement
in the rock
around
the underground
opening
is not symmetrical

Giang,
C.,C.,
et al./Journal
of Science
andand
Technology
in Civil
Engineering
but dependent on the specific geological structures. Fig. 4 shows the displacement on the boundary
of the opening, reflected across the boundary of3the3 opening after the displacement.

(a) Case 1

Case
(a) (a)
Case
1 1

(b) Case 2

Case
(b)(b)
Case
2 2

Figure 4. Displacement of the opening boundary after excavation

Figure
4. Displacement
of the

opening
boundary
after
excavation
Figure
4. Displacement
of the
opening
boundary
after
excavation
Figs. 5 and 6 show the formation of failure zone (area with symbol) in the rock mass around the
Similarly,
results
obtained
with
principle
show
to the
opening.
The
failure
zone
in obtained
both
cases
develops
mainly
inof
themovement

coal layer
andthat
tothat
the
surface
ofinfluence
the hard
Similarly,
thethe
results
with
thethe
principle
of
movement
show
duedue
to the
influence
of
the
rock
mass
layers,
movement
in
rock
mass
around
underground

opening
is
of
themass.
rock
mass
layers,
thethe
movement
thethe
rock
mass
around
underground
opening
notnot
rock
However,
comparing
the twoincases
with
different
orderthe
ofthe
rock
mass layers
showsis that
in
symmetrical
but

dependent
on
the
specific
geological
structures.
Fig.
4
shows
the
displacement
on
the
symmetrical
but
dependent
on
the
specific
geological
structures.
Fig.
4
shows
the
displacement
on
the
case 2, the failure zone is wider. The results clearly show the influence of the stratification structure
boundary the

of the
opening,
reflected
across
boundary
of the
opening
after
displacement.
boundary
opening,
reflected
across
thethe
boundary
of the
opening
after
thethe
displacement.
as well asofthe
order
of the
rock mass
layers
on the formation
of geohazards.
The failure state occur
Figs.
5stress

and
6 isshow
formation
astrength
failure
zone
(area
with
symbol)
inThe
the
rock
mass
around
when the
shear
more
than
the of
shear
of(area
rock
mass
element.
symbol
of
“*” in
Figs.
5 and
6 show

thethe
formation
aoffailure
zone
with
symbol)
in the
rock
mass
around
the
opening.
The
failure
zone
in
both
cases
develops
mainly
in
the
coal
layer
and
develop
the
The failure
bothelement
cases develops

mainly
in the and
coalthe
layer
and develop
to to
thethe
Fig.opening.
5 is indicated
that thezone
rockinmass
was failed
by shearing
symbol
of “x” indicating
surface
of
the
hard
rock
mass.
However,
comparing
the
two
cases
with
different
order
of

rock
mass
surface
the hard
rockwas
mass.
However,
comparing
the rockofmass
element
failed
in elasticity
state. the two cases with different order of rock mass
layers
shows
that
in
case
2,
the
failure
zone
is
wider.
The
results
clearly
show
the
influence

of
layers shows that in case 2, the failure zone is wider. The results clearly show the influence of thethe
stratification
structure
as well
as the
order
of the
rock
mass
layers
formation
of geohazards.
70mass
stratification
structure
as well
as the
order
of the
rock
layers
on on
thethe
formation
of geohazards.


Figs. 5 and 6 show the formation of a failure zone (area with symbol) in the rock mass around
Figs. 5 and 6 show the formation of a failure zone (area with symbol) in the rock mass around

the opening. The failure zone in both cases develops mainly in the coal layer and develop to the
the opening. The failure zone in both cases develops mainly in the coal layer and develop to the
surface of the hard rock mass. However, comparing the two cases with different order of rock mass
surface of the hard rock mass. However, comparing the two cases with different order of rock mass
layers shows that in case 2, the failure zone is wider. The results clearly show the influence of the
layers shows that in case 2, the failure zone is wider. The results clearly show the influence of the
stratification structure
as N.
well
the/ Journal
order of
the rockandmass
layers in
on the Engineering
formation of geohazards.
Giang,
C., as
et al.
of Science
Technology
stratification structure
as well
as
the order of
the rock mass
layers onCivil
the formation of geohazards.

5. Failure
zone around

Casex:1elastic failure)
Figure 5. FailureFigure
zone around
the opening,
case 1the
(*:opening:
shear failure;
Figure
5. Failure
zone around
the
opening:
Case 1

Figure 6. FailureFigure
zone around
the opening,
case 2the
(*:opening:
shear failure;
6. Failure
zone around
Casex:2elastic failure)

Figure 6. Failure zone around the opening: Case 2
Several comments can be drawn from the numerical
results:
4
4 principal stress redistribution, displacement of
- When the rock mass has a layered structure,

tunnel boundary and the formation of failure zones are complex. Rock formation does not behave as
homogeneous material, it requires therefore advanced numerical model to solve the problem;
- It is clear that the mechanical behavior of rock mass depends not only on the location of the
opening, but also on the order and distribution of the rock mass layers, which are clearly shown in the
numerical results;
- In the second model, the displacement and deformation processes achieve relatively larger values, although in case 2 there are both sandstone layers in pillars and cliffs;
- The change in the position of the layers clearly affects the processes of stress redistribution and
movement in the rock masses;
- The development of the failure zone in the latter case is stronger;
- In both cases, as the distance from the top of the structure to the surface is not wide the failure
zone is developed to the surface of hard rock mass layers. In this case, it may cause landslide or land
subsidence, with varying intensity.

4. Influence of tunnel shape on geomechanical process
To study the effect of the cross-section shape of underground opening to the redistribution of
stress states and failure zone, simulations were performed with the case of the circular shape which
71


subsidence, with varying intensity.

4. Influence of tunnel shape on geomechanical process
To study the effect of the cross-section shape of underground opening to the redistribution of
stress states and failureGiang,
zone,N. simulations
were
performed
with in
the
case

of the circular shape which
C., et al. / Journal
of Science
and Technology
Civil
Engineering
has a radius of 2m, with similar mechanical parameters and order of distribution of rock mass layers as
has a radius of 2 m, with similar mechanical parameters and order of distribution of rock mass layers
in Section 2. The obtained results show that, when the opening is a circular shape, the rules of stress
as in Section 2. The obtained results show that, when the opening is a circular shape, the rules of stress
redistribution and displacement also show dependence on the layering of the rock mass. However, the
redistribution and displacement also show dependence on the layering of the rock mass. However, the
failure zone does not develop to the surface. It also means that it is not likely to lead to landslides or
failure zone in this case does not develop to the surface. It also means that it is not likely to lead to
land subsidence
under the investigated conditions.
landslides or land subsidence under the investigated conditions.
7–9 show
the the
rulerule
of the
and minor
stress redistribution
as well as the
Figs. Figs.
7, 8 and
9 show
ofmajor
the major
and principal

minor principal
stress redistribution
as failure
well as the
of of
rock
mass
layers
are sandstone,
claystone,
coal andcoal
claystone.
failure zone,
zone,for
forthe
thecase
case
rock
mass
layers
are sandstone,
claystone,
and claystone.





Giang,
N. et

C.,al./Journal
et al./Journal
of Science
Technology
in Civil
Engineering
Giang,
N. C.,
of Science
and and
Technology
in Civil
Engineering
Figure 7. Modeling of a circular opening

Figure 7. Modeling of a circular opening

The numerical modeling results reveal that when the opening is a circular cross-section shape,
the rules of principal stress redistribution, displacement and deformation strongly depend on the shape
of the opening compared to the two cases analyzed above (Figs. 3 and 8). The failure zone is formed
within the coal layer, although there are also some local failure points on the hard rock mass, which
are not symmetrical, due to the inclined rock mass layers. Especially, when paying attention to ground
subsidence and landslides, it shows that when selecting a circular cross-section of opening the land
subsidence decreases, and it seems difficult that the failure reaches the surface (Fig. 9).
5

(a)

(b)

Figure
8. The
principle
of maximum
stress
redistribution
(left)(left)
and and
minimum
(right)
withwith
the circular
Figure
8. The
principle
of maximum
stress
redistribution
minimum
(right)
the circular
Figure 8. The principle of (a) maximum
and
(b)
minimum
stress
(Pa)
redistribution
with
the

circular
cross-section
of
opening
cross-section of opening
cross-section of opening

The numerical modeling results reveal that when the opening is a circular cross-section shape, the
rules of principal stress redistribution, displacement and deformation strongly depend on the shape
of the opening compared to the two cases analyzed above (Figs. 3 and 8). The failure zone is formed
72


Giang, N. C., et al. / Journal of Science and Technology in Civil Engineering

within the coal layer, although there are also some local failure points on the hard rock mass, which
symmetrical, due to the inclined rock mass layers. Especially, when paying attention to ground
Figureare8.not
The
principle of maximum stress redistribution (left) and minimum (right) with the circular
subsidence and landslides, it shows that when selecting a circular cross-section of opening the land
cross-section
ofthe
opening
subsidence decreases, and it is difficult
to collapse to
surface (Fig. 9).

Figure Figure
9. The failure

zone
aroundzone
the circular
(*: shear
failure; x:tunnel
elastic failure)
9. The
failure
(slash)tunnel
around
the circular

5. Conclusion
5. Conclusions

The numerical modeling results show that the numerical methods can solve the complex
numerical
modeling
resultsinshow
the numerical
methods
can solve
complexbehavior
prob- of
problems The
of the
tunneling
and mining
rockthat
masses

by taking
into account
thethe
complex
lems of thesuch
tunneling
and mining in rock
masses byheterogeneities.
taking into account
therules
complex
behavior
of rock
rock formation
as discontinuities,
anisotropic,
The
for stress
redistribution,
formation
as discontinuities,
and as
heterogeneities.
rules for stress
redistribution
deformation,
thesuch
development
of the anisotropic
failure zone,

well as theirThe
magnitude,
depend
clearly on the
and characteristics,
deformation, the development
of theof
failure
zone as
welllayers,
as theircross-section
magnitude, depend
clearly
on
structural
the arrangement
the rock
mass
shapes
of opening.
the
structural
characteristics,
arrangement
of
the
rock
mass
layers
and

cross-section
shapes
of
openObviously, in order to obtain accurately, the mechanical behavior in rock mass with complex
ing. Obviously,
to obtain accurately,
mechanical behavior
in rock
complex
geological
structures,initorder
is necessary
to analysethe
specificallytion
case by
case.mass
On with
the one
hand, by
geological
structures,
it
is
necessary
to
analyse
specifically
case
by
case.

On
the
one
hand,
by
using
using numerical method, it is possible to analyze the possibility and type of development of specific
numerical
method,
it islead
possible
to analyzeand
theaccidents",
possibility and
type ofthat
development
of specific
ge- the
geological
conditions
that
to "incidents
meaning
it is possible
to identify
conditions
that lead
to “incidents
and accidents”,
meaning

that On
it is the
possible
identify
type ofological
"geological
disaster"
which
can be caused
by human
factors.
othertohand,
bythe
clearly
type
of
“geological
disaster”
which
can
be
caused
by
human
factors.
On
the
other
hand,
by

clearly
understanding the rock masses behavior after excavated opening, it can be helpful for the designer to
the rock masses
after method,
excavatedsupport
opening,system
it can befor
helpful
for the designer
to the
select understanding
suitable cross-section
shape,behavior
excavation
the opening
to prevent
select
suitable
cross-section
shape,
excavation
method
and
support
system
for
the
opening
to
prevent

possibility of incidents and accidents, i.e. limiting the geological disaster.
the possibility of incidents and accidents, i.e. limiting the geological disaster.
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