Procedia
Engineering 26 (2011) Page No: 1726 – 1730
Feasibility
Analysis on Using Shaft in the Region with Large
Deformation
HUANG
Pinglua, CHEN Congxina, XIAO Guofenga
NATIONAL INSTITUTE OF INDUSTRIAL ENGINEERING
PGDIE-42
Submitted by
Jitendra Nayak
PGDIE-42
Roll No-118
Abstract
Based on results
of deformation monitoring and numerical simulation, feasibility of using shaft
in the region with large deformation is discussed. The results obtained show
that: although the original is big, and the deformation of rock around the
shaft will continue to increase. The tilting of shaft will seriously affect the
cage's running up and down. However, the total deformation is still in a
certain range, general damage of rock mass around the shaft won’t occur in the
near future. By taking some measures to stop rock deformation speeding up, to
reinforce the structures and the foundation of shaft, derrick and hoist room,
to promote safety management, coupled with comprehensive, systematic and
continuous site monitoring and prediction, the East Main Shaft can continue to
be used. The post-useof shaft validates the correctness of the findings. To
accurately explore the feasibility of using shaft, some basic work as
comprehensive grasp of engineering geology conditions, in-depth insight into
the rock deformation characteristics and mechanism, and accurate prediction of
rock deformation are really required. The research method and results obtained
may be of referential value to similar projects.
With the depth of
underground mining of mineral resources increased, the regulations of surface deformation
and rock movement caused by underground mining are becoming more and more
complex. In many large-scale mines, especially in the large metal mines, the
scope of surface deformation caused by underground mining far exceeds the
initial forecast, which not only results in the deformation or collapse of the
houses, factories, and other structures, but also makes the structures in the
rock mass like shafts move into deformation zone or collapse zone earlier than
expected. With the large deformation of rock layers, the shaft deforms
severely, which affects its normal use. Such as in Xiaoguanzhuang iron ore,
the main shaft
which is 600 m away from the exploitation border deforms dramatically. In the
eastern area of Chengchao iron mine, the surface and the structures around the
East Shaft cracks and produce a larger deformation with the mining depth is
less than 400m.
On the causes
and safety countermeasures of shaft deformation due to underground mining, some
research have been carried out and many valuable results have been obtained.
However, there are only few researches about the feasibility of using shaft in
the region with large deformation, and the systematic theory that can be
referred to have not been established. In this paper, based on deformation
monitoring and theoretical analysis, exploratory research on the issue is
carried out.
1. Project
Profile
1.1. Engineering geology and underground mining
Chengchao iron mine is a very
famous in China with an annual output of more than 3 million tons. The mine
surface belongs to hilly topography. The footwall rock of ore body is granite,
the hanging wall rocks are diorite and angular rocks from near to distant, and
rock above the ore body is marble. The rock layers strike almost EW, dips south
by west.
The geological
structures within the mining area are very complex, which is mainly manifested
by the well-developed faults. There are two main faults which are parallel to
the ore body. One is in the north of the ore body, and the other is in the
south of the ore body. There are also several faults that are perpendicular to
the direction of ore body. The maximum principal stress in the area is 1.4
times of the gravity, with the direction of nearly east-west. The second
principal stress is 1.1 times of the gravity, with the direction of nearly
south-north.
There are three
main ore bodies distributed in the mine area. The ores were mined from the
beginning of -16 m level since 1970, and the exploitation level is deep into
-360m in 2007. The sub-caving is used as the main mining method in the mine.
1.2. East Shaft
East Shaft of
Chengchao iron ore is located in the footwall of the ore body. It is about 300
m far from the ore body. As one of the main shaft in the mine, it was used to
hoist the ores and ventilate. The shaft was put into operation in 1966 and it
has made a great contribution to the mine production.
East Shaft began
to crack in April 1996. And from then the scope of surface cracking continually
expand northward. The cracks of shaft and hoist house foundation had been
becoming increasingly serious and the size of cage was force to reduce. The
lift system centre of the derrick had also been adjusted. Shaft had been running
in sick. According to the measurement, the wellhead has moved about 40cm in
horizontal direction till the end of 2006. The derrick tilted apparently and
the well cracking became more and more serious. However, the well had to be
used to promote waste rock from 2007 to 2009 according to mine production
planning. It is necessary to grasp the regulations and trends of shaft
deformation
before the decisions whether the well can be used continually or not were made.
2. Deformation
Monitoring and Prediction
2.1. Surface Deformation
Monitoring
The surface
deformation, including monitoring horizontal and vertical displacement, was conducted
from May 2007. GPS and Level technology were used in the horizontal and
vertical displacement monitoring respectively. The vertical and horizontal
displacement field diagrams obtained by site monitoring are shown in Fig.1.
According to the results of site monitoring, some conclusions can be drawn as
follows:
Firstly, the
surface deformation of the footwall rock extends gradually from south to north,
the direction of the surface displacement points to the southern mined-out
area. This indicates that the surface deformation is caused by underground
mining which is the controlling factor of the rock deformation around the East
Shaft.
Secondly, the
surface deformation is most obvious in horizontal direction. Displacement in
horizontal direction is far greater than in vertical direction at the same
location. Farther from the mined-out area, the greater is the ratio of the
surface horizontal displacement and vertical displacement
Firstly,
according to the monitoring results of surface deformation around the East
Shaft, the horizontal and vertical displacements of the wellhead are 4.0cm and
1.8cm respectively from May 12, 2007 to 17 September, 2007. And their
displacement rate are 0.314mm/d and 0.144mm/d respectively, based on which we
can predict that the horizontal and vertical displacement of the wellhead will
increase to 30.5cm and 12cmby the end of December 2009.
Horizontal
Vertical
Fig.1 Displacement field diagram obtained by
site monitoring
Horizontal Vertical
Fig.2
Displacement field by numerical simulation
Secondly, based
on the horizontal displacement of 40cm of the wellhead on April 2007, back
analysis was conducted by using FLAC3D. The vertical and horizontal displacement
field diagrams in December of 2009 obtained by numerical simulation are shown
in Fig.2. The results show that the horizontal displacement of the wellhead
will increase from 39cm to 66cm by 27cm in the next two years. The vertical
displacement of the wellhead will increase from 11cm from 22 cm by11cm.
Predictions of
surface deformation of the wellhead in December of 2009 are very similar by two
methods above. So we can think these predictions were acceptable.
3. Feasibility
Analysis on Using Shaft
By comprehensive
analyzing results obtained by site monitoring and numerical simulation, it can
be estimated that the horizontal and vertical displacement of the wellhead will
be 70cm and 23cm by the end of December 2009, with an increase of 30cm and
12cm.
It is obvious
that the rock around the wellhead will continue to deform, which no doubt will
increase the deformation of the foundation of the hoist and the tilting of the
derrick. It will seriously affect the cage run up and down. The use and safety
will also be affected by the deformation of the hoist hand hoist house.
Although further
deformation of the rock around the wellhead will be produced, the total amount
of deformation is still within a certain range. The main deformation of surface
is in horizontal direction and the vertical displacement is relatively smaller.
Large-scale slide and general damage won't occur in the area around the well.
By taking some measures to stop rock deformation speeding up, to reinforce the
structures and the foundation of shaft, derrick and hoist room, to promote
safety management, coupled with comprehensive, systematic and continuous
deformation monitoring and prediction, the East Shaft can continue to be used.
4. Verification
of Post-Use of Shaft
Based on the
results above, rock around the well, the well itself, and the lift system were
reinforced or modified. The main works were as follows:
·
Drilling
grouting treatment was done to the surface cracks around the well, which
effectively reinforce the shallow rock foundation in the area.
·
Clad steel processing wad done to the
brick columns of the hoist room structures and some channel ring beam was
added. Structural beams were pasted with steel plates. Defects of beams, walls,
and floors were repaired. Cracks in the walls and ground were treated by
filling cement slurry.
·
Hoop
was equipped at the wellhead and grouting treatment was done to the cracks on
the well. In different parts of the well, carbon fibres were bonded or steel
mesh was added.
·
The
derrick was corrected and reinforced. In order to facilitate later
re-adjustment, four adjustable constraints were set at the bottom corners of
the well. The hoist was corrected at the same time.
·
During
the use of East Shaft, the inclination was measured periodically. The
deformations of surface and well were also monitored to grasp the steady state
of the rock and structures. Necessary early warning and forecasting were made
in order to prevent safety accidents.
Based the
effective treatment above, East Shaft was used safely by the end of December
2009. Site monitoring results showed that the horizontal and vertical
displacement of the wellhead were increase by 28.9cm and 11.5cmrelative to the
beginning of 2007, which verify the accuracy of the forecasts.
5. Conclusions
Based on results
of deformation monitoring and numerical simulation, feasibility of using shaft
in the region with large deformation is discussed
·
The
rock around the wellhead will continue to deform, which no doubt will increase
the deformation of the foundation of the hoist and the tilting of the derrick.
It will seriously affect the cage's running up and down. The use and safety
will also be affected by the deformation of the hoist hand hoist house.
·
Although
further deformation of the rock around the wellhead will be produced, the total
amount of deformation is still within a certain range. The main deformation of
surface is in horizontal direction and the vertical displacement is relatively
smaller. Large-scale slide and general damage won’t occur in the area. By
taking some measures to stop rock deformation speeding up, to reinforce the
structures and the foundation of shaft, derrick and hoist room, to promote
safety management, coupled with comprehensive, systematic and continuous
deformation monitoring and prediction, the East Shaft can continue to be used.
·
Based
the effective treatments such as reinforcement or correcting of rock,
foundation and structures, East Shaft was used safely by the end of December
2009, which verify the accuracy of the research results.
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