10th Asian Regional Conference of IAEG (2015)

Numerical Analysis on Shaft Lining Stability during Aquifer Quick Drainage in Eastern
Chinese Coal Mines
Qing YU(1), Jinrong MA(2) and Jiaxing LIN(3)(1) School of Resources and Geosciences, China University of Mining and Technology, China
E-mail: yuqing@cumt.edu.cn(2) State Key Laboratory for Geo-mechanics and Deep Underground Engineering, China University of Mining
and Technology, China, (3) School of Mechanics and Civil Engineering, China University of Mining andTechnology, China
Abstract
In recent years, shaft lining ruptures have occurred in deep alluvium for many times
in the eastern Chinese coal mines, which caused huge losses to the coal mines. Stability ofthe shaft lining in deep alluvium is affected by complex factors, one of which is unstablebottom aquifer. This paper, based on the previous studies with long-term drainage ofbottom aquifer, researches the influence of the aquifer on shaft lining’s stability in thecondition of a large number of pumping in a short time. First, according to the documents,
the engineering geological and hydrogeological conditions of Baodian coal mine, which has
shaft lining ruptures once, have been gained. Then the paper analyzes the stress of shaft
lining under the limit state when the pore pressure in aquifer gets down in a short time. As
the result, the shaft lining may be unstable under that condition. Finally, with the finite
element software ADINA, the authors simulate a large number of pumping of bottom
aquifer in a short time in conditions of fluid-structure interaction of water and soil. The
results show that the concentrate area of shear stress transfers to the junction of bedrock andaquifer under the initial drainage. Also, the shear stress of inner shaft lining increases, andthe faster of pumping speed, the more it increases at the initial drainage. Besides, thenumerical simulation of drainage verifies that the pore pressure does not always reduce butcorresponds with Mandel-Cryer effects: the pore pressure decreases after the firstincreasing. Therefore, the numerical simulation has perfectly interpreted the effects of quick
drainage of bottom aquifer in deep alluvium on the stability of shaft lining.

Keywords: aquifer quick drainage, shaft lining stability, stress analysis, numerical simulation1.

occurred. During the water head fall, the soil layer
applies additional force to the outer shaft lining. As
the additional force increases with the effect of otherjoint forces, the condition of shaft lining gradually
goes into a plastic state, and then can be ruptured. As
the maximum additional stress occurs in the bottom
aquifer and near the bedrock surface, most of the
failures have happened in these zones (Cui and Cheng,
1991; Zhou and Cheng, 1995; Bi et al., 1997; Yang etal. 1997; Yang and Fu, 1999; Jing and Wang, 2000;
Liu et al., 2007).
For the mechanism of shaft lining rupture, there
are a few hypotheses that have been proposed bysome researchers such as the construction quality
hypothesis, the tectonic movement hypothesis, theearthquake hypothesis, and the vertical additional
force hypothesis (Yang et al. 1997; Jing and Wang,
2000). In these hypotheses, the vertical additional

Introduction

Environment damage caused by coal mining
operation has got more and more attention. A large
number of problems emerged during the coal
extraction such as shaft deformation, surroundingrock deformation, aquifer leakage, rock burst, andwater inrush (Jaiswal and Shrivastva, 2012; Sari et al.,
2004; Li, 2006). Furthermore, serious shaft lining
failures have often occurred in the eastern part ofChina, such as Datun, Xuzhou, Huaibei, Yanzhou,
Yingxia, Hebi, Dongrong, etc, since 1987 (Gu, 2000).
The geological conditions of all these spots arealmost the same. All these shaft linings pass throughdeep topsoil of Quaternary strata, for which thecomposition of the bottom aquifer is complex; before
shaft lining rupture, the water head of the bottom
aquifer fell dramatically and large scale subsidence1

10th Asian Regional Conference of IAEG (2015)
bottom aquifer dropped dramatically and persistently.
The water level in the bottom aquifer dropped morethan 20 m from 1985 to 1995 when the first shaft
lining failure occurred.

force hypothesis plays a dominant role and it isdescribed below. Shaft lining bears the horizontal
underground pressure, the self-weight (including
equipment weight) and the vertical additional force.
The research results of shaft lining destructive tests
and the in site experimental data in mining areas of
Huaibei, Xuzhou, etc. confirmed the existence ofvertical additional force and its impact on the shaft
lining rupture (Cui and Cheng, 1991; Yang and Fu,
1999). Researches on analysis of shaft lining stability
have been conducted in recent years and somemeasures including water-resistant key strata havebeen applied (Liang et al., 2009; Wang et al., 2010a;
Sui et al., 2010; Pu et al., 2008; Wang et al., 2010b).
However, stability of the shaft lining in deep
alluvium is affected by complex factors, one of whichis unstable bottom aquifer. This paper, based on theprevious studies with long-term drainage of bottom
aquifer, researches the influence of the aquifer on
shaft lining’s stability in in the condition of a large
number of pumping in a short time.
2.

Table 1 Geological condition of alluvium in Baodian
auxiliary shaft
Soil Depth Thickness
group
/m
/m

Humid soil, yellowish-brown

6.54

6.54

Upper 15.80
19.90
23.50

9.26
4.10
3.60

46.10
59.40
63.40

22.60
13.30
14.00

87.67

24.27

93.58

5.91

Clay

106.18116.45Lower 128.05
140.00148.60

12.60
10.27
11.60
11.95
8.60

Clayey coarse sandMiddleGeological Conditions

As the geological conditions are similar in eastern
Chinese coal mines, in this analysis, the Baodian coalmine was chosen as a typical example for the mines
which are located in eastern China. This coal minebelongs to Yanzhou Mining Group in Shandong
Province. The coalfield of this coal mine is buried in
the Quaternary stratum and Jurassic stratum. This
coal mine was commenced in June 1986 and the
production is over 3 million tons per year. The
mining level is now below -430 m from the surface
and the fully mechanized long wall mining system isadopted for coal extraction.
The geological conditions of the alluvium which
the Baodian auxiliary shaft passes through are shownin Table 1. The total thickness of the Quaternary
alluvium in which the shaft passes through was about
148 m, the cumulative thickness of the aquifer was
more than 20 m. The middle group has a goodimpermeability and can effectively block the vertical
recharge of Quaternary aquifer. The lower group has
three small sand layers, and in this study, the lower
group is considered the bottom aquifer which has thewater level drawdown.
The initial water pressure in the aquifer was 1.45
MPa, and by July 1995, the pressure had been
decreased to 0.65 MPa. The average of water
discharge pumped up in each year of this coal mine isshown in Fig. 1 (Liu et al., 2007). From 1991 to 2000,
the average water discharge was about 563.40 m3/h.
The permeability coherent K of the bottom aquifer
was 2.52-5.39 m/d (average 3.955 m/d). The variationof water level in the bottom aquifer of Baodian coalmine from 1985 to 2000 is shown in Fig. 2 (Liu et al.,2007). This figure shows that the water level in the

Description

clay
Sandy clay
Yellow gravel
Sandy clay, silty sand
Yellow sandy clay, clay
Clay with fine sand interbed
Clay
Clay with coarse sandinterbed

Sandy clay
Clayey silty sand
Clay
Fine sand, silty sand

Water discharge (m3/ h)

700
600
500
400

300
200
100
0
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Year

Fig. 1 Water discharge in past ten years of Baodian
coal mineFig. 2 Variation of water level in bottom aquifer2

10th Asian Regional Conference of IAEG (2015)
ground surface was about 24 mm/year.
On June 5, 1995, it was found that the cage
guides in the auxiliary shaft deformed torsionally at a
depth of -140 m. The cage guides, drainpipes andpressure ventilation pipes in the shaft bended in thelongitudinal direction due to the shaft lining failure.
On July 12, 1995, it was found that the main shaft
lining had another failure at a depth of -136 m~ -144
m. At that time, the concrete lining collapsed and fell
off in a large area. The sketches of the failure parts in
two shafts are shown in Fig. 4 (Liu and Zhang, 1995).
The crack in the shafts was distributed in horizontal
direction and its maximum width was over 1.0 m.

Mining field ground surface
Observation borehole

150 m-100 mAuxiliary shaft-50 m-120 m-140 m3.

Numerical Simulations

3.1 Numerical model
The influence of aquifer quick drainage on shaft
lining stability was analyzed by means of finite
element analysis software, ADINA. During thestructural-pore pressure coupling process, themultiphysics problem is characterized by the coupling
between the pore pressure and the deformation of aporous material consisting of a solid skeleton andpore fluid. Mechanical deformation changes the porepressure and change in the pore pressure causes
mechanical deformation (Multiphysics Capabilities of
ADINA, 2015).
Considering the focus of this study is theinfluence of aquifer quick drainage on the shaft lining
stability, the pore pressure change caused by drainage
and the stress change in shaft lining are the importantfactors. Therefore, in this simulation, thestructural-pore pressure coupling method was adopted,
without changing the actual load types, in order to get
the simulation results.
As the process of overburden deformation andchange of shaft lining stress was very complicate, thefollowing assumptions were made:[1] Shaft lining and strata were treated as thesymmetrical distribution belonging to the spaceaxial-symmetry.
[2] Concrete shaft lining, the surrounding strata were
homogeneous and isotropic. There was an interface
between the surrounding strata and shaft lining,which means the friction occurs in the interface.
According to the references (Tang et al., 2004; Xu etal., 2002), the friction coherent was set as 0.75.
[3] Drainage faces were only in outer edge of theaquifer. The aquifer unit was treated as the porous
material.
The basic model used in the analysis is shown in
Fig. 5. This model was used the typical geologicalconditions of Baodian coal mine. The net diameter ofmain shaft was 8 m and the thickness of shaft lining
was 1.0 m. The dimensions of the entire model were
420 m ×420 m wide and 220 m high, and it consistsof four layers: an aquifer, a top soil, a water-resistingFig. 3 Settlement at different depths

Fig. 4 Failure sketches of two shafts
Because of the drop of water level in aquifer, thislayer was consolidated and compressed, which could
cause the ground subsidence around the shaft. Fig. 3
shows the settlement at different depths of theindustry square in Baodian mine from May 1998 to
July 2000 (Liu et al., 2004). The observation borehole
was located at 150 m from the shaft. The settlementin 100 m depth was greater than any other depths
before July 2000. This depth was just the upper
location of the aquifer layer. This meant that a large
settlement had been occurred in the aquifer layer andthat caused the subsidence of ground surface. The
obvious settlement of ground surface in the mining
field was occurred in just two years and the last one
was over 51 mm. The average settlement of the3

10th Asian Regional Conference of IAEG (2015)
layer and a bedrock layer. From the above
assumptions, the four strata layers were defined
Mohr-Coulomb material and the shaft lining was
defined the elastic material.

direction.
[2]The lateral boundaries were fixed in horizontal
direction, the upper boundary was free.
[3]The both corner points in the lower boundary were
fully fixed.
3.2 Simulation tests
In order to find the influence of aquifer drainage
on the shaft lining stability, during the simulation, theconstant flow pumping method was used to instead ofthe drainage process. There are two steps in the
numerical simulation of aquifer drainage:[1] The first step is the initial stress equilibrium ofsoil and shaft lining under the undrained condition.
The initial stress is the soil weight and lateral pressure
under gravity.
[2] The second step is the aquifer drainage under the
initial stress state, which can make the soil
consolidation under self-weight.

Fig. 5 Numerical analysis model
Table 2 Mechanical properties used for numericalsimulation
Parameters

Top Claysoil layer

Aquifer Bedrock

Shaft
liningThickness
20 10040
60
1/mYoung'smodulus42 73.5
42
10,000 20,000/MPa
Poisson's
0.3 0.3
0.3
0.25 0.15
ratioInternal
friction angle 20 20
20
35
35
/°
Cohesion
0.03 0.035
0.04
11
35
/MPa
Unit weight
0.021 0.021 0.022
0.027 0.03
/MN/m3Tensilestrength0.06 0.07
0.075
6.0
16
/MPa
Permeability
coefficient ― ― 5.775×10-10 ――/m/s

Fig. 6.

Initial pore pressure.

Fig. 6 shows the pore pressure in aquifer and theprinciple stresses under the initial stress state. In
initial state, the pore pressure is uniform distribution
in aquifer. The drainage face was set at the edge ofthe bottom aquifer. The maximum shear stress inshaft lining is recognized around the aquifer andbedrock zone as shown in Fig. 7(a).
Considering the ratio of the actual mining area tothe simulation area is 209, the average water
discharge can reduce to 2.7 m3/h (64.8 m3/d). As aresult of lacking of correlation parameters such as
observation well data and effective radius, and also
the poor recharge conditions of bottom aquifer, thesimulated water discharge in this simulation was set
as the 8%-10% of the average water discharge, andthen we take 5.8 m3/d for the average value. In thissimulation tests, the 5 times, 10 times, and 12 times
water discharge were also simulated in order toclarify the influence of aquifer quick drainage better.

According to the conditions of engineering
geological and hydrogeological in Baodian coal mine,the parameters of strata and shaft lining are shown in
Table 2 (Zhao, 2009).
The analytical boundary conditions were set as
follows:[1]The lower boundary was fixed in vertical

3.3 Result analysis
Fig. 7 shows the maximum shear stress in shaft

4

10th Asian Regional Conference of IAEG (2015)
lining. The location of maximum shear stress of shaft
lining transfers from the bedrock layer to the aquifer
layer following the changes of the drainage status.
This shows the aquifer drainage can change the stressstate of shaft lining.

aquifer quick drainage in four circumstances. The
pore pressure curves in the figure also have the same
trends. At the beginning of the drainage, the porepressure in the aquifer has a sudden increase and thenbegins to reduce. And the larger drainage, thegradient becomes much larger. The pore pressure
does not always reduce but corresponds with
Mandel-Cryer effects: the pore pressure decreases
after the first increasing (Selvadurai and Shirazi,2004).

Fig. 7 Location change of maximum shear stress inshaft lining

Fig. 9 Maximum shear stress condition duringdrainage

Fig. 8 Maximum shear stress condition duringdrainage
Fig. 8 shows the Maximum shear stress condition
during drainage. The maximum shear stress appears
in the inner shaft lining and the position is farthest in
the shaft lining to the flow direction. It can be said
that the part of shaft lining which is facing thedirection of flow is the much more affected part. In
other words, the facing part of shaft lining is the weakpart and liable to failure.
Fig. 9 shows the maximum shear stress condition
during drainage. Four circumstances of drainage
conditions show in this figure, and the conditions ofmaximum shear stress in the shaft lining have thesame trends. Following the increase of the drainage ina short time, the value of maximum shear stress inshaft lining has a sudden increase, and at the
beginning of early drainage, it reaches to the
maximum, and then trends to constant. Obviously, thelarger drainage, the value of maximum shear stressbecomes much greater.
Fig. 10 shows the pore pressure condition during

Fig. 10 Pore pressure condition during drainage
4.

Conclusions

According to the above analyses and simulations,the following results can be obtained.
[1] During the short term aquifer drainage, thelocation of the maximum shear stress in inner shaft
lining transfers from bedrock layer to aquifer layer,
and the shear stress in inner shaft lining increases.
[2] Following the increase of the drainage in a shorttime, the value of maximum shear stress in shaft
lining has a sudden increase and then trends toconstant, and the pore pressure in the aquifer has asudden increase and then begins to reduce. The larger
drainage, the shear stress in shaft lining increases
drastically at the initial drainage, and the gradient ofpore pressure curves becomes much larger.
[3] As the maximum stress initiates around the5

10th Asian Regional Conference of IAEG (2015)
interface of bottom aquifer and bedrock, when porepressure has an obvious change, the shear stress ininner shaft lining reaches to maximum. Therefore, theearly drainage stage is a dangerous period to thestability of the shaft lining.

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Acknowledgements
The authors are grateful for financial assistanceprovided by the Basic research program of Jiangsu
province (Natural Science Foundation) (No.
BK20130179).

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