numerical simulation of static liquefaction in tailings pond
TRANSCRIPT
Numerical simulation of Static Liquefaction in tailings pond
Yang Liu1, a, Xuetong Zhao1, b,Hongxiang Yan1, c 1Department of Civil Engineering, University of Science and Technology Beijing, 100083, China
Keywords: Static Liquefaction; Numerical simulation; Tailings pond
Abstract. Static liquefaction is one of the main causes of flow slide destruction in tailings pond. This
paper analyzed the static liquefaction behaviors in tailings pond through the development of
displacement, deformation and pore pressure ratio. Based on the simulation results, some conclusions
were obtained. Fast discharge of tailings will fasten the increase of pore pressure. The dam-toe in
tailings pond is very easy to be eroded, leading to introverted destruction. The liquefaction of sand
layer in foundation would cause the tailings dam’s slip failure. With the arising of tailings, pore
pressure increased continuously expanding to the foundation under the dam.
Introduction
Tailing pond plays an very crucial role in the mine production, which is the most important facility
maintaining the normal production of mine. It is also an artificial debris flow sources involves much
potential energy, which will lead to dam break and bring about such serious accidents as inundating
the crops, channel filling, environment pollution. The destruction is much more serious than the dam
break of common dam[1,2].
The instability induced by liquefaction is one of the main causes leading to the dam break. One part
of sand liquefaction is caused by static loading and another part is the re-circulated liquefaction
caused by dynamic loading including earthquake, explosion and mechanical vibration. There are so
many researches on the re-circulated liquefaction, while only few researches focused on the static
liquefaction, static liquefaction didn’t draw attention in recent decades, so the research on static
liquefaction fall behind that of re-circulated liquefaction in China. Static liquefaction is the most
common destruction to tailings pond, it has drawn great attention abroad, but lacking of research at
home[3].
This paper adopt the Two-invariant Superior Sand Model developed by Boukpeti, then conduct a
numerical simulation on tailings pond under static loading, finally analyze the static liquefaction
behavior by the global stability, displacement, pore pressure and deformation[4,5].
Static liquefaction
Static liquefaction can be defined as pore pressure increases in saturated sand soil under static loading
decreasing the shear strength and effective stress, then sand will behave like fluid. The principle is
shown in fig1, stτ is the initial stress of sand, Φcv is the critical stress ratio. Curve 1 and curve 2 are
stress paths under monotonic load and cyclic load respectively. However, the transient load produced
by both of them will cause the liquefaction of sandy soil. As shown in fig1, when the stress exceeds
the failure line, the shear strength will decrease sharply to the stable state corresponding to the
residual strength uts . Although different stress path of monotonic load and cyclic load, they reach the
same final state.
In Fig1, the response of monotonic load suggests that sand’s shear strength reaches peak under
small strain and then decrease to the stable state correspond to the residual strength, during the shear
process, sand always in a state of shear shrinkage, at the same time, pore pressure increase constantly
and effective stress decrease, when reaches the later stage of the softening sand will deform
continuously under the condition of constant shear and constant strain.
Advanced Materials Research Vols. 671-674 (2013) pp 76-79Online available since 2013/Mar/11 at www.scientific.net© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.671-674.76
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Fig.1 The response of saturated loose sand of tailings under monotonic load and cyclic load
Numerical model
This paper adopt the Two-invariant Superior Sand Model developed by Boukpeti[6] which is
improved continuously, this model is an elastoplastic model with single yield surface, which consider
the basic characters of sand’s static liquefaction, and provide an good prediction ability. The
constitutive model is combined into FLAC to simulating the Canada liquefaction test（CANLEX）.
The materials yield, plastic fluid, softening, and the plastic strain after yield can be analyzed precisely
by FLAC, furthermore static and dynamic analysis also behave very well. CANLEX conducts the site
full-scale test for loose saturated sand’s liquefied flow slide under fast loading. In the test ,the dam is
constructed on the processed sandy soil foundation, Original water table in the sand is 318m, the dam
consist of clay, it’s 8m high and the ratio of slop is 2.5:1. Containment dam consists of sand and is
10m high. In the test, the loose saturated sand of tailings discharges rapidly. The test model is shown
in Fig.2 and material parameter is given in table.1.
Fig.4 Canada liquefaction test’s section view
Table.1 CANLEX material physical mechanical parameter
Material Bulk modulus
(kpa)
Shear modulus
(kpa)
cohesion
(kpa)
Internal frictional
angle(°)
Hydraulic
conductivity
(m/sec)
density
(T/m3)
Clay dam
Containment dam
Sand of tailings
Sand of foundation
30000
30000
10000
2100
30000
30000
100
210
30
0
2
3
0
36
0
33
1×10-8
8×10-6
1×10-4
3.25×10-7
1.5
2.0
1.7
1.9
Numerical results
Fig.2 and Fig.3 show the changes of pore pressure and pore pressure ratio. As shown in Fig.2, the pore
pressure value of the sand layer of foundation is larger than other areas and decrease in the clay dam’s
direction, which is caused by Seepage drainage of foundation. The pore pressure of dam-toe at clay
dam’s upstream changes a lot, while that of downstream changes little. With the rising of tailings, the
pore pressure of upstream increase and seepage developed continuously, and dam-toe eroded by pore
pressure and seepage.
Advanced Materials Research Vols. 671-674 77
Pore pressure ratio is shown in Fig.3, the pore pressure ratio of top layer is larger, which suggests
that tailings water hasn’t drained by seepage and the layer contain large water. Compare the pore
pressure ratio of 4m (Fig.3 (a)) with that of 8m (Fig.3 (b)), pore pressure of inside dam toe increase
continuously with the rising of tailings, at this development, inside dam toe will liquefy and flow, and
the dam will dump inside, at the same time, pore pressure ratio of the foundation layer under dam
increases and lead to the foundation’s liquefaction.
(a) Pore pressure of 4m
(b) Pore pressure 8m
Fig.2 Pore pressure at specific depth of tailings layer
(a) Pore pressure ratio of 4m
(b) Pore pressure ratio of 4m
Fig.3 Pore pressure ratio at specific depth of tailings layer
If the depth of the tailings reaches 16m, which can be realized in the test by increasing the weight
of the material, the simulation is shown in Fig.4, pore pressure ratio of the foundation under dam arise
to very large value, the pore pressure ratio reaches 0.7 to 0.9, so the foundation has liquefied, the
maximum of displacement reaches1.83cm, which means serious deformation, move outside at
upstream and arch upward obliquely at downstream.
(a). The pore pressure of 16m
78 Construction and Urban Planning
(b). The pore pressure ratio of 16m
(c) the displacement vector of 16m
Fig.4 Simulation results of 16m
Conclusion
This paper analyzed the static liquefaction behaviors in tailings pond and some conclusions were
obtained as following:
(1) Faster the tailings is discharged, harder the pore pressure dissipates; with the arise of tailings,
the pore pressure of foundation layer increases continuously expanding to the clay dam.
(2) The dam toe at the upstream of dam behave apparent rotational trend under the pushing of
tailings and seepage. However, the dam toe at the downstream of dam arches upward.
(3)The rapid arising of tailings will cause the foundation liquefied and flow, and then the dam
breaks.
Acknowledgments
The authors appreciate the financial support of the Program for New Century Excellent Talents in
University (No. NCET-11-0579) and the Fundamental Research Funds for the Central Universities of
China.
References
[1] Xuyang Xie, Wenqi Tian, Yunhai Wang, Xingkai Zhang: Journal of Safety Science and
Technology. Vol. 02 (2009), p5. (In Chinese)
[2] Lihong Yang, Quanming Li, Quangming Cheng, Yunhai Wang: Journal of Safety Science and
Technology, Vol. 4, No. 5 (2008), p28. (In Chinese)
[3] M. Rico, G.. Benito, A. Diez-Herrero: Journal of Hazardous Materials, Vol. 154, No. 1
(2008),p79.
[4] Psarropoulos, Prodromos N, Tsompanakis, Yiannia: Canadian Geotechnical Journal, Vol. 45, No.
5 (2008), p663.
[5] Claudio di Prisco, Silvia Imposimato: International Journal of Solids and Structures, Vol. 39, No.
13 (2002), p3523.
[6] Boukpeti N, Mroz Z, Drescher A: Canadian Geotechnical Journal, Vol. 39, No. 6 (2002), p1243.
Advanced Materials Research Vols. 671-674 79
Construction and Urban Planning 10.4028/www.scientific.net/AMR.671-674 Numerical Simulation of Static Liquefaction in Tailings Pond 10.4028/www.scientific.net/AMR.671-674.76
DOI References
[3] M. Rico, G. Benito, A. Diez-Herrero: Journal of Hazardous Materials, Vol. 154, No. 1 (2008), p.79.
http://dx.doi.org/10.1016/j.jhazmat.2007.09.110 [4] Psarropoulos, Prodromos N, Tsompanakis, Yiannia: Canadian Geotechnical Journal, Vol. 45, No. 5
(2008), p.663.
http://dx.doi.org/10.1139/T08-014 [5] Claudio di Prisco, Silvia Imposimato: International Journal of Solids and Structures, Vol. 39, No. 13
(2002), p.3523.
http://dx.doi.org/10.1016/S0020-7683(02)00164-6 [6] Boukpeti N, Mroz Z, Drescher A: Canadian Geotechnical Journal, Vol. 39, No. 6 (2002), p.1243.
http://dx.doi.org/10.1139/t02-066