10th Asian Regional Conference of IAEG (2015)

Interaction between countermeasure works and landsliding mass: a case study
Ning Ma(1), Huimin Ma(2) and Wenqiang Feng(3)(1) Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University,
Sichuan, 611756, China
E-mail: 870336786@qq.com(2) China Railway Academy Co., Ltd. Sichuan, China(3) Northwest Research Institute Co., Ltd. Gansu, China
Abstract
In this paper, we present differing filed monitoring data obtained from a landslide
located near an airport in southwest China. This landslide originates from a dip slope withweak bed rocks and high earth fill. To stabilize this landslide, differing function structures
had been constructed, and the deformation/displacement features of these structures hadthen been monitored and analyzed. We analyzed the possible stress state of these function
structures during their construction, and examined the most unprofitable stress state that
may result in large deformation of the structures. The relationship between the stress stateand large deformation of these structures, as well as their relationship to the stability ofslope, were analyzed. These results may not only provide good experience for us toperform countermeasures in stabilizing landslides in similar geoenvironment, but also canprovide scientific evidences for us to better understand deformation or sliding mechanismsof similar landslides.
Keywords: Landslide movement, deformation of function structure, interaction,
landslide stability, large deformation

1. Project Introduction

significant prestressed anchor-cable anti -slide pileson the slope toe.

A certain airport located on the gently-inclined
dip-slope regionally in the poor geoenvironment
was built in May 2000 in southwest China and themost extreme height of high embankment near west
runway goes up to 128m. So there has been sliding
and settlement deformation in existence.
The No.12 landslide slid massively andintegrally above the fossil landslide named
Yushuping, which as the reason triggered it revival.
As such, the landslide preventions especially flood
preventative engineering was implemented from
September 2009 to May 2010, which involved theanchor bolt frames, the steel pipe piles, shot-crete
support and so on. But the slope remained sliding
after the preventions had been implemented. Thenthe second emergency project were put out based on
the original preventions on the trailing edge of thelandslide, which arranged the anchor podiums, theanchor foundation beams and cluster steel pipe piles
with prestressed anchor-cables in order to restraint
the large deformation in the landslide and keep it
steady temporarily(Liu et al., 2004). Only in thisway can it be safe to continue constructing the most

2. Geological Summary
2.1 Geomorphology
Overall this field region is located in mountainravines to landscape of Zhongshan whose terrain is
ups and downs aslant from northwest to southeast.
the airport where is situated on south slope of theribbon mountain ridge where the strike trends toNE21° and approaches the south bank beside Jinsha
river, branch of Yangzi river. There has a high earth
fill left behind it with a height of about 128m and aaverage slope of 21° approximately.
The landslide area which lies east of the runway
pertains to the mountain landscape with erosion
landform. The topography of the landslide iscomplex and the average slope is 15-20° probably.
Meanwhile, gullies of the landslide body develop
entirely with spreading numerous ponds. Figure 1 isa photograph of the airport landslide profile(He etal., 2002).

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Fig. 1

2.3 Tectonics Profile
In view of regional tectonics, the filed area islocated on the south section of Panxi rift valley
where the middle of the north-south structural zone
in Chuan-Dian and "歹" shaped structural zone in
Dian-Zang intersect. In general, tectonic situationsuch as fold and fracture develops complicatedly
mainly based on the N-S and the E-W tectonic
condition and the E-W and the N-W tectonic
condition take second place.
The landslide area is based on syncline structure
whose axial direction is from N-W to S-E crossing
the center point of the runway nearby. The
occurrence shows 130-140°∠12-14°, as shown in
Figure 3.

the complete picture in landslide area

2.2 Stratigraphical lithology
The whole area of the landslide is underlain by
Quaternary(Q4) and Jurassic(J3Y) Yimen formation.
The Q4 stratum includes artificial fill, cumulative
material and residual material, which are composedof gravel soil with massive rock. All of them mainly
distribute fill section and posterior of the landslide.
The massive rock content with a width of about
8-45m is high in artificial fill. Simultaneously, thecumulative material and residual material consist of
gravel soil primarily with a width of about
15m-30m with fabricable status and water
permeability. The Jurassic stratum for Yimen
formation is based on carbonaceous mudstone andsandstone. One side, carbonaceous mudstonereflects moderate weathering even strong
weathering and the moderate weathering component
is argillic texture with weak anti-efflorescence andbeing apt to crumble and soften. The other side, thethick stratified sandstone reflects slight weatheringin which argillaceous cement exists. The two interbanding stratum form together the foundation of
the fill and the main body of the ancient dip
beddinglandslide
as well. The condition
illustrated in Figure 2.

Fig. 3

2.4 Meteorological and Hydrogeology
The climate of this area is tropical-DHV, which
performs long summer period, strong solar radiation
and undifferentiated seasons all year round. Rainfall
happens in the rainy season during May to October.
The largest annual rainfall is about 1000 mm andthe average is about 800 mm, 95% of the wholeyear. On the contrary, the period from earlyNovember to May the following year is the dry
season. The rainfall distribution is in the Figure 4.

Fig. 4
Fig. 2the sketch map about occurrence

average rainfall distribution in landslidearea(2005-2009)
The ground water of the landslide is subjected
greatly to the season and gives priority to theperception recharge but no unified undergroundthe Stratigraphical lithology in landslidearea

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water level. On one side, both sides of the platform
near runway accepts atmospheric perception andconverses it into the pore water in the fill. On theother side, the fissure water from the westernsandstone recharges the groundwater from west toeast alone the stratigraphical occurrence.
Meanwhile, the carbonaceous mudstone and theargillaceous shale act as the relative impermeable
layer.

highearth fill sliding alone the top of bedrock under.
Main sliding zone is the surface where the bottomside of the fill and residual layer of the sandstone
and mudstone intersect. So the reasons for sliding asfollows:
1. Yushuping ancient landslide which had slid
once is the basis of No. 12 landslide but sustains
always creeping slip. As such, sliding weakens
sliding resistance effected on the toe of thehighearth fill.
2. The lack of recognition to unfavorable
geological condition especially ancient landslideleaded to choose unreasonable airport position.
Generally , it is unsuited to load on such a fill here
particularly with a depth of about 60m-120m.
Furthermore, original retaining structures and shear
keys did not meet the requirement for stabilizing thehighearth fill insufficiently.
3. The infill in such a highearth fill(60m-80m)
spreads uneven with inferior gradation andsubstandard degree of compaction, which leads soil
mass to be loose and pores to be dense. It isconvenient to furnish channels for undergroundwater filtrating. Moreover, the settlement anddeformation makes the soil mass slake above thefree-draining face, which produces many strain
cracks and applies channels for superficial water
infiltrating.
4. The climate of tropical-HDV arouses rainfall
heavily and centrally here. So the slope area owns alarge collecting area and then rain filtrates into theinterface between the fill and bedrock to tenderizecarbonaceous mudstone, which afterwards forms
sliding zone. In addition, underground water line
rises in the slope rapidly and provides hydrostaticpressure to reduce the stability of the slope. As
show in Figure 6 is about the underground water
variable condition of detecting hole.

3. Landslide (No. 12) Mechanism and stabilizing
structures
The established procedure for NO. 12 landslide
continues almost 2 years.
Rainy season in 2010, some deformation was
detected on the fill with a height of 30m of thecrown in the No.12 landslide, which may lead tolarge scale sliding endangering the runway . So it isessential to take measure for emergency
projects(Liu et al.,2012).
April in 2011, the emergency engineering had
been accomplished. So the airport succeeded innavigating. But the stabilizing structure on
anti-slide piles were not executed before the rainyseason in 2011.
15th July in 2011, large sliding occurred fornumerous rainfall. Even though, some finishedprojects were ineffective.
The slide scope about No.12 landslide is similar
to Yushuping landslide generally. The back scrap
dislocates down about 40m with tractive cracks
approaching near the runway. The volume of thelandslide is totally about 320×104m3 with a lengthof about 540m and a width of about 350m.
Boreholes indicate the thickness of the landslide is
between20m and 30m, even the deepest point
reaches 35m. The furthest distance is 45m. All theinformation reveals the No.12 landslide proves to bea extreme large scale landslide. The failure
condition as seen in Figure 5.

Fig.6 the underground water variablecondition in detecting hole SJK 0
3.2 Landslide Stabilizing Engineering
Landslide Controlling Engineering mainly
includes support engineering and drainage
engineering. The specific measures are as follows:

Fig. 5 The failure condition of the anchor cable
frames
3.1 Formative mechanism
No.12 landslide is a accumulation landslide with3

10th Asian Regional Conference of IAEG (2015)

3.2.1 Support engineering
The landslide sliding force is mainly the force
caused by its own weight and the fill. As thelandslide is large scale and the thrust is huge, thereplacement and sliding belt destruction method
was used To improve the stability of the landslide,with double-row prestressed anchored anti-slide pilesin order to reduce the fill amount and the landslide
thrust, the reinforced soil was used after 85m of soil
surfaced area was left for traffic circulation. The
scheme for reducing landslide thrust is shown in
Figure 7(failure mode), and the one with the largest
decrease was chosen.

section size, and has 5-row prestressed anchors;
3-row prestressed anchor cable frame beam(Xiao etal., 2014) is built outside fifth stage (from top tobottom) fill. Five-level reinforced soil is used whenfilling. Support engineering of landslide is shown in
Figure 8.
3.2.2 Drainage engineering
It can be seen from the above analysis that
surface water and groundwater in landslide area
have significant effect on the stability of thelandslide and that drainage of groundwater is the
key to the successful landslide controlling. A
drainage tunnel with a length of 1.6km was
excavated on the west side of the airport to stop
bedrock fissure water from penetrating into thelandslide through sandstone and fissure. The water
is directly discharged to the north side of the airport
slope; the pore water between rolling soil andbedrock surface was discharged through thedrainage tunnel as well. Where landslide belt was
replaced, stepwise bottom was excavated, and a
block stone with thickness of not less than 2m wasput, which not only increase friction resistance atthe bottom, but also serves as the drainage passage
discharging the groundwater in sliding belt.
Surface water is one of the main supplying
sources of groundwater. Therefore, it should bedischarged from landslide when waterproof work isdone in the soil surfaced area. Drainage engineeringof landslide is shown in Figure 9.

Fig.7

the tropical failure mode of NO.12
landslideIn particular, stabilizing structure is composedof double-row prestressed anchored anti-slide piles
and prestressed anchored frame. In the front of
supporting structure is D pile, and at the back is A
pile. A pile is 2.8m × 3.8m in section size(Cao andZhou, 2005), and has 6 prestressed anchors which
are in a double row layout; D pile is 3.0m × 4.0m in

Fig.8

the sectional drawing for stabilizing structures4

10th Asian Regional Conference of IAEG (2015)

Fig.9

the drainage engineering system

4. Problems of the controlling
Engineering and the solutions Process sequenceand construction quality are key factors influencing
landslide controlling engineering. In the controlling
process of this landslide, large deformation
occurred to anti-slide piles and filling was stopped.
The experts first suspected that there were design
errors, but it turned out that it was caused byconstruction quality and process sequence.
Reinforcement was performed and landslide was
successfully controlled.

In order to reduce fill load at the back oflandslide, reinforced soil is used instead of a given
embank slope (Tang et al., 2011)rate after 85m ofsoil surfaced area is left for traffic circulation. Thismethod not only reduces the fill amount, reduces
the earthwork quantity by about 1/2, and reduces
the thrust of landslide, but also reduces thecontrolling engineering. But in the implementation
process, due to traffic pressure, reinforced earth
construction was not implemented according to thedesign requirements. As a result, each layer waswith lager thickness, and the degree of compaction
was far from enough (compaction degree is lessthan 85). Large displacement and settlement ofslope was followed. The maximum horizontal
displacement on the top of the slope was 520mm,
the beam 268mm; the settlement on the top of theslope was 470mm, the beam 6mm; the maximum
horizontal displacement on the top of the slope was
2070mm, the maximum settlement 2700mm. As
force of anchor in reality was far from the designed
one (as mentioned above), double-row prestressedanchor cable pier were set between beams, in orderto prevent the overall damage caused by tension offill imposed on beam. Two-year monitoring verified
that this measure was reasonable.

4.1 Large displacement of anchor anti-slide pile
The settlement of fill causes large secondary
force for anchor. Tension is reserved when tension
technique is applied, in case damage occurs toanchor due to large force. The construction
company did not obtain the tension technique. As aresult, the tension measured is far less than thatdesigned. According to the design, anchor frame
beam of the upper slope was 400 KN in tension, theback pile beam was 800 KN and the front pile beam
700 KN. The front pile beam measured was 250 KN
in tension and frame beam 180 KN. As a result,large deformation of pile occurred. The
displacement was far more than the design
requirements (2cm). In view of the above, filling
was stopped. After tension technique was applied,
force for anchor was still far from the designed
force. The front pile was only 450kN, and the frame
beam was 250kN. Prestressed anchor cable beam
was added to each anti-slide pile in the front toavoid excessive displacement of pile.

4.3 Deformation of back anti-slide pile
After the completion of back anti-slide pile,slide belt was replaced between piles. As force ofanchor in reality was far from the designed one,large displacement occurs to back anti-slide pilewhen plane was excavated 15m below the pile. To
allow traffic circulation, excavation of slide belt
was stopped. Instead, three blind ditches wereexcavated. It was believed that large deformation

4.2 Deformation of high and steep reinforced
slope

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10th Asian Regional Conference of IAEG (2015)

appeared later might be associated with thetermination of the excavation.

pp. 60-64.
Xiao, S. G., Zhang, T. F. and Zhou, D. P. (2014):
Design method for multi-frame beams withanchor bolts used to stabilize high soft-rockslope, Vol.49, No. 5, pp. 787-792.

4.4 water drainage blind ditch
The maximum drainage is 350m3/d for waterdrainage blind ditch (1.6km) on the east side of
runway in the rainy season, and less than 10m3/d in
dry season. This water drainage blind ditch is used
to discharge water delivered from bedrock tolandslide. The blind ditch landslide at the back ofslope has not yet been completed. It isstress-tolerant and the maximum drainage is 32m3/d.
Drainage of groundwater is one of the effectivemeans to control the landslide.
5. Conclusions
With regard to the comprehensive controllingengineering of NO.12 landslide with highearth fillnear the certain airport, there are many challenging
problems of design, construction, monitoring andmeasurement. These problems are how to perform
filling with 68×104m3 for the ancient landslide body,
how to maintain stability of up to 50 meters
reinforced soil slope, how to select destructionmode, how to handle the huge landslide thrust, how
to handle the deformation of anti-slide pile, andhow to handle secondary stress occurred in anchor
when filling. Problems mentioned above werehandled well with the engineering experience, andthis controlling project is a success in general. But
these problems will be further studied based ontheory and engineering practice, in order to provide
guidance and reference for the similar engineering.
References
Cao, X. S. and Zhou, D. P. (2005): Design ofanti-slide-pile with prestressed anchor rope forhigh slope of weak rockmass, Vol. 23, No. 4, pp.
447-552.
He, Z. Y., Zhou H, X. and Wu, G. X. (2002): The
field test study of high embankment foundationcompaction in pan Zhihua airport, Vol. 21, No.
1, pp. 51-55.
Liu, T. F., Liu, J. and Liu, Y. (2012): Sliding
mechanism of high-fill slope with pre-reinforced
piles at Pan Zhihua airport, Vol. 20, No. 5, pp.
721-730.
Liu, X. L., Zhang, Z. X. and Zhou, D. P. (2004):
Improved method for anti-sliding pile withanchoring cable, Vol. 23, No. 15, pp.
2568-2572.
Tang, X.S., Zheng, Y. R. and Wang, Y. F. (2011):
The application of reinforced earth retaining
wall with geogrid in the treatment engineeringof landslide in a certain airport, Vol. 44, No. 1,6