10th Asian Regional Conference of IAEG (2015)

Post-evaluation of effect of large-scale landslide control based onmonitoring measurement
Zhongping ZHANG(1), Honggang WU(1)(1) Northwest Research Institute Co., Ltd. of CREC, Lanzhou 730000,
ztxbywhg@yahoo.com.cn
Abstract
Post-evaluation of effect of landslide processes is essentially prevention informationcollection, analysis and feedback process. This paper based on an analysis by long-termmonitoring data of landslide of underground drainage holes, anti-sliding pile deformation ofretaining structure, internal displacement of the Sichuan-Tibet highway bridge before
bleaching ~ gentian section landslide No1, Monitoring data shows that after years of adverse conditions landslide No1 as a whole remained stable for the time being, there are no
obvious signs of quick slide. But the partial slope is still in the process of stress adjustment
under the adverse effects of external environmental factors which have a small settlement
and creep deformation, thus it should be added to the necessary engineering measures. It
will provide the basis for the future control design.
Keywords: landslide, monitoring measurement, post-evaluation
2. The landslide group profiles of Qian-Long paragraph in Sichuan-Tibet Highway
The paragraph Qiandiao Bridge to Longdan
Stream (K2710+600~K2732+200) of Sichuan-Tibet
Highway, whose full-length is 22.8Km, located at theeast slope of Erlang Mountain and upstream of
TianQuan River, is the key in the transportation between Sichuan and Tibet(Zeng,2003). This paragraphis in a complex natural environment. At the sametime, due to the construction behaviors of human being in rainy season, some sub grade diseases like collapse and landslide happened inevitably in this road.
Two rainstorm between July and August 1997
brought the road a more serious disasters(Zhang,2000). The subgrade and pavement of two
kilometers road from K2730 to K2732 deformed severely, and the rainstorm also induced the resurrection of some old landslides including No.1 landslide.
According to the on-site inspection, there were many
longitudinal jagged cracks on the cement board
pavement between road (K2729+920~K2730+425)
No.1 landslide, among which the longest cracks
reached about 60 meters. About 10cm dislocation
happened in this paragraph and local roads even appeared the pavement floating phenomenon. Bothsides of the highway had different degrees of slump.
The rear edge of slope occurred a ring tension crack
which nearly cut through the slope. (Fig.1).

1.Introduction
In terms of the evaluation of effect of landslide
process, most of us only have a completion acceptance according to the specification. However, weknow little about the operating conditions of the process after it completed. In this field, there’s still not aunified standard and evaluation system(Wang,1998).
Deng proceeded a study on the effect of highway
slope maintenance engineering in Shaanxi, and Zeng
did an evaluation about the treatment effect of Sichuan-Tibet
Highway
ErlangMountainslope(Deng,2002). But their studies are only limited
to some kind of construction or effect in the landslide
control engineering, such as the stress form of anti-slide pile, the influence of underground water to thesliding surface, and so on. There are little studies on
the post-evaluation of effect of landslide processes
based on monitoring measurement. Restricted to thequantity of the treatment engineering and observational data, people do not have a study in this field fora long time. This paper is for the post-evaluation oflandslide process in the Sichuan-Tibet Highway Qiandiao
BridgetoLongdanStream(K2710+600~K2732+200). It’s based on the monitoring measurement data of underground drainage
holes, anti-slide pile and retaining structure deformation and deep landslide displacement. And it do a
deep analysis on the data changes before, during andafter the engineering in order to evaluate landslide
stability under adverse conditions for many years.(Liuand Yu ,1984)

3. Controlling measures
No.1landslide belongs to the large complex

1

10th Asian Regional Conference of IAEG (2015)

landslide. The slope had been broken and a attained limiting equilibrium condition. So it must be
governed timely. As most of the slope average thickness are above 35 meters, general anti-slide pile isdifficult to meet the requirements of stabilizing force
Instead of prestressed anchor rope friction pile andprestressed anchor cable frame beam were used in themain works combined with the comprehensive management of drainage works. Figure 2 is the specificengineering measures. The project used a variety ofmeasures including pile, anchor frame, drain dyke,
anti-slide retaining wall, and elevation drain hole.

Fig.3 Anti-slide piles of western part
Eastern part: 14 general anti-slide pile are set up
in the east part of No.1landslide. The piles are madeof C20 reinforced concrete (Figure 4).

550

4 00

5 00
50

0

1990

3 50
6 00

1980

41.2m

1940
1930

30°

300

F2

50 0

1950

600

1960

49m

500

1970

l

0
20
20

4 00
3 00

2 50

视电阻率等值线

钢筋混凝土抗滑桩桩 长 30m

0

h

54.1m

1920
1910

NE3°

钻孔9-1
1942.09

c

0

2000

公路中心线
1962.60

25

2010

钻孔9-2
1964.202020

钻孔9-3-3
1987.69

2030

钻孔9-3
2001.63

2040

钻孔9-4
2023.50

高 程 (米 )

250

50.3m

400

100

1900

40.3m

500

软弱带

200

Fig.4 The east part of section (section photograph
XI-XI)
3.2 Prestressed anchor cable frame
Inside: Three pieces of anchor cable frame are installed on the inside of the road. They are controlled
by highway mileage and the distance from the centerof the road which is 8m from the center for all frames(Figure 5). Among them, 23 rib-columns are set up
from K2729+990 to K2730+78; 10 rib-columns are
installed from K2730+182 to K2730+222; and there
are 31 rib-columns from K2730+222 to K2730+342.
The material of rib-column and beam is C25 reinforced concrete.
Outside: We use 47 rib which are controlled by
the control point coordinates on the outside of theroad. Every rib-column has 3 bundles of anchors
whose specification is 15Φs15.2.

Fig.1 The landslide and stratification distribution diagram of the Sichuan-Tibet Highway from Qiandiao
Bridge to Long danxi Bridge

Fig.2 The layout of the No.1 landslide stabilizing
structures of segment of K2730 in Sichuan-Tibet
Highway
3.1 Anti-slide pilesWestern part: The west part of No.1 landslide is
the most active, the most severely damaged section. It
is the main target to restore. So 42 prestressed anchor
rope friction piles, which are made of C25 reinforced
concrete, are set up in this range (Figure 3). In viewof most anchor rope friction piles setting deeply,
there are 2 rows for a total of 20 grouting anchorswith diameter 36mm under every pile.(Zheng,2005)

Fig.5 Prestressed anchor cable frames
3.3 Retaining walls
Retaining wall of the riparian toe plays the significant role of retaining toe and erosion prevention.
It’s the necessary measure to prevent the failure ofanti-slide pile and frame caused by the continuing
erosion of the toe down to the slope. The design
height of the wall is 8 meters, following Figure 6.
3.4 Drain dyke
Drain dykes are divided into intercepting drain

2

10th Asian Regional Conference of IAEG (2015)

outside the landslide and drain inside the landslide.
There are two drain dykes outside the landslide andtwo groups of drains inside the landslide. The total
length of drains is 950 meters. The former should beconstructed as soon as possible, and the later may berelatively lagging ,following Figure 7.

process an engineering geological survey on the sections of the landslide and produce a treatment project
design based on the survey in 1998. In November
2000, Northwest Research Institute of C.R.E.C werecommissioned by Sichuan Provincial transportation
Department again to do a long-term monitoring on
the landslide with dynamic methods. And during
2002 to 2004, the institute were third commissioned
to carry out a follow-up observation after the projectof No.1 landslide and No.2landslide completed fortwo hydrological years in order to assess the project
objectively with scientific data and facts.
5. Monitoring and measuring results and analysis
5.1 The monitoring results of deep displacement
The results observed during many years before
2004 reveal: deformation of the No.1 landslide mainly focuses on the road and the shallow and middle
parts of slope below the road, severe deformation
phase is also mainly focused on the rainy season
when more rainfall concentrated from July to September every year, which indicates that slope affectedby the factor of rainfall is more prominent. Summarized as follows:

Fig.6 Retaining walls

5.1.1 Judging from the nature of the landslide
The rock and soil, constituting the No.1 landslide,is crushed, loose, severe weathered and the slope ishigh and steep, vegetation developmental, irregularity,of which the structure is very conducive to the infiltration of surface water which can cause apparent
effect on the erosion and softening for the sliding soil,
which leaded the slope to astatically develop. Analysis from the evolution process of landslide, justbecause of the stability losing of preceding stage ofthe landslide cause hinder stage of the landslide tolose support force and be towed to come into being
deformation. And now Sichuan-Tibet Highway is just
local to the junction of preceding stage and hinder
stage of the landslide, which appears apparent deformation by towing and pushing.

Fig.7 The rapid stream slot for drainage
3.5 Elevation drain holedeep drainage project design is a stronger technical work. Whether the accurate determination ofwater points or the actual construction could be carried out is extremely difficult to. 11 elevation drain
holes are supplemented timely after the investigation
for the additional design in the flied.
3.6 Slope processing
Slope processing is to supplement and improve
the whole project. It can be a part of the retaining
wall or slope protection construction, mainly to stabilize the slope, to fill cracks and green protection.

5.1.2 Judging from effects of the project before
and after treatment
Before the treatment (from March 1998 to October 1999): stability of landslide is relatively poor,
basically in a state of instability. Deformation ismainly in the middle slide zone of lower stage oflandslide, however deeper layers appear intermittent
creep deformation, the higher slide zone of landslide
mostly appear shallow deformation. In the construction of treatment (from October 1999 to the end of2002): disturbance in construction has apparent effecton the stability of the slope. Mainly after the construction of anti-sliding pile and anchor cable, just as"worse", whereas increasing loose surface, whichcause internal stress of the slope to concentrated re-

4. Long-term dynamic monitoring process
The occurrence of roadbed disease in this paragraph caused great attention of Ministry of Transportation Highway Division and Sichuan Provincial
Communications Department. They had organizedlandslide experts to view the situation on the scene
and discuss countermeasures for many times. Afterseveral expert reasoning conferences, the remediationfor original line program was adapted finally. To thisend, Sichuan Provincial transportation Department
entrusted Northwest Research Institute of C.R.E.C to3

10th Asian Regional Conference of IAEG (2015)lease. After completion of the treatment (from the endof 2002 to the end of 2004): landslides tend to bestable. In October 2002, retaining and strengthening
works was coming to late stage, the constructions ofanti-sliding pile and anchor were gradually playing a
supporting role, but intermittent or seasonal deformation persists, destructive deformation may still
occur. As a result of the treatment, the deformation
phenomenon of the landslide has been inhibited.
Whether the deep displacement monitoring of landslide or the results of stressing deformation monitoring of anti-slide piles all reveal which compared with
before the treatment, deformation in shallow andmiddle layer of the landslide has been largely discontinued, which in deep layer only appears seasonal orintermittent creeping, having no impact on the overall
stability of landslides. The observations of 2008 revealed: during observations, new slide zone was notfound in all of the three drilling holes, and there were
not any phenomena of sudden deformations which
once appeared in the old slide zone. Therefore, deformation of the landslide is still greatly influenced
by rainfall and activities of groundwater, the probability of coming up sudden destruction is verysmall. As shown in table 2-4.

5.2 Observation results of the structure stress
In order to detect the stress of anti-sliding piles
and retaining structure, in November 2001, three piles
embedded inclinometer tubes, including No.5plie(general anti-slide pile), No. 8 pile and No.20 pile
(anti-sliding pile with prestressed anchor cable), werechosen as testing piles to observe. As of November
2004 observations are as follows (as shown in table
5).
5.2.1 The monitoring for No.5 pileNo.5 pile, is a general pile, was located on thenature slope outside the highway in section Ⅸ-Ⅸ
and was completed on July 20, 2001. Monitoring of
deformation of the pile in early days has fully verified that general piles belong to the passive mechanical structure. The pile, at the beginning of completing, does not immediately play a supporting role.
When the thrust of landslide act on the pile, it
makes the pile come into being displacements anddeformation, only after the formation of subgroupreaction, can the pile play a supporting role.
The observation results of 2008 show that thedisplacement at the top of the pile was not obvious
and the overall trend was still in a small state. From

Table 1 The statistic table of observation points of No.1 landslide at the present stage
Position

Section No.

Hole No.

Depth(m)The time offorming hole

Detect depth at the
moment(m)West part

Section Ⅵ-Ⅵ
General pile

New 6-2#
5#

67.0
30.0

2001/7/25
2001/7/20

65.0
30.0

Section Ⅸ-Ⅸ

New 9-2#

61.5

2002/1/5

47.5

9-3#

40.2

1998/3/5

40.0

8#

47.5

2001/10/12

47.5

#

63.5
309.7

2001/12/12

63.5
293.5

5#
8#
20#
16#
25#

24
29
39
16
18
126

2001/7/20
2001/10/12
2001/12/12
2001/10/12
2001/12/12

4
25
13
14
13
69

5#
8#
20#
16#
25#

20
22
32
18
18
110

2001/7/20
2001/10/12
2001/12/12
2001/10/12
2001/12/12

3
15
13
15
13
59

8#
20#
16#
25#

4
4
3
3
14

2001/10/12
2001/12/12
2001/10/12
2001/12/12

0
4
3
3
10

East partAnti-sliding pile

20
Total
General pile
Anti-sliding pile
Soil pressure
Anchor frame
Total

Steel bargauge

General pile
Anti-sliding pile
Anchor frame
Total
Anti-sliding pile

Dynamometer

Anchor frame
Total

4

10th Asian Regional Conference of IAEG (2015)

the test data of earth pressure cells and steel bar
gauge buried in pile, the three test results from 2008
come to be approximately equal, which show thrustfrom the mountain side of the pile varies little.

state. From the test data of earth pressure cells andsteel bar gauge buried in pile, the three test resultsfrom 2008 come to be approximately equal, whichshow thrust from the mountain side of the pile varies
little this year.

5.2.2 The monitoring for No.8 pile
No.8 pile, a prestressed anti-sliding pile, waslocated on the nature slope outside the highway insection Ⅶ-Ⅶ and was completed on October 20,
2001. Preliminary observations indicate that the pile
was in elastic deformation during the observation
period from 2001 to 2002, the pile bore obvious
stress. The data tested from the earth pressure cells
and steel bar gauge buried in the No.8 pile before
2004 displays the basic law is that earth pressure
close to the side of the mountain gradually increased,
which decreased to the side of river, and the resistance of landslide is twice of the thrust. It shows
the rocks around the pile are soft-hard inter phase,
especially the rocks ahead the pile to the side of river,
was in poor stability, which moved down the slope.
The compressive stress of steel to the side of mountain continued to increase, the same to the tensilestress of steel upper to the side of river, which causedby the thrust of landslide. The top of the pile grew
displacement toward the side of river, which caused
anchor cable to elongate and the ensile stress to belarger.

Table 2 The S-T curve graph of 9-2# hole of 1# landslide in LongQian part of the Sichuan-Tibet Highway

Table 3 The S-T curve graph of 9-3# hole of 1# landslide in Long Qian part of the Sichuan-Tibet High- way

5.2.3 The monitoring for No.20 pile
No.20 pile, a prestressed anti-slide pile as well,
was located on the nature slope outside the highway
in section Ⅵ-Ⅵ and was completed on December 10,
2001. Preliminary observations indicate that the pile
was basically in elastic deformation in 2002, with thesame deformation characteristics as No.8 pile, andthere was significantly obvious weighted phenomenon within the depth range from 42 meters to 48 meters. The data tested from the earth pressure cells andsteel bar gauge buried in the No.20 pile before 2004
displays that the readings from earth pressure cells
located in the lower part of pile close to the side of
the mountain increased, from which can judge that in
the role of thrust coming from the middle layer of theslide zone above making the anti-slide pile generated
rotation, which can be described as the top of pile
moved to the side of river and the bottom of pile
moved to the side of mountain. Meanwhile, the landslide was mainly creepy in the middle and deep layer.
The tensile stress of steel bar meter by the river side
more than 19 meters continued to increase, which is
because the thrust of landslide to the side of mountain acting on the pile made the top of the pile comeinto being large displacement and the tension of theanchor increase.
The observation results of 2008 show that thedisplacement at the top of the pile was not obvious
and the overall development trend was in a stable

Table4 The S-T curve graph of 6-2# hole of 1#
landslide in LongQian part of the Sichuan-Tibet Highway

5

10th Asian Regional Conference of IAEG (2015)

Tab.5 The comparing of the observation results of 2008 with before of No.1 landslide in Long Danxi

Hole
No.

Test
depth
(m)

Slide zone

63

Top

Tendency(°)∑S(mm)

#

8

47.5

Top

Tendency(°)∑S(mm)

5#30

Total cu-

ment (mm)mulative

depth (m)∑S(mm)

20#

Annual cumulative value of displace-Top

Tendency(°)

amount

2001

2002

2003

2004

2008

--

37.52

73.45

24.01

7.6

262.6

--

300

313

311

13.18

14.49

35.61

24.1

27.2

248

63

43

346

70

46.98

11.01

8.12

5.32

12.4

153.6

15

14

66

8

6.Conclusion and recommendations
This paper based on the monitoring data, throughthe observations for years and field reconnaissance,
judging on the basis of whether the control targets andeffects have reached, reveal that theⅠ＃ landslide
temporarily remain stable overall, and there is no obvious sign of rapid sliding, which can provide the basis for the future engineering design of landslide control.
This area of the landslide was in complex situations on geological conditions, the causes and mechanisms of landslide deformation, and many affective
factors existed. Local parts of the slope was still in theprocess of the adjustment of stress, which would appear deformation of tiny sedimentation and creep age
under the adverse effects of external environmental
factors, then necessary engineering measures should
be added for it.

Annual inclination

Inclinationof the pile

(°)

(°)
2001

2002

2003

2004

2008

0.06%

0.12%

0.04%

0.01%

4.81%

0.03%

0.03%

0.08%

0.05%

0.05%

5.04%

0.16%

0.04%

0.03%

0.02%

0.04%

0.59%

Zhang Z Y. (2000). The present status, technicaladvance and development trends of landslide remedial measures. Journal of Geological Hazards and Environment Preservation, 11(2):1-9.

References
Deng D L. (2002). The effect of highway slope
protection engineering in Shanxi province. Xi’an:
Chang’An University.
Liu G D, Yu J M. (1984). Measurement and variation of landslide thrust. Landslide Symposium,
105-115.
Wang G X. (1998). The new progress in the
study of landslide disaster prevention and control in
China in the 21st century. Academic Symposium
about landslide and debris flow in Lanzhou province.
Lanzhou: Lanzhou University Press.
Zheng M X. (2005). Study on the post evaluation of the effectiveness of landslide control. Nanjing:
He Hai University.
Zeng Y H. (2003). The assessment of Sichuan-Xizang highway Erlang mountain K2370 section No.1 landslide control project. Nanchang: East
China Jiaotong University.

6