Reports on Geodesy vol. 94 /2013; pages 6-13
DOI: 10.2478/rgg-2013-0002
APPLICATION OF INCLINOMETER MEASUREMENTS FOR
RELATIVE HORIZONTAL DISPLACEMENT INVESTIGATIONS
ON LANDSLIDE GROUNDS
Ryszar Malarski, Kamil Nagórski, Marek Woźniak
Warsaw University of Technology
Faculty of Geodesy and Cartography
Department of Engineering Surveying
Warsaw, Poland
Abstract
One of the basic criterion for safety evaluation of structures erected on
embankment or sliding slopes is relative horizontal displacement at
different elevations. Relative horizontal displacements beneath ground
surfaces are performed with inclinometer measurements.
This report presents results on horizontal relative ground displacements
with the probe SISGEO S242SV30. Investigations were performed with two
inclinometer columns 14m height embedded in Warsaw Bank Slope.
Mean square error of single observation was determined and mean relative
errors of relative displacements in relation to column height.
On the basis measurement results several relevant recommendations and
practical hints were formulated allowing to avoid survey blunders and
discrepancies in measuring procedures often encountered.
Detailed inclinometer horizontal displacement measurements results at
Warsaw hillside St Ana’s Church grounds were listed and presented.
Keywords: displacement measurements, inclinometric measurements,
monitoring
1. Introduction
Military objects, castles, sacred objects are usually constructed on elevated grounds
where unfavourable geologic conditions for foundations are encountered. Location of
such objects is chosen to satisfy obstructed access for an enemy due to safety
measures and to obtain favourable vicinity over surrounding area. In case of sacred
objects location there is an additional need to overlook adjacent buildings.
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meter measureements …
Such a location has
h some essential
e
drawbacks namely:
- esscalation of
o soil weatthering close to the structure,
s
- in
ncreased erosion effe
ect,
- ob
bstruction of ground water flow
w close to structure
s
fo
oundation,
- en
nhanced landslide effect.
e
Locatio
ons of hisstoric strucctures are characterised by subsoil
s
un
nstability and
a
are
almost always cre
eating a po
otential sou
urce of risk
k to structture stabilitty. On lowlands or
with prroximity to river valle
eys where loose stru
ucture soil exist a sttrong influence of
subsoil water is inevitable. According
g to experie
ence gaine
ed there iss a constant need
g constru
uctions with
w
found
dation re
einforcements, esca
arpment
of strengthening
reinforccement with posts and electroosmosis
s and perpetual fixxing of sttructural
elemen
nts.
Due to
o historical value, co
osts consuming mea
asures to save
s
those
e monume
ents are
underta
aken.To co
ope with the problem
m and to cure the situation
s
in
n an efficie
ent way
there iss a must for
f monitorring displacements and
a deflecttions of ea
ach structu
ure with
geodettic and geo
otechnical methods
m
a tools.
and
One of the mosst preciouss historica
al structure
es is und
doubtedly St Ann’s Church
(Fig. 1.) threatene
ed with dissaster.
2. Mo
onitoring of Vistula
a slope and
a
st. An
nna’s church deform
mation
The Vistula slope
e and St. Anna’s Church has
s been und
der supervvising of surveyor
s
om Warsa
aw Universsity of Tecchnology, Faculty
F
of Geodesy and Carto
ography
staff fro
Department of En
ngineering Geodesy, since 200
09.
F 1. A vie
Fig.
ew of the ch
hurch, the Gothic
G
apse with buttressses and ba
aroque gable
date
ed back to 1667
St Anna's Church
h, the late Gothic Church famous for its classical
c
fro
ont facade
e, is one
of Warrsaw oldesst and mosst beautifu
ul churches
s. Situated
d on the high Vistula
a slope,
was fou
unded in the mid 15
5th centuryy by Prince
ess Anna of
o Mazovia
a and given
n to the
Bernard
dine monkks.
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Reports on
o Geodesy vo
ol. 94 /2013; pages
p
6-13
DOI: 1
10.2478/rgg-2
2013-0002
In 1949
9, during the
t
construction of Warsaw's
W
East-Westt Route, d
due to a fa
ailure to
secure the slope
es of a de
eep excava
ation, the walls and vaults of the churc
ch were
cracked
d as deep as the fou
undation le
evel. The apse
a
and the north-e
eastern parrt of the
church were slow
wly coming
g down. The
T
immed
diate intervvention of a commis
ssion of
expertss of variou
us professsions preve
ented the church fro
om collapssing. The ground
around the structture was re
einforced with
w steel-c
concrete po
osts and e
electroosmosis, its
foundations were
e embrace
ed with reinforced concrete,
c
a
and
concre
ete retaining wall
were built on excavation sid
de.
Last ye
ears St Anna's Churcch has its difficult
d
tim
me again. Slits
S
and frractures ap
ppeared
on its flloor, walls and vaultss.
Compre
ehensive monitoring
g of the church, outlook
o
to
ower (churrch belfry) slope
retainin
ng walls inccludes:
- de
etermining vertical diisplacemen
nts by prec
cise levellin
ng method
d,
- de
etermining of horizzontal dissplacementts by trig
gonometriccal metho
od with
su
upplementtary precise
e distance measurem
ments,
- de
etermining of crackss aperture and lengtth and othe
er wall and
d vault dec
cays by
ph
hotogramm
metric me
ethod, tach
heometric method an
nd according to join
nt meter
(cclearance gauge)
g
rea
adings
In addittion to survveying monitoring ge
eotechnica
al investiga
ations are tto be carrie
ed out.
Fiig.2. View of the St. Ann’s
A
Church during the
e construction
of Warsa
aw's East-W
West Route in 1949 (ori
rigin PAP)
It shou
uld be poin
nted out th
hat due to
o existing geological
g
morpholo
ogical patte
ern and
unfavourable watter conditio
ons in the proximity to the slope there is a possibility of
slope slide
s
near the
t temple foundation
n due to un
nstable sub
bsoil.
Inclinom
metric mea
asurementts were ap
pplied to de
etect changes in the slope at different
d
levels. In order to
o achieve that two 14m
1
deep inclinomettric column
ns were em
mbeded
beneatth ground level (Fig. 3.).
3
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Malarski, R., Nagórski, K., Woźniak, M.: Application of inclinometer measurements …
Fig. 3. The sketch of the location of inclinometer columns
3. Investigating the accuracy of the horizontal relative ground displacements
by SISGEO S242SV30 probe
It is a common practice to evaluate data collection accuracy according to specified
by instrument manufacturer precision in the instructions manual of an electronic
device.
Here, we avail ourselves an opportunity to present an easy procedure to evaluate
measurement results taken with an inclinometric probe.
The probe under test operates on two servo-accelerating converters detecting
simultaneously angular “zero offset” in two perpendicular planes.
Inclinometer measurements observations are taken in two reverse positions of probe
as a routine procedure to have an independent check and index error estimation.
Obtained double (twin) observations allow accuracy determination because the total
of results yields double ”zero offset” as an index error. Values of index error as
calculated from all measurements taken, and are determined by standard formula :
ci =
1
(O + O 2 ) .
2 1
Mean square error of singular index error ”zero offset” estimated by residuals is
determined by the formula :
mC =
[v i v i ]
,
n-1
where : vi = Cm - ci .
Then, the mean square error of singular observation is given by: mO = mC 2 .
It was set as a task to determine precision of those relative horizontal displacements.
To this respect 5 sets of measurements with two inclinometer columns were
performed at the sliding slope of St Ann’s Church Hill commencing from March 8th
2011 up to January 2nd 2012. As a result we achieved the mean square error of
single observation m0 = 41″ . This is equivalent to relative error of 0.10mm/0.5m.
It must be stated that obtaining such a high accuracy is possible only with data
debugging procedure. To this purpose it is essential to carry out observations with
double axis Probe at 4 positions at 90° apart each time. Results of testing are
presented in table below.
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Reports on
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p
6-13
DOI: 1
10.2478/rgg-2
2013-0002
Tablle 1. Resultts of testing of accuraccy of the horrizontal rela
ative ground
d displacem
ments
The tab
ble 1 show
ws listed forr each survvey:
Cm - mean value of index error
e
”zero offset” ,
mC - mean
m
squarre error of single observation off index erro
or ,
m0 - mean
m
squarre error of single observation,
nG - fre
equency number of blunders.
In the analysis
a
index error /”zero
/
offse
et”/ was regarded as instrumen
ntal non dis
scarded
angular residual . Error in reading
r
rela
ated to Pro
obe inclina
ation at the
e distance of 0.5m
ed in millim
metres. Real reading at display is a produ
uct of 2000
00sinα.
is quote
Before final evalu
uation of prrecision, blunder detection and
d eliminatio
on was carrried out
erion mC > 3.
according to crite
c
clinometerr measure
ements forr relative horizontal
h
displacem
ment grou
unds at
4. Inc
Wa
arsaw hills
side st. An
nna’s churrch
er to detectt possible ground slide movem
ments at hill slope, two inclino
ometers
In orde
were fixed
f
in th
he hill of St Ann’s Church in Warsaw
w, and ob
bservations were
comme
enced on March 8, 2011. Co
onsecutive series of measurem
ments were
e taken
on: Aprril 26, July 14, October 24, and
d January 2,
2 2012.
Inclinom
meter mea
asurement results in specified directions are presented on diagrams
in Fig.. 4. Thesse diagram
ms prese
ent isolate
ed geologiical strata
a (kind of soils)
encoun
ntered at th
he site of in
nclinomete
er investiga
ations.
The foo
ot of colum
mn No.1 iss located about
a
6m beneath
b
ad
djacent hilllside Now
wy Zjazd
street carriagew
way , and
d the colu
umn No.2 was emb
bedded 3.5m beneath the
carriageway of Trasa
T
W-Z
Z (W_Z Thrroughway)). Feet of the
t column
ns were em
mbeded
in Tertiary period half coarsse silty cla
ay, and hard silty clayy.
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Malarski,, R., Nagórski,, K., Woźniak, M.: Application of inclinom
meter measureements …
Fig. 4. The
T graphs of horizonttal displacement in rela
ation to hill sside foot
Observvations of inclinomete
i
er No.1 ind
dicate rela
ative horizo
ontal groun
nd displace
ements.
It is we
ell seen from diagram
m in Fig. 4 a displacem
ment trend
d due to he
eavy rainfa
all spell,
which subsides
s
d
during
the period
p
from
m July to October.
O
Data collected
c
with incliinometer No.2 indicate exisstence of relative ground
displaccement. Displacemen
nt trends towards retaining wa
all are distiinct. In the
e period
from October
O
201
11 up to Ja
anuary 2012 reverse
e trend is evident.
e
In the upperr part of
column
n sheltered
d by 5.5 m thick rettaining an
nd unshelte
ered (expo
osed) part at 3m
height could be explained by therm
mal expans
sion. One has to no
otice that ground
consistts mainly of
o sand and brick rub
bble in this
s area. No
oticeably, there is change of
displaccement trend from th
he base off column at
a the dep
pth of 11.5
5 m cross section
A1-A2 and for cro
oss section
n B1-B2 att the depth of 9m. It is suppose
ed that the column
gets th
hrough a la
ayer of Te
ertiary Period silty cla
ay. Relativve horizontal displac
cements
referrin
ng to level depth
d
of 11.5 m are presented
p
in Fig 5.
This exxample sho
ows how crucial
c
is in
n ground deformation
d
n measure
e-ments an
nd slope
ground deforma--tion meassurements, adequate
e positioning of inclinometer column
base.
c
with incliinometer No.2 indicate exisstence of relative ground
Data collected
displaccement. Dissplacemen
nt trends to
owards reta
aining wall are distincct.
In case
e of positio
oning colu
umn No.1 at the sam
me referen
nce level in
nstead of column
No.2 any significa
ant chang
ge in displa
acement off ground at the adjaccent layers
s of clay
and sandy loam could
c
have
e be found..
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Reports on Geodesy vol. 94 /2013; pages 6-13
DOI: 10.2478/rgg-2013-0002
Fig 5. The graph of relative horizontal displacements referring
to level depth of 11.5 m in column No.1
Appraisal of this phenomenon could be substantially facilitated if absolute horizontal
displacement of inclinometer column head is known.
Absolute horizontal displacements in columns No.1 and No.2 are presented on
diagrams in Fig 6.
Above values are obtained as a result of including inclinometric column heads
readings to angular-distance net. The net was established to determine absolute
horizontal displacements of objects located at St Ann’s Church Hill.
Taking comparison between relative displacements [Fig 4] and absolute
displacements [Fig 6] one can easily notice that detected changes take place in a
clay layer spread over several meters under ground surface.
Fig. 6. The graphs of absolute horizontal displacements in column No.1 and No.2
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Malarski, R., Nagórski, K., Woźniak, M.: Application of inclinometer measurements …
5. Conclusion
Mean errors or relative horizontal displacement with double axis probe SISGEO
S242SV30 at two perpendicular cross-sections do not exceed 0.6 mm of 10m column
depth.
It is a must to have a check during data collection and data processing on
observation of index error /”zero offset”/ constancy value obtained from double
position of probe.
To eliminate blunders or gross errors, it is essential prior to observation takings, to
define junction places of pipes on the basis of assembly works or experimental
surveys, for adequate positioning of probe.
Inclinometer observations should be extended and supplemented by absolute
horizontal displacement measurements of inclinometer head to asses thoroughly
ground position changes.
Analysis of inclinometric columns axis inclination indicate significant relation link to
geological strata location and pattern in the slope.
It was proved essential to carry out detailed soil mechanics investigations of slope
and adjacent grounds prior to column location in order to select its due horizontal
position and vertical foundation .
References
Malarski, R., Łapinski, S., Nagórski, K., Pasik, M. & Woźniak, M., (2011). Badanie
przemieszczeń poziomych i pionowych Kościoła Akademickiego Św.Anny
w Warszawie (Investigations horizontal and vertical displacements St.Ann’s
Academic Church in Warsaw), Description for Heritage Protection Department City
of Warsaw, Politechnika Warszawska
SISGEO S.r.l., (2006). Inclinometers, Instructions manual, Italy
Wolski, W., Furstenberg, A. & Sorbjan, P., (2007). Inclinometer Measurements
applied to assessment of structures safety state. Papers XXIII Conference on
“Structure Damages of 2007”.
Authors:
Ryszard Malarski1), PhD., [email protected]
Kamil Nagórski1), Msc., [email protected]
Marek Woźniak1), Prof., [email protected]
1)
Faculty of Geodesy and Cartography, Department of Engineering Surveying,
Warsaw University of Technology, Poland
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