Comparative Analysis of Geodetic Techniques for Monitoring Deformation in Large Structures

COMPARATIVE ANALYSIS OF GEODETIC TECHNIQUES FOR MONITORING DEFORMATION IN LARGE STRUCTURES BY ETEJE SYLVESTER OKIEMUTE REG: 2015337004F NNAMDI AZIKIWE UNIVERSITY, AWKA, NIGERIA

DOI: 10.5281/zenodo.3385044

MARCH, 2019 1

1.1 BRIEF BACKGROUND TO THE STUDY Deformation Survey is the systematic measurement and tracking of the alteration in the shape or dimensions of an object as a result of stress induced by applied loads. Deformation monitoring is to guarantee the structure (building) safety and detect the abnormal changes, make judgment on the stability and safety of the building.

The selection of the method of measurements depends upon the accuracy requirements for the survey. The implication of using deformation monitoring method that is not suitable in term of accuracy for the monitoring of a particular engineering structure has a significant effect on the magnitudes and directions of the determined deformations 2

1.2 STATEMENT OF THE PROBLEM

None comparison of the accuracy of two or more deformation monitoring methods for deformation monitoring of engineering structures. Determination of the structural integrity of Palm House, Benin City which has been in existence for over 40 years without monitoring. The building was commissioned in 1974, it is an old building. The tenth floor got burnt sometime years ago and was totally abandoned for about ten years without usage.

3

1.3 AIM AND OBJECTIVES Aim The aim of this study is to comparatively analyse geodetic techniques for monitoring deformation in large structure, with a view to determining which of the two horizontal methods is better in terms of accuracy. Its objectives are: Objectives To carry out observations (Total Station, Level and GPS observations) at 6 different epochs at interval of three months and processing of the observations to determine the coordinates and heights of the monitoring networks points. To carry out least squares adjustment and statistical analysis on the observations to determine the reliability as well as the precision, accuracy and uncertainty of the adjusted observations and those of the adjusted parameters. 4

To determine the magnitudes and confidence ellipses/intervals at 95% confidence level of the horizontal and vertical displacements of the monitoring points To compare the determined displacement magnitudes with their corresponding confidence ellipses/intervals to determine if the displacements are significant or not. To determine and differentiate the movement of the 10th floor from that of the entire building by comparing the results obtained from the two horizontal (GPS and total station) methods. To compare the results obtained from the two horizontal (GPS and total station) methods so as to determine which of the two horizontal methods is better in terms of accuracy. 5

1.4

JUSTIFICATION OF THE STUDY

Comparing the displacement magnitudes of the monitoring points with their respective 95% confidence level, and the accuracy of the two horizontal methods will enable:

The structural integrity of the building to be determined. The movement of the tenth floor to be differentiated from that of the entire building. The determination of which of the two methods is better in terms of accuracy so as to assist users (Geodesists and Engineers) in the selection of the method to apply in terms of the purpose of measurements, the magnitude and directions of the expected deformations. 6

1.5

STUDY AREA

Palm House is one of the Edo State Secretariat buildings in Benin City (Figure 1). It is a high rise building located along Benin Sapele road in Oredo Local Government Area of Edo State. The building is an eleven story building. It is 45m in length, 15m in breadth and 35m in height. It was commissioned 10th February, 1973. The study area lies between latitudes 060 01' 54"N and 060 25' 35"N and longitudes 050 26' 23"E and 050 50' 05"E. Figure 2 shows the map of the study area.

Fig. 1: Palm House, Benin City

Study Area

Fig. 2: Map of Benin City Showing Study Area Source: Ministry of Lands and Surveys, Benin City.

7

1.6 SCOPE OF THE STUDY

The scope of the study is as follows: Marking out of monitoring points (studs) on the building. Establishment of reference points (stations) on stable grounds or platforms round the building using DGPS. Determination of the orthometric heights of the reference stations using differential levelling.

Carrying out levelling, total station and GPS observations in different epochs on the building. Processing of the GPS observations and the transformation of the processed coordinates to Minna Datum coordinates using the seven datum transformation parameters. Least squares adjustment and statistical analysis of the processed and transformed GPS coordinates, the levelling data (orthometric heights) and the Total Station observations. 8

Evaluation of displacements magnitudes between the first epoch and the subsequent epochs observations, in horizontal and vertical relationship. Evaluation of the horizontal and vertical displacements confidence ellipses/intervals at 95% confidence level. Evaluation of significance of the computed displacements magnitudes between the first epoch and the subsequent epochs observations by comparing the computed displacements magnitudes with their corresponding confidence ellipses/intervals to determine if the reported movements were actual movements of the structure or not. Determination and differentiation of the movement of the 10th f loor from that of the entire building by comparing the results obtained from the two horizontal (GPS and total station) methods. comparison of the results obtained from the two horizontal (GPS and total station) methods in order to determine which of the two 9 horizontal methods is better in terms of accuracy.

2.0

THEORETICAL FRAMEWORK

2.1

DEFORMATION SURVEY / MONITORING

Terrasurv (2015) described deformation survey as a survey to determine if a structure or object is changing shape or moving. Traditional deformation monitoring techniques can be divided into geotechnical measurements and geomatics based surveys (Detchev, 2011). The geotechnical measurements are made with extensometers, tiltmeters, micrometers, etc., which yield the magnitude of the deformation relative to reference marks on the actual object being monitored. Geomatics-based surveys involves the use of precision Levels, Theodolites and Electronic Distance Measurement (EDM) devices, Global Navigation Satellite System (GNSS) Positioning, 3D Laser Scanner, Photogrammetry and InSAR. Geodetic methods supply information on the absolute and relative displacements (changes in coordinates) of the monitored object. 2.2 PURPOSE OF DEFORMATION MONITORING The main purpose for monitoring and analysis of structural deformations is to determine whether or not movement is taking place and subsequently whether the structure is stable. 10

2.3

LEAST SQUARES ADJUSTMENT MODEL

The system of observation equations is presented by matrix notation as (Mishima and Endo 2002): V = AX - L (1) where, A = Design Matrix, X = Vector of Unknowns, L = Calculated Values (lo) Minus Observed Values (lb), V = Residual Matrix That is, T

V A  v1   a11 a12     v2   a21 a22  ...    ... ...    v  a  m   m1 am 2

... ... ... ...

Where, m - n = r = Degree of freedom

Estimated parameter X 

 N  t  1

(3)

Where, N  AT WA  Normal Matrix,

    Q , X  A WA A WL  = Estimate, t  A WL , N 1  ATWA T

T

1

T

V WV V WV 2 X L (4) A Posteriori Variance, ˆ o   a1n  x1   l1  mn r     a2 n  x2   l2  (2) V T WV V T WV    (5) A Posteriori Standard Error, ̂ o mn r ...  ...   ...      amn  xn   lm 

T

W = Weighted Matrix

1

XX

The model for the computation of the standard error of the adjusted parameters is given as: (Ameh, 2013):

ˆ

xi

 ˆ  Qnn  ˆ 2 Qnn

(6)

Where, of Qnn is a diagonal element of the inverse 11 the normal matrix

Error Ellipse  x2   y2 Semi-major Axis,   2

 ( x2   y2 ) 2  2     xy , 4  

 x2   y2 Semi-minor Axis,   2

 ( x2   y2 ) 2  2     xy 4  

2 x

2 y

Orientation = tan 2  (7),

2 xy

  2 x

2 y

(8)

Trace The model for the computation of trace of the variance-covariance matrix is given as (Caspary, 1988): tr A   aii

(9)

Redundancy Number

ri  qi pi ,

(10)

rAv

n  R ( A)  n

(11)

ri = Redundancy number, p i = Weight of the ith observation. q i = Diagonal element of the estimated residual cofactor matrix, Qv, rAv = Average redundancy number n  R( A) = Degree of freedom or redundant observation, R( A) = Number of unknown parameter,

n

= Number of observation.

12

Standardized Residual

.

Standardiz ed Residual (Ti ) 

Adjusted Observatio n Residual (vi ) Residual Standard Deviation ( vi )

Standardized Residual Rejection Constant, Tau Statistics  v ,  Where,

t v 1, . v (v  1)  t v21,

(12)

 v , = Critical value from the Tau distribution at redundancy v and significance level  v = Number of degree of freedom

 = Significance level

t v , Critical value from the student's distribution at redundancy v and significance level 

13

Distance Observation Equation  X oj  X io    So dX i ij 

   

 Y jo  Yi o    So dYi ij 

   

dS ij

.

dS ij

 X oj  X io  dX j  S ijo

   

dS ij

 Y jo  Yi o  dY j  S ijo

dS ij

Azimuth Observation Equation Y o Y o j i  dX i  S ijO 2  dAij

(13)

   

Y o Y o j i   2  SO dX j ij 

   

Xo Xo j i    S O2 dYi ij 

   

Xo Xo j i  2 dYJ  S ijO 

   

dAij

   

dAij

dAij

(14)

Where, 0 (X’s and Y’s) = Unknown parameters, S ij = distance computed from approximate coordinates, X o , Y o , X o , X o

i

i

j

j

Computation of Magnitude and Direction of Displacement  x kj 1  xik  dx    k 1 k  y j  y i  dy    k 1 k z  z  dz   j i

x kj 1 , y kj 1 , z kj 1 = Coordinates of last epoch (15)

xik , y ik , z ik

Horizontal movement ds  (dx)  (dy ) 2

Vertical movement dH 

z

k 1 j

 z ik



2

Direction of movement( )  tan  i 



dyi dxi

= Coordinates of preceding epoch (16)

2

dz 2

(17) (18)

14

2.4 DEFORMATION ANALYSIS The ultimate goal of the geometrical analysis is to determine if the reported movements are statistically significant. The computed displacements =

D j  (x j ) 2  (y j ) 2

(19)

The corresponding 95% interval/ellipse = E j  1.96 (mkj1 ) 2  (mkj ) 2  1.96 M

(20)

where,

M  (mkj1 ) 2  (mkj ) 2

M  (mkj1 ) - Standard error in position for the K+1 epoch and

 (mkj )

- standard error in position for the previous epoch k.

Then, if D j  E j , It implies that movement did not take place b/w epochs observations But if on the other hand D j  E j then we conclude that point movement has occurred

15

3.0 LITERATURE REVIEW About 40 previous studies were reviewed. 3.1 IDENTIFIED GAPS None of the reviewed studies on deformation monitoring of engineering structures compared any two horizontal methods in terms of their accuracy so as to determine the method that is better in terms of accuracy.

None of the reviewed studies on deformation monitoring of high rise buildings segmented or partitioned the monitored object (building) into different sections Also, in the research works by Kok (2005), Ramin and Helmi (2009), and that by Vintilă et al (2014) the standard errors of the monitoring points were not analyzed statistically to see if the movements were significant or were as a results of 16 measurement errors.

4.1

METHODOLOGY

Data Acquisition GPS observations

Processing of GPS Data (Compass Software)

Transformation of GPS Coordinates (Compass Software)

Determination of Weighted Matrices

Precision and Accuracy Determination Evaluation of Displacements Confidence Intervals and Ellipses

Comparison between DGPS & Total Station Accuracy

Total Station Observations

Levelling

Design/Coefficient Matrices

Least Squares Adjustment and Statistical Evaluations of Levelling, Total Station & GPS observations (Columbus Software)

Comparison between Displacement Magnitudes and Confidence Intervals/Ellipses

Results Presentation and Analysis

Results Presentation and Analysis of DGPS Observations

Results Presentation and Analysis of Total Station Observations

Fig. 3: Flow Chart of the Proposed Methodology

Outlier Detection Computation of Adjusted Parameters

Computation of Coordinates and Levels differences between Epochs Observations Evaluation of Displacements Magnitudes between Epochs Observations

Results Presentation and Analysis of Digital Level Measurements

17

4.2

DATA ACQUISITION PROCESS

A

B

PALM HOUSE

A

B

PALM HOUSE

D

Fig.4 : Roof Monitoring Points Total Station Observation Network

C

Fig. 6: Base receiver at Fig. 7: Base receiver at Control Station FGPEDY06 Reference Station C

D

Fig. 5: GPS Observation Network

Fig. 8: Rover receiver at Monitoring point M

C

Fig. 9: Total Station 18 at Reference Station C

4.3

STATISTICAL EVALUATION

The statistical evaluations of the observations were carried out

using Columbus software and were divided into computation of:

A posteriori variance, a posteriori standard error, and standard errors of the adjusted coordinates and heights.

Chi-square test on a posteriori variance factor. Redundancy number. Standardized residual. Residual rejection constant (tau statistics). Confidence region (error ellipses) of the adjusted positions. Height confidence intervals.

19

5.1 DATA ANALYSIS, PRESENTATION AND DISCUSSION OF RESULTS

5.1.1 Analysis of the Levelling, GPS and the Total Station Observations Data The closing error for the first loop was 0.0057m while that of the second loop was 0.0005m (Table 1) which were within millimetres standard. The orthometric height of each of the monitoring points was able to be reproduced from not less than three reference stations. Table 1: Known and Observed Heights of the Closing Stations Station BC/BM03 C

Description Starting and Closing Station Starting and Closing Station

H(known) (m)

H(observed) (m)

ΔH (m)

54.026

54.0203

0.0057

52.1643

52.1638

0.0005 20

The processing results of the six epochs DGPS observations were seen to have passed the Network Adjustment Test which implies that the normal matrix generated was a regular one and inverted accordingly for calculation of residuals.

The total station observations results were seen to be in good shape and were accepted as the coordinates of each monitoring point were able to be reproduced from not less than three reference stations. 5.2 ANALYSIS OF THE ADJUSTED LEVELLING RESULTS USING LEAST SQUARES TECHNIQUE The maximum standard errors of the first to the

Table 2: A Posteriori Variance and A Posteriori Standard Errors of the Six Epochs Levelling A POSTERIORI

A POSTERIORI EPOCH

STANDARD

VARIANCE (m) ERROR (m)

FIRST

0.0000037164

0.001927807

SECOND

0.0000038406

0.001959743

THIRD

0.0000037923

0.001947370

FOURTH

0.0000036267

0.001904380

FIFTH

0.0000035372

0.001880736

SIXTH

0.0000036312

0.001905559

sixth epoch adjusted heights were respectively 0.0120462, 0.0111885m, 0.0121685m, 0.0118998m, 0.0117522m, and 0.0119072m The minimum and the average redundancy numbers were respectively 0.4287 and 0.625. Computed standardized residuals residuals rejection constant.

less

than

The maximum confidence intervals of the first to the sixth epochs adjusted heights were respectively 0.023603m, 0.0226232m, 0.0238426m, 0.023316m, 0.023027m and 0.023331m. 21

5.3 ANALYSIS OF THE ADJUSTED TENTH FLOOR MONITORING POINTS TOTAL STATION OBSERVATIONS RESULTS USING LEAST SQUARES TECHNIQUE Table 3: A Posteriori Variance and A Posteriori Standard Errors of the Six Epochs Total Station Observations A POSTERIORI

A POSTERIORI

EPOCH

VARIANCE (m)

STANDARD ERROR (m)

FIRST

0.17488

0.41819

SECOND

0.21221

0.46066

THIRD

0.20672

0.45467

FOURTH

0.18981

0.43568

FIFTH

0.16591

0.40733

SIXTH

0.22807

0.47757

The maximum standard errors in northing and easting of the first to the sixth epoch adjusted coordinates were respectively 0.00064m and 0.00069m, 0.00068m and 0.00057m, 0.00067m and 0.00056m, 0.00065m and 0.00054m, 0.00060m and 0.00051m, and 0.00071 and 0.00059.

The minimum redundancy number of the adjusted distances and azimuths were respectively 0.9999 and 0.0001 while the average redundancy number was 0.625. Computed standardized residuals less than residuals rejection constant.

The maximum scaled semi-major axis and semi-minor axis of the six epochs adjusted coordinates were respectively 0.0019242m and 0.001689m. The traces of the first to the sixth epoch observations were respectively 0.0000035148m, 0.000002485m, 0.00000242m, 0.000002222m, 0.000001942m and 0.00000267m 22

5.3.1 ANALYSIS OF THE ADJUSTED ROOF MONITORING POINTS TOTAL STATION OBSERVATIONS RESULTS USING LEAST SQUARES TECHNIQUE Table 3: A Posteriori Variance and A Posteriori Standard Errors of the Six Epochs Total Station Observations A POSTERIORI

A POSTERIORI

EPOCH

VARIANCE (m)

STANDARD ERROR (m)

FIRST

0.23161

0.48126

SECOND

0.13834

0.37195

THIRD

0.17570

0.41917

FOURTH

0.10443

0.32316

FIFTH

0.18068

0.42506

SIXTH

0.17951

0.472369

The maximum standard errors in northing and easting of the first to the sixth epoch adjusted coordinates were respectively 0.00092m and 0.00089m, 0.00065m and 0.00079m, 0.00099m and 0.00099m, and 0.00062m and 0.00074m.

The minimum redundancy number of the adjusted distances and azimuths were respectively 0.9999 and 0.0023 while the average redundancy number was 0.667. Computed standardized residuals less than residuals rejection constant.

The maximum scaled semi-major axis and semi-minor axis of the six epochs adjusted coordinates were respectively 0.0024234 m and 0.0024234 m. The traces of the first to the sixth epoch observations were respectively 0.000005577m, 0.000000755m, 0.000000958m, 0.000000569m, 0.000000985m and 0.000001027m 23

5.4

ANALYSIS OF THE ADJUSTED DGPS OBSERVATIONS RESULTS USING LEAST SQUARES TECHNIQUE The minimum redundancy number Table 4: A Posteriori Variance and A Posteriori Standard of the adjusted change in northing, Errors of the Six Epochs DGPS Observations change in easting and the average A POSTERIORI A POSTERIORI redundancy numbers was 0.75 VARIANCE (m) STANDARD ERROR (m) EPOCH FIRST

0.0000044705

0.002114344

SECOND

0.0000003131

0.000559521

THIRD

0.0000002144

0.000463080

FOURTH

0.0000060425

0.002458150

FIFTH

0.0000043369

0.002082528

SIXTH

0.0000228554

0.004780734

The maximum standard errors in northing and easting of the first to the sixth epoch adjusted coordinates were respectively 0.00045m and 0.00068m, 0.00027m and 0.00025m, 0.00019m and 0.00019m, 0.00032m and 0.00026m, 0.00029m and 0.00024m, and 0.00045m and 0.00029m.

Computed standardized residuals less than residuals rejection constant. The maximum scaled semi-major axis and semi-minor axis of the six epochs adjusted coordinates were respectively 0.001102m and 0.001665m The traces of the first to the sixth epoch observations were respectively 0.0000019786m, 0.000000392m, 0.000000223m, 0.000000425m, 0.000000308m and 0.00000051m 24

5.5

COMPARISON MAGNITUDES INTERVALS

BETWEEN AND THEIR

THE VERTICAL DISPLACEMENTS CORRESPONDING 95% CONFIDENCE

Table 5: Comparison of the Vertical Displacements Magnitudes with their Corresponding Confidence Intervals MONITORING POINT MAG6NITUDE SQRT((∆HT)2) (m) B/W 1ST & 2nd 1.96*(SQRT(M)) (m) EPOCHS

1ST &

B/W EPOCHS

1ST &

B/W EPOCHS

1ST &

B/W EPOCHS

1ST &

B/W EPOCHS

3rd

4th

5th

6th

E

F

G

H

I

J

0.0003973 0.0000999 0.0001727 0.0008375 0.0028527 0.0002430 0.0252411 0.0307612 0.0251137 0.0241149 0.0313804 0.0256615

DIFFERENCE (m) MAGNITUDE SQRT((∆HT)2) (m) 1.96*(SQRT(M)) (m)

0.0248438 0.0306613 0.0249410 0.0232774 0.0285277 0.0254185

DIFFERENCE (m) MAGNITUDE SQRT((∆HT)2) (m) 1.96*(SQRT(M)) (m)

0.0245542 0.0312278 0.0248649 0.0219362 0.0299076 0.0226330

DIFFERENCE (m) MAGNITUDE SQRT((∆HT)2) (m) 1.96*(SQRT(M)) (m)

0.0242645 0.0303083 0.0246879 0.0253621 0.0331422 0.0252061

DIFFERENCE (m) MAGNITUDE SQRT((∆HT)2) (m) 1.96*(SQRT(M)) (m)

0.0242363 0.0300231 0.0244280 0.0250721 0.0329773 0.0247706

DIFFERENCE (m)

25 0.0242880 0.0301318 0.0245725 0.0245954 0.0327624 0.0250175

0.0006723 0.0008573 0.0008740 0.0010974 0.0009902 0.0013523 0.0252265 0.0320851 0.0257389 0.0230336 0.0308978 0.0239853

0.0001253 0.0000143 0.0000678 0.0000071 0.0000459 0.0002682 0.0243898 0.0303226 0.0247557 0.0253692 0.0331881 0.0254743

0.0000045 0.0001142 0.0001765 0.0001421 0.0000081 0.0001340 0.0242408 0.0301373 0.0246045 0.0252142 0.0329854 0.0249046

0.0001092 0.0001999 0.0001907 0.0002366 0.0002984 0.0000477 0.0243972 0.0303317 0.0247632 0.0248320 0.0330608 0.0250652

0,035

0,03

0,025

0,02

VERTICAL DISPLACEMENT NAGNITUTE (m)

0,015

95% CONFIDENCE INTERVAL (m)

0,01

0,005

0 E F G H I B/W 1ST & 2nd EPOCHS

J E F G H I B/W 1ST & 3rd EPOCHS

J E F G H I B/W 1ST & 4th EPOCHS

J E F G H I B/W 1ST & 5th EPOCHS

J E F G H I

J

B/W 1ST & 6th EPOCHS

Fig 10: Plot of the Vertical Displacements Magnitudes and their Corresponding Confidence Intervals 26

5.6

COMPARISON BETWEEN THE TENTH FLOOR MONITORING PONITS TOTAL STATION OBSERVATIONS DISPLACEMENTS MAGNITUDES AND THEIR CORRESPONDING 95% CONFIDENCE ELLIPSES/REGIONS

Table 6: Comparison of the Horizontal (Tenth Floor Monitoring Points Total Station Observations) Displacement Magnitudes with their Corresponding Confidence Ellipses MONITORING POINT MAGNITUDE SQRT ((∆N)2+(∆E)2) (m) B/W 1ST & 2nd 1.96 (m )  (m ) (m) EPOCHS DIFFERENCE (m) MAGNITUDE SQRT ((∆N)2+(∆E)2) (m) B/W 1ST & 3rd 1.96 (m )  (m ) (m) EPOCHS DIFFERENCE (m) MAGNITUDE SQRT ((∆N)2+(∆E)2) (m) B/W 1ST & 4th 1.96 (m )  (m ) (m) EPOCHS DIFFERENCE (m) MAGNITUDE SQRT ((∆N)2+(∆E)2) (m) B/W 1ST & 5th 1.96 (m )  (m ) (m) EPOCHS DIFFERENCE (m) MAGNITUDE SQRT ((∆N)2+(∆E)2) (m) B/W 1ST & 6th 1.96 (m )  ( m ) ( m) EPOCHS DIFFERENCE (m) k 1 j

k 1 j

k 1 j

k 1 j

k 1 j

2

k j

2

k j

2

k j

2

k j

2

2

2

2

2

k j

2

P

Q

R

S

T

U

0.000282

0.000400

0.000400 0.000376 0.000714 0.000339

0.001783 0.001501

0.001977 0.001577

0.001993 0.002009 0.002085 0.001900 0.001593 0.001633 0.001371 0.001561

0.000449

0.000777

0.000400 0.000389 0.000446 0.000362

0.001775 0.001326

0.001955 0.001178

0.001977 0.002009 0.002063 0.001885 0.001577 0.001620 0.001617 0.001523

0.000449

0.000769

0.000581 0.000352 0.000714 0.000000

0.001760 0.001311

0.001910 0.001141

0.001963 0.001980 0.002011 0.001871 0.001382 0.001628 0.001297 0.001871

0.000114

0.000777

0.000581 0.000530 0.000707 0.000383

0.001724 0.001610

0.001819 0.001042

0.001926 0.001952 0.001949 0.001837 0.001345 0.001422 0.001242 0.001454

0.000273

0.000354

0.000400 0.000304 0.000412 0.000469

0.001798 0.001525

0.002027 0.001673

0.002008 0.002032 0.002128 0.001915 27 0.001608 0.001728 0.001716 0.001446

0,0025

0,002

0,0015 TENTH FLOOR MONITORING POINTS (TOTAL STATION OBSERVATION) DISPLACEMENT MAGNITUDE (m) 95% CONFIDENCE ELLIPSE (m)

0,001

0,0005

0 P Q R S T U P Q R S T U P Q R S T U P Q R S T U P Q R S T U B/W 1ST & 2nd EPOCHS

B/W 1ST & 3rd EPOCHS

B/W 1ST & 4th EPOCHS

B/W 1ST & 5th EPOCHS

B/W 1ST & 6th EPOCHS

Fig 11: Plot of the Horizontal (Tenth floor Monitoring Points Total Station Observations) Displacements Magnitudes and their Corresponding Confidence Ellipses 28

5.6.1

COMPARISON BETWEEN THE ROOF MONITORING PONITS TOTAL STATION OBSERVATIONS DISPLACEMENTS MAGNITUDES AND THEIR CORRESPONDING 95% CONFIDENCE ELLIPSES/REGIONS

Table 6: Comparison of the Horizontal (Roof Monitoring Points Total Station Observations) Displacement Magnitudes with their Corresponding Confidence Ellipses MONITORING POINT MAGNITUDE SQRT ((∆N)2+(∆E)2) (m)

B/W 1ST & 2nd EPOCHS

1.96 (mk j1 ) 2  (mk j ) 2 (m)

DIFFERENCE (m) MAGNITUDE SQRT ((∆N)2+(∆E)2) (m)

B/W 1ST & 3rd EPOCHS

1.96 (mk j1 ) 2  (mk j ) 2 (m)

DIFFERENCE (m) MAGNITUDE SQRT ((∆N)2+(∆E)2) (m)

B/W 1ST & 4th EPOCHS

1.96 (mk j1 ) 2  (mk j ) 2 (m)

DIFFERENCE (m) MAGNITUDE SQRT ((∆N)2+(∆E)2) (m)

B/W 1ST & 5th EPOCHS

1.96 (mk j1 ) 2  (mk j ) 2 (m)

DIFFERENCE (m) MAGNITUDE SQRT ((∆N)2+(∆E)2) (m)

B/W 1ST & 6th EPOCHS

1.96 (mk j1 ) 2  (mk j ) 2 (m)

DIFFERENCE (m)

K

L

M

N

0.001273106 0.000518652

0.000859884

0.000700357

0.00262984 0.00219931 0.001356734 0.001680658

0.00288906 0.002029176

0.00206359 0.001363233

0.001273106 0.000669403

0.001150695

0.000735459

0.002247 0.00266084 0.001387734 0.001577597

0.00292553 0.001774835

0.00210461 0.001369151

0.001729855 0.000994636

0.001968146

0.000697209

0.00259794 0.00215083 0.000868085 0.001156194

0.00285232 0.000884174

0.00202108 0.001323871

0.000850941 0.000228035

0.000653682

0.000130384

0.00266084 0.00250251 0.001809899 0.002274475

0.00293523 0.002281548

0.00210998 0.001979596

0.001399464

0.00063561

0.00084

0.000904434

0.00266084 0.001261376

0.00249644 0.00186083

0.00293005 0.00209005

0.00210998 29 0.001205546

0,0035

0,003

0,0025

0,002 ROOF MONITORING POINTS (TOTAL STATION OBSERVATION) DISPLACEMENT MAGNITUDE (m) 0,0015

95% CONFIDENCE ELLIPSE (m)

0,001

0,0005

0 K

L

M

N

B/W 1ST & 2nd EPOCHS

K

L

M

N

B/W 1ST & 3rd EPOCHS

K

L

M

N

B/W 1ST & 4th EPOCHS

K

L

M

N

B/W 1ST & 5th EPOCHS

K

L

M

N

B/W 1ST & 6th EPOCHS

Fig 12: Plot of the Horizontal (Roof Monitoring Points Total Station Observations) Displacement Magnitudes and their Corresponding Confidence Ellipses 30

5.7

COMPARISON BETWEEN THE DGPS OBSERVATIONS DISPLACEMENTS MAGNITUDES AND THEIR CORRESPONDING 95% CONFIDENCE ELLIPSES Table 7: Comparison of the Horizontal (DGPS Observations) Displacements Magnitudes with their Corresponding Confidence Ellipses

MONITORING POINT MAGNITUDE SQRT ((∆N)2+(∆E)2) (m) B/W 1ST & 2nd EPOCHS 1.96 (m )  (m ) (m) k 1 j

2

k j

2

DIFFERENCE (m) MAGNITUDE SQRT ((∆N)2+(∆E)2) (m) B/W 1ST & 3rd EPOCHS

N

0.000121655 0.000628013 0.000471699 0.000642884 0.00152855

0.00159086

0.00145582

0.0014549

0.001406895 0.000962847 0.000984121 0.000812016

0.00149668

0.00142757

0.00138051

0.000739778 0.001101757 0.000726927

0.00086437

MAGNITUDE SQRT ((∆N)2+(∆E)2) (m)

0.000790569

0.0009005

0.00060208

0.000383275

1.96 (mk j1 ) 2  (mk j ) 2 (m)

0.00152754

0.0015541

0.00146069

0.00152842

DIFFERENCE (m)

0.000736971

0.0006536

0.00085861

0.001145145

1.96 (mk j1 ) 2  (mk j ) 2 (m)

1.96 (mk j1 ) 2  (mk j ) 2 (m)

DIFFERENCE (m)

B/W 1ST & 6th EPOCHS

M

0.00051614

MAGNITUDE SQRT ((∆N)2+(∆E)2) (m)

B/W 1ST & 5th EPOCHS

L

0.000756902 0.000403113 0.000700643

DIFFERENCE (m)

B/W 1ST & 4th EPOCHS

K

0.00150487

0.000070711 0.000113137 0.000070711 0.000151327 0.00149565

0.00150142

0.00142999

0.00149243

0.001424939 0.001388283 0.001359279 0.001341103

MAGNITUDE SQRT ((∆N)2+(∆E)2) (m)

0.0007245

0.000471699 0.000750267 0.000509313

1.96 (mk j1 ) 2  (mk j ) 2 (m)

0.0014977

0.00154567

DIFFERENCE (m)

0.0007732

0.001073971 0.000965043 0.000897247

0.00171531

0.00140656 31

0,002

0,0018

0,0016

0,0014

0,0012

0,001 DGPS DISPLACEMENT MAGNITUDE (m)

95% CONFIDENCE ELLIPSE (m)

0,0008

0,0006

0,0004

0,0002

0 K

L

M N

K

L

M N

K

L

M N

K

L

M N

K

L

M N

B/W 1ST & 2nd B/W 1ST & 3rd B/W 1ST & 4th B/W 1ST & 5th B/W 1ST & 6th EPOCHS EPOCHS EPOCHS EPOCHS EPOCHS

Fig 13: Plot of the Horizontal (DGPS Observations) Displacements Magnitudes and their Corresponding Confidence Ellipses 32

5.8 COMPARISON BETWEEN THE TENTH FLOOR AND THE ROOF MONITORING POINTS DISPLACEMENTS The tenth floor and the roof monitoring points were compared to determine if movements have taken place at the tenth floor or not, that is to differentiate the movements of the tenth floor from those of the entire building. 5.10 COMPARISON OF THE TWO HORIZONTAL (ROOF MONITORING POINTS TOTAL STATION AND DGPS OBSERVATIONS) METHODS ACCURACY Table 8: Comparison between the A Posteriori Standard Errors of the Adjusted Total Station and DGPS Epochs Observations of the Roof Monitoring Points

A POSTERIORI STANDARD ERROR (m) (ROOF MONITORING POINTS) TOTAL STATION

DGPS

EPOCH 1

0.48126

0.002114344

EPOCH 2

0.37195

0.000559521

EPOCH 3

0.41917

0.000463080

EPOCH 4

0.32316

0.002458150

EPOCH 5

0.42506

0.002082528

EPOCH 6

0.42369

0.004780734

0,6 0,5 ROOF MONITORING POINTS TOTAL STATION A POSTERIORI STANDARD ERROR (m)

0,4

0,3

ROOF MONITORING POINTS DGPS A POSTERIORI STANDARD ERROR (m)

0,2

0,1 0

EPOCH EPOCH EPOCH EPOCH EPOCH EPOCH 1 2 3 4 5 6

Fig 14: Plot of the A Posteriori Standard Errors of the Adjusted Total Station and DGPS Epochs Observations of the Roof Monitoring Points 33

Table 9: Comparison between the Variance Co-variance Matrices Traces of the Adjusted Total Station and DGPS Epochs Observations of the Roof Monitoring Points VARIANCE CO-VARIANC MATRIX TRACE (m) (ROOF MONITORING POINTS) TOTAL STATION

DGPS

EPOCH 1

0.000005577

0.000001979

EPOCH 2

0.000000755

0.000000392

EPOCH 3

0.000000958

0.000000223

EPOCH 4

0.000000569

0.000000425

EPOCH 5

0.000000985

0.000000308

EPOCH 6

0.000001027

0.000000510

0,000006 0,000005

0,000004 0,000003

ROOF MONITORING POINTS TOTAL STATION TRACE (m)

0,000002

ROOF MONITORING POINTS DGPS TRACE (m)

0,000001 0

EPOCH 1

EPOCH 2

EPOCH 3

EPOCH 4

EPOCH 5

EPOCH 6

Fig 15: Plot of the Variance Co-variance Matrices Traces of the Adjusted Total Station and DGPS Epochs Observations of the Roof Monitoring Points

34

6.1

CONTRIBUTION TO KNOWLEDGE

This study has monitored the vertical and horizontal deformation of Palm House, Benin City, compared the accuracy of the two employed horizontal methods and has made the following notable contributions to knowledge: The study has shown that the monitored structure, Palm House, Benin City was stable during the period of observation as there was no significant movement between epochs observations which in turn shows that the structure is still fit for usage. An approach for comparison of the two horizontal methods (DGPS and Total Station) using their standard error of unit weights and variance covariance matrices has been developed in this study.

35

7.1

CONCLUSION AND RECOMMENDATIONS

7.1.1

CONCLUSION

The results of this study have shown that the building (Palm House) was stable during the period of observation. The study has also shown that the DGPS method is better than the total station method in terms of accuracy for deformation monitoring of engineering structures. This will assist users to decide on the method to apply as the selection of method depends upon the accuracy requirements for the survey. 7.1.2

RECOMMENDATIONS

The monitoring of engineering structures using more appropriate and accurate method for safety purpose cannot be undermined. Based on the result obtained from this study, the following recommendations were made:

That whenever more suitable and accurate method of monitoring of engineering structures is to be employed between the DGPS and the total station methods, the DGPS method should be selected as this study has demonstrated and compared the accuracy of the two methods and shown that the DGPS method is better. 36

That other geodetic methods of monitoring such as InSAR, etc should be compared with any of the two traditional (DGPS and Total Station) methods of monitoring of engineering structures to determine which is better in terms of accuracy. That the concrete strength of the monitored building (Palm House) should be investigated using non destructive measures such as Schmidt Hammer techniques as age and change in temperature affect the properties of the materials with which any engineering structure is being constructed and as there is a large crack on one of the walls of the 10th floor of the building. 7.3

SUGGESTIONS FOR FURTHER STUDIES

In the course of this study, it became understandable that other related researchable areas could not be covered in this work. Therefore, the topics below are posited for future study participation and contributions: Comparative analysis of DGPS and InSAR accuracy for horizontal deformation monitoring of engineering structures. Comparative analysis of Total Station and 3D laser scanning accuracy for horizontal deformation monitoring of engineering structures. Monitoring and modelling of the deformation of engineering structures using InSAR technology. 37

THANK YOU AND GOD BLESS

38