1. Chapter 9: Deformation Monitoring and Analysis: Geodetic Techniques
Dr. John Ogundare
BCIT, Burnaby

2. Chapter Objectives (1/2)
Be able to do the following:
Discuss the role of geodetic deformation monitoring and analysis.
Discuss the characteristics of geodetic deformation monitoring techniques in contrast with other similar techniques.
Discuss the important differences between absolute and relative geodetic networks and the importance of datum definition.
Discuss the differences between deformation monitoring and control surveys.
Use the design elements of deformation monitoring schemes to carry out deformation monitoring surveys.
Describe the various monumentation and targeting requirements for deformation monitoring networks.
Perform geodetic deformation monitoring surveys for hydro-electric dam structures and for subsidence areas.
Reduce deformation monitoring data for input into least squares network adjustment software package for further processing.

3. Chapter Objectives (2/2)
Be able to do the following:
Explain the importance of single-point movement in absolute geodetic deformation monitoring networks.
Explain the concept of the iterative weighted similarity transformation (IWST) and use it to solve the problem of datum instability.
Discuss the differences between the observation-difference and coordinate-difference approaches in deformation analysis.
Perform statistical and graphical trend analyses of deformations.
Discuss the new developments in the automation of geodetic deformation monitoring of slope walls in open pit mining.
Discuss the geodetic techniques for deformation monitoring of tunnels during their construction.
Discuss the use of geodetic levelling procedure in deducing tilt, strain and curvature resulting from ground subsidence.

4. Overview
Deformation – changes in shape, dimension & position of object
Vertical deformation of ground surface is ground subsidence
Most common parameters of deformable object commonly monitored are deformation, strain, load, stress, ground water pressure, etc.
Deformation is of main interest in surveying
Deformation monitoring techniques:
Produce absolute data
Allow geotechnical instrumentation to be connected together
Deformation analysis – detect, localize and model point movements based on deformation measurements

5. Role of Deformation Monitoring
Provide safety assurance against possible failure of monitored object- comparing measured deformations with known tolerances
Gaining better understanding of the mechanism of rock deformation through experiment and research
Verify behaviors of rock masses against their predicted patterns to refine prediction models or validate design assumptions
Deriving information in order to resolve dispute on effects on mining impact on surface infrastructure and to help protect the structure
Derive information in order to identify and separate various causes of deformation

6. Causes of Deformation
Objects requiring monitoring: dams, tunnels, high-rise buildings, bridges, industrial complexes, slopes, glaciers, and areas of landslide, subsidence, recent crustal motion, etc.
Possible causes of deformation – tidal effect, changing ground water level, mining activities, tectonic, landslide, alkaline aggregate reaction expansion of concrete, changeable water load on dam structures, seasonal thermal-induced deformations, etc.

7. Characteristics of Geodetic Monitoring Techniques
Characteristics of geodetic techniques compared with high-definition surveying and remote sensing and geotechnical instrumentation techniques
They measure ground surface deformations using ground surface network of interconnected points
They provide redundant measurements so that they are more reliable
They provide overall picture of deformation trend of the whole object monitored with reference to stable points
They are labor-intensive and not done frequently, except in automated mode
Automation may be very expensive
They require intervisibility between observing stations and are affected by the environment

8. Geodetic Monitoring Networks
Two classes of geodetic monitoring networks:
Absolute geodetic network – stable points (reference network or reference datum) and unstable points being monitored (object points)
Will allow both strain components and absolute movements of object points
Relative geodetic network – all points are assumed unstable (object points); no stable points as reference
Will allow detection of strain components

9. Advanced Geodetic Technologies
Some of the advanced geodetic technologies for deformation monitoring are robotic total stations, precise level, GNSS with or without pseudolites (Table 9.1)
They are all affected by atmospheric refraction and/or tropospheric delay
With regard to GNSS, better solution is obtained with 12 h of observations with error in the vertical being twice that of the horizontal
Not all are suitable for fully automated and continuous monitoring

10. Deformation Monitoring and Control Surveys
Deformation Monitoring Surveys
Control Surveys
1. Absolute positions of points are of interest
Changes in positions between epochs are of interest
2. Common systematic errors (constant refraction, calibration error, scale error, configuration defects) are expected to cancel out if the same in all epochs
Must be physically removed from measurements or randomized to minimize the effects
3. Absolute scale of network is not required but ability to detect and control change in scale between epochs
Absolute scale of network is required
4. Configuration defects (eccentricities of instruments/targets, triangular misclosures are permitted
Not permitted
5. Correlation between repeated observations of the same observable is encouraged: same environment and observation conditions, etc.
Not encouraged; but randomizes effects of sources of errors

11. Deformation Monitoring Measurements: Error Sources
Geodetic measurements are contaminated with effects of:
Observation random errors (due to reading, pointing, centering and leveling of instruments)
Systematic errors due to instrument construction errors, atmospheric effects
Seasonal (thermal) cyclic expansion of measured objects
Other systematic errors due to lack of calibration of instruments

12. Deformation Monitoring Schemes
Monitoring Scheme – total plan of action, including:
Choices of types and locations of observables,
Timing of measurement campaign
Stability of reference points
Selecting monitoring techniques and suitable instrumentation
Type of monumentation and targeting
Determining data processing and analysis techniques
Determining actual deformations
Criteria for Design of monitoring scheme include
Accuracy and reliability
Temporal and spatial continuity dictating frequency of monitoring and adequacy of distribution of reference and object points
Stability of reference points must be confirmed
Cost-effectiveness
Choice of monitoring technology

13. Specifications for Dam Monitoring Schemes
No universally accepted standards and specifications for choice of monitoring schemes
Monitoring schemes are designed by dam owners or individuals
Accuracy of monitoring both horizontal and vertical displacements in concrete dams is 1-2 mm up to 10 mm for horizontal displacements for embankment dams
Initial design of monitoring schemes must be revisited time to time with regard to:
Configuration (or geometry) of reference and object points – if network points are damaged or lost between epochs, new stations are needed to strengthen the network or new instruments are available
Types of observables
Timing of campaigns – at intervals needed to detect deformation
Accuracy of measurements
Economy – if schemes must be reduced to reduce cost

14. Typical Elements of Dam Monitoring Schemes
Typical deformation monitoring scheme of a dam consists of:
Horizontal angle or horizontal direction measurements
Distance measurements reduced to mark-to-mark and corrected for possible systematic errors
Zenith angle measurements for reducing slope distances
Orthometric height difference measurements from leveling
Forced-centering monuments with only few tripod setups
Choice of reference points in suitable locations
Ability to confirm stability of well-protected reference points
Good spread of object points with suitable target designs
Settlement monitoring with leveling rune
Huge refraction problems on the crest prevents use of optical alignment on the crest
X, Y plane coordinates are based on local coordinate system
Map projection coordinate system can also be used

15. Typical Observables in Dam Monitoring
Two-way distance measurements between two stations
Measured 15 times each way with standard deviation of the distance computed from the measurements
Measurements with discrepancy greater than twice the standard deviation is eliminated as outlier
Outlier-free measurements are corrected for atmospheric effects and reduced to mark to mark values
Computed standard deviations are only used to eliminate inconsistent measurements; the manufacturer-specified standard deviation of the equipment is used for each observation in least squares adjustment
Angles or directions are measured in several sets (not less than 3 sets) with re-leveling of instrument between sets
Mean of the sets is used as the angle at the point
Current trend in dam monitoring is to integrate various geotechnical/structural and geodetic surveys techniques

16. Monumentation and Targeting
Types of monuments and targets depend on the level of accuracy of monitoring survey and location of monitored object
Two monument design philosophies:
Reference network points must be durable stable
Object points located to be able to reveal local movements
Monument design requires knowing durability and stability of rock and soil where reference points will be located – requires expertise of soil and geotechnical specialists before constructing the monuments
Centering devices needed on monuments and targets –forced centering types (with typical centering error of ± 0.1 mm)
Reference and object points can allow instrument setup, target setup or both
Points are usually pillars installed into bedrock below the surface
Typical reference control pillar for geodetic dam monitoring is shown in Fig. 9.1

17. Typical Reference Control Pillar
Fig. 9.1
Extensometer anchor point is for
stability test of the pillar
Fig. 9.2 Instrument pillar design
At least 2 of the reference pillars must be stable to be safe

18. Checking Local Pillar Movements
Monitoring pillar with
survey marker
Fig. 9.3(a)
Fig. 9.3(b)
Extensometer anchor point on the control pillar and the survey markers on the
monitoring pillars (Monitor 1 and Monitor 2) are measured with tape
extensometer and the measurements used to perform stability test of
control pillar
Monitor 1 and Monitor 2 are to be flush with the ground in practice
Zenith and horizontal angles and distances are measured from reference
pillar to the two monitoring monuments
Perform measurement every month for 1 year and determine relative
movements by using least squares adjustment method
Unstable reference point is isolated from the other reference points

19. Dam Slope and Crest Monuments and Targets
Survey requirement is to monitor the surface and near-surface movements (1.5 – 1.8 m depth) of downstream slope of dams
Monument design must be able to accommodate standard targets and prism holders
Accurate repeatability of centering in (X, Y, Z) coordinates must be ensured for targets (using specially designed circular spirit leveling device)
Crest monument design is similar to that of slope monument (but monuments are flush with the ground surface) – Fig. 9.4 is a typical crest monument

20. Typical Dam Crest Monument
The monument is a brass disk embedded in
concrete
It can serve as reference and object points
Suitable target plates are to be used for
slope and crest monuments
Concentric circle insert target can be
used for the ball and socket centering
device installed in the instrument pillars
Or specially designed omnidirectional
types

21. Monuments for Subsidence Monitoring
Some of the monuments used in mining subsidence monitoring
are drilled to between 1.5 and 3.4 m depth depending on the
nature of the soil (Fig. 9.5)
Typical monuments are made
of drilled-in 4“ pipes with
survey markers welded to the
inner surfaces of the pipes
Fig. 9.5

22. Horizontal Monitoring and Analysis
Traditional geodetic techniques use
Terrestrial positioning with total station, theodolites, EDM
Space-borne GPS survey augmented with GLONASS
Typical GPS survey of a mining area may require:
Simultaneous use of up to 6 or more geodetic grade receivers/antennas in static relative positioning mode
Data rate set at 10 s
A high-precision GPS control point is fixed for the network adjustment
Horizontal coordinates are commonly provided in map projection grid coordinate system, such as UTM
Typical GPS setups are shown in Fig. 9.6

23. GPS Unit Setup for Mining Subsidence Monitoring
GPS survey procedure is
a repetitive one:
Tripod/tribrach and GPS
antenna are centered on
a monitoring point
Slant antenna height
from survey point to the
antenna center is
measured
Fig. 9.6
If the visibility to GPS satellites is poor in the area, total station traverse
survey subnet connecting to the main project network can be created
using three-baseline surveys (Fig. 9.7)

24. GPS Three-Baseline Survey
This is an example of total station
sub-network traverse controlled by
GPS control points C1, C2 and C3:
Dotted lines are measured GPS
baselines
TPD3 and TPD4 are local GPS points
whose positions are determined in
relation to GPS control points
Perform open traverse to connect
points D8 and D9 using RTS
Forced-centering procedure followed
Location of TP3 and TP4 are such that GPS control points, GPS satellites and unknown points D8 and D9 are inter-visible from
TP3 and TP4
Series of distance, vertical, horizontal angles and meteorological values are measured from TP3 and TP4

25. Adjustment of GPS Three-Baseline and Traverse Surveys
Determine the adjusted coordinates of points D8 and D9 by combined least squares adjustment of the following:
GPS determined coordinates of TPD3 and TPD4 with their covariance matrices and
Total station measurements and their estimated standard deviations

26. Data Preprocessing (1/2)
Common types of measurements to be pre-processed before use in network adjustment: slope distances, horizontal angles, directions, zenith (or vertical) angles and height differences
With regard to EDM distance observables
Calibrate the EDM near the structure being monitored
Measure about 15 measurements each way in two-way measurement of a distance observable
Compute the mean and the standard deviation of the 15 distance measurements, prescreening each measurement using twice the standard deviation as tolerance limit between any two measurements
Perform slope reduction using height differences based on differential leveling
Correct reduced distances for atmospheric conditions and for the effects of elevation differences between stations, producing corrected mark-to-mark distances
Reduce mark-to-mark distances to mapping plane if required
Assign variance to the reduced distance using manufacturer specified accuracy

27. Data Preprocessing (2/2)
With regard to angle and direction observables
Each angle or round of directions must be measured in at least 3 sets with re-leveling between sets and sampling circle readings at various positions of the horizontal circle
Determine discrepancies between reduced directions and the average values
In correcting for the effects of refractions, the effect on the vertical is at least one order of magnitude larger than the effect on the horizontal direction
Angular observations must be made quickly since coefficient of refraction may change rapidly within a short time
In trigonometric leveling or 3D triangulation networks, it may be necessary to reduce zenith angles to their mark-to-mark equivalent (or applying eye-to-object correction) due to differences in heights of instruments and targets
To account for non-parallelism of local verticals at the observing stations, the zenith angles must be corrected appropriately

28. Data Processing Techniques (1/3)
Measurements must first be transformed to displacements between epochs at network points in two approaches:
Two-epoch (or coordinate differencing) approach
Observation differencing approach
Concepts of least squares parametric model adjustment method are applied in each approach
Two-epoch approach consists of least squares adjustment of single-epoch measurements in two separate epochs and their results are compared to determine deformations between the epochs
In least squares adjustment, each epoch measurements are expressed using parametric model:
(9.9)

29. Data Processing Techniques (2/3)
The following are needed to solve Eqn. (9.9):
Geodetic datum (origin of coordinate system, orientation of axes and the scale of the coordinate system) must be defined
Approximate coordinates (x0) of network points – determined from first epoch of measurements and used in subsequent epochs
The adjusted coordinates can be determined:
(9.13)
(9.12)
w is a vector of misclosures between approximate measurements determined from approximate coordinates and the corresponding actual measurements; P is a weight matrix of observations

30. Data Processing Techniques (3/3)
Cofactor matrix of adjusted parameters for a given epoch:
Variance factor of unit weight is calculated as:
(9.15)
Note: solution of Eqn. (9.12) will not be possible without proper
Definition of datum, solution is possible when there is no datum defect

31. Datum Definition Datum is defined as follows: Note:
For 2D geodetic networks: fix 2 coordinates of a point, one scale (or distance measurements) and one orientation (azimuth of a line)
For 3D geodetic networks: fix 3 coordinates of a point, three rotations (one azimuth and angle measurements) and one scale (or distance measurements)
Note:
Distance measurements in a network provide scale for the datum
Gyrotheodolite aziumth provides orientation
Network adjustment that has a minimal amount of information just to define a datum is called minimal constraint or free network adjustment

32. Free Network Adjustment (1/2)
If the coordinates of network points are fixed in defining the datum, the network is externally constrained
A minimal constraint adjustment in which the center of gravity of the network is fixed is known as inner constraint adjustment or free network adjustment
Free network adjustment have the following constraints:
No change in the coordinates of the centroid or center of gravity (fixed) after adjustment
Average bearing from the centroid to each other point remains unchanged after adjustment (no differential rotation of network)
Average distance from the centroid to each other point remains unchanged after adjustment (no scale change)
Generally, initial coordinate values assigned to each of the network points at the start of least squares adjustment define the datum

33. Free Network Adjustment (2/2)
Two types of models are adjusted;
Parametric model relating observations to unknown coordinates
Equations relating all the constraints on the unknown coordinates (forming constraint model) – the number of constraint equations is equal to the number of datum defects
Constraint model ensures that shape and size remains fixed after adjustment – internal geometry is fixed
Constrain model can be given mathematically as
GT = (9.21)

34. Precision Surveying /Chapter 9
G-Matrix Defined
For 2-D network constraints: no fixed point, no azimuth and no
distance: shape of network is fixed; G matrix can be given as
(9.22)
(9.24)
Row 1: constrains translations in x
Row 2: constrains translations in y
Row 3: constrains orientation with respect to center of gravity
Row 4: Constrains the scale (for distances)
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35. Free Network Adjustment – Steps
Define parametric and constraint models:
Linearized parametric model:
(9.11)
Constraints:
(9.21)
v is a vector of residual corrections to original observations
Solution of free network adjustment:
(9.27)
(9.28)

36. Free Network Adjustment –Nuisance Parameter Elimination (1/2)
Consider coordinate corrections (1) and nuisance (2) with
corresponding design matrices A1 for coordinates, A2 for
nuisance parameters:
Modified Solution of free network adjusted coordinates:
(9.32)
(9.29)
(9.30)
(9.31)

37. Free Network Adjustment –Nuisance Parameter Elimination (2/2)
Residual vector of the observations can be given as:
(9.34)
Covariance matrix of free network adjusted coordinates:
(9.35)
A posteriori variance factor of unit weight:
(9.36)
n is the number of observations, d is the number of parameters
to fix to define the datum, u is the number of unknown
parameters in the network adjustment

38. Statistical Analysis of Single-Epoch Measurements
Statistical analysis involves
Assessment of observation quality to decide whether to include the observation or not in adjustment (through least squares blunder or outlier detection)
Assignment of relative weights, ensuring that variance factors computed for pairs of epochs are compatible
Outlier detection for each single-epoch adjustment is important
Any undetected outlier in one epoch may be assessed as deformation in later analysis
Outlier detection in least squares is based on global and local tests based on minimal constraint
For outlier detection, the number of observations most be approximately twice the number of unknown coordinates

39. Global Test

40. Local Test n as the number of observations, df is the number of
n as the number of observations, df is the number of
degrees of freedom , 0 = /n for in-context test,  is the
Significance level used in global test
The associated observation is an outlier if the above condition is not satisfied

41. Deformation Estimation: Two-Epoch Measurements
Prerequisites for using the approach:
Same geodetic datum (fixed points, network scale, orientation of network) used in the two epochs of measurements
Appropriate standard deviations for observations are available for weighting the observations
Same approximate coordinates for the common stations have been used for linearization purpose
Advantages of the approach:
No need of measuring the same observable in each epoch
Each epoch of measurements can be statistically assessed for blunders
Disadvantages:
Problem of datum definition and stability of reference datum between epochs
May not be able to handle contamination of observations due to systematic errors, which impact variance factor of unit weight

42. Deformation Estimation: Two-Epoch Analysis Steps (1/3)
(9.40)
Subscripts 1 and 2 are for epochs 1 and 2 respectively

43. Deformation Estimation: Two-Epoch Analysis Steps (2/3)
(9.41)
with  referring to upper-tail area of F-distribution
(9.42)
(9.44)
(9.43)

44. Deformation Estimation: Two-Epoch Analysis Steps (3/3)

45. Iterative Weighted Similarity Transformation (1/2)
Use Helmert (Similarity) Transformation matrix (S) will
transform from one datum to another datum
The transformation process will preserve network geometry
by translating, rotating and scaling the given network from
one datum (i) into other (j) using well-chosen transformation
matrix Sj:
(9.45)
(9.46)
with
(9.47)
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46. Iterative weighted Similarity Transformation (IWST) (2/2)
I = identity matrix with principal diagonal elements as one and
off diagonal elements as zero
Pj = special identity matrix – unity for coordinates
defining datum with other elements as zero
Pj is an identity matrix for inner constraint adjustment
Using Eqns. (9.45) – (9.47) requires iteration until the results
converge
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47. IWST: Steps

48. Observation-Differencing Adjustment Approach
Corresponding observations are differenced and adjusted by least squares method
Adjusted coordinate differences & their covariance matrices are determined
Appropriate datum must exist for the adjustment
Conditions satisfied before adjustment:
Same approximate coordinates (same geometry) for the 2 epochs
Same observables, observers, same conditions

49. Observation-Differencing: Advantages and Disadvantages
Advantages of using observation-differencing approach:
Common systematic errors due to instrumentation, observer and atmosphere will be removed
Strain analysis can be done if datum is unstable between epochs
It can easily accommodate geotechnical data, such as tiltmeter and extensometer measurements
Geometric defects (due to eccentric targets, etc.) are permitted
Disadvantages:
Need to measure the same observables, same instrumentation, observers, etc. which may be impossible practically
Statistical analysis of each epoch for blunders is not possible

50. Geometrical Analysis of Deformation Measurements
Deformation is a consequence of dynamic process or dynamic system, which is composed of 3 elements:
Factors causing deformation
Physical properties of the monitored object
Response of the object in form of deformation or other form
Dynamic processes are completely described and explained by dynamic models
They help to study the 3 elements of dynamic system and to make predictions
The model is called deterministic if the factor causing the deformation and the physical properties of the monitored object are known and the deformations of the object are only to be predicted
The model is called integrated model if the factor causing the deformation and the physical properties of the monitored object are known with deformation measurements available from geodetic monitoring

51. Dynamic Models
Dynamic models can be broken into 3 types: kinematic, static and geometrical
Kinematic models consider
Monitored object points are moving continuously as function of time
No acting forces or loads are involved in the modeling
Deformation is described in form of velocity and acceleration of object points using time function and no regard for factors causing the deformation
Static models consider
No time is involved
Monitored objects are not in continuous motion (at least not moving during monitoring time), but are at equilibrium under acting forces (loads)
Deformation is a function of only acting forces (loads), not of time
Physical and geometric structures of the object, material properties, etc. of the object must be known
Response of the object in form of deformation or other form

52. Geometric Models Geometric models consider Geometric models
Object as a set of discrete points in space
The object points move only within certain intervals in time and not continuously , but the object is considered as being in equilibrium under the acting forces (loads)
Time is not explicitly considered
Acting forces (loads) are not considered
Geometric models
Models monitoring network points or changes in geometry of the monitored object in space and time
The models are used in geometrical deformation analysis
Geometrical deformation analysis is about detecting, localizing, and modeling monitoring network point movements based on deformation monitoring

53. Geometrical Deformation Analysis (1/2)
Problem of geometrical deformation analysis with regard to absolute monitoring networks
Confirm the stability of the reference points and to identify the possible single-point movement that may be due to local phenomena or wrong monumentation of survey markers
If unstable reference points are not identified, the object points and other reference points (that are stable) will show movement even when they are truly stable.
Geometrical deformation analysis is not easy with regard to relative monitoring networks
There may be single-point movement as well as relative movements (due to strains in the materials of the object) of all the network points
If there is a discontinuity (due to tectonic faults) in the object, there may be relative rigid translations and rotations of a block of the object with respect to other possible blocks
Main problem will be how to identify the deformations caused by strains, relative rigid body translations, and single-point movements

54. Geometrical Deformation Analysis (2/2)
Analysis of relative monitoring network
First establish whether any group of points in the network is stable between epochs using IWST
If stable group of points exists, treat the network as absolute network with the stable points as datum otherwise, analyze the network using IWST
Overall task of deformation analysis is to obtain a displacement function (deformation model) in space and time
Once the displacement function is determined, all the basic deformation parameters such as strain components, rotations, and rigid body movements can be calculated at any desired point of the monitored object

55. Statistical Trend Analysis of Deformation (1/3)
After adjustments and IWST transformation, deformation must be detected using two-epoch analysis
Using single-point statistical test
Using trend analysis
Statistical trend analysis of deformation steps:
Perform minimal constraint least squares estimation of the coordinates of points and the covariance matrices
Determine datum-dependent displacements from the estimated coordinates
Perform IWST of the displacements to obtain datum-independent relative displacements and identify the stable reference points

56. Statistical Trend Analysis of Deformation (2/3)
(9.57)

57. Statistical Trend Analysis of Deformation (3/3)
In the case where the a priori variance factor is considered known, Eqn. (9.57) can be replaced by the equivalent Chi-squares value
Any point with satisfying the following Chi-squares expression is flagged as unstable:
Model the stable points as fixed reference block and determine the displacements of the object points
The whole process in step 4 is statistical analysis of deformation trend or the localization of deformation
Trend analysis is an intermediate link between deformation measurements and the deformation modeling

58. Graphical Trend Analysis of Deformation
Graphical trend analysis consists of:
Plotting network points displacement vectors with their
corresponding error ellipses
The plot shows the spatial trend over time interval between the
two epochs
If a displacement vector extends outside the error ellipse, the
movement is considered significant at the given significance level
and the associated point is considered unstable
The point displacement error ellipse is constructed from
sub-matrix of displacement cofactor for the given point

59. Displacement Error Ellipse (1/2)
(9.59)
The semi-major axis (a), semi-minor axis (b) and orientation ()
of the displacement error ellipse can be calculated as follows
(9.60)
(9.61)
(9.62)

60. Displacement Error Ellipse (2/2)
(9.66)
(9.67)
(9.68)

61. Main Features of a Typical Hydroelectric Dam
Sources of deformation
of hydro dams:
Alkaline aggregate
reaction of concrete
Instability of bedrock
Changeable water
load on the dam
Seasonal thermal-
induced deformations
Possible seismic
events
Fig. 9.8

62. Simulated Dam deformation
Points A, B, C constitute the
reference network
Point P on the crest of the dam
is the object point to be
monitored
displacement of
Angles and distances are
measured
External minimal constraints
and IWST are applied
Statistical analysis and graphical trend analyses detected the movement
of object point P

63. External Minimally Constrained Displacements
Displacement at point P
is outside the error
ellipse (95% confidence)
Point C is barely stable
which is not supposed to be
Fig. 9.10

64. Displacement Field After IWST
Displacement at point P
is outside the error
ellipse (95% confidence)
Point C is stable as
expected
Fig. 9.11

65. Typical Trilateration Network on a Dam
Monitoring is based on
precise differential
leveling and horizontal
control networks
Reference and object
Networks are well-
chosen
Fig. 9.12

66. GPS Surveys Points GPS unit installation as part of traditional
monitoring system of an
hydroelectric dam
Fig. 9.13

67. Deformation Monitoring of Slope Walls
Current trend in monitoring and deformation surveys of slope walls in open-pit mines includes
Creating fully automated monitoring scheme based on RTSs and active GPS, and assortment of geotechnical instrumentations
Integrating a number of monitoring techniques, including GPS, total stations, reflectorless EDM, and differential leveling
In open-pit mines, slope walls can be a few hundred meters deep and 1 or 2 km long and wide
Steep mine slopes are designed to reduce cost of mining
The steepness of slopes increases the frequency of slope failures, requiring the need for monitoring the slopes
Geotechnical instruments are commonly used since they are easily automated
Conventional surveying procedures are now common

68. Advantages and Disadvantages of Automatic Monitoring System
Reduction of manpower
More frequent data and
Fewer errors
Disadvantages:
Large volume of data to be managed
Initial cost;
wrong use of collected data;
needs for special personnel

69. Automatic Monitoring with Robotic Total Station
Robotic total stations (RTS) are the primary measurement sensors in the automated monitoring system in open-pit mines
Target prisms are located strategically throughout the pit on the pit walls
Distances, horizontal directions and zenith angles are measured to the targets continuously to determine 3D positions of prisms
RTSs can be programmed for sequential self-pointing to a set of target prisms at predetermined time intervals and measurements can be transmitted to remote stations via a telemetry link
Important sources of error: refraction and random pointing errors and instability of RTSs

70. Minimizing Errors in RTS Automatic Monitoring
Minimizing effects of both refraction and random pointing errors
Maintain short distances from the RTSs to target prisms
Take observations in several steps and spread the observations over long periods to randomize refraction effects; measurements can be corrected for meteorological effects
Keep lines of sight away from strong sources of heat radiation
Instability of RTSs will cause displacements determined to be biased
Use RTS with GPS antennas to take care of instability of RTSs

71. Collocating GPS Antenna with RTS (1/2)
Two ways to collocate GPS antenna with RTS to correct instability of the RTS in an open-pit mine monitoring:
Collocate GPS antenna and RTS in the unstable region of the mine and do the following
Use two other GPS antennas collocated with 360º prisms: Collocated Antenna /Prism A is located on a stable point S (outside the mining region); the other Collocated Antenna/Prism B is located within the unstable mining region U
Stable point S must be within m for best results with ATR in the RTS
Use Antenna/Prism A to provide orientation for the main RTS in the shelter; GPS will update the position of RTS
Updated Position of RTS and the orientation to Antenna/Prism A are used to correct measurements to targets on the unstable object points

72. Collocating GPS Antenna with RTS (2/2)
Collocate GPS antennas with 360º prisms and position them on at least 3 stable points (forming reference points), probably outside the mining region (but within m of the main RTS for best ATR results) and do the following
Sheltered main RTS (in an unstable region) will measure to 3 or more reference points in free station computation to determine its position and orientation before making measurements to the targets on the unstable object points
The reference points are to be positioned so as to form a strong geometry in order to ensure that free station calculates with high accuracy

73. Main Challenges in Using GPS in Open-Pit Mines
Steep walls – results in poor geometry
Large height differences (700 m) between master and rover stations – affects accuracy of positioning
Needs for fully automated GPS processor for continuous update in real-time
Multipath problem resulting in accurate measurements
Power supply to GPS units (difficult in inaccessible or not frequently accessed areas)
Sheltering instrument in harsh conditions & against vandalism - Loss of RTS preferred to loss of GPS units

74. Concerns in Using RTS in Open-Pit Mines
Refraction & pointing errors (for pit’s diameter > 1 km) since long sights are involved (>1 km)
Complex behaviour of pit (stability problem) as it responds to changes in environment (e.g., excavation, increase in water saturation, etc.) – causes instability of instrument also

75. Deformation Monitoring of Tunnels
Interest:
Movement of tunnel walls (inward, settlement, heave and 3-D displacement)
Deformation around and ahead of tunnel excavation face
Deformation (settlement, tilt, lateral displacement & 3-D displacement) at or near ground surface (structures and utilities) – ensure structures at the ground surface are not harmed by tunneling operations
Causes of tunnel deformation:
Adverse ground and groundwater regimes
Large overburden pressures – due to sensitive or utilities in urban tunnels
Intense tectonic activities
Concerns: Mountain region – caving in; Urban – damages to utilities

76. Tunnel Monitoring Instruments
Instruments on the ground surface or in the tunnel
Ground deformation is likely at the place ahead or close to tunnel face
install instrument so as not to interfere with support system (sprayed concrete, steel sets, etc.)
Geodetic and geotechnical instruments to complement each other
Geodetic provides absolute 3D coordinates – e.g., total stations on brackets and reflectors
Geotechnical provides relative displacements in one direction – e.g., extensometers

77. Vertical Deformation Monitoring and Analysis
Special-order or first-order geodetic leveling procedures can be used in monitoring object in order to determine:
Tilts based on height difference measurements in bases of virtually limitless lengths between pairs of benchmarks
Vertical expansion (settlement, uplift, or subsidence)
Absolute height changes with respect to stable points
Major problem of differential leveling:
Vertical atmospheric refraction is a major source of systematic errors
Usual increase in random errors due to rod scale error and settlement of instruments and rods when a large number of setups are involved

78. Vertical Deformation Monitoring with GPS
For reasonable results, three-baseline GPS surveys can be used
This method economizes GPS surveys since one can carry out the field operation unassisted
Three-baseline method is illustrated in Fig with points C1, C2, C3 representing control points with continuously operating GPS receivers and point P as the point whose position is to be determined

79. Three-Baseline GPS Approach
Set up GPS receiver on the monitoring point P and determine
its position by measuring three GPS baselines B1, B2 and B3
The duration of observation sessions must be up to 12 h in order to achieve sub-centimeter accuracy in vertical positioning at 95% confidence level
Fig. 9.14

80. Tilt, Strain and Curvature Determination from Leveling
Tilt – deviation () of a surface relative to horizontal reference surface (Fig. 9.15a)
Inclination – deviation () of a surface relative to vertical plane (Fig. 9.15b)
Advantage of using geodetic approach over geotechnical approach in tilt determination
limitless length of base is possible with geodetic approach unlike in geotechnical approach where short bases are usually involved
Accuracy of 0.1“ in tilt is possible over 1 km with geodetic method

81. Tilt and Inclination
Based on Fig (a), the tilt angle  (in radians) can be determined
by geodetic leveling as
Leveling between
points P1 and P2
can be done along
any route
Fig. 9.15

82. Horizontal Strain and Curvature
Deformation tolerances for assessing impact of ground subsidence on infrastructure are usually based on criteria:
tilt (vertical displacement)
horizontal strain (or horizontal displacements
Curvature of subsidence trough
Subsidence has not significantly impacted surface structures if the following are satisfied:
tilt and horizontal strain around the structures have not exceeded deformation tolerance of 2.5 and 1.5 mm/m, respectively
radius of ground curvature around the structures is larger than 20 km
Consider points P1, P2 and P3 located on a subsidence bowl (Fig. 9.16)

83. Tilt, Strain and Curvature of Subsidence Bowl
Tilt (T), Strain () and curvature of subsidence bowl (K) can be given as
(9.70)
(9.71)
(9.72)

84. Integrated Leveling Surveys (1/2)
Geodetic leveling surveys in a gallery of a dam can be used to determine tilt and absolute height changes of the dam structures
The setup of level instruments in Fig can be used to determine elevations of unknown points and the borehole extensometer collar location
The points (e.g., Pi and Pj) are monitored with the setup after to determine relative movements of the points
Control is taken from known benchmark (BM)
Two scales (one at upper floor and the other at lower floor) attached to suspended plumbline are used

85. Integrated Leveling Surveys (2/2)
(9.73)
(9.74)
For k = 1,…n:
Fig. 9.17

86. Tilt and Strain Rate Determination
A plot of yk against time xk can be fitted with a sinusoid to derive
vertical displacement rate (mm/year)
When the displacement rate is divided by the horizontal separation
between Pi and Pj tilt rate (mm/m/year) is obtained
When the displacement rate is divided by the vertical separation
between Pi and Pj extension or strain rate (mm/m/year) is obtained
Equation (9.74) can be expressed from Fig (given that
Δhab will always be constant) as
(9.79)