Deformation Surveys

8/10/2019 Deformation Surveys

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Deformation SurveysDeformation surveys, or deformation monitoring, has increased dramatically over the last

10 years or so among the civil and building professions. There can be many reasons whythis type of work would need to be carried out. Monitoring of building foundations,

structural retaining walls, and embankments or even in the control of mechanical

processes.

The purpose of a deformation survey is to determine whether or not movement is taking

place and subsequently whether the structure is stable and safe. Movement can be furtheranalyed to see if it is due to seasonal factors, daily variances etc. and then more

importantly use the information to determine future movement of the structure.

!ccuracies required for deformation surveys depend on many factors but generally

accuracy to the millimetre or better may be required.

These types of work are classifies, as local scale as the network involves is relatively

small in area.

The tasks in deformation monitoring survey require acquisition of observation dataobtained from more than one campaign of field measurements. Type of instruments used

in data acquiring is depending on the nature of works and also on logistical consideration."ormally, for a small network the use of theodolite and total station seems good enough

in measuring the required directions or horiontal angles and distances. The subsequent

task is to perform the least squares ad#ustment to determine the coordinates of all thereference as well as the ob#ect points in the network for each epoch of measurements.

$urther, in monitoring works the e%ercise is continues with the analysis of deformation

emphasiing on two important aspects i.e., the solution to datum defect and selection of

the right datum &'hen, 1()*+. These tasks are necessary in order to determine the correctdisplacements vector for all the monitoring points.

This handout provides technical guidance for performing precise structural deformation

surveys of locks, dams, and other hydraulic flood control or navigation structures. !ccuracy,

procedural, and quality control standards are defined for monitoring displacements inhydraulic structures.

a. Structural deformation. Dams, locks, levees, embankments, and other flood controlstructures are sub#ect to e%ternal loads that cause deformation and permeation of the structure

itself, as well as its foundations. !ny indication of abnormal behavior may threaten the safetyof the structure. 'areful monitoring of the loads on a structure and its response to them can

aid in determining abnormal behavior of that structure. n general, monitoring consists ofboth measurements and visual inspections. To facilitate the monitoring of hydraulic

structures, they should be permanently equipped with proper instrumentation and-ormonitoring points according to the goals of the observation,

structure type and sie, and site conditions.b. Concrete structures. t should be intuitive that deformations and periodic observations will

vary according to the type of structure. Differences in construction materials are one of thelarger influences on how a structure deforms. $or e%ample, concrete dams deform differently

than earthen or embankment dams. $or concrete dams and other concrete flood control

devices, deformation is mainly elastic and highly dependent on reservoir water pressure and


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temperature variations. ermanent deformation of the structure can sometimes occur as thesubsoil adapts to new loads, concrete aging, or foundation rock fatigue. /uch deformation is

not considered unsafe if it does not go beyond a predetermined critical value. Therefore,periodic observations are typically configured to observing relatively longterm movement

trends, to include abnormal settlements, heaving, or lateral movements. 'onventional

geodetic survey methods from e%ternal points and of centimeterlevel accuracy are

sufficient to monitor these longterm trends. ighly accurate, shortterm deflections orrelative movements between monoliths due to varying temperature or hydraulic loading are

more rarely required.These may include crack measurements or relative movements between monoliths over

different hydraulic loadings. 2elative movement deflections to the 30.01cm accuracy levelare common.

c. Earthen embankment structures. 4arthen or embankment dams and levees obviously willdeform altogether differently than concrete ones. 5ith earthen dams, the deformation is

largely characteried as more permanent. The selfweight of the embankment and thehydrostatic pressure of the reservoir water largely force the fill material &and in turn, the

foundation, if it too consists of soil+ to settle, resulting in a vertical deflection of the structure.

The reservoir water pressure also causes permanent horiontal deformation perpendicular tothe embankment centerline. 5ith earthen dams, elastic behavior is slight. Deformation survey

accuracy requirements are less rigid for earthen embankments, and traditional construction

survey methods will usually provide sufficient accuracy.Typical surveys include periodic measurement of embankment crest elevations and slopes to

monitor settlements and slope stability. $or embankment structures, surveys accuracies at the30.1 cm level are usually sufficient for monitoring longterm settlements and movements.

d. Long-term deformation monitoring. Depending on the type and condition of structure,

monitoring systems may need to be capable of measuring both longterm movement trendsand shortterm loading deformations. 6ongterm measurements are far more common and

somewhat more comple% given their e%ternal nature. 6ongterm monitoring of a structure7smovement typically requires observations to monitoring points on the structure from e%ternal

reference points. These e%ternal reference points are established on stable ground wellremoved from the structure or its construction influence. These e%ternal reference points are

interconnected and termed the 8reference network.8 The reference network must also be

monitored at lessfrequent intervals to ensure these reference points have not themselves

moved. Traditional geodetic survey instruments and techniques may be employed toestablish and monitor the reference network points.

Deformation Survey Techniquesa. Reference and target points. The general procedures to monitor the deformation of a

structure and its foundation involve measuring the spatial displacement of selected ob#ect

points &i.e., target points+$rom e%ternal reference points that are fi%ed in position. 9oth terrestrial and satellite methods

are used to measure these geospatial displacements. 5hen the reference points are located inthe structure, only relative deformation is determinede.g., micrometer #oint measurements

are relative observations.

!bsolute deformation or displacement is possible if the reference points are located outside

the actual structure, in the foundation or surrounding terrain and beyond the area that may be


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affected by the dam or reservoir. /ubsequent periodic observations are then made relative tothese absolute reference points.

!ssessment of permanent deformations requires absolute data.

b. Reference point network. n general, for concrete dams it is ideal to place the reference

points in a rock foundation at a depth unaffected by the reservoir. :nce permanently

monumented, these reference points can be easily accessed to perform deformation surveys

with simple measurement devices.$i%ed reference points located within the vicinity of the dam but outside the range of its

impact are essential to determination of the deformation behavior of the structure. Thus,monitoring networks in the dam plane should be supplemented by and connected to

triangulation networks and vertical control whenever possible.

c. Monitoring techniques. The monitoring of dam or foundation deformation must be done

in a manner such that the displacement is measured both horiontally and vertically &i.e.,measurement along horiontal and vertical lines+. /uch measurements must include the

foundation and e%tend as far as possible into it. 2edundancy is essential in this form ofdeformation monitoring and is achieved through measuring at the points intersecting the

orthogonal lines of the deformation network. f a dam includes inspection galleries and

shafts, deformation values along vertical lines can be obtained by using hanging and-orinverted plumb lines and along horiontal lines by traversesboth of these methods are

standard practice for deformation monitoring. 5here there are no galleries or shafts &e.g.,

embankment dams, thin arch dams, or small gravity dams+, the same result can be achievedby an orthogonal network of survey targets on the downstream face. These targets are sighted

by angle measurements &typically combined with optical distance measurements+ fromreference points outside the dam.

d. Relative displacement observations. ! more routine, less costly, and more frequentmonitoring process can be employed to monitor the short term behavior of dams by simply

confining observation to trends at selected points along the crest and sometimes vertical lines./uch procedures typically involve simple angle measurement or alignment &supplementing

the measuring installation+ along the crest to determine horiontal displacement, andelevation determination by leveling to determine vertical displacement &i.e., settlement+. 4ven

with this monitoring process, it is essential to e%tend leveling to some distance beyond theabutments. !lternative methods to that described include settlement gauges, hose leveling

devices, or e%tensometers.

Life Cycle Project Management!s outlined structural stability assessment surveys may be required through the entire life

cycle of a pro#ect, spanning decades in many cases. During the early planning phases of apro#ect, a comprehensive monitoring plan should be developed which considers survey

requirements over a pro#ect7s life cycle, with a goal of eliminating duplicate or redundant

surveys to the ma%imum e%tent possible. During initial design and preconstruction phases of

a pro#ect, reference points should be permanently monumented and situated in areas that areconducive to the performance of periodic monitoring surveys. During construction, fi%ed

monitoring points should be established on the structure at points called for in thecomprehensive monitoring plan.


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Monitoring high-rise building deformation using Global Positioning System

Deformation of engineering structures is often measured in order to ensure that the

structure is e%hibiting a safe deformation behaviour. $or e%ample, the deformation of

highrise building can be monitored by using geodetic method such as ;lobal ositioning/ystem &;/+.

Introduction

4ngineering structures &such as dams, bridges, high rise buildings, etc.+ are sub#ect to

deformation due to factors such as changes of ground water level, tidal phenomena,

tectonic phenomena, etc. 'ost is more than offset by savings and by improvements insafety both during and after constructions. !s a result, the design, e%ecution and analysis

of such surveys are a matter of considerable practical importance. 4%panded resource

development, the trend towards potentiallydeformationsensitivity engineering andconstruction pro#ects, and growing geosciencetific interest in the study of crustal

movement have all combined to increase awareness of the need for a comprehensive

integrated approach to the design and analysis of such deformation surveys. Deformation

refers to the changes of a deformable body &natural or manmade ob#ects+ undergoes in itsshapes, dimension and position. Therefore it is important to measure this movements for

the purpose of safety assessment and as well as preventing any disaster in the future.

Deformation measurement techniques generally can be divided into geotechnical,

structural and geodetic methods &Teskey and oster, 1())+. The geodetic methods &highly

understood by land surveyors+ that can be used are ;lobal ositioning /ystem &;/+,close range photogrammetry, total station &terrestrial survey+, very long baseline

interferometry and satellite laser ranging. The survey methods can be further subdivided

into the survey network method and direct measurement methods. n geodetic method

there are two types of geodetic networks, namely the reference &absolute+ and relativenetwork &'hranowski et. al., 1()


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The e%ecution process that runs a designed network into reality which deals with both the

documentation of the proposed network stations and the actual field measurement

techniques, andThe network analysis that deals with the processing and analysis of the collected geodetic

data.

GPS Background and Structural High Rise Building;/ is satellite based positioning system, which has been developed by the >/

Department of Defense &DoD+ for real time navigation since the end of the ?0@s. t has

made a strong impact on the geodetic world. The main goal of the ;/ is to provideworldwide, all weather, continuous radio navigation support to users to determine

position, velocity and time throughout the world. t consists of three segments= the space,

control and user segment. The ;/ can be used for absolute and relative geodetic point

positioning. ts primary task is to measure distances between AB satellites in known orbitsabout A0,000 km above the earth and provide the user with the information of

determining user@s position, e%pressed in the geocentric *D coordinate system &5;/)B+.

;/ techniques have several advantages as a monitoring tool. The surprisingly highaccuracies of relative ;/ measurements are finding an application in monitoring

surveys in areas where stations require intervisibility and weather conditions. 'urrently,with the deployment of the full satellite constellation, continuous and automated

monitoring using ;/ will become increasingly practical and costeffective. Thus, the

potentials of ;/ as a super positioning tools brought a fresh air to the field ofmonitoring surveys, especially in areas where quick results could save lives and property.

n principle, the monitoring of highrise building using ;/ can be performed

episodically &epoch intervals+ or continuously. 'urrent ;/ accuracy estimates range

from 1CA ppm for regional baseline vectors determined using commercial productionsoftware &De6oach, 1()(+.

ighrise building is defines as a multistory building tall enough to require the use of asystem of mechanical vertical transportation such as elevators. !lthough originally

designed for commercial purposes, many highrise buildings are now planned for

multiple uses. They arose in urban areas where increased land prices and great populationdensities created a demand for buildings that rose vertically rather than spread

horiontally, thus occupying less precious land area. The foundation of highrise

buildings must support very heavy gravity loads and they usually consist of concrete

piers, piles or caissons that are sunk into the ground. The most important factor in thedesign of highrise buildings is the building@s need to withstand the lateral forces imposed

by winds and potential and ground movements. Most highrise buildings have frames

made of high strength steel and concrete. Their frames are constructed of columns&verticalsupport members+ and beams &horiontalsupport members+. 'ross bracing or

shear walls may be used to provide structural frame with greater lateral rigidity in order

to withstand wind stress. 4ven more stable frames use closely spaced columns at thebuilding@s perimeter, or they use the bundledtube system, in which a number of framing

tubes are bundled together to form e%ceptionally rigid columns. 'urtain walls enclose

highrise buildings these are nonloadbearing sheets of glass, masonry, stone or metal


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that is affi%ed to the building@s frame through a series of vertical and horiontal members

called mullions and muntins.

Deformation Surveys

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