Deformation Surveying

)

Surveying

Notebook

Doç. Dr. Yunus KALKAN STRUCTURAL Lecture Notebook (

Deformation Surveying Doç.Dr. Yunus Kalkan

İTÜ İnşaat Fakültesi Jeodezi ve Fotogrametri MühendisliğiBölümüi Bölümü Ölçme Tekniği Anabilim Dalı

Görüşme Saati: Çarşamba 11:00-15:00 Oda No: INB-407 Tel: 0212 285 38 18 FkFaks: 0212 285 34 14 E-posta: [email protected] Web sayfası: http://www.ins.itu.edu.tr/olcme/indextr.htm REFERENCES

• Engineering And Design Structural Deformation SiSurveying US Army Corps o f Eng ineers EM 1110-2-1009

• W.F . Caspary , J. M. Rüeger, Concepts of Network and Deformation Analyses, National Library of Australia, 1987 • Engineering surveying technology / edited by T.J.M. Kennie and G. Petrie Merkez Küt.Ders Kitapları -- TA562 .E54 1990 • Surveying : with construction applications / Barry F. Kavanagh Merkez Küt.Ders Kitapları -- TA625 .K38 2004 Başarı Değerlendirme Ölçütleri

Mid-term Not Mid-tEterm Exam %60 + QiQuiz %15 + Hk%25Homework % 25 Minimum Devam: %70 Mid-term Exam : 1 %24% 24 Quiz : 1 % 6 Homework : 1 % 10

Final Not Mid-term Not %40 + Final Exam Not %60 .

Analysis

Measurement

Requirements Deformation

for

Settlement

Networks Accuracy

and

and examples

Reference

Design, Deflection

application

onitoring Reference Networks Deformation Monitoring Surveys Deformation Monitoring Planning, M Periodic Deflection and Settlement Some application examples for Deformation Analysis Surveys : : :

Contents Week : Week : Week

. . 1. Week :1. Week :2. Week 3 Introduction 4. Week : General Definitions :Week 5. 6. Deformation Week : Monitoring Deformation Specifications Standards for and 7. Week : :8. Week 9. Horizontal Week Control : Survey Techniques Vertical Control Survey Techniques Conventional Adjustment for surveys Survey Structural Deformation Monitoring Surveys 10. Week : Examination 11. Week :Week 11. 12. Structural application examples Some for 14 13. Week : Deformation Analysis Vertical Rotation rotation Horizontal Vertical Transition Transition transition Rotation Horizontal Outer(exterior) Geometrical Change Deformation eformation is a geometrical changing in the objects (material, body,...) D To be Erosion Irregular Deformation Hollowed out

Deformation: nner geometrical Change İ Bent Verbal To twist Regular To exceed Inclination Deformation

Calibrations

Observations

Instrument

Leveling Observations . and

Geom

Error

Precise - Measurement

Surveys

Structural Deformation Surveying of

Sources of Measurement Error and Instrument Calibrations Settlement Surveys : : 4 6

Chapter 1: Introduction Accuracy Requirements Chapter 2: Planning, Design, and Alignment Instrumentation and Chapter 3: Deformation Measurement Chapter 4 Chapter 5:Angle and Distance Observations-Theo., Total Stations and EDM Chapter 6 - Measurement 7:Alignment, Deflection, and Crack Chapter Chapter 8:Monitoring Structural Deformations Using the GPS Adjustment Chapter 9:Pre-analysis and Network Assessment Methods Chapter 10:Relative Distance Ratio Assessment of Results and Chapter 11:Analysis Presentation and Final Reports 12:Data Chapter Chapter 1- Backround, Structural deformation, Deformation Survey Techniques,

1- Purpose

This Manual provides technical guidance for performing precise structural deformation surveys of locks, dams, and other hydraulic flood control or navigation structures. Accuracy, procedural, and quality control standarts are defined for monitoring displacements in hydraulic structures.

2- Background

The Crops of Engineers has constructed hundereds of dams,locks, levees, and other flood control structures that require periodic surveys to monitor long-term movements and settlements, or to monitor short-term deflections and deformation. . Any indication of abnormal behavior may threaten the of the structure. Carefullsafety monitoring of the loads on a structure and its response to them can aid in determining abnormal behavior of that structure. Structural Deformation Surveying

a. Structural deformation Structural a. Dams, locks, levees, embankments, and flood other control structures subject to external loads that are deformation and permeation cause of the structure itself, as well its foundations er p ro p . ed with pp ui q e y ermanentl p should be y ypyqpppp In general, monitoring consists of both measurements and visual inspections facilitate the monitoring of hydraulic structures, To the instrumentation and/or monitoring points according to the goals of observation, type and size, site conditions. structure

Structural Deformation Surveying

mainly For . is

er influences g dams

deformation

embankment

b. Concrete structures Differences in construction Structural Deformation Surveying or devices,

concrete dams and other concrete flood concrete elastic and highly dependent on reservoir elastic water pressure and temperature variations. materials are one of the lar are materials on how a structure deforms. For example; dams deform differently than concrete earthen or embankment dams For control devices, deformation is mainly

e iv at l e r o

s n o i ect fl de rm te de ect o s o e at e - t r o h s

ate, r accu

y hl g . Hi ds Conventional geodetic survey methods from external points n e b. Concrete structures

Structural Deformation Surveying r t e ds g y accu ate, s o t rm and of centimeter-level accuracy are sufficient to monitor these long- and of centimeter-level accuracy te between monoliths due to varying temperature or hydraulic movements loading are more rarely required. and Earthen or embankment dams differently than concrete ones. With earthen dams, the deformation is largely as more permanent. The characterized reservoir water pressure also causes permanent horizontal deformation perpendicular to the embankment earthen dams, elastic centerline. With behavior is slight. levees obviously will deform altogether

Structural Deformation Surveying c. Earthen or Embankment Structures. y. bilit a t ope s l s d s an t emen ttl Structural Deformation Surveying c. Earthen embankment structures. or se it o mon Deformation survey accuracy are less rigid requirements for earthen. embankments, and traditional construction survey methods will usually Typical provide sufficient accuracy. of include periodic measurement surveys embankment crest elevations and slopes t it ttl t d l t bilit

the

." The complex

points

movement

term movement - monitoring Long-term

long to

somewhat

both and

observations

common

Long-term monitoring of a structure's measuring .

oints have not themselves moved. oints have not themselves of

p more

requires

far

capable are

typically

Structural Deformation Surveying need

d. Long-term deformation monitoring. oints are inter-connected and termed the "reference network oints are inter-connected and termed the "reference trends and short-term loading deformations. points. from external reference These external reference structure given their external nature Depending on the type and condition of structure, monitoring systems may need to be capable of measuring both long measurements are far more common and somewhat more complex movement typically requires observations to monitoring points on the p network must also be monitored at less-frequent intervals to reference ensure these reference Both Deformation Survey Techniques

Structural Deformation Surveying a. Reference and target points a. Reference The general procedures to The general procedures structure and its foundation involve measuring the spatial displacement of object points (i.e., target selected points points) from external reference that are fixed in position. and satellite methods are terrestrial used to measure these geo spatial displacements. monitor the deformation of a 1-7. Deformation Survey Techniques

When the reference points are located in the structure, only relative deformation is determined-e.g., micrometer joint measurements are relative observations. Absolute 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 affected by the dam or reservoir. .

Structural Deformation Surveying These reference points to perform deformation These reference can be easily accessed surveys with simple measurement devices. In general, for concrete dams it is ideal to place the reference points in a rock foundation at a depth unaffected by the reservoir. b. Reference point b. Reference network is y both measured is ossible into it. Redundanc displacement p the that such manner a c. Monitoring techniques in The monitoring of dam or foundation deformation must be

Structural Deformation Surveying done horizontally and vertically. Suchfoundation measurements and must extend includeessential as in the far this as formthrough measuring of at the deformation points monitoring intersectingthe the deformation and orthogonal network. lines is of achieved an ere y Wh . ng i or it i on mon ti orma f e dfd ti or f the same result can be achieved b ce ti ), prac dams d y ar d ravit an g gy tdd t

Structural Deformation Surveying sares or small c. Monitoring techniques d , o th d there are nodams galleries or shafts (e.g., embankment dams, thin arch If a dam includesalong inspection vertical galleries lines and can shafts, beplumb deformation obtained values lines by using and hangingme along and/or horizontal inverted lines by traverses—both of these orthogonal network of survey targets on the downstream face. Structural Deformation Surveying )

T) T İ İ T ) D İ ı KES KES ( PLAN ) (

( PLAN ) ( PLAN (KES ( Noktalar ı Yer Alt C Galeri 4 3 4 s s Kuyu 3 1 1 c c' 2 2 c c' e e 2 2 2 2 s s 1 1 s s 1 1 ı B B Structural Deformation Surveying Yer Üstü Noktalar A A

uent gauges t or q

n displacement, emen

o ttl t se e

servati d and more fre u measurement

b l

y, horizontal

nc i

extensometers. d angle e

ib , or

acement o less costl

l , ,y,q determine escr

simple d

isp to t d a th o crest t

ative involve

l s d Structural Deformation Surveying the

o . Re A more routine A

dld dl b th d t th t d ib d i l d monitoring process can be employed to monitor the monitoring process short term behavior of dams by simply confining observation to trends at selected points along the lines. Such procedures vertical and sometimes crest typically involve simple angle measurement or along the crest to determine horizontal displacement, to extend leveling monitoring process, it is essential Alternative some distance beyond the abutments. me alignment (supplementing the measuring installation) hose leveling devices and elevation determination by leveling to determine displacement (i.e., vertical settlement). Even with this Chapter 2- Planning, Design, and Accuracy Requirements

2-1. Standards for Deformation Surveys

a. General. This chapter provides guidance for planning and implementing structural deformation surveys b. Dam safety. US Army Corps of Engineers owns and operates a wide range of large engineering structures, including major inf rast ruct ure f aciliti es f or navi gati on, fl ood prot ecti on, and l arge d ams.

c. Engineer regulations. Standards for conducting instrumentation surveys andfd for peridiiiodic inspecti ons. GidGuidance fCiilWkfor Civil Works proj jtects provides for an adequate level of instrumentation to enable designers to monitor and evaluate the safety of the structures. d. Specialized standards. Specialized standards for conducting deformation surveys are justified as long as products are consistent with effective government wide coordination and efficient. Planning, Desig ne and Acuracy Req uiretments

Deformation monitoring often requires specilidialized surveyi ng meth thdods th thtat are pl anned and executed according to specialized techniques and procedures. 10-15 cm et Points g roach/Outlet mm pp 2 . Levees: 0 A , ,

+02 + Dams

Basins g Rockfill Dams Levees: - Stillin , s , Outlet Works, Locks, Intake Structures: , Outlet Works, y uirements for Structure Tar Earth q illwa Re p py,g ,pp y yq g Structures

nment + 20-30 mm Alignment

g -Term Movement + : -Term 5-10 mm g

Structural Deformation Surveying Lon Table 2-1. Accurac Concrete Structures Dams Deflections Relative Short-Term Crack/Joint movements Monolith Alignment Vertical Stability/SettlementEmbankment Structures Slope/crest StabilityCrest Ali + 2 mm Settlement measurementsControl Structures S Channels, Reservoirs Scour/Erosion/Silting + 20-30 mm + 10 mm + 0.2 to 0.5 foot- 2. Accuracy Requirements for Performing Deformation Surveys - 2 or / . ) 1 - 2 gure (Fi ng system i tor i e mon h or t f

Each monitored structure should have a technical d ope l eve d e b

Structural Deformation Surveying ld 2-3. Overview of Deformation Surveying Design ormance. Monitoring plan. A project specific measurement scheme and its operating procedures project specific measurement A f Separate designs should be completed for the instrumentation plan ou h ldb d l df h i i (Fi 2 report or design memorandum published for the instrumentation and per s and for the proposed measurement scheme. surveying scheme to document the monitoring plan and its intended scheme surveying DataFlow y

Monitoring Plan ure 2-1. Deformation Surve Deformation 2-1. ure g Fi 1 2 Survey System Data Design Collection

İnstrumentation Measurement Plan scheme Accuraacy

• Required equipment, supplies, and materials, • Predicted performance of the structure, • Monument types, function, and • Measurement accuracy requirements, operating principles, • Positioning accuracy requirements, Reliability • Procedures for the installation and • Number and types of measurements, protection of monuments, • Selection of instrument type and precision, • Location and coverage of monitoring points • Data collection and field procedures, on the project, • Data reduction and processing procedures, • Maintenance and inspection of • Data analysis and modeling procedures, 3 the monitoring network. • Reporting standards and formats, Data • Project management and data archiving. Processing

• Applying pre -determined calibration values to the raw measurements, • Finding mean values for repeated measurements of the same observable, • Data quality assessment and statistical testing during least squares adjustment, • Measurement outlier detection and data cleaning prior to the final adjustment. 5 4 6 Data DtData Data Analyses presentation management y the , on may ti a le, a stud t p applications rumen t . Although in both . ns iti tti For exam d monitoring ques an i n measurements h ec thi t various ng i sis remain the same. or y it i deformation between the emon of Survey System Design. Structural Deformation Surveying th 1. eometrical anal differ, the same basic methodology applies to the design and Although accuracyconsiderably andbasic principles sensitivity of the design of criteriag monitoring schemes and may their on differ the stabilityrequire of determination magnetsaccuracy of in of +0.05 a relative mmdam nuclear while may displacements a accelerator require settlement withcases, may only study of +10 an a mm rock-fill accuracy analysis g : r o f ons ti p i escr materials, diti d

d and

concerned with buildin y ures, an d monuments.

supplies,

and

lan is mainl p ons, proce ti ca equipment,

ifi ti instruments

Structural Deformation Surveying Procedures and protection of monuments, for the installation Required equipment, supplies, and materials, and operating principles, Monument types, function, points on the project, and coverage of monitoring Location network. Maintenance and inspection of the monitoring The plan contains drawings, product specifications, and other

a. Instrumentation plan (design) an are spec l he instrumentation T or installing the physical network offor surface a movement monitoring points project. Contained inp the instrumentation documents that completely describe the proposed instrumentation, and completely describe the proposed instrumentation, documents that and protection testing; installation; methods for fabrication; maintenance of instruments and monuments. or f emes h network sc t g e measuremen t , ua l Software applications specially eva precision, t scheme should include analysis scheme t

d are used to compute expected error and

procedures n an

ig type es

d o t

modeling d

and

network pre-analysis." instrument

dence for all surveyed points in the monitorin dence for all surveyed points in the que use i i of cations for: f

i n f h analysis con ec

t g n Structural Deformation Surveying i Predicted performance of the structure, Measurement accuracy requirements, Positioning accuracy requirements, Number and types of measurements, Selection of instrument type and precision, Data collection and field procedures, Data reduction and processing procedures, Data analysis and modeling procedures Reporting standards and formats, and data archiving. management Project and speci b. Measurement scheme (design). e ma The design of the survey measuremen Th i t h i d t d i d l t t h f and positionin (see Chapter 9). accuracy is known as " accuracy is known written for pre-analysis and adjustment

. acceptance

cally prescribed cally prescribed i specifications

ensure

to ensure acceptance justment. d a manufacturer reliability

k and from results can be verified during data can be verified results

e networ h t f accuracy

determined

ysis o both lfhkd l

are of

ures. ures. d levels post-ana

in levels of both . - instructions

built

Structural Deformation Surveying ng proce i

2. Data collection. The data collection required on a project survey is specif is survey a project on required The data collection serv bib d of the raw data. of the raw Minimum instrument resolution, data Minimum instrument resolution, collection options, and proper of network to the results according The actual data is executed collection the of quality that the so pre-analysis provide built monitoring surveys is based for on Achieving the required accuracy instrument performance, o operating instructions are determined from manufacturer specifications an processing by the results of network pre-analysis. The data collection scheme must scheme The data collection network pre-analysis. of by the results a. Accuracy

. h g hi

requires ld

e i s can y d o h measurements

raw ng met i . the

c survey i et d

b. Reliability eo redundant measurements, geometric sufficient closure, in the network configuration and strength a system of Reliability in the raw measurements requires GdiG i hd ildhih Structural Deformation Surveying redundancy in the design of data collection scheme..

prior

cleaning

data

and

detection

outlier

re-determined calibration values to the raw values re-determined calibration p

g in observable, y

l pp y g p A Finding mean values for repeated measurements of the Data quality assessment and testing statistical during Measurement outlier detection and data cleaning prior Structural Deformation Surveying to the final adjustment. to the final measurements, same observable, 3. Data processing. 3. Data least squares adjustment, Raw survey data must be converted into meaningful major categories of data reductions are: categories of data major engineering values during the data processing stage. Several

point

. expressed

lacements. p direction

atial dis p and

ze s y campaign (f), from the coordinates Collectively, these vectors describe number

): point number n magnitude

n= n has

is used to anal is used to for g gypp is the yis the coordinate displacement

is the x displacement coordinate is the z coordinate displacement is the t time difference surveys between z) z) for vector i

Δ Δ i i i , y y -t -x –y –z Δ Δ f f f f , x Δ ( t = t t x= x x= z = z y= y y= n Structural Deformation Surveying Δ Δ d Δ Δ movement

4. Data analysis Geometric modelin Geometric Point displacements are calculated by differencing the adjusted differencing the calculated by displacements are Point Each movement vector has magnitude and direction expressed as point General movement trends are described using a sufficient number of trends are described using a sufficient number movement General discrete point displacements (d displacement coordinate differences. displacement field over a given time interval. the obtained at some reference time (i), for example coordinate displacement reference time obtained at some coordinates for the most recent survey coordinates for the is the standard error in i σ is the standard error in f , σ ), and where 2 ) ), n i e σ ( ) of the displacement the magnitude is 2 + z < 2 | |( Δ f n σ + d 2 y Δ + ) = max dimension of combined 95% confidence ellipse n 2 x (e Δ

, Structural Deformation Surveying )

n | = sqrt ( Comparison of the magnitude of the calculated displacement and its of the magnitude calculated Comparison n | d associated survey accuracy indicates whether the reported indicates movement is survey accuracy associated more likely due to survey error: more likely (for point for point n = (1.96) sqrt ( or most recent survey, for the (final) position position for the (initial) or reference survey. for the (initial) position e: b

ld b wou in the initial n

n t n i or po f s t componen t acemen l sp m di

d e 000 . t a l cu 1000 000 l = 1000.002 m = 1000.006 m = 2 mm = 1000.002 m = 1000.002 = 1000.000 m = 1000.000 m = 1000.000 =

z = 2 mm z x = 6 mm x y i i f f f i Structural Deformation Surveying z x y z y Δ Δ Δ x For example e ca were: y th For example, if the adjusted coordinates for point For example, if en th th l l t d di l t t f i t and the adjusted coordinates for the same point in the final survey were: survey the final the same point in the adjusted coordinates for and surve in the n 2 mm . 4 > mm 6.3 idence in the horizontal displacement ⇒

) , as reported from the adjustment results, n e ( mm > n ⏐ h d = 2.0 ⏐ v σ ) = sqrt (36 + 4) 6.3 mm ) = (1.96) sqrt (2.25 + 2.25) ~ 4.2 mm at 95% confidence 2 2 i y σ Δ + + 2

Structural Deformation Surveying 2 f x σ Δ for both surveys, and similarly the vertical position has a : mm be

= sqrt ( d n Assuming that the horizontal position has a standard deviation of l ⏐ = 1.5 h ou d be =(1.96) sqrt ( h d n σ standard deviation of e ⏐ These results show that the horizontal component exceeds the expected error margin and is likelysurvey due to actual movement of point horizontal plane. then the combined (95 percent) conf w The magnitude of the horizontal displacement is: : 5.5 mm s < i t n e m 2.0 mm ace l ⇒ ) n sp i (e d l < ⏐ v ca i ) = (1.96) sqrt (4 + 4) ~ 5.5 mm at 95% confidence d t 2 r ⏐ vi e σ v + e 2 h t vf f σ o Structural Deformation Surveying tude ni ag = 2.0 mm m ) = (1.96) sqrt ( ⏐ n e ag tude o t e e t ca d sp ace e t s v d (e Confidence in the vertical displacement would be: Th ⏐

d ze di ar d ave a stan h

ld ou h ects s j ng pro i tor i or mon fiijhldhddid f

Structural Deformation Surveying 5. Data presentation 5. Data format. Survey reports

of g ete l p m co preparing

d n a and

, ts r epo eneral understandin eneral r g ey sis and evaluation of sis and evaluation assurance y

rv su

quality , for anal for dcopy g r a h ineerin ants should have a have ants should g gg y p oduce adjustment r

artici d l p pp g g ll ou A h network s l , e lan.

nn p so r Structural Deformation Surveying pe

processing ement , ey electronic copies of these reports. electronic g gp rv 6. Data management 6. Data Su ey pe so e s ou d p oduce a dcopy su ey epo ts a d co p ete

Mana requests, planning and monitoring Engineering for General data requirements), or contract data (in-house for collection Surveying En Geotechnical and Structural data Support for management, archiving, computer resources, Technical requirements for the complete evaluation process. the complete evaluation for requirements measures, assurance quality and data and results, of preparation/presentation reduction processing network adjustment quality assurance and preparing and of findings and results preparation recommendations, support. information and electronic final reports, archiving survey reports, survey

f ng o

e d new

mo d Ground and

. s on l

e 4

v which has e ees surveys ll

a n o i with its Committee on with its Committee at rn Commission 4 on Ground ate movement, an ate movement, l te deformation surveys and new Commission on Recent Commission on Crustal Recent in c p i d (ICOLD) n (ISM)

a l (FIG) Commission 6 (FIG) Commission (IAG) a n o i cs, tecton integrated i at

n Surveying of

ynam d Mine

oups r analysis for

l Within the most active international organizations that are international organizations active the most Within ng geo a idii il ddlif . n o i Society

ess Structural Deformation Surveying f o r geometrical

y n and

a y p o ess o a g oups at at o a a d te at o a 2-4. Professional Associations 2-4. Professional M Organizations International Federation of Surveyors Surveyors of Federation International Dams Large on Commission International Geodesy of Association International International Society for Mine Surveying ovements, concern concepts for analyses and modeling of deformations; analyses and modeling of for concepts involved ininvolved studies one should list: deformation Subsidence and in mining areas; Protection Surface significantly contributed the of new methods for development the recent to regional earth crustregional deformation. design and geometrical analysis of integrated Monitoring of Dams and their Foundations; M

lateral

or e dams , g Such . heaving , fatigue

rock

elastic and for lar y yg settlements

does not go beyond a pre-determined foundation

ing to overturning and downstream creep or , abnormal , aging

. including , concrete , trends

Structural Deformation Surveying loads

new

movement

2-5. Causes of Dam Failure Deformation in concrete structures is mainl Deformation highly dependent on reservoir water pressure and temperature variations. subsoil occur as the structure can sometimes of the deformation Permanent adapts to new loads concrete aging or foundation rock fatigue Such term movement trends including abnormal settlements heaving orUplift at the base of gravity dams lead lateral failure or buttress collapse in single or multiple arched Foundation dams that are susceptible to internal erosion. Surrounding embankments deformation is not considered unsafe if it is not deformation critical value. Monitoring is typically configured to observing relatively long- movements. Some ways concrete dams can fail are: ways concrete Some movements.

a. Concrete a. structures

anisotropic

take

ressure also causes to

p of failure in earthen dams are structure

consolidate resulting in vertical the

. cause

water that

defects

interstitial

b. Embankment structures settlement of the structure. Reservoir water of settlement Deformation is largely inelastic with earthen dams characterized by earthen is largely inelastic with Deformation and the embankment of the changes in shape. Self-weight permanent hydrostatic pressure of the reservoir water force the fill material and the foundation (if it consists of soil) to permanent horizontal deformation mostly perpendicular to the centerline. Some causes of damage embankment to earthen dams are: Construction defects that cause the structure to take on anisotropic controlled interstitial water examination. Other well-known causes overtopping at extreme flood stage and liquefaction due to ground overtopping at extreme motion during earthquakes. Usually these changes are slow and not readily discerned by visual readily discerned by and not slow changes are Usually these characteristics over time, characteristics over · · seepage resulting in inadequately pressures and paths of Internal

r e t

project

wa a . and

s of

m da f o

s, groun l e r u operation eve

il l a r embankments i

l f the

a to i

t n inhibit

pote

e adjacent

h ons, reservo t ti could or r

a o d f that

ce oun n f embankments such as in earth or rockfill embankments such dams de seismic events of local or regional areas, vi slopes of spillway channels, locks, and failure foundation e

ures, t e r the a

ruc t s in

n , bridge piers, lock wall, floodwalls), g n s i potential i

or g

rnin anges a h subsidence

w distress Structural Deformation Surveying g

win o ll localized o s, amage or c

t f d

e o o g a gsg saee deceo t epoteta a ueo da s or t

c. Structural distress c. Structural Th men t can indications u

btb t ifi a structures, or endanger life and property. gn Sinkholes or localized subsidence in the foundation or adjacent to embankments and Si ifi t dOther indications of distress or potential failure that could inhibit the operation of a project h i t t f d ti i l l d t

· Movement in levees, bridge abutments or · · Significant sloughs, settlement, or slides in or sliding of intake towers · Tilting · conditions and adjacent terrain as a result of · Erratic movement, binding, excessive deflection, or vibration of outlet and spillway gates, · Unusual vertical · Unusual or horizontal movement cracking of embankments abutments, · · Excessive deflection, displacement, or vibration of concrete structures

can

dams

adient to change, and may also rockfill

mechanically compacted. In some mechanically Settlement

) are common evidences of foundation ı nt ı z ı shifting.

Structural Deformation Surveying . settlement 2-6. Foundation Problems in Dams

Differential settlement, sliding, high piezometric pressures, and Differential a. General Pumping from underground can cause foundation settlement as the distress. Cracks in the dam, even minor ones, can indicate a foundation in the dam, even Cracks distress. problem. b. Consolidation or the gradient changed. Loading is removed supporting water pressure and wetting will also cause the pressure gr cause settlement or shifting. Settlement in rockfill dams can be impervious(geçirimsiz) element of a rockfill dam. uncontrolled seepage(s significantly reduced if the rockfill is ways, a compacted earth core is superior to concrete slab as the r o

t, n e ore m f e e l b

d e sett

t correc d seepage, f an o

d e t ate r ec t e . Any leakage at an earth . e h t d e in b as h y can Seeping water can chemically attack the ll suc

) ı ges, n nt ı a z h ı c ency usua

i y c n Structural Deformation Surveying fi a e d n o s

Thi Water movement through a dam or through its foundation Water is one of c. Seepage(s ocused o a y c a ges, suc as t e ate o seepage, sett e e t, o ace. Embankments may be susceptible to erosion unless protected from wave action on the upstream face and surface runoff on the downstream runoff and surface face action on the upstream wave the important indicators of the condition of the structure and may be a important indicators of the condition and may the of the structure quickly is potentially dangerous, as rapid erosion may embankment serious source of trouble. in the character of escaping water enlarge an initially minor defect. d. Erosion f Thidfii ll b dt td d tdbf components of the dam foundation, and constant attention must be f serious damage occurs. n

i , e id ream s t e ups etent foundation p th e on lid ve s i e concrete. Visible clues to the e concrete. Visible ) alternative. ) a mass d rakip ) ence i ma bozulma ş la ı v ı s am exper D

. Structural Deformation Surveying k aces. f ec P

ation at the time focused blame on an incom t g gp, or y sur F e. Liquefaction( lk e a Hydraulic fill dams are particularly susceptible to earthquake damage. Liquefaction is a potential problem for any embankment that has hlkh f Chemical and physical factors can ag 1938, which brought the hydraulic fill 1938, dam under suspicion. The investi f. Concrete deterioration( Th F t P k Dbut few hydraulic fills were built after the 1930's. Heavy compaction equipment became available in the 1940's, and rolled embankment dam became the competitive( i d ic lid th t id i deterioration include expansion, cracking, gelatinous discharge, and continuous layers of soil with uniform gradation and fine grain size. continuous layers

the

check

possible

field

quick

are the two principal a

accurately

ysis of structural deformations is: ysis of projects

displacements from surveying data. displacements from recommended for most applications most recommended for describe

monitoring

behavior,

term monitoring projects or as a quick field check on - short

abnormal

Structural Deformation Surveying for

l of a r e n used

case

Ge e a 2-8. Deformation Parameters the

To check whether the behavior of the investigated object and its and investigated object the behavior of check whether the To actual deformation status that could be used for the determination of the used for could be actual deformation status that causative factors which trigger the deformation. environment follow the predicted pattern so that any unpredicted deformations could be detected at an early stage. observation differencing and differencing Coordinate Coordinate differencing methods are mainly used for short methods used to determine structural Observation differencing is periodic monitoring. require long-term that the raw data as it is collected. raw data as it the In the case of abnormal behavior, to describe as accurately as possible the The main purpose for monitoring and anal · ·

. g and ,

survey

corrections

each

that

coordinate differencin and with the same and y , calibration

method

uration g servation differencing is efficient, and ced to determine point displacements. rveys to reveal any observed change in change rveys to reveal any observed instrument lacements b

to remove any systematic errors in the p for blunders and data adjustment all dinates, it has the drawback that

differencing

. The method of observation differencing . Monitoring point positions from two independent applying

coordinate

the

uired to determine dis example of q

for , Structural Deformation Surveying s are re y yq p y g advantage

or must collect data in an identical must collect data in an confi or y yg, 1. Coordinate differencing final The adjusted Cartesian coordinates (i.e., the coordinate components) from 2. Observation differencing surve major

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c i Monitoring point targets ron t ec El t i tChaining points t l t ti • •EDM prisms. •Leveling points. •Panel points. •Optical theodolites. • marks. •GPS reference Design of Measurement Schemes

Optimal Design Methods

• The oppgpgtimization of geodetic positioning networks is concerned with accuracy, reliability, and economy of the survey scheme as the design criteria. • Design of deformation monitoring schemes is more complex and differs in many respects from the design of simple positioning networks. Accuracy requirements.

• Positioning accuracy required for each monitored point is directly related to the maximum expected displacement occurring under normal operating conditions.

• Accuracyyq requirements are comppyqguted by equating the maximum allowable positioning error to some portion of the total magnitude of movement that is expected at each point. Specifically, the positioning accuracy (at the 95% probability level) should be equal to one fourth (0.25 times) the predicted value of the maximum displacement for the given span of time between the repeated measurements. Accuracy requirements.

Survey error budget.

• Accuracy should be less than one-third of the predicted value for the maximum expected displacement (D max ) over the given span of time between two surveys. P error < (1/3) D max

P error = allowed positioning error D max = maximum expected displacement

• Displacements are calculated by differencing coordinates obtained from two monitoring surveys .

σd = sqrt (σ1 + σ2)

σ1 = positioning uncertainty of initial survey

σ2 = positioning uncertainty of final survey Accuracy requirements.

Survey error budget.

2 2 2 σ0 = σ1 = σ2 2 σd = sqrt (2 σ0 )

Perror = (σd )/ sqrt (2) 2-14. Measurement Reliability

Reliability addresses the geometric strength of the observation scheme, measurement redundancy, and techniques for minimizing measurement biases. Statistical methods can determine the maximum level of undetected systematic error using outlier detection. Some reliability factors • Redundant measurements, • External checks on the validity of the data, •Instrument calibrations, •Reference network stability analysis, • Rigorous data processing techniques , • Multiple connections between stations. 2-15. Freqqyuency of Measurements

Geodetic monitoring surveys (for periodic inspections) are conducted at regular time intervals rather than by continuous measurements that are more typical of automated structural or geotechnical instrumentation.

The time interval between deformation surveys will vary according to the purpose for monitoring, but is generally correlated to condition of the structure .

Continuous monitoring Guidelines for the frequency for conducting monitoring surveys (1) Pre-construction. (2) Initial filling. (3) Stabilizing phase. (4) Normal operation. (5) Remedial phase. Chapter 3 Deformation Measurement and Alignment Instrumentation

This chapter describes the different techniques and equipment that are used in measuring external structural deformations. •Geodetic and Geotechnical Measurements -Geodetic surveys include conventional (terrestrial), photogrammetric satellite, and some special techniques (interferometry, hydrostatic leveling, alignment, etc.) -Geotechnical measurements are local deformations using lasers, tiltmeters, strainmeters, extensometers, joint-meters, plumb lines, micrometers, etc.

Comparison of measurement methods •Geodetic surveys, through a network of points interconnected by angle and/or distance measurements, usually supply a sufficient redundancy of observations for the statistical evaluation of their quality and for a detection of errors .

•Geotechnical instruments are easier to adapt for automatic and continuous monitoring than conventional geodetic instruments They give very localized and , very frequently , locally disturbed information without any check unless compared with some other independent measurements.. Accuracy of the Geodetic surveys

Geodetic surveys with optical and electro-magnetic instruments (including satellite techniques) have positioning accuracy to about ±1 ppm to ±2 ppm (at the standard deviation level) of the distance.

•Extensometers in relative deformation surveys have accuracies of ±0.3 mm

•Geodetic leveling, with an achievable accuracy of better than ±0.1 mm over distances of 20 m

•New developments in three-dimensional coordinating systems may provide relative positioning in almost real-time to an accuracy of ±0.05 mm over distances of several meters. 3.2- Angle and Distance Measurements

• Electronic theodolites.

The angle measurements has been mainly in the automation of the readout systems of the horizontal and vertical circles of the theodolites.

• Three-dimensional coordinating systems Two or more electronic theodolites linked to a microcomputer create a three- dimensional (3D) coordinating (positioning) system with real-time calculations of the coordinates. The systems are used for the highest precision positioning and deformation monitoring surveys over small areas.

• Electronic Distance Measurements (EDM) Short range (several kilometers), electro-optical EDM instruments with visible or near infrared continuous radiation are used widely in engineering surveys. Angle and Distance Measurements

Figure 3 -1. Lieca TCA 2003 an d TM 5100 el ect roni c t ot al st ati ons used f or hi gh precision machine alignment and deformation measurements. Accuracy specified at 1.0 mm (distance) and 0.5 sec (angular) Angle and Distance Measurements • Pulse type measurement These instruments, having a high energy transmitted signal, may be used without reflectors to measure short distances ((pup to 200 m ) directl y to walls or natural flat surfaces with an accuracy of about 10 millimeters(Figure 3-2). • Dual frequency instruments OlOnly a f ew un its of a d ual lf frequency i nst rument t(T (Terramet er LDM2 LDM2bT by Terra Technology) are available around the world. They are bulky and capricious in use but one may achieve with them a standard deviation of ± 01mm0.1 mm ± 010.1 ppm. • Total stations Any electronic theodolite linked to an EDM instrument and to a computer creates a total surveying station. It allows for a simultaneous measurement of the three basic positioning parameters, distance, horizontal direction, and vertical angle, from which relative horizontal and vertical positions of the observe d po int s can b e d et ermi ned di rectl y i n th e fi eld . Pulse type measurement.

Figure 3-2. Real-time laser modeling during 1999 construction of Portugues Dam near Ponce, Puerto Rico--Cyrax Model 2400 Angle and Distance Measurements

• Theomat Coaxial Automated Total Station (TCA) It is desigggned for conducting deformation monitoring gy surveys. The EDM system specifications are 0.6 mm resolution at 120 meters and for 1 mm and 1 ppm precision to a single prism at a range of 2500 feet

• Automatic Target Recognition (ATR) Early automated vision systems were installed in precision theodolites by the 1980's. Its operating components consisted of an external video camera iiimaging syst em and a separat e servomot tdior drive.

• Survey robots . For continuous or frequent deformation measurements, a fully automatic system based on computerized and motorized total stations has recently been developed. 3-3. Differential Leveling

Differential leveling provides height difference measurements between a series of benchmarks. Vertical positions are determined to very high accuracy (±1 mm) over short distances (10-100's of meters) using precision levels.

• Automatic levels The old method of geometrical leveling with horizontal lines of sight (using spirit or compensated levels) is still the most reliable and accurate, though slow, surveying method. It has a standard deviation smaller than 0.1 mm per set-up

• Digital levels The recentl y d evel oped di git al aut omati c l eveli ng syst ems with h e ight and distance readout from encoded leveling rods (Figure 3-3). It has considerably increased the speed of leveling (by about 30%) and decreased the number of personnel needed on the survey crew. Differential Leveling

Figure 3-3. Lieca NA 2002 automated digital level and section from bar-coded invar level rod Differential Leveling

• Tilt measurements by leveling Monolith tilt on dams can be determined from leveling observations using the dimensions and tilting axis of the object. 3-4. Total Station Trigonometric Elevations

• Zenith angle methods High precision electronic theodolites and EDM equipment allow for the replacement of geodetic leveling with more economical trigonometric height measurements. An accuracy better than 1 mm may be achieved in height difference determination between two targets 200 m apart using precision electronic theodolites for vertical angle measurements and an EDM instrument. Measurement accuracy: Trigggg(ponometric height traversing (reciprocal or with balanced lines of sight) with precision theodolites and with the lines of sight not exceeding 250 m can give a standard deviation smaller than 2 mm per km. 3-5. Global Positioning System (GPS)

• The satellite Global Positioning System (shown in Figures 3-4 and 3-5) offers advantages over conventional terrestrial methods. Global Positioning System (GPS)

• GPS ppgyositioning accuracy: Experience with the use of GPS in various deformation studies indicate that with the available technology the accuracy of GPS relative positioning over areas of up to 50 km in diameter can be expressed in terms of the variance of the horizontal components of the GPS baselines over a distance (S):

2 2 -6 2 σ = ( 3mm ) + ( 10 · S km) The accuracy of verti cal component s of th e b aseli nes i s 15t1.5 to 25ti2.5 times worse than the horizontal components. Systematic measurement errors over short distances (up to a few hundred meters) are usually negligible and the horizontal components of the GPS baselines can be determined with a standard deviation of 3 mm or even smaller. Global Positioning System (GPS)

Figure 3-6. GPS deformation monitoring surveys on a dam. GPS monitoring was first applied at Dworshak Dam, 3-6. Photogrammetric Techniques

•Using a camera with f = 100 mm, at a distance S = 100 m, with the accuracy of the image coordinates of 10 µm, the coordinates of the object points can be determined with the accuracy of 10 mm.

• Special large format cameras with long focal length are used in close range industrial applications of high precision . For instance , the model CRC - 1 (Geodetic Services, Inc.) camera with f = 240 mm, can give sub- millimeter accuracy in ‘mapping’ objects up to a few tens of meters away.

• Continuous monitoring with real time photogrammetry becomes possible with the new developments in CCD cameras and digital image processing thitechniques. 3-7. Alignment Measurements

Aliggynment surveys cover an extremel ypggy wide spectrum of engineering applications from the tooling industry, through measurements of amplitude of vibrations of engineering structures, to deformation monitoring of nuclear accelerometers several kilometers long. Each application may require different specialized equipment. The methods used in ppyractice may be classified accordin g to the method of establishing the reference line: • Mechanical method in which stretched wire (e.g., steel, nylon) establishes the reference line, • Direct optical method (collimation) with optical line of sight or a laser beam to mark the line , • Diffraction method where a reference line is created by projecting a pattern of diffraction slits. Alignment Measurements

Figure 3-7. Direct optical alignment technique. Deflection angle method used to measure baseline offsets in conventional alignment surveys 3-8. Extension and Strain Measurements • TfttTypes of extensometers Various types of instruments, mainly

Mechanical and Electromechanical,

are used to measure changes in distance in order to

• Determine compaction or upheaval(yükselme) of soil,

• Convergence of walls in engineering structures and

• Underground excavations,

• Strain in rocks and in man-made materials,

• StibtklSeparation between rock layers aroun dditld driven tunnels,

• Slope stability, and

• Movements of structures with respect to the foundation rocks. 3-8. Extension and Strain Measurements

Same Instrument may be named

Extensometer, Strainmeter, Convergencemeter, Fissuremeter, Cracmeter

Borehole extesometer

wire resistance strain gage 3-8. Extension and Strain Measurements • Types of extensometers • Wire and tape extensometers • Rod, tube, and torpedo extensometers • Interferometric measurements of linear displacements • UftilfibUse of optical fiber sensors • Precise concrete crack measurements

Wire and tape extensometers Both instruments use invar wires and special constant tensioning devices which, if properly calibrated and used, can give accuracies of 0.05 mm or better in measurements of changes of distances over lengths from about 1 m to about 20 meters. When only small changes in temperature are expected or a smaller precision (0.1 mm to 1 mm) is required, then steel wires or steel tapes are more comfortable to use. Extension and Strain Measurements

Rod, tube, and torpedo extensometers

Steel, invar, aluminum, or fiberglass rods of various lengths, together with sensors of their movements , may be used depending on the application . A typical accuracy of 0.1 mm to 0.5 mm may be achieved up to a total lengg(ygth of 200 m (usually in segments of 3 m to 6 m ).

Interferometric measurements of linear displacements

Various kinds of interferometers using lasers as a source of monochromatic radia tion are b ecomi ng common t ool s i n preci si on di spl acement measurements. A linear resolution of 0.01 µm, or even better, is achievable. Extension and Strain Measurements

• Use of optical fiber sensors A new development in the measurements of extensions and changes in crack-width employs a fully automatic extensometer that utilizes the principle of electro -optical distance measurements within fiber optic conduits. The change in length of the fiber optic sensors are sensed electro- optically and are computer controlled.

• Precise concrete crack measurements Distances between cracks in concrete structures are typically measured using precision micrometers or calipers, such as those as shown in Figure 3-8. Extension and Strain Measurements

Figure 3-8. Micrometers and calipers that can be used for measuring short distances in concrete structures to an accuracy of 0.0005 inch or better 3-9. Tilt and Inclination Measurements

Methods of tilt measurement

The measurement of tilt is usually understood as the determination of a deviation from the horizontal plane, while inclination is interpreted as a deviation from the vertical. The same instrument that measures tilt at a point can be called either a tiltmeter or an inclinometer depending on the interpretation of the results. Geodetic leveling techniques can achieve an accuracy of 0 .1 mm over a distance of 20 m, which would be equivalent to about 1.0 inch of angular tilt. • Engggineering Tiltmeters and Inclinometers • Suspended and Inverted Plumb Lines • Hydrostatic Levels 3-9. Tilt and Inclination Measurements

Figure: Inclinometer

Figure: Inclinometer Figure: Principle of Inclinometer Operation Figure: Piezometer Schematic of double fluid settlement gage

Figure: Settlement gage Tilt and Inclination Measurements

Tiltmeters and inclinometers. There are many reasonably priced models of various liquid, electrolytic, vibrating wire, and pendulum type tiltmeters that satisfy most of the needfds of eng ineeri ng surveys. Tiltmeters have a wide range of applications. •A series of tiltmeters if arranged along a terrain profile may replace geodetic leveling in the determination of ground subsidence. • Deformation profiles of tall structures may be determined by placing a series of tiltmeters at different levels of the structure. • A popular application of tiltmeters in geomechanical engineering is in slope stability studies and in monitoring embankment dams using the torpedo (scanning) type borehole inclinometers (usually the servo- acceleromet er t ype tilt met ers) . Automatic data acquisition system geotechnical instrumentation 3-9. Tilt and Inclination Measurements

Suspppended and inverted plumb lines Two kinds of mechanical plumbing are used in controlling the stability of vertical structures: (1) Suspended Plumb Lines, (2) Floating or Inverted Plumb Lines.

• Generaly, invar wire is used for the inverted plumb line, vertical movements ofhf the investi gated structure wi ihth respect to th e b bdedrock can al so be determined.

• The plumb wire can be positioned with respect to reference lines of a recordingg( (coordinatin g) table to an accurac y of ±0.1 mm or better. Tilt and Inclination Measurements

Optical plummets Higgph precision op tical p lummets ( (ge.g., Leica ZL (zenith) and NL (nadir ) plummets) offer accuracy of up to 1/200,000 for precise centering, and both can be equipped with laser. Atmospheric refraction remains as a major source offilif error for optical instruments.

Hydrostatic leveling If two connected containers are partially filled with a liquid, then the heights h1 and h2 of the liquid in the containers are related through the hydrostatic equation h1 + P1 / (g1 r1) = h2 + P2 / (g2 r2) = constant (Eq 3 -5) where P is the barometric pressure, g is gravity, and r is the density of the liqu id which is a fu nction of temperat ure . The acc urac y ranges from 0 .1 mm to 0.01 mm over a few tens of meters depending on the types of instruments. 3-10. Non-Geodetic Measurements

Deformation of large structures (e.g., dams) is caused mainly by reservoir loads, temperature, self-weight of the dam, and earth pressure. A monitoring system should therefore include regular measurements of the reservoir level and temperature and pressure data. • Reservoir level measurement • Temperature measurement • Precipitation measurement • Seepage rate • Chemical property analysis • Pore-water pressure measurement • Uplift pressure • Discharge measurement 3-11. Optical Tooling Technology

Optical tooling uses the principle that light travels in straight lines so as to enable ppyprecise measurements and level lines with every point is perpendicular to the force of gravity (e.g., plumb lines can be set to a given level datum). Four basic alignment elements are used . • straightness • flatness • squareness • plumb

Straightness: A tight wire is often used as a reference line. Laser alignment The Line of Sight Optical Tooling Technology

Flatness(düzlük): Conventional bubble levels and "laser levels," offer a wayyp to produce a level datum over a wide area. This high degree of levelness is accomplished by horizontally sweeping the laser beam manually or via a motor driven rotary stage. This revolving line of laser light becomes a horizontal "plane of sight," giving a precise horizontal reference datum, sometimes called a waterline. Squareness: Perfect squareness implies that one plane forms a 90 degree angle with another in tersec ting pl ane. Plumb: A plumbline and pendulum are used to establish a single vertical reference line. This reference line is accomplished by a line of sight or laser beam. 3-12. Laser Tooling Method

• Straightness alignment • Alignment transfer • Oriented alignment • Alignment plane

3-14. Laser Alignment Techniques • Singggle target laser ali gnment • Two target laser alignment Laser Alignment Techniques

Two target laser alignment

Figure 3-9. Geometry of a two target laser alignment. Laser Beam Propagation

Table 3-3. Depth of Field for Different Laser Beam Diameters Laser Alignment Equipment This secti on d escrib es some laser a lignmen t equ ipmen t(Figure 3 -11).

Figure 3-11. Laser alignment system from ON-TRAK Photonics, Inc. Laser Alignment and Scanning Systems

Table 3-4 contains a partial list of manufacturers of laser alignment and scanning systems with tabulated measurement ranges, target capture areas, accuracies, and product data such as whether the vendor can design scanning, alignment, and custom systems . Construction Lasers and Machine Control Systems produces a commercial laser alignment and digital laser theodolite package used for tunneling, mining, and alignment control. Components of the system are: · Laser transmitter · Alignment Base Plate · Digital laser theodolite Laser surveyyy accuracy evaluation.

σ = + 0.042 inches (1.07 mm), meaning that the derived deflections would have a 95% confidence value of:

(1.07) (sqr t (2)) (1 .96) = 2. 97 mm.

3-19. Suspended and Inverted Plumblines

Plumbline readings since 1991 indicate that both monoliths are stable within

+0.25 mm (0.01 inch) in the U/D direction and within +1mm (0.04 inch) along the axis of the dam. Suspended and Inverted Plumblines Comparison of Alignment System Comparison of Alignment System Comparison of Alignment and Plumbline Systems Sources of Measurement Error and Instrument Calibrations

Surveying Measurement Errors

Random error • pointing error • centitering error • leveling error • reading error

Systematic error • EDM/prism zero error • EDM scale error • EDM signal refraction error • EDM cyclic error Settlement Surveys (Vertical deformation Surveying)

Vertical settlement determined by precision differential leveling is performed using compensatory autocollimation or sprit leveling instruments with fixed or attached parallel plate micrometers, and observing invar double (offset) scale metric rods with supporting struts. Settlement Surveys Precise Differential Leveling Observations Precise Level Precise Differential (Geometrical) Leveling

When determining elevation by precise spirit leveling, the followinggg guidelines will be followed.

1. Double-run level section 2. Sigh ti ng conventi on. 3. Rod readings. 4. Stadia distance. 5. Foresight sideshots. 6. Rod settlement. 7. Rod index error. 8. Ground refraction. Aliggynment, Deflection, and Crack Measurement Surveys --Micrometer Observations

This chapter describes micrometer observation methods for accurately measuring small relative deflections or absolute deformations in hdhydrauli c structures. Figure 7-1. Alignment micrometer measurements relative to fixed baseline Relative Alignment Deflections from Fixed Baseline

Deflections of points along structural sections can be monitored by observing their offset from an alignment established by two baseline control points. The deflection of a point relative to a fixed baseline is observed either by micrometer target methods Figure 7-2. Typical relative alignment deflection measurements of concrete structures relative to fixed baseline. Micrometer Crack Measurement Observations

This section describes absolute micrometer joint or crack measurement procedures using micrometers.

Expected s ho rt -term accu racy is o n t he o rde r o f ± 0.0005 inch, relati ve t o th e fi xed calib rati on ref erence b ar.

Estimated long-term crack measurement accuracy is at the ± 0.005 to 0.010 inch level; Micrometer Crack Measurement Observations

Figure 7-5. Starrett vernier caliper crack measurements between monoliths. GPS

GLOBAL POSİTİONİNG SYSTEM Monitoring Structural Deformations Using the Global Positioning System

This chapter provides technical guidance on the use of the Global Positioning System (GPS) for monitoring and measuring three - dimensional (3D) displacements on large engineering structures. Applications of GPS for the determination of long -term stability and movement on dams, navigation locks, and other similar types of construction projects are described. • Monitoring Structural Deformations with GPS • GPS Performance on Monitoring Networks • Data Quality Assessment for Precise GPS Surveying • MitiMitigati on of M ulti path Sig Sinal s. Global Positioning System

1. Purpose 2. Background 3. Scope of Chapter 4. Surveying Requirements 5S5. Survey ing P roced ures 6. Data Processing Procedures 7. GPS Monitoring Applications 8. GPS Surveyyp Reportin g and Results 9. GPS Performance on Monitoring Networks GPS Performance on Monitoring Networks

Figure 8-3. Accuracy convergence time plotted as log session length needed to exceed average baseline position error. GPS Performance on Monitoring Networks

Figure 8 -2. GPS coor dinat e component repeat abilit y f rom 15 -mitinute sessi ons over short baselines. GPS Surveying Session length.

Figure 8-6. Convergence of coordinate component discrepancies to the true posiiition wi ihth a si mul ated ddi displ acement of f25 2.5 mm. F or each sessi on th e components are plotted north, east, height respectively. Global Positioning System

Figure 8 -7. Network map of 10 monitoring points compared between GPS and precise conventional surveying results. Error ellipses are plotted at ten times actual size. Overall differences are less than 2-3 mm in all cases. Adjustment Output Parameters

Figure 9.5. Adjustment output plots showing the reference network and monitoring network. The left-hand plot shows only the reference network stations with their error ellipses. The right -hand plot shows both the reference stations and the structure monitoring points with their error ellipses. Network Maps connections between points

Figure 9. 13. Adjustment network map showing station names and connections between points based on observations made during data collection. R-1 thru R-4 are reference stations, C -1thruC1 thru C-5 are centerline monitoring points, U-1thruU1 thru U-3 are upstream monitoring points at the base of the structure, D-1 thru D-3 are downstream monitoring points at the base of the structure. Network Maps Network Points and Confidence Ellipses

Figure 9.12. Adjustment network map (plan view) showing station names, relative locations, and the point confidence ellipse (95 percent) for horizontal positioning plotted around each point. Network map and confidence ellipses are plotted at different scales. Circles indicate monitoring points and diamonds represent reference stations. Deformation Monitoring Using Ratio Methods

This section ppgrovides guidance on performin g deformation surve ygys using EDM ratio difference techniques. These surveys are done using an EDM or total station. Standard trilateration techniques are used to compute movements. This process requires measurement of the reference control network and the structure itself.