N.79 21477Local Precision Nets for Monitoring Movements of Faults and

Large Engineering StructuresHeinz G. Henneberg

Escuela de Geodesia, Universidad del ZuliaMaracaibo, Venezuela

Foreword. Althoughthe title of the pa-per indicates a general presentation, I amexposing only some special cases from ourcountry, Venezuela. Naturally, these specialcases may contribute to general conclusionslater on. It was a splendid idea from Dr.Charles Whitten to include in this presenta-tion man-made big structures. As I see itnow, in discussing crustal deformations, bigstructures cannot be excluded because they areaffected too, as well as the geodetic netswhich should control the structure. Thereexists a certain public interest in the stabi-lity and security of structures and we mayfurther this interest for more support for ourprograms. We should see "local deformationand movement measurements" as a program whichincludes deformations and movements of struc*tures like bridges, dams, tunnels etc., earthsurface deformations as subsidences and hor-zontal components caused by water- and oilwithdrawals and the natural neo tectonic move-ments and deformations; that is because some-times there could be a superposition of com-ponents coming from different sources.

Abstract. Along Bocono Fault were instal-led local high precision geodetic nets to ob-serve the possible horizontal crustal defor-mations and movementso In the fault areathere are fan big structures which are alsoincluded in the mentioned investigation. Inthe near future, measurements shall be exten-ded to other sites of Bocono Fault and also tothe El Pilar Fault. In the same way and by si-milar methods high precisian geodetic nets areapplied in Venezuela to observe the behaviorof big structures , as bridges and large damsand of earth surface deformations due to indu-strial activities,) This presentation givessome general and detailed information aboutthe measurements and net installations at thefollbwiiig sites and the mentioned structures:(a) Bocono Fault and dam at Mitisus, (b) Boco-no Fault at Mucubaji, (c) Bocono Fault and tun-nel at Yacambu, \.d) faults and dams at UribanteCaparo, (e) Guri Dam, (f) Maracaibo-Lake-Bridge(g) Orinoco River Bridge, (h) oilfield of Tiaouana, (i) Socuy-Tule dams.

Introduction. As a result of geologicalinvestigations the Bocono- and the El PilarFault separate the Caribbean Plate from theSouth American as is shown in figure 1. Be-tween the ecological department of IVIC (in-stituto Venezolano de Investigaciones Cienti-ficas) and the geodetic department of ZuliaUniversity was established a geodetic investi-gation program to control the behavior offault sites and of some big structures located

Proc. of the 9th GEOP Conference, An Interniilioiutl Symposium an the Applications ofGrade** to Crailymimii-s. Ociobrr2-S. 1978. Dept. of Geodetic Science Rept. No. 280. TheOhio Stale Univ.. Columbus. Ohio 43210.

in the fault area (fig.4). This program issupported principally by CADAFE (Empresa deEnergia Electrica del Estado Venezolano}, byConicit (Consejo Nacional de InvestigacionesCientificas y Tecnologicas - Venezuelan re-search counsel), and by the engineering fa-culty of Zulia University. The observationsof bridge behavior are made through a coope-ration program with the MTC (Ministerio deTransporte y Comunicaciones), the Socuy-Tuledams with MARN (.Ministerio del Ambiente y Ke-cursos Katurales), the Guri Dam with EDEIX3A(Electrificacion del Caroni) as part of CVG(Corporacion venezolano de Guayana), the oil-field measurements with Maraven (Venezuelanoil company) and the Yacambu tunnel measures'ments with TRAHARG (Venezuelan geodetic com-pany). In figures 2 and 3 we see the sites offaults and structures, subjects of geodeticinvestigationso In figure 5 are shown in aschematic representation the geodetic netinstallations at Tia Juana oilfield, Socuy-Tule dams, Maracaibo-Lake-Bridge, Guri Dam,Uribante-Caparo project and Orinoco Bridge.

Mucubaji

In the Mucubaji i'ault area were installed twolocal precision netst The principal net with10.5 km maximum extention and the secondary netas a small extention net with maximum sidelengths of 1.8 km (fig.6). The principal netcovers laterally the total fault area and theobservation stations are anchored in solidrock, as is shown in fig.6 (.bottom). The smallnet extends around the visible fault trace andis located on moraines in consolidated soil oron individual rock sites. The foundation ofthe observation stations as shown in fig. 6 va-ries according to the soil conditions. All ob-servation stations have the forced centeringdevice for all types of instruments and tar*gets. The two nets were measured as com-bined trilateration-triangulation. In theprincipal net only five distances could bemeasured in the first net determination dueto topographic and weather conditions at thattime. Two distances were measured severaltimes with the Geodimeter Model 8 Laser andthree distances several times with Tellurome-ter 1000. (it should be mentioned that thelaser instrument can only be operated in twodistances of the principal net due to its ownweight and the very difficult accessibility ofthe stations). Angular measurements were madewith T3 and DKM 3 theodolites and as targetswere used specially constructed metal plates.The distances in the small net were measuredwith Hekometers, ELDI 2 and ELDI 3 instrumentsand angles were measured with T3 and DKM 3instruments. The Mekometers were run by per-sonnel from Prof. Linkwitz's institute atStuttgart University in a cooperation program.

113

https://ntrs.nasa.gov/search.jsp?R=19790013306 2018-05-26T16:46:38+00:00Z

RepublicaDominicana

ColombiaI

s Venezuela ^*\

, —* SOUTH AMERICANBOCONO FAULT PLATE

0 200 400

KM

Pig. 1 Schematic representation of tectonic relations in the Caribbean area.The arrows show relative movements. The Caribbean Plate is seperated from theSouth American Plate by the Bocono and the Pilar tfault. (Molnar and Sykes 19695Schubert 19?0a).

.SOOJy-TULE DAMS\ ^

JUANAI OILFIELD ,

L PILAR FAULTO !r' -— " -— -" '-"^^—• . t

URIBANTE CAPARO PROJECT^_ B o o o T a ; . r<s_

702 652 602

Fig. 2 Map of Venezuela, showing the principal faults and the sites ofSocuy-Tule Dams, Lake Bridge, Tia Juana oilfield, Orinoco Bridge, Guri Damand Tfribante-Caparo project.

Fig. 3 Bocono Fault system in the Venezuelan Andes mountains showing thestudy sites Mucubaji, Mitisus and Yacambuo

Measurements started in spring 1975 and lastedabout one year in the principal net. Thesmall net was measured three timesi 1975, 1976and 1977« The 1975 and 1976 measurements arecombined trilateration-triangulation with Me-kometers and T3/DKM 3, and in 1977 only dis-tances were measured with ELDI 2 and ELDI 3«In the principal net the free net work adjust-ments gave an accuracy range from +0.8 to+2.1 cm in coordenates (see table 1). In thesecondary net the free net work adjustmentsgave accuracy ranges in coordenates: 1975 from+_ 0.8 to +_ 1.6 mm -Mekometer with angles-,1976 from + 0.7 to + 1.4 mm -Mekometer withangles-, 1977 from +_ 1.5 to +_. 2.8 mm -onlyELDI length measurements-, (see table 2).

TABLE 1. Computacion Results In The Prin-cipal Net At Mucubaji

P.No. iMx(cm) y(m) ^My(om)

12345678

13579,78015378,92215343,66614664,42910000,00110583,62010259,22910000,006

0,81,20,90,91,11,01,10,9

7632,52113350,64317040,82917826,73417446,14214584,28410787,58010000,011

1,50,90,90,91,21,11,82,1

TABLE 2 Computation Results Of The SmallMucubaji Network

P. No. Year (m)(mm) (mm)

9

10

11

12

13

14

15

16

197519761977197519761977197519761977197519761977197519761977197519761977197519761977197519761977

9593

10000

10444

10671

10519

10400

10000

9465

,748,744,747,002,005,005,733,736,735,059,056,056,561,559,555,740,741,742,000,003,001,427,426,429

112111111112102102112112

,5,3,6,0,0,5,0,1,6,5,4,3,2,8,8,6,9,5,1,2,0,0.0,5

9843

10000

10099

10169

11445

11315

10985

10560

,714,714,717,000,001,006,985,986,983,278,280,278,089,089,086,878,878,875,165,163,166,885,885,884

002002001001002102001111

,8,9,0,8.9,5,9.8,9,9,9,9,8,7,1,0,7,2,8,9,7,0,0,9

115

GEODETIC SYSTEM

PLANNED

ARACAY PASS

GEODETIC SYSTEMPLANNED

FAULT AND DAM

3 NETS

(schematic representation without scale)

rig. 4 Schematic representation of geodetic systems installed and plannedalong Bocono and Pilar Fault.

116

(1) TIA JUANA OILFIELD

o2 Km(First Part)

(2) GURI - DAM

9 Km

(3) SOCUY - TULE - DAMS

7 Km2.5 Km

(4) URIBANTE - CAPARO

HYDROELECTRICAL PROJECT

4 DAMS4 TUNNELS

First Netinstallationsunder way

(5) MARACAIBO - LAKE - BRIDGE

10Km

(6) ORINOCO BRIDGE

3Km

(Schematic representation without scale)

Pig. 5 Schematic representation of geodetic stystems to investigate movementsof structures and earth surface.

117

3 EL GAV«_ANl(4O6Om)

4 EL GAVILANH(396O»>

OBSERVATOHtO(3520m)

EL FRAILE(3500m)

MUCUBAJI(3800m)

8 EL CABALLO (3800m)

SCALE OF THE SMALLNET - SEE FIGURE 7

XSEE B FOR

DETAIL

L4016

B

JX ! JIT

Fig. 6 Principal (large) and secondary (small) net at Mucubaji site includingtype of structure of observation stations.

118

7

BOCONO

FAULT

(Vectors)

200 400

Fig. 7 Difference vectors as result of coordentate determination in the smallMucubaji net 1975 (.initial;, 1976, 1977*

La Mitisus

At "La Mitisus" (figure 3) we have three pre-cision nets: 1. the principal dam system, 2.the "Pentagon" as security system of the damsystem (the two systems are shown in figure 9)3. the fault system as shown in figure 8,where the "Pentagon" mentioned before, consti-tutes the center part. The observation sta-tions, constructed at each point, are similarto those installed at Mucubaji and as demon-strated in figure 6. Due to the differentprecisions, the measurements and computationsare independent in the dam system and in thefault system (see tables 4 and 5). There areused two local coordenate systems: The faultsystem has Fb as origin and Fb - Fd as maindirection? the dam system is computed in UTMwith local coordenates. The two systems areconnected in between through the "Pentagon"which belongs to the two coordenate systems.Measurements started in September 1973 at thedam site to observe the deformation of thestructure and its surroundings which are si-tuated in the Bocono Fault zone. The measure-ments for the dam are made through triangula-tions, using T 2 and sometimes T 3 instruments.The accuracies after adjustments after eachtriangulation vary between 0.3 to 1.4 mm in

the coordenates. In this way the movement vec-tors of the damcrest are shown with high sig-nificance, as we can. see in figure 10, wherethe movement vectors indicate the horizontalcrest components of the dam deformation be-tween low- and high water in the reservoir.In the figure the dashed line represents thedam axis. The dam is a doble curved concretestructure, 70m high and 210m long. The power-house lies about 16 km from the dam at aheight difference of approx. 900m below.The energy capacity is of 240 MW. The faultsystem was measured first in 1974/5 and shallbe observed again in 1979. The coordenatesand accuracies are shown in table 4= The.scale, of the fault system was obtained througha trilateration in the Pentagon, applying aHP 3800 (see table 3). Later, T3 measurementscompleted the fault system observations.

Yacambu

The "Yacambu project", consists of two bigstructures: a doble-arc concrete dam of 150mheight and a 24 km tunnel, which transports thewater of the Yacambu river through the mountainchain of the Andes from south to north. Thetunnel crosses Bocono Fault at Km 15 from thesouth entrance. Along the curved tunnel pro-

119

Fig. 8 Fault net at Mitisus

TABIiE 3 Double Distance Measurements WithHP 3800 In The Pentagon

D

Fb -PdFb -PcFb -F2Fb -FJF2 -FoF2 -FdF2 -F3F3 -FnFJ -FdFd -Fc

1

656,624490,599509,092580,804667,522627,080202,222527,926465,020266,246

: 2

,627,604,100,806,527,087,220,927,023,245

.'M

,6255,6015,096,805,5245,0835,221,9265,0215,2455

D - Hor.

656, 6u6487,530508,827580,749666,427626,978202.044571,018465,012261,551

TABLE 4 Coordenates And Accuracies In TheFault Betwork.

FaFbFcFdFePfF1P2F3F4P5

X

9818,47110000,00010457,21610656,6099800,97210097,6759741,67310226,11910420,46910904,22710383,998

+ Mx(mm) y ± I

1,9 10023,1780 10000,000

2,8 10169,2591,7 10000,0002,7 10449,1792,9 10625,5252,3 9654,5992,1 9544,1752,o 9599,4082,9 9101,3581,7 8909,294

r̂(mm)

1,30

2,60

3,22,92,21,41,42,83,3

Fig. 9 Santo Domingo Dam triangulation with security system (pentagon F2, F3, Fb,Fc, Fd as part of the fault net).

120

1-2-75 •

10-5-75 ©

0 2 4 6[ I I I I I i i

mm

Fig. 10 Movement vectors of the dam creat between February and May 1975(low- and high water in the reserveir)o

jection a typical combined trilateration-tri-angulation was installed. The narrow band ofthe net work has the advantage of a high pre-cision traverse: strong lateral rigidy by an-gular measurements and strong longitudinal ri-gidy through the distances (figure 11). i'orthe distance measurements was used an "Elec-trotape". There were measured 45 distancesand 76 angles, having thus 121 observationequations for 34 unknowns. For the final com-putations, shown in this paper, the "free net-work adjustment method" was used. Measure-ments were made at two epochs: 1973 and 1975*Between the two measurements strong coorde-nate differences showed a change of sign,where the network passes Bocono Fault (table6). The question arose, if these coordenatedifferences were significant enough in com-parison with the coordenate accuracies to de-

TABLE 5 Coordenate Accuracies uf Three inde-pendent Determinations Of 2 Fault -points(>1,N2> And 2 Dampoints(l,Il)In The Dain Network (in mm)

Station I M x i My + MX I My ± MX ±

H1H2III

0,90,40,40,4

0,90,6u,60,4

1,30,80,10,6

1,41,2U,80,6

0,60,4u,30,4

0,7u > 60,50,4

termine a possible crustal deformation, dueto Bocono Fault. As shown in table 6,themaximum value in coordenate changes is 52mmin x-direction at point 6, 47nun in y-direc-tion at point 10. The maximum difference

121

Fig. 11 Combined triangulation-trilateration for Yacambu tunnel and differencevectors 1973 - 1975

122

vector exists atpoint 6 with 63 mm. In thementioned point the accuracies in the coorde-nates by single determination are 20 to 25 mm.V/e see that the coordenate accuracies show er-rors still too high for real significant move-ment. Nevertheless, at points 6 and 7, wherewe have strong difference vectors south of Bo-cono i'ault, we may come to a certain expres-sion about the existence of movement. Atthese points the cofactors of the variance -covariance matrix are (.values from 1973)!

point 6 - Qxx = 0.14, Qyy = 0.11, Qxy =- 0.0037, point 7 - Qxx = 0.13, Qyy = 0.13,Qxy = - 0.0026, The low covariance values incomparison with the variance values show verylittle correlation. At these points the com-putation of the accuracy values for the dif-ference vectors gave: point 6 - Differencevector it = 63mm, MD = +_ 32mm, point 7 - dif-ference vector D = 56mm, MD = 31mm. Thus, wecan say, that the accuracy values expressed in"mean square errors" have the half size incomparison with the vectors. This is trueonly for points 6 and 7« As we may deductfrom table 6, in the other points the rela-tion is not so good. Therefore, I incline tosay that it is still too early to speak of sig-nificant movements in the fault area. But itis still interesting to outline: 1. the changeof, sign of the coordenate differences at BoconoJ'ault trace, 2. the directions of vectors,showing all toward Bocono Fault trace, 3. in-creasing values of vectors approaching BoconoFault, specially in points 6, 7> 10, 12.Therefore, we may interprete these results asan obvious trend situation, showing possiblecompression in the 1'ault surroundings. Atrend analysis, as used sometimes in gravitymeasurement computations, may be very usefulfor the interpretation of the existing results.Further measurements shall bring more infor-mation.

Uribante - Caparo - Project

The Bribante - Caparo project is one of thelargest hydroelectrical enterprises on the con-tinent. Several net work installations are un-der way at this moment to investigate the beha-vior of dam- and tunnel structures, their sur-roundings and the existence of fault traces inthe area. The net installations are very simi-lar to those discussed before. Definite infor-mation about measurements, instrumentation andresults shall be given at later events. The pro-ject consists in the interconnection of fourlarge dams from Uribante River at 1104 m abovesea level down to Caparo River at 277 a.s.l.The interconnections are realised through tunnelconstructions. The dimensions of the struc-tures are: La Honda Dam - L= 450m, H=» 118m; LasCuevas Dam - L= 740m, H= 106m; Borde Seco Dam-L= 340m, H= 108m; La Vueltosa Dam - L= 430m, iH= 118mj Uribante Doradas Tunnel - L= 7884m;Doradas Camburito Tunnel - L= 4484m; Agua Lin-da Doradas Tunnel - L= 5500m; Camburito Capa-ro Tunnel - L= 640nu The total hydroelectricalcapacity of the final project is 2.260 MW. The

project is situated in the Tachira, Merida yBarinas states of Venezuela in the west, southof Maracaibo Lake, near'San Cristobal, capitalof Tachira. The total length of influencedarea of dams, tunnels and reservoirs comprisesabout 80 km.

Guri

Guri Dam is the biggest hydroelectrical insta-llation in Venezuela and shall be at completionone of the biggest on the continent. At thismoment the energy capacity is of 2.100 MW, atthe final stage of construction will be about9.000 MW. The dam is situated on Caroni Hiverin the south eastern part of Venezuela (seefigure 2). The Uaroni River contributes tothe Orinoco River from the south and is thesecond river of the country. The hydroelec-trical generation is principally used for thedevelopment of the industrial area, situatednear Ciudad Guayana at the entrance of Caroniin the Orinoco River. The act ual length andmaximum height of Guri Dam are: L= 690m,H= 106m (main dam), the final length and max.height are: L= 6-7 km, H= 160m (see figure 12).The first geodetic measurements in situ star^ted in 1956. 1950 Cartografia Kacional (na-tional survey) completed the Caroni triangu-lation. From that time on several local networks were used for construction surveys andbehavior measurements. Actually, .precisionmeasurements through triangulations andlevellings are applied to determine the beha-vior of the dam structure. In figure 13» wesee the results in a three dimentional re-presentation of the movement of point 19» si-tuated on the right side rock fill dam.This movement is the consequence of the conso-lidation deformation of the dam, as we cannote from the down-slowing motion of the dif-ferent components. The movements as functionsof time have already an asymtotic approach.For the final project development of Guri allexisting geodetic network shall vanish be-cause of the extention of the new reservoirat 54 m uplift of lake level. Therefore, anew observation system was planned and is ac-tually in execution as shown in figure 12.This network is a combined triangulation -trilateration system and in the observationpoints will be concrete pillars as shown inMucubaji and Mitisus.This geodetic program is going to work in com-bination with geophysical measurements, spe-cially with the microseismological net alrea-dy prepared in the dam and reservoir area. Theextention of the observation net is planned,as shown in figure 12, to the surroundings ofthe future lake.

Maracaibo Lake Bridge

Maracaibo Lake Bridge has a length of 9 km andis situated in the southern part of Maracai-bo city. The bridge spans Maracaibo Lake atone of the narrowest parts. The maximumheight of the bridge table is 50m above lakelevel at the bridge site. The bridge is a pre-

123

\DOWNSTREAMRIVERBED

SPILLWAY

Fig. 12 Geodetic observation system for the final construction stage of Guri DamTABLE 6 Results Of The 1973 And 1975 Net -

work Computations At Yacambu

Pig.. 13 Accumulated.3 dimensional movements ofpoint 19 located in the actual right side rockfilldam of Guri.

1975 - 1973 1973 1975

P. x y D ±Mx(mm) (mm) (mm) -(mm) (mm) (mm) (mm)

12345678910111213H151617

44354541265249-21-37-31-24-43-197

-1_

-30

-14-15-28-31-27-36-2720114740339412_.19

46385351376356293856475421812_

35

272726262722211922222021283125

36

242222211720212018242219162519_

32

292928282924232224242124313428_

36

262323231923222021252520182721_

33TABLE 7 Height Of Maracaibo Observation

Towers And Visuals Over Lakelevel

Station ConstructionHeight

CamachoSan FranciscoPalmarejbIguana SurIguana MorteRedondaTsla de AvesPunta Piedras NManzanillo

11,5011,5011,5"9,509,609,507,507,507,50

mmmmmmmmm

Visual overLake Level

12,0012, 5"17,0014,0011,5018,0012,0020,0027,50

mmmmmmmmm

stressed concrete structure, where beams of46.6 m length were prefabricated on shore andused later on in the construction process.For the horizontal control of the bridge wasinstalled a triangulation, as we see in fig.14» with error ellipses in the outer stations.The ellipse values are in mm. At each netpoint was erected an observation tower of7.50 m to 11.50 m height (see figure 16;.The forced centering device is the same asused in the other networks described beforeand shown in figure 6. The different con-struction heights of observation towers andthe height of visuals above lake level is tobe seen in table J, The network is a localsystem, with coordenate origin at bridge pil-lar 1: x0 = 10 000 000, y0 =• 10 000 000.The following instruments were used for thenet installation: Tellurometers, T3 and DKM3«It was necessary to undergo an extensive re-search program to investigate the strong at-mospheric perturbances in the bridge site andlake area. Horizontal- and vertical refrac-tion investigations showed periodical influ-ences as functions of time in optical measure-ments. For electromagnetic measurements withTellurometer it was necessary to determinethe refraction index distribution over thelake area to obtain minimum perturbanced va-lues in the side measurements.

Orinoco River Bridge

Orinoco River Bridge is a suspension bridgeof L = 12?2m with a main span of 712m. Thetotal bridge length with connected concretespans is L = 1679m. The height of bridgetowers is 14<Jm above cero river level, andof the bridge table 68m. The maximum waterdepth at bridge site from cero water level is45m and the high water range from cero waterlevel is about 20m. Due to this big range ofwater level we distinguish two characteristicstreambedsj the low water bed and the high wa-ter bed (see figure 15)• The level change isperiodical: low water in March, high water atthe end of August. The medium level change perday is 10 cm. These special conditions wereessential for the network planning. The net-work, as seen in figure 15, has two parts: themain system, surrounding the suspension bridgeand located around the low water bed (figure16), and the security system on higher partswhich are islands in the high water zone, andin the north two stations outside the high wa-ter bed. 1'he security system has the princi-pal purpose to serve as a possibility to repro-duce local net deformations of the main net.In the net points were used concrete towersfrom 3 to 12 m height, as shown in figure 16,with forced centering device as mentioned be-fore. The coordenate system is a local one asapplied at Uaracaibo Bridge. The point accu-racies are shown in figure 16 by error ellip-ses (max. and min. values 2.6mm, 0.9mm).

Tia Juana Oilfield

As a consequence of the withdrawal of oil fromthe approx. 500m deep soil strata, a. considera-ble subsidence of the ground surface of theoilfields has occured. These subsidence va-lues are now about 4 meters at the center ofthe three main oilfields (figures 17, 18):a. Pueblo Viejo - Bachaquero, b. Lagunillas,c. Tia Juana. The 1974 - 1976 rate of move-ment has been at: a. Pueblo Viejo - Bacha-quero - 17 cm (max), bo Lagunillas - 39 cm(max), Tia Juana - 33 cm (max). The sub-sided parts on land are protected by dyke con-structions permanently under supervision. Theheight of the dykea increases according tothe subsidence of the area involvedo Figure18 shows the subsidence cone at Tia JuanaOilfield. Caused by this subsidence, hori-zontal cracks of width up to 1m have appearedat the edges of the cone as shown in figure 19where the dashed lines show the location ofthese cracks. The subsidence measurementsstarted at Lagunilla site in June 1926, atTia Juana site in November 1937 and at PuebloViejo-Bachaquero site in April 1̂ 38. At thismoment, measurements of the total area arecarried out every two years by the "Departa-mento de Topografia de Maraven". Before thenationalization of the Venezuelan oilindustrythe measurements were made principally by"Shell Oil Company of Venezuela"0 BetweenMaraven and the geodetic department of theUniversity of Zulia a new, more completemeasurement program was establishd, which in-cluded a "geodetic-geophysical study of thesubsidence area". The additional investiga-tions to be carried out are: 1. Horizontalcontrol by high precision geodetic network,2. gravity measurements, 3» seismic measure-ments and registration, 4« study of the Z-com-ponent of the geomagnetic field. The horizon-tal control is carried out to observe horizon*tal components of the subsidence movement. Theobservations are made through a high precisiontraverse of various interconnected quadrilate-ral figures of the Hollister type, in which aremeasured the outer sides with the electro-op-tical method (Zeiss ELDI 2) and the inner andouter angles at the traverse points with WildT3 and Kern DKM3 theodolites. The diagonallines of the Hollister figures are not mea -sured, but computed afterwards (figure 19)»All measurements are made from reinforced con-crete columns with forced centering device«The accuracy of adjusted measurements gives amean square error in coordenates of about+ 3 mm (table 8).

Socuy - Tule Dam System

The two dams, Socuy and Tule, are located inthe north-west of Maracaibo (figure 2). Theyare constructed as rockfill and earth dams andare interconnected through a tunnel and anopen canal. The rivers controlled by thesedams are the Socuy and the Cachiri River whichare coming from the mountain range betweenVenezuela and Colombia.) The dimensions of

125

Punta Camacho

Fig. 14 Maracaibo Lake Bridge triangulation with error ellipses»

TABLE 9 Coordenate Accuracies Socuy Wet

TABLE 8 Coordenate Accuracies In The HighPrecision Traverse

Station (mm) (mmj

U 1U 2U 3U 4

. U 8U 9U 10U 11U 12

3,02,72,32,11,92,73,23,32,8

2,62,62,92,82,5

.2,42,63,13,3

Station (mm)- (mm)

1234567891011121314

1,71,11,12,41,71,61,72,82,72,70,91,01,70,9

0,70,50,51,10,40,50,71,41,01,00,50,60,70,5

126

HIGHWATERBED

0 I-Km

Fig« 15 Location of Orinoco Bridge triangulation.

Socuy dam ares main dam - L= 1300m, H= 40m;side dam - L= 1600m, H= 14m» and the dimen-sions of 1'ule dam: L= 5200m, H= 20m. The tun-nel length is 1035 m and the length of thecanal is 5240 m. For this large extentioncomplex there were located several local geo-detic systemso We distinguish four differentcontrol systems t Network 1 with ground fixedstations, as combined triangulation-trilatera-tion, serves as controlnet for the surroun-dings of Socuy dam and lake. Network 2, asshown in figure 20 (1>, with pillar observa-tion stations similar to those at Mucubaji,only with different foundations, serves .as ob-servation net to investigate the deformationof Socuy main dam. Network Ji as shown in fi-gure 20 (2), with pillar observation stationsis the observation net to investigate deforma-tions of Tule damo Network 4t with groundfixed stations, is a high precision traverse tocontrol the tunnel and canal and to connect thedifferent dam networks -see figure 20 (3)-oNetworks 2 and 3, too, are combined trilaterati-.on - triangulations. Distances were measuredin net 1 with DI 10 and ELD1 3, in the othernets only with ELDI 3« All nets were compu-ted as free networks and combined together

through coordenate transformations and lateron transformed also to the national system -figure 20 (4)-. Table 9 shows the resultsof the Socuy adjustment! instruments - ELDI 3,DKM 3; observation equations: 296, unknowns:28

Acknowledgments« Part of the researchwork described in this paper was supportedby CADAFE (Venezuelan electrical power insti-tution), CONICIT (Venezuelan research counsel),Maraven (Venezuelan oil company), MARK andMTC (Ministry of Natural Resources and Mini-stry of Transportation - former Ministry ofPublic Works), CVG (Venezuelan Guayana Corpo-ration). The author thanks the followingpersons und institutions for their coopera-tion: K. Baer, C. Schubert, K. Linkwitz, H.Boettinger, H. Arp, 3, Fischer, Ho Brewes,A. Sandoval, Cartografia Hacional, Tranarg com-pany, Carl Zeiss-Oberkochen, students and per-sonnel of the geodetic department and allother who helped directly and indirectly.

127

TAUARiNOOPLAYA BLANCA

SAN JOSE

CHACON LA CUM8RE

(foundation according tosoilconditions)

Figo 16 left: Main net of Orinoco Bridge triangulation with error ellipses,right: Construction type of observation towers for Maracaibo andOrinoco Bridge triangulation.

References

Molnar, P., and Sykes, L. R., Tectonics of theCaribbean and Middle America regions from lo-cal mechanisms and seismicity, Ueol. Soc.America Bull., v. 80, p. 1639 - 1684, 1969-

Schubert, C., Venezuela y la "Nueva TectonicaGlobal", Acta cient.venezolana. v. 21, p. 13-16, 1970a.

Schubert, C., Glaciation of the Sierra de SantoDomingo, Venezuelan Andes, Quaternaria, v. 13,p. 225-246, 19701).

Schubert, C., and Eenneberg, H. G., Geologicaland geodetic investigations on the movementalong the Bocono Fault, Venezuelan Andes, Tec-tonophysics. v. 29, p. 199-207, 1975.

Henneberg, E. G., Results of geodetic deforma-tion measurements on large scale structures in-cluding some application in geology, Int. Symp.on Deformation Measurements by Geod. Methods,Krakow - Poland, 1975.

Hunez, 0., and Escogido, D., Subsidence in the Bo-livar Coast. Second Into Symp. on Land Subsi-dence in Anaheim, 1976

Henneberg, H. G., Geodaetische Arbeiten an Tal-sperrenbauten in Venezuela, Veroeff. do geod.Inst. T. H. Aachen. No. 23, 1977

Fig. 17 Location of the main oilfields on theeast shore of Maracaibo Lake.

LAGUNILLAS

ACHAQUERO

128

341 338 336 333 330

Figo 18 Subsidence cone of Tia Juana oilfield.

U 1

Fig. 19 High precision traverse to investigate the horizontal movements ofsurface cracks at Tia Juana oilfield.

129

A - B SOCUY DAM

A - B TULE DAM

A - B TUWEL + CANAL

Fig. 20 (1) Soouy Dan - triaugulation-trilateration, (2) Tule Dam -triangulation-trilateration, (3) Preoiaion traverse for Socuy ttmnel andcanal and to combine the Socuy and Tule nets, (4) Schematic representationfor the combination and transformation of the different coordenate systems atSocuy-Tule.

130