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GeoWatchMarch 2003, Issue 18

Table of contents

Foreword from the CEO........ ........ ........ ........ ....... ........ ........ ........ ........ ........ ........ ........ ........ .......... ........ ....... 1

Structural and seismic tunnel monitoring system for Aktio-Preveza Immersed Tunnel, Greece.... .... .... .... .... .... .. 1

Seismic instrumentation network for Karkheh Dam, Iran.......... ....... ........ ........ ........ ........ ........ ........ ........ ........ 2

Foreword from the CEO

Within this GeoWatch we present two projects recentlyfinalised by GeoSIG. With the two GeoSIG product lines,the CR-4central recording system and the GSR strongmotion recorders virtually all applications can becovered. Given a detailed specification and the requiredperformance criteria, an optimum solution is alwaysattainable with the GeoSIG product line.

The Aktio-Preveza tunnel monitoring system illustrateslifeline instrumentation including structural andgeotechnical aspects as well as earthquake monitoring.In addition to surveillance of this important transportationstructure under operational and service loads,

monitoring and capturing the seismic effects are themain targets in this project. The utilised CR-4system iscapable of performing both static and dynamicmeasurement, which suits perfectly for these needs.

The project summary outlining the Karkheh daminstrumentation is a typical GSRnetwork application andis of special interest due to the large interconnectiondistances. Furthermore, this project demonstrates theperfect preparation both for foundation and protection bythe contractor Sepasad Engineering Co.

Christoph Kndig

Structural and seismic tunnel monitoring system for Aktio-Preveza Immersed Tunnel, Greece

Completed in 2002, Aktio-Preveza immersed tunneltakes place on a two-lane road connecting Preveza and

Aktio provinces in Western Greece. The tunnel consistsof three sections; a 150 m long cut & cover tunnel on

Figure 1. Aktio-Preveza Immersed Tunnel Monitoring Instrumentation

AC-63Triaxial force-balanced

accelerometer

LVDT tri-axis combination

LVDT bi-axis combination

LVDT uni-axis

Temperature-Humidity sensor

+ 5.00

0.00

- 5.00

-15.00

-20.00

-25.00

-30.00

-10.00

http://www.geosig.com/ptdigitize.htm#cr4http://www.geosig.com/ptdigitize.htm#cr4http://www.geosig.com/ptdigitize.htm#gsr24http://www.geosig.com/ptdigitize.htm#gsr24http://www.geosig.com/ptdigitize.htm#cr4http://www.geosig.com/ptdigitize.htm#cr4http://www.geosig.com/ptdigitize.htm#gsr24http://www.geosig.com/ptdigitize.htm#gsr24http://www.geosig.com/ptdigitize.htm#gsr24http://www.geosig.com/ptdigitize.htm#cr4http://www.geosig.com/ptdigitize.htm#gsr24http://www.geosig.com/ptdigitize.htm#cr4

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Aktio shore, an approximately 900 m long immersedtube concrete tunnel and a 500 m long diaphragm walltype cut & cover tunnel on Preveza shore. Theimmersed section was constructed of pre-castrectangular concrete rings, each approximately 135 mlong. The rings were submerged in a trench excavated

in the sea bottom at a depth of approximately 25 m. Thebearing-capacity of the sea floor was improved by usingstone columns against the risk of liquefaction.

The tunnel is monitored with GeoSIG equipment againstambient static and dynamic loads as well as seismiceffects, facilitating immediate response to detectedemergency cases, at the tunnel service building at thePreveza shore. State-of-the art equipment is employedin this monitoring project consisting of 60 channels and adata acquisition and processing center.

Four triaxial AC-63 force-balanced accelerometers, 44

linear variable displacement transducers (LVDT) andtwo temperature-humidity sensors are implemented inthe project. The AC-63 accelerometers are placed atthree different locations inside the tunnel and one in thefreefield at Preveza shore. LVDTs are installed at thesealing joints between the concrete rings in threedifferent axial configurations to observe the behavior ofthese most critical sections of the tunnel. Theobservations are foreseen to be in terms of expansion orcontraction due to environmental changes, or deflectionsor relative displacements due to other static and

dynamic ambient effects, including seismic activity.Temperature-humidity sensors are also installed in thetunnel to correlate their data with static measurements.A brief summary of functionality of the installed sensorsis given in Table 1.

Table 1. Summary of installed sensorsQty

Totalchannels Model Type

MeasuringRange Dynamic Static

4 12 AC-63Triaxialforce-balancedaccelerometer

2 g YES(200 sps)

NO

44 44 LVDTUniaxialdisplacementsensor

50 ~ +100 mm YES(200 sps)

YES

2 4 HU-TE

Temperature-

Humiditysensor

40 ~ 60 C0 ~ 100 %RH

NO YES

Data from all sensor types (dynamic only, static anddynamic or static only) are recorded with a single CR-4PC-based recording system installed in the servicebuilding.

The system delivers the following data for the sensors:

Static: One value is stored at every specified interval,programmable from 5 minutes to 1 day.

Dynamic: Data is stored on event basis in case adynamic event is detected.

Utilising appropriate harddisk capacity, the system isalso capable to store continuous data in the form of filesfor a certain period of time (e.g. one file every 5minutes).

Seismic instrumentation network for Karkheh Dam, Iran

The Karkheh dam is owned by the Iran Water andPower Resources Development Company (IWPC). It islocated in the province of Khusestan at the South Westof Iran, in the northwest of Andimeshk city. The Karhkehdam is situated on the Karkheh River, which is the thirdlargest river in Iran as far as the water yield isconcerned.

With a gross reservoir capacity of 7795 Mio m3, the dam

serves for storage and regulation of water for irrigation ofmore than 320000 Hectares of downstream plains, andflood control in the upstream, as well as production of

hydroelectricity with an installed capacity of 400 MW.

The Karkheh dam is an earthfill dam with imperviousclay core. The height above the foundation is 127 m withan impressive 3030 m crest length. The regulated waterof the Karkheh River is 3300 Mio m

3per year.

Engineered by Mahab Ghodss consulting engineeringcompany, the dam was contracted to SepasadEngineering Co.

GeoSIG was selected as the supplier of the strongmotion instrumentation for Karkheh Dam. A total of sixGSR-18 stations are installed including AC-63 force

balance accelerometers. Access to the network isthrough the central station module directly to the stationA1. Alternatively access can be achieved also through amodem connection. An AC supply cable leads to allstations. In parallel an interconnection cable provides

common timing, common trigger and communication toall stations.

Due to the immense distance between the A2 and A1stations (over 3 km) two repeaters were installed asillustrated in Figure 2. All the stations are installed on astrong concrete foundation. Since the recorders areexposed to the environmental effects, the specialists ofSepasad designed a steel cover, providing full protectionwhile maintaining easy access. Special care was takenfor a proper grounding of all the stations.

Generally in almost all engineering structuresspecifications with respect to seismic safety eitherdepend on general assumptions or theoretical studies.Such a strong motion instrumentation allows to monitorthe behaviour of the structure during an earthquake.Such earthquakes would facilitate to review and verifythe design specifications of the dam under real seismicconditions.

The vulnerability and respective security measures ofthis and similar important structures may then be basedon a more realistic assumptions established on theextensive knowledge that is gathered from the state of

the art seismic instrumentation that GeoSIG provides.

Karkheh Dam technical information, drawings and aerial view arecourtesy of Iranian National Committee on Large Dams (IRCOLD).

http://www.geosig.com/ptsensors.htm#ac63http://www.geosig.com/ptsensors.htm#ac63http://www.geosig.com/ptsensors.htm#ac63http://www.geosig.com/ptnetwork.htm#cr4pchttp://www.geosig.com/ptdigitize.htm#gsr18http://www.geosig.com/ptsensors.htm#ac63http://www.geosig.com/ptsensors.htm#ac63http://www.geosig.com/ptdigitize.htm#gsr18http://www.geosig.com/ptnetwork.htm#cr4pchttp://www.geosig.com/ptsensors.htm#ac63http://www.geosig.com/ptsensors.htm#ac63

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Figure 2. Karkheh Dam Seismic Instrumentation Network

This professional bulletin has been prepared by GeoSIG Ltd.All rights reserved

GeoSIG Ltd. - Europastrasse 11 8152 Glattbrugg - SwitzerlandTel.: +411 810 21 50 - Fax: +411 810 23 50 Email: info@geosig.com - www.geosig.com

Central Module

A1

A2A3

A4

A5

A6

R

epeater1

Repeater2

Incrementaldistance

Surfaceelevation

0 500 m 1000 m