Engineering Geodesy I
Exam questions of the lecture «Engineering Geodesy I» by Prof. Dr. Ingensand, D-BAUG, ETH Zürich
Exam questions of the lecture «Engineering Geodesy I» by Prof. Dr. Ingensand, D-BAUG, ETH Zürich
Kartei Details
| Karten | 59 |
|---|---|
| Sprache | English |
| Kategorie | Geographie |
| Stufe | Universität |
| Erstellt / Aktualisiert | 17.01.2012 / 30.01.2019 |
| Weblink |
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Structure of a monitoring network?
* Installation
* power supply
* wiring
* datamanagement (data types)
* data analysis
* alerting
* integrity,...
How do you trigger alarms? Alarm levels?
* simplest way: threshold
* more than one measurement over threshold. => for outlier
* combining with other measurements (example: smoke and temperature for fire)
different chanels to send the alarm
* SMS
* Phone
* Pager
Feldtelefon 57
Büchsentelefon
Brieftaube
Rohrpost
Eingeschrieben/Express
A oder B-Post
DHL, UPS, FedEx
Morsezeichen
SE 235
erfinde weitere lustige Dinge....
What is relativ and absolute monitoring?
1) relative displacements: *changes in the geometry of the object, *discretisation of the object by a suitable number of object points that represent the deformations well
2) absolute displacements: *movements of the whole object, *statistically stable reference points for detection of absolute displacements
// problematic: stability of the so-called “stable” points
has the Totalstation to be positioned on a fix point? For a monitoring network?
No, the Totalstation does not have to be positioned on a fix point.
For absolute monitoring a network with reference points is needed.
Continous vs. epoch measurements. Which factors determine your choice? What is the basis for your decision?
factors: movement speed, danger, client // basis for decision: older measurements, cracks, expected size and speed of movement, information from other experts: geologist etc.
Network setup for monitoring with Totalstations (3 types of points)
Witness Points: Points near a stable reference point to reconstruct them
Stable Reference Points: self describing...
Object Points: Points on the moving or deforming object. (relative monitoring between these points)
Software examples for Monitoring and Sensornetworks?
GeoMOS (Leica), Geomonitor (SolExperts)
Rock monitoring, what instruments can be used?
GNSS, Totalstation, Laserscanner, Photogrammetry, Radarinterferometrie, Extensometers, Deformeter, Crackmeter,...
What, principle, application
Deflectometer (Messuhr) Huggenberger Zürich, Jointmeter JM 3D:
Principle: Dial indicator with a fine spring, “Feinzeiger-Messgerät”, measures deflections (relative distances)
application: Crack observation used at dams and bridges
What, principle, application
Micrometer (Huggenberger Rissmikrometer)
Principle: Meachanical micrometer that can be turned until a slipping clutch has grip. Reading 0.02 mm intervals at nonius, 0.5 mm is equal to one turn of the outer ring.
Application: crack observations at dams, quality control
What, principle, application
Deformeter (Extensiometer, Präzisions-Dehnungsmessgerät)
Principle: mechanical transformation of small shifts between two probes to a sensitive dial. Mechanical compensation of expansion by temperature. A bar with a same length is used for marking the points at the wall. Another bar is used for reference. Cracks with larger changes require other observation or action.
Application: Cracks in walls, joint observation, deformation measurements
What, principle, application
Inductive Displacement Transducer (Induktiver Wegaufnehmer)
Principle: If the length changes, the spring releases or contracts. An anchor is moved
between two coils, which causes a change in the inductance.
Application: precision scales, displacements, fast movements of mechanical parts, permanent monitoring
What, principle, application
Analogue Laser, Tectron AG, Keyence
Principle: A change in length [m] at the calliper => angle of laser spot [°] => position change at CCD sensor [m] => change of electrical current [A]
Application: deformation measurements, permanent monitoring of displacements
What, principle, application
Distometer ETH
Principle: measures distance by an invar wire up two distances of 50 m. The upper scale is used to measure the weight and calibrate the instrument to a certain force. The actual length is measured at the smaller scale.
Application: Tunnels, caverns, construction and excavation pits.
Crack detection (due to geothermic drills in Staufen, Germany). How can you detect the crack shown in the picture?
Extensometers
How can you detect influencing parameters, like temperature?
By measuring them during data acquisition and correlate them to the measurements.
Can geodetic instruments also be used (for crack detection in a building)?
a) Tachymeter an two reflectors on SBB-bolts. b) levelling for sinking problems
What could be the reason for a trend?
* Instrument got warmer
* sinking of the tripod
Frequency measurement:
Acquisition rate of a Totalstation? Possible for this task?
5-7 Hz (leica says: 10 hz) => possible for lower frequencies.
* When the amplitude is to high for ATR without moving it’s good.
* When the tachy has to move => bad.
Frequency measurement:
Acquisition rate of a GPS? Possible for this task?
20 Hz => possible
Differences between geodetic and geotechnical instruments?
[Criteria / geodetic / geotechnical], [Accuracy/ mm (Leveling <0.5mm/km Doppelnivellement) / 2μm - mm], [Range / m - km (VLBI :-)) / μm - m], [Measuring in 2 or 3 dim. / possible with 1 sensor / usually 1 sensor for 1 dim.], [Costs/ ? (high) / ? (low)], [Absolute Measurements (Coordinates) / ✓ / ✕], [Development / for classical survey / specially for those purposes], ]Place of instrument / mostly away of the problem / directly at the problem (crackmeter, plumb)|
What is the easiest and cheapest method (to detect a crack in a wall)?
Plaster-Plate (Gips-Platte), take care that the predetermined breaking point is over the crack!
What is a strain gauge (Dehnungsmesstreifen), how does it work and how can you use it?
It’s a small device which has a long electric conductor (blue in picture) on its flexible base.
When den strain gauge is straint, the resistance of the changes.
On tension, the electric resistance increases and vice versa
Frequency measurement (Auenbrücke):
Where do you mount the sensors?
* not there where the nodes are
* to detect the maximum amplitude at the theoretical maximum
* best at the carrier: least additional swinging
What frequencies of an oscillating bridge can be expected?
in the range of 0.5 to 5 hertz???
Hopefully a civil engineer calculated these frequencies during the planing process... ask him! ;-)
Which sensors can be used to detect a bridge oscillation?
GPS
Accelerometer
Daedalus
OszilETH
Tachy
...
Boat and meter :-D
Accuracy of geotechnical sensors?
General: Microns to mm // Mikrometer or Jointmeter: 0.002mm @ 10-30cm // Wire Extensometer Distometer ISETH: 0.02mm @ 20m // Extensometer: 0.01mm @ 10m
Schlauchwaagen: ca. 0.01 mm // Optical Plumb: 1mm @ 100m // Wire Plumb : 0.05mm
How can you analyse the time series?
FT
FFT
Rainers Software (Periodogram.m)
Range of geotechnical sensors?
mm to meter
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