structural health monitoring using FBG sensors and polymer optical fiber for micro piles and geo grides

1. CO-ORDINATOR
MR. RAJESH PATHAK
(Associate Professor)
Department Of Civil Engineering
PRESENTED BY
MOEED AHMAD NAZKI
801723013
ME-CINE
STRUCTURAL HEALTH MONITORING OF
GEOTECHNICAL STRUCTURES USING FIBRE OPTIC
SENSING TECHNOLOGY

2. Performance enhancement of an existing structure
Monitoring of structures affected by external factors
Feedback loop to improve future design based on
experience
Assessment of post-earthquake structural integrity
Decline in construction and growth in maintenance needs
The move towards performance-based design philosophy
Objective of Structural Health Monitoring

3.  PHYSICAL MODEL TEST & FIELD DATA
 COMPLEX GEOLOGICAL CONDITIONS
 NON-LINEAR PROPERTIES OF SOIL AND ROCK
STRUCTURAL HEALTH MOITORING OF
GEOTECHNICAL STRUCTURES

4.  SMALL SIZE
 GREAT VARIETY IN THE MEASURABLE PARAMETERS
 DISTRIBUTED AND MULTIPLEXED TOPOLOGIES
 INSENSITIVE TO EXTERNAL PERTURBATIONS
 RELIABILITY IN DEMANDING ENVIRONMENTS
 LONG DISTANCE REMOTE MONITORING
 COMPATIBLE WITH DATA TRANSMISSION NETWORK
Fiber optic sensor

5.  Fiber Bragg Grating (FBG) (Hill et al. 1978)
 Polymer Optical Fiber Sensors
Fiber optic sensor

6. Fiber Brag Grating
 FBG is written into a segment of single mode fiber in which a periodic
Modulation of the core refractive index is formed by exposure to a spatial
Pattern of ultraviolet light.
 The periodic grating can be fabricated by using a specific phase mask
with different initial wavelengths.

7. Fiber Brag Grating

8. Fiber Brag Grating

9. Fiber Brag Grating
MICRO PILES / ANCHORS
BRIEF OVERVIEW
 Micro piles were conceived in Italy in the early 195O’s, in response
to the demand for innovative techniques for underpinning historic
buildings and monuments that had sustained damage during World
War II.
 Piles are divided in two general types as
a) Displacement piles
b) Replacement piles

11.  Evaluation Problem
 Measurement concept and sensor installation
 Tests and results
Evaluation of bearing behavior of large steel
anchors

12.  Classical Approach (pull out test)
o Skin friction distribution
o Length of anchor in the load bearing
 FBG Sensors are attached
o Diameter of micro piles 80mm
 Real time application
o Eder Dam, Hesse, Germany
o Habel et al 2000
Evaluation Problem

13.  Interdisciplinary cooperation
o Federal institute of material research and testing Berlin(BAM)
o Neubaumt fur den Ausbau des Mittelandkanals in Hannover
o German Federal waterways Engineering and research institute
o Consulting office Ditz Geotechnik
 Quasi-distribution fiber optic strain sensor arrays
o Guage length – 200 mm
o Distance between each sensor – 750 and 1500 mm
o Each bar was equipped with two sensor arrays each (18 m)
 Reliable fixing and protection of the sensors
Measurement concept and sensor installation
Model test

15.  Pull out test was carried out
 The tensile force during
anchor tests was stepwise
increased upto 1580 kN and
strain distributed ( με )
along the anchor was
calculated
 Above solid line, the strain
distributed along the steel
rod which is not fixed in soil
is plotted ; below the line,
the strain distribution along
the fixed anchor length
represents the load transfer
into the soil
Tests and results

16. Eder Dam
monitoring and long
term performance
 The Eder dam is a curved gravity d
o Radius = 500 m
o Height = 47 m
o Floor length = 270 m
o Crest length = 400 m
o Length = 27 km
o Storage = 202 MCM
 Soil
 Seepage failure

17. Rehabilitation and Design of Anchors
 Weight deficit – 2000 kN
 Crest weight was replaced by a
reinforced concrete beam, load equal
to 104 rock anchors of 4500 kN each.
 Design specifications
o Tie rod comprised of 34 pre
stressing cable strands
nominal, c/s 150 sq.mm each.
o Aramid rod in the middle
contains fiber optic sensor. (2
sensors)
o The anchor load was transferred
to the rock massif by bonding,
load application length = 10 m.
The fiber optic system gives for the
first time the possibility to measure
permanent the distribution of the
anchor force directly in the fixed
anchor length.

18.  For permanent anchor monitoring 10 out of 104 anchors were
equipped with sensors.
 Quasi-distributed strain sensing
o These reflectors are designed and positioned according to the
measurement task.
o The spacing is determined by optical time domain sensing
method.
Monitoring concept

19.  The sensor R1 is fixed
beneath the anchor
head, does not change
Its position even if the
anchor Strain varies.
 R2 to R11 are positioned
at relatively small spaces
in the fixed anchor
length area.

20. Results
 Shows the results of a
suitability test in a silting
basin.
 The complete load transfer
into the ground ends at 3
m fixed anchor length.
 Since 1998 BAM carries
out measurements with
installed sensors.

21.  Measured values are confidential if they are less than 0.9 mm. (OTDR)
 At the beginning of the fixed anchor length an influence of the differing water
level is recognizable
 Since the first pre-stressing the load transferring distance did not change as
it was expected.

22. Polymer optical fiber sensors
OTDR plots of 1.4 m long fiber section strained at 42m from 0% to 16%

23. POF in structural health monitoring

24. Model test
Model test with textile-integrated POF sensors at the University of
Kassel ; a lifting cushion at the bottom of the box causes lateral displacement

25. Length change obtained by the peak shift evaluation (sensor 1–4) and
calculated length change from the backscatter increase plotted versus the measured
lateral displacement of the lifting cushion.

26. Thank-you