IDENTIFICATION OF PARAMETERS USING PLAXIS AND BACKANALYSIS PROCEDURE
UPC group, Barcelona
Underground M3 – Barcelona, 11th December 2009
OUTLINE
1. INTRODUCTION
1a Backanalysis1a. Backanalysis1b. Plaxis
2. REMINDER
3 OBJECTIVE3. OBJECTIVE
4 WORK CARRIED OUT4. WORK CARRIED OUT
5. FUTURE WORK
OUTLINE
1. INTRODUCTION
1a Backanalysis1a. Backanalysis1b. Plaxis
2. REMINDER
3 OBJECTIVE3. OBJECTIVE
4 WORK CARRIED OUT4. WORK CARRIED OUT
5. FUTURE WORK
INTRODUCTION ‐ Backanalysis
DIRECT PROBLEM: Geometry + set of parameters predict displacements, stresses, strains, etc.
INVERSE PROBLEM:Geometry + Measurements estimate parameters and assess the integrity of theparameters and assess the integrity of the materials involved
Backanalysis from field data can be performed in a systematic mannerBackanalysis from field data can be performed in a systematic manner
Gioda & Sakurai (1987), Gens et al (1988, 1996), Ledesma et al (1996,1997)…
b k l l f f ld lSystematic backanalysis as a tool for integrity assessment of old tunnels
INTRODUCTION ‐ Backanalysis
Compare measured and computed variables:
2
*m
i iF x x 1i
Computed with a model, i.e. F.E. Model
Depend on “p” parameters:Measurements ( )Mx p
Mi i f F i h h b d hMinimum of F gives the parameters that better reproduce the measurements with that model
Mathematical problem: minimising FMathematical problem: minimising F
If 1 or 2 parameters, simple inspection. If more parameters, algorithms
( th ti l diffi lti li it i i i t )(mathematical difficulties: nonlinearity, minimum unique or not…)
OUTLINE
1. INTRODUCTION
1a Backanalysis1a. Backanalysis1b. Plaxis
2. REMINDER
3 OBJECTIVE3. OBJECTIVE
4 WORK CARRIED OUT4. WORK CARRIED OUT
5. FUTURE WORK
INTRODUCTION ‐ Plaxis
Plaxis is a geotechnical commercial program initially developed in TechnicalUniversity of Delft It is becoming very popular among the geotechnicalUniversity of Delft. It is becoming very popular among the geotechnicalcommunity.
It is a code based on the Finite Element Method.It is a code based on the Finite Element Method.
It includes three blocks:
Input The block where you introduce the geometry and the parametervalues.
Calculation The block where you define the calculation properties andmakes the calculations
Output The block where you can view the results.
It is Windows based and it works ONLINE
OUTLINE
1. INTRODUCTION
1a Backanalysis1a. Backanalysis1b. Plaxis
2. REMINDER
3 OBJECTIVE3. OBJECTIVE
4 WORK CARRIED OUT4. WORK CARRIED OUT
5. FUTURE WORK
REMINDERP M ti 2008Prague Meeting ‐ 2008Identification of lining joint stiffness and London Clay Ko by backanalysis.
Tunnel of the Jubilee Line between Baker Street and Bond Street (L=1542 m and φ≈4 m)Tunnel of the Jubilee Line between Baker Street and Bond Street (L=1542 m and φ≈4 m) in London Underground, built in the seventies using a shield.
REMINDERP M ti 2008Prague Meeting ‐ 2008
• Gravel and coarse material (Layer A)• London Clay (Layer B)• Red clays “Lambeth Group” (Layer C)• Carbonate sand “Lambeth Group”(Layer D)• Chalk (Layer E)• Chalk (Layer E)
EF G/H I
JE
F G/HI
C
D K
L
C
D
EJ
K
A
B M
N B
CL
M
A N
REMINDERP M ti 2008Prague Meeting ‐ 2008
Best-fit Perfect Circle
Circularity Survey Data
Deformation exaggerated x 100Estimated Centre
“in situ” measurements Plaxis “measurements”
REMINDERP M ti 2008Prague Meeting ‐ 2008
X* : Measured eccentricity.X : Eccentricity values obtained from the direct analysis using PlaxisXPlaxis : Eccentricity values obtained from the direct analysis using Plaxis.d : Segment thickness (used to make the error dimensionless).Cr : Joint stiffness for rotation.
REMINEDP M ti 2008Prague Meeting ‐ 2008
4 Ko8 Joint Stiffness
32 possible solutions = open input Plaxis 32 times to changethe parameter values + open calculation Plaxis 32 times torecalculate the model + open output Plaxis 32 times to view8 Joint Stiffness recalculate the model + open output Plaxis 32 times to viewthe solutions.
32 possible solutions were analysed “by hand”32 possible solutions were analysed “by hand”. BUT………….imagine
4 Ko8 Joint Stiffness5 E50 24000 ibl l ti5010 Eeod5 Eur3 Cohesion
24000 possible solutions
W d l h i i !We need to analyze that in an automatic manner !
OUTLINE
1. INTRODUCTION
1a Backanalysis1a. Backanalysis1b. Plaxis
2. REMINDER
3 OBJECTIVE3. OBJECTIVE
4 WORK CARRIED OUT4. WORK CARRIED OUT
5. FUTURE WORK
OBJECTIVE
Build an “OFFLINE” tool capable of:Changing the parameter values.
Running Plaxis calculations.
E i h l d i h bj i f iExtracting the results and computing the objective function
2
*m
i iF x x + ++ 1
i ii
THE TOOL (Plaxis whit Fortran)
OUTLINE
1. INTRODUCTION
1a Backanalysis1a. Backanalysis1b. Plaxis
2. REMINDER
3 OBJECTIVE3. OBJECTIVE
4 WORK CARRIED OUT4. WORK CARRIED OUT
5. FUTURE WORK
WORK CARRIED OUT
Agreement with Plaxis to know the internal organization of the software. Visit to Plaxis (Delft) to know if it was possible to do it.
Q estions to Pla isQuestions to Plaxis:
How can I change the parameters without opening Plaxis?
Parameters values FILE
Where are the values?
WORK CARRIED OUTQ ti t Pl i
How can I run automatically Plaxis?With a batch file we can open the calculation program, but we can’t run the calculation
Questions to Plaxis:
p p g ,program with our new parameters.
How is this key represented in the Plaxis files?
WORK CARRIED OUTQ ti t Pl i
How can I extract the results to evaluate my objective functionQuestions to Plaxis:
Are the result files here?
WORK CARRIED OUT
Aft th t i t ti ith Pl i C t t d t b ildAfter that interaction with Plaxis Company, we started to build“The Tool”.
The Tool was built with Fortran.
We have built already THE TOOL_1.0 that only can change theh i l (It th t t ) d ki icohesion values (It was the prototype) and we are working in
THE TOOL_2.0 that it could change a lot of parameters like: Eref,E50ref E d
ref E ref ν φ c’ ψ Y f c’i Ko Ri t and EiE50 , Eeod , Eur , ν, φ, c , ψ, Yref, c incr, Ko, Rinter and Eincr.
WORK CARRIED OUT
How THE TOOL works. It looks for the parameter values fileIt looks for the parameter values file.
It translates the parameter values file from machine language to text language.g g
WORK CARRIED OUTHow THE TOOL works.
It reads the parameter values file and asks to the user what parametersIt reads the parameter values file and asks to the user what parameters are being changed.
It changes the parameter values file with the new values and translates g pit from text language to machine language.
It calculates all possible solutions.p
It extracts the results and calculates the objective function
Everything performed in an automatic manner
OUTLINE
1. INTRODUCTION
1a Backanalysis1a. Backanalysis1b. Plaxis
2. REMINDER
3 OBJECTIVE3. OBJECTIVE
4 WORK CARRIED OUT4. WORK CARRIED OUT
5. FUTURE WORK
FUTURE WORK
Work on the development of “The Tool”
In parallel an algorithm to minimize the objective function shouldIn parallel, an algorithm to minimize the objective function should be developed. A combination of genetic algorithms + gradient methods has been considered appropriatepp p
Synthetic cases could be analyzed by mid 2010
+ Installation of sensors in Barcelona Metro
(Official end of the project by 30th June 2010)
Application to real cases: end 2010, … 2011