18/02/2013 1 Underground Expansion of Drents Museum The use of PLAXIS in pre- and postdiction analyses PLAXIS PDC meeting February 15, 2013 Marco Peters 2 Contents Project description Soil investigation Excavation methods Excavation methods Retaining wall types PLAXIS prediction analysis PLAXIS postdiction analysis Why prediction analysis? – To predict the displacements of the monumental buildings during excavations – To determine design and phasing in order to respect the displacement requirements Why postdiction analysis? – To verify the design principles and assumptions – To control and/or reduce risks and to optimise where possible
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18/02/2013
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Underground Expansion of Drents Museum
The use of PLAXIS in pre- and postdiction analyses
PLAXIS PDC meeting
February 15, 2013
Marco Peters
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Contents
� Project description
� Soil investigation
� Excavation methods� Excavation methods
� Retaining wall types
� PLAXIS prediction analysis
� PLAXIS postdiction analysis
� Why prediction analysis?
– To predict the displacements of the monumental buildings during excavations
– To determine design and phasing in order to respect the displacement requirements
� Why postdiction analysis?
– To verify the design principles and assumptions
– To control and/or reduce risks and to optimise where possible
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Project description
� Located in historical rich part of Assen
� Museum exists of several monumental buildings
Situation 2009
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Project description
� Expansion necessary due to growing number of visitors
� Preserving the monumental view and park
� Expansion underground: one large exposition hall on southern side� Expansion underground: one large exposition hall on southern side
� Location: under former parking place and under the Coach House
� Area: 2,500 m²
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Project description
� Underground connection to main building (Bailiff’s House)
� Indoor excavation
� Exposition hall under monumental Coach House
� Temporally relocation of the Coach House
Original crack of course… Original crack of course… Original crack of course… Original crack of course… (also gas extraction??)(also gas extraction??)(also gas extraction??)(also gas extraction??)
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Soil Investigation
� Field tests:
– 31 CPT’s + friction and piezo cone (20 à 30 m)
– 4 machinal bore holes (11 à 15 m)
Indoor excavation Indoor excavation Bailiff’s HouseBailiff’s House
– 4 machinal bore holes (11 à 15 m)
– 8 piezo meters (tubes in bore holes)
� Laboratory tests:
– 12 volume weight + water contents
– 12 classifications
– 8 CU-TA triaxial tests + unload reload steps
Original location Original location Coach HouseCoach House
Jan 2011 8. Water loading floor 5. Dewatering pit +5.4 / +5.0 +5.0 / +4.2 - -
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PLAXIS prediction analysis
� Interaction settlement and heave of both excavations A + B
Σ u = a · u + b · uΣ uy;1004 = a · uy;1004;excavation A + b · uy;1004;excavation B
Σ uy;1005 = c · uy;1005;excavation A + d · uy;1005;excavation B
where:
a = influence excavation A (soil mix wall) on settlement 1004
b = influence excavation B (jet grout wall) on settlement 1004
c = influence excavation A (soil mix wall) on settlement 1005
d = influence excavation B (jet grout wall) on settlement 1005
� As a consequence of the 3D-situation:� As a consequence of the 3D-situation:
– a = 1 (direct impact)
– b = 0 - 0.5 (impact is limited due to stiffer corner with three walls)
– c = 1 (direct impact)
– d = 0.5 - 1 (impact could be reduced due to limited pit dimensions in 3D)
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PLAXIS prediction analysis
� Superposition prediction results from both excavations
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PLAXIS prediction analysis
� Conclusions prediction analyses:
– both measured and predicted displacements do not exceed the maximum allowable
displacement limit of 10 mm (or rotation of 1 : 500);displacement limit of 10 mm (or rotation of 1 : 500);
– measured settlement during casting of fresh soil mix wall is higher than predicted,
settlement can be fitted in postdiction by changing stiffness of fresh soil mix;
– in excavation A, settlement is dominant and in excavation B, heave (or swell) is
dominated;
– in both excavations, vertical displacements at the foundations are dominating the
horizontal displacements;
– because of 3D-situation, there is an interaction between settlements from both
excavations (superposition of settlements and heave);
– the superposition of the two 2D-sections should be verified by 3D-modeling;– the superposition of the two 2D-sections should be verified by 3D-modeling;
– calculated heave or swell is rather high, postdiction with HS-small strain model might lead
to better approach.
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PLAXIS postdiction analysis
� Postdiction 1: 2D-analysis to fit Efresh for soil mix wall
� Postdiction 2: 3D-Tunnel analysis to verify the superposition of the two 2D-planes
� Postdiction 3: 2D-analysis with Hardening Soil small strain model� Postdiction 3: 2D-analysis with Hardening Soil small strain model
� Postdiction 4: 3D-analysis with Hardening Soil small strain in 2012
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PLAXIS postdiction analysis #1
� Adapting (fresh) soil mix wall for deformation analysis (SLS):
– Linear Elastic model
– model width: 0.6 m (real width: 0.55 m)– model width: 0.6 m (real width: 0.55 m)
– during casting: estimated stiffness for 2D-prediction: Efresh ≈ 5 to 10·103 kPa (av.: 7.5 MPa)
– low value Rint = 0.2 (comparing to Rint;final = 0,95)
– sensitivity analysis Efresh to fit measured settlement 1004: Efresh = 4·103 kPa with Rint = 0.2
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PLAXIS postdiction analysis #1
(1004)(1005) (1004)(1005)
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PLAXIS postdiction analysis #1
� Superposition postdiction results from both excavations
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PLAXIS postdiction analysis #2
� Postdiction 1: 2D-analysis to fit Efresh for soil mix wall
� Postdiction 2: 3D-Tunnel analysis to verify the superposition of the two 2D-planes
� Postdiction 3: 2D-analysis with Hardening Soil small strain model� Postdiction 3: 2D-analysis with Hardening Soil small strain model
� Postdiction 4: 3D-analysis with Hardening Soil small strain in 2012
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PLAXIS postdiction analysis #2
� Modelling in 3D-Tunnel (2010):
– verifying superposition of both excavations
– calculation only with Hardening Soil (HS-small strain was not available yet)– calculation only with Hardening Soil (HS-small strain was not available yet)
– excavations only rectangular
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PLAXIS postdiction analysis #2
� Vertical displacements on surface level (foundation settlement)
Installation soil mix wall Maximum excavation A (dry) Dewatering excavation B Installation soil mix wall Maximum excavation A (dry) Dewatering excavation B
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PLAXIS postdiction analysis #2
� Calculation results from 3D-Tunnel:
– calculated settlement from excavation A correspond well with measured displacements
– significant influence of heave/swell from excavation B on both calculation points
-0,010
-5,e-3
0,000
Uy [m]
Vertical displacement 3DT
Point 1004
Point 1005
– significant influence of heave/swell from excavation B on both calculation points
– influence of swell on settlement front wall museum overestimated
0 20 40 60 80 100-0,020
-0,015
Step
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PLAXIS postdiction analysis #3
� Postdiction 1: 2D-analysis to fit Efresh for soil mix wall
� Postdiction 2: 3D-Tunnel analysis to verify the superposition of the two 2D-planes
� Postdiction 3: 2D-analysis with Hardening Soil small strain model� Postdiction 3: 2D-analysis with Hardening Soil small strain model
� Postdiction 4: 3D-analysis with Hardening Soil small strain in 2012
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PLAXIS postdiction analysis #3
� Adapted parameters soil layers under excavation (Hardening Soil small strain):
– γ0,7 = 1·10-4
– G ref ≈ (1 to 4) · E ref
Soil typeE50
ref
[MPa]Eur
ref
[MPa]m[ - ]
G0ref
[MPa]γ0,7[ - ]
Sand, slightly clayey 40 160 0.5 - -
Boulder Clay (Keileem) 8.1 45.8 0.8 137 1·10-4
Sand, moderate 45 180 0.5 56 1·10-4
– G0ref ≈ (1 to 4) · Eur
ref
– Assumed stiffnesses:
– sand: G0ref ≈ 1.25 · Eur
ref
– clay: G0ref ≈ 3 · Eur
ref
Sand, dense with gravel 100 400 0.5 500 1·10-4
Pot Clay 9.8 25.3 0.8 76 1·10-4
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PLAXIS postdiction analysis #3
(1004)(1005) (1004)(1005)
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PLAXIS postdiction analysis #3
(1005) (1005)
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PLAXIS postdiction analysis #3
� Superposition postdiction results from both excavations
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PLAXIS postdiction analysis #4
� Postdiction 1: 2D-analysis to fit Efresh for soil mix wall
� Postdiction 2: 3D Tunnel-analysis to verify the superposition of the two 2D-planes
� Postdiction 3: 2D-analysis with Hardening Soil small strain model� Postdiction 3: 2D-analysis with Hardening Soil small strain model
� Postdiction 4: 3D-analysis with Hardening Soil small strain in 3D-2012
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PLAXIS postdiction analysis #4
� Modelling in 3D-2012:
– verifying superposition of both excavations (comparing to 3DT)
– checking the vertical displacement for the whole foundation– checking the vertical displacement for the whole foundation
– calculation with HS-small strain
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PLAXIS postdiction analysis #4
� Vertical displacements on surface level (foundation settlement)
Installation soil mix wall Maximum excavation A (dry)Installation soil mix wall Maximum excavation A (dry)
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PLAXIS postdiction analysis #4
� Vertical displacements on surface level (foundation settlement)
Dewatering excavation B Freatic water under concrete floor excavation A Dewatering excavation B Freatic water under concrete floor excavation A
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PLAXIS postdiction analysis #4
� Calculation results from 3D-2012:
– calculated settlement from excavations correspond well with measured displacements
– swell is reduced by 20 to 30%, but is still slightly overestimated comparing with measured – swell is reduced by 20 to 30%, but is still slightly overestimated comparing with measured
displacements (about 25% more settlements at point 1004)
correction reference = 1,5 mm
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Conclusions PLAXIS pre- and postdictions
� Conclusions 2D-and 3D-analyses:
– Both measured and predicted displacements do not exceed the maximum allowable displacement limit of 10 mm (or relative rotation of 1 : 500).
– Effect of fresh soil mix dominates the settlement, a realistic (average) stiffness is essential – Effect of fresh soil mix dominates the settlement, a realistic (average) stiffness is essential to make a proper prediction.
– Verification superposition of two 2D-plane strain with 3D-analyses is satisfactory.
– Modelling with HS-small leads to better approach, especially for the effect of excavation B.
– Assumed values for G0ref seem to be proper values (after some sensitivity analyses).
– With HS-small strain model, maximum heave or swell is reduced by 20 à 30%.
– Swell is slightly overestimated (but other effects might have led to measured settlement).
� Recommendations:
– Installation of soil mix walls might lead to small but significant displacements. – Installation of soil mix walls might lead to small but significant displacements.
– To define Go from CU-tests more punctually, smaller strains have to be investigated.
– Further analysis of swell in general is recommended.(special attention to undrained and consolidation behaviour might be useful during the different stages, especially to make distinction to different swell mechanisms - initial volume-constant and elastic swell, primary swell with degree of consolidation, secondary swell etc. - this is one of the investigation topics of
CUR committee C202).
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Project team
� Client: Provincie Drenthe
� Project developer: Draaijer & Partners
� Main contractor: Geveke Bouw BV (TBI)� Main contractor: Geveke Bouw BV (TBI)
� Structural design: IB Wassenaar BV
� Geotechnical design & consult: Grontmij Nederland BV
� Contractor underground constructions: Franki Foundations Group (Besix)