From Modelling to Practice in Geotechnical Engineering
Comité Français de Mécanique des Sols et de Géotechnique
Soil-footing interaction of a building submitted to lateral cyclic loading : centrifuge modelling Luc THOREL, Jacques GARNIER, Gérard RAULT Paris, BGA / CFMS joint meeting
25th november 2005
Outline Introduction Case History Centrifuge test programme Experimental setup Results Conclusions and prospects
Introduction Topic A : Fault-Rupture Soil Structure Interaction Topic B: Strong Seismic Response of Composite Foundation Systems QUAKER B2 : Non linearity of Effect of pile inclination soil-footing interaction Structure
Soft soil
s
D
Horizontal load H
Inclined pile Rough interface
Elastic layer
Vertical load V
B
2B
Bedrock (bottom of the container) B
Saturated clay
Introduction : Objectives Main objectives
Rotation of buildings on shallow footings (cyclic overturning moments)
Determine the relationship between the horizontal load and the rotation of the foundation under static and cyclic horizontal loading
Cyclic loads
Saturated clay
Case History (1)
Izmit (Turkey), 17th august 1999 [AFPS picture]
Case History (2)
Izmit (Turkey), 17th august 1999 Tigcilar District, Adapazari [Gazetas et al. 2003]
Centrifuge test programme (1) 1 - Building •
Geometry : square footing (B = 10 m)
•
Vertical load = Dead weight
•
2 – Soil
Two buildings
Soft saturated clay : Undrained shear strength increasing linearly with depth (CPT tests)
3 – Loading programmes •
Vertical monotonic loading to failure
(→ Determination of vertical bearing capacity)
•
Horizontal monotonic loading to failure (with constant vertical dead weights M1 or M2)
•
Cyclic horizontal loading under self weight (with and without a sand layer below the footing)
Centrifuge test programme (2) Seven containers (Tub1 to Tub7), fifteen tests (T1 to T15) Vertical bearing capacity : Four tests in Tub1, Tub2 & Tub3 Horizontal monotonic loading -Without sand layer -With a sand layer Horizontal cyclic loading -Without sand layer -With a sand layer
Building M1 : 4 tests (T7, T9, T10, T14) Building M2 : 1 test (T12) Building M1 : 1 test (T13) Building M2 : 1 test (T15)
Building M1 : 2 test (T9, T10) Building M2 : 1 test (T11) Building M1 : 1 test (T13) Building M2 : 1 test (T15)
Experimental set-up Lateral cyclic loading under constant vertical load Vertical dispa cem ent transducers servo-actuator displacem ent transducer
Settlem en t transducers
H orizontal displacem ent transducer
Fork Load cell Axe
C-D64 & C-D17
IDH 76
B Beam
A D D W ater level
Soil vertical displacem ent transducer Soil level
W ater level
H W D 32 P P T (C -P 8 0 - 60 m m )
Connecting pipe P PT (C -P9 7 -16 0 m m )
Clay layer n°4
Clay layer n°3
C lay layer n°2 WP107 L ayer n °1 - dra ining sa n d
Experimental set-up : Model building Two model buildings (100G tests) - Heavy building M1 (Weight 1370 t)
Vertical load = 60% of vertical bearing capacity
- Light building M2 (Weight 580t)
Vertical load = 26% of vertical bearing capacity
Square footing: 10m x 10m
PPTs PPTs
Model building M1
Model building M2
Experimental set-up : lateral loading device Cyclic loading device
Model M2 after the test
Servo-jack LVDTs
Load cell
LVDTs
Loading direction Load cell Building model
PPTs
Experimental set-up : Instrumentation
Load cell Building M1
Vertical and horizontal displacements ID V 6 2
ID V 6 3 ID V 6 6
ID H 7 6
L o a d cell F 5 1
IP 76 IP 98 IP 118 IP 116
SD 79 SD 58
+ /- 0 .1 2 b
0 .2 2 b 0 .2 5 b
+ /-0 .3 5 b
Pore pressure at the base
Pore pressure below the footing
Loading direction
Experimental set-up : In the Centrifuge
Building M1
Building M2
Results : Vertical undrained loading tests Comparison between theoretical and experimental data
cu = 0.19σ ' v OCR 0.59
1-Undrained shear strength cu
Shear strength at depth z = 15m (about 1.5B to 2B) Theoretical value:
'c=560kPa
'v=15x7=105kPa
Experimental values (100G CPT tests):
cu=54kPa
Tub01 cu= 64kPa Tub03 (1st consolidation) cu= 81kPa Tub04 (last consolidation) cu= 66kPa Tub05 (last consolidation) cu= 75kPa
2-Vertical bearing capacity qr Tub & Test
qr (kPa) Exper.
qc (kPa)
Ncz (Tables JPG)
qr (kPa) Theor.
Tub01-Test01 Tub02-Test03 Tub02-Test04 Tub03-Test06
156 258 240 220
12.5+3.24z No CPT test No CPT test 18.5+4.24z
9.49 ??? ??? 9.83
141 ??? ??? 216
Results : Monotonic lateral loading 2.5 2.0
Lateral static resistance
1.5 1.0 0.5 0.0 -0.5 -1.0
test 9 - fir
-1.5
m notonic loading
Test 7
te t 9 - las mo ot nic loadi g
t 0
b
d un oadin (
Test e 9
er ycli sequences (se
Model M1
-2.0 0.0
0.2
0.4
0.6
Prototype horizontal displacement at the gravity center (m)
0.8
Results of monotonic lateral loading on building M1 (Tests 7 and 9) Ultimate monotonic resistance before cyclic loading (HR & MR) Building M1 Building M2
HR = 1.4 MN HR = 0.75 MN
(MR = 14 MN x m) (MR = 7.5 MN x m)
Results : Horizontal cyclic loading (1) Building M2 without sand layer
Load vs. Time
3a
10
Cyclic sequences (LC) : 1a & 1b – 1st cyclic sequence : 2 x 10 cycles at 0.16 HZ ± 3 daN
Force (daN)
5
1a
1b
2
4
2a
4
3b
2b
0
-5
2a & 2b – 2nd cyclic sequence : 2 x 10 cycles at 0.16 Hz ± 6 daN
-10 0
6
8
10
12
14
T im e (m inu te) vs. Time Horizontal displacement
16
18
16
18
20
4 – 4th cyclic sequence : 8 cycles at 0.16 Hz ± 10 daN
Failure under the 4th cyclic loading sequence : HR ~ 1MN prototype scale
horizontal displacem ent at the head of the building : ID H 76 Horizontal displacement (mm)
3a & 3b – 3rd cyclic sequence : 2 x 10 cycles at 0.16 Hz ± 8 daN
H orizontal displacem ent at the gravity center : W aSV 1 15 ID H
10 7
L oa
5
76
W aS
5 d F5
V1
dim en sio ns o f the fo undation b = 100 m m ; h = 165 m m
0 0
2
4
6
8
10
T im e (m inu te)
12
(Test T11, Tub 5)
14
11
Results : Horizontal cyclic loading (2) Vertical displacement vs. Time
Building M2 without sand layer
10 ID V 63
2a & 2b – 2nd cyclic sequence : 2 x 10 cycles at 0.16 Hz ± 6 daN 3a & 3b – 3rd cyclic sequence : 2 x 10 cycles at 0.16 Hz ± 8 daN 4 – 4th cyclic sequence : 8 cycles at 0.16 Hz ± 10 daN
Failure under the 4th cyclic loading sequence (HR ~ 1MN)
Vertical settlement (mm)
1a & 1b – 1st cyclic sequence : 2 x 10 cycles at 0.16 HZ ± 3 daN
ID H 76
ID V 63 & ID V 66
S D 79 S D 58
6
L oad ce ll F55 b /4
4
0 .2 2 b 0 .2 5 b
2
ID V 62 S D 79 SD 58
0
θ (°)
0
2
4
6
8
10
12
Tim e (m inute)
14
16
18
16
18
Rotation vs. Time
0.0
1a
-1.0 Pressure variation (kPa)
Cyclic sequences (LC) :
ID V 62
ID V 66
8
1b
-2.0
2a
2b
3a
-3.0
3b
-4.0 -5.0
4
-6.0 -7.0 -8.0 0
2
4
6
8
10
Tim e (m inute)
12
(Test T11, Tub 5)
14
12
Results : Horizontal cyclic loading (3) Building M2 without sand layer
Pore pressures at the interface soil building vs. Time 30
2a & 2b – 2nd cyclic sequence : 2 x 10 cycles at 0.16 Hz ± 6 daN
1a
10
-10
3a
3b
P Pt IP 121 (at +0.12 b : interface soil/building)
-20
P Pt IP 119 (at -0.12 b : interface soil/building)
4
P Pt IP 120 (at -0.35 b : interface soil/building
-30
3a & 3b – 3rd cyclic sequence : 2 x 10 cycles at 0.16 Hz ± 8 daN
2
4
6
8
12
14
16
18
Pore pressures below the building B2
IP 120 IP 119 IP 121 IP 122
L o ad cell F 55
-5 b /6
-b /3 + b /3
IP 112
20.0
IP 105
30.0 IP 115
Pressure variation (kPa)
10
Tim e (m inute)
50.0
40.0
Failure under the 4th cyclic loading sequence (HR ~ 1MN)
1b
P Pt IP 122 (at +0.35 b : interface soil/building)
0
4 – 4th cyclic sequence : 8 cycles at 0.16 Hz ±10 daN
2b
0
IP 113
1a & 1b – 1st cyclic sequence : 2 x 10 cycles at 0.16 HZ ± 3 daN
2a
20 Pressure variation (kPa)
Cyclic sequences (LC) :
+ 5 b /6
10.0
0.0
-10.0 0
2
4
6
8
10
Tim e (m inute)
12
(Test T11, Tub 5)
14
16
18
13
Results : Horizontal cyclic loading (4)
Cyclic sequences (LC) :
1a & 1b – 1st cyclic sequence :
2 x 10 cycles at 0.16 HZ ± 3 daN
2a & 2b – 2nd cyclic sequence :
5 Loa
0
4 – 4th cyclic sequence :
8 cycles at 0.16 Hz ±10 daN
Failure under the 4th cyclic loading sequence (HR ~ 1MN)
IDV 62
76
5
5 d F5
0
dim en sio ns of th e fou nd ation b = 100 m m ; h = 165 m m
-5
1a & 1b
2a & 2b
-10
-10 -0.20
Overturning moment prototype (MN x m)
2 x 10 cycles at 0.16 Hz ± 8 daN
ID H
-5
2 x 10 cycles at 0.16 Hz ± 6 daN
3a & 3b – 3rd cyclic sequence :
10 IDV 66
10 IDV 63
Overturning moment prototype (MN x m)
Building M2 without sand layer
Overturning moment prototype vs rotation
-0.10
R otation (degree)
0.00
-0.4
10
10
5
5
0
0
-5
-5
-10
3a & 3b -2.0
-1.0
0.0
0.0
4
-10
rotation (degree)
-0.2
R otation (degree)
-8
-6
-4
-2
R otation (degree)
(Test T11, Tub 5)
0
14
Results : Horizontal cyclic loading (5) Effect of a sand layer below the footing (e=0.05B)
Filling with sand
Excavation in the clay
Two tests with a sand layer - Building M1 (Test T13) - Building M2 (Test T15) View after loading the test
Results : Horizontal cyclic loading (6) Effect of a sand layer below the footing 2
Lateral static resistance
Load Controlled
1 0 -1 -2 0
10
20
30
40
50
Time (mn) 60
Example of cyclic lateral loading sequences (Test 13) 80
Vertical displacements
60
3
40 20 0 -20
Horizontal displacements
-40 -60 -80 0
10
20
30
40
50
Time (mn)60
Building displacements under the cyclic loading sequences (Test 13)
(T13, M1)
Results : Horizontal cyclic loading (7) Effect of a sand layer below the footing ID V 62
ID V 63
15
ID V 66
ID H 76
10 L o a d ce ll F 5 5 S D 79
5
SD 58
0
-5
0 .2 2 b
42
43
44
Time (mn)
0.2 5 b
+ /- 0 . 1 2 b
45
+ /- 0. 35 b
Pore pressure at the base (Test 13, last cyclic loading sequence) 40.0
IDV 63
ID V 62
I DV 66
IDH 76
30.0 20.0 S D 79
10.0
SD 5 8
L o a d c ell F55
0.0 b/4
-10.0 42
43
44
Time (mn)
-b /3
45
- 5 b/6
+ b/ 3 + 5b /6
Pore pressure below the footing at depth B/4 (Test 13, last cyclic loading sequence)
Results : Effect of cyclic sequences on lateral resistance
M (MN.m)
2 5 .0
Test T9 (after cycles) 3 Test T10 (after cycles)
2 0 .0
1 5 .0
Test T14 Test T7 Test T9
1 0 .0
5 .0
Tests on Building M1
2
0 .0
1
-5 .0
-1 0 .0
1 - r e m o v i n g t h e b u i l d in g in t h e in it i a l p o s it io n 2 - s h if t d u e to c y c lic s e q u e n c e s 3 - la s t h o r iz o n ta l s ta tic s e q u e n c e
- 3 .0
-2 .0
-1 .0
Rotation(degree)
θ (°) 0 .0
Results : Effect of cyclic sequences on lateral resistance (2)
V (MN)
30
Vertic al load (M N )
25 20 15
Building M1
Be fo re cycle s
10
Afte r cycle s
Building M2
5 0 0
5
10
15
20
Ov erturning moment (MN x m)
Failure envelope from the centrifuge tests
M (MN.m)
Conclusions & prospects Non-linear load-displacement behaviour Strain accumulation : settlement & rotation Large amount of work being dissipated in the foundation (M-θ curve) Effect of a draining layer at the base of the footing Development (or not) of “suction” on the soil-foundation interface Smaller and more localised variations of pressure below the foundation
Effect of two vertical weight => failure envelope Comparison with numerical analysis (collaboration with University of Athens) Soil reinforcement below the foundation (e.g. piled embankment) Seismic loading (e.g. with the LCPC Shaker)
Contacts : www.lcpc.fr/rms
[email protected] tel : (33) (0)24084 5816 fax : (33) (0)24084 5997
QUAKER Programme : www.dundee.ac.uk/civileng/quaker/
Thank you for your attention
