Embed Size (px)
Citation preview
EFFICIENT DESIGN OF EFFICIENT DESIGN OF VERTICAL MICROPILE
SYSTEMS TO SYSTEMS TO LATERAL LOADING
D J ú Gó P EDr. Jesús Gómez, P.E.
Andy Baxter, P.G.y ,
OutlineOutline
When are micropiles subject to lateral load?How do we analyze them?
Shear Friction Concept“Bending Friction”
ExampleThe case of Crystal Bridges
Where are micropiles subject to lateral l d?load?
Building foundations (earthquake, wind)Basement wall foundationsRetaining wall foundationsExcavation supportTower and stack foundationsMachine foundationsSlope stabilizationSlope stabilization
Bridge and tower foundations
Courtesy: Fundaciones Franki, C.A.
Bridge and tower foundations
Courtesy: Precomprimidos- Venezuela
Bridge and tower foundations
Courtesy: Precomprimidos- Venezuela
Building foundations
PV
Why just not use battered micropiles?
Analysis of vertical micropiles subject to lateral l dloads
A micropile is not good for lateral loading when working aloneIn soils, 10-20 kip is typical maximumUse pile cap-micropile system instead
Shear FrictionShear Friction
Shear FrictionShear FrictionDoes not consider lateral resistance of pile itselfitself
Lateral resistance offered by soil acting on pileShear or bending resistance of pile
Does not consider moment equilibriumOnly translational movement
“Bending Friction”Bending Friction
“Bending Friction”Bending FrictionDoes not consider lateral resistance of pile itselfitself
Lateral resistance offered by soil acting on pileShear or bending resistance of pile
Considers moment equilibriumOnly rotational movementThe larger the lateral load, the larger the resistanceClosed form sol tion ass ming linear elasticClosed form solution assuming linear elastic materials
“Bending Friction”Bending FrictionFailure occurs as:
B i it f il f il/ kBearing capacity failure of soil/rockGeotechnical or structural failure of pile in upliftStructural failure of pile cap in shear or bendingStructural failure of pile cap in shear or bending
In rock, capacity can be very largeIn soils capacity can be larger thanIn soils, capacity can be larger than expectedEfficient design is finding suitable pile capEfficient design is finding suitable pile cap dimensions
“Bending Friction”Bending FrictionShear friction, shear and bending
i t f i il l d lresistance of micropile also develop We have not combined all formulationsThis is not necessarily new. Tiedowns used sometimes in the heel of L-shaped retaining walls
Formulation
FormulationFormulationH
at
σ
l’l’
Formulation
2
bsEl'bpEsE22pEpE
a⋅
⋅⋅⋅⋅++−=
2absE1al'bsE
1tH
sΔ⋅⋅−⋅⋅⋅
⋅=
( ) Δal'Δ
absE6albsE2
−( )sΔapΔ =
ExampleExampleb = 5 ftAllowable bearing pressure = 5 ksfPile cap-soil interface friction angle = 32 p gdegreesYoung’s modulus of soil = 1 000 ksfYoung s modulus of soil 1,000 ksfMicropile : 1 # 14 bar, Fy = 75 ksi. Apparent elastic length = 10 ft Tallow = 108 kipelastic length = 10 ft. Tallow = 108 kipLateral load 30 kip per micropile
Example
20 0
25.0
f)
t = 3 ftt = 4 5 ft
15.0
20.0
Stre
ss (k
sf t = 4.5 ftt = 6 ft
10.0
um B
earin
g
qallow
5.0Max
imu
0.03 3.5 4 4.5 5 5.5 6 6.5 7
Width 'l' of pile cap (ft)Width l of pile cap (ft)
Example
2 00
2.50
g
t = 3 ftt = 4.5 ft
1.50
2.00
ains
t Slid
in t = 6 ft
1.00
of s
afet
y ag
0.50Fact
or o
0.003 3.5 4 4.5 5 5.5 6 6.5 7
Width 'l' of pile cap (ft)Width l of pile cap (ft)
Example
1.20
1.40
t = 3 ftt = 4.5 ft
0 80
1.00
Cap
(deg
) t = 6 ft
0.60
0.80
tion
of P
ile C
0.20
0.40
Rot
at
0.003 3.5 4 4.5 5 5.5 6 6.5 7
Width 'l' of pile cap (ft)
Example
100
120
t = 3 ftt = 4.5 ft
80
100
pile
(kip
)
t = 6 ft
40
60
ift o
n M
icro
p
20
40
Upl
i
03 3.5 4 4.5 5 5.5 6 6.5 7
Width 'l' of pile cap (ft)
Crystal Bridges Museum of American Art
Site Location
Crystal Bridges
Crystal Bridges
Micropile Installation
#20 Williams bar, Fy = 75 ksi, L = 13 ft5.5-inch casing, Fy = 80 ksi, L = 3.5 ftOpen hole drillingp g
Micropiles under wall
Lateral Load Test
Lateral Load Test
0 000 40 80 120 160 200 240 280 320 360 400
Load (kips)
0.00
ches
)
0.10
emen
t (in
c
0.20
Dis
plac
e
0.30
Lateral Load Test
-0.5-0.4-0.3-0.2-0.100.1
Rotation (deg)
0
50
100
150(kip
)
200
250
Load
300
350350
Evidence of lateral deflection
Strain Gauges
Lateral Load TestVERIFICATION LOAD TEST - LOAD TRANSFER FROM STRAIN GAGE DATA
-100 0 100 200 300 400 500 600Load (kip)
Ground Surface
0.00
1.00
2.00
3.00
4 004.00
5.00
6.00
7.00
8.00
Dep
th [f
t]
9.00
10.00
11.00
12.00
13 0013.00
14.00
15.00
16.00
50% DTL 75% DTL 100% DTL 150% DTL 200% DTL50% DTL 75% DTL 100% DTL 150% DTL 200% DTL
Lateral Load Test
Conclusions
Vertical micropile systems can resist significant lateral loadsgTwelve micropiles in rock loaded to 160+ kip without signs of failureIn soils possible to obtain large lateralIn soils, possible to obtain large lateral capacities through efficient design of laterally loaded systemsTesting of micropile systems in soils needed (research effort)Naturally battered micropiles seem moreNaturally, battered micropiles seem more efficient for lateral resistance, but not always practical
Acknowledgement
Andy Baxter, P.G., co-authorPaul Gintonio, Foundation Specialists, installed micropilesAllen Cadden, P.E.
Jesús Gómez, Ph.D., P.E., Schnabel [email protected]
Jesús Gómez, Ph.D., P.E., Schnabel [email protected]@schnabel eng.comjgomez@schnabel eng.com
