Transcript AASHTO Section 10 Revisions - Virginia Department of

AASHTO LRFD
Section 10.7 and 10.8
Deep Foundations
“BY FAR THIS SECTION HAS BEEN
IDENTIFIED AS THE MOST PROBLEMATIC
SECTION OF THE AASHTO LRFD SPECS.
BY THE STATE DOTS”
10.7
10.7.1
10.7.1.1
10.7.1.2
10.7.1.3
10.7.1.4
10.7.1.5
10.7.1.5.1
10.7.1.5.2
10.7.1.5.3
10.7.2
10.7.2.1
10.7.2.2
10.7.2.3
10.7.2.3.1
10.7.2.3.2
10.7.2.4
10.7.2.5
10.7.2.6
10.7.3
10.7.3.1
10.7.3.1.1
10.7.3.1.2
10.7.3.2
10.7.3.3
10.7.3.3.1
10.7.3.3.2
10.7.3.4
DRIVEN PILES
General
MINIMUM PILE SPACING, CLEARANCE AND EMBEDMENT INTO CAP
PILES THROUGH EMBANKMENT FILL
BATTER PILES
PILE DESIGN REQUIREMENTS
Determination of Pile Loads
Downdrag
Uplift Due to Expansive Soils
Nearby Structures
Service Limit State Design
GENERAL
TOLERABLE MOVEMENTS
settlement
Pile Groups in Cohesive Soil
Pile Groups in Cohesionless Soil
HORIZONTAL PILE FOUNDATION MOVEMENT
SETTLEMENT DUE TO DOWNDRAG
lateral squeeze
Strength Limit State Design
POINT BEARING PILES ON ROCK
Piles Driven to Soft Rock
Piles Driven to Hard Rock
pile length estimates for contract documents
nominal axial RESISTANCE CHANGE AFTER PILE DRIVING
Relaxation
Setup
groundwater effects and BUOYANCY
Deep Foundations Overview

10.7 Driven Piles
 Total re-write

10.8 Drilled Shafts
 Re-organized + new & updated content
Service Limit State (10.7.2)



Vertical Displacement
 Additional equivalent footing diagrams
added
Horizontal Displacement
 P-y method for analysis of horizontal
displacement now specifically called out
 P multipliers for group effects updated
and specified
Overall stability
Vertical Displacement
Horizontal Displacement
(P-y method)
Qt
Ht
Properties
A, E, I
Mt
y
P
y
y
S
P
P
Pm * P
y
D
P-multiplier (Pm)
Spacing (S)
Row 1 Row 2
3D
0.7
0.5
5D
1.0
0.85
Row 3
0.35
0.7
From Table 10.7.2.4-1
Overall Stability
Strength Limit State (10.7.3)



Geotechnical Resistance
 Emphasis of pile resistance verification
during construction
 De-emphasis on use of static analysis
methods except for estimation of pile
length for contract drawings
Structural Resistance
 Axial
 Combined bending and axial
 Shear
Driven Resistance (10.7.7)
Axial Geotechnical Resistance
Static Load Test
Settlement
Load
Pile top settlement
Davidson Method Specified
Dynamic Load Test (PDA)
Method & equations are
now prescribed
Driving Formulas
Driving Formulas

FHWA Gates Method
 Method & Equation Prescribed

Engineering News Method
 Equation Modified to Produce
Ultimate Resistance by Removing the
Built-in Factor of Safety = 6
Driving Formula Limitations

Design “stresses” must be limited if a
driveability analysis is not performed
 limiting stresses prescribed

Limited to nominal resistances below 300
tons
Geotechnical Safety Factors for Piles
Design Basis &
Increasing Design/Const.
Const. Control
Control
Subsurface Expl.
X
X
X
X
X
Static Calculation X
X
X
X
X
Dynamic Formula X
Wave Equation
X
X
X
X
CAPWAP
X
X
Static Load Test
X
X
FS
3.50 2.75 2.25 2.00 1.90
Static Analysis Methods


Existing Methods Retained
FHWA Nordland/Thurman Method Added
Applicability limited to:
- Prediction of pile penetration (used
without resistance factors)
- Rare case of driving to prescribed
penetration or depth (no field
determination of pile axial resistance)
Geotechnical Resistance Factors
Pile Static Analysis Methods
Method
 - Method
 - Method
 - Method
Nordlund-Thurman
SPT
CPT
Group
Comp
0.4
0.35
0.4
0.45
0.3
0.45
0.6
Ten
0.3
0.25
0.3
0.25
0.35
0.5
From Table 10.5.5.2.2-1
Table 10.5.5.2.2-1 Resistance Factors for Driven Piles
CONDITION/RESISTANCE DETERMINATION METHOD
Driving criteria established by static load test(s);
quality control by dynamic testing and/or calibrated
wave equation, or minimum driving resistance
combined with minimum delivered hammer energy
from the load test(s). For the last case, the hammer
used for the test pile(s) shall be used for the
production piles.
Nominal Resistance of
Single Pile in Axial
Compression – Dynamic
Analysis and Static Load
Test Methods, dyn
RESISTANCE FACTOR
Values in Table 2
Driving criteria established by dynamic test with
signal matching at beginning of redrive conditions
only of at least one production pile per pier, but no
less than the number of tests per site provided in
Table 3.
Quality control of remaining piles by
calibrated wave equation and/or dynamic testing.
0.65
Wave equation analysis, without pile dynamic
measurements or load test, at end of drive conditions
only
0.40
FHWA-modified Gates dynamic pile formula (End Of
Drive condition only)
0.40
Engineering News Record (as defined in Article
10.7.3.7.4) dynamic pile formula (End Of Drive
condition only)
0.10
Table 10.5.5.2.2-2 Relationship between Number of Static Load Tests
Conducted per Site and  (after Paikowsky, et al., 2004)
Resistance Factor, 
Number of
Static Load
Tests per Site
Low*
Medium*
High*
1
0.80
0.70
0.55
2
0.90
0.75
0.65
3
0.90
0.85
0.75
>4
0.90
0.90
0.80
Site Variability*
Table 10.5.5.2.2-3 Number of Dynamic Tests with Signal Matching Analysis per Site to Be Conducted
During Production Pile Driving (after Paikowsky, et al., 2004)
Low*
Medium*
High*
Site
Variability*
Number of
Piles
Located
within Site
Number of Piles with Dynamic Tests and Signal
Matching Analysis Required (BOR)
< 15
3
4
6
16-25
3
5
8
26-50
4
6
9
51-100
4
7
10
101-500
4
7
12
> 500
4
7
12
Structural Axial Failure Mode
Structural Flexure Failure
Mode
Structural Shear Failure
Mode
Methods for determining
structural resistance



Axial compression
Combined axial and flexure
Shear
Concrete – Section 5
LRFD
Specifications
Steel – Section 6
Wood – Section 8
Driven Performance Limit
Drivability Analysis (10.7.7)


Specifically required
Purpose is to verify that the specified pile
can be driven:
 To the required minimum penetration
 To the required ultimate resistance
 Using a commonly available hammer
 Without exceeding the permissible
driving stress
 At a reasonable penetration rate
37.5 ksi
Comp Str
ksi
Tens Str
ksi
30
20
10
Ult Cap
kips
550 kip
Stroke
800
ft
16.0
600
12.0
400
8.0
200
4.0
0
160
120 bpf
320
480 Blows/ft
Driven Performance Limit
Extreme Event Limit State (10.7.4 )

New section
with limited
guidance
regarding
extreme events
(no guidance
previously
provided)
Piles - Other Considerations



10.7.5 Corrosion and Deterioration
 Moved from section 10.7.1 with no
major changes
10.7.6 Determination of Minimum Pile
Penetration
 New section combining some of the
existing material from section 10.7.1
with additional guidance.
Downdrag provisions extensively
modified
Downdrag


New provisions in article 3.11.8 regarding
determination of downdrag as a load
Revisions to load factors pending
additional analysis/research
Prediction Method
Piles, -Tomlinson
Piles, -Method
Drilled shafts, O’Neill
and Reese (1999)
Maximum
Minimum
1.4
1.05
-
1.25
-
10.8 DRILLED SHAFTS





Article re-organized to follow section 10.7
Most provisions refer back to section 10.7
Service limit state provisions removed
from strength limit state resistance
determination
Provisions for resistance determination
updated
Detailed procedures for evaluation of
combined side friction and end bearing in
rock added to commentary
10.8
DRILLED SHAFTS
10.8.1
10.8.1.1
10.8.1.2
10.8.1.3
10.8.1.4
10.8.1.5
10.8.1.6
10.8.1.6.1
10.8.1.6.2
10.8.1.6.3
10.8.2
10.8.2.1
10.8.2.2
10.8.2.2.1
10.8.2.2.2
10.8.2.2.3
10.8.2.2.4
10.8.2.3
10.8.2.4
10.8.2.5
10.8.3
10.8.3.1
10.8.3.2
10.8.3.3
10.8.3.4
General
scope
shaft spacing, clearance and embedment into cap
shaft diameter and enlarged bases
batterED shafts
drilled SHAFT resistance
DETERMINATION OF Shaft Loads
General
Downdrag
Uplift
Service Limit State Design
tolerable movements
settlement
General
Settlement of Single-Drilled Shaft
Intermediate Geo Materials (IGM’s)
Group Settlement
HORIZONTAL MOVEMENT OF SHAFTS AND SHAFT GROUPS
settlement due to downdrag
lateral squeeze
Strength Limit State Design
general
ground water table and bouyancy
Scour
downdrag
10.8.3.5
10.8.3.5.1
10.8.3.5.1a
10.8.3.5.1b
10.8.3.5.2
NOMINAL axial COMPRESSION resistance of single drilled shafts
Estimation of Drilled Shaft Resistance in Cohesive Soils
Side Resistance
Tip Resistance
Estimation of Drilled Shaft Resistance in Cohesionless Soils
Drilled Shaft Resistance in Rock
Resistance
Total Resistance
QS
QP
A
Side Resistance
D
Tip Resistance
Displacement
QR = fQn = fqpQp + fqsQs
B
C
Geotechnical Resistance Factors
Drilled Shafts
Method
 - Method (side)
 - Method (side)
Clay or Sand (tip)
Rock (side)
Rock (tip)
Group (sand or clay)
Load Test
Comp
0.55
0.55
0.5
0.55
0.55
0.55
0.7
Ten
0.45
0.45
0.45
0.45
AASHTO Table 10.5.5.2.3-1