Dynamic Earth pressure - Myths, Realities
and Practical Ways for Design
Carlos Coronado and Javeed Munshi
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Presentation Outline
 Introduction and Background
 Standard Practice

Simplified Determination of Lateral Earth Pressures

Hydrodynamic Fluid Pressures

Review of Lateral Soil Pressure Theories

Recent Experimental Results
 Detailed Seismic Fluid Soil Structure Interaction

Detailed fluid-structure interaction

Simplified fluid modeling

Seismic soil structure interaction
 Case Study Intake Pump Station
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Introduction and Background
Force Diagram of Subsurface Walls - Static
Conditions
STATIC
surcharge, w
ground surface
compaction
groundwater
compaction
Building Weight, W
H
surcharge
surcharge
Hw
water
at-rest
Hydrostatic
Uplift, U
water
at-rest
K0g'H
K0w
gwHw
N=W-U
Applicable loads
at-rest earth pressure
surcharge stress from surface loading
compaction stresses from Duncan's method (1991 and 1993)
U = buoyancy due to water table
N = normal stress along basemat
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Force Diagram of Subsurface Walls – Seismic
Without Movement
SEISMIC - NO MOVEMENT
surcharge, w
ground surface
compaction
groundwater
compaction
Building inertia
Building Weight, W
seismic increment
H
surcharge
Hw
water
at-rest
Vertical
Seismic, V
surcharge
traction
(front and
back walls)
Hydrostatic
Uplift, U
water
at-rest
K0g'H
Base Friction = m N , where N = W - U - V
+ Base adhesion
K0w
gwHw
Applicable loads
at-rest earth pressure
surcharge stress from surface loading
compaction stresses from Duncan's method (1991 and 1993)
U = buoyancy due to water table
V = vertical seismic force
N = normal stress along basemat
base friction using interface coefficient, m
traction = friction along building sides = at-rest pressure x msides
msides = friction coefficient along sidewalls of structure
seismic increment = horizontal base forces from SASSI output include all driving forces,
composed of those from seismic, at-rest, and building inertia
Sliding check
Compare SASSI basemat horizontal forces (Demand = D)
against basemat frictional/adhesional resistance (Capacity = C).
If FS = C/D  1.1, then building is stable against sliding
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Force Diagram of Subsurface Walls – Seismic
With Movement
SEISMIC - WITH MOVEMENT
surcharge, w
ground surface
groundwater
Building inertia
Hw
K = at-rest
increasing to
passive with
movement
seismic
increment
Building Weight, W
H
traction
(front and
back walls)
Vertical
Seismic, V
active
Hydrostatic
Uplift, U
Kag'H
Kg'H
Base Friction = m N (m reduced 25%)
where N = W - U - V
+ Base adhesion
Applicable loads
resisting earth pressure is dependent on amount of movement
surcharge stress from surface loading
U = buoyancy due to water table
V = vertical seismic force
N = normal stress along basemat
reduced base friction using interface coefficient, mred
reduced traction = friction along building sides = at-rest pressure x msides_red
msides_red = reduced friction coefficient along sidewalls of structure
seismic increment = horizontal base forces from SASSI output include all driving forces,
composed of those from seismic, at-rest, and building inertia
Sliding check
Compare SASSI basemat horizontal driving forces (Demand = D)
against basemat friction/adhesion + side friction + passive resistance (Capacity = C)
using reduced resistance coefficients for frictional/adhesional components
If FS = C/D  1.1, then building is stable against further sliding
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Standard Practice for Partially or Fully
Buried Liquid-containing Structures
Total Base Shear and Wall Pressures
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Practical Earth Pressure Analysis
 Select all potential critical interface combinations at the
base and sides of the structure on which to determine the
minimum base frictional resistance.
 Compare base and side frictional resistance to seismic atrest demand. If C/D > 1.0, then use seismic at-rest
demand to design walls.
 If the C/D < FS, then sliding will occur. Then reduce base
and side friction coefficients by 25%. loading side of the
structure will be subject to the active earth pressure, the
seismic lateral active earth pressure increment, and the
building inertia. Increase resisting load on the passive
side, until C/D ≥ 1.0.
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Sliding or wall rotation must occur for K < K0
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Hydrodynamic Pressures (ACI 350)
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Seismic Active and At-Rest Lateral Earth
Pressure
NCHRP 611
𝑐𝑜𝑠 2 (𝜙 − 𝜃 − 𝛽)
𝐾𝐴𝐸 =
𝟐
cos 𝜃 cos 2 𝜷 cos(𝛽 + 𝜃 + 𝛿) 1 +
PAE = 0.5gH2(KA+DKAE)
sin 𝜙 + 𝛿 sin(𝜙 − 𝜃 − 𝑖)
cos(𝛽 + 𝜃 + 𝛿) ∗ cos(𝑖 − 𝛽)
pAD = DKAE·g·(H-z) DKAE~0.75kh
𝜽 = tan−1
𝑘ℎ
1 − 𝑘𝑣
p0D = 2DKAE·g·(H-z)
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Dynamic Soil Pressures ASCE 4-98
(Wood 1973)
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Soil Pressures Sample Calculation
H = 20 ft.
q = tan-1(0.25) = 14o
KAE = = 0.48
KA = 0.31
DKAE = 0.48-0.31 = 0.17
DKAE ~ 3/4·0.25 = 0.1875, use 0.17
g moist = 120 pcf
g sub = 120-62.4 = 57.6 pcf
EL 0’
EL -5’
g = 120 pcf
Kh = 0.25
K0S = 1-sin(32o) = 0.47, use K0S = 0.5
DK0E = 2DKAE = 2·0.17 = 0.34
0’
-5’
 = 320
EL -20’
249 (498) psf
249 (498) psf
0 psf
186 (300) psf
333 (594) psf
147 (294) psf
-20’
454 (732) psf
Static Earth Pressure
0 psf
Seismic Earth Pressure
936 psf
Hydrostatic Pressure
1390 (1668) psf
Total Pressure
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Ground Water Considerations
 if the backfill is well drained, seismic ground water
pressures need not be considered. In this case,
only hydrostatic pressures are taken into
consideration:
pW = gWz
Whitman, RV (1990) suggests that the seismic ground
water thrust exceeds 35% of the hydrostatic thrust for
kh>0.3g.
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Influence of Wall Movement on Intensity of
Earth Pressures in Cohesionless Materials
SEISMIC - NO MOVEMENT
surcharge, w
ground surface
compaction
groundwater
compaction
Building inertia
Building Weight, W
seismic increment
H
surcharge
Hw
traction
(front and
back walls)
water
at-rest
surcharge
Vertical
Seismic, V
Hydrostatic
Uplift, U
water
at-rest
K0g'H
K0w
Base Friction = m N , where N = W - U - V
+ Base adhesion
ground surface
gwHw
Applicable loads
at-rest earth pressure
SEISMIC
- WITH MOVEMENT
surcharge stress from
surface loading
compaction stresses from Duncan's method (1991 and 1993)
U = buoyancy due to water table
V = vertical seismic force
N = normal stress along basemat
base friction using interface coefficient, m
traction = friction along building sides = at-rest pressure x msides
w
m
= friction coefficientsurcharge,
along sidewalls
of structure
sides
seismic increment = horizontal base forces from SASSI output include all driving
forces,
groundwater
composedBuilding
of thoseinertia
from seismic, at-rest, and building inertia
Sliding check
K = at-rest
increasing to
passive with
movement
Compare SASSI basemat horizontal forces (Demand = D)
Building Weight, resistance
W
against basemat
frictional/adhesional
(Capacity = C).
H
If FS = C/D  1.1, then building is stable against sliding
Hw
traction
(front and
back walls)
active
Hydrostatic
Vertical
Uplift, U
Seismic, V
seismic
increment
Kag'H
Kg'H
Base Friction = m N (m reduced 25%)
where N = W - U - V
+ Base adhesion
Applicable loads
resisting earth pressure is dependent on amount of movement
surcharge stress from surface loading
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
U = buoyancy due to water table
Experimental Results
Recent Experimental Studies (PEER 2007/06)
Centrifuge model configuration
Stiff and flexible model structures configuration
L. Atik and N. Sitar (2007)
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Representative Experimental Results
L. Atik and N. Sitar (2007)
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Maximum total dynamic pressure
distributions measured and estimated
L. Atik and N. Sitar (2007)
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Detailed Seismic Fluid Soil Structure
Interaction
Fluid Structure Interaction
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Seismic Soil Structure Interaction
Substructuring in the Flexible Volume Method
Substructuring in the Substructure Subtraction Method
(SASSI2010 Theory Manual)
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Case Study: Intake Pump Station
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Structure Geometry
Traveling Screen
Enclosure
2'-0"
EL. + 26'-6"
EL. + 11'-6"
(Operating Deck)
Pump house Enclosure
EL. + 11'-6"
(Operating Deck)
Slanting/
Skimmer Wall
EL. + 20'-6"
Pump Room
Slanting/
Skimmer Wall
2'-0"
EL. +0'-0" (Maximum
Operating Level in Forebay)
Baffle Wall
EL. (-) 8'-0"
EL. (-) 11'-0"
Baffle
Wall
EL. (-) 10'-0"
Bar Screens
EL. + 10'-6"
EL. + 10'-0"
3'-0"
3'-0"
Expansion
Joint
Staircase
Enclosure
EL. + 3'-0" (GWT)
EL. (-) 5'-6"
5'-0"
EL. (-) 10'-0"
UHS Electrical
Building
Y
EL. (-) 22'-6"
X
Circulating Water
Intake Structure
5'-0"
Forebay Structure
UHS Intake Structure
X
60" dia.
Intake Pipe (TYP)
Debris Basin
Slab
Z
105'-11" (including
slab on grade portion)
59'-0"
33'-0"
18'-6"
CWS Makeup Water
Intake Structure
74'-0"
7'-0"
60'-0"
36'-6"
Pump House
Enclosure
Electrical
Room Slab
100'-0" (clear
dimension)
Debris Basin
Slab
Expansion
Joint
80'-0" (clear
dimension)
Pump House Enclosure
Slab on grade
Forebay Structure
UHS Electrical
Building
UHS Makeup Water
Intake Structure
CCNPP
Unit 3
NORTH
26'-6"
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Overall Analysis/Design Approach

The finite element model of the structures is developed
using GT STRUDL Version 29.1.

Lumped Mass is used to model the Hydrodynamic Load.

The SSI analysis is performed using Site-Specific Input
Ground Motion and three soil cases (UB, BE and LB).

The FE model used for the SSI analysis is modified to
obtain the static response of the structure, using GT
STRUDL.

Only critical panels are designed. Microsoft Excel
Workbook is used to combine element forces and
moments from static and SSI analyses, for these critical
panels.
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Finite Element Model, Showing Critical Panels
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Hydrodynamic loads
CCNPP Unit 3 NORTH
208, 1454
208, 1454
207, 1449
(a) Actual distribution
(b) Idealized distribution
Equivalent weights of accelerating liquid
207, 1449
Impulsive Weight Distributions
Wiy.ew( y ) 
Wi.ew
2

208, 1454
208, 1454
L 


 tanh 0.866 ew  

HL  


 W
Wi.ew  
 L
L
ew


 0.866 H

L


Height to centers of gravity EBP
 4HL  6 hi.ew   6 HL  12 hi.ew   Hy


 L
HL
2
hi.ew 
Lew 
L

  H if ew  1.333
0.5  0.09375
L

HL 
HL


( 0.375)  HL otherwise
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Comparison of Acceleration Transfer
Functions
EQx
EQy
EQz
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
SSI Model
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Sample Results
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Design of Walls and Slabs
Forces and moments computed after combination of seismic
and static results are used for the design of each critical
panel, using a Microsoft Excel Workbook, as outlined next
and described in detail later.
a. Design for In-plane shear using full section cuts.
b. Design vertical and horizontal sections for out-of-plane
moments and axial forces using a P-M interaction
analysis.
c. Conservatively add the reinforcement from steps a and b
d. Check out-of-plane shear for the whole wall, or whole
segments on either side of openings, based on average
shear.
e. Check for punching shear where required.
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Design of Walls and Slabs
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Conclusions
Simplified and detailed approached for the dynamic
analysis of embedded liquid containing structures
where presented. Conclusions and recommendations
are as follows:
 Additional guidelines are required for the calculations
of dynamic earth pressures. In particular regarding
the use of active or at rest dynamic soil pressures.
 Detailed soil structure interaction analyses can
provide additional inside regarding the behavior of
embedded liquid containing structures. However they
are only warranted for critical structures.
Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Thank You!