37C_Chowdhury_GeoTech Challenges in Levee Inv_Design

2014 Floodplain Management
Annual Conference
Santa Clara, California
September 3, 2014
GEOTECHNICAL CHALLENGES IN LEVEE
INVESTIGATION AND DESIGN
Khaled Chowdhury, PE, GE
URS Corporation
Sacramento, California
Outline
 Distress Modes for Evaluation
 Integrated Approach for Geotechnical Evaluation of
Levees
 Construction History, Past Performance, and
Geomorphology
 Examples of Levee Evaluations and Design
oTs ……………………
 Connecting the d
 Acknowledgements
LESSONS FROM LEVEE PROJECTS
IN THE CENTRAL VALLEY
Urban and Non
Urban Levee
Evaluations
Periodic
Inspection and
Levee Screening
Feather River
West Levee
Project
North Area
Streams Levee
Improvement
Project
INTEGRATED LEVEE EVALUATION APPROACH
Geotechnical Analysis
Construction History
 CONSIDERATIONS OF RECENT UPDATES IN
 LEVEE CONSTRUCTION PRACTICE OF THE
EARLY TWENTIETH CENTURY
STATE OF THE PRACTICE AND CALIBRATE
WITH PAST PERFORMANCE
Past Performance
 DETAIL DOCUMENT REVIEW UNDER
DWR/URS STUDY
Topography and Bathymetry
 LiDAR TOPOGRAPHY AND BATHYMETRY
Geology and Geomorphology
 LEVEL 2-II GEOMORPHOLOGY
Geophysical Survey
 DIFFERENTIAL RESISTIVITY PROFILE FROM
HEM SURVEY
Subsurface Investigations
 SUBSURFACE INVESTIGATION AT TARGETED
LOCATIONS
Cost Effective Mitigation Measures
 A BETTER UNDERSTANDING OF PAST
PERFORMANCE AND EXISTING CONDITIONS
RESULTS IN COST-EFFECTIVE SOLUTIONS
Original Construction of the Central Valley Levees
Typical Levee and Distress Mechanisms
Slope Stability
Through Seepage
Underseepage
Blanket (Low Permeability)
Aquifer
Aquiclude
4
Levee Distress Mechanisms in Action
Geotechnical Levee Failure in Major Floods
1955 Feather River West Levee Break Near
Yuba City – Underseepage
1986 Linda Levee Break Near Yuba
River - Underseepage
1997 Feather River East Levee Break
Near Arboga– Underseepage
Heavy
Seepage
Past Performance and Geomorphology
of the Yuba City Area
Bank Erosion
Bank and Levee
Erosion
Heavy Seepage
and Boils
Heavy Seepage
and Boils
Bank Erosion at
Pump Structure
Scour in Bank
26 Sink Holes
17 Boils
3 Boils
2 Boils
6 Boils
Source: Letter
from LD1 to Local
Congressman Vic
Fazio, February
17, 1997
Boils
Slope Caving
at Toe Ditch
Recent Channel (Rch), Alluvium
(Ra), and Meander Scroll (Rms)
Deposits in Yuba City Area
Recent Crevasse Splay (Rcs), Overbank
(Rob), and Channel (Rch) Deposits in
Abbott Lake/Star Bend Area
COST SAVING MEASURES IN FRWL PROJECT
Phase 1:
 37 MILES OF LEVEE
IMPROVEMENT PROJECT
 Contract Award: 2010 Spring
 Geotech for Pre-Design
Formulation: 2011 Spring
 Final GDRR: 2012 October
 Construction Begin: 2013
Summer for northern 37
miles
 Construction
Complete:
2015 December
Rebuilt levee degrade portion with a “Clay Core”
and re-usable existing materials in shells
Cutoff Walls– Deep Fully-Penetrating vs.
Shallow “STITCHED BLANKET” Conditions
Seepage Berm in Dredge Tailing Area
with Locally Available Materials
ABBOTT LAKE:
FULLY PENETRATING WALL (SOUTHERNPART) AND
PARTIALLY PENETRATING WALL WITH RELIEF WELLS (NORTHERN PART)
 Heavy seepage and boil in
previous flood events
 Waterside borrow likely to
eliminate blanket and
increased underseepage risk
 Existing relief wells did not
prevent heavy seepage and
boils (as high release points)
 Thin fine-grained blanket
underlain by thick aquifer
directly connected with river
ABBOTT LAKE:
FULLY PENETRATING WALL (SOUTHERNPART) AND
PARTIALLY PENETRATING WALL WITH RELIEF WELLS (NORTHERN PART)
 Differential resistivity profile
match well with borings and CPTs
 Fully-penetrating wall when
aquiclude is thick and continuous
 Relief wells to complement
partially penetrating cutoff walls
when thin and discontinuous
aquiclude
- Use of existing pump station
- Use of conventional wall system
instead of DSM or DMM
LOCATION OF A SAND BOIL (REMNANTS STILL VISIBLE)
 Remnants of a sand boil from 1986
flood – about 10 feet diameter
 Recent deposits such as Overflow
Channels (Rofc), Overbank (Rob),
Alluvium (Ra)
 Ponds on both sides reduce
blanket
LOCATION OF A SAND BOIL (REMNANTS VISIBLE)
 HEM match well with
subsurface - thin finegrained blanket
 Ponds on both sides reduce
blanket
 Fully-penetrating cutoff
wall
FULLY PENETRATING WALL IN 1955 LEVEE BREACH AREA
 Recent Meander Scroll (Rms) deposits i.e.
River used to be here
 HEM – Differential Resistivity profiles
match well with subsurface explorations
 Thin blanket underlain by thick aquifer
 Coarse-grained (SP-SM) levee
 Fully – penetrating cutoff wall
CUTOFF WALL (DMM AND CONVENTIONAL)
CONSTRUCTION IN 1955 LEVEE BREAK AREA
DMM Wall Construction
Shallower Conventional Wall
NEMDC EAST LEVEE IN SACRAMENTO
 Subsurface Explorations, Differential
Resistivity Profile, and Geomorphology
Maps – Presence of Mapped Recent
Channels
 Cost Effective Measure (Waterside Toe
CB Cutoff Wall) as an Extension to
SAFCA’s Previous Work in 1990s
 Shallow Cutoff Wall Confined in Younger
Alluvium
“You can't connect
the dots looking forward; you can only
Topography
/Bathymetrybackwards. So you have to trust that
connect them looking
the dots will somehow connect in your
future.”
Subsurface
Construction
Investigations
Steve Jobs
History
Geology/
Geomorph
Geophysical
Survey
Strategy for geotechnical evaluation and design of
Past projects: CONNECT THE SCATTERED
levee
Performance
Cost
DOTS IN EARLY STAGES OF THE PROJECT
oTs ……
d
Geotechnical
…… Analysis ……
……
Effective
Mitigation
Measures
Any Question on the
oTs ……………………
d