Page 22 - Nov/Dec Vol34 No5

2016 CONFERENCE TECHNICAL SESSION CHATTANOOGA
Ross’s Landing
21st Century Waterfront
Repair Design & Construction
Amid Chattanooga’s successful down-
town revitalization efforts, the city’s eco- ommendations and full
nomic development group moved forward
with enhancements along the Tennessee
River, effectively turning a moderately
equipped boat dock into a world-class
recreation area. Built in 2005, Ross’s Land- repairs.
ing Park was the centerpiece of the City
of Chattanooga’s 21st Century Waterfront
effort to entice residents and visitors to
embrace this picturesque section of the
Tennessee River that intersects the city’s
downtown.
The park hosts numerous events,
including Riverbend Music Festival, the
Head of the Hooch Rowing Regatta and,
most recently, the Iron Man triathlon,
as well as many other craft, music, and
regional festivals, drawing local, national, steep slope, erosion and
and even international spectators and
participants. Ross’s Landing Park is quite
literally the “front porch for the city,”
representing both a link to its past and a
window to its future.
A Crack in the Plan
The cosmetic features of the 21st Cen-
tury Waterfront project include terraced
steps from which a verdant park stretches
inland, a marina, and a generous river
walk with wide walkways and utility-
equipped, modern moorings for daytime
and overnight boaters. But relatively soon
after the project was finished by the con-
struction contractor in 2005, through no
fault of the city, the new sidewalk panels
started to crack, settle, and collapse at
intermittent locations along the shoreline.
It became apparent that settling of terrace
beams, sinkholes around utility boxes, and
concrete cracks and spalls were occurring,
resulting in significant, and potentially
hazardous, structural deterioration of this
relatively new structure.
HDR, a global international engineer-
ing and architectural firm with an office in
Chattanooga, was selected for a multi-
year, three-phase approach to address
the issues: evaluate and investigate the
structure and underlying causes, provide
22 TPW November/December 2016
By Shane R. Womack
schematic design rec- Top: Anchor posts tensioned to the bedrock. Middle:
Pile-cap rebar installation at the mooring pocket.
design documents, and Bottom: Cyclists enjoying the new riverfront.
oversee bid and con-
struction administration Lessons Learned
for improvements and While it would be great to think that
everything always goes according to plan
An in-depth, above- on a major project, it often doesn’t. When
and below-water inves- portions of the 60-foot terrace beams were
tigation of the entire removed from the lowest level, support
riverfront area revealed systems installed by the contractor were
that there was significant not fully effective and the adjacent terrace
loss of material, which beams began to shift and crack. Instead of
was being washed away replacing terrace beams only at the lowest
from the terraced area level of the terraced steps, the design was
below the pile-supported adjusted to also replace adjacent beams
river walk. Identified and supporting material, protecting the
problems included: the terraced steps and walkways on either
side, as well as the upper sections. In the
settlement of the riprap, modified design, the entire lowest terrace
which was allowing fill section was integrated into the sheet-pile
material to migrate; the wall cap.
concrete showed mul-
tiple cracks; fill material was able to shift Construction included the installa-
because it was not well-consolidated and tion of an anchored steel sheet pile wall
because it contained inconsistent and between the river walk and terraced area.
under-compacted materials; and there This anchor wall eliminated migration of
were differences between current on-site the support material below the terraces
conditions and the original construction
drawings, which resulted in unknowns
during the reconstruction process.
The flow of the Tennessee River, con-
trolled by dams upriver, was creating un-
derwater turbulence that was slowly erod-
ing away fill material supporting the river
walk’s structures, including the walkways
and terraced steps. Semi-annual surges
from dam releases caused water levels to
rise as much as 12 feet, evacuating even
greater amounts of fill material from
beneath shoreline structures. Portions
of the structure were literally collapsing
and significant repairs were necessary to
protect the highly trafficked landmark.
The recommended design called for
the replacement of only the lowest level of
terrace beams to facilitate the installation
of sheet piles. These piles would form a
wall to retain the fill material and prevent
it from migrating into the river.