Iowa Trenchless’s Lower Connor Creek Interceptor project
involved installing more than 12,500 linear feet (LF) of
36-in. gravity sewer pipe, and more than 5,000 LF of 16-in.
force main for Wyandotte County, Kansas, and Kansas City,
Kansas. For 2,600 LF of the project, trenchless construction
methods were required.
The 2020 contract was awarded to Rodriguez Mechanical Contractors of
Kansas City, with the trenchless work being a collaboration between NUCA
members Midwest Mole and Iowa Trenchless. Before the work began,
open-communication and teamwork between the municipal owners,
engineer, prime and subcontractors was essential in identifying the need
for additional geotechnical exploration. Once the results of that exploration
were obtained, it was used to better define the right trenchless methods for
Due to the nature and location of the dirt-rock interface, each trenchless
section had a possibility of encountering a mixed-ground (soil and rock)
condition. Because the project stakeholders undertook several rounds of
additional subsurface exploration along both project alignments, a better
plan forward was developed. The open-communication and the additional
geotechnical work proved to be key to the success of each trenchless
Bedrock conditions in the project areas was found to be higher than
expected, which conflicted with the soft ground tunnel method originally
chosen by engineers. Had this subsurface condition gone undetected
and the tunnel started with a soft ground tunnel boring machine
(TBM), it would have been potentially disastrous to the project. It could
have resulted in the abandonment of the TBM and unfinished tunnel,
or emergency excavation in the roadway right-of-way
approaching 50-ft. deep. Additional permitting requirements,
a significant disruption to the public, along with additional
costs would have followed. This supplemental subsurface
exploration saved the owners and contractors a substantial
amount of expense and additional work.
A unique mix of three trenchless methods were used to cross
a local highway and a Class 1 railroad track:
• Tunnel A: 640 LF of soft ground tunnel boring machine
pipe jacking with steel casing
• Tunnel B: 1,300 LF of rock tunneling with ribs and
• 640 LF of other multiple pilot-tube guided auger bores
with steel casing.
Tunnel A consisted of 640 LF of 59.5-in. steel casing in soft
ground. The additional geotechnical subsurface investigation
discovered a bedrock knoll between the tunnel’s start and
ending points. This new information allowed a re-evaluation
of the original route, which led to the tunnel’s realignment
and lengthening (from 570 LF to 640 LF). This extra length
was required by Kansas DOT interstate requirements and to
avoid the subsurface rock knoll.
This crossing design was completed with an Akkerman 480
TBM with a closed-face cutterhead. Iowa Trenchless used
59.5-in. OD Permalok steel casing as the initial tunnel liner
and pushed with a 1200-ton hydraulic jacking frame. The
selection of interlocking steel casing pipe helped achieve
production rates as high as 60-feet per shift, with an average
of 35-feet per shift. Lubrication of the tunnel was also a
contributing factor in the successful installation, with no
intermediate jacking stations needed.
Tunnel B was designed to be installed in 1,300 feet of
interbedded limestone and shale bedrock, but little was
known about the quality and characteristics of the rock.
Communication and the additional geotechnical work
identified hard, consistent, quality limestone strata across the
route. This led to the decision to use a custom-built 66-in.
TBM heavily modified to achieve optimized penetration rates
in the solid rock. Midwest Mole used steel ring beam and
wood lagging as the tunnel liner, with sets being built behind
the ATM and expanded to match the 67.25-in. cutterhead
The decision to select this segmented tunnel lining approach
was found to be the key to success, as it significantly
reduced the jacking required for the 1,300 foot crossing.
Tunnels A and B each housed the final product of 36-in.
HOBAS Pipe CCFRMP used as the sanitary interceptor
sewer for the municipality owners. The final product pipe
was threaded, blocked, and grouted in place with lowdensity
cellular concrete placed in multiple lifts.
Guided Auger Boring of Stell Casing:
Other trenchless methods used for the project included
24-in. and 30-in. steel casings installed using an Akkerman
240A guided boring machine (GBM) and Michael Byrne
and Barbco auger boring machines (ABM).
What made this project unique was the panoply of
work being performed within a single contract: A strong
stakeholder team, communication resulting in recognizing
the need of additional geotechnical work, and the physical
requirement of soft ground tunneling, hard rock tunneling,
and guided auger boring.
Successful communication and strong collaboration by
Rodriguez Mechanical, Iowa Trenchless, Midwest Mole,
George Butler Associates (professional engineering
services), Unified Government of Wynadotte County Public
Works Department, and Kansas City, Kansas, overcame the
many challenges of this project and made it a success.
Iowa Trenchless was able to perform the work within the
proposed schedule. The lessons learned by the project
• Strong communication between the project’s
stakeholders, starting before the first phases of any
• Additional geotechnical exploration discovered several
rock formations that changed the original plans and
cost estimates before any construction began.