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

each section.

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

phase.

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

board

• 640 LF of other multiple pilot-tube guided auger bores

with steel casing.

Tunnel A:

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:

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

head diameter.

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.

Lessons Learned

Iowa Trenchless was able to perform the work within the

proposed schedule. The lessons learned by the project

team were:

• Strong communication between the project’s

stakeholders, starting before the first phases of any

in-ground construction

• Additional geotechnical exploration discovered several

rock formations that changed the original plans and

cost estimates before any construction began.