By: Andy Duck
When one of our core builders called us to announce their prospective client’s desire to completely redo their beach house on the Sound in Corolla, NC, they mentioned that a new concrete pool would be part of the project. Steve Daniels, of Renaissance Construction Company, Inc., had his designer, Paul Gilbertson, send us preliminary information on the prospective property and the client’s wish list for the backyard. To call it a transformation is a significant understatement
Florent Pastorelli is currently completing his master’s degree in mechanical engineering at Université Laval in Québec City, QC,Canada. Originally from France, where he trained as a mechanical engineer at the Arts & Métiers school, Florent decided to pursue his education in Québec City in the field of robotic engineering. His research project focuses on the automation and optimization of shotcrete placement by the use of a computer controlled robotic arm. This project is part of a larger project developed by Marc Jolin’s Shotcrete Research Team, the SPARO project (Shotcrete Placement Automated by Robot)
By: Steve Kanoza
located in El Paso, TX, the El Paso Zoo sits on 35 acres (1400 m2 ) of land and houses over 220 animal species from around the world. Accredited by the Association of Zoos & Aquariums (AZA), the El Paso Zoo’s mission is to celebrate the value of animals and natural resources and create opportunities for people to rediscover their connection to nature. Locally recognized as the “Best Place to Take Your Kiddos,” the El Paso Zoo features family favorite attractions like African Star Train, Foster Tree House Playground, and now home to the award winning Chihuahuan Desert exhibit.
By: Ryan Oakes
Bald Head Island, off the southern shores of North Carolina is a 6 mi2 (16 km2) island, accessed only by ferry, for guests, and by barge, for construction. It is steeped in history, playing a part in both the American Revolution and the Civil War. Feared by seamen, it is well protected by 30 mi (48 km) of shoals right off the cape into the Atlantic Ocean, known as the Frying Pan Shoals. North Carolina is famous for its barrier islands that
The 15th annual Carl E. Akeley Award was presented to Antoine Gagnon, Marc Jolin, and Jean-Daniel Lemay from Université Laval, for their article, “Performance of Synthetic Sheet Waterproofing Membranes Sprayed with Steel Fiber-Reinforced Shotcrete Testing for Waterproofing Membrane Integrity After Spraying,” published in Shotcrete magazine, Fall issue of 2019. This article is aimed at evaluating the potential damage and performance reduction of synthetic sheet waterproofing membrane when using steel fiber-reinforced shotcrete.
By: Jeff Bacon
In 2015, the U.S. Army Corps of Engineering began construction on the Davis Barracks at West Point, NY. The 172 million dollar barracks became a state-of-the-art facility. The new barracks was built to house 650 cadets, three in each room, consisting of 297,392 ft2 (27,629 m2).
The barracks building is located on the side of a mountain, below the cadet chapel, which in of itself is a famous landmark. The site for the barracks posed numerous challenges which included the removal of 285,000 tons (259,000 metric tons) of granite for the building’s foundation. Between 2015 and 2017, during the construction, over
By: Matthew Wallace
Recruiting, training, and retaining skilled shotcrete nozzlemen is mission-critical for a company’s success. Virtual, immersive training offers an effective, engaging mode of learning that supports the modern trainee. For beginning nozzlemen, virtual reality training gives them a safe, repeatable experience that can be completed in a classroom, free of job costs. Practice without cost or risk also helps improve job performance and satisfaction. These disruptive virtual reality (VR) technologies can provide safe, hands-on learning experiences without the field costs associated with hands-on training. Virtual learning is also valuable in today’s socially distanced world with its shifting remote learning requirements. Interactive digital tools will deliver meaningful, adaptive training for skilled trades now and in the future. Though some level of hand nozzling experience is still needed the best nozzlemen will be trained, in part, using virtual reality.
By: Position Statement #3 ASA Underground Committee
Using shotcrete for the placement of concrete for tunnel final linings is becoming more common. In the past the use of shotcrete final linings was typically limited to non-public or emergency egress areas, however, shotcrete is being used more and more in public areas. The use of shotcrete is typically an attractive alternative to form-and-pour final lining installation where formwork costs are high or technically challenging, pose a scheduling issue, or where labor rates are very high. Typical examples for successful use of shotcrete final linings are complex lining geometries, intersecting or merging tunnels, widenings, short tunnels without sufficient repeating utilization of the forms, or underground systems where formwork would block passing traffic.
By: Position Statement #4 ASA Underground Committee
The manual hand application of shotcrete began over 100 years ago and continues today in a wide range of applications and projects. To provide a proper distance of the shotcrete nozzle tip to the underground surface wall, surface receiving shotcrete or ‘substrate,’ the hand application of shotcrete in larger diameter underground structures required the nozzlemen to operate from a man-lift or similar equipment. Working from elevated platforms and the close proximity of the nozzleman to the substrate added safety challenges to projects. Thus, as more underground projects started to use the wetmix shotcrete process, spraying shotcrete with mechanical arms began to address these safety concerns.
By: Derek Pay
Although many shotcrete workers “claim” to be capable of placing massive amounts of concrete in a daily shift, or shooting with the pump turned “wide open,” in reality, the nozzleman tends to ultimately be the limiting factor on production speed and daily placement volume. Plain and simple they get tired. Shooting too fast diminishes accuracy and overall quality.
By: Oscar Duckworth
We have all seen those small letters and numbers that mark practically everything we use in construction. To most, these are meaningless markings that are meant for someone else. However, with shotcrete, nothing could be farther from the truth.
By: Ted W. Sofis
The COVID-19 Pandemic affected our lives in ways none of us have ever experienced in our lifetimes. I’ve been in construction for 45 years and I have never seen our economy shut down, businesses closed, or people required to stay at home. In 2001, the attacks of September 11th temporarily shut down air travel and the stock market, but the American economy remained intact and air travel resumed within a couple of weeks. However, COVID-19, has affected our lives in ways that we could never have imagined. Schools and universities were closed; professional, collegiate and high school sports seasons were suspended and canceled; and restaurants and businesses were closed. We were told to stay home and work remotely, if possible, and businesses across the country followed those directives.
By: Mike Ballou
Show me a person who tells you that safety on a mine site is just plain common sense, and I’ll show you someone who doesn’t understand mine safety completely. Mine safety is not simply common sense. It is that, and a whole lot more. Most mines have their own set of mine-specific regulations and rules. Nearly all mines, in Canada, the USA, and Mexico, are required by law, to follow government-mandated requirements such as U.S. Department of Labor- Mining Health & Safety Administration (MSHA) and/or the Occupational Safety & Health Administration (OSHA). Canada and Mexico have their government agencies governing mining as well. Even with strict government regulations, most mines have safety regulations specific to each individual mine. Anyone who desires to visit a mine site needs to accept one thing- whatever the rules and regulations are for a particular mine- these regulations are serious business and are meant to be enforced.
By: Kasturi Projects PVT, LTD
The storm water drains in the city of Mumbai, India, are over 100 years old and constructed with brick arch masonry during the British Era (Fig. 1). The storm water drains (SWD) were prone to frequent cave-ins. To prevent cave-ins, enhance their safety, and maintain the SWD system, the Municipal Corporation of Greater Mumbai (MCGM), under the Central Government of India “BRIMSTOWAD” Scheme, initiated a detailed survey and mapping of the SWD for the City of Mumbai.
By: Charles S. Hanskat
This is a revised version of the original article printed in the Summer 2016 of Shotcrete magazine before the OSHA rule was put in place. This revision has added site measured values for air monitoring of crew members on shotcrete projects, as well as ASA’s response to OSHA’s request for information in August 2019. Also, included is a short section on applicable respirators. With this revision our intent is to put the current information you need about the OSHA rule and its impact on shotcrete operations in one place for ready reference.
By: Raul Bracamontes
Because of its durability, strength, and flexibility in application, shotcrete is often used for the construction and stabilization of tunnels and other underground structures. The fact that tunneling involves general construction risks as well as tunnel specific environmental risks, makes this type of application potentially quite dangerous, and must be treated with caution. Risks cannot be eliminated, but we can implement measures to lower the risk.
By: Ted W. Sofis
This year, 2020, we have been challenged in a manner unlike anything we have experienced in America since the 1918 influenza pandemic that killed millions worldwide. The coronavirus (COVID-19) was identified in Wuhan, China, after initially being reported as a cluster of pneumonia cases in December 2019. Despite efforts to contain the virus, it rapidly spread to Italy and the rest of Europe and eventually the United States. As a result, on February 26, the first cases of COVID-19 began to appear in the Seattle,
Wash. area. Acting rapidly, many state governors issued
emergency restrictions and stay-at-home orders. Across
America we all watched the coronavirus task force briefings and New York Governor Andrew Cuomo’s morning
broadcasts, as the response unfolded in especially
hard-hit New York. In Pennsylvania we were issued
stay-at-home orders by our Governor Tom Wolf for all
but life-sustaining businesses. Which resulted in PennDOT closing down construction projects. In the months
that followed, state governors began to reopen their
economies. With the return to work there are protocols
and procedures we will need to follow to keep our crews
safe and well. Below are some guidelines and information that I hope you will find helpful.
INTENT OF PROGRAM
COVID-19 is an easily transmitted disease, especially
in group settings. It is essential that positive actions be
implemented to slow or stop the spread of the virus to
safeguard the public safety. Construction is vital to our
nation’s economy. Recognizing this, we need to find
ways to accomplish our work while not endangering
our employees. This requires several precautions to
protect our workers, their families, and members of
the community. It is necessary that all businesses in
the construction industry conducting person-to-person
activities follow the directives and requirements of their
state governments. Other local political units or privately
owned companies may elect to impose more stringent
requirements. In such cases we must adhere to the
client or owner’s requirements.
• Follow all applicable provisions that your State
government has provided for business safety
• Requiring that every person present at a work
site wear a face mask or face coverings.
Dealing with COVID-19
By Ted W. Sofis
Fig. 1: Social distancing with mask inside Fig. 2: Hand Sanitizer and Disinfectant Wipes
www.shotcrete.org Spring 2020 | Shotcrete 35
• Establish protocols for action to be taken when
cases or probable cases of COVID-19 are
discovered or whenever people in the company
could have possibly been exposed to someone
who may have the virus.
• Require social distancing with a 6 ft (2 m) minimum distance between workers, unless the safety of the workers makes an exception necessary,
(for example, team lifting.)
• Follow other Department of Health (DOH) and
Centers for Disease Control and Prevention
• Provide hand washing stations at appropriate
locations on your job sites, such as building entrances, break areas, offices, trailers and job site
• Implement cleaning or sanitizing protocols at all
construction sites and projects. Identify and regularly clean and disinfect areas that are high risk
for transmission. Establish requirements to clean
common areas and regularly trafficked areas
• Ensure all gatherings are limited to no more than
the maximum gathering size mandated by the
state where your project is located. Maintain 6 ft
(2 m) social distancing at all times when required
to meet, even when meeting outside.
• Use virtual meetings and distribute information
electronically whenever possible.
• Stagger shifts, work breaks, work areas, and
different trades, wherever feasible, to minimize
the number of workers on site.
• Limit tool sharing and sanitize tools or equipment
if they must be shared.
• Employ jobsite screening based on CDC guidance to determine if employees should be
working. Prohibit employees with any symptoms
of Covid-19 from working. Encourage any sick
employees to stay at home.
• Prohibit unnecessary visitors to any project
or work site and limit the number of supplier
• Limit access to enclosed spaces as much as
• Ensure workers are traveling to and from the
jobsite in separate vehicles. Whenever possible,
make sure that they do not share a vehicle.
• Identify a Coronavirus Safety Officer for each
project or work site, or (on a large-scale project)
for each contractor or subcontractor at the site.
The primary responsibility of the Safety Officer is
to convey, implement and enforce the social distancing and other requirements of the company
program for the protection of employees, suppliers, and other personnel at the site.
Fig. 3: Social distancing with mask outside
36 Shotcrete | Spring 2020 www.shotcrete.org
Ultimately, as a contractor, I realize the difficulties
involved in implementing and following coronavirus
guidelines, while at the same time trying to efficiently
perform and complete our projects. The reality is
that we have no other option. This pandemic is so
widespread and highly contagious that it forced
the shutdown of our nation’s economy for months.
Nothing like this has ever happened before in our
lifetimes. To ignore this, we jeopardize the lives of
our employees and their families. For the safety of
everyone involved and the communities where we
live, we need to get through this together. A vaccine
for COVID-19 will be developed and therapeutic
medications for treating the virus will become
available. In the interim, we need to find ways to
be safe and productive. I hope that you find these
guidelines helpful. More importantly, it is my hope that
all of you and all of your employees make it through
this construction season safely and in good health.
Ted Sofis and his brother, William J.
Sofis Jr., are the Principal Owners of
Sofis Company, Inc. After he received
his BA in 1975 from Muskingum College,
New Concord, OH, Ted began working
full time as a shotcrete nozzleman and
operator servicing the steel industry. He
began managing Sofis Company, Inc., in
1984 and has over 40 years of experience in the shotcrete
industry. He is a member of various ASA committees and an
ACI Shotcrete Nozzleman Examiner for shotcrete certification. Over the years, Sofis Company, Inc., has been involved
in bridge, dam, and slope projects using shotcrete and
refractory installations in power plants and steel mills. Sofis
Company, Inc., is a member of the Pittsburgh Section of the
American Society of Highway Engineers (ASHE) and ASA.
Fig. 4: Face mask protection in close proximity Fig. 5: The respiratory protection worn during gunning operations
fulfills the COVID-19 face mask directive.
By: Satoru Kobayashi
The decline in the number of workers in the construction industry is a severe problem in Japan. Formwork is indispensable for concrete structures, but due to the shortage of carpenters, formwork assembly tends to be slow and can cause project delays. To deal with this problem, new workers are being hired and formwork carpenters are being trained, but the payoff is not immediate because the acquisition of the required skills takes several years of education and experience. The “formless construction method” that eschews
formwork, might be a possible solution (Fig. 1), substituting an outer shell formed with sprayed mortar. The
reinforced concrete structure is then created by placing
reinforcing bar and casting self-compacting concrete
(SCC) inside the outer shell.
In this approach, the lateral pressure of the fresh concrete stresses the outer shell during concrete casting, so
the shell must have high tensile strength. Since Japan is
an earthquake-prone country, structures are required to
have strong deformation performance and must resist
the large bending and compressive stresses generated during earthquakes. Furthermore, to reduce the life
cycle cost of the structure and increase its sustainability,
both high durability and maintenance-free design of the
structure are required. Thus, the outer shell must have
a high resistance to chloride ion penetration and other
To satisfy the performance requirements, we decided
to use Ultra High Strength Fiber Reinforced Concrete
New Application Method of
By Satoru Kobayashi
Fig. 1: Concept of formless construction method
(UHPFRC) as the sprayed material. UHPFRC is a highstrength and high-ductility material with compressive
strength of 22,000 to 36,000 lb/in2
(150 to 250 MPa)
and tensile strength not lower than 1200 lb/in2
It is also characterized by a highly dense concrete matrix
with very low water and air permeability and thus high
chloride resistance. In Japan, UHPFRC has been used
mainly for factory produced precast products. Recently,
with the advent of mass manufacturing of precast members with large sections, the application of UHPFRC
to civil engineering structures has been increasing. The
largest such project to date is the application of UHPFRC for the floor slabs of Runway D at Tokyo International Airport with a UHPFRC volume of approx. 26,000
Thus far, UHPFR has rarely been used with sprayed
placement, and forming the outer shell of a structure
with sprayed UHPFRC is a novel challenge. This article
outlines the experimental method developed and used
to form the outer shell of a structure with sprayed
We focused on columns as the target structure. This
formless construction method requires a core material
that is easy to install and remove. Air tubes were adopted as the core material. Figure 2 shows the installation
of the air tubes. The thickness of the member was 16 x
16 in. (400 × 400 mm), and the thickness of UHPFRC
was 1.6 in. (40 mm). The height of the columns was 59
in. (1500 mm).
In this experiment, a mortar pump (squeeze type),
maximum discharge rate 8 yd3
/hr (100 L/min) and a
delivery hose with a diameter of 2 in. (55 mm) were used.
Fig. 2: Installation of air tubes
www.shotcrete.org Spring 2020 | Shotcrete 33
The diameter of the tip nozzle was
0.6 in. (15 mm). The sprayed material was required to stick on vertical
surfaces without sagging. To this
end, a non-alkali hardening accelerator was added at the nozzle.
Figure 3 shows the spraying of
UHPFRC. The material adhered to
the vertical surfaces of the air tubes
without sagging, and coverage of
the sprayed material to the required
thickness and height of 5 ft (1.5 m)
was achieved without problem.
Figure 4 shows the removal of
the air tubes that was easily accomplished.
As the next steps, reinforcing
bars will be set and SCC will be
cast inside the outer shell. The
structural performance will be evaluated by flexural strength testing.
Fig. 3: Spraying of UHPFRC on air tubes Fig. 4: Removal of the air tubes
is a senior
in Japan. He
Hiroshima University where he studied
the durability of concrete. He is highly
skilled in concrete, for example, selfcompacting concrete, anti-washout
underwater concrete, dam concrete,
and shotcrete. Recently his research
project focuses on the new application
method of UHPFRC and various
ways to use it at the construction site
effectively in order to improve the
durability of the structure and the
productivity of the construction process.
By: Benny Chen, Christian Reich, Peter Ayres, and Nicholas Carter
Construction of sprayed concrete lining (SCL) ground support across the world utilizes the construct, verify and rework cycle. This methodology typically requires survey verification of the as-built result against design for each stage of the ground support installation. However, processing and analyzing the measurement data is a time consuming and often intensive manual process. Often once the survey information is available the construction crew will have already left, this will require rework on the next cycle.
Leveraging the latest in high-density LiDAR and
high-speed computing technologies, provides the
ability for construction crews to receive near realtime feedback of their SCL construction against
design. This potentially can significantly improve the
efficiency and quality of SCL reinforcement, while
reducing waste in construction.
In a typical shotcrete application stage, the thickness of shotcrete applied is highly dependent on the
skill and experience of the nozzlemen. Upon completion of the shotcrete placement the compliance
of the sprayed concrete thickness with the design
requirements is not known until after a survey is
completed. The survey results highlight areas of over
spray (excessive thickness) or under spray (deficient
thickness), resulting in shotcrete wastage or costly
For example, during application of shotcrete
nozzlemen often use bolt tips as guidance to allow
them to gauge the approximate depth of their placement. The nozzleman’s experience plays a large role
in ensuring that the correct thickness is achieved.
However, to reduce the amount of under spray sections and prevent rework the nozzleman may choose
to place more shotcrete than required.
In many tunnel and cavern projects, the design
profile of the tunnel or cavern is critical and requires
strict thickness tolerances during SCL construction
to ensure the as-built sections fall within the design
profile specifications. In these types of construction,
both under spray and over spray could result in
non-compliance which then requires very costly and
time-consuming rework. Often depth pins and string
lines are installed in the area to provide guidance to
the nozzlemen, allowing them to visually gauge when
they have achieved profile. The process of installing
depth pins and string lines are time consuming
and labor intensive. This significantly increases the
time and cost of construction. Once installed, the
nozzlemen will have to estimate the placement
thickness between the string lines, which once again
is heavily dependent on the skill and experience of
www.shotcrete.org Spring 2020 | Shotcrete 25
STATE OF THE ART CONSTRUCTION
Since the introduction of the Building Information
Modeling (BIM) standards, governments around the
world are rapidly adapting BIM for their construction
projects. This is evident in countries including Hong
Kong, Singapore, Norway and Sweden. Figure 1
show the core BIM construction workflow where
design and authoring of the architectural and tunnel
designs are done in 3D CAD software, such as Revit
and Civil3D, where a full 3D model of the completed
section is created. This is followed by the Virtual Design
and Construction (VDC) process where a complete
construction simulation is run using the CAD models.
This helps validate the both the construction process
and the schedule. Clash detection is also accomplished
with the design model to detect any potential design
conflicts before the construction plan is approved.
By using FPGA based System-on-Chip (SoC) technology, similar to the Zynq-mp processor core technology that can deliver teraflops of computing performance,
computationally intensive signal processing algorithms
can be implemented in the hardware using the
Programmable Logic portion of the system (see Figure
2). The Programmable Logic area, in yellow, allows the
computer designer to create custom digital signal processing cores, like GPUs, and execute them in parallel,
allowing high speed processing of large datasets. The
Programmable Logic area also has the benefit of having
dedicated memory banks that support concurrent
access, unlike conventional computer memory access,
via a common bus architecture. The architecture above
makes it possible to process high-density data, like
the 3D point cloud data produced by laser scanners in
REAL-TIME IN-SITU MEASUREMENT
Real-time in-situ measurement technology refers to a
portable measurement device equipped with onboard
high-speed computing capabilities to deliver live or near
real-time high-resolution information. One example is the
production of information such as deformation or shotcrete thickness results in 3D. Figure 3 shows the comparison between using a conventional LiDAR against an
in-situ LiDAR technology, in this case the Geotechnical
Monitoring LiDAR (GML).
BIM construction is one of the key reasons for the
use of laser scanner technology. 3D Laser scanners
are used to scan as-built construction elements.
Scanning is typically carried out by a survey team
where the laser scanner is deployed in the excavation
heading to collect the as-built scan data. This scan
data is then brought up to the project office, where
a powerful desktop computer analyses the data in a
georeferenced coordinate system. This point cloud data
set often requires some manual processing to correct
for measurement errors and to correlate with the design
data. The entire process is required before producing a
report that can be used for analysis and then feedback
to the construction crew. This process typically takes
between 2 to 4 hours per station. Hence, the use of
such technology in civil constructions are limited.
Since 2016 the rapid adoption of high-speed
embedded computing platforms, like FieldProgrammable Gate Array (FPGA) and Graphics
Processing Unit (GPU) processor cores for embedded
systems, advanced data processing has become
prevalent. These technologies allow battery-powered
devices to achieve computing performance of one trillion
floating-point operations per second (1teraFLOPS). Part
of this rapid adoption is due to the global development
of algorithms and processor cores for machine learning
platforms and real-time autonomous vehicle projects.
Fig. 1: BIM Construction Workflow
Fig. 2: Xilinx FPGA Architecture
26 Shotcrete | Spring 2020 www.shotcrete.org
In the above comparison, the ability to analyze and
report the desired construction results automatically and
in minutes has the potential to significantly change SCL
GEOTECHNICAL MONITORING LIDAR
The GML technology was designed and developed by
GroundProbe, a mining technology company that supplies slope stability monitoring radar systems such as
the SSR-XT for the mining industry. Figure 4 shows the
GML system as a complete standalone battery-operated
LiDAR solution, that was designed to be a one person
operation. This technology is equipped with an onboard
high-speed computing device and signal processing
software, that can produce high density point cloud
information in real-time.
The first proof of suitability for the new technology was
to verify the measurement accuracy for shotcrete thickness measurements, against the existing total station
pick up by survey control.
The GML was deployed in various control environments in a tunnel project to verify the thickness measurements. The first method was to compare the results
of existing shotcrete thickness reports produced by
the survey pick-ups against the thickness reported by
the GML scanner. In this process, the GML was setup
next to the total station during conventional pickup to
scan the excavated sections before any shotcrete was
installed. Upon installation of the bolts and shotcrete,
both the GML and the total station were redeployed to
complete the final as-placed scan. These results were
tabulated in typical profile section views as per Figure 5.
Fig. 3: LiDAR vs In-situ LiDAR Workflow Comparison
In Figure 5, the GML results are in blue and the
results of the total station survey are in pink. Results can
be seen in all four scans, the GML results were almost
identical to the total station measurements.
In another verification test, core samples were drilled
to check the thickness against the GML measurements.
In this test, the GML was deployed to scan the section
before any shotcrete was installed. Once the shotcrete
had been placed and cured the drill rig was deployed to
drill four test holes, where the depth of the cores were
measured. These four holes were marked on the tunnel
surface to allow the user to locate the holes in the GML
Figure 6 shows the drill results in the GML SSR-Viewer software. The image was produced by the GML data
and clearly shows the marked holes. For each marked
hole a group of points were selected, creating the annotated figures shown in the figure. An average thickness
measurement was computed for each of the annotated
group of points and displayed in the charts.
Fig. 5: GML & Total Station Comparison Results
Fig. 4: Geotechnical Monitoring LiDAR (GML)
www.shotcrete.org Spring 2020 | Shotcrete 27
CHECK AGAINST DESIGN PROFILE
When operating in Profile Mode, the GML can import
BIM CAD models into the device and automatically
calculate the deviations against the design model. This
allowed the construction crew to have real-time feedback of their work while in the tunnel. Figure 7 shows
an example of the software operating in Construction
Guidance Mode in a tunnel excavation operation.
In Figure 7, the grey point cloud is the scan data and
it overlays the different design profile data, shown in purple and blue. The software automatically calculates the
Fig. 6: GML & Drill Test Comparison Results
Fig. 7: GML Profile Mode
Table 1: GML & Drill Test Comparison Results Table
Table 1 shows the core sample measurements,
against the GML measured results, for the placed
shotcrete thickness. The GML thickness measurements
were accurate to within 1-2 mm (0.04 to 0.08 in.). However, there was a large discrepancy with the results for
Fig 10373RH, as notated in the table below. This was
subsequently investigated, and it was found the core
samples had not been measured correctly.
Figure Name Drilled Results GML Results
Fig 10373 C 110mm 109.3mm
Fig 10372 75mm 75.4mm
Fig 10372 RH 120mm 118.2mm
Fig 10373 RH 100mm 52mm
distance (in millimeters) to and from the selected profile
lines, to produce the deviations in a hot-cold heat map.
LIVE SHOTCRETE SPRAY GUIDANCE
The following case study was based on data from an
Australian tunneling project in 2018. The project used
GML for managing the shotcrete thickness for the primary lining ground support in a road header cut tunnel.
The typical construction issue faced in this project
was the amount of shotcrete being ordered for each cut.
Quantities were based on a calculated estimation, often
with large amounts of excess material being ordered
to accommodate rebound and the spraying skill of the
nozzlemen. During the spraying stage, the nozzlemen
have depth pins to gauge the spray thickness, hence
the final sprayed thickness varies widely depending on
the skill of the nozzleman.
In this project, the GML was used to provide in-situ
feedback to the nozzlemen to guide them to spray to
the required design thickness. Since the GML was introduced in a later stage of the project it was challenging
to change the operating procedure. This required
significant planning to be able to train and guide the
nozzlemen to spray to the correct thickness. Using
the GML system helped to reduce the overall shotcrete
usage for the project.
In the early stages of implementation, the GML was
used to characterize the quality of shotcrete application
by the different nozzlemen. Figure 8 shows the typical
spray quality before use of the GML to guide the
nozzlemen. The shotcrete thickness in the images were
represented with red for areas under design thickness,
purple for areas over design thickness and green for
areas with the desired design thickness. As illustrated
in in Figure 8a, the sprayer was able to cover the bolts
correctly but left large areas under sprayed between
the bolts. Figure 8b, shows the opposite. Often the
nozzlemen would overspray the entire area just to
ensure there were no under spray areas resulting in
using significantly more shotcrete than necessary.
28 Shotcrete | Spring 2020 www.shotcrete.org
The GML was used in the project for a total of eight
months and after the first month using the GML the project was able to reduce the shotcrete material orders by
30% for the remaining seven months of operation.
SHOTCRETE FINAL LINING
The following case study was based on data from another Australian tunneling project between March and May
of 2019. The project utilized GML for controlling the shotcrete spraying process for the tunnel-wide, final lining, to
reduce or eliminate rework due to shotcrete not meeting
the required minimum thickness.
In this final lining shotcrete application, shotcrete was
sprayed continuously between cross passage (CP) to
cross passage, completing a 390 ft (120 m) section at a
time. This required the shotcrete rig and crew to move
13 to 20 ft (4 to 6 m) each time, to complete shotcreting
the entire section. Given the design requirements for
thickness and the tunnel design profile, depth pins and
string lines were installed as guides prior to the spraying
of the final shotcrete lining. The string lines were installed
by a crew of two operators, one surveyor and the use of
Mobile Elevated Work Platform (MEWP). The installation
took the crews approximately two shifts to complete
each section. Figure 11 shows a tunnel section that has
the depth-pins and string-lines installed.
Fig. 8: Detection of overspray and under spray of shotcrete
During the first four weeks of the project, after buy-in
from the site engineers, foremen and nozzlemen, the
project started seeing improvement in the spray quality.
The sprayer was able to use the GML guidance to cover
up the thin spots as seen in Figure 8b. However, there
were still some amount of overspray. Figure 9 shows an
example where the nozzlemen was able to detect thin
areas and rectify them immediately using the GML.
Shortly after the first month, the majority of the nozzlemen were able to use the GML to guide their shotcrete placement to reduce the amount of over spray.
Figure 10 shows the reduction of overspray areas. In
this example, the nozzlemen were able to reduce 33%
of shotcrete usage by using the GML. More importantly,
this was achieved within two weeks.
Fig. 9: Nozzlemen guided to fix up thin spots in shotcrete application
Fig. 10: Reduction of shotcrete usage
www.shotcrete.org Spring 2020 | Shotcrete 29
Fig. 11: Depth-pin and string line installation in tunnel section
Fig. 12: GML scan showing under spray sections in Red
Fig. 13: GML Scan Color threshold for spray thickness
Prior to the use of GML, the nozzlemen were using
the string lines as a guide to spray the desired thickness
and profile. Once the spray was completed, the section
was surveyed to verify the shotcrete placement against
the design profile and required thickness. The project
ran for months and found there were too many thin
spots that required rework, despite the installation of
depth pins and string lines. The GML was then deployed
simply as a verification tool to capture the construction
baseline. Figure 12 shows a typical rework issue on the
Figure 12 shows thin spots represented in the hot
color palette (red) and over sprayed sections in the cold
color palette (purple). The thin spots were spread across
the entire sections requiring significant amounts of
rework and verification by dedicated rework crews.
GML DEPLOYMENT CHALLENGES
The first key question regarding deployment of the
technology was whether it can operate in cycle, particularly during the SCL stage of the tunnel construction
process, to monitor spray conformance.
During spray conformance monitoring, the GML is
typically deployed next to the front stabilization jack
of the shotcrete rig and remains in place during the
entire spray sequence. This position allows a wide scan
area to be captured with minimal obstruction from the
shotcrete rig. The GML completes a baseline scan
under two minutes before the shotcrete operator starts
to spray. Once the shotcrete operator is satisfied with
the first pass, the boom is lowered, and a second scan
is captured. As shown in Figure 13, the results are then
presented to the shotcrete operator on a tablet to indicate any areas that have not reached the required thickness. The scanner operator then uses a laser pointer
or cap lamp to guide the shotcrete operator to respray
the thin areas. Once both operators are satisfied, a final
scan is taken to confirm the results.
The other key issue was the nature of the final lining
spraying process, were the shotcrete rig and crew
needed to advance at every 13 to 20 ft section. This
required the GML to be relocated with the rig to operate
30 Shotcrete | Spring 2020 www.shotcrete.org
in cycle. The GroundProbe team worked closely with
the shotcrete crew along with engineers to develop a
shotcreting sequence that allows the GML to operate in
cycle. Leveraging the rapid processing capabilities of the
GML, the system was able to operate without delay for
the majority of the construction.
Given the support of the engineering and final lining
team, and lots of teamwork, the project was able to
begin to achieve the desired results within the second
week of deployment. Figure 14 shows the desired spray
result. In Figure 14, it can clearly be seen that there were
no thin spots and the reduction of over sprayed sections
This was a considerable improvement on the project
and the technology was introduced to cover more areas
of final lining construction within the project. Inside the
initial two months of deployment, the final lining teams
were able to complete 2.6 miles (4.2km) of final lining
construction without rework, significantly reducing the
amount of shotcrete material used for the project.
The rapid progression of powerful embedded computing
and LiDAR technology enables the development of near
real-time in-situ scanning solutions. These advances
allowed application of the new technology into SCL
construction operations and enabled modifying current
practices to achieve improved safety, quality and cost
The rapid advancements in computing technology is
certainly a key enabler, allowing technology designers to
develop tools that could significantly evolve the mining
and construction industry. However, the success of such
technology relies heavily on the people operating in the
industry. Our experience shows that the success of the
case studies referenced in this paper, depended heavily
on the engagement of the engineering and construction
crews, especially the nozzlemen. One of the biggest
challenges faced was the management of change in the
construction processes. Effective communication and a
collaborative approach, to reach a desired solution, was
critical to the success of introducing the changes. Leveraging the experience of the foreman and nozzlemen also
was a key element in the development of the technology
and the construction process.
Fig. 14: GML guided spray with zero non-compliant thin spots
Finally, project management teams also play an
important role in fostering the development of innovative technologies by adopting them at an early stage of
a project. This is critical for any emerging technology
to achieve the desired potential, and to incrementally
change the current state of the art.
We would like to thank the excavation and final lining
teams mentioned in this article, especially the nozzlemen
and site engineers for their contribution to the technology.
We would also like to thank the monitoring team from
21MT, led by Christian Reich, for their highly skilled operators that helped to train and integrate the GML technologies into the construction projects.
1. Chen, B.; Mares, D.; Carter, N.; Ayres, P.; Voysey, G., 2020,
“Leveraging Super-Computing and High-Density Lidar Technologies
for Real-Time Verification and Rectification of Tunnel Construction
Against Design,” ITA–AITES World Tunnel Congress AND 46th
2. Bergmann, N. W., 2005, FPGA-Based reconfigurable system-onchip. Very Large-Scale Integration System-on-Chip (VLSI-SoC2005),
Perth, Australia, 17-19 October, 2005. Perth, Australia: International
Federation of Information.
3. D. Lv, X. Ying, Y. Cui, J. Song, K. Qian and M. Li, “Research on
the technology of LIDAR data processing,” 2017 First International
Conference on Electronics Instrumentation & Information Systems
(EIIS), Harbin, 2017, pp. 1-5. doi: 10.1109/EIIS.2017.8298694.
4. Processing. Altameemi, A. A., & Bergmann, N. W. (2016).
Enhancing FPGA softcore processors for digital signal processing
applications. 2016 Sixth International Symposium on Embedded
Computing and System Design (ISED), 294–298.
5. Zynq-mp-core-dual.png (800×900). (n.d.). Retrieved 18 September 2019, from https://www.xilinx.com/content/dam/xilinx/imgs/
www.shotcrete.org Spring 2020 | Shotcrete 31
HULL .125 AD HORIZONTAL PLACEHOLDER.
Did not see in the folder.
For the last 11 years, Ben Chen has played a lead technical and commercial role in delivering the
technology roadmap and his team was able to deliver an array of technologies to significantly diversify and grow the company’s brand, market share and revenue. More recently, his team has delivered
the Geotechnical Monitoring Lidar (GML) technology that won the Financial Review 2018 Most Innovative Products and Most Innovative Company awards. In the same year they also delivered the Geotechical Monitoring Station (GMS) technology that won the 2018 Good Product Design Awards.
Peter Ayres is the Lead – Tunnelling Solutions for GroundProbe and a former Technical Services Manager for
Orica. Currently he is working with the GroundProbe’s Product Development team in the development and
implementation of the GML system globally to both Mining and Civil industry. Over the past 12 years, he has
worked as a Tunnel Designer with Arup in New York, USA, followed by 6 years with Leighton Contractors (Asia)
Ltd. in Hong Kong as a Tunnelling Engineer and Blasting Engineer. Projects have included the 7 Line Extension, NY; West Kowloon Terminus & XRL822, HK; Harbour Area Treatment Scheme, HK; and the Tseung Kwan
O – Lam Tin Tunnel, HK. Peter has an M.Eng. in Mining Engineer from Camborne School of Mines – University
of Exeter and is currently studying for an LLM in Construction Law and Arbitration at Robert Gordon University.
Christian Reich is the Founder and Managing Director of 21MT, an Australian company committed
to implementing innovative technologies and solutions in the mining and tunneling industries. Since
2018, Christian has led 21MT in developing extensive experience using Groundprobe’s real-time GML
scan technology in Australian tunneling projects and has established a proven track record of efficiency improvements by integrating real-time scanning into the excavation cycle. Previously Christian
worked at Atlas Copco in Germany as the Product Manager for underground rock excavation equipment.
He graduated from Technische Universität Clausthal in mining engineering and business studies.
Nick Carter is the Lead – Technical Solutions at GroundProbe and has been involved in the innovation and
development of GroundProbe’s emerging technologies since 2011. He has travelled to the farthest and deepest
expanses of the earth to provide mining and civil markets with these technologies and globalized understanding
of the application requirements. He currently works on the Geotechnical Monitoring Lidar (GML) technology
with a small, core team of talented people who regularly solve challenging problems with creative solutions.
The GML has received innovation awards from the Australian Financial Review and most recently won the
Technology Transfer Award at the 2019 Institution of Engineering Technology (IET) Innovation Awards in London.
By: Pierre Siccardi, Achraf Laradh, Simon Bérubé, and Marc Jolin
Shotcrete placement is by definition driven by the particles’ high velocities. The kinetic energy provided by the velocity is how we obtain the desired consolidation of the in-place material upon impact to achieve good performances. Thus, it is important to look at the velocities found in the shotcrete spray using a rigorous approach to compare different nozzles.
WHAT WE KNOW
In the past, some researchers have tried to explore
the rebound phase of shotcrete placement. The most
advanced work, made by Armelin (1997), led to a model
of a single particle impact on an elasto-plastic substrate.
His work especially outlines the importance of the velocity on the particle impact energy, and more widely, on
To have a better understanding of what is going
on during the spraying, the placement and rebound
phases, this theory had to be extended from a single
particle to the entire spray stream. Past research at
the Université Laval Shotcrete Laboratory discovered
specific patterns in the shotcrete spray for each process
and equipment employed. Nicolas Ginouse was the
first to develop a method to properly measure particle
velocities from the nozzle tip to the receiving surface. By
filming the spray with a high-speed camera and tracking
the particles frame by frame, he was able to evaluate the
particles’ velocities in the entire spray stream. Noteworthy, he found that particles kept accelerating after exiting
the nozzle as the maximal velocities measured are greater at 1.0 m (3.2 ft) than at 0.5 m (1.6 ft) from the nozzle
tip (Fig. 1).
Also, velocities are not uniformly distributed around
the central axis of the spray stream. The wet-mix process produces more uniform velocities than the dry-mix
process. This means that a higher proportion of particles
are travelling at a faster speed in wet-mix (Ginouse &
Finally, one can observe that in dry-mix the exact
velocity pattern changes with the type of nozzle tip.
The speed reduction at the edges is more important
with the double-bubble nozzle-type (in green) than the
spirolet nozzle (in red).
These discoveries have provided a major step forward in our understanding of the shotcrete placement
process. According to Armelin (1997), rebound is linked
with the ratio between the kinetic energy of a particle
and the debonding energy. Given that kinetic energy depends on the square of the speed, it is logical to believe
that velocity spray patterns play a key role in rebound.
Thus, the hypothesis that the lower value of rebound
produced with wet-mix compared to dry-mix is partly
due to their very different velocity profile within the spray
stream. Thus, efficiency of the nozzle can be evaluated
through analysis of the velocity patterns.
One key observation of Ginouse’s study is that a
shotcrete spray can be simply characterized by two parameters: the maximum velocity and the spray opening
The results of Ginouse’s research have opened many
R&D topics. Thus, a series of projects have emerged
to extend the research effort on the study of the shotFig. 1: Fitted velocity profiles at 0.5m and 1.0 m for the wet-mix
(in blue) and dry-mix (in green and red)
www.shotcrete.org Spring 2020 | Shotcrete 17
Fig. 2: Experimental imaging device (Bérubé, 2017)
Fig. 4: Close-up of the nozzle tips
Fig. 3: Tested nozzles during experiments – ACME (top) and 1978
(bottom) (Bérubé, 2017)
crete spray. One of these research topics was about the
influence of the equipment (nozzle) on the performance,
especially concerning rebound, in each process.
Simon Bérubé has been a part of this momentum
established at Université Laval Shotcrete Laboratory. His
research (Bérubé, 2017) has focused on the influence of
the nozzle on the particle velocities in wet-mix shotcrete,
and on the mass distribution in the dry-mix spray stream
This article develops one specific aspect of Bérubé’s
project. By using the same setup as Ginouse, this
research evaluated the influence of the nozzle body and
the nozzle tip shape on the spray pattern in wet-mix
This study took place in a controlled laboratory environment with conventional industrial shotcrete equipment.
A shotcrete hydraulic cylinder pump, an Allentown
Powercreter 10, was used to pump a modern shotcrete
mixture designed for wet-mix placement. To lubricate
the 50 mm (2 in.) 20 m (65 ft) long delivery hose, a
cement grout with the same water/binder ratio as the
concrete, was pumped before the spraying.
Fig. 2 shows the experimental set-up for the imaging
device used in our facility. The 1250 frames per second capacity camera is positioned perpendicular to the
screen and the shotcrete spray. The white screen helps
to ensure a adequate contrast to discern particles in the
spray when the processing on captured images is done.
When shotcreting, the nozzle is held in a static support
and kept motionless to avoid the effects due to movement of the nozzle and the material stream.
Images are then post-processed with specialized
software to track the particles image by image. With the
data acquired, particle velocity profile and spray limits
can be defined.
Two conventional nozzles, the so-called ACME
Nozzle and the 1978 Nozzle (Fig. 3), were put to the
test. Those nozzles present some interesting differences:
while both air rings are similar (8 holes), the air plenum of
the 1978 Nozzle is clearly thinner and narrower than the
one found on the ACME Nozzle, and the ACME Nozzle
has a 19.1 mm (0.75 in.) air inlet whereas the 1978
Nozzle has a 12.7 mm (0.5 in.).
Moreover, the nozzle tips have noticeable differences
(Fig. 4). The ACME Nozzle tip (referred to as long nozzle
tip) is 193 mm (7.6 in.) long and has a 31 mm (1.2 in.)
diameter outlet, whereas the 1978 Nozzle tip (referred
to as short nozzle tip) is 130 mm (5.1 in.) long and has a
36 mm (1.4 in.) diameter outlet. The ACME Nozzle tip is
therefore longer and more tapered than the 1978 Nozzle
tip. Furthermore, these two nozzle tips have different
rigidity due to their thicknesses and the rubber used.
The long nozzle tip is stiffer.
18 Shotcrete | Spring 2020 www.shotcrete.org
The first trials of the project brought to light interesting
differences in the concrete spray produced by the two
nozzles presented before.
Table 1 presents the spray characteristics at 1.0 m
from the nozzle outlet for the two nozzles and for two
As shown in Table 1, particles in the spray produced
by the ACME Nozzle travels around 50% faster than
the one in the 1978 spray for both airflows. Moreover,
the ACME spray is half narrower than the 1978 spray.
The first interesting observation is the nozzle (body
and nozzle tip) has a noticeable effect on the particle
velocities and spray limits. To investigate the origin of
those differences, the second step of this project was
to focus more on this piece of equipment.
To explore further, the nozzle tips were switched. This
way, the long nozzle tip was put on the 1978 Nozzle
body, and the short nozzle tip likewise switched to the
ACME Nozzle body. Table 2 presents the experimental
program and the results obtained with each
Characteristics ACME 1978
/min) 150 200 150 200
Vmax (m/s) 24.0 23.5 16.0 16.9
Angle (°) 28.2 27.2 49.6 52.0
Long 24.0 23.5
Short 18.5 23.0
Long 19.5 22.4
Short 16.0 16.9
Table 1: Spray Characteristics for the two nozzles
Table 2: Maximum velocity for each nozzle configuration
From a theoretical rebound point of view, the ACME
Nozzle body combined with the long nozzle tip proved
to be the best configuration achievable, considering
the particles velocities. For both 150 and 200 ft3
air flow, particles traveled around 24 m/s (79 ft/s). The
worst configuration would be the 1978 Nozzle body
combined with the short nozzle tip. Particles travel
around 16 to 17 m/s (52 to 56 ft/s) regardless of the
INFLUENCE OF THE NOZZLE BODY
To evaluate the nozzle tip efficiency in future research,
velocities will be compared using the 150 ft3
/min air flow
since that is the more critical case for spray velocities.
Using the same nozzle body, the short nozzle tip always
produced lower particle velocities compared to the long
It is interesting to mention that, at 200 ft3
/min, a good
nozzle body (ACME) combined with the extra airflow
helped to reduce the “bad” effect of the short nozzle tip.
This brief study showed the importance of choosing
both the right nozzle body and the right nozzle tip to ensure optimal placement conditions. Moreover, it seems
that increasing the airflow will not always increase particle velocities. Cutting the end of the nozzle tip reduces
back thrust and may facilitate nozzle movement for the
nozzleman and is sometimes seen on construction sites.
However, this practice will lead to a reduction in the
shotcrete spray velocity and in turn reduce the shotcrete
placement quality and overall performance.
The authors would like to acknowledge Andy
Kultgen with ConForms for his help and suggestions in
this project, as well as supplying the different nozzles
used in this study.
1. Armelin, H. S. (1997). Rebound and toughening mechanisms in
steel fiber reinforced dry-mix shotcrete. (PhD. Thesis), University of
British Columbia, Vancouver.
2. Bérubé, S. (2017). Effect of the projection nozzle on the projected concrete bounce. (M.Sc.), Université Laval, Quebec.
3. Ginouse, N. & Jolin, M. (2014) Effect of Equipment on Spray
Velocity Distribution in Shotcrete Applications. Construction and
www.shotcrete.org Spring 2020 | Shotcrete 19
Following a bachelor’s degree in mechanical engineering from the Arts et Métiers
in France, Pierre Siccardi pursued his
studies at Université Laval, Québec,
Canada where he obtained his master’s degree. His research project on
shotcrete nozzles led to the filing of a
patent. He is currently pursuing his PhD
under the supervision of Prof. Marc Jolin. His project now
focuses on the homogeneity and the adjustment of concrete mixes in a mixer truck using an on-board system.
Simon Bérubé earned his civil engineering
bachelor’s degree from Université Laval
in 2014. Following that, he completed his
master’s degree in the same field in 2018
under Dr. Marc Jolin, during which he
undertook a research project on shotcrete
equipment modelization. Simon Bérubé
now works for CIMA+ since 2016, a private
engineering firm located in Quebec City.
Achraf Laradh is a master’s student in the
Department of Civil and Water Engineering at
Université Laval, Québec City, QC, Canada.
The focus of his graduate research project is
to model the spray of concrete to evaluate the
placement quality considering the rebound
of the shotcrete. He received his engineering
degree at Arts et Métiers Paristech, France.
Marc Jolin, FACI, is a Full Professor
in the Department of Civil and Water
Engineering at Université Laval. He
received his PhD from the University
of British Columbia, Vancouver, BC,
Canada, in 1999. An active member of
Centre de Recherche sur les Infrastructures en Béton (CRIB), he is involved in
projects on service life, reinforcement encasement quality,
fibers, admixtures and rheology of shotcrete. He is Past
Chair of the ACI Comittee 506 Shotcreting, and secretary
of ACI Subcommitee C601-I, Shotcrete Inspector, Shotcrete Inspector, and is a member and Past Chair of ACI
committee C660, Shotcrete Nozzleman Certification.