Conventional dry-mix shotcrete (where water is added at the nozzle) or wet-mix shotcrete (where air...
In July 2012, Shotcrete Technologies was contacted by Michigan Engineers of Mumbai, India to provide technical expertise, training and robotic shotcrete systems to rehabilitate portions of the aging storm water system in Mumbai with shotcrete.
The city of Mumbai, India, with its teaming millions of inhabitants, had been experiencing numerous failures of its one-hundred-year-old plus storm water system. Badly collapsed areas affected traffic during peak hours, and bursting sewer pipes created further cave- ins with disastrous effects. The old brick-lined system is badly in need of preventative maintenance, repairs and reconstruction.
The first phase of this massive project identified particular areas to be repaired – mainly storm water drains and sewer lines that needed urgent attention, or they would fail. The most common problem is leakages within the system causing erosions, or the sewer lines choking up, culminating in a road collapse (sink-hole).
Delinking sewer and storm water drainage systems were also goals of the project, to reduce coastal pollution and environmental hazards created when flooding occurs through the storm water system.
Michigan Engineers was awarded an initial contract to rehabilitate sixteen different sizes and shapes of storm water tunnels in old Mumbai, near the central rail station. The pipes ranged in diameter from 1.5m (4.5ft) to 4.5m (14ft) and were of various shapes – oval, horseshoe-shaped, round and box culverts with lengths varying from 16m (50ft) to 2400m (7500ft) Specifications called for a Shotcrete lining between 50mm – 200mm thickness (2in – 10in), with a total of 20,000 cubic meters (27,000CY) of shotcrete to be applied.
The variety of shapes and sizes and challenging site locations called for a versatile application method that was cost-effective, simple to operate, and that was mobile and relatively fool-proof.
To meet the needs of the client Shotcrete Technologies provided three Shot-Tech robotic arms, one Model 350, and 2 Models 160, and one robotic shotlining system. These would provide the most flexibility and cover the necessary range of shapes, sizes and lengths. Transcrete Concrete Pumps were chosen for Shotcrete delivery through two inch hoses. To complete the system, locally-sourced carriers were used to mount the Robotic arms.
To keep costs as low as possible, STI sent out technicians to the site, and advised Michigan on what types of carriers sourced locally would be suitable for each unit, and what type of locally fabricated parts could be used; as much material and equipment as possible was sourced in locally.
Once the shotcrete units were delivered, our technical personnel assisted Michigan engineers in mounting the units on the various types of carriers. Then crews were trained and the shotcreting began in earnest.
The 40 MPA (5800psi) sand mix with 10% silica fume was designed to pump more than 100m to the nearest manhole, and then re-pumped another 200ft away. Concrete delivery is challenging – during the day, traffic (both pedestrian and vehicles) is too congested and concrete delivery is nearly impossible. Work is now only performed at night between 9pm and 7am. With the proper mix, the shotcrete is often pumped hundreds of meters at a time.
As anticipated, the Shot-Tech robotic arms and system are proving their versatility and productivity in extremely challenging conditions. The 20,000 cubic meters is anticipated to be complete in 150 working days.
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