Trenchless technology, often referred to as “no dig”, is a rapidly growing engineering industry that eliminates the need for surface excavation. It provides cost-effective sewer asset management through pipe and sewer inspection, rehabilitation and cleaning services. One of the most recent developments in trenchless technology is the use of robotics which provides users with digital data. This includes sonar sewer profiling which allows for pipe inspection while the pipe is in service.
Virtual CCTV pipe inspection is another trenchless technology that provides you with a high resolution, front hemispherical picture of the pipe giving you the ability to pan, zoom, tilt, and classify defects from a desktop computer.
Some trenchless robots are also capable of laser scanning. Laser scanning creates a three dimensional model of the surrounding environment, allowing for measurable results and visualization of features that may not be visible with CCTV pipe inspection.
Indian subsurface infrastructure has a varied age, starting from newly laid pipes to ones that are as old as 200 years. Lengthwise, New Delhi has one of the largest subsurface pipe networks with approximately 5,000km in length. There are functional sewers in old cities such as Benaras, Kolkata or Mumbai, with pipe ages exceeding 100 years.
Probably the first use of trenchless technology in India was the lining of a 2.4 feet x 3.75 feet brick sewer in Maharshi Karve Road in Mumbai by a Baltiboi-ITI joint venture. Though the project was complicated and had several pitfalls, it was finally completed well over budget but demonstrably up to all technical standards of the day.
Application-wise, the largest need for trenchless techniques is in the water and sewer sector, where the networks are either failing badly or deteriorated to an extent where new installations are becoming a necessity. There are, however, lines where rehabilitation work can still be done and even this work is substantial.
Said Saurin Patel, Managing Director, Michigan Engineers Pvt. Ltd, Mumbai, pioneers in the trenchless technology, “Rehabilitation of old sewer lines running underground in urban areas, using modern module like fiberglass gives it a lease of life by another 100 years, besides it increases the velocity of flow causing less frictional loss and in default increasing the capacity of these lines. These lines can be in shapes like circle, oval, ovoid, egg-shaped, basket handles or boxes that are under rehabilitation all over India. Egg shapes and circles are the most common. From GPO to Lovegrove pumping station in Worli, there are three main networks coming into the pumping station, that will be rehabilitated by either this year end or mid next year. Delhi has horseshoe, circles, boxes and egg shaped sewer on which the rehabilitation is on. In Kolkata, you have eggs, ovoid and basket handles. Rehabilitation is going on in the metro, including the Rashbehari Avenue, Bose Road, Beaten street and Canning Street. We are one of the few Indian companies to have the expertise to provide such services, as most of them working on the Indian sewer lines are international service providers. Now with the sewer lines being rehabilitated, the only preventive maintenance method that can be used is the suction jetting system.”
But trenchless technology is not just the need of the hour but the only option available where rehabilitation of the Indian lines are concerned, said Ashok Gandhi of Gravit Engineering Works, who are in this field for over 28 years. “Relaying is not a practical option. It requires digging up of roads, pulling out the existing lines and fitting in new pipes, calling for colossal expenses and causing inconvenience to traffic. The Delhi and Mumbai municipal corporations have extensively adopted this European technology to rehabilitate the sewer lines. There are seven to eight technology in the trenchless method, including GRP lining/coating, In-situ form CIPP, uPVC spiral, micro tunneling, pipe bursting and cast in-situ (GRP coating). But in India, we are using the man-entry trenchless technology whereby taking a small pit at one place the fibre glass pipe is pushed inside relaying the entire pipe. We too offer this technology availed from Denmark but we are more into consultancy, compiling data and assessment.”
Unlike janitors in other sectors, the sewer cleaners are one of the most unskilled labourers who are prepared to enter a manhole filled with sewage just for a price. At a time when cleaning contractors are facing a crunch of labourers, sewer cleaners are still available in abundance, said Krishna. But, he warned, the scene is likely to change for the better soon. “Gone are the days when a bhungee’s son or daughter is a bhungee too. Today, with increasing reservations, children in this community are opting for higher education. Sewer cleaning essentially calls for manual entry into the sewer line at one point or the other. Even in other Western countries, workers do enter the manhole but are equipped with the right gadgets and suit to protect them. The mask, the cylinder, suit, boots, etc., are part of any worker. But, in India, the worker would want to jump into the manhole without caring to carry a cylinder on his shoulder.”
In a paper on Partial Automation of the Current Sewer Cleaning System, Ajay Kumar Shrivastava, Ashish Verma and S.P. Singh have proposed a robtic vehicle that goes inside the sewage pipeline, locates the blockage and also places the nozzle of the pressure pipe at the point. It can work in water-filled pipes and therefore, no human being will be required to go inside the sewage water.
The complete system will consist of robotic vehicle, a sensor unit and two robotic arms and embedded system to control the working of the system.
The detection of blockage will be done by using ultrasonic sensors, which can work satisfactorily inside water & sewage filled sewer network. The sensor will be moved inside the sewer line by the robotic vehicle. The direction of the sensor can be varied by a robotic arm. The embedded hardware and software will provide proper signal to the ultrasonic transmitter and also receive signal from the receiver.
A cart can be attached to the same robotic vehicle. Solid materials like polythene bags, bricks, etc., of the blockage can be collected by the arm and placed in the cart. A crusher can also be added to crush some solid materials. It can also be useful for other pipeline system inspection like oil pipeline, gas pipeline and drinking water pipeline, with some small changes.
Why Sewer Cleaning?
A wastewater collection system is typically a network of pipes, manholes, clean outs, traps, siphons, lift stations and other required structures to collect all the wastewater from an area and transport it to an environment safe place such as a treatment plant or disposal system.
Sewer systems are located underground, typically running parallel to streets. This series of pipes and culverts are engineered as gravity flow systems, built on a slight grade to assist material flow.
Most sewers are designed to convey material at a velocity of 2 feet (61cm) per second. When velocity falls below this rate, solids remain at the bottom of the pipe, reduce flow capacity and eventually cause a blockage. If the velocity is designed to flow greater than 10 feet (300cm) per second, solids could separate from the flow during low usage. At high velocity splashing occurs when the water changes directions, releasing odours and accelerating corrosion of concrete structures.
Partial or complete interruption of the flow may result from an obstruction in a sewer, when such interruption occurs, material will backup and eventfully overflow affecting the neighboring streets, homes and businesses.
The objective of a Sewer Cleaning and Maintenance Programme is to operate & maintain the wastewater collection system. The regular maintenance programme will minimize the number of stoppages per length of sewer pipe, reduce odour complaints and lift station failures.
- Poor maintenance: The majority of the branch sewerage system is at any time either completely blocked or its capacity is severely reduced by silt and solid waste. Sewer maintenance is restricted to emergency clearing of blockages and is given low priority.
- Silting and surcharging: Sections of the trunk sewers are heavily silted. Reduced capacity from silting results in sewage overflows from manholes to surface drains during peak flow periods. Problems may also be caused by structural damage in some sections.
- Ageing infrastructure: The existing trunk sewer system is over 75 years old and has been allowed to deteriorate to the point where rehabilitation or replacement is necessary. Many of the sewers have not been inspected.
- Storm water and solid waste ingress to sewers: Damaged manholes, sewer defects particularly around the drains and linking of drains to the sewerage system have led to increased risk of solid waste entering and blocking the system.