Anchoring: A Key Aspect Diaphragm Wall Construction

Diaphragm wall construction is very crucial for modern super structures like residential and commercial complexes with basements. These reinforced concrete walls provide the much required underground support and stability to the structure. And what ensures that these diaphragm walls are sturdy enough to keep these structures intact is Anchoring. All diaphragm wall construction companies will unanimously agree that Anchoring is one of the most important aspects of diaphragm wall construction. Here’s why…

What exactly is Anchoring a diaphragm wall?

In diaphragm wall construction, ground anchor bolts are used in order to link the structural and non-structural elements of the D-wall to the concrete. The process of casting these anchors into the diaphragm wall is known as Anchoring. The Anchoring activity begins 7 days after the diaphragm wall panels are cast.

How does Anchoring help in the diaphragm wall construction?

Anchoring assists in transferring the tension and shear forces between these structural elements and lateral support to the diaphragm wall to sustain force from the top. It involves anchor bolts, steel plates, sleeves and stiffeners to form the anchor on the diaphragm wall.

If anchoring is not done by diaphragm wall construction companies, then they have to increase the depth of the wall into the ground to almost double the size required. For instance, if the requirement is to construct a basement of 10 ft., the diaphragm wall must go deeper into the ground by 10 ft. more, in order to ensure it doesn’t collapse. Constructing a diaphragm wall without anchoring increases the cost of labor, the amount of concrete and steel used in the process, thus adding to the cost of the project.

What are the anchors used in Anchoring?

The tool used in the process of anchoring is called a Grouted Ground Anchor. There are three important elements you’ll see in an anchor, and they are Steel Tendons, Spacers and End Cone. Top civil engineering companies in India like Heritage Infraspace Pvt Ltd used steel tendon grouted ground anchors manufactured by Tata or Usha Martin.

This is the breakdown of an Anchor that goes into the diaphragm wall

Now, these steel tendons are generally 12.7 MM wide and come in 7 ply form (7 different wires coming together to form one single tendon). The spacers, just like its name, create spaces between these wires to ensure that they do not touch each other and that the cement flowing into the sleeve of the anchor is regulated.

The End Cone, is a conical shaped protector attached on the interior end of the anchor, which protects the wires from touching the soil base.

The Anchoring process

Anchoring is done post casting of the diaphragm wall. There are multiple levels of anchoring, with one anchor level in every basement. When the diaphragm wall cages are made, there are slots left open in equal distance on them. They are called anchoring sleeves. The distance maintained between them is ideally 5 meters. But the depth can be increased, given the quality of the soil the diaphragm wall construction companies are dealing with.

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HIPL X Central Vista: Revamping India’s Administrative Capital for the Future

The Client – Government of India, Larsen & Toubro

The Central Vista, India’s central administrative area located near Raisina Hill, New Delhi. The area was originally designed by Sir Edwin Lutyens and Sir Herbert Baker during British colonial rule and was retained by the Government of India after independence.

Scheduled between 2020 and 2024, the Central Vista Redevelopment project aims to revamp a 3 km (1.9 mi) long Rajpath between Rashtrapati Bhavan and India Gate, convert North and South Blocks to publicly accessible museums by creating a new common Central Secretariat to house all ministries, a new Parliament building near the present one with increased seating capacity for future expansion, new residence and office for the Vice-President and the Prime Minister near the North Block and South Block and convert some of the older structures into museums.

A set of ten doughnut-shaped buildings on four plots as Secretariat will be built on either side of Rajpath. The height of all the buildings will be less than 42 meters (height of India Gate) and they will have 7 floors. Exteriors of all buildings will be similar to surrounding Lutyens buildings and they will be connected to each other and to the Delhi Metro network by electric people-movers in underground ways and overground buses.

In 2021, infrastructure company Larsen & Toubro Limited was awarded the contract for the construction as well as maintenance of the first three buildings of the Common Central Secretariat under the Central Vista Redevelopment project by the Central Public Works Department.

Projects awarded to HIPL

Under L&T, HIPL was awarded the projects for diaphragm wall construction and Soil Anchoring for the Central Secretariat building in the Parliament Complex.

The concrete diaphragm walls are being built in a periphery of 1500 running mts. The diaphragm wall ranges between 600 to 800 mm, and they are being constructed 20 mts and above.

The soil anchoring was done with the standard distance of 2.5 meters between each struts and anchors.

Challenges faced

The safety standards for the entire project is very high and its maintenance requires meticulous planning from every department.

One of the initial challenges was to ensure the smooth process of the security verification of every member involved in the project.

Secondly, the team had to be very cautious with all forms of excavations and drilling activities, as a lot of the surrounding structures have a historical significance and cannot afford even minimal damage.

In the midst of the Heritage Infraspace diaphragm wall construction activity, the team of engineers discovered water flushing outside, during the anchoring activity. This was plugged using our water stoppers.

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HIPL and Its Contribution to Modern Metro Construction in India

Metro Rail has changed the way people commute within cities in India. Constructing such a complex transit system in a populated country like India is a herculean task. And we at Heritage Infraspace Pvt. Ltd, as a leading construction company in India, take great pride in the fact that we’ve contributed towards the metro construction in India with our diaphragm wall technology, piling and shoring services.

HIPL has provided intelligent ground engineering solutions for various metro construction in India and have executed them with excellence in collaboration with multiple government departments and some of the top construction company in India.

Working with the best

Heritage Infraspace metro construction include the thriving Krishna Park station at Delhi Metro, the elevated station stretch of Kalamasherry-Muttam-Pulinchodu-Aluva for the Kochi Metro, the Bada Chauraha and Chunni Ganj stations of Kanpur Metro and the launching shaft for Ahmedabad Metro.

HIPL worked with some of the biggest names like Larsen & Toubro on the Kochi and Ahmedabad Metro, Gulermak for the Kanpur Metro and Hindustan Construction Company for the Delhi Metro Project. While construction companies in India were the major project executioners, HIPL were awarded with the crucial task of diaphragm wall construction for deep basement underground metro stations.

The Kochi Metro was the first project awarded to HIPL, where we provided our piling services for the elevated stations, constructing 296 piles. HIPL was invited to work on this project when almost every major construction company in India refused to work on the site, majorly because it was close to the dumping yard, which ended up degrading the soil quality and it required some high level soil management and ground engineering to work on it.

Modern problems require modern solutions

Metros always run amidst the hustle and bustle of the modern cities today, hence the construction of underground stations require innovative engineering solutions with state of the art equipment to execute them perfectly. HIPL uses the top of the line machinery from its fleet for its metro projects, like the Jint SG 35 in Ahmedabad, Casagrande B125 for Delhi Metro and Casagrande B200 in Kanpur. Another crucial piece of machinery which we use regularly on our sites is the Ultrasonic Drilling Monitor, an intelligent utility device for complex civil engineering and foundation work. We sourced it from Koden in Japan, and use it to maintain the verticality of the construction, where every 10 meters the bore’s verticality is checked with a sensor, and precise measurement, display and recording of perpendicularity of drilled holes and the shapes of cross-sections.

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