Bentonite to Polymer Slurry, the Sustainable Route to Building Reinforced Concrete Diaphragm Walls

Bentonite has been a crucial construction element in building reinforced concrete diaphragm walls for deep basement structures. But over the years, civil construction companies have started using polymer in their excavation fluids and slurry.

Read on to understand the importance of both the materials in constructing concrete diaphragm walls, the differences between them, and how polymer is growing as a more sustainable option in excavation activity while bentonite remains the foolproof back plan for civil engineers.

What are Bentonite and Polymer Slurries?

Bentonite clay is formed by the alteration and weathering of volcanic ash and is abundant in the clay mineral montmorillonite, which swells when mixed with water and possesses exchangeable irons on the surface that produce thixotropic suspensions. Typically mined in Rajasthan India, it is extensively used in diaphragm wall construction as an excavation fluid. Bentonite clay (in powder form) is combined with water in a colloidal mixer where the clay particles bond with one another to form a gel-like texture.

The mixing process continues till the standard quality is achieved for the slurry.

Polymer slurry is prepared with the combination of water and hydrophilic superabsorbent polymers like polyethylene glycol, polyvinyl alcohol, or carboxymethylcellulose to form a thick, viscous mix. These water-soluble polymers have been used to stabilise deep excavations for reinforced concrete diaphragm wall trenches. When compared with conventional bentonite slurries,this engineered fluid is known to offer a variety of advantages including smaller site footprint and lesser environmental impact.

How is a bentonite slurry or polymer slurry prepared?

The slurry is prepared with the aim of attaining maximum hydration of bentonite clay or polymers. Hence, it must be slowly added into the mixing water to ensure all particles are irrigated and do not get lumped. Potable fresh water should be used in the mixing process to obtain the best results. Alongside this a chemical analysis, as listed out by the Indian Standard Code of Practice for Construction of Diaphragm Wall, must be conducted to ascertain the suitability of water. If needed, chemical treatment is given to the water before its usage.

The preparation of the slurry is done either in batches or in a continuous process, depending on the type of equipment used. The components are added in a high shear mixer through a simple venturi-hopper. To assure the dispersion of all the individual particles in the mixing water, the mixing equipment must generate sufficient shear. Once prepared, it is moved to storage tanks, and from there they are supplied to the excavation point, to be filled into the cavity of the soil. This entire process, including the testing is done on-site by the civil construction company assigned to build the diaphragm wall.

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Shaligram Group X HIPL – A Modern Residential Structure in Ahmedabad

Heritage Infraspace Pvt Limited (HIPL) is known in the infrastructure industry as the best diaphragm wall construction service provider for deep basements in India. As pioneers of the deep basement diaphragm walls, HIPL has worked on several residential and commercial projects collaborating with prominent names from the real estate industry. One such residential complex project is the Super Shaligram under Shaligram Group in Gurgaon.

Here’s a deep-dive into the observations made, challenges faced, and solutions provided during the construction phase of this project.

The client – Shaligram Group

Shaligram Group is an Ahmedabad-based construction company specialising in residential and commercial property construction. Shaligram Group joined hands with Heritage Infraspace Private Limited for this particular project since they have the experience of building many modern high rise residential projects, while HIPL is the pioneer in providing the best diaphragm wall construction service in the country.

Projects awarded to HIPL for Super Shaligram

The Shaligram group wanted only the top diaphragm wall construction contractors in India to work on this project, as it is considered to be one of the marquee projects in their portfolio. This project began in August 2022 and HIPL was assigned to build an 18.5 metres deep diaphragm wall for the 3- basement project named Super Shaligram. HIPL also did 2 levels of anchoring alongside the diaphragm wall construction.

(Note: This is an ongoing project, HIPL plans to complete it by mid-November 2022)

Challenges in this project

This project was located in the Gota area of Ahmedabad, which has a lot of trees and vegetation in and around the main streets and lanes.

During the excavation for the deep basement diaphragm wall, a few previously built structures in and around the plot had to be broken down.

The plot of land chosen for construction was earlier used as a recreational ground where a lot of outdoor events were held. As these events usually set up temporary tents and stages, the top strata of the soil had become very soft.

Another major challenge was that this project was green lit when the monsoon season was in full swing. This is a problem that causes concerns for all diaphragm wall construction contractors in India.

As the excavation for panelling began, a water bore pipeline was discovered inside. And it was informed that this line cannot be removed or moved away.

There was another ongoing project happening at the next plot and additional care had to be taken so as to ensure no damage to their part of the plot occurs due to the excavation.

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Importance of Diaphragm Walls in Metros – A Case Study

India’s first metro rail started back in 1984 in Kolkata (then Calcutta), West Bengal . Ever since, India has seen a rapid expansion of metro rail in various cities, with Delhi leading, and other cities catching up like Ahmedabad, Bengaluru, Gurugram, Kanpur, Kochi, Lucknow, Mumbai and now even Agra.

India being a country with densely populated cities, building metro railway lines and stations is nothing short of a challenge. Heritage Infraspace Pvt Limited has assisted and provided metro diaphragm wall construction services to many metro contractors in India. Here, we break down the importance of diaphragm walls in the construction of metro railways, as an interesting case study.

Types of stations built by metro contractors in India

There are majorly two types of metro stations: elevated and underground stations.

An elevated metro railway station or elevated train station is a railway platform alongside the tracks above street level on a viaduct or other elevated structure, usually constructed from steel, cast iron, concrete, or bricks by metro contractors in India.

An underground metro railway station is where the platform is built multiple levels beneath the ground as deep basements. The metro rail tracks run parallel to these stations, with a bustling city above it.

Elevated railways are normally found in urban areas where there would otherwise be multiple level crossings. Usually, the tracks of elevated railways that run on steel viaducts can be seen from street level.

Underground metro stations are generally proposed in older, dense parts of the cities where roads are narrow and sharp turns do not allow elevated rail alignment without major demolitions.

Importance of diaphragm walls for underground metro stations

Diaphragm walls are sturdy underground structures that can act as a permanent structural wall. Diaphragm walls can be installed to deeper depths, which helps in building multi-basement stations.

Compared to construction of a station on an elevated metro corridor, underground metro diaphragm wall construction services require less temporary propping. The top-down construction method can be applied in building an underground metro railway station.

The diaphragm wall is a rigid structure, hence the ground movement induced by basement excavation for underground metro is lesser compared to usage of flexible retaining walls. Diaphragm walls act as a strong guide wall for the launching shaft for metro stations.

Challenges faced by HIPL Ground Team

A major challenge HIPL faces as a commercial construction company in India working on various underground metro projects is accurately/precisely identifying the quality of the soil. With urbanisation, soil quality cannot be determined with a single inspection, and as the excavation takes place, the teams come across various forms of soil, which affects the metro diaphragm wall construction to a great extent.

The other challenges are as below:

Metro construction area sees a lot of activity and hence securing an entire stretch for the excavation work and diverting the traffic is a challenge.

Transportation of various construction materials, utilities, machinery, etc. is a big challenge, as urban areas have constant and heavy flow of vehicular and foot traffic in congested spaces.

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Safety on Site: Diaphragm Wall Construction by Heritage Infraspace

Apart from being the pioneers of diaphragm wall construction for deep basements, what makes Heritage Infraspace Pvt Ltd (HIPL) rank as the one of the top construction company in India is their approach to safety on site. Safety on construction sites protects the workers and keeps the public safe.

The construction sites commissioned to HIPL are typically congested locations in bustling cities with high pedestrian and vehicular traffic. Inadequate safety procedures could lead to mishaps involving construction employees, heavy equipment and onlookers, placing them in severe and sometimes life-threatening danger.

Here are some of the steps HIPL follows, as a responsible diaphragm wall construction company in Ahmedabad, India, to ensure the safety of workers and general people around the site, right from implementing a health, safety and environment plan to an internal checklist of to-dos by the safety team of HIPL.

General Workers’ Safety

Every member on the ground, including the labourers and engineers, is provided with reflective safety jackets, standard safety helmets and safety shoes with steel toes.

Those working in reinforcement get hand gloves, and shoulder pads as they carry heavy and long rods of steel bars and welded wire fabrics.

Welders are provided with a proper faceguard, gloves and safety aprons, to protect them from the sparks flying off the metal during the process.

Teams working with concrete in Diaphragm wall construction are also provided with special gum boots and hand gloves.

Site Safety Protocols

At every HIPL construction project site, a safety officer assists the project manager in implementing safety guidelines and reviewing risk assessment. Together they conduct multiple levels of safety inspections at site on a continuous basis, making on-the-spot corrections.

Before the beginning of any project operations, the safety officer and the project manager conduct a safety meeting with all staff members. This session educates everyone involved in the project about the various steps to be taken to avert any untoward incident that might put anyone in danger or cause loss of property.

Hard Barrication is done prior to construction commencement. Clear and visible signages like Deep Excavation, Non PPE Zone, Active Drilling in Process, Electrical DG Set Zone, Cage Making in Progress etc are placed to ensure site identification.

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