Strengthening soil with synthetic fibres

As a schoolgirl in Surat, Uma Chaduvula once saw the flooring of her house get damaged due to expansive marine soil underneath. Little did this research scholar with the IITB-Monash Research Academy imagine then that she would one day conduct research to find solutions to this problem.

Soil is available in abundance, and, in theory, can be used as construction material. However, its main drawback is lack of sufficient tensile strength and durability under wet/dry/thermal cycles, due to which it is replaced by other materials at construction sites.

The swelling and shrinkage of soil (in the presence and absence of water, respectively) can cause substantial damage to multi-storeyed buildings, roads, pipelines, and railway lines. Uma’s project aims to modify the properties of expansive soil through synthetic fibre reinforcement, thereby rendering this soil effective for sustainable use.

The Academy is a collaboration between India and Australia that endeavours to strengthen scientific relationships between the two countries. Graduate research scholars like Uma study for a dually-badged PhD from both IIT Bombay and Monash University, spending time at both institutions to enrich their research experience.

Expansive soil can be used as a sustainable material in construction if its engineering properties are modified with suitable additives, explains Uma. “Methods such as soil replacement, construction of belled piers, and chemical stabilisation using lime and cement have been adopted to mitigate the problems posed by expansive soils.”

Discrete fibre reinforcement is emerging as a possible method to modify and improve the engineering behaviour of soils. In this, synthetic or natural fibres are distributed discretely throughout the mass of soil, she adds.

“Modified expansive soil can be used as waste containment systems, barriers, and slurry walls,” says Uma. “Fibre reinforcement helps in preventing tensile crack formation, gives better ductility, and reduces swelling and thermal conductivity. Synthetic fibres like polypropylene, polyester, polyethylene, glass, steel and polyvinyl alcohol have better strength, life, availability and versatility as compared to natural fibres like jute, sisal and coir.”

“The fibres,”she adds, “decrease the connectivity of crack networks, as shown in Figure 2.” During her research, she found that the mixing of synthetic fibres in expansive soil improves its performance significantly. Fibre reinforcement was found to be effective in restraining desiccation cracking of expansive soil. The addition of fibres controlled the crack width, the cracked area, and the propagation of cracks.

Figure 2. Plan view of crack propagation in unreinforced and fibre-reinforced specimens at the end of 450 minutes of drying (after Chaduvula et al. 2017)

Says Prof Murali Sastry, CEO, IITB-Monash Research Academy, “As the reputation of the Academy continues to grow and as more organisations start collaborating with us, we anticipate that the Academy will contribute to maintaining India’s reputation as a leading-edge global research hub. Uma is attempting to advance fundamental knowledge in modelling thermo/hydro/mechanical behaviour of reactive soils. The models developed will have multiple uses – from helping assess moisture and temperature changes on the ground and how it affects the geo infrastructure such as roads, houses, etc., to assisting in nuclear waste isolation.”

So, the next time you spot a building that stands tall in spite of the expansive soil underneath, you know who contributed to making this possible