Ground improvement & pavement stabilisation with geosynthetics products

A case study on ground improvement & pavement stabilisation with a range of geosynthetics products

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Ground improvement
The project site of Talegaon-Katvi Road in Pune

Talegaon Dabhade is a town in Mawal Taluka, Pune district, in the Indian state of Maharashtra. It is 120 km from Mumbai and 35 km from Pune. Situated very close to Lonavala, which is a hill station, Talegaon receives ample rainfall during monsoon. The Talegaon – Katvi road is situated right next to the MIDC area of Talegaon. Katvi and Ambi are two areas adjacent to each other which are the upcoming locations on Talegaon MIDC Road. At the project site of Gat No 40/1, Talegaon-Katvi Road, Village Katvi, Maval Taluka, District Pune, a site visit was conducted by Engosym consultants based on the request of the client M/s Earnest Group. Aayush Park is a land development project planned and developed by M/s Earnest Group which is surrounded by meandering Indrayani river and Sahyadri hills. The soil investigation report indicated the presence of weathered basaltic rock under a layer of overburden. The overburden consisted of filling, brownish stiff clay and clay with rounded rock fragments. The thickness of the overburden layer was observed to vary from 3m to 6m deep from the existing ground level. Geotechnical investigation report also indicated presence of ground water table at a depth of 0.5m to 2m from the existing ground level. The approach road to the plot to be developed was at a lower elevation as compared to the elevation of the main plot. The natural topography of the site was such that the entire surface flow of water was directed towards the approach road location. To add to the complexity, a stream is flowing below the approach road which flows full to its capacity during monsoon as it carried a certain amount of discharge of the Indrayani river.

The client wanted to ensure sale of the development scheme and which was possible only if the area had a good, safe and smooth access to the site. In addition to all the criticalities cited in the earlier paragraphs, consistent passing of heavy loaded vehicles was also expected during the development stage of the area.

Considering the critical factors like poor conditions of the underlying soil, shallow groundwater table, heavy rains and the loading expected on the pavement, it was suggested to strengthen the approach area zone with flexible and permeable measures.

Composite solutions with a range of geosynthetic products were considered and designs were carried out based on the in-situ parameters and the relevant characteristics of the geosynthetic product in consideration for the intended application. The approach road was excavated to a depth of 1.5m and the area had to be dewatered completely before commencing any treatment measure. The base layer was sun dried and was dusted with a layer of Murrum (Murrum soil comes under laterite soil. Laterite is a soil and a rock type rich in iron and aluminium. Murrum soil is also referred to as being a rock type but it is not a rock). Once a firm base was created, a layer of non-woven geotextile was provided to act as a separator between the underlying soil and the treated layer. This geotextile would also act as filter media at the base level.

The geotextile layer was followed by a 100mm to 150mm thick layer of murrum filling that was compacted and prepared for laying a layer of polyester geogrid. This geogrid would act as a basal reinforcement layer and its function is to uniformly distribute the stresses to the base strata. A layer of geomembrane was provided towards the top of the pavement to prevent the infiltration of the surface water to the base layer. Bi-axial geogrid was laid at the topmost layer to act as tensile membrane to effectively transmit the stresses to the base layers.

Conventional pavement layers were laid followed by the final bitumen layer. It is interesting to note that Gabion layers were provided on the edge of the roads to act as confining elements and ensure retention of the filled-up layers.

Geosynthetics have been used for pavement stabilisation to address various functions like separation, filtration, drainage, sealing and reinforcement. The improved performance of pavement due to geosynthetic reinforcement can be attributed to three mechanisms, lateral restraint, increased bearing capacity and tensioned membrane effect. These methods effectively solve the problem with advantages like assured quality, being ready for factory-made products, ease in installation, reduced carbon footprints, saving natural resources and cost effectiveness. With the cited advantages, attention to quality control of installation at site assures the performance of the solution as per design and hence a problem free structure was achieved. In the project discussed above, the client is satisfied with the solution provided as there was no water logging or settlement observed at the approach road and a smooth ride was assured to the prospective clients of Earnest group.

Authored by:-

Annapoorni Iyer, Founder, Engosym Consultants (Channel Partner of Gripple Hangers and Joiners Private Limited)

About Author

Annapoorni Iyer has 16+ years of experience working in infrastructure projects involving solutions to core Geotechnical problems. Experience in handling projects in Sectors like Roads, Highways, Railways, Mining, River Training, Coastal Protection, focused on providing solutions to Geotechnical and Hydraulics related problems. She holds B. E (Civil), MBA (Infrastructure and Construction) and Chartered Engineer degrees.

Website- https://engosym.com/