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Indian Journal of Geosynthetics and Ground Improvement
Year : 2012, Volume : 1, Issue : 1
First page : ( 30) Last page : ( 31)
Print ISSN : 2277-5625. Online ISSN : 2277-5633.

Behaviour of Geocell in Cohesionless Soil – an Experimental Study

Biswas Sefali, Assistant Engineer

PWD, Government of West Bengal, Kolkata

Online published on 29 May, 2012.

Abstract

A numbers of ground improvement techniques are available for improving the load carrying capacity and engineering properties of those soils which otherwise are not suitable for normal construction. An examination of the existing literature indicates that the bearing capacity is considerable improved with planar geogrid. Present work is focused on 3D reinforcement i.e. geocell. However, a comparative study has also been done on the performances of geocells and planar geogrids. The soil used in the model tests was locally collected Solani river sand with relative density as 60% and shear parameters c=0 & Ø=320. The soil classification was SP. A rigid square steel tank of size 1130 mm x 1130mm x 800 mm was used in the laboratory model test. The footing was 200 mm x 200 mm x 10 mm steel rigid M S plate. Two types of reinforcements e.g. planar geogrid and 3D geocell were used. The geocell were made by using RE 80 Tensar uniaxial geogrid with tensile strength 88.7 kN/m. The geocell had aperture size of 200 mm x 200 mm with diamond pattern and cell height of 200 mm.

Numerical analysis results obtained by PLAXIS software had been compared with those obtained from experiments and were found to be in good agreement. A parametric study revealed the role of reinforcement on bearing capacity in terms of its length, spacing between layers etc. The study shows that the improvement in bearing capacity with respect to unreinforced soil was of the order of 93.75% and settlement reduction was 13.07% for single layer of geocell which for double layers of geocell is 298% and 86.48% respectively. Study shows that the savings in cost is 21.6% for single of layer of geocell and 91.5% for double layers of geocell with respect to unreinforced soil.The total length of reinforcement used in model test was 700 mm. Location of reinforcement from top for single layer of geogrid was kept as 0.5 times the width (B) of footing. In case of double layers of geogrid, first layer was placed at 0.5 B and second layer was placed at 1B from top surface of soil. In the case of geocell tests, the single layer was placed at 0.5B depth and for double layers tests, the geocell were placed at 0.5 B depth and 1.75B from top.

For verification of the the results obtained by model test with Plaxis Software, the value of was obtained by conducting large size direct shear tests, conducted on soil sample of 300 mm x 300 mm x 200 mm size. The results obtained by experimental work and by Plaxis analysis were within ± 12%. The cost comparison was done for a virtual problem of a RCC column of size 400 mm x 400 mm, proposed to cater a load of 1500 kN, the foundation of which was proposed either on unreinforced soil or soil reinforced with geocell. The design was done for 25mm permissible settlement, (Structural design done as per IS 456:2000). The same is explained in following table (rates as per current prevailing rates in West Bengal PWD)

ItemsVirgin SoilSoil reinforced with single layer of geocellSoil reinforced with double layers of geocell

Bearing capacity104 kN/m2193.75 kN/m2759 kN/m2
Foundation size4200 mm x 4200 mm (RCC isolated footing)3000 mm x 3000 mm (RCC isolated footing)1500 mm x 1500 mm (RCC isolated footing)
Concrete volume5.36 m32.99 m31.04 m3
Steel542 kg304 Kg66 Kg
Geocell Cost-Rs 17,820/-.Rs. 9,460/-.
Total CostRs. 55,616/-Rs. 48,916/-Rs. 18,568/-

From this study, it is concluded that foundations supported on geocell reinforced soil are very economical and smaller in size as compared to those supported on soil without reinforcement.

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