Stabilization of expansive subgrades using geogrid reinforcement – An experimental study

K, Charan and Umashankar, B (2019) Stabilization of expansive subgrades using geogrid reinforcement – An experimental study. Masters thesis, Indian institute of technology Hyderabad.

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Abstract

In India, there are one-fifth lands covered with expansive soils, which are not viable to construct any kind of structures. In recent years, many problems have been observed in structures on expansive soils. Since many years, lot of researchers have proposed new modifications techniques to improve expansive soils to construct infrastructure facilities on such deposits. The present research work aims at contributing to improve the expansive soils by installing geogrid reinforcement to resist uplift forces. The main objective of the present study is to check the performance of geogrid reinforcement to reduce swelling strains. In addition, it aims to estimate the performance of geogrid in terms of reduction in swelling strains in expansive soils. A 300mm-diameter swell measuring equipment had been fabricated to check the geogrid performance in terms of strains due to swelling of soil. Soil sample of 300mm diameter and 58mm height was prepared at dry of optimum water content to ensure more swell strains that may occur in practice. The equipment had provision to connect to taps to maintain water supply throughout the test. Soil sample was prepared in between two sand layers of 30 mm of each to function as a porous material at top and bottom. 58mm-thick black cotton soil sample is placed in between these two sand layers and swell strains were monitored. Vertical sand drains were provided to saturate the soil sample more quickly. The geogrid is installed just above the 58mm thick soil sample and below top sand layer. The geogrid is anchored with L-shaped nails to hold it in position. This setup was monitored for a week by using the dial gauges. The first stage of the research work was aimed at fabricating the 300mm diameter swell measuring equipment. It was observed that using geogrid with anchoring has reduced the swell strains significantly. The geogrid aperture size effect was also studied in this research. Finally, the effect of type of interface soil layers with the geogrids reinforcement on expansive behaviour was also studied. The control section swell strains for the soil SW_S1 is 7.9% and for SW_S2 was 19.6%. The research emphasized on reducing tis swell strains by using geogrid reinforcement. The geogrid without anchored was shown no significant reduction in swell strains it was similar to the control section results. The geogrid which is placed with anchoring was reduced significant swell strains for SW_S1 soil the swell strains reduced to 4.6%. And the next series of tests conducted to find out the effect of geogrid types in reducing swell strains. The two types of types of geogrid were used in this series of tests the results were fort the SW_S1 by using GG-1 was reduced to 4.6% and by using GG-2 was reduced to 4.7%. For the SW_S2 soil with GG-1 strains were reduced to 13.1% and for GG-2 strains were reduced to 13.6%. Further, the effect of the soil type reinforcement interface effect studied. Results of this test series of tests were for SW_S1 soil at C-G-S reduced to 4.6% from 7.8%. And for S-G-S strains were reduced to 6.1% from 7.8%. Hence it was advised to use the geogrid at C-G-S interface

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