Behaviour of Subgrade Soil Reinforced with Geogrid

Abstract

The beneficial effects of reinforcing subgrade soils with a single layer of geogrid and their behaviour under static and cyclic loading are investigated. Three types of soil and two types of geogrid varying in their stiffness were selected. CBR, static triaxial and unconfined compression tests were conducted by reinforcing the samples at different depths within the sample height. The optimum position was decided based upon the CBR value, the modulus of elasticity (E-value), and deviator stress at failure. Cyclic triaxial tests were conducted for unreinforced specimens as well as reinforced specimens at the deduced optimum position of the geogrid to study their behavior under repetitive loads. The results showed that CBR and E-values increase with reinforcement and attain the highest values when geogrid is placed at a depth between 72 and 76% from top of the specimen. Height of specimen in laboratory for all practical purposes means thickness of compacted layer of subgrade soil in the field. The results of cyclic triaxial tests indicated that the resilient strain in unreinforced soil samples decreased by almost 35% with geogrid reinforcement. Further, geogrids can play an important role in the control of the rut formation in the pavement system as the permanent strain in reinforced samples decreased by 44% of that in unreinforced samples.

Keywords:

• CBR
• Triaxial
• Geogrids
• Resilient modulus
• Permanent strain

Notes

ASTM D1557-02 standard test methods for laboratory compaction characteristics of soil using modified effort.

ASTM D1883-99 standard test method for CBR (California Bearing Ratio) of laboratory-compacted soils.

ASTM D2850-03 standard test method for unconsolidated-undrained triaxial compression test on cohesive soils.

ASTM D5311-92 standard test method for load controlled cyclic triaxial strength of soil.