Pull out behaviour of geosynthetics when tested at bench scale

Abstract

Geosynthetic products are used for various applications and functions in pavement construction and design. The benefits in using geosynthetics in pavement applications have led to proliferation of geosynthetic products. This report investigates effectiveness of the lateritic gravel soil and geosynthetics used in constructing high fills or stabilized earth walls in the rehabilitation of the Nyamasaria - Kisumu Road project. The increase of using geosynthetics in high fills has enhanced the necessity to evaluate the interface resistance and the pullout properties in different types of backfills. This report studies the use of lateritic gravel as an appropriate backfill in high fills. The interface considerations between the geotextile and soil was assessed in pull-out tests. Testing programs included carrying out laboratory pull-out tests on geotextile. Laboratory pullout testing was done using pull-out testing equipment at the University of Nairobi, Civil Engineering Department. It was deduced that the pull-out load increased with increased surcharge pressure tested. An increase in the pull-out load was attributed to additional resistance caused by bearing stresses acting on the strap edges when the pressure was increased. The interaction between soil particles and surface of geobelt was increased when the surcharge pressure exerted was increased as compared to the control soil sample where lateritic soil offered less resistance resulting in a low bearing stress and consequently a low resistance. Similar to the test results on the geobelt, the effect of the specimen length was measured near the peak load at the late stage of pull-out. Thus, surcharge pressure of 5 kN/m2 at a constant compaction had an output pull-out load of 1060N this was much lower as compared with a surcharge pressure of 10 kN/m2 producing a pull-out load <1400N. This out-put is progressive as it increases as the surcharge pressure increases. An increase in the pull-out load was attributed to additional resistance caused by bearing stresses acting on the strap edges when the pressure is increased. These stresses resulted as the geobelt strap was pulled against motion and force exerted away from the centreline. The interaction between soil particles and surface of geobelt is increased when the surcharge pressure exerted is increased as compared to the control soil sample where lateritic soil offers less resistance resulting in a low bearing stress and consequently a low resistance. Thus lateritic gravel as a backfill and foundation material showed very small deformations. Since permeability is more for gravel and drainage is good. Consequently, there was less excess pore water pressure developed behind and beneath the pullout box.