Influence of specimen stiffness and in-soil temperature on pullout response of PET straps

The study reports the results of a testing program to evaluate the pullout response of PET strap reinforcement of different grades at various vertical stresses and in-soil temperatures. Tests were carried out using a well-graded, granular soil with small fines content. Pullout response and reinforcement longitudinal stiffness were evaluated using measured pullout loads and front- and tail-end displacement measurements. Pullout resistance was observed to increase non-linearly with increasing vertical pressure (or depth). Overall, temperature variations in the range of 15°C to 35°C did not result in practical differences in peak pullout resistance. However, in-soil temperature appears to influence reinforcement longitudinal stiffness, more so than vertical pressure calculated, at peak pullout load. The accuracy of four analytical models for pullout resistance and friction interaction factor was quantified using bias statistics. Data showed higher spread between measured and calculated values at shallow depths, attributed to a greater sensitivity of the dilatant response to vertical pressure and compaction conditions. Model accuracy dependency with calculated pullout resistance and vertical pressure was explored. Bi-linear and non-linear pullout models were found to be statistically more accurate than the linear pullout model which appears in many design codes.