Pipe-CLSM Interface Bond Strength From Axial Pullout Testing

Abstract

Buried pipeline systems form the backbone of the oil and gas transportation infrastructure, and the performance of these systems located in areas subject to potential ground movements is a critical consideration in engineering design. In mitigating against future or on-going ground displacement hazards, there are instances where the axial soil restraint (soil anchoring capacity) needs to be increased to avoid transferring loads to adjacent potentially vulnerable components in the pipeline system. One method to increase axial soil restraint is to increase the effective diameter of the pipeline. This can be done by encasing the pipeline in controlled, low-strength material (CLSM). The use of CLSM to increase axial soil restraint on buried pipelines requires that the axial load to produce pipe-CLSM interface bond failure be greater than that required for failure at the CLSM-soil interface. To advance the state of knowledge of the axial failure mechanisms of the soil-CLSM-pipe composite, a systematic full-scale testing program was undertaken using the Advanced Soil Pipe Interaction Research (ASPIRe™) modeling chamber at the University of British Columbia. Research findings from 22 axial pullout tests that were completed to assess the bond strength at the interface between CLSM and NPS 8 steel pipe specimens with various coatings are presented. The tests reveal that the bond strengths as a percentage of compressional strength measured in studies of CLSM cast around cold-formed steel align closely to the values measured from these tests.