Modelling box culverts on the geotechnical centrifuge

Abstract

Testing scale-models of buried structures on the geotechnical centrifuge allows the user to simulate load conditions on buried prototype structures. The advantages of testing centrifuge models over testing full-scale prototypes are that centrifuge modeling requires much less time and materials and can be done at a much lower cost. This study involved testing box culvert models on the geotechnical centrifuge operated by the Civil Engineering Department at the University of New Brunswick, Fredericton, New Brunswick. The main purpose of this study was to determine if soil arching occurred during these tests. The soil arching occurs in situations where there is a downward deflection due to loading across the roof of the culvert. Thus, the culvert roof is, in theory, bearing less pressure than would be predicted from the standard equation of the unit weight multiplied by the height of fill. The design implications are that a structure may be over-designed if the actual load conditions are less than the design loads. That is, the structure may be over-designed if the occurrence of soil arching was not taken into account when calculating the load on the roof. A solid, plywood model culvert was constructed for the model. The dimensions of the model in millimeters were 200L, 77W and 5OH . A plywood strongbox was built to house the model and fill above and around the culvert during the testing. Diaphragm-type pressure transducers were installed on the top and side of the model. The fill heights, measured from the top of the model, were 25, 50, 65 and 80 mm. A separate calibration test was also performed in which a plywood sheet with transducers was installed in the strongbox in place of the model culvert and buried under 97 mm of fill. All linear dimensions in the centrifuge models can be converted to their corresponding prototype dimensions by multiplying the model dimension by the maximum g-level generated during the testing, which in this case was 30. The results indicated that no soil arching took place. That is, the measured pressures at the top of the culvert agreed reasonably well with pressures predicted from the unit weight of the fill multiplied by the fill heights. Therefore, no design modifications were recommended for the fill heights and culvert rigidity studied in this research.