Field monitoring and analysis of twin 3660 mm inside diameter induced trench culverts installed under 21.7 m of fill

Abstract

Although several induced trench field instrumentations have been reported in the literature, none have been for twin culverts. This paper describes a field instrumentation of twin 3660 mm inside diameter concrete culverts installed in an induced trench under 21.7 m of fill. Earth pressures were measured at the crown, shoulder, springline, haunch, and invert locations. Average earth pressures measured at the crown and springline were 0.67 and 0.32 times the overburden, respectively. Due to the large culvert size, proper compaction in the haunch regions was not achieved and the bedding was lightly compacted for constructability reasons. These factors resulted in high earth pressures at the inverts (greater than approximately 1400 kPa) and low pressures at the haunches (32–165 kPa). Numerical modelling was used to determine a vertical earth load of 0.87 times the soil prism load. The twin induced trench condition resulted in vertical earth loads 6% higher and 30% lower than the single induced trench and twin positive projecting conditions, respectively. The induced trench method therefore appears to be a viable installation option for large-diameter twin culverts, provided that issues related to bedding and constructability are addressed.