Publication no. 74, Load reduction on buried rigid pipes
Abstract
Buried culverts are extensively used in road construction. Arching is a soil-structure interaction concept that plays a key role in most of the culvert installations. In effect, arching is the behaviour of the soil-structure system involving redistribution of soil stresses around the structure from the values that would occur if the structure were not present. In positive arching a portion of the load over the structure is transmitted to the soil around the condiut. Negative arching is unfavourable and implies that the culvert is drawing more load than the column weight of soil over it. Terziahgi described arching action in soils as "One of the most universal phenomena encountered in soils both in field and in the laboratory. Since arching is maintained solely by shearing stresses in the soil, it is no less permanent than any other state of stress in the soil wich depends on the existence of shearing stresses, such as the state of stress beneath the footing of a column. " Terziaghi also stated that the amount of arching can only be obtained by direct measurement on full scale structures in the field. Arching is important in two types of buried culverts: • long-span flexible steel culverts • imperfect ditch culverts. The imperfect ditch method involves incorporating a compressible layer within the backfill above a rigid culvert. As the backfill is placed, the soft zone compresses more than the surrounding soil and thus induces positive arching above the culvert. Two flexible steel culverts, two concrete pipes and one east in place box culvert are instrumented for monitoring the behaviour during construcion and on a long-term basis. Expanded polystyrene is used as compressible material in the fill above the rigid culverts. A shorter version of the second paper "Load reduction on rigid culverts beneath high fills. Long-term behaviour" received the K. B. Woods award at the 73rd annual meeting at the Transportation Research Board in Washington in January 1994. The K. B. Woods award is presented for the outstanding paper in the field of design and construction of transportation facilities. The work in the first paper was published in Pipeline Crossing Proceedings, Special Conference, Pipeline Division ASCE, Denver Colorado March 25-27, 1991. The work in the second paper was published in Transportation Research Record no. 1415, Transportation Research Board, National Research Council, Washington D. C. 1993. The work in the third paper was published in Transportation Research Record no. 1231, Transportation Research Board, National Research Council, Washington D.C. 1989. The county roads offices in Buskerud, Hordaland, Oppland and Telemark are greatly acknowledged for making it possible to perform instrumentation on the field installations. Tor Helge Johansen and Willy Holm are greatly acknowledged for their careful work on the instrumentation and field operations.
Description
Publication no. 74, Load reduction on buried rigid pipes