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The use of controlled low strength material (CLSM) as a pipe bedding and backfill material requires characterization in terms of traditional design parameters such as bedding factors for rigid pipe and modulus of soil reaction, or E', values for flexible pipe. Triaxial compression and one-dimensional consolidation tests were conducted on two mixes of air-modified CLSM to establish parameters for use in finite element analyses of buried pipe installations. Both trial mixes contained 25 to 30% entrained air to provide flowability. The tests were conducted at ages of 16 hours, 7 days and 28 days to evaluate the change in strength and stiffness with time.
Results of the tests were analyzed to fit parameters to the Duncan hyperbolic soil model with the Selig bulk modulus model. These parameters were then used in analyses of flexible and rigid pipe installations, backfilled with CLSM, to determine traditional installation design parameters.
The finite element analyses indicate that bedding factors for rigid pipe installations range from 1.8, for trench installations backfilled at an age of 16 hours, to 2.5 for trench installations backfilled at an age of 28 days. Bedding factors for embankment installations of rigid pipe range from 2.5 to 4.8 for ages from 16 hours to 28 days, respectively. Values for the modulus of soil reaction (E') for installation of flexible pipe range from 7 MPa to 21 MPa (1,000 psi to 3,000 psi) for ages from 16 hours to 28 days respectively.
buried pipe, CLSM, flowable fill, backfill, modulus of soil reaction, bedding factor, triaxial testing, fly ash
Principal, Simpson Gumpertz & Heger Inc., Arlington, MA
Technical Services Engineer, Grace Construction Products, Cambridge, MA