The effect of dynamic compaction forces is ignored in the analysis and design of underground structures. Several failure cases have been reported in which longitudinal cracks are observed during installation and compaction processes. Because, in the current specifications, compacting forces are not considered as design parameters, this study aims at determining the effect of dynamic compaction forces on RC pipes of different sizes. Thus, complete nonlinear three-dimensional finite-element models of pipe and soil are developed and verified against full-scale experimental testing. Particularly, crack initiation and propagation are modeled and predicted. Finally, the effects of dynamic forces are identified on the RC pipe.

Nonlinear Finite-Element Modeling Analysis of Soil-Pipe Interaction

Experimental-numerical study on the structural failure of concrete sewer pipes

Excavator-mounted hydraulic plate compactors have been widely used in utility trench backfill compaction due to their efficiency. However, there are industry concerns on the possibility of pipe damage due to the combination of static downward earth pressure exerted by the excavator arm and dynamic earth pressure induced by the excavator-mounted hydraulic plate compactor. This paper presents the results of a field study that aims to compare the performances of utility trench compaction using a conventional walk-behind vibratory plate compactor with a lift thickness of 200 mm (8 in.) and an excavator-mounted hydraulic plate compactor with a lift thickness of 200 mm (8 in.), 300 mm (12 in.), 450 mm (18 in.), and 600 mm (24 in.). A flexible PVC pipe was used. The field test results indicate that the excavator-mounted hydraulic plate compactor delivered comparable compacted dry mass densities with a lift thickness of 200 and 300 mm as the walk-behind vibratory plate compactor did with a lift thickness of 200 mm; however, the excavator-mounted hydraulic plate compactor was not able to consistently achieve adequate compacted dry mass densities with a lift thickness of 450 and 600 mm. The excavator-mounted hydraulic plate compactor induced larger dynamic vertical earth pressures than did the walk-behind vibratory plate compactor.

Utility trench backfill compaction using vibratory plate compactor versus excavator-mounted hydraulic plate compactor

Evaluation of Aggregate Compaction Using Excavator-mounted Hydraulic Plate Compactors

Effect of biochemical attack on the mechanical performance of used concrete sewer pipes

Laboratory testing of buried pipe was conducted to evaluate the pipe-soil interactions that take place as pipes are backfilled. The program consisted of 25 tests with metal, plastic, or concrete pipe. In addition to pipe type, test variables included trench conditions, backfill material, compaction method, haunching effort, and bedding condition. The tests were conducted in an indoor test facility designed to allow for the installation of pipe in a realistic manner. Pipe and soil behavior were monitored during installation, and measurements included pipe deflections, pipe strain, pipe-soil interface pressures, soil density, soil strength, and horizontal soil stresses. Backfill was placed to at least 150 mm above the spring line to observe the effects in the important haunch zone. Ten of the tests were continued until the backfill was at least 300 mm over the pipe. The results indicated significant variations in pipe behavior because of installation practices. The wider trench produced greater upward deflections during sidefill compaction. The rammer compactor was the most effective means of achieving high backfill density and stiffness, forcing backfill into the haunch zone, and developing beneficial lateral soil stresses at the sides of the pipe. Installation in trenches with walls of soft materials results in lower lateral pressures and higher invert pressures on the pipe. The coarser-grained backfill material achieved suitable soil unit weight and stiffness with less compactive energy than the finer-grained material. The haunching effort provided improved pipe support in the lower haunch zone.

Glen V. Zoladz

Papers

Laboratory Tests of Buried Pipe Installation Procedures