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Due to insufficient backfilling and compaction, voids existing around the bottom of a buried pipe can have a negative effect on the mechanical behavior of the pipe. Expanded polystyrene (EPS) has been widely utilized in civil engineering as fill, backfill, moisture cutoff, and impact mitigation materials for falling rocks because of its light weight and workability. In this study, centrifuge model tests were conducted in order to investigate the possibility of pipe failure when voids existed around the bottom of the buried pipe, and the effect of installing EPS blocks as a countermeasure. In the test, a model polyvinyl chloride (PVC) pipe having a diameter of 140 mm was buried in the dry sand and loaded at the ground surface in a centrifugal field of 21G. Cases with voids around the bottom of the buried pipe and with EPS blocks were studied, and the differences in the pipe mechanical behavior under standard backfill conditions were discussed. The loading conditions and the shape of the EPS were varied. The test results showed that the loss of soil around the bottom of the pipe caused a stress concentration by a factor of more than 2.5 compared to the typical burial condition, and could directly cause pipe failure. In addition, it is clear that EPS installation was an effective countermeasure to avoid the risk of insufficient compaction, because it did not significantly affect pipe deformation and strain distribution, although the earth pressure tended to concentrate slightly at the bottom of the pipe. Practical Applications: Pipelines that are buried in the ground usually need to be backfilled uniformly with soil around the pipe. However, due to difficulties in construction, the backfilling and compaction may be insufficient on the bottom sides of the pipe, resulting in voids or localized low-density areas. In this study, centrifuge model tests were conducted to investigate the behavior of pipes buried in such nonuniform ground and the effectiveness of a countermeasure to install expanded polystyrene foam (EPS) blocks as a foundation instead of backfilling with soil. In the tests, a 150-mm-diameter polyvinyl chloride (PVC) pipe was buried in a container, and the strain of the pipe was measured in detail when a vertical load of up to 140 kPa was applied to the ground surface in a 20G centrifugal force field. As a result, when the soil in the lower part of the pipe is not uniform, a large strain is concentrated at the bottom of the pipe, which may lead to the pipe failure. Then, when EPS was installed, no large strains were measured, indicating that EPS installations are effective as a countermeasure. [ABSTRACT FROM AUTHOR]

The existing design guidelines for buried flexible pipes are limited to depth up to l0 m. The increasing use of difficult terrains for infrastructure, landfills, and residential and industrial developments has prompted installation of drainage pipelines under 20-30 m high fills. This paper presents the behavior of an instrumented flexible pipe buried under a 47.1 m deep fill. For filling above 20 m, the measured vertical stress above the pipe exhibited a concave distribution, corresponding to 90 and 110% of the average vertical pressure at the center and edges of the pipe, respectively. The measured results suggest that a triangular lateral pressure distribution can lead to overly conservative and uneconomical results for high fills while Spangler's analysis is unconservative. Based on the measured results, a revised vertical and lateral earth pressure diagram was proposed for the design of flexible pipe under high fills >20 m. This paper proposes closed-form analyses for estimating the moments and displacements of the pipe subjected to high fill earth pressures. These closed-form solutions agree well with the measured pipe displacements and strains. CE Database subject headings: Pipelines; Fills; Flexible pipes; Earth pressure; Deflection.

This study focused on the behavior of a large-diameter burial pipe with special reference to its stability against flotation subject to soil liquefaction. Centrifugal modeling technique was used where the results are presented for a total of eight shaking table tests conducted on the burial pipe in a laminar box under 30g gravitational field. The ground was prepared with Nevada sand at a relative density of 38% and shaken with a sinusoidal wave at an amplitude of 0.5g. The use of a viscous fluid in a saturated soil deposit satisfied the time scaling relationships of both dynamic and dissipation phenomena. The centrifugal modeling technique simulated flotation of pipeline as the soil liquefied. A technique that used gravels and geosynthetic material was used to mitigate flotation. The response of the soil deposit, in terms of acceleration and excess pore pressure, was investigated. The uplifting of the pipe, earth pressure response and ground surface deformation were also presented. Based on the test results, a design procedure was proposed for the burial pipe in resisting flotation due to soil liquefaction. The deadweight and stiffness of the gravel unit, which was confined by geosynthetic, were important items in design. DOI: 10.1061/(ASCE)1090-0241(2003)129:12(1092) CE Database subject headings: Centrifugal models; Liquefaction; Geosynthetics; Buffed pipes; Nevada; Remedial action.

Equations are provided and discussed for calculating the long-term settlement rate of solid waste within sanitary landfills. Topics include distinction between settlement and decomposition, and the appropriateness of a model.

The tensile behavior of three commonly used polymeric geogrids (polypropylene, polyester, and high-density polyethylene) under cyclic loading was investigated. The tests were strain controlled and were conducted for 100 cycles at different load ratios. The stiffness and damping ratio of geogrids at all load cycles were compared with the primary loading curve. The stiffness increased while the damping ratio decreased with more loading cycles at any load ratio. A higher load ratio decreased the stiffness ratio and increased the damping ratio. The strengths of prestressed and virgin specimens were also compared. Negligible strength reduction resulted from short-term cyclic loading. The strength obtained from static tests appears reasonable when used for design considering short-term cyclic loading. An empirical relationship is proposed to determine the strain accumulated from cyclic loading under different load ratios.

The municipal solid waste landfill suffers from large postclosure settlement that occurs over an extended period of time. A large differential settlement may impair foundations, utilities, and other associated facilities constructed on top of a landfill. It may also lead to breakage of the geomembrane and damage of the cover system in a modern municipal solid waste landfill. The waste material exhibits heterogeneous engineering properties that vary over locations and time within a landfill. These factors, combined with the fact that a landfill is not fully saturated, render a traditional soil mechanics approach less attractive for settlement prediction. An empirical approach of expressing settlement rate using logarithmic and power relationships is commonly used in conjunction with an observational procedure. In this paper, validity of these functions is reexamined based on published settlement results from three landfill sites. A hyperbolic function is proposed as an improved tool to simulate the settlement-time relationships, as well as to detect final settlement. The relationships between the parameters of these empirical functions and water content are examined.

The scour observed at the landside ground behind coastal protection facilities, such as seawalls and coastal dikes, due to tsunami overflows is the main reason for failures in such constructions. In this study, we focused on sheet-like (two-dimensional) scour countermeasures, which do not require large-scale excavation of the ground, and experimentally verified the effects of geonet and mesh sheets. By applying a vertical jet directly on the ground and increasing the external force, a situation close to the real scale conditions was reproduced. The experimental results show that the geonet material is able to significantly reduce the scour depth on both non-liquefied and liquefied grounds. We show that in the most effective case, the maximum pore-water pressure and the scour depth are reduced by about 91% and 86%, respectively, by the mesh sheet on the sand-bed surface. [ABSTRACT FROM AUTHOR]

To reduce the damage caused when a tsunami overflows coastal dikes, this study performs hydraulic experiments and numerical simulations and proposes a new method for slowing the tsunami by intentionally eroding parts of the ground. The effectiveness of the proposed method is assessed, velocity-reduction mechanism is clarified, and reduced tsunami velocity is predicted. Using crushed expanded polystyrene (EPS) as the ground material, vertical erosion is enhanced and a large depression is formed that changes the flow from supercritical to subcritical, thereby decelerating it. Assuming a constant tsunami overflow rate, the tsunami velocity after deceleration can be predicted with ∼ 2 0 % uncertainty. [ABSTRACT FROM AUTHOR]