The Use and Role of Lightweight Backfilling Materials in the Installation and Performance of Buried Pipelines/Culverts

The special collection on The Use and Role of Lightweight Backfilling Materials in the Installation and Performance of Buried Pipelines/Culverts is available in the ASCE Library (https://ascelibrary.org/jpsea2/lightweight_backfilling_buried_pipelines)

Analysis of buried pipelines and culverts shows that vertical earth pressures play a significant influence on the sizing of these types of buried structures, especially for those structures buried under high fills. The use of lightweight backfilling materials can be highly beneficial to buried pipes and culverts due to the fact that they are able to reduce the vertical earth pressures—both immediately and in the long term—on the previously stated buried structures, and therefore the stresses and/or deflections in the same structures. The reduced earth pressures also allow savings in the design for the pipe/culvert walls. Furthermore, the use of lightweight backfilling materials offers significant savings in time, cost, and quality compared to the use of natural fill materials.

Lightweight materials (LWMs) can consist of a variety of materials, both natural and/or derived from industrial process [e.g., expanded polystyrene blocks (EPS-geofoam), cellular concrete (foamed concrete), lightweight aggregate like expanded clay aggregate, foam-glass aggregates, recycled tire chips mixed with soil]. Thanks to their own mechanical and physical properties, lightweight backfilling materials are rapidly gaining acceptance and application in the installation of buried structures. Therefore, the comprehension of their mechanical behavior and the interaction with the buried structures is fundamental in creating an optimum and safe design of the same buried structures.

This special collection focuses on the use and role of lightweight backfilling materials in the installation and performance of buried pipes/culverts in order to gain further insights into a crucial issue and to ensure the desired performance of buried pipeline systems, especially when buried under high fills. Papers in this special collection will be invaluable to practicing engineers and researchers in the field of pipeline engineering.

This special collection contains six technical papers and one case study focused in this area, which cover the topics regarding the mechanical behavior and physical properties of the LWMs, laboratory scale tests on LWMs, and full-scale tests of buried pipes/culverts installed using LWMs.

The paper by Mahgoub and El Naggar (2019) focuses on tire-derived aggregate (TDA), which is an engineered, lightweight backfilling material produced from recycled scrap tires. In the literature, TDA is often referred to as tire chips or tire shreds. TDA has excellent geotechnical properties, maintains its structural integrity, and weighs 50%–60% less than conventional earth fill. In this paper, two full-scale field tests were conducted to evaluate the usefulness of using a layer of TDA above existing metal pipes to enhance the stress arching mechanism (i.e., stress bridging). In addition, the complicated pipe–soil interaction was investigated by monitoring the surface settlement, change of the pipe’s wall strains, and the pressure distribution over and around the pipe. The field results showed that using a layer of TDA over the pipe is significantly effective in reducing the pipe’s stresses and the magnitude of transferred pressures compared to using conventional backfill. Furthermore, three-dimensional (3D) finite-element models (FEM) of the tests were developed to study the interaction mechanism of the considered problem, in which the developed models were validated against the field tests results. An excellent agreement was observed between the measured pipe’s strain values and surface settlements and the numerically obtained results. Additionally, an extensive parametric study was conducted to examine the effect of changing some key parameters on the performance of the investigated system (i.e., the thickness of the TDA layer, shape and configuration of the TDA cross section, and the pipe’s stiffness). This study illustrated that using a layer of TDA backfill above preexisting buried pipes is an excellent construction alternative to enhance the stress bridging mechanism under static loading conditions. The proposed system may lead to avoiding the costly pipeline rerouting option when there is a need for building over preexisting pipes.

The paper by Sparkes et al. (2019) focuses on the compressibility and shear strength properties of tire-derived aggregate mixed with lightweight aggregate. TDAs have been successfully used in the design and construction of induced trench culverts. A laboratory testing program determines the geotechnical properties of expanded shale lightweight aggregate (a lightweight material), tire-derived aggregate, and their mixtures using a large direct shear box, one-dimensional compression testing equipment, and a split-ring apparatus. Various mixtures are evaluated for shear strength, compressibility, and coefficient of earth pressure at rest.

The paper presented by Kılıç and Akınay (2019) focuses on an experimental study investigating the effects of using expanded polystyrene as compressible inclusion on buried high-density polyethylene (HDPE) pipe behavior. A series of full-scale tests was conducted using a laboratory testing facility to investigate the effects of using EPS on the behavior of a 300-mm nominal-diameter lined corrugated-wall HDPE pipe buried in a poorly graded sand medium. For this purpose, five different compressible inclusion geometries were designed. EPS with $10\mathrm{kg}/{\mathrm{m}}^3$ nominal density was used as the compressible material. In order to simulate geostatic stresses imposed by shallow and high soil fills, vertical surcharge stresses up to 200 kPa were applied on surface of the burial medium. The experimental results show that a single EPS panel above the pipe crown, which is as wide as one pipe’s outside diameter and as thick as 1/6 of the pipe’s nominal diameter, offers the best solution in terms of vertical stress reduction at the pipe crown (up to of 76%) and horizontal stress on the pipe walls at the springline (up to of 65%), as well as a considerable reduction of vertical and horizontal pipe deflections.

Another experimental study presented by Al-Naddaf et al. (2019) investigates the effects of EPS geofoam, including geofoam stiffness and thickness, on the distribution of vertical stresses above a rectangular concrete culvert under static and cyclic footing loads. Reduced-scale models were constructed in a test box under a plane-strain condition. This study adopted the induced trench installation (ITI) method to place the concrete culvert overlaid with an EPS geofoam. The backfill material was a dry, poorly graded Kansas River sand. The footing load was applied parallel to the culvert axis. Earth pressure cells were used to monitor the vertical stress distributions above the geofoam and surrounding soil. The experimental results show that the EPS geofoam reduced the vertical stresses on the buried structure due to the mobilization of soil arching. The lower stiffness and thin geofoam had more effect on the vertical stress reduction. Cyclic loading minimized the soil arching effect induced by the compressible geofoam. In addition, the paper also examines the test results with available analytical solutions. The effects of soil arching and the induced vertical stress above the rigid structure under static footing load were considered separately. The analytical solutions were found to match well with the experimental results.

Liebscher et al. (2019) present an examination of the state of the art on the use of EPS bedding materials in pipeline installation, focusing on their mechanical properties, quality control, and durability against chemical, physical, and biological environmental impacts. The long-term behavior of installed EPS materials and the possibility of their use on several construction sites are assessed. In addition, using finite-element calculations, stress and deformation of installed EPS material with particular regard to creeping and buoyancy effects are investigated. Finally, the results from the product tests, experimental results, and calculations together with recommendations for their practical application are presented.

The paper by Puppala et al. (2019) presents EPS geofoam characterization through laboratory and field investigations, and enhances the understanding of this material to reduce the performance disparity between the laboratory and the field. The laboratory characterization studies involved evaluation of densities, stiffness, and unconfined compressive strength (UCS). The field characterization studies involved evaluating stress distribution by instrumenting the EPS geofoam with pressure cells. It was observed that the stress distribution in the EPS 22 geofoam material was different from that determined by the methods published in the literature. This paper highlights the comprehensive analysis of material characterization and behavior of EPS 22 geofoam under laboratory and field conditions.

Negussey et al. (2019) present a case study regarding a wide culvert reconstruction failure, specifically the I-88 culvert crossing of Carrs Creek in Sidney, New York, which completely collapsed during record flooding. A rapidly reconstructed culvert using geofoam as lightweight fill settled excessively shortly after completion. The failure was investigated in a previous study by NYSDOT (2009). Field observations, test results, and conclusions presented in the prior investigation are reexamined in this study. Through computer modeling and alternative laboratory tests, different conclusions for the failure are proposed. Lessons learned from the failure are used to provide an alternative design. Suggestions to improve rapid construction practice with geofoam are provided using the I-88 failure as an example in retrospect.

It is my hope that this collection provides an impetus for further work in this area of pipeline engineering.