Steven F. Bartlett

Numerical Modeling of Geofoam Embankments

In 2001, the Utah Department of Transportation completed a 4-year

Multilinear Regression Equations for Predicting Lateral Spread Displacement from Soil Type and Cone Penetration Test Data

1.4 billion I-15 reconstruction project in Salt Lake City, Utah. This project included widespread use of expanded polystyrene geofoam as lightweight embankment at important utility crossings and where close proximity to existing buildings necessitated minimizing consolidation settlement. This paper presents construction and long-term monitoring results for some of these embankments with numerical modeling of the field measurements. Fast Lagrangian Analysis of Continua, a finite-difference program, was used to estimate the complex stress distribution and the displacements (i.e., strain) that developed in select geofoam embankments. The writers used a bilinear elastic model to produce reasonable estimates of gap closure, block seating, and the subsequent elastic compression of the geofoam embankment at higher stress levels. Such estimations are important for modeling and designing geofoam embankments and potential connections with other systems. The calculation of the complex stress distribution and displacements that develops in a geofoam embankment has application to settlement, lateral earth pressure against retaining and buried walls, slope stability, and seismic design of geofoam embankments.

Confining Stress Effects on the Stress-Strain Response of EPS Geofoam in Cyclic Triaxial Tests

AbstractIn the 1990s, Bartlett and Youd introduced empirical equations for predicting horizontal displacement from liquefaction-induced lateral spreading; these equations have become popular in engineering practice. The equations were developed by multilinear regression (MLR) of lateral spreading case history data compiled by these researchers. In 2002, these equations were revised and updated to include additional case history data. The regressions indicated that the amount of horizontal displacement is statistically related to the topography, earthquake magnitude, and distance from the seismic energy source. It is also related to the thickness, fines content, and mean grain size of the saturated, granular sediments with corrected standard penetration test blow count values less than 15. This paper proposes to modify the MLR empirical equations by replacing the fines content and mean grain size factors with soil description factors. Such modification allows investigators performing preliminary evaluation...

Protection of Pipelines and Buried Structures Using EPS Geofoam

This paper summarizes the results of a laboratory study addressing the cyclic stress-strain response of expanded polystyrene (EPS) geofoam under various confining stresses. Experimental results from cyclic uniaxial and triaxial compression tests conducted in the viscoelastic domain revealed that the normalized shear modulus degradation curve is insensitive to the static confining stress, whereas the damping ratio of EPS geofoam appears to increase with increasing static confining stress. The visco-elasto-plastic response of EPS geofoam also seems to be affected by the magnitude of the applied static confining stress in cyclic triaxial tests. An increase in the static confining stress is associated with a reduction in the accumulated permanent (plastic) strain for a specific number of applied loading cycles.

Estimation of Time Rate of Settlement for Multilayered Clays Undergoing Radial Drainage

Expanded Polystyrene (EPS) geofoam is a lightweight, compressible material that can be used to protect buried infrastructure in areas with high to moderate seismicity. This paper summarizes recent research conducted at the University of Utah regarding the seismic design and construction of EPS geosystems to improve the seismic resiliency of pipelines and buried structures, particularly at normal fault crossings. It discusses the development and verification of an EPS cover/backfill system to protect buried pipelines and other structures from potential rupture caused by permanent ground deformation (e.g., tectonic faulting, subsidence, liquefaction, land sliding, etc. Full-scale experiments and numerical modeling show that a light-weight cover system constructed, in part, with EPS block offers significant benefits in protecting buried pipelines from the damaging effects of offset caused by permanent ground deformation. The prototype EPS cover system significantly reduced the vertical uplift force and stresses imposed on the buried pipe system as it was subjected to uplift through the EPS cover system.

Performance of lime cement-stabilized soils for the I-15 reconstruction project: Salt Lake City, Utah

This paper demonstrates how the finite difference technique can be used to estimate the time rate of settlement for soft, compressible clayey soils treated with prefabricated vertical drains at sites where primary consolidation settlement is occurring in a multilayered system at varying rates. Semiempirical methods based on surface settlement monitoring have typically been used to estimate the progression of primary consolidation settlement. However, interpretation of such methods can be problematic for multilayered soil profiles. For such sites, it is crucial to obtain a reasonable characterization of the foundation soils’ horizontal drainage properties and include these estimates in the time rate of settlement projections. Field monitoring of subsurface instrumentation is extremely valuable in providing additional information about the consolidation behavior of different layers. When subsurface field measurements are coupled with the proposed numerical method, far more reliable projections are obtained. This paper focuses on how to integrate field and laboratory data with projections of time rate of settlement obtained from semiempirical and finite difference methods to predict more accurately the time rate of consolidation behavior of multilayered foundation soils.

Bridge Foundations Supported by EPS Geofoam Embankments on Soft Soil

The application and performance monitoring of lime cement stabilization were studied for the Interstate-15 Reconstruction Project at 300 West Street in Salt Lake City, Utah. Lime cement columns (LCCs) were used to support a large mechanically stabilized earth (MSE) wall constructed over soft foundation soils and in close proximity to a commercial building. The Utah Department of Transportation has installed instrumentation at this site to measure the construction and postconstruction deformation within the treated zone and around the adjacent building. Also, total pressure cells have been installed atop the treated zone and in an adjacent untreated area to measure differences in load transfer. The use of LCC-stabilized soil has reduced the amount of primary settlement from about 1 m without treatment to about 0.2 m in the treated zone. Ground settlement at the nearest wall of the adjacent building has been about 5 cm total during a 2.5-year monitoring period with 3 of the 5 cm occurring during MSE wall construction and surcharge placement. Also, measurements indicate that the global stability of the MSE wall foundation has been notably improved. It is hoped that the data gathered from this array will provide a valuable case history of LCC performance for evaluation and modeling.

Full-Scale Testing of an EPS Geofoam Cover System to Protect Pipelines at Locations of Lateral Soil Displacement

EPS geofoam can be used to support highway bridge structures without the aid of deep foundations. The development of this technology is important to accelerate construction on soft compressible soil. EPS geofoam allows for the rapid construction of bridge foundations on such soils without the time and cost involved in installing traditional foundations. Because EPS geofoam is an extremely light weight fill, it can be used to avoid settlement impacts at bridge approaches. In Norway, bridges have been directly supported by EPS geofoam. Norwegian Public Roads Administration has pioneered this application for a few bridges underlain by soft, clayey deposit where the bridge structure rests solely on EPS geofoam blocks. Investigating bridge foundations supported by EPS geofoam embankments is a joint effort starting summer 2013 between the University of Utah, University of Memphis and Norwegian Public Roads Administration. This paper includes some tasks and conceptual designs that address development of performance goals, design criteria, material testing, prototype analyses, numerical modeling and constructability of this innovative bridge support system.

Development of Seismic Design Approach for Freestanding Freight Railroad Embankment Comprised of Lightweight Cellular Concrete

Buried pipelines can be damaged by permanent ground displacement (PGD) resulting from faulting, landslides, liquefaction, etc. The mitigation of PGD below grade is an important area of research. Recent research has explored how expanded polystyrene (EPS) Geofoam can be used in trench systems to reduce the deleterious effects of PGD moving a pipe laterally beneath ground surface. This paper shows how EPS Geofoam can be used in trenches as a compressible inclusion to reduce potential pipeline damage from lateral pipe movement. As part of the testing methodology, a pipe was moved into an EPS Geofoam and sand backfill surrounding the pipe to measure the non-linear interaction between EPS Geofoam and the pipe and to develop the soil-EPS non-linear springs required for pipeline design. The relationships obtained from EPS-soil system were compared to the soil-structure interaction springs from common backfill. The research team found that the EPS-soil system significantly reduces pipeline stress for the case where the pipeline undergoes horizontal offset when placed correctly for maximum benefit.

INSTRUMENTATION AND CONSTRUCTION PERFORMANCE MONITORING FOR I-15 RECONSTRUCTION PROJECT IN SALT LAKE CITY, UTAH

Recent advances in research, laboratory testing and field evaluations of lightweight cellular concrete have led to an increased understanding about its application as a geomaterial. Recently, lightweight cellular concrete has been used to construct a 40-foot high by 50-foot wide freestanding railroad embankment with vertical sidewalls near Colton, California. The embankment and flyover structures are about 7,000 feet long and consist of 220,000 cubic yards of lightweight cellular concrete. The embankment was designed to support 3 simultaneous Cooper E-80 freight railroad live loads and seismic loading from a 2500-year return period earthquake event. In order to provide an earthquake resilient material, cellular concrete was selected because of its relatively low density (25 to 37 pounds per cubic foot) and high compressive strength (140 to 425 pounds per square inch), when compared with traditional backfill materials. This alternative also provided a reduced embankment footprint and corresponding dead load, which reduced foundation settlement and possible inertial interaction with nearby utilities and infrastructure. Comprehensive seismic design guidance for lightweight cellular concrete embankments has not been fully developed in the U.S, but a rational approach has been developed for freestanding geofoam embankments. A similar approach was incorporated in the design process of the Colton, California embankment. This paper discusses the design process including: (1) selection and development of spectrum- compatible time histories for both horizontal and vertical components of strong ground motion; (2) development of design and evaluation methodologies; (3) detailed numerical evaluation using finite element (QUAKE/W) and finite difference techniques (FLAC 2D); (4) assessment of the load-deformation characteristics of the embankment system under seismic ground motion and (5) assessment of benefit of shear keys and ground improvement on limiting basal sliding during a seismic event.