5          Creep Behavior of An EPS Embankment

5.1         Introduction

As shown in chapter three, as long as the applied stress is within 30% of the strength at 5% strain creep can be considered negligible. This result was based on experimental work on specimens of height ranging 0.05m to 0.6m. It was shown also that the larger the specimen is the less the strain obtained due to creep. This was due to two main items; edge effects were higher in small specimens and also the flatness of the small specimens, which were trimmed in the lab was less.

  An interstate highway embankment, I15 in Salt Lake City, was constructed utilizing up to 8m height of EPS geofoam as shown in photos 5-1 through 5-3. The purpose for using geofoam is to eliminate settlement on utility pipes existing below portions of the highway. The soft ground would experience up to 1m of immediate settlement if normal fill was used in constructing such portions of the embankment (Bartlett et al, 2000). Type VIII EPS geofoam was used in this project.  The blocks were 0.8m high by 1.2m wide by 4.9m long and confirmed to the specified tolerance of ±0.5% dimensional and 5% flatness. The compressive resistance of these 18kg/m³ minimum density blocks was 97kPa as indicated from the 10% strain per min of the 0.05m cube laboratory tests (Bartlett et al, 2000).

The bottom layer of geofoam was placed on 0.2m of sand bedding. The upper layer was covered with a 0.15m concrete slab, which was covered later by an approximately 1.2m height of fill material covered by the pavement. The total design stress applied on the geofoam was 27.5 kPa, which includes the stresses produced from the own weight of the concrete, the fill and the pavement material.

Leveling tolerance for the sand bedding and subsequent layers of geofoam were maintained at 0.01m over 3m. Blocks were placed to be tightly fitting to reduce gaps, which were usually less than 0.02m. In such case, nine layers of foam can have up to 0.16m of gaps.

This chapter highlights the creep behavior of the EPS geofoam at 3300 South of the I-15 highway. Two vertical geofoam sections are studied. The first section will be named the south array and the other section will be named the middle array as shown in figure 5-1. The south array cross section is a nine layers height of foam with an approximate height of 7.2m, while the middle array is an eight layers height of foam with a total height of 6.4m. Magnet extensometers were installed in both sections at levels zero, two, four, six and eight. In addition a magnet plate was installed in level nine in the south array section. Readings for the levels of the magnets was taken frequently with a reference to an outside object. It was believed that the outside object was affected by the settlement occurring in the project area, hence all readings are referenced to level zero in each array. In such case readings will show the creep behavior of EPS geofoam and will show nothing about the soil settlement. Vertical stress cells are installed at level zero, the bottom and the top level of the load distribution slab. The load distribution slab was poured on 22 April 1999. The 1.2m of fill were placed within three days starting on 15 May of the same year. Construction was ended on the fifth of August. Records continue to be taken and the last reported result is for June of 2000. Analyses of the field results are presented in this chapter. Comparison of these records with both laboratory results and mathematical modeling are shown. Important results are concluded.

Photo 5‑1 Side View of EPS Embankment on I-15 at 3400 South

Photo 5‑2 An EPS Approach Ramp at State Street

Photo 5‑3 An EPS Embankment Joint with a Bridge on I-15 at 900 South

Figure 5‑1 The Two Geofoam Cross Sections Investigated in this Study