Load Distribution, from a Bridge Abutment, in a Layered EPS Embankment with different Compressive Strength: Lastspredning, under belastning av et brolandkar, i en lagdelt EPS fylling med ulik trykkstyrke

Abstract

The load distribution in expanded polystyrene (EPS) embankments is complex. Three different case studies were selected in order to find a simple way of estimating the stresses by depth. Three distribution theories that were selected are Newmark, 2(vertical):1(horizontal) and strip load distribution. Complimentary finite element (FE) calculations were performed using two different material models; linear elastic and hardening soil. The reason for using finite element method (FEM) was to get a more detailed overview of the distribution and see if it could be used as a valid estimation tool for future EPS embankments. The FEM and hand estimates were compared to the cases studies monitored stresses. The results showed that strip load distribution is the safest estimate and it is also comparable to the FEM results, however, they both overestimate the vertical stresses compared to the measured stresses. The three case studies showed a scatter in the monitored stresses and a clear tendency could not be identified. In addition to other reasons, that is why a hypothetic embankment was chosen for cost optimization.The key to cost optimize an embankment is being certain of the stresses that will occur in the future structure. When we know the stresses, we can build a structure that limit the stresses as close as possible to the materials stress limits, i.e. not over dimensioning the material and embankment by selecting a too high quality of EPS. The performed cost optimization was calculated with two different approaches for stress distribution and two different design limits.The two alternative calculations used for cost optimization were the American Association of State Highway and Transportation Officials (AASHTO s) load bearing and FE calculations in Plaxis. The different results showed that the load bearing estimated lower stresses through the embankment compared to the finite element calculations. If we regard them both as correct, the calculation model chosen would be AASHTO s load bearing, because it gives lower stresses, which means lower compressive stress resistance for the selected EPS. EPS with lower compressive resistance is cheaper than an EPS with higher resistance. The two different limits are compressive stress at 1% strain and 30% of compressive stress at 5% strain, and are found by conducting an uniaxial test. The latter will give lower design values and results in selecting an EPS with higher compressive stress resistance, which is more expensive.The cost optimization is optimized when using AASHTO s load bearing stress distribution, and the use of the compressive stress at 1% strain as the design limit.