CLARIFIER Project

Project Scope

To answer the research questions about the feasibility of modelling peat in a geotechnical centrifuge and about failure mechanisms of light weight embankments, two types of tests were conducted:

• Modelling-of-models tests at 30 g, 50 g, and 70 g. Testing models scaled from the same prototype dimension to different sizes/g-levels helps to understand whether the established scaling laws hold for a specific test material or setup. In the current tests, the peat was loaded with a load plate. The height of the peat layer (7.5 m at prototype scale) and the width of the load plate (5 m at prototype scale) were scaled to the different g-levels to achieve comparable models.
• Embankment tests at 50 g. In these tests, an embankment was constructed on the peat surface. The height of the embankment was chosen following the experience from four trial embankments that were constructed in Norway in 1963-64. In these, the settlement of the embankment under self-weight resulted in the saw dust layer being fully saturated and the sand layer staying mostly dry. Traffic loads were simulated using a double t-shaped loading device.

Three tests were conducted using the same test setup to examine the variability of results that could result from differences in the peat samples. An additional test was conducted introducing a geotextile underneath the embankment. All tests were performed using peat samples from a test site in Trondheim, Norway. The samples were cut in place, transported in custom made boxes, and arrived at the testing facilities without any visual change. As such, they were here considered to be undisturbed.

In all tests, mini-CPTs were conducted to provide strength profiles and gain additional insight into potentials of centrifuge testing of peat.

Innovative Aspects & Main Results

Model testing in geotechnical centrifuges has proven an effective tool to study deformation and failure mechanisms in soil materials. However, available research about modelling peat in a centrifuge is limited and there are some concerns regarding the influence of fibers at model vs. prototype scale. Few experiments are known to the user group where intact samples of natural fibrous peat samples were tested. Investigating the potential of and possible limitations to studying peat in the centrifuge, CLARIFIER contributes to a recent body of knowledge that will facilitate research for sustainable and resilient infrastructure construction on peatlands.

Furthermore, traditional bearing capacity models do not apply to infrastructures founded on peat and CLARIFIER contributes to the understanding of failure mechanisms in these materials under lightweight embankments from sawdust and sand. Different to natural sands and gravels that are in short supply in most European countries, sawdust is generally available and thus costs are low. Its limited weight makes it attractive to explore for use as a fill material for construction in peat areas. The aim is to maximise the use of sawdust and minimise the use of natural sand in these constructions.