Calculation method for permanent deformation of unbound pavement materials

An analytical-mechanistic method for the calculation of permanent deformations of pavements has been developed at the Technical Research Centre of Finland (VTT) over some years by the author. The calculation method is needed in the analytical design procedure of pavements. This research concentrated on the calculation method for permanent deformations in unbound pavement materials. The calculation method was generated based on the results of full-scale accelerated pavement tests along with the complementary laboratory tests together with finite element calculations. The objective was to develop a relatively simple material model for unbound materials, which is an analytical, nonlinear elasto-plastic model. The stress distribution studies of traffic load showed that it is very important to calculate stresses in pavements with an elasto-plastic material model to avoid false tensile stresses in unbound materials, especially when the asphalt layers are thin. The new material deformation model can take into account the amount of the loading, the number of vehicle or wheel passes, the deformation capacity of the material and its stress state. The strains in each layer and subgrade are calculated and converted to the vertical deformations and then summed to obtain the total rutting. The method was verified against two Finnish accelerated pavement tests. The results indicated that the material model gave tolerable results for the relatively high load levels used in these Heavy Vehicle Simulator (HVS) tests as the relative error was around ± 30%. For the structures with thicker bound layers and therefore lower stress state in the unbound layers, the method gave more reliable results. The material parameters have been defined only for the most common Finnish unbound materials in a few basic situations. The wider use of the method requires material parameter definitions for a larger range of materials. However, even in the current form the method can be applied in a relatively reliable way to compare the sensitivity of different structures against rutting. The most important factors affecting rutting were studied to find a method to include their effect on the calculation method. These factors were loading rate, stress history, temperature and the geometry of the road embankment. The modelled examples proved that the most important factor of rate effect is the change in stress state due to the change in the resilient properties of bound layers, while the rate effects on the unbound material itself has a smaller role. The accelerated pavement test proved that rut depth depends greatly on the temperature: the rut depth grows from 10% to 15% at +10 °C and 20 to 25% at +25 °C compared to rut depths at +5 °C due to the changes in the stiffness of the bound layer. The unloading-reloading cycles have only a slight effect on the permanent deformation. The introduced geometric factor describes an average, structurally independent, increase in the rate of rutting, which depends on the steepness of the side slope and on the distance to the edge of the structure

Mass Stabilization as a Ground Improvement Method for Soft Peaty

Construction of road embankments or other infrastructures on soft peat is a challenge. The main problems are high compressibility and rather low undrained shear strength of peat. Mass stabilization provides a solution to improve the properties of a peaty subgrade. Mass stabilization is a ground improvement method, where hardened soil mass is created by adding binder into soil and by controlled in situ mixing. Mass stabilization poses an alternative solution for conventional mass replacement or other techniques, which leave peat in place. The chapter deals with mass stabilization of soft peat soil. Specific attention is paid to design, research and construction considerations, and experience obtained during last three decades. Peat properties before and after stabilization, design methods including pre-testing, stabilization technique and machinery, quality control methods and practices, binder technology, long-term performance of mass stabilized peat, environmental effects, feasibility, applications, and limitations are all presented and discussed in this chapter. The long-term observations (during the last 25 years) have shown that the strength of stabilized peat has continued to increase in average 1.6 times from the strength of 30 days. Therefore, mass stabilization has proven to be a flexible ground improvement method for peat layers with maximum thickness of 8 m

Calculating rutting of some thin flexible pavements from repeated load triaxial test data

This paper describes parts of a Nordic pavement performance prediction model study (at the project level of the NordFoU project) where a material performance model, developed at VTT research centre in Finland, has been selected as a mean of calculating the permanently accumulated (plastic) deformation (i.e. rutting) of unbound granular materials (UGMs) in flexible pavements subjected to trafficking. The paper aims to assess the suitability of this VTT model application to Swedish roads comprising thin asphalt layers over a thick UGM base. To achieve this, the VTT model has been used to calculate the deformations of two tested road sections in Sweden. These calculations have been compared with another permanent deformation model for UGM (the Gidel model) and with rutting measurements from trafficked pavements. It is shown from this study that the applied rutting prediction method with VTT model is capable of predicting the development of rutting depth despite some overestimations

Characterization of sedimentary depositional environments for land use and urban planning in Espoo, Finland

AbstractThe capital region of Finland is growing rapidly and into areas with challenging construction conditions such as deep fine-grained sediments. In the coastal city of Espoo, present land use is mainly focused in the southern and central parts, which were submerged by the Baltic Sea during the early and mid-Holocene. These areas have experienced saline and brackish water phases during the history of the Baltic Sea Basin. The deposition environments of the presently studied onshore areas are an analogue for the present day offshore Baltic Sea sedimentation settings for fine-grained material. The results from Baltic Sea studies have demonstrated that the seabed topography has a significant role in the deposition of sediments and their properties. In this study, paleotopographic models were created for the ancient Baltic Sea Basin in the Espoo area 1) after deglaciation and 2) during the Litorina transgression and classified into bathymetric (terrain) zones and structures. Topographic classification was combined with the water depth of the Litorina stage, the thickness of fine-grained deposits and wind fetch to establish the overall characteristics of sedimentary environments in the coastal area. Fine-grained sediments can be found mainly in depressions that are classified here as broad, narrow or local. The study found the most challenging environments for construction purposes in sheltered narrow depressions that contain thick layers of fine-grained sediments deposited during the Litorina transgression. These are mainly located in the southern and central parts of Espoo. Minor deep canyons were also found in the northern parts of Espoo. This study provides new prior knowledge for urban planning and construction design in Espoo. The methodology could be applied to other Baltic Sea coastal cities and areas with fine-grained sediments.</p

HVS-Nordic : the activity of the second period in Finland 2000-2003

3200832E, Finnra Report