Rockfill Pavements on Soft Subsoil - Construction and Compaction
Analytical or mechanistic design models are today available, which all require predictable material properties of the materials involved. However, the efficiency of compaction of pavements on soft subsoil is often questioned, since such pavements mostly show lower pavement quality and poorer performance, it seems like the full potential of the fill material not is utilised. An improved knowledge concerning compaction at soft subsoil is therefore needed.
The objective of this study was to achieve a better understanding of vibratory compaction of pavement materials on soft subsoil with the specific aim to find decisive factors for optimal construction procedures.
Comprehensive field tests were performed where different compaction and construction procedures were used, number of layers, roller's operating condition, grain size of rock-fill. Stresses and accelerations were monitored to study the pavement response during compaction, and the achieved bearing capacity was used as a measure of the compaction effect. Simulations of compaction were conducted to study how stress level and stress distribution was affected by the soft subsoil and by the loading frequency.
The pavement quality was found to be strongly dependent of the number of performed roller passes, but surprisingly independent of other factors, such as utilised dynamic load and frequency of the roller as well as of compaction in layers. A high modulus has generally been achieved in the pavements, except at perhaps a limited zone just above the subsoil.
The soft subsoil increases the stress distribution which drastically reduces the induced stresses in the lower half of the pavement, which might be important since a critical stress/strain level probably must be exceeded in order to cause compaction. Furthermore, a relation between drum acceleration and induced stresses was established. Finally it is found that to achieve a good pavement, not only high quality material is required, but also a certain pavement thickness.