The effect of soil properties on the compaction of the subgrade at negative air temperatures

Анотація

Problem. In connection with the increase in annual volumes and rates of road construction, the increase in the length of the construction period with the transition under certain conditions to year-round construction of roads deserves special attention. The limited time for technological operations on the construction of the subgrade at negative temperatures required the use of new, advanced technologies for working with soil. Goal. When constructing the roadbed of roads under negative temperatures, the responsible operation which determines the formation, and then the behavior of the entire road structure during operation, is compaction. The aim of the work is to study the effect of freezing of thin soil layers during compaction in embankments at low temperatures. Methodology. Analysis of heat transfer processes in the soil layers during the filling of the subgrade which are determined by the following features: temperature changes in a given period of time; humidity variation range; biphasic moisture migration (liquid phase + water vapor) moisture potential. Results. On the basis of theoretical and experimental data processing, the normalization of the permissible freezing depth of the sealing layer is proposed. As a result of studies the influence of frozen inclusions on the coefficient of compaction is established. Practical value. To erect a subgrade in winter is only possible when using thawed soil, in which frozen breasts with a maximum size of 100–150 mm are no more than
5–10 % when compaction of the embankment with pneumatic wheels and vibratory rollers and 200–
250 mm no more than 20–25 % when compaction with trellis rollers and shock machines. Analysis of road-building machines, taking into account the above requirements, proves that a high-quality subgrade can be built only at air temperatures up to
–10 ° C and is carried out in several cases at temperatures up to –15–20 ° C.