Effect of Soil Moisture on the Deformation Characteristics of Forest Road Subgrade Soils Due to Climatic Change

The service life of road pavements, including forest roads, depends on many factors. When designing forest road pavements, it is essential to take into account the behaviour of the subgrade and the factors affecting its physical-mechanical properties, especially soil moisture, which significantly affect the deformation characteristics of the soil. This issue is becoming increasingly important with the increasing climate change. Poor design or intensive use can accelerate the road degradation, leading to environmental damage and reduced exploitation potential. A fundamental parameter for assessing the resistance of soil to repeated loading is the resilient modulus Mr, which is determined from a cyclic load test that simulates the effect of passing traffic. For low-volume roads, including forest roads, this modulus can be determined using a cyclic test with standard California Bearing Ratio testing equipment by applying repeated cyclic loading. One of these innovative cycling test machines was developed at the Mendel University in Brno. The paper presents the results of tests investigating the effect of soil moisture and compaction level on both the resilient modulus and the permanent and elastic deformations of two soil types. The obtained results confirm that the soil moisture content far from the optimum value should result in lower material stiffness and thus to smaller resilient modulus value. Also, they confirm that a larger resilient modulus should be obtained when the soil is compacted with higher compacting energy.