Swelling behavior of some soils, especially soils with high clay content, has a great impact on forest roads. Moisture variation in expansive soils results in their volume change. If the soil can not swell freely, it will apply pressure to surrounding structures which may eventually cause some damage or complete destruction. Therefore, it is essential to assess the swelling potential of the foundation soils and take appropriate measures to overcome such problem. In the present study, the effects of RPP as a polymer stabilizer to control swelling of expansive soils were investigated. For this purpose, different tests including Atterberg Limits, standard compaction, swelling potential, and swelling pressure, were conducted on control and treated soil samples using different Percentage of Polymer (RPP) (0.019, 0.04 and 0.06%). Also California Bearing Ratio (CBR) tests were conducted on control and treated samples based on manufacturer recommendation. To assess the effect of time on performance of polymer treated soil, samples with 0.019% RPP content were prepared and kept in sealed plastic bags for 7 and 14 days periods and then tested for Atterberg Limits, swelling potential and swelling pressure. The results showed that soil treatment with RPP, resulted in improvement of CBR and maximum dry density and reduction in Atterberg Limits, swelling potential and swelling pressure. The results also indicated that the curing 7–14 days periods had no significant effect on plasticity and swelling properties of the treated samples.

Engineering properties of the subgrade layer are important in roadway development, especially in forest roads. In most cases, well-graded soil is not available near forest road construction sites and its supply incorporates high transportation costs. Therefore, in situ treatment can be a practical alternative for improving the engineering properties of the subgrade. The objective of this research was to assess the stabilization effect of two polymer agents (CBR Plus and Road Packer Plus) at three doses each, on high-plasticity clay soils. Soil tests, including Atterberg limits, standard Proctor, California Bearing Ratio (CBR), and free swelling were conducted on the control and treated soil samples with different percentages of each agent. Results showed that CBR Plus and RPP agents improved the engineering properties of the soil and their effectiveness was relative to their concentrations. Generally, the Atterberg limits and free swelling of the treated samples yielded smaller values than the control sample (natural condition) and their amounts of reduction increased with higher percentages of both agents. Maximum dry density and CBR increased compared to the control sample when any of the polymer agents were applied and they increased more with higher doses. ANCOVA test results yielded no significant statistical difference between the two polymers in terms of their effectiveness on soil stabilization. CBR Plus and RPP proved promising results for the stabilization of road material and thus warrant field testing.

Fine-grained soils cause problems for forest road construction and often require improvements of their mechanical properties. One of the methods of improving mechanical properties of clay soils is soil stabilization. In this study, the effect of a conventional (lime) and a non-conventional (sodium nanoalginate) stabilizer on improving the characteristics of a high plasticity forest soil was compared. Atterberg limits including liquid limit, plastic limit and plasticity index, standard Proctor, UCS (Unconfined Compression Strength) and CBR (California Bearing Ratio) tests were performed on control (untreated) and soil samples treated with different doses (3%, 5% and 7%) of lime and sodium nanoalginate, according to the standard procedures. Moreover, to evaluate the effect of curing time, additional tests were performed on the soil samples treated with 3% lime and 3% sodium nanoalginate at 7, 14 and 28 days after the treatment. The results indicated that adding sodium nanoalginate and lime to the forest soil improves the Atterberg limits. Additionally, adding sodium nanoalginate to the forest soil increases the maximum dry density (γ_dmax) and decreases the optimum moisture content (OMC), whereas adding lime to the forest soil reduces the maximum dry density and increases the optimum moisture content. Adding sodium nanoalginate and lime in different doses (3%, 5% and 7%) increased UCS and CBR as the main indices of soil strength. The increment range of UCS for the soil stabilized with sodium nanoalginate and lime was 42.59%–160.14% and 31.34%–56.65%, respectively, and the range of CBR improvement for soil stabilized with sodium nanoalginate and lime was 28.72%–122.97% and 13.83%–45.59%, respectively. Increasing the curing time improved the mechanical properties of the forest soil in the samples treated with both stabilizers, but sodium nanoalginate performed better in soil stabilization.