The Topsoil’s Compression And Rebound Characters Of Typical Black Soil

In order to research the compressibility, rebound capacity, load support capacity of topsoil in typical black soil region systematically, we tested the soil compression and rebound indices of different reclamation years, different recovery years, and different patterns of Grain for Green used the fast oedometer test, analyzed the effect of reclamation years, recovery years, and patterns of Grain for Green on soil compressibility, rebound capacity, and load support capacity, then we explored the influence factor of soil compressibility, rebound capacity, and load support capacity used the path analysis. Our research had laid a foundation for further explore the stress-strain relationship in the compacting process and the evolvement rule of mechanical properties of black soil.The results showed that, soil void ratio, compression index, compression coefficient and swelling index decreased with reclamation time increasing. The values of compression index, compression coefficient and swelling index varied from 0.250 to 0.467,0.00212 to 0.00417 kpa"1,0.039 to 0.083, respectively. The compression index, compression coefficient, swelling index of un-reclaimed secondary forest land were significantly higher than that of reclaimed black soil (p<0.05). We also found that, soil organic matter decreased and bulk density increased with increasing reclamation years, and good linear regression was obtained between organic matter, bulk density and soil mechanical properties. Organic matter had a positive influence on compression index (R2=0.797), compression coefficient (R2=0.537), swelling index (R2=0.644); bulk density had a negative influence on compression index (R2=0.781), compression coefficient (R2=817), swelling index (R2=705). In conclusion, degree of soil compaction increases, and soil swelling capacity and susceptibility to compaction decrease with increasing reclamation years; the conceivable reasons for decreasing the index values of soil mechanical properties were the decrease of soil organic matter and the increase of bulk density due to reclamation interference.With the years of vegetation restoration increasing, soil void ratio, compression index, and pre-compression stress increased. The values of compression index, pre-compression stress varied from 0.231-0.399,4.2-100.0kPa, respectively. The compression index and pre-compression stress of soils at different age larch plantations were significantly higher than that of tillage soil (p<0.05), it indicated that, the compression index, pre-compression stress and the tilth of soil increased with increasing restored years. We also found that, soil bulk density, clay proportion decreased and the mass fraction of organic matter increased with increasing restored years, and good linear regression was obtained between bulk density, clay proportion, the mass fraction of organic matter and soil mechanical properties. Bulk density had a negative influence on compression index (p<0.05), the correlation between the mass fraction of organic matter, clay proportion and compression index were closer (p<0.01). Clay proportion also had a negative influence on pre-compression stress (p<0.01). In conclusion, degree of soil compaction decrease, soil compressibility and load support capacity increase with increasing restored years. The conceivable reasons for increasing the soil compressibility and load support capacity were the decrease of soil bulk density, clay proportion and the increase of the mass fraction of organic matter due to the vegetation recovery.Compared with the arable land, P. simonii x P. nigra forest only increased the soil compression index significantly (p<0.05), Ulmus pumila L. forest increased the soil compression index and rebound index significantly (p<0.05), and Salix matsudana Koidz. forest can increased all the soil compression index, rebound index and pre-compression stress significantly (p<0.05). The values of compression index, rebound index and pre-compression stress varied from 0.222-0.321,0.030～0.051,2-50.2kPa, respectively. In addition, strong correlations were obtained between soil compression index, rebound index, pre-compression stress and the sum of silt and clay.The path analysis indicated that, the largest direct impact and the largest sum of indirect impact factor on soil compression index was clay content, the highest determination coefficient of soil properties on soil compression index was clay content, too; the largest direct impact factor on soil rebound index was soil water content, and the largest sum of indirect impact factor on soil rebound index was clay content, the highest determination coefficient of soil properties on soil rebound index was soil water content; the largest direct impact factor on soil pre-compression stress was soil bulk density, and the largest sum of indirect impact factor on soil pre-compression stress was organic carbon content, the highest determination coefficient of soil properties on soil pre-compression stress was soil bulk density.