The soil compaction by mechanical and hydraulic stresses is a major factor responsible for physical degradation of cultivated soils with low structural stability in arid and semi-arid regions of the world. Incorporation of organic manures into soil can partially help to prevent soil degradation. Confined and plate sinkage compression tests (CCT and PST, respectively) are usually performed to characterize the compression properties of soil. Two main forms of compression curve have been observed: (i) the bi-linear curve having an elastic rebound curve at low stresses and a linear virgin compression curve at higher stresses and (ii) the S-shaped curve having deviation of the virgin compression curve at high stresses. In the present work, soil samples collected from the topsoil (0-20 cm layer) of experimental plots in which farmyard manure was added to the soil at three rates (25, 50 and 100 Mg ha-1) for 7 years successively under annual wheat (Triticum aestivum L.) - corn (Zea mays L.) rotation. Large remould specimens were prepared by applying 100 kPa load at two gravimetric water contents (17.1 and 20.9%). The center section of the preloaded soil specimen was firstly submitted to a 50 mm PST; then immediately one cylindrical sample was cored for CCT. The S-shaped compression curves were observed with CCT, whereas bi-linear curves were obtained with PST. The PST and CCT are semiconfined and confined loading tests, respectively. In the PST, because high soil volume was available in the large pre-compressed soil specimen, the elastic deformation of the soil structure and the reduction of the air-pore volume were dominated. For the CCT, the S-shaped form appeared because the flow of water from meso-pores storing free water subjected to high capillary forces became significant at higher stresses. These different processes could explain the observed bi-linear and Sshaped curves under PST and CCT, respectively
کلید واژگان :Confined compression test, Plate sinkage test, Precompaction stress, Compression index, Compression curve
ارزش ریالی : 300000 ریال
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