A Study of Soil Nutrients in the Terrace Field Changed from Mountain Slope in Three Gorges Reservoir Region

In order to accurately grasp the soil fertility in Three Gorges Reservoir Region after changing mountain slope into terrace field,we take Wushan County for example,and use the spatio-temporal substitution method to analyze the soil nutrient status and trend about the terrace field changed from mountain slope under different length of implementation.The results show that the soil fertility is generally low in the study area,and according to the soil nutrient grading standards in the second national land survey,the average content of total nitrogen,available potassium,organic matter and available phosphorus reaches Standard III,Standard III,Standard IV and Standard V,respectively,and the spatial heterogeneity of soil nutrients is small.Compared to the sloping land,the terrace field changed from mountain slope has increasing soil nutrients on the whole with the length of farming.The mean of various indicators about soil nutrients in the terrace field changed from mountain slope for 2 years is lower than in the sloping land,and there is the biggest difference in soil fertility,while the mean of various indicators about soil nutrients in the terrace field changed from mountain slope for 14 years shows a linear upward trend,and the difference in soil fertility decreases.

Evaluation of the stability of terraced slopes in clayey gravel soil using a novel numerical technique

Conventional geotechnical software limits the use of the strength reduction method(SRM)based on the Mohr–Coulomb failure criterion to analyze the slope safety factor(SF).The use of this constitutive model is impractical for predicting the behavior of all soil types.In the present study,an innovative numerical technique based on SRM was developed to determine SF using the finite element method and considering the extended Cam–clay constitutive model for clayey gravel soil as opposed to the Mohr–Coulomb model.In this regard,a novel user subroutine code was employed in ABAQUS to reduce the stabilizing forces to determine the failure surfaces and resist and drive shear stresses on a slope.After validating the proposed technique,it was employed to investigate the performance of terraced slopes in the context of a case study.The impacts of geometric parameters and different water table elevations on the SF were examined.The results indicated that an increase in the upper and lower slope heights led to a decrease in SF,and a slight increase in the horizontal offset led to an increase in the SF.Moreover,when the water table elevation was lower than the toe of the terraced slope,the SF increased because of the increase in the uplift force as a resistant component.