دانلود رایگان مقاله انگلیسی مدل سازی تنش در مقابل رفتار نشست فونداسیون های سطحی در خاک های غیر اشباع - الزویر 2018

Abstract

The mechanical behavior of unsaturated soils can be interpreted using either modified total stress or a modified effective stress approach depending on the type of soils and various scenarios of drainage conditions of pore-water and pore-air. Recent studies suggest that the bearing capacity of unsaturated cohesive soils can be more reliably estimated using the modified total stress approach (MTSA) rather than the modified effective stress approach (MESA). In the present study, a modeling technique (extending Finite Element Analysis, FEA) is proposed to estimate the bearing capacity of shallow foundations in unsaturated cohesive soils by simulating the vertical stress versus surface settlement behaviors of shallow foundations extending the MTSA. The proposed technique is verified with the model footing test results in unsaturated cohesive soils. Commercial finite element software, SIGMA/W (GeoStudio 2012, Geo-Slope Int. Ltd.) is used for this study. Details of estimating the unsaturated soil parameters (i.e. total cohesion, modulus of elasticity and Poisson’s ratio) required for the FEA are also presented taking account of the influence of matric suction. Good agreements were observed between the measured bearing capacity values and those from the FEA extending the MTSA.

5. Summary and conclusions

In the present study, a simple Finite Element Analysis (FEA) approach extending Modified Total Stress Approach (MTSA) is proposed to estimate the bearing capacity of unsaturated cohesive soils. The conclusions obtained from the research can be summarized as below.

1. Poisson’s ratio affects the stress versus settlement (SVS) behaviors of shallow foundations in unsaturated cohesive soils. Bearing capacity values estimated based on the SVS behaviors increase with increasing the Poisson’s ratio. For saturated condition, the SVS behavior predicted using m = 0.495 provided better agreement with the measured SVS behavior. On the other hand, low values of Poisson’s ratio (i.e. less than 0.3) are recommended to predict the SVS behaviors for unsaturated cohesive soils.

2. The SVS behaviors are not influenced by K0 when the FEA is carried out extending the Modified Total Stress Approach (MTSA) due to the use of the zero internal friction angle.

3. Among the Modified Effective Stress Approach (MESA), Modified Total Stress Approach (MTSA), and FEA with MTSA (present study), the FEA with MTSA provided the most reasonable bearing capacity values when compared with measured bearing capacity values. These comparison studies suggest that the MTSA can be successfully extended in the simulation of the SVS behavior for shallow foundations in unsaturated cohesive soils.

4. The SVS behaviors in unsaturated soils can be reliably predicted using the concept of average matric suction without significant error.