Calibration of resistance factors for bearing resistance design of shallow foundations under seismic and wind loading

Although the geotechnical resistance 19 factors at ultimate limit state used for dynamic loading conditions should be different from those for static loading conditions, most current structural and geotechnical design codes do not specifically provide dynamic resistance factors. In this paper, the ultimate limit state reliability analysis of individual shallow foundations for drained and undrained soil conditions under seismic (pseudo-dynamic) and wind loads using the Random Finite Element Method is carried out using the provisions of the National Building Code of Canada. The geotechnical resistance factors required to achieve target maximum lifetime failure probabilities are estimated for a few major Canadian cities. The results indicate that the failure probability for drained soil conditions is slightly greater than that for undrained soil conditions. In addition, the results suggest that the dynamic resistance factors for foundation bearing capacity design at ULS are lower than those for static foundation design specified by the code. The current analysis can be used to guide the calibration of these geotechnical resistance factors.

Research of undrained shear strength of till fine soils (moraine)

The undrained soil strength is specific to fine soils or to sands with a lot of fines. It is very important characteristic and the evaluation of accurate value is significant step. The undrained soil shear strength can be estimated directly in laboratory and indirectly in field using in-situ methods. The values of undrained shear strength estimated with different methods usually are different, sometimes very much. In geotechnical practice a lot of empirical equations are used to calculate undrained shear strength (cu), however it corrects only in specific conditions and can’t be used universally. The empirical factor (Nk), which is used in mentioned equations, varies in wide range. It depends on many factors. The research of glacial genesis fine soils (various moraines) is complicated because it specific grain size distributions and genesis. In this article we will study relation between different laboratory and field methods to estimate of undrained shear strength (cu) of till soils. For these purposes we will used upper Pleistocene, upper Nemunas formation till fine soils.

Failure Mechanism and Factor of Safety for Spatially Variable Undrained Soil Slope

This paper aims to investigate the differences in factor of safety (FS) and failure mechanism (FM) for spatially variable undrained soil slope between using finite element method (FEM) , finite difference method (FDM), and limit equilibrium method (LEM). The undrained shear strength of cohesive soil slope is modeled by a one-dimensional random field in the vertical direction. The FS and FM for a specific realization of random field are determined by SRT embedded in FEM- and FDM-based software (e.g., Phase2 6.0 and FLAC) and LEM, respectively. The comparative study has demonstrated that the bishop method (with circular failure surface) exhibits performance as fairly good as that of SRT both in FS and FM for the undrained slope cases where no preferable controlling surfaces such as hydraulic tension crack and inclined weak seams dominate the failure mechanism. It is, however, worthwhile to point out that unconservative FM is provided by the Bishop method from the aspect of failure consequence (i.e., the failure consequence indicated by the FM from the Bishop method is smaller than that from SRT). The rigorous LEM (e.g., M-P and Spencer method with noncircular failure surface) is not recommended in the stability analysis of spatially variable soil slopes before the local minima and failure to converge issues are fully addressed. The SRT in combination with FEM and/or FDM provides a rigorous and powerful tool and is highly preferable for slope reliability of spatially variable undrained slope.