On the evaluation of undrained shear strength and preconsolidation pressure from common field tests in clay

2005 ◽  
Vol 42 (4) ◽  
pp. 1221-1231 ◽  
Author(s):  
Rolf Larsson ◽  
Helen Åhnberg
Keyword(s):  
Shear Strength ◽  
Soft Clay ◽  
Field Tests ◽  
Undrained Shear Strength ◽  
Test Field ◽  
Cone Penetration ◽  
In Situ Tests ◽  
Cone Penetration Tests ◽  
The Stability ◽  
Undrained Shear

The undrained shear strength is a key parameter in the estimation of the stability of natural slopes and man-made constructions in soft clay. It is therefore important to develop relevant methods to evaluate the operative strength. Results from an investigation regarding the effect of excavations at slope crests to increase the stability of clay slopes are presented. This study has provided an opportunity to study the effect of overconsolidation on the evaluated parameters from common in situ tests in homogeneous and truly overconsolidated clays. Certain inconsistencies in the commonly used methods of interpretation of field vane tests, cone penetration tests, and dilatometer tests are highlighted, and modified interpretation methods taking the effects of overconsolidation into account are proposed.Key words: clay, overconsolidation, undrained shear strength, cone penetration test, field vane test, dilatometer test.

Study on Influence of Unloading of Vacuum on Stability of Embankment Improved by Vacuum Combined with Preloading

2012 ◽  
Vol 178-181 ◽  
pp. 1688-1693
Author(s):  
Ji Fu Liu ◽  
Guan Feng An ◽  
Gang Zheng
Keyword(s):  
Shear Strength ◽  
Theoretical Analysis ◽  
Safety Factor ◽  
Laboratory Tests ◽  
Soft Clay ◽  
Undrained Shear Strength ◽  
Soft Ground ◽  
Analysis Laboratory ◽  
The Stability ◽  
Undrained Shear

In order to study influence of unloading of vacuum on stability of embankment whose soft ground is improved by vacuum combined with preloading, the change of effective stress of soft clay in the improved area is analyzed when vacuum is unloaded and the undrained shear strength of soft clay in the improved area after unloading of vacuum is deduced. Changes of undrained shear strength of soil and stability of embankment owing to unloading of surcharge are also analyzed for comparison. It is shown by theoretical analysis, laboratory tests and a project that the undrained shear strength of soft clay improved by vacuum combined preloading is decreased after unloading of vacuum and the stability of embankment after unloading of vacuum should be taken into account for design. Safety factor of stability of embankment increases after unloading of surcharge since decrease ratio of load of embankment is more than decrease ratio of undrained shear strength of clay.

scholarly journals Cone Penetration Test in Stiff Over Soft Clay in Centrifuge Test

2019 ◽  
Author(s):  
Qiang Xie ◽  
Yuxia Hu ◽  
Mark Cassidy ◽  
Alireza Salehi
Keyword(s):  
Shear Strength ◽  
Layer Thickness ◽  
Soft Clay ◽  
Undrained Shear Strength ◽  
Centrifuge Test ◽  
Clay Layer ◽  
Penetration Test ◽  
Cone Penetration ◽  
Cone Resistance ◽  
Undrained Shear

Abstract This paper describes a numerical study on soil characterization of stiff over soft clays in centrifuge test using cone penetration test (CPT), especially when the top stiff layer is thin relative to the centrifuge cone size. An extensive parametric study was conducted using large deformation finite element (LDFE) analysis, with the cone penetrating continuously from the soil surface. The LDFE model has been validated against existing physical test data with very good agreement. Since the bottom soft clay was normally thick enough to fully mobilise the ultimate cone resistance, its undrained shear strength can be interpreted by the existing approach for cone deep penetration in a uniform clay layer. Thus, the challenge was to interpret the strength of the top stiff layer, where the layer thickness was not thick enough to fully mobilise its ultimate resistance. Both top layer thickness ratios (to the cone diameter) and layer strength ratios were considered in the parametric study. Based on the results from LDFE analyses, the interpretation formula of the undrained shear strength in the top stiff layer was proposed as a set of new bearing factors. The proposed cone bearing factor was a function of the ratio of the measured peak cone resistance in the top layer to the stable/ultimate cone resistance in the bottom layer and the ratio between the top layer thickness to the cone diameter. The formula can be used directly when the top layer thickness was known based on the sample preparation. However, the layer interface can be identified based on the study here, if the top layer thickness was not certain. A design flow chart was provided for interpretations of top clay layer strength and top layer thickness based on the cone resistance profile obtained from CPT test.

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