Evaluation of the Shear Punching Test - A comparative analysis with fall-cone and direct simple shear test

Abstract

Between the years 2019 and 2023, SGI developed a new method to assess the undrained shear strength in cohesive soils. The new test, named the shear punching test, is developed to possibly replace or compliment existing test methods, particularly the fall-cone test. The fall-cone test, which is an index test for evaluating the shear strength of soil, is based on empirical analyses. This makes it challenging to derive mathematically and often underestimates the results. A method similar to the shear punching test was devised by Bror Fellenius 1935. Although the results were considered promising at the time, the method came to nothing. This thesis aims to investigate the potential of the shear punching test to become a standardized test in geotechnical investigations by analyzing the correlation between the shear punching test, fall-cone test and direct simple shear test (DSS). This is achieved by conducting a literature review and analyzing results from soil samples where all relevant methods have been performed. Furthermore a numerical model of the shear punching apparatus is developed using Plaxis 2D, and an in depth stability analysis is conducted on a section from Gamleby Harbor in Västervik using Geostudio SLOPE/W. The results show that the shear strength that is calibrated to the DSS test aligns reasonably well with empiricism and naturally in relation to the shear strength obtained from DSS tests. The normalized shear strength however, shows a wide spreading within 2 standard deviations as well as a few outliers. Numerical modeling in Plaxis can to some extent recreate results from the laboratory tests. During evaluation of the shear strength trend for the use in stability analysis, the shear punching test leads to an increase in cases where the DSS test is excluded. In conclusion, the shear punching test cannot be considered a complete replacement for the fall-cone test as an index test, as the sensitivity of the soil cannot be determined. However, it can be used as a complement to other tests for the evaluation of the undrained shear strength in cohesive soils. Due to the scatter in the normalized shear strength, no specific range for certain parameters can be observed where shear punching is relevant or not. It can be concluded that it is possible to recreate the shear punching numerically and obtain results that reasonably align with laboratory results. Including results from the shear punching test in the evaluation of the shear strength trend will only have an effect if more reliable test methods are not included.