Determination of erosion thickness by numerical back analysis: The case study of Badenian clays in the Carpathian Foredeep, Czech Republic

• Determination of erosion thickness is complicated task in case of aged soils.
• A new technique was developed – geotechnical numerical back analysis (GNBA).
• GNBA results are not distorted by ageing effects.
• The method is demonstrated on the Miocene marine clay “Tegl” in the Czech Rep.

The paper describes an application of the geotechnical numerical back analysis in estimating the thickness of eroded sedimentary overburden in shallow basinal sediments. The approach is based on the back-analysis of the coefficient of earth pressure at rest K0 and on estimating the unloading from the obtained K0 value. This approach is compared with the conventional methods represented by Baldwin–Butler's “compaction curves” and Casagrande's concept of “preconsolidation stress”. The results of these two commonly used methods are incorrect if the sedimentary profile is affected by “ageing” effects, such as cementation, secondary compression etc. The method is demonstrated on the Lower Miocene marine clay, often called “Tegl” which was deposited in the Carpathian Foredeep in the vicinity of Brno, Czech Republic. The numerical back analysis was applied to galleries and adits opened during site investigation of the Královo Pole Tunnels in Brno. The application of Baldwin–Butler's equation suggested the erosion thickness of 180–270 m and Casagrande's method of 100–800 m, while the numerical back analysis of 0–40 m.