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

Abstract 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 K 0 and on estimating the unloading from the obtained K 0 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 Kralovo 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.