*Article* **Reliability Assessment Approach for the Quality of Railroad Subgrade**

**Janusz Vitalis Kozubal 1, Piotr Wyborski 1,\*, Matylda Tankiewicz <sup>2</sup> and Igor Gisterek <sup>1</sup>**

<sup>2</sup> Department of Civil Engineering, Wrocław University of Environmental and Life Sciences, 50-375 Wrocław, Poland; matylda.tankiewicz@upwr.edu.pl

**Abstract:** The static load plate test is the standard subgrade acceptance test for new or modernised railway lines. Examinations are performed at regular spacings on the track section and a lack of acceptance for even a single test disqualifies a section, forcing remedial treatments on the whole section. In this paper, a nondeterministic description of stiffness related to the spatial characteristics of acceptance measurement results is proposed for a more rational assessment of substructure quality. The concept is based on geostatistical analysis and one-dimensional distributions of stiffness values. The paper also proposes a new concept of rail infrastructure acceptance based on a reliability index already codified in European standards. The functioning of the postulated criterion is presented on the example of an existing railway line and the actual test results.

**Keywords:** subgrade; static load test; deformation modulus; reliability

### **Citation:** Kozubal, J.V.; Wyborski, P.; Tankiewicz, M.; Gisterek, I. Reliability Assessment Approach for the Quality of Railroad Subgrade. *Materials* **2022**, *15*, 1864. https://doi.org/10.3390/

Academic Editors: Sukhoon Pyo and Siegfried Schmauder

Received: 15 December 2021 Accepted: 28 February 2022 Published: 2 March 2022

ma15051864

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).
