On the Measurement of Time-Dependent Pre-Sliding Along Callovo–Oxfordian Claystone Interfaces

Abstract:

Progressive and anisotropic tunnel convergence observed in the Callovo–Oxfordian (COx) claystone at the Meuse/Haute-Marne Underground Research Laboratory has been widely attributed to time-dependent pre-sliding along shear fractures within the excavation induced fractured zone, occurring under shear stresses lower than the Coulomb static friction threshold [1]. While this mechanism has been supported by numerical investigations, direct experimental evidence has remained scarce because of the extreme thermo-hydric sensitivity of the claystone, which induces deformations of the same order of magnitude as the expected pre-sliding displacements.

This study presents an experimental methodology designed to measure and characterize viscous pre-sliding under controlled thermo-hydric conditions. The experimental setup consists of three stacked claystone blocks forming two shear interfaces. A constant normal load is applied while the central block is subjected to a controlled horizontal displacement. Two ultra-high-resolution cameras monitor both sides of the specimen, and Digital Image Correlation (DIC) is employed to quantify interface slip as well as deformation within the surrounding claystone matrix.

To evaluate the capability of the setup to identify a local constitutive law for interface creep, a numerical digital twin was developed using the Disroc finite element code. Simulations demonstrate that DIC measurements provide an accurate characterization of the local interface response, even when the claystone matrix exhibits viscoelastic behavior, whereas Linear Variable Displacement Transducer (LVDT) measurements are significantly affected by matrix creep.

Particular attention was devoted to minimizing experimental uncertainties through strict control of temperature and relative humidity, careful preparation and characterization of interface roughness, and dedicated analyses of DIC measurement errors.

A first experiment conducted under near in situ conditions (92% relative humidity and 21°C) successfully captured viscous slip of approximately 5–6 µm over 20 hours. Despite the spatial heterogeneity of slip measured along the interface, the average slip evolution shows that the slip rate decreases progressively with time and follows a power-law behavior.

The experimental data were subsequently analyzed using two different modeling approaches. First, the parameters of Lemaitre’s creep law were fitted to the measured slip evolution. Second, the parameters of a logarithmic expression derived from empirical rate-and-state frictional laws [2] were identified using the same experimental data. The analogy between the two laws provides further insight into the physical mechanisms governing time-dependent pre-sliding.

References:

[1] S. Jung, ‘Modeling and characterization of the time-dependent behavior of the fractured zone around underground storage structures in Callovo-Oxfordian claystone’, 2022.

[2] K. Sirorattanakul, S. Larochelle, V. Rubino, N. Lapusta, and A. J. Rosakis, ‘Sliding and healing of frictional interfaces that appear stationary’, Nature, vol. 639, no. 8056, pp. 947–953, Mar. 2025, doi: 10.1038/s41586-025-08673-0.

Short bio:

Akram is a Civil and Public Works Engineer. In the fall of 2023, he joined École Nationale des Ponts et Chaussées to pursue a research Master’s degree in Geomechanics and Geotechnics (MSROE). During this program, he joined Navier Laboratory as a research intern, where he worked on synthetic rocks to investigate scale linkage in mechanical behavior and gas migration. He is currently pursuing a PhD focusing on the behavior of the excavation-induced fractured zone in clayey rock formations for deep geological radioactive waste storage.