1st Scientific Colloquium - Large Scale Testing (Linking Research and Industry)

Sep 13, 2026, 4:50 PM → Sep 15, 2026, 4:40 PM Europe/Berlin

Geb. 40.50 (KIT Campus Süd)

Hans Henning Stutz (IBF-KIT)

1st Scientific Colloquium - Large Scale Testing (Linking Research and Industry)

LST - 2026

The event brings together international researchers, industry experts, and young scholars to exchange insights on experimental geomechanics, highlighting that coarse large fabric materials such as rockfill, gravels or fibrous soils require dedicated large-scale testing techniques beyond standard laboratory methods.

Workshop2026 - Final.pdf

Sun, September 13

Registration: Registration 1 - Ice Breaker - Light Festival Karlsruhe (depending on the weather conditions)

Mon, September 14

Registration: Registration 2

Address: Welcome Address KIT, Welcome Address Prof. Stutz, TC101 Mr. Ibraim

Keynote: Testing the Untestable? Sandra Linero Molina

10:00 AM Coffe Break

GeoTalks: A Good Fit Is Not a Failure Criterion - When Fitting Breaks Mohr Tangency. Marco Arrieta

Engineering application

1 Optimisation of an excavation pit through large-scale triaxial tests on gravel Niederterrassenschotter Basel

A 70 m long, 35 m wide and 22 m deep excavation pit was created in Basel for the construction of a new research tower block. The excavation pit is located in the inner city, in the middle of the industrial and research area of a pharmaceutical company with sensitive neighbouring buildings (adjacent to the tallest building in Switzerland at 205 m).

To protect against earth pressure and water pressure of up to 9 m in the highly permeable subsoil (gravel), only one support in the form of a spacer slab was constructed. This was done both at the request of the client, who wanted an anchor-free excavation pit, and in order to optimise the planning and ecological balance of the excavation pit. This was achieved by means of large triaxial tests on the existing gravel (Niederterrassenschotter) to determine the effective shear parameters. The results of the tests showed a significant improvement in the shear parameters, which made it possible to completely dispense with anchoring the excavation pit.

Speaker: Konrad Westermann (Gruner AG)

2 Bearing Capacity Assessment of Rubble Mounds Composed of Porous Rock: A Case Study Toward Practical Application

The use of porous rock is generally not adopted in rubble mound foundations due to its higher porosity, which results in lower apparent specific gravity and unconfined compressive strength (UCS). However, in response to rising rock material costs, a rubble mound foundation at Shimizu Port, Japan, is planned to utilize materials sourced from Mount Fuji, including both dense and porous rocks. To evaluate the feasibility of porous rock, the bearing capacity behavior of the two materials was examined through two approaches: (1) large-scale triaxial tests with a specimen diameter of 0.3 m conducted under confining pressures of 50, 200, and 400 kPa to determine shear strength parameters for the Bishop method, and (2) centrifuge model tests of a caisson on rubble mounds performed at a centrifugal acceleration of 50g to reproduce the behavior of large-scale structures. The results indicate that the apparent cohesion and mobilized internal friction angle are within a similar range for both materials ($c_d$ = 29.49 kPa and $ϕ_d$ = 36.97° for dense rock; $c_p$ = 32.95 kPa and $ϕ_p$ = 35.62° for porous rock), despite an approximately threefold difference in UCS. Consequently, the allowable operational load for porous rock is reduced by only about 8% compared with dense rock, which has an estimated bearing capacity of approximately 1430 kPa at a safety factor of 1 based on the Bishop method. The response of rubble mounds under caisson overburden stress obtained from centrifuge model tests also demonstrates nearly identical displacements for both materials up to 300 kPa, corresponding to the expected operational stress level of a 15-m-high caisson, as well as ultimate bearing capacities consistent with theoretical predictions. These results suggest that porous rock can also provide adequate performance for rubble mound foundations. By bridging the gap between theoretical analysis and practical engineering applications through laboratory testing, this study highlights the potential of porous rock as an alternative material for port foundation construction.

Speaker: Rawiwan Sukhumkitcharoen (Port and Airport Research Institute)

3 Characterization of coarse mine waste rockfill using AI-assisted pressuremeter testing, large triaxial testing and CPTu

The mining industry requires solving a wide range of geotechnical problems, many of which involve large-scale particles and coarse materials, such as heap leach piles, spent ore dumps, ROM piles, open pits, and foundation material.

Over the years, the industry has relied on large-scale laboratory testing, geophysics, and in-situ testing; however, there does not appear to be a single method that consistently dominates practice, as is the case with CPTu for tailings.

Pressuremeters can test a large volume of material and have been used worldwide for over 70 years. Nevertheless, its full potential has been limited by traditional interpretation methods. Today, with the aid of advanced numerical modelling and artificial intelligence, this limitation can be overcome.

This work presents the use of pressuremeter tests to characterise a 40 m-high spent ore dump in northern Chile. The tests are back-analysed using advanced constitutive models and an AI-assisted software tool (DAARWIN) to match numerical predictions with measured responses. The resulting soil parameters are then used to model the structure, and the predictions are compared against field monitoring data, SCPTu tests, and large-scale triaxial testing results.

Speaker: Rafael Martinez (Pangea Geotecnia)

4 Large-Scale Geotechnical Testing: Technical and Operational Challenges in the South American Mining Industry

The mechanical characterization of coarse granular materials represents a critical challenge in geotechnical engineering, particularly in urban infrastructure and mining projects. Since 2001, the Centro de Investigación, Desarrollo e Innovación de Estructuras y Materiales (IDIEM) at the University of Chile has developed and implemented large-scale instrumentation, initially motivated by the need to evaluate granular soils for the Santiago Metro extensions. Currently, the equipment allows to performance triaxial tests on specimens with a maximum particle size of 6 inches (152,4 mm), under confining pressures of up to 2000 kPa. This capability is essential for accurately modeling the behavior of rockfill materials and granular mixtures used in the construction and expansion of Run-Of-Mine (ROM) pads and Tailings Storage Facilities (TSF). This article presents the technical and operational challenges related to geotechnical campaigns involving large-scale laboratory tests. In particular, the study adresses the working methodology from covering planning, material transportation, specimen preparation and test execution, emphasizing in the importance of collaboration between academic researchers and industry to obtain representative strength, deformability and permeability parameters at a scale consistent with the Particle Size Distribution (PSD) present in the field, thereby enabling more efficient and sustainable design of large-scale earth and rockfill structures.

Speakers: Ms Danae Momberg (IDIEM Universidad de Chile), Mr Eduardo Fuenzalida (IDIEM Universidad de Chile)

12:00 PM Lunch

Engineering application

5 Large scale testing of reinforced unbound railway base courses

Geosynthetics have become commonplace construction materials. The diverse properties of these materials enable them to fulfil a variety of functions. In the disciplines of geotechnical engineering and transport infrastructure construction, geogrids are utilised to improve soil behaviour and carry tensile forces. In the context of unbound base courses, geogrids are most frequently implemented to stabilise and reinforce the base course material. The geogrid restricts the movement of grains, minimising deformation while saving material.

Triaxial tests were conducted to investigate the system behaviour of geogrids and unbound base courses. In order to reduce the amount of work and material consumption, as well as to use a standard triaxial device, samples with dimensions of d x h = 100 x 200 mm were examined. Therefore, it was necessary to scale geometrically both the base course material and the geogrid. The experimental study consisted of tests performed under monotonic and cyclic axial loading conditions. The objective of the cyclic triaxial tests was to simulate the service loads occurring in unbound base courses of railway tracks.

Due to the geometric scaling of the materials, the resulting effects had to be examined. For this purpose, large triaxial tests were performed on test specimens with dimensions d x h = 350 x 700 mm. With this specimen size, commercially available geogrids and a 0/45 base course material could be used. In order to investigate the scaling effects, one stress level was examined in each of the monotonic and cyclic tests. Both, unreinforced and reinforced test specimens were investigated.

The positive effect of the geogrid reinforcement in the base course material was demonstrated in both scales. In the monotonic triaxial tests, the geogrid reinforcement demonstrated an increase in the stress that can be transferred at the equal deformation. In the cyclic triaxial tests, it was shown that the accumulated strain decreases for the geogrid reinforcement. The effects of the different specimen sizes were evaluated.

Speaker: Claudia Bräunig

6 Extrapolation limits of small-scale triaxial testing for large rockfill and waste dump

Conventional triaxial devices typically operate below approximately 1-2 MPa, a stress range in which coarse granular materials exhibit predominantly friction-controlled behavior. Within this domain, differences in gradation, density state, and structure often produce limited separation in shear envelopes, encouraging the use of smooth empirical extrapolations.

Large rockfill and waste dumps operate at substantially higher stress levels, where particle breakage, densification, and contact-network restructuring influence load transfer. Large-scale triaxial datasets extending into the multi-megapascal range demonstrate systematic divergence from low-stress trends. Shear-envelope curvature increases, peak strain evolves, volumetric response shifts toward contraction, and available breakage indicators intensify with stress level.

This work evaluates the mechanical implications of extending low-stress envelopes into higher stress domains. Analysis of compiled large-scale datasets shows that curvature parameter m and associated response metrics are stress-range dependent rather than constant material properties. The apparent continuity suggested by low-stress testing conceals a transition in governing mechanisms.

The results indicate that stress range, not specimen size alone, controls the observable mechanical regime. Large-scale testing is required to access the stress domains governing large rockfill and waste dumps. A stress-regime interpretation framework is proposed to replace routine extrapolation practices in coarse granular systems.

Speakers: Hans Henning Stutz (KIT-IBF), Marco Arrieta (University of Oulu)

Fundamentals and experimental testing for soil

7 Experimental and numerical study of the scalping effect on the behaviour of coarse soils

Earth-filled embankments, dykes, dams and their foundations are often built with coarse soils. These soils are characterised by a very widely graded particle size distribution and the presence of large particles. To characterise the mechanical behaviour of this type of soils, a triaxial bench was developed to test samples with a diameter of 300 mm and a height of 600 mm. In addition, a methodology has been developed to place an undisturbed sample with a diameter of 200 mm in a triaxial configuration. However, some soils may contain grains larger than 50 mm, which requires scalping procedures (granulometric reconstitution) due to the presence of oversized particles with respect to the size of the test device. Our work in partnership with Verbund and EDF aims to study the consequences of two scalping procedures (simple scalping and substitution) on the mechanical properties of coarse soils. For simple scalping, the oversized fraction is removed and replaced by an equal mass of finer materials.
Using the Discrete Element Method (DEM), numerical samples constituted by granular mixtures with discontinuous particle size distributions are tested. Experimental triaxial compression tests are also carried out on mixtures of glass beads, sand and gravel using triaxial devices of different diameters from 50 to 300 mm. The numerical and experimental samples are scalped and substituted. The density is controlled using different soil compactness parameters. The influence of the percentage of fines, particle size distribution and the properties of the replacement materials is studied.
The results show that simple scalping leads to an overestimation or underestimation of mechanical strength, depending on the original fine content and the choice of soil density control parameter. The effect of substitution on the mechanical characteristics of coarse soils stems from the reduction in the particle size distribution of the coarse fraction. Furthermore, it has been shown that an overestimation, a correct estimation or an underestimation can be obtained depending on the strength properties of the particles of the material replacing the non-admissible fraction. Based on the results, some recommendations are proposed to limit the differences in shear strength between scalped soils and original ones.

Speaker: Prof. Didier Marot (Nantes University, Ecole Centrale Nantes, CNRS, GeM, UMR 6183)

8 Compressibility of an andesitic rockfill and a scaled gravel

ABSTRACT
The construction of large dams, currently mainly concrete faced rockfill dams, as well as high road embankments and mining deposits resulting from blasting, requires the knowledge of the mechanical behavior of roills for their design, construction, and maintenance. Significant efforts are made to study them, though most often using smaller specimens, due to the practical difficulties and high cost of large-scale equipment testing; this results in uncertainties arising from scaling implications. As a starting point, it is relevant to recognize and keep in mind the experiences and results developed in Mexico by Professor R. J. Marsal decades ago, when testing rocky fragments up to 20 cm in size using giant triaxial equipment (specimens with a diameter of 1.13 m, height of 2.5 m, confining stress up to 2.5 MPa, maximum deviatoric stress of 15 MPa), and a 1.14 m diameter oedometer to apply compressive stresses up to 10 MPa. This review is carried out as a prelude to the doctoral work of the second author, which aims to investigate the scale effect on the compressibility of an andesitic rockfill through gravel and sand. The recent results of the geotechnical characterization of a rockfill with a maximum size of 16 cm and its uniaxial compression tests in a 97 cm-diameter oedometer are presented. Likewise, the results of gravel used as scaled rockfill are shown, tested in a 38 cm-diameter, 40 cm-high oedometer. The compressibility of these specimens under different relative densities was studied, highlighting the strong influence of moisture conditions (dry and saturated). These laboratory tests confirm what has been observed and measured in the field: noticeable settlements in rockfill road embankments during the annual season of heavy rains, persisting for at least 3 years after construction.

Keywords: Rockfill, compressibility, grain breakage, rocky embankments, scaling.

Authors: Manuel J.Mendoza and Juan S. Sanabria

Speaker: Manuel J. Mendoza López (Instituto de Ingeniería, Universidad Nacional Autónoma de México)

Development of large - scale testing and specimen preparation

9 Large scale shear tests between pipe/cable segment and coarse fabric materials

The presentation will focus on the development and application of a new medium-scale shear rig to investigate the interaction between subsea linear infrastructure and the soil to support the offshore energy sector. The rig incorporates a representative pipe or cable segment that can be subjected to axial or longitudinal shearing against a wide range of seabed conditions, spanning from fine granular soils to coarse, cobble dominated seabeds.
The initial development of the rig was aimed at investigating the axial friction behaviour of polypropylene coated pipelines in contact with various seabed materials under low stress conditions. Extensive validation was conducted through direct comparison with small scale direct shear box tests in sands. The experimental programme was subsequently extended to granular materials with particle sizes ranging from sand to gravel, cobbles, and analogue rocky seabed conditions.
In response to evolving industrial needs, the rig was further developed to study the lateral interaction between electrical cable protection systems (CPS) and scour protection for offshore wind turbines. The upgraded rig allows testing of full scale CPS specimens (up to 40 cm in diameter and approximately 1 m in length) placed over realistic rock armour used in scour protection systems. Large cumulative displacements over repeated cycles are imposed to simulate operational lifetime conditions, enabling assessment of the evolution of resistance forces acting on the cable protection system, and abrasion of the CPS over its service life.

Speaker: Andrea Diambra (University of Bristol)

10 Robotic Air Pluviation for Large-Scale Sand Specimens

For coarse-grained granular materials, manual specimen preparation is inherently associated with variability, particularly with respect to the density. This effect is expected to be even more pronounced for large-scale specimens, where the larger volume and increased handling requirements can further amplify density variations and substantially increase labor intensity.
The Robotic Automated Specimen Preparation (RASP) system enables an automated specimen preparation with the air pluviation out of a single nozzle technique using a programmable robotic arm, allowing controlled adjustment of fall height, deposition rate and spatial trajectory. By prescribing layer-wise motion paths and monitoring the deposited mass, both global and local void ratios can be reproducibly achieved. Previous investigations have already demonstrated a high degree of homogeneity for small-scale specimens prepared using RASP.
In the present study, the RASP air-pluviation concept was extended to substantially larger specimen diameters using Karlsruhe Sand. Cylindrical specimens with a diameter of 50 cm were prepared by robotic deposition. Stacked rings were used exclusively as a geometric control system to determine vertical density uniformity and to quantify potential density gradients. The experimental results showed that homogeneous large-scale samples with predefined target density can be reliably generated using robotic deposition alone. The measured density profiles confirmed that the spatial variability remained within the same order of magnitude as previously attained for small-scale specimens.
A mechanical comparison between homogeneous small and large specimens prepared to the same target density using the RASP method was subsequently performed. One-dimensional compression tests on Karlsruhe Sand were conducted on conventional oedometer specimens (75 mm diameter) and compared with large-scale specimens (500 mm diameter). Compressibility, constrained modulus evolution and stress-dependent stiffness were evaluated to identify scale-dependent behavior.
The study demonstrated that the RASP method can be successfully implemented for large-scale specimens, reduce labor effort and provides a reproducible experimental framework for systematically investigating intrinsic specimen size effects in granular soils by decoupling preparation quality from mechanical testing.

Speaker: Peña Carlos (IBF-KIT)

3:20 PM Coffe Break

GeoTalks: High-capacity large-scale direct shear test with floating upper box. Kartal Toker

Development of large - scale testing and specimen preparation

11 Preparation of large sand samples using the air pluviation method – investigation of factors influencing homogeneity

Air pluviation is a well-established technique for preparing sand specimens for model and laboratory tests. In this method, dry sand is discharged from a hopper onto a perforated plate that controls the rate of bulk flow. Below this plate, layers of wire mesh or parts of similar geometry are installed to distribute the grains as uniformly as possible across the specimen surface. The distance between the lowest mesh layer and the specimen surface (i.e., the drop height), along with the rate of bulk flow, governs the resulting void ratio and, consequently, the relative density. Achieving a high degree of homogeneity—both in terms of density and grain-size distribution, i.e., avoiding segregation—is essential. Only a well-controlled and reproducible specimen preparation allows for the reliable derivation of soil parameters in element tests or the validation of system responses in geotechnical boundary-value problems using physical modelling.
To validate the suitability of the air-pluviation technique for a specific sand prior to large-scale model testing, a framework was developed that enables systematic investigation with a limited number of experiments. Particular emphasis was placed on assessing specimen homogeneity in pluviated samples of comparably large dimensions and identifying material-specific application limits of the method. Air-pluviation trials were performed with varying rates of bulk flow and drop heights. The resulting specimens were deconstructed layer by layer and subdivided into several sampling volumes to quantify homogeneity throughout the sample and, within a single test configuration, to quantify the influence of drop height.
For density determination, volumes of subsamples were measured at comparatively high spatial resolution using a 2D laser profile scanner; density was then obtained by weighing the extracted material. Additionally, granulometric analyses of the subsamples were conducted using a high-resolution optical device (Camsizer). Across two test series, it was demonstrated that air turbulence within the specimen can lead to non-uniform density distributions; however, this effect can be eliminated by a minor improvement of the pluviation device.

Speaker: Michael Niebler (Technische Universität München, Zentrum Geotechnik, Lehrstuhl und Prüfamt für Grundbau, Bodenmechanik, Felsmechanik und Tunnelbau)

12 Development of a Large-Scale Geotechnical Calibration Chamber for Controlled Cone Penetration Testing

Cone penetration tests (CPT) are widely used as a cost-effective and rapidly deployable method for ge-otechnical site investigation. However, the derivation of geotechnical design parameters from CPT data remains insufficiently standardized within the current German framework (DIN 1997-2:2010-10;DIN 4020:2010-12). Existing empirical correlations are often restricted to specific soil types and deposi-tional conditions and are not directly applicable to many types of non-cohesive soils encountered in northern Germany.

To address this gap, a large-scale geotechnical calibration chamber is currently being designed by the Federal Waterways Engineering and Research Institute (BAW) in cooperation with the Helmut-Schmidt-University, Hamburg (HSU). The facility is intended to enable controlled laboratory CPTs in homogeneous soil specimens of known density and grain size distribution. The cylindrical chamber will have an internal diameter of 1.8 m and a height of 2.2 m, making it unique in scale and allowing boundary effects to be minimized. Sand specimens will be prepared using an integrated air pluviation system, which is part of the calibration chamber setup, that produces a uniform sand rain across the entire chamber cross-section while main-taining a constant drop height. This method enables the reproducible preparation of homogeneous soil specimens with defined relative densities. In addition, the feasibility of performing pluviation under vacuum conditions is being investigated in order to further improve sample homogeneity and reduce particle segregation. The chamber is designed to allow independent application of both axial and radial stresses. Radial stress will be applied via a water-pressurized membrane enclosing the specimen, con-ceptually similar to a large-scale triaxial cell. Axial stress will be applied either through hydraulic cylin-ders located beneath the specimen or via a pressurized membrane at the base. Controlled saturation from the base permits investigation under both drained and saturated conditions.

Although the project is currently in the final design phase and experimental results are not yet availa-ble, this contribution presents the conceptual design, technical challenges, and anticipated capabilities of the calibration chamber. The facility will form the basis for future systematic CPT investigations aimed at developing improved, soil-specific correlations for non-cohesive soils.

Speaker: Axel Wolfsteller (Federal Waterways Engineering and Research Institute (BAW), Referat Geotechnik Nord, Abteilung Geotechnik)

13 Large-scale shear tests to determine the shear parameters of existing earthfill dams

For many old structures like earthfill dams, there is a lack of information about the geotechnical parameters. Often, it is not documented how the values for friction angle and cohesion have been determined, especially the boundary conditions, e.g. the used test apparatus, the modification of the grading curve etc. Normally, new calculations have to be performed based on newly verified parameters, which means to carry out new laboratory tests. Having maximum grain diameters of up to 400 – 800 mm, it is difficult to get and to define a representative sample. With the use of direct shear boxes of 500 mm x 500 mm, grain diameters up to 63 mm can be tested with a satisfying accuracy.
In this paper selected case studies are presented to describe the procedure used in the TU Wien soil mechanics laboratory to determine the shear parameters for earth static calculations using large-scale shear tests on dam fill materials. It shows how the grain size distributions for the tests were modified (restriction of the maximum grain size) and how the desired density for the tests can be achieved. Furthermore, the boundary conditions for conducting the tests are presented, with particular attention paid to equipment- and test-related factors that can influence the test results and must therefore be taken into account when conducting the tests. These include, for example, the influence of the behavior of the upper shear frame, which can be either “fixed” or “floating and weight-compensated.” Measurements have shown that this can significantly influence the shear parameters.

Speakers: Mr Florian Landstorfer (VERBUND Hydro Power GmbH), Roman Markiewicz (TU Wien, Institut für Geotechnik)

Tue, September 15

Keynote: Micro-to-macro mechanisms behind size effects in coarse granular soils. Carlos Ovalle

GeoTalks: Development of A New Large Scale Triaxial Test Facility. Greg Siemens

GeoTalks: Subsea 7

10:00 AM Coffe Break

Fundamentals and experimental testing for rock and rock mass

14 Large-scale true-triaxial rock testing apparatus

The True-Triaxial Apparatus is designed to accommodate 30 x 30 x 45 cm rock specimens at the Institute of Geomechanics and Underground Technology (GUT), RWTH Aachen. Initial experiments were designed to observe fracture propagation and rock behavior of dry igneous rocks undergoing hydraulic fracturing, with the aim to improve understanding of enhanced geothermal systems at target depths of 3-5 km. A suite of monitoring sensors, including embedded seismic sensors, for AE fracture detection and location, provide a live data feed during experiments in which three sets of flat-jacks induce independent axial stresses on the specimen of up to 35 MPa. Since the initial experimental campaign, the setup has been extended to include conventional cylindrical specimens (diameter = 25 cm; height = 45 cm) to determine the effect of stress on permeability of reservoir rocks; split specimens for shear testing and stress monitoring in fractures, exploring the relationship between fracture roughness on shear strength; and embedded sensor testing in concrete blocks for radioactive deep geological repositories. This contribution focuses on the description of the equipment, initial use cases and future extensions.

Speaker: Mr Alexander Cadmus (GUT, Rwth Aachen)

15 Observations from large-scale triaxial compression tests at jointed slaking rock masses

Triaxial compression tests are commonly used to characterise strength and deformation behaviour of rock to get parameters for engineering design and modelling. For classic triaxial tests, samples are usually selected that they can be considered intact, in order to determine parameters of the intact rock. However, large-scale tests enable the investigation of inhomogeneous samples, which may also be interspersed with joints and can therefore be considered as representative samples of the rock mass. For this study a sedimentary slaking rock mass was examined. The rock mass were formed by sediment deposition in a sea and consists of layers of different materials, on the one hand silty mud stone layers and on the other hand layers of sand with varying degrees of cementation, some of these are also water-bearing. The triaxial compression tests were carried out with a sample height of 120 cm and a diameter of 60 cm. These dimensions make it possible to better replicate in situ conditions. To derive more information from one sample, multi-stage testing is an often carried out technique in classic triaxial tests. In this process, several stress states can be achieved with a single sample at different radial pressures. This type of test is even more cost-effective for large samples, as obtaining large samples involves a significant amount of effort. The results show that the greatest axial and lateral deformations occurred in the softer layers and along the pre existing joints. However, deformations also caused adjacent harder layers to deform laterally. Due to the heterogeneity of the sample, various failure mechanisms could be observed. On the one hand, shear failure occurred both within a layer and at the layer boundaries, on the other hand, axial splitting of the material also occurred.

Speaker: Jonathan Caspar Walter (IBF)

16 From facility development to multiphysics measurements including predictive and retrospective TH2M-coupled numerical simulations: A large-scale triaxial test system for repository engineering

Reliable repository engineering requires experimental systems that can reproduce coupled thermal, hydraulic, and mechanical boundary conditions at a scale far beyond standard laboratory testing. This contribution presents the development, qualification, and strategic re-use of a large-scale triaxial test system developed at Clausthal University of Technology (TUC) – Chair for Geomechanics and Multiphysics Systems (GEMS). The facility was originally conceived within a multi-phase research program on shaft sealing elements made of salt cut bricks (SSB), where the central objective was to establish a technically robust platform for investigating engineered sealing systems made of SSB under controlled multiphysics loading conditions.
This paper focuses primarily on the testing facility itself. Its development included the design of dedicated hydraulic and thermal components, EMC devices for controlling gas and confining pressure, and a heating device for temperature control. In parallel, specimen concepts had to be developed specifically for the apparatus, including brick geometries, joint configurations, and manufacturing procedures. CNC-based fabrication enabled reliable production of salt cut bricks with planar and curved surfaces. The realization phase further comprised construction of the facility, calibration with a steel dummy, and manufacturing as well as assembly of several full-scale test specimen made of 375 salt cut bricks each, demonstrating that highly controlled large-scale triaxial testing of engineered SSB-based systems is technically feasible.
Beyond the experimental infrastructure, the facility is embedded in a workflow combining multiphysics measurements with predictive TH2M-coupled numerical simulations and retrospective analyses. In the SSB projects, numerical analyses were used both to interpret measured behaviour and to retrospectively assess test results and boundary effects.
Following completion of the salt cut brick investigations, the same triaxial apparatus is intended to be upgraded and re-used for a highly instrumented large-scale test on claystone-bentonite interaction, including optical fibers, humidity and pressure sensors, radial wetting, and thermal loading. Predictive simulations will support the definition of relevant time scales, admissible stress and pore-pressure levels, and feasible specimen dimensions for this new large-scale claystone-bentonite experiment. The resulting platform is expected to provide a unique large-scale multiphysics dataset for repository engineering and for benchmarking advanced numerical simulators.

Speaker: Ralf Wolters-Zhao (TU Clausthal)

17 Large Scale Testing of Jointed Rock Mass: True Triaxial Loading and Anisotropy

Large scale tests on cylindrical specimen are well established in major rock engineering projects in Germany. Suggested methods of ISRM and DGGT describe the standard procedures. The paper reviews two case studies of LST where testing procedures exceeded the given standards:
• for the 1060 MW Goldisthal Pumped Storage Project prismatic samples were tested under true triaxial loading conditions.
• for the foundation of the ca. 100m high Leibis-Lichte concrete gravity dam, the anisotropy of the schistous rock mass was investigated
PSP Goldisthal in the Thuringian Forrest, developed by VEAG and now owned and operated by Vattenfall, was built from 1997 to 2003. The true triaxial LSTs on the prismatic slate/quartzite rock samples (62 x 62 x 120 cm³) simulated the potential failure mode in the long side walls of the powerhouse cavern (width 25.8 m, height 48.5 m, length 137.4 m) and supported the optimization of the rock support design.

The design of the Leibis-Lichte concrete gravity dam (owned by the Thüringer Fernwasserversorgung and commissioned in 2005) has required the determination of the strength and deformability of the foundation in schistous rock mass. LST on cylindrical and prismatic samples were performed on specimens, which had orientations of the planes of schistosity parallel and normal to the maximum principal stress. Additionally, the strength and deformability of the discontinuities were investigated in direct shear tests. It can be shown, that laboratory tests, combined with the numerical triaxial tests give robust results of the strength and deformation parameters of the rock mass.

The authors are convinced that the above described tests performed in the 1990ies delivered valuable results to the respective owners that supported the definition of reasonable parameters, allowing for optimized designs. The paper intends to promote the use of true triaxial LST in rock for situations where the rock mass shows distinct anisotropy, which may be tested representatively in a LST with triaxial loading conditions and will show examples of recent or ongoing projects where the availability of LST could lead to optimized or safer designs or reduced risk, which would justify more extensive testing programs, including true triaxial LST.

Speakers: Mr Bernhard Stabel (Fichtner GmbH & Co. KG), Mr Hans-Joachim Stech (Holzhäuser Ingenieur Consult GmbH), Thomas Mutschler (Past: KIT, Institute of Soil Mechanics and Rock Mechaniks)

GeoTalks: Simulating the Seabed: Characterizing Homogeneity for Trawling Geomechanics. Sudhanshu Rathore

12:00 PM Lunch

Fundamentals and experimental testing for soil

18 Large-Scale Monotonic and Cyclic Testing of Gravel for Offshore Applications

Design of gravel beds for offshore wind turbines gravity foundations is commonly constrained by the lack of laboratory testing methods capable of representing the true mechanical behaviour of coarse granular materials. Standard tests are often unsuitable due to particle size and scale effects, boundary conditions, and installation challenges leading to significant uncertainty in material parameters used in foundation design. This paper introduces a conceptual large-scale testing approach developed to bridge the gap between conventional laboratory testing and field-relevant behaviour of gravel beds. At a scale where particle size effects and specimen fabric are more realistically represented, the current concept provides insights that are otherwise difficult to obtain for coarse gravel materials. Conceptual testing typically requires a significantly larger and costlier effort than conventional testing; hence, the campaigns are often small. The present concept is thus demonstrated on a campaign including 3 monotonic, and 9 cyclic, large-scale consolidated anisotropically drained triaxial tests conducted in a 50 × 50 cm triaxial cell. The cell of this size is allowing testing of very coarse gravels and stone or blasted rock materials typically used under large foundations for their large bearing capacity and large permeability. The testing setup enables realistic specimen reconstitution, stable installation of coarse gravel, controlled anisotropic stress paths, and reliable measurement of axial and volumetric strains under both monotonic and cyclic loading. Monotonic tests are used to establish mobilized shear strength and stress–strain behaviour across a wide strain range and define a reference shear stress for cyclic testing. Cyclic tests capture stiffness degradation and strain accumulation under loading regimes relevant to offshore wind turbines. The paper demonstrates how representative parameters can be measured. Furthermore, the applicability of hypothesis confirmation testing in place of full investigative programs is addressed in the light of reducing uncertainty in parameters and improving confidence in the assessment of gravel beds supporting offshore wind gravity-based foundations. The paper concludes that large-scale conceptual testing offers a practical and scalable pathway for the offshore wind industry to better characterize gravel foundation behaviour, supporting more robust and efficient design of gravity-based foundations under combined monotonic and cyclic loading.

Speaker: Dr Abdalla Mustafa Abdalla Almukashfi (Geo)

19 Scale Effects in Triaxial Compression Testing of Rockfill: Correlating Small-, Medium-, and Large-Scale Results through Parallel Gradings

In Japanese port facilities, rubble mound foundations supporting gravity-type structures such as breakwater caissons are designed using Mohr–Coulomb strength parameters—apparent cohesion (c) and friction angle (φ)—that have been established from large-scale triaxial compression tests on specimens of 300 mm diameter or larger. However, such tests demand specialized equipment and considerable cost, limiting the number of tests that can be practically conducted. If the same strength parameters could be reliably obtained from small-scale specimens prepared with parallel, scaled-down grain size distributions, the quality assessment of rock materials for port construction would become substantially more accessible and economical. This study presents a systematic experimental program of consolidated drained (CD) triaxial compression tests at two specimen scales: large-scale (D = 300 mm, H = 600 mm) with a gradation named Grading X (maximum particle size 40 mm), and small-scale (D = 50 mm, H = 100 mm) with six parallel gradations (Gradings A through F) whose dmax/D ratios were systematically varied. Each gradation was prepared as a parallel curve on the grain size distribution chart, preserving the shape of the prototype grading while adjusting the maximum particle size. The materials tested are mixtures of dense stone (DS) and porous stone (PS) at mass-based PS contents of 0%, 50% and 100%, in order to examine whether the scale correspondence holds not only for dense rockfill but also for porous, highly crushable materials. All specimens were prepared at comparable initial dry densities and tested under confining pressures of 50–200 kPa. The results indicate that the secant friction angle φ₀ from both specimen sizes shows a reasonably consistent trend when plotted against dmax/D, suggesting that parallel gradation scaling may offer a viable approach for estimating large-scale strength parameters from small-scale tests. This tendency was observed across the range of PS contents examined, including fully porous specimens, suggesting that applying parallel gradation scaling to small-scale triaxial tests may provide a more efficient and accessible approach to evaluating the strength of non-standard rock materials used in Japanese port facilities.

Speaker: Itsuki Sato (Port and Airport Research Institute)

Modelling

20 Semi-Technical Scale Experiments and Digital Twins for Bentonite-Based Shaft Seals

This contribution highlights research conducted on sealing elements for underground repositories, with a focus on bentonite-based barrier systems for shaft and drift sealing. A central challenge in this field is the reliable transfer of laboratory-scale material data to full-scale repository applications. While in-situ experiments provide valuable insights, their limited controllability of boundary conditions restricts systematic analysis. This gap is addressed through semi-technical scale laboratory experiments that combine realistic dimensions with controlled testing environments.

A key research infrastructure is a cylindrical steel pressure cell with an inner length of 1.90 m and a diameter of 0.80 m, designed for fluid pressures up to 20 MPa. Since the late 1990s, this facility has been used to investigate bentonite seals and multilayer “sandwich” sealing systems consisting of bentonite sealing segments and sandy to silty equipotential segments. These systems are pressurized with saline solutions representative of mining environments to simulate repository conditions. The bentonite swells upon hydration, generating sealing pressure, while fluid injection, moisture migration, and stress development are continuously monitored.

The experimental setup allows both vertical and horizontal operation, enabling simulations of shaft and drift seals. A comprehensive sensor network records axial and radial stresses, isotropic pressures, pore pressures, moisture distribution, and in-situ displacements. Advanced measurement techniques, including earth pressure transducers, TDR sensors, and novel deformation monitoring systems, provide detailed spatial and temporal data on the evolving hydro-mechanical behavior.

The facility effectively bridges the scale gap between small-scale laboratory tests and in-situ experiments, offering stress levels and material volumes relevant for practical applications. It is particularly valuable for studying layered sealing systems and bentonite–sand mixtures and is currently used in major research initiatives such as the Mt. Terri Sandwich project and EURAD-2 ANCHORS.

Experimental investigations are complemented by coupled thermo-hydro-mechanical numerical simulations. These models account for partial saturation, swelling behavior, wall friction, and structural heterogeneities that influence fluid flow and stress development. The development of digital twins of the experimental setups enables systematic testing of mechanistic hypotheses and improves interpretation of complex sensor data. Combined with small-scale and in-situ modeling, this integrated approach enhances the predictive capability for long-term repository sealing performance.

Speaker: Thomas Nagel (TU Bergakademie Freiberg)

21 Finding a generalized compaction model for 19 oedometric tests on granular salt

For the final disposal of radioactive waste in salt formations, researchers are examining not only the stabilizing function of granular salt as a backfill material but also its ability to act as a barrier against incoming and outgoing fluids.
The time required to compact initially loose granular salt into an impermeable backfill is foremost determined by the on-site rate of cavity convergence. However, this rate depends – along with other environmental factors – on the dynamically increasing load resistance of the salt backfill, which, in turn, is controlled by a range of complex interacting factors, whose relative contributions have not yet been fully quantified.
In an empirical approach, we re-evaluate 17 oedometric compaction tests, in which the increase of backfill resistance was experimentally determined for varying boundary conditions.
First, we show to what extent the increase varies across all experiments. Subsequent, we highlight how this variation correlates with the deliberately varied test conditions, foremost compaction rate and initial humidity. To this end, polynomial models of varying degree were fitted to each experiment. Based on the adjusted coefficient of determination ($R^{2}_{adj}$), a fourth-degree polynomial was found to provide the best representation of the observed variability ($R^{2}_{adj} = 0.3$).
When fitting prediction models based on data grouped by compaction rate ($6.9*10^{-6}$ 1/s, $6.9*10^{-7}$ 1/s, $6.9*10^{-8}$ 1/s, $6.9*10^{-9}$ 1/s) the mean adjusted $R^{2}$ improves over all groups to $0.6$. While this illustrates that a generalized, empirical model may benefit from incorporating a compaction rate parameter, it remains uncertain whether the model can be enhanced by further parametrization of other influencing factors, too, like humidity or grain size. Here, we present our current work addressing this challenge, arising from the complex interplay of multiple deformation mechanisms that give rise to interdependent relationships among the governing factors.

Speaker: Mara Tews (BGR Hannover)

22 GPU-accelerated SPH study of large-scale debris flow impact and overflow on dual barriers

Debris flows are among the most destructive geohazards owing to their high impact force, complex rheology, and pronounced scale-dependent behavior. In practical hazard mitigation, dual or multiple barriers are frequently installed in series to intercept large-volume debris flows through a cascading process of momentum reduction and energy dissipation. Although large-scale physical experiments have provided valuable insights into debris-flow-barrier interaction, the fundamental mechanisms governing overflow and impact within multi-barrier systems remain insufficiently understood. In this study, the interaction between debris flow and dual barriers is investigated numerically using a graphics processing unit (GPU)-accelerated smoothed particle hydrodynamics (SPH) framework, in which the granular phase is described by a Bingham-type constitutive model. The numerical results demonstrate that the adopted framework can reproduce the key dynamic features reported in large-scale experiments, including jet-like overflow, the temporal evolution of overflow distance, and rebound following impact. The simulations further suggest that the principal role of debris-resisting barriers may be to intercept the highly energetic flow front, whereas a substantial proportion of the energy carried by the subsequent flow mass is dissipated through internal shearing and progressive flow--barrier interaction. These findings highlight the potential of GPU-accelerated SPH for investigating debris-flow impact mechanisms and supporting the rational design of dual-barrier mitigation systems.

Speaker: Mr Hongcheng Jiao (Institute of Geotechnical Engineering, BOKU University)

23 Critical State Behaviour of Coarse Granular Materials: NorSand Calibration from Large-Scale Triaxial Testing

While critical state soil mechanics (CSSM) and advanced constitutive models, such as NorSand, have been widely applied to natural soils and tailings, their extension to coarser grained materials such as rockfill and mine waste rock has not been comprehensively evaluated. This limitation is important for the analysis and design of large geotechnical structures, where design decisions are often informed by a limited number of large‑scale laboratory tests and assumptions regarding material state dependent behaviour.
This paper presents a comparative study of NorSand constitutive model calibrations based on 30 large-scale triaxial test results performed on four types of coarse granular materials, including rockfill, mine waste rock, and blast debris. These materials were sourced from multiple geographically and geologically distinct sites across US and Canada, and were tested using a large-scale triaxial apparatus with specimen diameter of approximately 300 mm.
All materials exhibited well-defined critical state lines (CSLs) in e–log p′ space, with slopes and intercepts that were parallel or near-parallel across the material types. The critical state friction angles (φ′cs) fell within a narrow range of 38° to 42°. The derived NorSand plastic hardening parameters (Ho, Hψ) and dilation parameters (N, χtc) were found to be of similar magnitude, indicating comparable post-peak softening and dilative tendencies.
These findings may support the broader applicability of critical state soil mechanics (CSSM) to coarse granular materials and reinforce the utility of the NorSand model in capturing the state dependent behaviour of rockfill and waste rock. The observed parameter consistency provides a compelling basis for developing generalized NorSand parameter sets for preliminary design and numerical modelling of large-scale geotechnical structures such as tailings dams, waste dumps, and embankments.

Speaker: Chang-Gyun (CJ) Jeong (BGC Engineering Inc.)

Address: Closing Address